Investigation of the role of SRC in capacitation-associated tyrosine phosphorylation of human spermatozoa.

The process of capacitation is a pre-requisite for mammalian spermatozoa allowing them to gain the ability to fertilize an oocyte. A fundamental part of this mechanism is a dramatic increase in the level of tyrosine phosphorylation. Implicated in this process is a unique cAMP/protein kinase A (PKA)-mediated pathway involving an intermediate PKA-activated tyrosine kinase suggested to be pp60(c-src) (SRC) in the mouse. This study has verified the importance of SRC as a key intermediate kinase in promoting the tyrosine phosphorylation events associated with human sperm capacitation. The presence of SRC in human spermatozoa was confirmed immunocytochemically and the kinase was localized to subcellular domains compatible with a role in tyrosine phosphorylation. Additionally SRC co-immunoprecipitated with PKA and became activated by phosphorylation of the Y416 residue during human sperm capacitation. Furthermore, the suppression of PKA and SRC through the application of specific inhibitors led to a dramatic decrease in tyrosine phosphorylation. However, although the inhibition of PKA was also accompanied by a suppression of sperm motility, SRC inhibition did not induce a similar response.