Phorbol ester treatment stimulates tyrosine phosphorylation of a sea urchin egg cortex protein

Fertilization of the sea urchin egg results in the phosphorylation, on tyrosine, of a high molecular weight protein localized in the egg cortex. In the present study, treatment of unfertilized eggs with the phorbol ester 12-O-tetradecanoylphorbol 13-acetate stimulated tyrosine phosphorylation of the high molecular weight cortical protein to levels three- to fivefold higher than that occurring in response to fertilization. Experiments using agents that inhibit the egg Na+/H+ exchange system or mimic the fertilization-induced shift in cytoplasmic pHi, suggest a signal transduction pathway in which protein kinase C activates the egg Na+/H+ exchange system and the resultant cytoplasmic pHi shift promotes tyrosine phosphorylation of the high molecular weight cortical protein.