STIMULATION OF PROTEIN-TYROSINE PHOSPHORYLATION BY PLATELET-ACTIVATING-FACTOR AND PROGESTERONE IN HUMAN SPERMATOZOA

Tyrosine phosphorylation of proteins is involved in several sperm func tions, including capacitation, motility, and acrosome reaction of sper matozoa. This study was undertaken to determine changes of tyrosine ph osphorylation during 'in vitro' capacitation as well as the ability of platelet-activating factor (PAF) and progesterone (P), two known acti vators of sperm functions, to stimulate tyrosine phosphorylation of hu man sperm proteins. Spermatozoa were capacitated in BSA-containing med ium and incubated with PAF (10-1000 nM) and progesterone (0.1-1 mu g/m l). After SDS-PAGE, sperm proteins were transferred to nitrocellulose and tyrosine phosphorylated proteins immunodetected by reacting with a nti-phosphotyrosine antibody. The antibody mainly reacted with two pro teins of approximately 97 and 75 kDa. The level of phosphorylation inc reased in these two proteins as a function of capacitation time, with a maximum between 120 and 180 min. In addition, phosphorylation in the se two proteins was increased in capacitated spermatozoa by treatment with progesterone and PAF and was greatly reduced by pre-incubation wi th the tyrosine kinase inhibitor erbstatin. Furthermore, pre-incubatio n with the two tyrosine kinase inhibitors erbstatin and genistein inhi bited the induction of acrosome reaction by progesterone and, partiall y, by PAP. Our results suggest a role for tyrosine kinase(s) in the me chanism of capacitation and activation of human spermatozoa by PAF and progesterone.