Protein kinase C activity, protein phosphorylation and germinal vesicle breakdown in Spisula oocytes.
To test the possible role of protein kinase C (C-kinase) in regulating germinal vesicle breakdown (GVBD) in Spisula oocytes, we studied the effects of phorbol esters and antagonists of C-kinase on GVBD and protein phosphorylation. Responses to these agents were compared to those elicited by fertilization or increased extracellular K+. The tumor-promoting phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), a potent agonist of C-kinase, elicited GVBD with half-maximal stimulation at 20 nM. By contrast, 4 alpha-phorbol-12,13-didecanoate, a phorbol ester which does not stimulate C-kinase, did not trigger GVBD. TPA accelerated GVBD when induced by excess K+, but it did not affect the time course of the process when initiated by fertilization. Three structurally different antagonists of C-kinase (W-7, H-7, and retinol) all blocked GVBD when induced by fertilization or TPA. When oocytes were preincubated with [32P]orthophosphate and then stimulated to undergo GVBD by fertilization, TPA, or 45 mM K+, protein phosphorylation was greatly increased, especially for a polypeptide(s) of about 45 kDa. Phosphorylation increased prior to GVBD. Retinol inhibited phosphorylation in activated eggs. C-kinase activity was demonstrated in oocyte extracts. These results strongly suggest that protein phosphorylation by C-kinase is involved in the pathway that regulates GVBD in Spisula oocytes.
Eckberg
W R
WR
Department of Zoology, Howard University, Washington, D.C. 20059.
Szuts
E Z
EZ
Carroll
A G
AG
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000818:Animals; D049872:Bivalvia / Q000502:physiology*; D005306:Fertilization; D007546:Isoquinolines / Q000494:pharmacology; D009865:Oocytes / Q000187:drug effects / Q000502:physiology*; D010703:Phorbol Esters / Q000494:pharmacology; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D010879:Piperazines / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013449:Sulfonamides / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014801:Vitamin A / Q000494:pharmacology
D007546:Isoquinolines; D010703:Phorbol Esters; D010750:Phosphoproteins; D010879:Piperazines; D013449:Sulfonamides; D014801:Vitamin A; C008876:phorbol-12,13-didecanoate; C017967:W 7; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D011188:Potassium