Molecular biology of the type I human T-cell leukemia virus (HTLV-I) and adult T-cell leukemia.

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Authors

M R Smith, W C Greene

Interaction of recombinant apolipoprotein(a) and lipoprotein(a) with macrophages.

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Elevated plasma levels of lipoprotein(a), Lp(a), represent a major, inherited risk factor for coronary heart disease, although the mechanism of its action remains unknown. Lp(a) is distinguished from the related LDL particle by the addition of apolipoprotein(a), apo(a). The presence of this large glycoprotein is likely to affect the binding of the particle to the LDL receptor and/or other receptors which may contribute to the atherogenic potential of Lp(a). Here we demonstrate the binding to macrophages of Lp(a) and pure recombinant apo(a) protein, via a specific, high-affinity receptor. This binding could lead to foam cell formation and the localization of Lp(a) to atherosclerotic plaques.

Authors

T F Zioncheck, L M Powell, G C Rice, D L Eaton, R M Lawn

Acquired cisplatin resistance in human ovarian cancer cells is associated with enhanced repair of cisplatin-DNA lesions and reduced drug accumulation.

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Studies were undertaken to investigate acquired resistance to cisplatin in human ovarian cancer cells. The cell lines A2780 and A2780/CP70 were studied to assess their respective characteristics of drug accumulation and efflux, cytosolic inactivation of drug, and DNA repair. All experiments were performed using 1-h drug exposures. The A2780/CP70 cell line was 13-fold more resistant to cisplatin than A2780 cells. When studied at their respective IC50 doses, drug accumulation rates were similar for the two cell lines. However, the resistant cell line was twofold more efficient at effluxing drug, which was associated with reduced total drug accumulation for equivalent micromolar drug exposures. At equivalent levels of total cellular drug accumulation, the two cell lines formed the same levels of cisplatin-DNA damage, suggesting that cytosolic inactivation of drug does not contribute to the differential in resistance between these cell lines. Resistant cells were also twofold more efficient at repairing cisplatin-DNA lesions in cellular DNA and in transfected plasmid DNA. We conclude that in these paired cell lines, alterations in drug uptake/efflux and in DNA repair are the major contributing factors to acquired resistance to cisplatin.

Authors

R J Parker, A Eastman, F Bostick-Bruton, E Reed

Ca2+ responses to interleukin 1 and tumor necrosis factor in cultured human skin fibroblasts. Possible implications for Reye syndrome.

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Elevated concentrations of cytokines were found in the plasma of patients acutely ill with Reye syndrome (RS) but not in control subjects or recovered RS patients. To determine whether this disorder involves a genetically determined abnormal response to cytokines, the effects of tumor necrosis factor (TNF) and IL-1 on intracellular free Ca2+ were compared in cultured skin fibroblasts from control subjects and patients with RS. IL-1 and TNF caused rapid, transient, and concentration-dependent increases in cytosolic free Ca2+. The peak cytosolic free Ca2+ was greater and occurred at higher concentrations of IL-1 and TNF in patient cells than in cells from age-matched controls. In control cells, the Ca2+ transient diminished sharply with increasing amounts of IL-1 or TNF above the maximum stimulatory concentration. In contrast, in patient fibroblast this bell-shaped curve of concentration dependency was much less apparent. Bradykinin-stimulated Ca2+ transients were similar in the two groups and did not exhibit the bell-shaped concentration dependency. Thus, plasma cytokine levels are elevated in RS patients and the Ca2+ response to cytokines is increased in cells derived from these patients. We propose that the increased response reflects a genetic defect in cytokine receptor-modulated signal transduction.

Authors

B E Corkey, J F Geschwind, J T Deeney, D E Hale, S D Douglas, L Kilpatrick

Mycoplasma pulmonis infections cause long-lasting potentiation of neurogenic inflammation in the respiratory tract of the rat.

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These experiments were done to learn whether Mycoplasma pulmonis infections of the respiratory tract of rats can potentiate "neurogenic inflammation" and whether this potentiation is amplified by factors that exacerbate the infections. Pathogen-free F344 rats were inoculated intranasally with M. pulmonis or with sterile culture medium and then lived for 4 wk in an ammonia-free atmosphere or in air containing ammonia (100 parts per million). Neurogenic inflammation was evoked by an intravenous injection of capsaicin, and 5 min later the magnitude of the response was quantified by measuring the amount of extravasation of two tracers, Monastral blue pigment and Evans blue dye. We found that vascular permeability in the tracheas of all rats was normal in the absence of capsaicin. However, a 75-micrograms/kg dose of capsaicin, which caused almost no extravasation of Evans blue in the tracheas of pathogen-free controls (17 +/- 3 ng/mg; mean +/- SE), produced extensive extravasation in the infected rats (135 +/- 18 ng/mg; P less than 0.001). Similarly, this dose of capsaicin produced 30 times as much Monastral blue extravasation in the infected rats (area density = 47 +/- 8% of surface area) as it did in the pathogen-free rats (1.6 +/- 0.5%; P less than 0.001), a difference that resulted from increases in the number of Monastral blue-labeled postcapillary venules and in the amount of labeling per venule. Exposure of the infected rats to ammonia exacerbated the infections, further increased the number of Monastral blue-labeled vessels and the amount of labeling per vessel, and made the rats so sensitive to capsaicin that a normally tolerable dose of 150 micrograms/kg i.v. caused fatal apnea. Ammonia did not have these effects in pathogen-free rats. We conclude that M. pulmonis infections of the airway mucosa cause a potent, long-lasting potentiation of neurogenic inflammation, which results in part from an increase in the number and responsiveness of mediator-sensitive postcapillary venules. These changes can be amplified by environmental factors such as ammonia which exacerbate the infections.

Authors

D M McDonald, T R Schoeb, J R Lindsey

Renal nerves modulate renin gene expression in the developing rat kidney with ureteral obstruction.

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Chronic unilateral ureteral obstruction (UUO) in newborn rats activates renin gene expression in the obstructed kidney, and increases renin distribution along afferent glomerular arterioles in both kidneys. To investigate the role of the renal nerves in this response, 2-d-old Sprague-Dawley rats were subjected to UUO or sham operation. Chemical sympathectomy was performed by injection of guanethidine, whereas, control groups received saline vehicle. At 4-5 wk, renal renin distribution was determined by immunocytochemistry, and renin mRNA levels were determined by Northern blot hybridization. Compared to the saline-treated rats with UUO, renin remained localized to the juxtaglomerular region in both kidneys of rats with UUO receiving guanethidine (P less than 0.05). Moreover, renin mRNA levels were eightfold lower in obstructed kidneys of rats receiving guanethidine than in those receiving saline. Additional groups of rats with UUO were subjected to unilateral mechanical renal denervation: renin gene expression in the obstructed kidney was suppressed by ipsilateral but not by contralateral renal denervation. These findings indicate that either chemical or mechanical denervation suppressed the increase in renin gene expression of the neonatal kidney with ipsilateral UUO. We conclude that the renal sympathetic nerves modulate renin gene expression in the developing kidney with chronic UUO.

Authors

S S el-Dahr, R A Gomez, M S Gray, M J Peach, R M Carey, R L Chevalier

Plasticity of integrin expression by nerve-derived connective tissue cells. Human Schwann cells, perineurial cells, and fibroblasts express markedly different patterns of beta 1 integrins during nerve development, neoplasia, and in vitro.

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Strikingly selective expression patterns of beta 1, alpha 2, alpha 3, and alpha 5 integrin subunits were revealed in endoneurium, perineurium, and epineurium of fetal and adult human peripheral nerve by immunostaining with specific antibodies. The alpha 2 subunit was expressed only on Schwann cells both in fetal and adult nerve, whereas the alpha 3 epitopes were expressed exclusively in the adult tissue and were primarily present on perineurial cells. The alpha 5 epitopes were expressed only on the innermost cell layer of perineurium of fetal and adult nerve. The tumor cells within schwannomas and cutaneous neurofibromas expressed both alpha 2 and alpha 3 subunits, indicating that Schwann cells have the potential to express also the alpha 3 subunit in vivo. Cell cultures established from human fetal nerve and neurofibromas revealed expression of the alpha 2 and alpha 5 epitopes on Schwann cells, perineurial cells, and fibroblasts, whereas only Schwann cells contained the alpha 3 epitopes which were occasionally concentrated on the adjacent Schwann cells at cell-cell contacts. Our findings emphasize that nerve connective tissue cells change their profiles for expression of extracellular matrix receptors under conditions which have different regulatory control signals exerted by, for example, axons, humoral factors, or the extracellular matrix of the peripheral nerve. This plasticity may play an important role during nerve development and in neoplastic processes affecting the connective tissue compartments of peripheral nerve.

Authors

L L Hsiao, J Peltonen, S Jaakkola, H Gralnick, J Uitto

Effects of maternal diabetes on fetal rat lung ion transport. Contribution of alveolar and bronchiolar epithelial cells to Na+,K(+)-ATPase expression.

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Fetuses of streptozotocin-induced diabetic rats exhibited delayed lung maturation and a 40% reduction in the steady-state level of lung Na+,K(+)-ATPase alpha 1 subunit mRNA and Na+,K(+)-ATPase activity at 21 d of gestation. In in situ hybridization experiments the signal specific for Na(+)-pump alpha 1 subunit message was strongest above columnar epithelial cells of air-conducting structures. Strong labeling was also present above cuboidal cells lining the forming alveoli, but not above mesenchymal cells. Immunocytochemical localization of the protein paralleled the distribution of the mRNA. Mesenchymal cells were more abundant in fetal lungs of diabetic mothers, and thus the decreased overall levels of Na+,K(+)-ATPase may result from the observed morphological pulmonary immaturity. One day after birth there was no apparent difference in lung morphology at the light microscopic level, in the localization or the steady-state level of Na+,K(+)-ATPase alpha 1 isoform mRNA, or in enzyme activity. Na+,K(+)-ATPase has a likely role in the active phase of fluid absorption in the airways of newborns before the onset of breathing. Decreased fluid clearance and lack of thinning of the lung's connective tissue may contribute to the increased risk for respiratory distress in infants of diabetic mothers.

