Determination of the role of ubiquitin proteasome system proteins on human sperm capatitation and acrosomal reaction and effect on fertilization

Ubiquitin proteasome system (UPS) have roles in sperm capacitation, acrosome reaction, binding of sperm to zona-pellucida (ZP) in mammalian reproductive system. In these processes, proteins and inhibitors associated with sperm proteasome affect fertilization; however, effects of UPS proteins p97/VCP (Valosine containing protein), PAWP (Postacrosomal Sheath WW Domain Binding Protein) and NEDL2 (Nedd4-like ligase 2) on sperm capacitation, acrosome reaction, and fertility process have not yet been investigated. We hypothesized p97/VCP, PAWP, and NEDL2 may have role in sperm capacitation, acrosomal reaction, and infertiliy process. Expression of these proteins were determined by immunoflouresecence labelling, flow cytometry, image-based flow cytometry, and Western blotting. The phosphorlytation of p97/VCP increased in sperm tail and the expression of p97/VCP decreased by DBEQ during in vitro capacitation. While expression of NEDL2 decreased significatly, PAWP expression did not change during this process. p97/VCP and NEDL2 interacted with 26S proteasomes during capacitation and PAWP did not interact. Expression of PSA increased during captitation and decreased by presence of inhibitors. While expression of p97/VCP was higher in infertile men when compared to fertile men, infertile men had lower expression level of NEDL2 than fertile men. These results indicate that p97/VCP, NEDL2 and PAWP have roles in human sperm capacitation, acrosomal reaction. And p97/VCP and Nedl2 may allow the usage of these proteins at infertility evaluation. Key words: Capacitation, human sperm, infertility, NEDL2, PAWP, p97/VCP, Ubiquitin proteasome system