Protein kinase Cε interacts with cytochrome c oxidase subunit IV and enhances cytochrome c oxidase activity in neonatal cardiac myocyte preconditioning

We have previously identified a phorbol ester-induced PKCε (protein kinase Cε) interaction with the (∼18 kDa) COIV [CO (cytochrome c oxidase) subunit IV] in NCMs (neonatal cardiac myocytes). Since PKCε has been implicated as a key mediator of cardiac PC (preconditioning), we examined whether hypoxic PC could induce PKCε-COIV interactions. Similar to our recent study with phorbol esters [Ogbi, Chew, Pohl, Stuchlik, Ogbi and Johnson (2004) Biochem. J. 382, 923-932], we observed a time-dependent increase in the in vitro phosphorylation of an approx. 18 kDa protein in particulate cell fractions isolated from NCMs subjected to 1-60 min of hypoxia. Introduction of a PKCε-selective translocation inhibitor into cells attenuated this in vitro phosphorylation. Furthermore, when mitochondria isolated from NCMs exposed to 30 min of hypoxia were subjected to immunoprecipitation analyses using PKCε-selective antisera, we observed an 11.1-fold increase in PKCε-COIV co-precipitation. In addition, we observed up to 4-fold increases in CO activity after brief NCM hypoxia exposures that were also attenuated by introducing a PKCε-selective translocation inhibitor into the cells. Finally, in Western-blot analyses, we observed a > 2-fold PC-induced protection of COIV levels after 9 h index hypoxia. Our studies suggest that a PKCε-COIV interaction and an enhancement of CO activity occur in NCM hypoxic PC. We therefore propose novel mechanisms of PKCε-mediated PC involving enhanced energetics, decreased mitochondrial reactive oxygen species production and the preservation of COIV levels.