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Identification of Ras and Its Downstream Signaling Elements and Their Potential Role in Hamster Sperm Motility¹

^a Department of Cell Biology, Vanderbilt University, Nashville, Tennessee 37232

Ras, a member of the small G-protein family, regulates multiple signaling pathways in somatic cells. The objectives of the present study included the characterization and localization of Ras and the identification of its downstream effectors in hamster spermatozoa. Immunoblot analysis with a pan-Ras monoclonal antibody localized Ras to the particulate fraction of sonicated testicular and caput and cauda epididymal spermatozoa. However, Ras was present in both the particulate and soluble fractions of spermatocytes and round spermatids, suggesting that its membrane recruitment is completed during spermiogenesis. Immunoblots of plasma membrane fractions demonstrated that hamster spermatozoa express both N-Ras and K-Ras. Indirect immunofluorescence with pan-Ras antibody localized Ras to the flagellum. Immunoblot analysis of sperm plasma membrane fractions demonstrated the presence of phosphatidylinositol 3-kinase (PI3-kinase) and protein kinase C (PKC), the downstream targets of Ras, and coimmunoprecipitation analysis demonstrated their interaction with Ras. Inhibitors of PI3-kinase (wortmannin and 2-(4- morpholinyl)-8-phenyl-4H-1-benzopyran-4-one) and PKC (staurosporine) inhibited the hyperactivation of sperm motility during capacitation in a dose-dependent manner, indicating that both PI3-kinase and PKC are associated with development of this motility pattern. The interaction of Ras with both PI3-kinase and PKC suggests that Ras may regulate several signaling pathways in spermatozoa.

¹ This research was supported by NIH grants HD20419 and HD36824. Some of these data were presented in abstract form for the 34th Annual Meeting of the Society for Reproduction (Biol Reprod 2001; 64(suppl 1):195).

² Correspondence. FAX: 615 343 4539; subir.nag-das{at}mcmail.vanderbilt.edu

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