Cross-regulation of Novel Protein Kinase C (PKC) Isoform Function in Cardiomyocytes

• Published in: The Journal of biological chemistry 2003-04, Vol.278 (16), p.14555-14564
• Main Authors: Rybin, Vitalyi O., Sabri, Abdelkarim, Short, Jacob, Braz, Julian C., Molkentin, Jeffery D., Steinberg, Susan F.
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M212644200

Recent studies identify conventional protein kinase C (PKC) isoform phosphorylations at conserved residues in the activation loop and C terminus as maturational events that influence enzyme activity and targeting but are not dynamically regulated by second messengers. In contrast, this study identifies phorbol 12-myristoyl 13-acetate (PMA)- and norepinephrine-induced phosphorylations of PKCε (at the C-terminal hydrophobic motif) and PKCδ (at the activation loop) as events that accompany endogenous novel PKC (nPKC) isoform activation in neonatal rat cardiomyocytes. Agonist-induced nPKC phosphorylations are prevented (and the kinetics of PMA-dependent PKC down-regulation are slowed) by pharmacologic inhibitors of nPKC kinase activity. PKCδ is recovered from PMA-treated cultures with increasedin vitro lipid-independent kinase activity (and altered substrate specificity); the PMA-dependent increase in PKCδ kinase activity is attenuated when PKCδ activation loop phosphorylation is prevented. To distinguish roles of individual nPKC isoforms in nPKC phosphorylations, wild-type (WT) and dominant negative (DN) PKCδ and PKCε mutants were introduced into cardiomyocyte cultures using adenovirus-mediated gene transfer. WT-PKCδ and WT-PKCε are highly phosphorylated at activation loop and hydrophobic motif sites, even in the absence of allosteric activators. DN-PKCδ is phosphorylated at the activation loop but not the hydrophobic motif; DN-PKCε is phosphorylated at the hydrophobic motif but not the activation loop. Collectively, these results identify a role for PKCε in nPKC activation loop phosphorylations and PKCδ in nPKC hydrophobic motif phosphorylations. Agonist-induced nPKC isoform phosphorylations that accompany activation/translocation of the enzyme contribute to the regulation of PKCδ kinase activity, may influence nPKC isoform trafficking/down-regulation, and introduce functionally important cross-talk for nPKC signaling pathways in cardiomyocytes.