Research Article
Abstract
Sterol regulatory element–binding protein 1c (SREBP-1c) is a central regulator of lipogenesis whose activity is controlled by proteolytic cleavage. The metabolic factors that affect its processing are incompletely understood. Here, we show that dynamic changes in the acyl chain composition of ER phospholipids affect SREBP-1c maturation in physiology and disease. The abundance of polyunsaturated phosphatidylcholine in liver ER is selectively increased in response to feeding and in the setting of obesity-linked insulin resistance. Exogenous delivery of polyunsaturated phosphatidylcholine to ER accelerated SREBP-1c processing through a mechanism that required an intact SREBP cleavage–activating protein (SCAP) pathway. Furthermore, induction of the phospholipid-remodeling enzyme LPCAT3 in response to liver X receptor (LXR) activation promoted SREBP-1c processing by driving the incorporation of polyunsaturated fatty acids into ER. Conversely, LPCAT3 deficiency increased membrane saturation, reduced nuclear SREBP-1c abundance, and blunted the lipogenic response to feeding, LXR agonist treatment, or obesity-linked insulin resistance. Desaturation of the ER membrane may serve as an auxiliary signal of the fed state that promotes lipid synthesis in response to nutrient availability.
Authors
Xin Rong, Bo Wang, Elisa N.D. Palladino, Thomas Q. de Aguiar Vallim, David A. Ford, Peter Tontonoz
Abstract
The tumor suppressor p53, a master regulator of the cellular response to stress, is tightly regulated by the E3 ubiquitin ligase MDM2 via an autoregulatory feedback loop. In addition to its well-established role in tumorigenesis, p53 has also been associated with aging in mice. Several mouse models with aberrantly increased p53 activity display signs of premature aging. However, the relationship between dysfunction of the MDM2/p53 axis and human aging remains elusive. Here, we have identified an antiterminating homozygous germline mutation in MDM2 in a patient affected by a segmental progeroid syndrome. We show that this mutation abrogates MDM2 activity, thereby resulting in enhanced levels and stability of p53. Analysis of the patient’s primary cells, genome-edited cells, and in vitro and in vivo analyses confirmed the MDM2 mutation’s aberrant regulation of p53 activity. Functional data from a zebrafish model further demonstrated that mutant Mdm2 was unable to rescue a p53-induced apoptotic phenotype. Altogether, our findings indicate that mutant MDM2 is a likely driver of the observed segmental form of progeria.
Authors
Davor Lessel, Danyi Wu, Carlos Trujillo, Thomas Ramezani, Ivana Lessel, Mohammad K. Alwasiyah, Bidisha Saha, Fuki M. Hisama, Katrin Rading, Ingrid Goebel, Petra Schütz, Günter Speit, Josef Högel, Holger Thiele, Gudrun Nürnberg, Peter Nürnberg, Matthias Hammerschmidt, Yan Zhu, David R. Tong, Chen Katz, George M. Martin, Junko Oshima, Carol Prives, Christian Kubisch
Abstract
The histone H3K36 methyltransferase SETD2 is frequently mutated or deleted in a variety of human tumors. Nevertheless, the role of SETD2 loss in oncogenesis remains largely undefined. Here, we found that SETD2 counteracts Wnt signaling and its inactivation promotes intestinal tumorigenesis in mouse models of colorectal cancer (CRC). SETD2 was not required for intestinal homeostasis under steady state; however, upon irradiation, genetic inactivation of Setd2 in mouse intestinal epithelium facilitated the self-renewal of intestinal stem/progenitor cells as well as tissue regeneration. Furthermore, depletion of SETD2 enhanced the susceptibility to tumorigenesis in the context of dysregulated Wnt signaling. Mechanistic characterizations indicated that SETD2 downregulation affects the alternative splicing of a subset of genes implicated in tumorigenesis. Importantly, we uncovered that SETD2 ablation reduces intron retention of dishevelled segment polarity protein 2 (DVL2) pre-mRNA, which would otherwise be degraded by nonsense-mediated decay, thereby augmenting Wnt signaling. The signaling cascades mediated by SETD2 were further substantiated by a CRC patient cohort analysis. Together, our studies highlight SETD2 as an integral regulator of Wnt signaling through epigenetic regulation of RNA processing during tissue regeneration and tumorigenesis.
Authors
Huairui Yuan, Ni Li, Da Fu, Jiale Ren, Jingyi Hui, Junjie Peng, Yongfeng Liu, Tong Qiu, Min Jiang, Qiang Pan, Ying Han, Xiaoming Wang, Qintong Li, Jun Qin
Abstract
Acute myelogenous leukemia (AML) frequently relapses after complete remission (CR), necessitating improved detection and phenotypic characterization of treatment-resistant residual disease. In this work, we have optimized droplet digital PCR to broadly measure mutated alleles of recurrently mutated genes in CR marrows of AML patients at levels as low as 0.002% variant allele frequency. Most gene mutations persisted in CR, albeit at highly variable and gene-dependent levels. The majority of AML cases demonstrated residual aberrant oligoclonal hematopoiesis. Importantly, we detected very rare cells (as few as 1 in 15,000) that were genomically similar to the dominant blast populations at diagnosis and were fully clonally represented at relapse, identifying these rare cells as one common source of AML relapse. Clinically, the mutant allele burden was associated with overall survival in AML, and our findings narrow the repertoire of gene mutations useful in minimal residual disease–based prognostication in AML. Overall, this work delineates rare cell populations that cause AML relapse, with direct implications for AML research directions and strategies to improve AML therapies and outcome.
