Activation of protein kinase Ceta triggers cortical granule exocytosis in Xenopus oocytes.

Previous work has shown that phorbol esters or diacylglycerol trigger cortical granule exocytosis in Xenopus oocytes. We sought to identify the isoform(s) of protein kinase C (PKC) that mediate(s) this regulated secretory event. Because this process is initiated by lipid activators of PKC but is independent of calcium ions, we focused on the family of novel (calcium-independent) PKCs. Pharmacological investigations using Gö6976 and Gö6983 tended to exclude PKCdelta, epsilon and mu as secretory triggers. Subcellular fractionation and immunoblot data revealed that these oocytes expressed all five members of the novel PKC family, but it was only PKCeta that colocalized with cortical granules. Finally, expression of wild type or constitutively active forms of PKCdelta and eta strongly supported the conclusion that it is PKCeta that initiates cortical granule exocytosis in these cells. These observations represent an important step in identifying the mechanism of secretory triggering in this system.