REGULATION OF PROTEIN-TYROSINE PHOSPHORYLATION IN HUMAN SPERM BY A CALCIUM CALMODULIN-DEPENDENT MECHANISM - IDENTIFICATION OF A KINASE ANCHOR PROTEINS AS MAJOR SUBSTRATES FOR TYROSINE PHOSPHORYLATION/

Signal transduction pathways regulate various aspects of mammalian spe rm function. When human sperm were incubated in a medium supporting ca pacitation, proteins became tyrosine-phosphorylated in a time-dependen t manner. This phosphorylation was inhibited by genistein, a protein t yrosine kinase inhibitor. Phosphorylation was also reduced when sperm were incubated either in the presence of increasing concentrations of extracellular Ca2+ or in a medium containing the Ca2+ ionophore A23187 . This Ca2+-induced dephosphorylation was calmodulin-dependent, sugges ting that calcineurin was involved. Zn this regard, the calcineurin in hibitor deltamethrin inhibited the Ca2+ ionophore-induced dephosphoryl ation. A limited number of M(r) 80,000-105,000 polypeptides were the m ost prominent phosphotyrosine-containing proteins present in human spe rm. Unlike mouse sperm, which contains a tyrosine-phosphorylated isofo rm of hexokinase, a phosphotyrosine-containing hexokinase in human spe rm was not detected. Most of the tyrosine-phosphorylated proteins were Triton X-100-insoluble and were localized to the principal piece of t he flagellum, the region where the cytoskeletal fibrous sheath is foun d. Prominent phosphotyrosine-containing proteins of M(r) 82,000 and 97 ,000 were identified as the human homologues of mouse sperm AKAP82, th e major fibrous sheath protein, and pro-AKAP82, its precursor polypept ide, respectively. These proteins are A Kinase Anchor Proteins, polype ptides that sequester protein kinase A to subcellular locations. Taken together, these results suggest that protein tyrosine phosphorylation may be part of a signal transduction cascade(s) regulating events per taining to capacitation and/or motility in mammalian sperm and that an interrelationship between tyrosine kinase and cAMP signaling pathways exists in these cells. (C) 1996 Academic Press, Inc.