Stimulation of protein tyrosine phosphorylation by platelet-activating factor and progesterone in human spermatozoa

Tyrosine phosphorylation of proteins is involved in several sperm functions, including capacitation, motility, and acrosome reaction of spermatozoa. This study was undertaken to determine changes of tyrosine phosphorylation during 'in vitro' capacitation as well as the ability of platelet-activating factor (PAF) and progesterone (P), two known activators of sperm functions, to stimulate tyrosine phosphorylation of human sperm proteins. Spermatozoa were capacitated in BSA-containing medium and incubated with PAF (10-1000 nM) and progesterone (0.1-1 microgram/ml). After SDS-PAGE, sperm proteins were transferred to nitrocellulose and tyrosine phosphorylated proteins immunodetected by reacting with anti-phosphotyrosine antibody. The antibody mainly reacted with two proteins of approximately 97 and 75 kDa. The level of phosphorylation increased in these two proteins as a function of capacitation time, with a maximum between 120 and 180 min. In addition, phosphorylation in these two proteins was increased in capacitated spermatozoa by treatment with progesterone and PAF and was greatly reduced by pre-incubation with the tryosine kinase inhibitor erbstatin. Furthermore, pre-incubation with the two tyrosine kinase inhibitors erbstatin and genistein inhibited the induction of acrosome reaction by progesterone and, partially, by PAF. Our results suggest a role for tyrosine kinase(s) in the mechanism of capacitation and activation of human spermatozoa by PAF and progesterone.