Authors

E Pinter, J A Peyman, K Snow, J D Jamieson, J B Warshaw

Long-term antidepressant administration alters corticotropin-releasing hormone, tyrosine hydroxylase, and mineralocorticoid receptor gene expression in rat brain. Therapeutic implications.

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Imipramine is the prototypic tricyclic antidepressant utilized in the treatment of major depression and exerts its therapeutic efficacy only after prolonged administration. We report a study of the effects of short-term (2 wk) and long-term (8 wk) administration of imipramine on the expression of central nervous system genes among those thought to be dysregulated in imipramine-responsive major depression. As assessed by in situ hybridization, 8 wk of daily imipramine treatment (5 mg/kg, i.p.) in rats decreased corticotropin-releasing hormone (CRH) mRNA levels by 37% in the paraventricular nucleus (PVN) of the hypothalamus and decreased tyrosine hydroxylase (TH) mRNA levels by 40% in the locus coeruleus (LC). These changes were associated with a 70% increase in mRNA levels of the hippocampal mineralocorticoid receptor (MR, type I) that is thought to play an important role in mediating the negative feedback effects of low levels of steroids on the hypothalamic-pituitary-adrenal (HPA) axis. Imipramine also decreased proopiomelanocortin (POMC) mRNA levels by 38% and glucocorticoid receptor (GR, type II) mRNA levels by 51% in the anterior pituitary. With the exception of a 20% decrease in TH mRNA in the LC after 2 wk of imipramine administration, none of these changes in gene expression were evident as a consequence of short-term administration of the drug. In the light of data that major depression is associated with an activation of brain CRH and LC-NE systems, the time-dependent effect of long-term imipramine administration on decreasing the gene expression of CRH in the hypothalamus and TH in the LC may be relevant to the therapeutic efficacy of this agent in depression.

Authors

L S Brady, H J Whitfield Jr, R J Fox, P W Gold, M Herkenham

Tumor necrosis factor downregulates granulocyte-colony-stimulating factor receptor expression on human acute myeloid leukemia cells and granulocytes.

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Tumor necrosis factor (TNF) inhibits granulocyte-colony-stimulating factor (G-CSF)-induced human acute myeloid leukemia (AML) growth in vitro. Incubation of blasts from three patients with AML in serum-free medium with TNF (10(3) U/ml), and subsequent binding studies using 125I-G-CSF reveal that TNF downregulates the numbers of G-CSF receptors by approximately 70%. G-CSF receptor numbers on purified blood granulocytes are also downmodulated by TNF. Downregulation of G-CSF receptor expression becomes evident within 10 min after incubation of the cells with TNF at 37 degrees C and is not associated with an apparent change of the dissociation constant (Kd). The TNF effect does not occur at 0 degrees C and cannot be induced by IL-2, IL-6, or GM-CSF. TNF probably exerts its effect through activation of protein kinase C (PKC) as the TNF effect on G-CSF receptor levels can be mimicked by 12-O-tetradecanoylphorbol-13- acetate. The PKC inhibitor Staurosporine (Sigma Chemical Co., St. Louis, MO) as well as protease inhibitors can completely prevent G-CSF receptor downmodulation. Thus, it appears TNF may act as a regulator of G-CSF receptor expression in myeloid cells and shut off G-CSF dependent hematopoiesis. The regulatory ability of TNF may explain the antagonism between TNF and G-CSF stimulation.

Authors

O Elbaz, L M Budel, H Hoogerbrugge, I P Touw, R Delwel, L A Mahmoud, B Löwenberg

Antibodies elicited by pneumococcal antigens bear an anti-DNA--associated idiotype.

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There is evidence in both murine and human lupus that the production of anti-DNA antibodies may be triggered by environmental antigens. To explore this further, we studied the serum of 10 nonautoimmune individuals immunized with a polyvalent pneumococcal polysaccharide vaccine. All 10 patients showed a rise in the titer of antipneumococcal antibodies bearing an anti-DNA-associated idiotype. The antipneumococcal response was specific as no idiotypic antitetanus antibodies were detected. Furthermore, no anti-DNA antibodies were present in postvaccination sera. The molecular analysis of antipneumococcal and anti-DNA antibodies bearing a common idiotype will help elucidate how foreign antigen might lead to the production of anti-DNA antibodies in susceptible individuals.

Authors

A Grayzel, A Solomon, C Aranow, B Diamond

Expression of smooth muscle cell phenotype by rat mesangial cells in immune complex nephritis. Alpha-smooth muscle actin is a marker of mesangial cell proliferation.

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Mesangial cell proliferation is common in glomerulonephritis but it is unclear if proliferation is associated with any in vivo alteration in phenotype. We investigated whether mesangial of mesangial proliferative nephritis induced with antibody to the Thy-1 antigen present on mesangial cells. At day 3 glomeruli displayed de novo immunostaining for alpha-smooth muscle actin in a mesangial pattern, correlating with the onset of proliferation, and persisting until day 14. An increase in desmin and vimentin in mesangial regions was also noted. Immunoelectron microscopy confirmed that the actin-positive cells were mesangial cells, and double immunolabeling demonstrated that the smooth muscle actin-positive cells were actively proliferating. Northern analysis of isolated glomerular RNA confirmed an increase in alpha and beta/gamma actin mRNA at days 3 and 5. Complement depletion or platelet depletion prevented or reduced proliferation, respectively; these maneuvers also prevented smooth muscle actin and actin gene expression. Studies of five other experimental models of nephritis confirmed that smooth muscle actin expression is a marker for mesangial cell injury. Thus, mesangial cell proliferation in glomerulonephritis in the rat is associated with a distinct phenotypic change in which mesangial cell assume smooth muscle cell characteristics.

Authors

R J Johnson, H Iida, C E Alpers, M W Majesky, S M Schwartz, P Pritzi, K Gordon, A M Gown

Infantile form of carnitine palmitoyltransferase II deficiency with hepatomuscular symptoms and sudden death. Physiopathological approach to carnitine palmitoyltransferase II deficiencies.

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Reported cases of carnitine palmitoyltransferase II (CPT II) deficiency are characterized only by a muscular symptomatology in young adults although the defect is expressed in extra-muscular tissues as well as in skeletal muscle. We describe here a CPT II deficiency associating hypoketotic hypoglycemia, high plasma creatine kinase level, heart beat disorders, and sudden death in a 3-mo-old boy. CPT II defect (-90%) diagnosed in fibroblasts is qualitatively similar to that (-75%) of two "classical" CPT II-deficient patients previously studied: It resulted from a decreased amount of CPT II probably arising from its reduced biosynthesis. Consequences of CPT II deficiency studied in fibroblasts differed in both sets of patients. An impaired oxidation of long-chain fatty acids was found in the proband but not in patients with the "classical" form of the deficiency. The metabolic and clinical consequences of CPT II deficiency might depend, in part, on the magnitude of residual CPT II activity. With 25% residual activity CPT II would become rate limiting in skeletal muscle but not in liver, heart, and fibroblasts. As observed in the patient described herein, CPT II activity ought to be more reduced to induce an impaired oxidation of long-chain fatty acids in these tissues.

Authors

F Demaugre, J P Bonnefont, M Colonna, C Cepanec, J P Leroux, J M Saudubray

Apical secretion of lysosomal enzymes in rabbit pancreas occurs via a secretagogue regulated pathway and is increased after pancreatic duct obstruction.

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Lysosomal hydrolases such as cathepsin B are apically secreted from rabbit pancreatic acinar cells via a regulated as opposed to a constitutive pathway. Intravenous infusion of the cholecystokinin analogue caerulein results in highly correlated apical secretion of digestive and lysosomal enzymes, suggesting that they are discharged from the same presecretory compartment (zymogen granules). Lysosomal enzymes appear to enter that compartment as a result of missorting. After 7 h of duct obstruction is relieved, caerulein-stimulated apical secretion of cathepsin B and amylase is increased, but the ratio of cathepsin B to amylase secretion is not different than that following caerulein stimulation of animals never obstructed. These findings indicate that duct obstruction causes an increased amount of both lysosomal and digestive enzymes to accumulate within the secretagogue releasable compartment but that duct obstruction does not increase the degree of lysosomal enzyme missorting into that compartment. Pancreatic duct obstruction causes lysosomal hydrolases to become colocalized with digestive enzymes in organelles that, in size and distribution, resemble zymogen granules but that are not subject to secretion in response to secretagogue stimulation. These organelles may be of importance in the development of pancreatitis.

Authors

T Hirano, A Saluja, P Ramarao, M M Lerch, M Saluja, M L Steer

Glucocorticoids increase the synthesis of immunoglobulin E by interleukin 4-stimulated human lymphocytes.

