Evidence for Involvement of Protein Kinase C in Germinal Vesicle Breakdown in Chaetopterus

We have examined the possible involvement of protein kinase C (C-kinase) in the initiation of germinal vesicle breakdown (GVBD) in Chaetopterus oocytes. Two tumor-promoting phorbol esters (phorbol-12, 13-dibezoate and 12-0-tetradecanoylphorbol-13-acetate TPA]) and a permeant diacylglycerol (1-oleoyl-2-acetylglycerol), potent activators of C-Kinase, triggered GVBD. Two other phorbol esters (phorbol-13-monoacetate and 4α-phorbol-12, 13-didecanoate), which do not activate C-kinase, were inactive. Three C-kinase antagonists (W-7, H-7 and retinol) inhibited both naturally-and TPA-induced GVBD, whereas W–5, a much less inhibitory W–7 analog, had no effect on GVBD. Triggering of GVBD by TPA was independent of extracellular Ca²⁺. Although naturally-induced GVBD was blocked by micromolar concentrations of the calmodulin antagonist, calmidazolium (R24571), and by millimolar concentrations of the permeant cAMP analog, dibutryryl cAMP, TPA-induced GVBD was not affected by these agents. These results support the hypothesis that both C-kinase and calmodulin are involved in the sequence of events leading to GVBD in this species.