REGULATION OF MATURATION-PROMOTING FACTOR BY PROTEIN-KINASE-C IN CHAETOPTERUS OOCYTES

We present the results of a variety of studies showing that activation of protein kinase C (PKC) in oocytes of Chaetopterus pergamentaceus r esults in germinal vesicle breakdown (GVBD). Phorbol esters and diacyl glycerol can initiate a morphologically normal GVBD accompanied by a s pectrum of associated biochemical processes, including increased prote in phosphorylation, a shift in protein synthesis and activation of a p rotein kinase, maturation promoting factor (MPF). MPF activation is es sential for GVBD in response to phorbol esters. In addition, inhibitor s of PKC can block naturally-induced GVBD. We also present evidence th at PKC can phosphorylate p34(cdc2), the catalytic subunit of MPF and t hat phosphorylation by PKC increases the histone H1 kinase activity of immunoprecipitated MPF. Immunoblot studies show that Chaetopterus ooc yte p34(cdc2) is not tyrosine phosphorylated prior to the initiation o f GVBD, indicating that activation of MPF at GVBD in this species does not require p80(cdc25), th,activator of MPF at mitosis. These results suggest that PKC is an essential regulator of GVBD which can directly phosphorylate and regulate p34(cdc2). Since PKC is the intracellular receptor for and is directly activated by tumor-promoters, tumor promo tion might involve acceleration of the cell cycle through modification of the enzymatic activity of MPF by PKC.