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This study indicates that hydrocortisone (HC) markedly increases the synthesis of immunoglobulin E (IgE) by interleukin 4 (IL-4)-stimulated human lymphocytes. The effect is glucocorticoid specific and is obtained with low concentrations of HC (0.1-10 microM). In both the early and the late phase of the IL-4-induced response HC exerts its effects which are respectively IL-4 dependent and IL-4 independent. The IgE potentiation cannot be explained by the inhibition of interferon-gamma (IFN-gamma) production since it is observed in the absence of endogenous secretion of IFN-gamma. HC inhibits the production of IgE-binding factors (soluble CD23) and the expression of the low-affinity receptor for IgE, also known as the (Fc epsilon RII) CD23 antigen; however, the residual expression of Fc epsilon RII by IL-4- and HC-treated peripheral blood mononuclear cells (PBMCs) is important since the IgE response of these cells is markedly inhibited by anti-CD23 monoclonal antibody. HC acts mainly by amplifying the cellular interactions between monocytes and lymphocytes; indeed, HC has no effect on monocyte-depleted PBMCs, and moreover, monocytes cannot be replaced by soluble factors. Most importantly, T cells are not required for the induction of IgE synthesis by costimulation with IL-4 and HC. However, the IgE response of rigorously T cell-depleted PBMCs may be further increased by the addition of T cells. Further analysis of the permissive effect of HC on the synthesis of IgE by T cell-depleted PBMCs suggests that HC acts in synergy with IL-4 to trigger the activation and the differentiation of B cells into IgE-producing cells.

Authors

C Y Wu, M Sarfati, C Heusser, S Fournier, M Rubio-Trujillo, R Peleman, G Delespesse

High-affinity binding of interferon-gamma to a basement membrane complex (matrigel).

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Recently it was demonstrated that growth factors are bound to the extracellular matrix, and can regulate cell behavior. Using three different types of binding assays, we have examined the interaction of interferon-gamma with a basement membrane produced by the Engelbreth-Holm-Swarm tumor. Basement membrane was found to bind interferon-gamma in both a time- and concentration-dependent manner. Equilibrium binding analysis revealed a high-affinity site with a dissociation constant of 1.5 10(-9) M and a maximum binding capacity of 1.6 10(9) sites/mm2 of basement membrane. Competition studies show that the binding is inhibited by heparan sulfate, suggesting that basement membrane-heparan sulfate proteoglycan could be the binding site. This interaction was clearly confirmed by native polyacrylamide gel electrophoresis and dot-blot analysis with purified basement membrane molecules. Furthermore, the carboxy-terminal part of the interferon-gamma molecule contains an amino acid cluster, very closely related to a consensus sequence, present in more than 20 proteins known to bind sulfated glycosaminoglycans such as heparin. These data demonstrate a possible role of extracellular matrix components in storing cytokines and in modulating the cellular response to such factors.

Authors

H Lortat-Jacob, H K Kleinman, J A Grimaud

Regulation of parathyroid hormone-like peptide in cultured normal human keratinocytes. Effect of growth factors and 1,25 dihydroxyvitamin D3 on gene expression and secretion.

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We have examined the expression and secretion of endogenous parathyroid hormone-like peptide (PLP) in primary cultures of normal human keratinocytes. In response to growth factors and fetal bovine serum, PLP mRNA expression and immunoreactive PLP release into conditioned medium was rapidly increased (within hours) whereas these effects were inhibited by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. These early responses were not influenced by raising the medium calcium concentration from 0.15 to 1.0 mM. In contrast, increasing the medium calcium concentration to 1.0 mM, addition of 1,25(OH)2D3, or a combination of both, resulted in a delayed augmentation (after several days) in PLP production which was associated with an increase in cellular differentiation as assessed by production of high molecular weight keratin. To investigate whether these factors were acting at the level of transcription of the PLP gene, a series of vectors were prepared by fusing segments of the 5' flanking region of the rat PLP gene to a growth hormone reporter gene. Transient transfection of these constructs into cultured keratinocytes and measurement of immunoreactive growth hormone in the medium showed that a region stimulated by growth factors is located in a 1.9-kb fragment of the 5' flanking region and that a PLP gene promoter region less than 1.2 kb and greater than 0.3 kb upstream of the cap site contains cis-acting elements which respond positively to serum, and negatively to 1,25(OH)2D3. These combined studies demonstrate that, in normal human keratinocytes, growth factors may acutely stimulate PLP mRNA levels and PLP release, whereas 1,25(OH)2D3 inhibits these responses. At least part of these effects are at the level of gene transcription. Additionally, PLP synthesis and release are enhanced under conditions in which keratinocyte differentiation is induced.

Authors

R Kremer, A C Karaplis, J Henderson, W Gulliver, D Banville, G N Hendy, D Goltzman

Soluble surface proteins from Helicobacter pylori activate monocytes/macrophages by lipopolysaccharide-independent mechanism.

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The inflammatory lesions associated with Helicobacter pylori gastritis and duodenitis contain large numbers of mononuclear cells. The close proximity of H. pylori to gastric mucosa suggests that the organism interacts with mononuclear cells, thereby modulating the inflammatory response. To investigate the role of monocytes/macrophages in this response, we examined the effect of whole H. pylori bacteria, H. pylori surface proteins, and H. pylori lipopolysaccharide (LPS) on purified human monocytes. Whole H. pylori and the extracted LPS induced expression of the monocyte surface antigen HLA-DR and interleukin-2 receptors, production of the inflammatory cytokines interleukin 1 and tumor necrosis factor (peptide and messenger RNA), and secretion of the reactive oxygen intermediate superoxide anion. Since H. pylori in vivo does not invade mucosal tissue, we determined whether soluble constituents of the bacteria could activate monocytes. Soluble H. pylori surface proteins, which are enriched for urease and do not contain LPS, stimulated phenotypic, transcriptional, and functional changes consistent with highly activated monocytes. These findings indicate that H. pylori is capable of activating human monocytes by an LPS-independent as well as an LPS-dependent mechanism. H. pylori activation of resident lamina propria macrophages and monocytes trafficking through the mucosa, leading to the secretion of increased amounts of inflammatory cytokines and reactive oxygen intermediates, could play an important role in mediating the inflammatory response associated with H. pylori gastritis and duodenitis.

Authors

U E Mai, G I Perez-Perez, L M Wahl, S M Wahl, M J Blaser, P D Smith

Increase in the expression of a family of small guanosine triphosphate-binding proteins, rab proteins, during induced phagocyte differentiation.

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Rab is a newly identified family of small G-proteins that share 35-70% homology with the yeast Sec4p and Ypt1p involved in the regulation of the secretory pathway. Mature phagocytes display functions requiring organized intracellular traffic and, for this reason, we questioned whether phagocyte differentiation could correlate with the increased expression of rab proteins. Rabbit antisera raised against the recombinant proteins rab1Ap, 2p, 4p, and 6p were able to detect the corresponding proteins in the human monoblast leukemic cell line U937. When these cells were induced to differentiate into monocyte/macrophage-like cells displaying functional characteristics of a normal phagocyte, rab1Ap, 2p, 4p, and 6p were increased and this correlated with an increase in the rab transcripts. Using a rab5 probe, we also observed an increased expression of the rab5 gene in differentiated cells. Similarly, differentiation of the human leukemic myeloblast HL60 cell line along either monocyte or granulocyte pathways induced an increased expression of the rab proteins. Rab proteins were also detected in human neutrophils and in guinea pig alveolar macrophages. As degranulation is one of the phagocyte functions acquired in the late stage of differentiation, we investigated whether rab proteins would be involved in this process. Although rab proteins were tightly membrane bound, none of them was detected in the specific or azurophil granules purified from human neutrophils. The increased expression of rab proteins in mature phagocytes suggests that they may promote functions highly developed in these cells.

Authors

I Maridonneau-Parini, C Z Yang, M Bornens, B Goud

Hypoxia induces a specific set of stress proteins in cultured endothelial cells.

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Vascular endothelial cells (EC) are the initial cells within the vascular wall exposed to decreases in blood ambient oxygen concentration. The mechanisms by which they tolerate low levels of oxygen are unknown, but may parallel the response to other cellular stresses, such as heat shock. After 4-8 h of hypoxia, we found a decrease in total protein synthesis in both cultured bovine aortic and pulmonary arterial EC. SDS-PAGE and autoradiographic analysis of [35S]methionine-labeled proteins demonstrated the concomitant induction of a specific set of proteins (Mr 34, 36, 47, and 56 kD) in both cell types. These hypoxia-associated proteins (HAPs) were cell-associated and up-regulated in a time- and oxygen concentration-dependent manner. Comparison of these proteins with heat shock proteins (HSPs) demonstrated that HAPs were distinct from HSPs. EC maintained chronically in 3% O2 continued to synthesize elevated levels of HAPs, yet further up-regulated these proteins when exposed to 0% O2. The presence of five times the normal media glucose concentration did not alter the appearance of HAPs. Hypoxia sensitive renal tubular epithelial cells up-regulated no proteins corresponding to HAPs and were irreversibly damaged within 8 h of exposure to 0% O2. In vitro translation experiments demonstrated that the steady-state level of several mRNAs was higher in the anoxic EC than in normoxic EC and encoded for proteins of Mr 32, 35, 37, 40, and 48 kD that were different from proteins encoded by HSP mRNAs. The induction of HAPs during acute hypoxia and their continued synthesis in chronic hypoxia suggest that HAPs may be important in the maintenance of endothelial cell integrity under conditions of decreased ambient oxygen.

Authors

L H Zimmerman, R A Levine, H W Farber

Differential diagnosis of mut and cbl methylmalonic aciduria by DNA-mediated gene transfer in primary fibroblasts.

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Methylmalonic aciduria can be caused by mutations in the gene encoding the methylmalonyl coenzyme A mutase apoenzyme (mut) or genes required for the provision of cofactor B12 (cbl). The mut and cbl forms are classically differentiated by somatic cell complementation. We describe a novel method for differential diagnosis of mut and cbl methylmalonic aciduria using DNA-mediated gene transfer of a methylmalonyl CoA mutase cDNA clone. Gene transfer of a functional methylmalonyl CoA mutase cDNA clone into mut fibroblasts reconstitutes holoenzyme activity measured by metabolism of [14C]-propionate in culture. Identical gene transfers into cbl fibroblasts have no effect. This method is used for the differential diagnosis of mut and cbl genotypes in cells from patients with a clinical diagnosis of methylmalonic aciduria and is shown to be a facile, sensitive, and specific method for genetic diagnosis. This work establishes the principle of using DNA-mediated gene transfer to identify the genotype of diseases which can result from mutations at several different genetic loci. This type of differential genotypic diagnosis will be particularly important for establishing the applicability of somatic gene therapy in individual patients.

