Treatment of human spermatozoa with seminal plasma inhibits protein tyrosine phosphorylation

It has long been known that seminal plasma contains factors that influencethe fertilizing capacity of spermatozoa in many different ways. However,little is understood of the biochemical cascades triggered when spermatozoaand seminal plasma interact. In this study, we examined how incubation withseminal plasma affected protein tyrosine phosphorylation in humanspermatozoa. Increased protein tyrosine phosphorylation is a hallmark ofsperm capacitation in several mammalian species, including human. Seminalplasma blocks protein tyrosine phosphorylation when added to washed,non-capacitated spermatozoa. Removal of seminal plasma and incubation incapacitating medium led to partial recovery of the tyrosine phosphorylationcascade. Addition of seminal plasma to a suspension of spermatozoapreviously incubated for 5 h under capacitating conditions decreased thelevel of tyrosine phosphorylation on all proteins in a dose-dependentmanner. In this case, the phosphotyrosine signal did not increase uponremoval of seminal plasma followed by overnight incubation in freshcapacitating media, indicating that removal of seminal plasma was necessarybut not sufficient for protein tyrosine phosphorylation to occur. Theseresults indicate that human seminal plasma contains factors that influencethe tyrosine phosphorylation status of human spermatozoa.