Authors
Brian Parkin, Angelina Londoño-Joshi, Qing Kang, Muneesh Tewari, Andrew D. Rhim, Sami N. Malek
Abstract
Demyelination in the central nervous system (CNS) leads to severe neurological deficits that can be partially reversed by spontaneous remyelination. Because the CNS is isolated from the peripheral milieu by the blood-brain barrier, remyelination is thought to be controlled by the CNS microenvironment. However, in this work we found that factors derived from peripheral tissue leak into the CNS after injury and promote remyelination in a murine model of toxin-induced demyelination. Mechanistically, leakage of circulating fibroblast growth factor 21 (FGF21), which is predominantly expressed by the pancreas, drives proliferation of oligodendrocyte precursor cells (OPCs) through interactions with β-klotho, an essential coreceptor of FGF21. We further confirmed that human OPCs expressed β-klotho and proliferated in response to FGF21 in vitro. Vascular barrier disruption is a common feature of many CNS disorders; thus, our findings reveal a potentially important role for the peripheral milieu in promoting CNS regeneration.
Authors
Mariko Kuroda, Rieko Muramatsu, Noriko Maedera, Yoshihisa Koyama, Machika Hamaguchi, Harutoshi Fujimura, Mari Yoshida, Morichika Konishi, Nobuyuki Itoh, Hideki Mochizuki, Toshihide Yamashita
Abstract
Claudin-low breast cancer is an aggressive subtype that confers poor prognosis and is found largely within the clinical triple-negative group of breast cancer patients. Here, we have shown that intrinsic and immune cell gene signatures distinguish the claudin-low subtype clinically as well as in mouse models of other breast cancer subtypes. Despite adaptive immune cell infiltration in claudin-low tumors, treatment with immune checkpoint inhibitory antibodies against cytotoxic T lymphocyte–associated protein 4 (CTLA-4) and programmed death receptor 1 (PD-1) were ineffective in controlling tumor growth. CD4+FoxP3+ Tregs represented a large proportion of the tumor-infiltrating lymphocytes (TILs) in claudin-low tumors, and Tregs isolated from tumor-bearing mice were able to suppress effector T cell responses. Tregs in the tumor microenvironment highly expressed PD-1 and were recruited partly through tumor generation of the chemokine CXCL12. Antitumor efficacy required stringent Treg depletion combined with checkpoint inhibition; delays in tumor growth were not observed using therapies that modestly diminished the number of Tregs in the tumor microenvironment. This study provides evidence that the recruitment of Tregs to the tumor microenvironment inhibits an effective antitumor immune response and highlights early Treg recruitment as a possible mechanism for the lack of response to immune checkpoint blockade antibodies in specific subtypes of cancer that are heavily infiltrated with adaptive immune cells.
Authors
Nicholas A. Taylor, Sarah C. Vick, Michael D. Iglesia, W. June Brickey, Bentley R. Midkiff, Karen P. McKinnon, Shannon Reisdorf, Carey K. Anders, Lisa A. Carey, Joel S. Parker, Charles M. Perou, Benjamin G. Vincent, Jonathan S. Serody
Abstract
Neural stem cells (NSCs) differentiate into both neurons and glia, and strategies using human NSCs have the potential to restore function following spinal cord injury (SCI). However, the time period of maturation for human NSCs in adult injured CNS is not well defined, posing fundamental questions about the design and implementation of NSC-based therapies. This work assessed human H9 NSCs that were implanted into sites of SCI in immunodeficient rats over a period of 1.5 years. Notably, grafts showed evidence of continued maturation over the entire assessment period. Markers of neuronal maturity were first expressed 3 months after grafting. However, neurogenesis, neuronal pruning, and neuronal enlargement continued over the next year, while total graft size remained stable over time. Axons emerged early from grafts in very high numbers, and half of these projections persisted by 1.5 years. Mature astrocyte markers first appeared after 6 months, while more mature oligodendrocyte markers were not present until 1 year after grafting. Astrocytes slowly migrated from grafts. Notably, functional recovery began more than 1 year after grafting. Thus, human NSCs retain an intrinsic human rate of maturation, despite implantation into the injured rodent spinal cord, yet they support delayed functional recovery, a finding of great importance in planning human clinical trials.