Authors

M F Wilkemeyer, A M Crane, F D Ledley

Decreased content and surface expression of alpha-granule membrane protein GMP-140 in one of two types of platelet alpha delta storage pool deficiency.

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To determine whether alpha-granule membranes are present in platelets of patients with storage pool deficiencies of both alpha and dense granules (alpha delta-SPD), we examined the content and surface expression of the alpha-granule membrane protein GMP-140 in one patient (J.C.) with a severe alpha-granule deficiency and in three members of a family (family C) with milder alpha-granule deficiencies. Surface expression of GMP-140 in stimulated platelets, assessed by flow cytometric measurements of the binding of two anti-GMP-140 monoclonal antibodies, was 24-38% of normal values in platelets from patient J.C., vs. 60-95% of normal values in family C. Total platelet content of GMP-140, determined in platelet lysates by antigen-capture ELISA, was 49% of normal in patient J.C., but normal in the members of family C. Platelets of patient J.C. were found to be heterogeneous with respect to GMP-140 content and surface expression by both flow cytometry and immunogold electron microscopy. Approximately 80% of her platelets expressed little or no GMP-140 after stimulation, whereas the remaining 20% expressed normal amounts of GMP-140 and showed extensive immunogold labeling of typical alpha-granules and clear vacuoles. No such heterogeneity was found in platelets from family C. These findings in the severe alpha delta-SPD patient are in clear contrast to the observations of normal GMP-140 content in the three other alpha delta-SPD patients, and in patients with the gray platelet syndrome, reported previously by others. These results illustrate the phenotypic heterogeneity of alpha-granule deficiencies in human platelets, and suggest that a defect in granule formation in the megakaryocytes may account for the alpha-granule defect in at least one form of alpha delta-SPD.

Authors

B Lages, S J Shattil, D F Bainton, H J Weiss

Intraportal glucose delivery alters the relationship between net hepatic glucose uptake and the insulin concentration.

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To examine the relationship between net hepatic glucose uptake (NHGU) and the insulin level and to determine the effects of portal glucose delivery on that relationship, NHGU was evaluated at three different insulin levels in seven 42-h-fasted, conscious dogs during peripheral glucose delivery and during a combination of peripheral and portal glucose delivery. During peripheral glucose delivery, at arterial blood glucose levels of approximately 175 mg/dl and insulin levels reaching the liver of 51 +/- 2, 92 +/- 6, and 191 +/- 6 microU/ml, respectively, NHGUs were 0.55 +/- 0.30, 1.52 +/- 0.44, and 3.04 +/- 0.79 mg/kg per min, respectively. At hepatic glucose loads comparable to those achieved during peripheral glucose delivery and inflowing insulin levels of 50 +/- 4, 96 +/- 5, and 170 +/- 8 microU per ml, respectively, NHGUs were 1.96 +/- 0.48, 3.67 +/- 0.68, and 5.52 +/- 0.92 mg/kg per min when a portion of the glucose load was delivered directly into the portal vein. The results of these studies thus indicate that net hepatic glucose uptake is dependent on both the plasma insulin level and the route of glucose delivery and that under physiological conditions the "portal" signal is at least as important as insulin in the determination of net hepatic glucose uptake.

Authors

S R Myers, O P McGuinness, D W Neal, A D Cherrington

Guanine ribonucleotide depletion inhibits T cell activation. Mechanism of action of the immunosuppressive drug mizoribine.

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Abstract

The immunosuppressive drug, mizoribine, has been used to prevent rejection of organ allografts in humans and in animal models. Based on studies in cell lines, mizoribine has been postulated to be an inhibitor of inosine monophosphate (IMP) dehydrogenase (EC1.2.1.14), a pivotal enzyme in the formation of guanine ribonucleotides from IMP. To further characterize the mechanism of action of this drug, we studied the effect of mizoribine on human peripheral blood T cells stimulated with alloantigen, anti-CD3 MAb, or pharmacologic mitogens. Mizoribine (1-50 micrograms/ml) was able to inhibit T cell proliferation by 10-100% in a dose-dependent fashion to all stimuli tested. Measurements of purine ribonucleotide pools by HPLC showed that mizoribine led to a decrease in intracellular GTP levels, and that repletion of GTP reversed its antiproliferative effects. We also examined sequential events occurring after T cell stimulation. Early events in T cell activation, as assessed by steady-state mRNA levels of c-myc, IL-2, c-myb, histone, and cdc2 kinase, as well as surface IL-2 receptor expression, were unaffected. However, cell cycle analysis revealed decreased numbers of cells in S, G2, and M phases, and showed that the G1/S block was reversed with GTP repletion. These data indicate that mizoribine has an effect on T cell proliferation by a mechanism distinct from that of cyclosporine or corticosteroids, and therefore may be useful in combination immunosuppressive regimens.

Authors

L A Turka, J Dayton, G Sinclair, C B Thompson, B S Mitchell

Identification of lymphotoxin and tumor necrosis factor in multiple sclerosis lesions.

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Abstract

Multiple sclerosis (MS) brain tissue, spleen, and PBMC were studied using immunocytochemistry and FACS for immunoreactivity for lymphotoxin (LT) and TNF. Both cytokines were identified in acute and chronic active MS lesions but were absent from chronic silent lesions. LT was associated with CD3+ lymphocytes and Leu-M5+ microglia cells at the lesion edge and to a lesser extent, in adjacent white matter. TNF was associated with astrocytes in all areas of the lesion, and with foamy macrophages in the center of the active lesion. In acute lesions, immunoreactivity for TNF in endothelial cells was noted at the lesion edge. No LT or TNF reactivity was detected in Alzheimer's or Parkinson's disease brain tissues but was present at lower levels in central nervous system (CNS) tissue from other inflammatory conditions, except for adrenoleucodystrophy which displayed high levels of LT in microglia. No increase in LT and TNF reactivity was detected in spleen and PBMC of MS patients suggesting specific reactivity within the CNS. These results indicate that LT and TNF may be involved in the immunopathogenesis of MS, and can be detected in both inflammatory cells and cells endogenous to the CNS.

Authors

K Selmaj, C S Raine, B Cannella, C F Brosnan

Role of adenosine triphosphate (ATP) and NaK ATPase in the inhibition of proximal tubule transport with intracellular cystine loading.

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Abstract

Cellular cystine loading with cystine dimethyl ester inhibits volume absorption, transepithelial potential difference, glucose transport, and bicarbonate transport in proximal convoluted tubules perfused in vitro. This study examined the roles of ATP and NaK ATPase in this in vitro model of the Fanconi syndrome of cystinosis. Intracellular ATP was measured using the luciferin-luciferase assay. Intracellular ATP was reduced by 60% in proximal convoluted tubules incubated with 0.5 mM cystine dimethyl ester for 15 min at 37 degrees C (P less than 0.001). Incubation of cystine loaded tubules with 1 mM exogenous ATP increased intracellular ATP to levels not significantly different than that of controls. On the other hand, Vmax NaK ATPase activity was unchanged even though the incubation times and the concentration of cystine dimethyl ester were doubled to 30 min and 1 mM, respectively. In proximal convoluted tubules perfused in vitro, 0.5 mM cystine dimethyl ester resulted in an 89% inhibition in volume absorption (0.81 +/- 0.14 to 0.09 +/- 0.09 nl/mm.min), while there was only a 45% inhibition in volume absorption (P less than 0.01) due to cellular cystine loading in the presence of 1 mM lumen and bath ATP (0.94 +/- 0.05 to 0.52 +/- 0.11 nl/mm.min). These data demonstrate that proximal tubule cellular cystine loading decreases cellular ATP concentration, but does not directly inhibit NaK ATPase activity. The inhibition in transport and decrease in intracellular ATP due to cellular cystine loading was ameliorated by exogenous ATP. These data are consistent with cellular ATP depletion playing a major role in the inhibition of proximal tubule transport due to intracellular cystine loading.

Authors

C Coor, R F Salmon, R Quigley, D Marver, M Baum

Sites of synthesis of urokinase and tissue-type plasminogen activators in the murine kidney.

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Abstract

Kidneys have long been recognized as a major source of plasminogen activators (PAs). However, neither the sites of synthesis of the enzymes nor their role in renal function have been elucidated. By the combined use of zymographies on tissue sections and in situ hybridizations, we have explored the cellular distribution of urokinase-type (u-PA) and tissue-type (t-PA) plasminogen activators and of their mRNAs in developing and adult mouse kidneys. In 17.5-d old embryos, renal tubules synthesize u-PA, while S-shaped bodies produce t-PA. In the adult kidney, u-PA is synthesized and released in urine by the epithelial cells lining the straight parts of both proximal and distal tubules. In contrast, t-PA is produced by glomerular cells and by epithelial cells lining the distal part of collecting ducts. The precise segmental distribution of PAs suggests that both enzymes may be implicated in the maintenance of tubular patency, by catalyzing extracellular proteolysis to prevent or circumvent protein precipitation.

Authors

A P Sappino, J Huarte, J D Vassalli, D Belin

Defective polymorphonuclear leukocyte formyl peptide receptor(s) in juvenile periodontitis.

