Protein kinase C activity and protein phosphorylation in mouse sperm

It has been suggested that the Ca2+ and phospholipid dependent protein kinase (protein kinase C; PKC) plays some intermediary roles in the regulation of the zona pellucida-induced acrosome reaction in mouse sperm. We here demonstrated that PKC activity is in the cytosol fraction of mouse sperm and that treatment of sperm with a PKC activator, 12-O-tetradecanoyl phorbol 13-acetate (TPA), induces translocation of PKC to the membrane fraction. Treatment of epididymal sperm with 20 ng/ml TPA or 20 microM of the Ca2+ ionophore A23187 did not induce any specific protein phosphorylation. However, two specific proteins, with molecular weights of 215 kDa and 35 kDa, were significantly phosphorylated when sperm were incubated with A23187 prior to TPA treatment. A similar synergistic effect of TPA and A23187 was observed in Ca2+ accumulation in sperm. We also demonstrated that exogenous PKC purified from human pancreatic cells catalyzes the phosphorylation of these two proteins in vitro as well. The present data support the idea that the activation of PKC and subsequent protein phosphorylation are involved in the regulation of the zona pellucida-induced acrosome reaction.