Protein kinase A activity and protein phosphorylation during the mouse sperm acrosomal reaction

Using two-dimensional gel electrophoresis, changes in protein phosphorylation caused by cyclic nucleotide-dependent protein kinases were analyzed with or without exposure to a protein kinase inhibitor, H-8, during the mouse sperm acrosomal reaction. The acrosomal reaction, induced by the treatment of sperm with dibutyryl cyclic AMP or dibutyryl cyclic GMP, was inhibited by H-8. The activities of cyclic AMP-dependent protein kinase (PKA) and cyclic GMP-dependent protein kinase induced by the sperm extract were also inhibited by H-8. When endogenous PKA in sperm was activated by the addition of cyclic AMP, a 45-kDa protein spot identified by electrophoresis indicated the occurrence of phosphorylation in vivo. Furthermore, the enhanced phosphorylation of the 45-kDa protein spot was inhibited by H-8. These results suggest that the PKA-catalyzed phosphorylation of the 45-kDa protein may be involved in the regulation of the mouse sperm acrosomal reaction.