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Abstract

Juvenile periodontitis (JP) is a disease characterized by severe gingival infections. PMN from some JP patients exhibit abnormal chemotactic responsiveness when challenged with the synthetic formyl peptide, FMLP. While investigating PMN function in JP, we found a patient in whom abnormal PMN chemotactic responses to FMLP were associated with a defective population of PMN formyl peptide receptor(s) (FPR). JP PMN failed to respond chemotactically when challenged with FMLP, but exhibited normal chemotactic responses upon exposure to purified human C5a. Furthermore, JP PMN were capable of degranulating and generating superoxide anion radicals as well as normal PMN upon exposure to FMLP. Binding studies demonstrated that JP PMN had a diminution in the number of high-affinity FPR. Studies in which FPR was radiolabeled by chemical cross-linking demonstrated that JP PMN FPR exhibited the same molecular weight and N-linked glycosylation as normal PMN FPR. JP PMN FPR, however, was more resistant to papain cleavage than normal PMN FPR. Autoradiograms obtained from 2D-PAGE of normal and JP PMN FPR demonstrated decreased amounts of FPR isoforms in JP PMN.

Authors

H D Perez, E Kelly, F Elfman, G Armitage, J Winkler

Evidence that tumor necrosis factor plays a pathogenetic role in the paraneoplastic syndromes of cachexia, hypercalcemia, and leukocytosis in a human tumor in nude mice.

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Abstract

Recently, we have established a human squamous cell carcinoma of the maxilla (called MH-85) associated with hypercalcemia, leukocytosis, and cachexia in culture. MH-85 tumor cells caused the same paraneoplastic syndromes in tumor-bearing nude mice. We found that there was a sixfold increase in splenic size in MH-85 tumor-bearing mice. This increase paralleled tumor growth and was reversed by surgical removal of the tumor. Splenectomy in nude mice 1 wk before or 6 wk after tumor inoculation resulted in a decrease in tumor growth, and impairment of hypercalcemia, leukocytosis, and cachexia. In MH-85 tumor-bearing animals that had been pretreated by splenectomy, intravenous injection of fresh normal spleen cells caused an immediate reversal of leukocytosis, hypercalcemia, and cachexia. Since the presence of cachexia in both the patient and the mice carrying the tumor suggested tumor necrosis factor (TNF) may be overproduced, we injected polyclonal neutralizing antibodies raised against murine TNF into tumor-bearing mice. There was a rapid and reproducible decrease in blood ionized calcium, accompanied by suppression of osteoclast activity. No changes in blood ionized calcium were seen in mice injected with normal immune sera. In addition, there was an increase in body weight and decrease in white cell count. Plasma immunoreactive TNF was increased almost fourfold in tumor-bearing nude mice compared with control nude mice. Although TNF activity was undetectable in MH-85 culture supernatants, cells of the macrophage lineage, including spleen cells, released increased amounts of TNF when cultured with MH-85 tumor-conditioned media. These results suggest that splenic cytokines such as TNF may influence the development of the paraneoplastic syndromes of hypercalcemia, leukocytosis, and cachexia in these animals, as well as tumor growth. They also show that paraneoplastic syndromes may be due to factors produced by normal host cells stimulated by the presence of the tumor.

Authors

T Yoneda, M A Alsina, J B Chavez, L Bonewald, R Nishimura, G R Mundy

In vitro and in vivo activation of endothelial cells by colony-stimulating factors.

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Abstract

This study was designed to identify the set of functions activated in cultured endothelial cells by the hematopoietic growth factors, granulocyte colony-stimulating factor (G-CSF) and granulocyte macrophage-colony-stimulating factor (GM-CSF), and to compare them with those elicited by prototypic cytokines active on these cells. Moreover, indications as to the in vivo relevance of in vitro effects were obtained. G-CSF and GM-CSF induced endothelial cells to proliferate and migrate. In contrast, unlike appropriate reference cytokines (IL-1 and tumor necrosis factor, IFN-gamma), G-CSF and GM-CSF did not modulate endothelial cell functions related to hemostasis-thrombosis (production of procoagulant activity and of platelet activating factor), inflammation (expression of leukocyte adhesion molecule-1 and production of platelet activating factor), and accessory function (expression of class II antigens of MHC). Other colony-stimulating factors (IL-3 and macrophage-colony-stimulating factor) were inactive on all functions tested. In comparison to basic fibroblast growth factor (bFGF), G-CSF and GM-CSF induced lower maximal proliferation of endothelial cells, whereas migration was of the same order of magnitude. G-CSF and GM-CSF stimulated repair of mechanically wounded endothelial monolayers. Exposure to both cytokines induced shape changes and cytoskeletal reorganization consistent with a migratory phenotype. To explore the in vivo relevance of the in vitro effects of these cytokines on endothelium, we studied the angiogenic activity of human G-CSF in the rabbit cornea. G-CSF, but not the heat-inactivated molecule, had definite angiogenic activity, without any sign of inflammatory reactions. G-CSF was less active than bFGF. However, the combination of a nonangiogenic dose of bFGF with G-CSF resulted in an angiogenic response higher than that elicited by either individual cytokines. Thus, G-CSF and GM-CSF induce endothelial cells to express an activation/differentiation program (including proliferation and migration) related to angiogenesis.

Authors

F Bussolino, M Ziche, J M Wang, D Alessi, L Morbidelli, O Cremona, A Bosia, P C Marchisio, A Mantovani

Endogenous blockade of 1,25-dihydroxyvitamin D-receptor binding in New World primate cells.

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Abstract

When assessed by 1,25-dihydroxyvitamin D3 (1,25(OH)2-D3)-receptor (VDR) binding analysis or 1,25(OH)2-D3-VDR-directed bioresponsiveness, cultured cells from some New World primates (platyrrhines) demonstrate a variable decrement in VDR when compared with Old World primate (catarrhine) cells. To study this difference in VDR expression among primates, we performed immunoblot analysis of the VDR in cultured dermal fibroblasts from platyrrhines in the genera Pithecia and Aotus and from catarrhines in the genus Presbytis; although a platyrrhine, the owl monkey (Aotus) expresses a VDR of the catarrhine (wild type) phenotype. Despite a 10-fold difference in the content of VDR by ligand binding analysis among cells from the three prototypic primate genera, there was a less than or equal to 10% difference in the steady-state level of 50-kD VDR detected by immunoblot analysis of cellular extracts. We investigated this apparent discrepancy in the content of VDR in immunoblots and ligand binding analyses by mixing VDR-containing nuclear extracts of equivalent protein concentration from the various primates. Coincubation of Pithecia and Aotus fibroblast extracts with Presbytis extract diminished specific 1,25(OH)2-D3 binding in the mix by 90% and 95% respectively. Similar results were obtained by mixing nuclear extracts of the owl monkey cell line, OMK, and the vitamin D resistant marmoset B-lymphoblast cell line B95-8. A wild type 1,25(OH)2-D3-binding profile was restored in mixtures after trypsin or heat treatment of the B95-8 extract. These data indicate that some New World primate cells contain a soluble protein that prevents intracellular 1,25(OH)2-D3-VDR binding. It is possible that the quantitative differences in the expression of this protein are responsible for 1,25(OH)2-D3 and other steroid hormone resistant states of variable severity in New World primates.

Authors

M A Gacad, J S Adams

Arterial mechanical properties in dilated cardiomyopathy. Aging and the response to nitroprusside.

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Abstract

The effects of aging on arterial mechanical properties and the response to nitroprusside were examined in 25 patients with dilated cardiomyopathy. High-fidelity pressures were recorded with a multisensor catheter. Pulse wave velocity was determined between two sensors in the thoracic aorta. Arterial compliance was determined by an analysis of the diastolic waveform and cardiac output. At baseline, despite a similar systemic vascular resistance, the pulsatile load (e.g., arterial compliance) and wave transmission characteristics (e.g., pulse wave velocity) were altered with aging. Arterial compliance was reduced in older (greater than 50 yr, n = 8) versus younger (less than 35 yr, n = 8) patients (0.51 +/- 0.17 vs. 1.33 +/- 0.63 ml/mmHg, P less than 0.01) and intermediate in those 35-50 yr of age (n = 9, 0.72 +/- 0.40 ml/mmHg). There was a positive correlation between age and pulse wave velocity (r = +0.90). Nitroprusside infusion decreased resistance, increased arterial compliance, and lowered pulse wave velocity in all groups. Yet, advancing age was associated with a greater fall in wave velocity for a given fall in aortic pressure. The slope (K) of the relation between pulse wave velocity and aortic diastolic pressure progressively increased with age (0.01 +/- 0.03, 0.06 +/- 0.02, and 0.09 +/- 0.03 m/s-mmHg). Multiple linear regression analysis revealed a significant relation between K and age. These data demonstrate that in older patients with dilated cardiomyopathy the left ventricle is coupled to an arterial circulation that has a greater pulsatile load, despite a similar steady load. Furthermore, these age-related changes in the arterial system affect the hemodynamic response to pharmacologically-induced vasodilatation.

Authors

J D Carroll, S Shroff, P Wirth, M Halsted, S I Rajfer

Transforming growth factor-beta and suppression of humoral immune responses in HIV infection.

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Abstract

We reported previously that PBMC from HIV+ patients spontaneously release increased levels of TGF beta 1, contributing to defects in cellular immune responses. This study defines the implications of TGF beta overexpression for humoral immunity in HIV infection. We found that upon Staphylococcus aureus Cowan I (SAC) stimulation of cells from HIV+ donors, B-lymphocyte proliferative responses were decreased. This deficiency correlated closely (r = 0.7, P less than 0.001) with increased TGF beta secretion by PBMC from HIV-infected donors. Conditioned medium from HIV+ PBMC and purified TGF beta 1 had similar inhibitory effects on SAC- or EBV-induced B-cell proliferation, and B cells from HIV-infected donors were as sensitive to inhibition by TGF beta as cells from normal donors. Antibodies to TGF beta 1 neutralized the inhibitory effect of HIV+ culture supernatants on normal B cells and increased low proliferative responses by HIV+ cells. Using PWM as stimulus for B cell differentiation, it was shown that activated TGF beta from HIV+ PBMC is able to significantly reduce the induction of immunoglobulins and this effect was also abrogated by anti-TGF beta. These studies support the concept that in HIV infection, TGF beta is a potent suppressor, not only of the cellular, but of the humoral immune responses as well.

