Regulation of Protein Tyrosine Phosphorylation during Bovine Sperm Capacitation by a Cyclic Adenosine 3',5'-Monophosphate-Dependent Pathway1
Biology of Reproduction
Mammalian sperm capacitation, defined as an obligatory maturational process leading to the development of the fertilization-competent state, results from a poorly understood series of morphological and molecular events. We report here that ejaculated bovine sperm, incubated under conditions that support capacitation in vitro, display a reproducible pattern of protein tyrosine phosphorylations that are regulated by a cAMP-dependent pathway. The appearance of these tyrosine phosphorylated
... correlated temporally with the time course of capacitation induced by heparin, and these phosphorylations displayed a similar heparin concentration dependence. Glucose, which inhibits capacitation, inhibited these protein tyrosine phosphorylations in media containing heparin. The biologically active cAMP analogues (dibutyryl cAMP [db-cAMP], 8-bromo cAMP, Sp-cAMPS) and the phosphodiesterase inhibitor 3-isobutyl-1methylxanthine (IBMX) induced the same protein tyrosine phosphorylation patterns as seen with heparin. Moreover, these cAMP agonists could overcome the inhibition of the heparininduced tyrosine phosphorylations by glucose. In contrast, Rp-adenosine-3',5'-cyclic monophosphorothioate (Rp-cAMPS), a protein kinase A (PK-A) antagonist, blocked the capacitationassociated increases in protein tyrosine phosphorylation. This cAMP regulation of the protein tyrosine phosphorylation pattern is mediated by PK-A since N-[2-(p-bromocinnamylamino)ethyll-5-isoquinolinesulfonamide-dihydrochloride (H89), another in- hibitor of PK-A, inhibited the heparin-induced protein tyrosine phosphorylation pattern in a concentration-dependent manner in either the absence or presence of db-cAMP, IBMX, and glucose. These data support a model for sperm capacitation that includes protein tyrosine phosphorylation as an important regulatory pathway, and a role for cAMP/PK-A in the regulation of this pathway leading to capacitation. These studies are the first to report a unique interrelationship between tyrosine kinase/ phosphatase and cAMP signaling pathways at the level of PK-A in bovine sperm capacitation.