Smap1 deficiency perturbs receptor trafficking and predisposes mice to myelodysplasia
Shunsuke Kon, … , Takuro Nakamura, Masanobu Satake
Shunsuke Kon, … , Takuro Nakamura, Masanobu Satake
Published February 22, 2013
Citation Information: J Clin Invest. 2013;123(3):1123-1137. https://doi.org/10.1172/JCI63711.
View: Text | PDF
Research Article Hematology

Smap1 deficiency perturbs receptor trafficking and predisposes mice to myelodysplasia

Abstract

The formation of clathrin-coated vesicles is essential for intracellular membrane trafficking between subcellular compartments and is triggered by the ARF family of small GTPases. We previously identified SMAP1 as an ARF6 GTPase-activating protein that functions in clathrin-dependent endocytosis. Because abnormalities in clathrin-dependent trafficking are often associated with oncogenesis, we targeted Smap1 in mice to examine its physiological and pathological significance. Smap1-deficent mice exhibited healthy growth, but their erythroblasts showed enhanced transferrin endocytosis. In mast cells cultured in SCF, Smap1 deficiency did not affect the internalization of c-KIT but impaired the sorting of internalized c-KIT from multivesicular bodies to lysosomes, resulting in intracellular accumulation of undegraded c-KIT that was accompanied by enhanced activation of ERK and increased cell growth. Interestingly, approximately 50% of aged Smap1-deficient mice developed anemia associated with morphologically dysplastic cells of erythroid-myeloid lineage, which are hematological abnormalities similar to myelodysplastic syndrome (MDS) in humans. Furthermore, some Smap1-deficient mice developed acute myeloid leukemia (AML) of various subtypes. Collectively, to our knowledge these results provide the first evidence in a mouse model that the deregulation of clathrin-dependent membrane trafficking may be involved in the development of MDS and subsequent AML.

Authors

Shunsuke Kon, Naoko Minegishi, Kenji Tanabe, Toshio Watanabe, Tomo Funaki, Won Fen Wong, Daisuke Sakamoto, Yudai Higuchi, Hiroshi Kiyonari, Katsutoshi Asano, Yoichiro Iwakura, Manabu Fukumoto, Motomi Osato, Masashi Sanada, Seishi Ogawa, Takuro Nakamura, Masanobu Satake

×

Figure 7

Enhanced erythropoiesis in Smap1–/– mice with MDS (ID no.

Options: View larger image (or click on image) Download as PowerPoint
Enhanced erythropoiesis in Smap1–/– mice with MDS (ID no. 47; see Tabl...
47; see Table 3). (A and G) Flow cytometry analyses of (A) bone marrow cells and (G) splenocytes prepared from Smap1+/+ and Smap1–/– mice. The cells were stained for indicated hematopoietic lineage markers. The numbers represent percentages of cells in each gated box. Flow cytometry analyses were performed for all Smap1–/– mice with MDS, and reproducible results were obtained. (B–F) Histology of spleens. (B) A macroscopic view of the spleen. Note the enlargement of the Smap1–/– spleen. (C and D) Sections were stained by hematoxylin and eosin. Note the enrichment of cells with densely stained nuclei in the red pulp of the targeted spleen. (E and F) Smears of Giemsa-stained splenocytes. Erythroblasts with densely stained nuclei are evident in the Smap1–/– smear. Scale bar: 10 μm. (H) CFU-C assay of bone marrow cells. Cells from wild-type and Smap1–/– mice were assayed in vitro for their CFU-C activity. The numbers of colonies were counted under a microscope, and the morphology was classified as shown. Triplicate cultures were prepared from each mouse, and 4 independent pairs of older than 1 year Smap1+/+ and Smap1–/– mice were used. The panel shows the averages ± SD of CFU-C values obtained from 12 cultures from each genotype. *P < 0.0. (I) Estimation of replicating cells in the spleen. Splenocytes from Smap1+/+ and Smap1–/– mice were processed for flow cytometry analysis of GATA1 and TOPRO3. 2N and 4N represent the diploid and tetraploid status of chromatin.