Authors

J Kekow, W Wachsman, J A McCutchan, W L Gross, M Zachariah, D A Carson, M Lotz

Activation of skeletal muscle casein kinase II by insulin is not diminished in subjects with insulin resistance.

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Abstract

Insulin resistance, which may precede the development of non-insulin-dependent diabetes mellitus in Pima Indians, appears to result from a postreceptor defect in signal transduction in skeletal muscle. To identify the putative postreceptor lesion responsible for insulin resistance in Pima Indians, we investigated the influence of insulin on the activity of casein kinase II (CKII) in skeletal muscle of seven insulin-sensitive, four insulin-resistant, nondiabetic, and five insulin-resistant diabetic Pima Indians during a 2 h hyperinsulinemic, euglycemic clamp. In sensitive subjects, CKII was transiently activated reaching a maximum over basal activity (42%) at 45 min before declining. CKII was also stimulated in resistant (19%) and diabetic (34%) subjects. Basal CKII activity in resistant subjects was 40% higher than in either sensitive or diabetic subjects, although the concentration of CKII protein, as determined by Western blotting, was equal among the three groups. Basal CKII activity was correlated with fasting plasma insulin concentrations, suggesting that the higher activity in resistant subjects resulted from insulin action. Extracts of muscle obtained from all three groups either before or after insulin administration were treated with immobilized alkaline phosphatase, which reduced and equalized CKII activity. These results suggest that insulin stimulates CKII activity in human skeletal muscle by a mechanism involving phosphorylation of either CKII or of an effector molecule, and support the idea that elevated basal activity in resistant subjects results from insulin action. It appears that the ability of insulin to activate CKII in skeletal muscle is not impaired in insulin-resistant Pima Indians, and that the biochemical lesion responsible for insulin resistance occurs either downstream from CKII or in a different pathway of insulin action.

Authors

R Maeda, I Raz, F Zurlo, J Sommercorn

Diastolic dysfunction in hypertrophic cardiomyopathy. Effect on active force generation during systole.

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Abstract

We tested the hypothesis that intracellular Ca++ [( Ca++]i) overload underlies the diastolic dysfunction of patients with hypertrophic cardiomyopathy. Myocardial tissue was obtained at the time of surgery or transplantation from patients with hypertrophic cardiomyopathy and was compared with control myocardium obtained from patients without heart disease. The isometric contractions and electrophysiologic properties of all myocardial specimens were recorded by standard techniques and [Ca++]i was measured with the bioluminescent calcium indicator aequorin. In contrast to the controls, action potentials, Ca++ transients, and isometric contraction and relaxation were markedly prolonged in the hypertrophic myocardium, and the Ca++ transients consisted of two distinct components. At 38 degrees C and 1 Hz pacing frequency, a state of relative Ca++ overload appeared develop, which produced a rise in end-diastolic [Ca++]i, incomplete relaxation, and fusion of twitches with a resultant decrease in active tension development. We also found that drugs with increase [Ca++]i, such as digitalis, exacerbated these abnormalities, whereas drugs that lower [Ca++]i, such as verapamil, or agents that increase cyclic AMP, such as forskolin, prevented them. These results may explain why patients with hypertrophic cardiomyopathy tolerate tachycardia poorly, and may have important implications with regard to the pharmacologic treatment of patients with hypertrophic cardiomyopathy.

Authors

J K Gwathmey, S E Warren, G M Briggs, L Copelas, M D Feldman, P J Phillips, M Callahan Jr, F J Schoen, W Grossman, J P Morgan

Propranolol ameliorates the development of portal-systemic shunting in a chronic murine schistosomiasis model of portal hypertension.

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Abstract

We investigated the role of early portal hypotensive pharmacotherapy in preventing the development of portal-systemic shunting in a portal hypertensive model of chronic murine schistosomiasis induced by infecting C3H mice with 60 cercariae of Schistosoma mansoni. Propranolol was administered in drinking water to 20 animals for a period of 6 wk at a dose of 10 mg.kg-1d-1, starting at 5 wk of schistosomal infection. 32 age-matched mice with chronic schistosomal infection served as controls. All animals were studied 11 wk after the infection. Compared with controls the portal pressure (10.8 +/- 0.40 mmHg) was significantly lower (P less than 0.001) in the propranolol-treated animals (7.9 +/- 0.80 mmHg). Portal-systemic shunting was decreased by 79%, from 12.2 +/- 3.34% in controls to 2.5 +/- 0.99% in the propranolol group (P less than 0.05). Portal venous inflow was reduced by 38% in the propranolol treated animals (2.50 +/- 0.73 ml/min; n = 6) compared with controls (4.00 +/- 0.34 ml/min; n = 8; P less than 0.05). The worm burden, the granulomatous reaction, the collagen content of the liver, and the serum bile acid levels were not significantly different between the two groups of animals. These results demonstrate that in chronic liver disease induced by schistosomiasis, the development of portal-systemic shunting can be decreased or prevented by the reduction of flow and pressure in the portal system.

Authors

S K Sarin, R J Groszmann, P G Mosca, M Rojkind, M J Stadecker, R Bhatnagar, A Reuben, Y Dayal

Mucin production by human colonic carcinoma cells correlates with their metastatic potential in animal models of colon cancer metastasis.

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Abstract

Patients with mucinous colorectal cancers characteristically present with advanced disease, however, the relationship between mucin production by colon cancer cells and their metastatic potential remains unclear. We therefore sought to define the relationship between mucin production by human colon cancer cells and metastatic ability by employing animal models of colon cancer metastasis. LS LiM 6, a colon carcinoma cell line with high liver metastasizing ability during cecal growth in nude mice produced twofold more metabolically labeled intracellular mucin and secreted four- to fivefold more mucin into the culture medium compared to poorly metastatic parental line LS174T. This was accompanied by a similar elevation in poly(A)+ RNA detected by blot hybridization with a human intestinal mucin cDNA probe, and increases in mucin core carbohydrate antigens determined immunohistochemically. Variants of LS174T selected for high (HM 7) or low (LM 12) mucin synthesizing capacity also yielded metastases after cecal growth and colonized the liver after splenic-portal injection in proportion to their ability to produce mucin. Inhibition of mucin glycosylation by the arylglycoside benzyl-alpha-N-acetyl-galactosamine greatly reduced liver colonization after splenic-portal injection of the tumor cells. These data suggest that mucin production by human colon cancer cells correlates with their metastatic potential and affects their ability to colonize the liver in experimental model systems.

Authors

R S Bresalier, Y Niv, J C Byrd, Q Y Duh, N W Toribara, R W Rockwell, R Dahiya, Y S Kim

Temperature-sensitive tyrosinase associated with peripheral pigmentation in oculocutaneous albinism.

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Abstract

Several types of autosomal recessive oculocutaneous albinism (OCA) are associated with abnormal tyrosinase function and a generalized reduction in or absence of cutaneous and eye melanin. Each is thought to result from a different mutant allele at the tyrosinase locus, with the mutation producing an enzyme with little or no activity in all involved tissues. In this paper, we report a new type of OCA that results from a tyrosinase allele producing a temperature-sensitive enzyme. The proband had white hair in the warmer areas (scalp and axilla) and progressively darker hair in the cooler areas (extremities) of her body. Melanocyte and melanosome architecture were normal. Quantitative hairbulb tyrosinase (dopa oxidase) assay demonstrated a loss of activity above 35-37 degrees C. Plasma pheomelanin and urine eumelanin intermediates were reduced and correlated with hair melanin content. This is the first temperature-sensitive tyrosinase mutation to be reported in humans and is analogous to the Siamese mutation in the cat and the Himalayan mutation in the mouse.

Authors

R A King, D Townsend, W Oetting, C G Summers, D P Olds, J G White, R A Spritz

Vaccination with Legionella pneumophila membranes induces cell-mediated and protective immunity in a guinea pig model of Legionnaires' disease. Protective immunity independent of the major secretory protein of Legionella pneumophila.

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Abstract

We have examined the capacity of Legionella pneumophila membranes to induce cell-mediated immune responses and protective immunity in a guinea pig model of Legionnaires' disease. Guinea pigs immunized by aerosol with L. pneumophila membranes developed strong cell-mediated immune responses to L. pneumophila membranes as demonstrated by cutaneous delayed-type hypersensitivity and in vitro splenic lymphocyte proliferation. Guinea pigs immunized by aerosol or by subcutaneous inoculation with L. pneumophila membranes developed strong protective immunity against lethal aerosol challenge with L. pneumophila. Overall, in six independent experiments, 39 of 49 (80%) guinea pigs immunized with L. pneumophila membranes survived challenge compared with 2 of 40 (5%) sham-immunized controls (P = 2 x 10(-13). In contrast, guinea pigs immunized by aerosol with formalin-killed L. pneumophila did not develop either a strong cell-mediated immune response to L. pneumophila antigens or protective immunity to lethal aerosol challenge. The capacity of L. pneumophila membranes to induce protective immunity was independent of the major secretory protein of L. pneumophila, which we previously demonstrated is an immunoprotective molecule. Purified L. pneumophila membranes did not contain detectable major secretory protein (MSP) on immunoblots; immunization of guinea pigs with L. pneumophila membranes did not induce anti-MSP antibody; and guinea pigs developed comparable protective immunity after immunization with membranes from either an L. pneumophila strain that secretes the major secretory protein or an isogenic mutant that does not. This study demonstrates that (a) immunization with L. pneumophila membranes but not formalin-killed L. pneumophila induces strong cell-mediated immune responses and protective immunity, (b) L. pneumophila membranes contain immunoprotective molecules distinct from the major secretory protein of L. pneumophila, and (c) L. pneumophila membranes have potential as a vaccine against Legionnaires' disease.