Authors
Paul Lu, Steven Ceto, Yaozhi Wang, Lori Graham, Di Wu, Hiromi Kumamaru, Eileen Staufenberg, Mark H. Tuszynski
Abstract
Fully activated innate immune cells are required for effective responses to infection, but their prompt deactivation and removal are essential for limiting tissue damage. Here, we have identified a critical role for the prolyl hydroxylase enzyme Phd2 in maintaining the balance between appropriate, predominantly neutrophil-mediated pathogen clearance and resolution of the innate immune response. We demonstrate that myeloid-specific loss of Phd2 resulted in an exaggerated inflammatory response to Streptococcus pneumonia, with increases in neutrophil motility, functional capacity, and survival. These enhanced neutrophil responses were dependent upon increases in glycolytic flux and glycogen stores. Systemic administration of a HIF–prolyl hydroxylase inhibitor replicated the Phd2-deficient phenotype of delayed inflammation resolution. Together, these data identify Phd2 as the dominant HIF-hydroxylase in neutrophils under normoxic conditions and link intrinsic regulation of glycolysis and glycogen stores to the resolution of neutrophil-mediated inflammatory responses. These results demonstrate the therapeutic potential of targeting metabolic pathways in the treatment of inflammatory disease.
Authors
Pranvera Sadiku, Joseph A. Willson, Rebecca S. Dickinson, Fiona Murphy, Alison J. Harris, Amy Lewis, David Sammut, Ananda S. Mirchandani, Eilise Ryan, Emily R. Watts, A.A. Roger Thompson, Helen M. Marriott, David H. Dockrell, Cormac T. Taylor, Martin Schneider, Patrick H. Maxwell, Edwin R. Chilvers, Massimilliano Mazzone, Veronica Moral, Chris W. Pugh, Peter J. Ratcliffe, Christopher J. Schofield, Bart Ghesquiere, Peter Carmeliet, Moira K.B. Whyte, Sarah R. Walmsley
Abstract
The pathophysiological function of the forkhead transcription factor FOXN3 remains to be explored. Here we report that FOXN3 is a transcriptional repressor that is physically associated with the SIN3A repressor complex in estrogen receptor–positive (ER+) cells. RNA immunoprecipitation–coupled high-throughput sequencing identified that NEAT1, an estrogen-inducible long noncoding RNA, is required for FOXN3 interactions with the SIN3A complex. ChIP-Seq and deep sequencing of RNA genomic targets revealed that the FOXN3-NEAT1-SIN3A complex represses genes including GATA3 that are critically involved in epithelial-to-mesenchymal transition (EMT). We demonstrated that the FOXN3-NEAT1-SIN3A complex promotes EMT and invasion of breast cancer cells in vitro as well as dissemination and metastasis of breast cancer in vivo. Interestingly, the FOXN3-NEAT1-SIN3A complex transrepresses ER itself, forming a negative-feedback loop in transcription regulation. Elevation of both FOXN3 and NEAT1 expression during breast cancer progression corresponded to diminished GATA3 expression, and high levels of FOXN3 and NEAT1 strongly correlated with higher histological grades and poor prognosis. Our experiments uncovered that NEAT1 is a facultative component of the SIN3A complex, shedding light on the mechanistic actions of NEAT1 and the SIN3A complex. Further, our study identified the ERα-NEAT1-FOXN3/NEAT1/SIN3A-GATA3 axis that is implicated in breast cancer metastasis, providing a mechanistic insight into the pathophysiological function of FOXN3.
Authors
Wanjin Li, Zihan Zhang, Xinhua Liu, Xiao Cheng, Yi Zhang, Xiao Han, Yu Zhang, Shumeng Liu, Jianguo Yang, Bosen Xu, Lin He, Luyang Sun, Jing Liang, Yongfeng Shang
Abstract
Angiogenesis is a multistep process that requires coordinated migration, proliferation, and junction formation of vascular endothelial cells (ECs) to form new vessel branches in response to growth stimuli. Major intracellular signaling pathways that regulate angiogenesis have been well elucidated, but key transcriptional regulators that mediate these signaling pathways and control EC behaviors are only beginning to be understood. Here, we show that YAP/TAZ, a transcriptional coactivator that acts as an end effector of Hippo signaling, is critical for sprouting angiogenesis and vascular barrier formation and maturation. In mice, endothelial-specific deletion of Yap/Taz led to blunted-end, aneurysm-like tip ECs with fewer and dysmorphic filopodia at the vascular front, a hyper-pruned vascular network, reduced and disarranged distributions of tight and adherens junction proteins, disrupted barrier integrity, subsequent hemorrhage in growing retina and brain vessels, and reduced pathological choroidal neovascularization. Mechanistically, YAP/TAZ activates actin cytoskeleton remodeling, an important component of filopodia formation and junction assembly. Moreover, YAP/TAZ coordinates EC proliferation and metabolic activity by upregulating MYC signaling. Overall, these results show that YAP/TAZ plays multifaceted roles for EC behaviors, proliferation, junction assembly, and metabolism in sprouting angiogenesis and barrier formation and maturation and could be a potential therapeutic target for treating neovascular diseases.
Authors
Jongshin Kim, Yoo Hyung Kim, Jaeryung Kim, Do Young Park, Hosung Bae, Da-Hye Lee, Kyun Hoo Kim, Seon Pyo Hong, Seung Pil Jang, Yoshiaki Kubota, Young-Guen Kwon, Dae-Sik Lim, Gou Young Koh
Copyright © 2017 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)