Stem cell factor/c-kit up-regulates cyclin D3 and promotes cell cycle progression via the phosphoinositide 3-kinase/p70 S6 kinase pathway in spermatogonia.
Stem cell factor (SCF)/c-kit plays an important role in the regulation of hematopoiesis, melanogenesis, and spermatogenesis. In the testis, the SCF/c-kit system is believed to regulate germ cell proliferation, meiosis, and apoptosis. Studies with type A spermatogonia in vivo and in vitro have indicated that SCF induces DNA synthesis and proliferation. However, the signaling pathway for this function of SCF/c-kit has not been elucidated. We now demonstrate that SCF activates phosphoinositide 3-kinase (PI3-K) and p70 S6 kinase (p70S6K) and that rapamycin, a FRAP/mammalian target of rapamycin-dependent inhibitor of p70S6K, completely inhibited bromodeoxyuridine incorporation induced by SCF in primary cultures of spermatogonia. SCF induced cyclin D3 expression and phosphorylation of the retinoblastoma protein through a pathway that is sensitive to both wortmannin and rapamycin. Furthermore, AKT, but not protein kinase C-zeta, is used by SCF/c-kit/PI3-K to activate p70S6K. Dominant negative AKT-K179M completely abolished p70S6K phosphorylation induced by the constitutively active PI3-K catalytic subunit p110. Constitutively active v-AKT highly phosphorylated p70S6K, which was totally inhibited by rapamycin. Thus, SCF/c-kit uses a rapamycin-sensitive PI3-K/AKT/p70S6K/cyclin D3 pathway to promote spermatogonial cell proliferation.
Feng
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Department of Cell Biology, Georgetown University Medical Center, Washington, DC. 20007, USA.
Ravindranath
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D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D029681:Arabidopsis Proteins; D001973:Bromodeoxyuridine / Q000378:metabolism; D002453:Cell Cycle / Q000502:physiology*; D002455:Cell Division / Q000502:physiology; D056743:Cyclin D3; D016213:Cyclins / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015151:Immunoblotting; D007166:Immunosuppressive Agents / Q000494:pharmacology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008954:Models, Biological; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D010940:Plant Proteins / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D011493:Protein Kinase C / Q000378:metabolism; D019009:Proto-Oncogene Proteins c-kit / Q000378:metabolism* / Q000502:physiology; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism*; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D013093:Spermatogonia / Q000378:metabolism*; D019089:Stem Cell Factor / Q000378:metabolism* / Q000502:physiology; D015854:Up-Regulation; D000077191:Wortmannin; D000099221:Protein Kinase C zeta
D000730:Androstadienes; D029681:Arabidopsis Proteins; D001973:Bromodeoxyuridine; D056743:Cyclin D3; D016213:Cyclins; D004791:Enzyme Inhibitors; D007166:Immunosuppressive Agents; D019869:Phosphatidylinositol 3-Kinases; D010940:Plant Proteins; D015221:Potassium Channels; D011493:Protein Kinase C; D019009:Proto-Oncogene Proteins c-kit; D019893:Ribosomal Protein S6 Kinases; D020123:Sirolimus; D019089:Stem Cell Factor; D000077191:Wortmannin; D000099221:Protein Kinase C zeta; C534697:Ccnd3 protein, mouse; C074500:AKT1 protein, Arabidopsis