Translocation of the Classic Protein Kinase C Isoforms in Porcine Oocytes: Implications of Protein Kinase C Involvement in the Regulation of Nuclear Activity and Cortical Granule Exocytosis

Abstract

Protein kinase C (PKC) is a family of Ser/Thr protein kinases categorized into three subfamilies: classical, novel, and atypical. The subcellular localization of classical PKCα, -βI, and -γ in the process of porcine oocyte maturation, fertilization, and parthenogenetic activation and their involvement in cortical granule (CG) exocytosis were investigated. The results of Western blot showed that PKCα, -βI, and -γ were expressed in the oocytes at the germinal vesicle (GV) and metaphase II (MII) stages. Confocal microscopy revealed that the three PKC isoforms were concentrated in the GV but evenly distributed in the cytoplasm of MII eggs. PKCα and -γ were translocated to the plasma membrane soon after sperm penetration. cPKCs migrated into the pronucleus in fertilized eggs. Following treatment with a PKC activator, phorbol 12-myristate 13-acetate (PMA), CGs were released and PKCα and -γ were translocated to the membrane. The CG exocytosis and PKC redistribution induced by PMA could be blocked by the PKC inhibitor staurosporine. Parthenogenetic stimulation with ionophore A23187 or electrical pulse also induced cPKC translocation and CG exocytosis. Eggs injected with PKCα isoform-specific antibody failed to undergo CG exocytosis after PMA treatment or fertilization. The results suggest that cPKCs, especially the α-isotype, regulate nuclear function and CG exocytosis in porcine eggs.