Authors

S J Blander, M A Horwitz

Risk factors for emphysema. Cigarette smoking is associated with a reduction in the association rate constant of lung alpha 1-antitrypsin for neutrophil elastase.

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Abstract

The increased risk of developing emphysema among individuals who smoke cigarettes and who have normal levels of alpha 1-antitrypsin (alpha 1AT) is hypothesized to result from a decrease in the antineutrophil elastase capacity of the lower respiratory tract alpha 1AT of smokers compared with nonsmokers. To evaluate this hypothesis we compared the time-dependent kinetics of the inhibition of neutrophil elastase by lung alpha 1AT from healthy, young cigarette smokers (n = 8) and nonsmokers (n = 12). alpha 1-antitrypsin was purified from lavage fluid using affinity and molecular sieve chromatography, and the association rate constant (k assoc) for neutrophil elastase quantified. The k assoc of smoker plasma alpha 1AT (9.5 +/- 0.5 X 10(6) M-1s-1) was similar to that of nonsmoker plasma (9.3 +/- 0.7 X 10(6) M-1s-1, P greater than 0.5). In marked contrast, the k assoc of smoker lower respiratory tract alpha 1AT was significantly lower than that of nonsmoker alpha 1AT (6.5 +/- 0.4 X 10(6) M-1s-1 vs. 8.1 +/- 0.5 X 10(6) M-1s-1, P less than 0.01). Furthermore, the smoker lower respiratory tract alpha 1AT k assoc was significantly less than that of autologous plasma (P less than 0.01). When considered in the context of the concentration of alpha 1AT in the lower respiratory tract epithelial lining fluid, the inhibition time for neutrophil elastase of smoker lung alpha 1AT was twofold greater than that of nonsmoker lung alpha 1AT (smoker: 0.34 +/- 0.05 s vs. nonsmoker: 0.17 +/- 0.05 s, P less than 0.01). Consequently, for concentrations of alpha 1AT in the lower respiratory tract it takes twice as long for an equivalent amount of neutrophil elastase to be inhibited in the smoker's lung compared with the nonsmoker's lung. These observations support the concept that cigarette smoking is associated with a decrease in the lower respiratory tract neutrophil elastase inhibitory capacity, thus increasing the vulnerability of the lung to elastolytic destruction and thereby increasing the risk for the development of emphysema.

Authors

F Ogushi, R C Hubbard, C Vogelmeier, G A Fells, R G Crystal

Human keratinocytes produce but do not process pro-interleukin-1 (IL-1) beta. Different strategies of IL-1 production and processing in monocytes and keratinocytes.

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Abstract

Keratinocytes comprise the majority of cells in the epidermis, the interleukin-1 rich layer of tissue contiguous with the outside world. Keratinocytes produce IL-1 alpha and beta mRNA in vitro, but only IL-1 alpha biological activity has been identified in keratinocyte cultures. In contrast, monocytes secrete biological activities attributable to both species of IL-1. Using several monoclonal antibodies to IL-1 beta, significant amounts of IL-1 beta protein could be found in keratinocyte cultures; all of this immunoreactive IL-1 beta was in the 31-kD form. This latent cytokine has been shown to bind inefficiently to the IL-1 receptor and to be (in relative terms) biologically inactive. Chymotrypsin cleaves 31-kD IL-1 beta at Tyr 113-Val 114, generating an 18-kD IL-1 species with activity equivalent to the authentic mature IL-1 beta (NH2-terminal Ala 117). Treatment of 31-kD keratinocyte IL-1 beta with chymotrypsin also generated an 18-kD molecule and significant IL-1 activity. Monocytes contain an IL-1 convertase enzyme that cleaves the IL-1 beta promolecule at Ala 117. We demonstrate here that keratinocytes do not contain such an IL-1 convertase activity, nor do they contain any activity capable of productively processing 31-kD IL-1 beta into a biologically active form. These data suggest that keratinocytes (and other non-bone marrow-derived cells) produce IL-1 beta in an inactive form that can be processed only after leaving the cell.

Authors

H Mizutani, R Black, T S Kupper

Pretranslational suppression of a glucose transporter protein causes insulin resistance in adipocytes from patients with non-insulin-dependent diabetes mellitus and obesity.

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Abstract

A major portion of insulin-mediated glucose uptake occurs via the translocation of GLUT 4 glucose transporter proteins from an intracellular depot to the plasma membrane. We have examined gene expression for the GLUT 4 transporter isoform in subcutaneous adipocytes, a classic insulin target cell, to better understand molecular mechanisms causing insulin resistance in non-insulin-dependent diabetes mellitus (NIDDM) and obesity. In subgroups of lean (body mass index [BMI] = 24 +/- 1) and obese (BMI = 32 +/- 2) controls and in obese NIDDM (BMI = 35 +/- 2) patients, the number of GLUT 4 glucose transporters was measured in total postnuclear and subcellular membrane fractions using specific antibodies on Western blots. Relative to lean controls, the cellular content of GLUT 4 was decreased 40% in obesity and 85% in NIDDM in total cellular membranes. In obesity, cellular depletion of GLUT 4 primarily involved low density microsomes (LDM), leaving fewer transporters available for insulin-mediated recruitment to the plasma membrane (PM). In NIDDM, loss of GLUT 4 was profound in all membrane subfractions, PM, LDM, as well as high density microsomes. These observations corresponded with decrements in maximally stimulated glucose transport rates in intact cells. To assess mechanisms responsible for depletion of GLUT 4, we quantitated levels of mRNA specifically hybridizing with human GLUT 4 cDNA on Northern blots. In obesity, GLUT 4 mRNA was decreased 36% compared with lean controls, and the level was well correlated (r = + 0.77) with the cellular content of GLUT 4 protein over a wide spectrum of body weight. GLUT 4 mRNA in adipocytes from NIDDM patients was profoundly reduced by 86% compared with lean controls and by 78% relative to their weight-matched nondiabetic counterparts (whether expressed per RNA, per cell, or for the amount of CHO-B mRNA). Interestingly, GLUT 4 mRNA levels in patients with impaired glucose tolerance (BMI = 34 +/- 4) were decreased to the same level as in overt NIDDM. We conclude that, in obesity, insulin resistance in adipocytes is due to depletion of GLUT 4 glucose transporters, and that the cellular content of GLUT 4 is determined by the level of encoding mRNA over a wide range of body weight. In NIDDM, more profound insulin resistance is caused by a further reduction in GLUT 4 mRNA and protein than is attributable to obesity per se. Suppression of GLUT 4 mRNA is observed in patients with impaired glucose tolerance, and therefore, may occur early in the evolution of diabetes. Thus, pretranslational suppression of GLUT 4 transporter gene expression may be an important mechanism that produces and maintains cellular insulin resistance in NIDDM.

Authors

W T Garvey, L Maianu, T P Huecksteadt, M J Birnbaum, J M Molina, T P Ciaraldi

Soluble fibrin degradation products potentiate tissue plasminogen activator-induced fibrinogen proteolysis.

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Abstract

Despite its affinity for fibrin, tissue plasminogen activator (t-PA) administration causes systemic fibrinogenolysis. To investigate the mechanism, t-PA was incubated with plasma in the presence or absence of a fibrin clot, and the extent of fibrinogenolysis was determined by measuring B beta 1-42. In the presence of fibrin, there is a 21-fold increase in B beta 1-42 levels. The potentiation of fibrinogenolysis in the presence of fibrin is mediated by soluble fibrin degradation products because (a) the extent of t-PA induced fibrinogenolysis and clot lysis are directly related, (b) once clot lysis has been initiated, fibrinogenolysis continues even after the clot is removed, and (c) lysates of cross-linked fibrin clots potentiate t-PA-mediated fibrinogenolysis. Fibrin degradation products stimulate fibrinogenolysis by binding t-PA and plasminogen because approximately 70% of the labeled material in the clot lysates binds to both t-PA- and plasminogen-Sepharose, and only the bound fractions have potentiating activity. The binding site for t-PA and plasminogen is on the E domain because characterization of the potentiating fragments using gel filtration followed by PAGE and immunoblotting indicates that the major species is (DD)E complex, whereas minor components include high-molecular weight derivatives containing the (DD)E complex and fragment E. In contrast, D-dimer is the predominant species found in the fractions that do not bind to the adsorbants, and it has no potentiating activity. Thus, soluble products of t-PA-induced lysis of cross-linked fibrin potentiate t-PA-mediated fibrinogenolysis by providing a surface for t-PA and plasminogen binding thereby promoting plasmin generation. The occurrence of this phenomenon after therapeutic thrombolysis may explain the limited clot selectivity of t-PA.

Authors

J I Weitz, B Leslie, J Ginsberg

An autocrine role for urokinase in phorbol ester-mediated differentiation of myeloid cell lines.

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Abstract

The human myeloid cell line HL60 secretes urokinase-type plasminogen activator (uPA) and expresses its receptor. When stimulated with phorbol myristate acetate (PMA), both secretion of uPA and the expression of its receptor are up-regulated, and these cells differentiate to an adherent phenotype. This adhesive response is markedly reduced in the presence of uPA antibodies. The PMA response is restored by the addition of native uPA, an amino-terminal fragment of uPA (residues 1-143) devoid of proteolytic activity, or a synthetic peptide (residues 12-32) from the uPA growth factor domain known to mediate receptor binding. In contrast, the addition of catalytically active low molecular weight uPA, which is missing the growth factor domain, or a peptide from the catalytic domain (residues 247-266) is ineffective. The influence of uPA antibodies on a second marker of macrophage differentiation, cysteine proteinase activity, was also examined. Cysteine proteinase activity of HL60 cells is increased in PMA-treated cells after 24 h but it fails to increase in the presence of anti-uPA. This increase in cathepsin B-like activity is also restored by exogenous uPA. These experiments indicate that an autocrine interaction of the growth factor domain of uPA with its receptor mediates an essential step in PMA-mediated myeloid cell differentiation.

Authors

A R Nusrat, H A Chapman Jr

Recurrent nonsense mutations in the growth hormone receptor from patients with Laron dwarfism.

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Abstract

In addition to its classical effects on growth, growth hormone (GH) has been shown to have a number of other actions, all of which are initiated by an interaction with specific high affinity receptors present in a variety of tissues. Purification of a rabbit liver protein via its ability to bind GH has allowed the isolation of a cDNA encoding a putative human growth hormone receptor that belongs to a new class of transmembrane receptors. We have previously shown that this putative growth hormone receptor gene is genetically linked to Laron dwarfism, a rare autosomal recessive syndrome caused by target resistance to GH. Nevertheless, the inability to express the corresponding full-length coding sequence and the lack of a test for growth-promoting function have hampered a direct confirmation of its role in growth. We have now identified three nonsense mutations within this growth hormone receptor gene, lying at positions corresponding to the amino terminal extremity and causing a truncation of the molecule, thereby deleting a large portion of both the GH binding domain and the full transmembrane and intracellular domains. Three independent patients with Laron dwarfism born of consanguineous parents were homozygous for these defects. Two defects were identical and consisted of a CG to TG transition. Not only do these results confirm the growth-promoting activity of this receptor but they also suggest that CpG doublets may represent hot spots for mutations in the growth hormone receptor gene that are responsible for hereditary dwarfism.

Authors

S Amselem, M L Sobrier, P Duquesnoy, R Rappaport, M C Postel-Vinay, M Gourmelen, B Dallapiccola, M Goossens

1,25-dihydroxyvitamin D3 prevents the in vivo induction of murine experimental autoimmune encephalomyelitis.

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Abstract

The hormone, 1,25-dihydroxyvitamin D3 (1,25-[OH]2-D3), inhibits lymphocyte activation in vitro. We studied the ability of the vitamin D metabolite to interfere in vivo with a primary T cell-mediated model of autoimmunity, murine experimental autoimmune encephalomyelitis (EAE). Within 2 wk of antigenic challenge, immunized animals will develop acute paralysis with central nervous tissue inflammation. If mice survive, a rise in antibody titer develops within a month. The administration of 0.1 microgram 1,25-(OH)2-D3 i.p. given every other day for 15 d, starting 3 d before immunization, significantly prevented the development of EAE. The rise in antibody titer to myelin basic protein was also abrogated. Histopathologic lesions of EAE were inhibited by treatment with the sterol. These results suggest a potent immunosuppressive role for 1,25-(OH)2-D3 in vivo in the modulation of a cell-mediated model of autoimmunity.

Authors

J M Lemire, D C Archer

Transforming growth factor beta 1 suppresses acute and chronic arthritis in experimental animals.

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Abstract

Systemic administration of the cytokine, TGF beta 1, profoundly antagonized the development of polyarthritis in susceptible rats. TGF beta 1 administration (1 or 5 micrograms/animal), initiated one day before an arthritogenic dose of streptococcal cell wall (SCW) fragments, virtually eliminated the joint swelling and distortion typically observed during both the acute phase (articular index, AI = 2.5 vs. 11; P less than 0.025) and the chronic phase (AI = 0 vs. 12.5) of the disease. Moreover, TGF beta 1 suppressed the evolution of arthritis even when administration was begun after the acute phase of the disease. Histopathological examination of the joint revealed the systemic TGF beta 1 treatment greatly reduced inflammatory cell infiltration, pannus formation, and joint erosion. Consistent with the inhibition of inflammatory cell recruitment into the synovium, TGF beta 1 reversed the leukocytosis associated with the chronic phase of the arthritis. Control animals subjected to the same TGF beta 1 dosing regimen displayed no discernable immunosuppressive or toxic effects even after 4 wk of treatment. These observations not only provide insight into the immunoregulatory effects of TGF beta, but also implicate this cytokine as a potentially important therapeutic agent.

Authors

M E Brandes, J B Allen, Y Ogawa, S M Wahl

Activation of phospholipase C in human B cells is dependent on tyrosine phosphorylation.

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Abstract

Cross-linking of the surface antigen receptor on B lymphocytes has been demonstrated to lead to activation of phospholipase C (PLC) with subsequent increases in production of inositol phosphates and diacylglycerol. In turn, these second messengers increase cytosolic free calcium [( Ca2+]i) and activate the serine threonine phosphotransferase protein kinase C (PKC). These processes are thought to play a major role in B cell activation and proliferation. However, the mechanism linking the B lymphocyte antigen receptor to phospholipase C remains to be identified. We demonstrate herein that activation of the antigen receptor on human lymphocytes, in addition to activation of PLC, increases tyrosine phosphorylation of specific substrates. Tyrphostins, a new class of tyrosine kinase inhibitors which compete for substrate binding site of specific tyrosine kinases have recently been synthesized. Preincubation of B lymphocytes with two different tyrphostins blocked anti-IgM-induced proliferation, oncogene expression, tyrosine phosphorylation, increases in [Ca2+]i, and production of inositol phosphates. The same inhibitors were without effect on B cell proliferation induced by phorbol esters and cation ionophores which directly activate PKC and increase [Ca2+]i thus bypassing PLC. These findings strongly indicate that tyrphostins do not exhibit significant nonspecific toxicity and suggest that they act proximal to PLC. The ability of the tyrphostins to block increases in [Ca2+]i and inositol phosphate production, after activation of the B cell antigen receptor, indicates that a tyrosine kinase acts as an essential link between the B cell antigen receptor and PLC.

Authors

S Padeh, A Levitzki, A Gazit, G B Mills, C M Roifman

A tyrosinase gene missense mutation in temperature-sensitive type I oculocutaneous albinism. A human homologue to the Siamese cat and the Himalayan mouse.

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Abstract

Type I oculocutaneous albinism (OCA) is an autosomal recessive disorder in which deficient synthesis of melanin pigment results from abnormal activity of melanocyte tyrosinase. A novel type I OCA phenotype in which hypopigmentation is related to local body temperature is associated with a missense substitution in tyrosinase, codon 422 CGG (Arg)----CAG (Gln). This substitution results in a tyrosinase polypeptide that is temperature-sensitive. This form of type I OCA thus is homologous to the temperature-related forms of albinism seen in the Siamese cat and the Himalayan mouse.

Authors

L B Giebel, R K Tripathi, R A King, R A Spritz

A mutation in the DNA-binding domain of the androgen receptor gene causes complete testicular feminization in a patient with receptor-positive androgen resistance.

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Abstract

Androgen resistance is associated with a wide range of quantitative and qualitative defects in the androgen receptor. However, fibroblast cultures from approximately 10% of patients with the clinical, endocrine, and genetic features characteristic of androgen resistance express normal quantities of apparently normal androgen receptor in cultured genital skin fibroblasts (receptor-positive androgen resistance). We have analyzed the androgen receptor gene of one patient (P321) with receptor-positive, complete testicular feminization and detected a single nucleotide substitution at nucleotide 2006 (G----C) within the second "zinc finger" of the DNA-binding domain that results in the conversion of the arginine residue at position 615 into a proline residue. Introduction of this mutation into the androgen receptor cDNA and transfection of the expression plasmid into eukaryotic cells lead to the synthesis of a receptor protein that displays normal binding kinetics but is inactive in functional assays of receptor activity. We conclude that substitution mutations in the DNA-binding domain of the androgen receptor are one cause of "receptor-positive" androgen resistance.

Authors

M Marcelli, S Zoppi, P B Grino, J E Griffin, J D Wilson, M J McPhaul

Differential regulation of adipose tissue glucose transporters in genetic obesity (fatty rat). Selective increase in the adipose cell/muscle glucose transporter (GLUT 4) expression.

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Abstract

Adipocytes from young obese Zucker rats exhibit a hyperresponsive insulin-mediated glucose transport, together with a marked increase in cytochalasin B binding as compared with lean rat adipocytes. Here, we examined in these cells the expression of two isoforms of glucose transporter, the erythroid (GLUT 1) and the adipose cell/muscle (GLUT 4) types, in rats aged 16 or 30 d, i.e., before and after the emergence of hyperinsulinemia. GLUT 1 protein and mRNA levels were identical in the two genotypes at both ages. In contrast, the levels of GLUT 4 protein in obese rat adipocytes were 2.4- and 4.5-fold those of lean littermates at 16 and 30 d of age, respectively, in perfect agreement with the genotype effect on insulin-stimulated glucose transport activity. The levels of GLUT 4 mRNA per fat pad were increased 2.3- and 6.2-fold in obese vs. lean rats 16- and 30-d-old, indicating a pretranslational level of regulation. The obese phenotype was not associated with overexpression of GLUT 4 mRNA in gastrocnemius muscle. This work indicates that the fa gene exerts a differential control on the expression of GLUT 1 and GLUT 4 in adipose tissue and provides evidence that independent of hyperinsulinemia, genotype is a major regulatory factor of GLUT 4 expression in this tissue.

Authors

I Hainault, M Guerre-Millo, C Guichard, M Lavau