title: Differential inhibition by alpha and epsilonPKC pseudosubstrate sequences: a putative mechanism for preferential PKC activation in neonatal cardiac myocytes.
abstract: The aims of the current study were: 1) to determine if the epsilonPKC pseudosubstrate peptide (epsilonphi) (NH(2)-RKRQGAVRRRVHQVNG-COOH) could be used as an epsilonPKC-selective inhibitor in neonatal cardiac myocytes (NCMs) and 2) to determine if differences in the alpha and epsilonPKC autoinhibitory pseudosubstrate mechanisms could play roles in alpha and epsilonPKC-selective functions. Introduction of the epsilonphi into NCMs by transient permeabilization modestly attenuated 3 nM 4-beta PMA-induced slowing of contraction rate, an epsilonPKC mediated response (Circ Res. 76:654-663; J. Biol. Chem. 271:24962-24966). In contrast, the alphaPKC pseudosubstrate peptide (alphaphi) (NH(2)-RFARKGALRQKNVHEVK-COOH) was 6- to 10-fold more potent at antagonizing the 3 nM 4-beta PMA-induced slowing of contraction rate. Addition of purified PKC to the particulate cell fraction of NCMs promoted (32)P incorporation into 3 proteins of approximately 18, approximately 46 and approximately 97 kDa. The alphaphi antagonized these phosphorylations with IC(50) values of 1 - 5 microM. These IC(50) values were 1.8 - 4.7-fold lower than those observed for the epsilonphi. In in vitro phosphorylation assays with recombinant alpha or epsilon PKC isozymes the phi failed to inhibit the PKC isozyme as potently as the alphaphi peptide but both the alphaphi and the epsilonphi were equally effective inhibitors of the recombinant alphaPKC isozyme. In addition, in vitro cleavage of the epsilonphi by the protease Arg-C in lysates from NCMs treated with 3 nM 4-beta PMA was greatly enhanced when compared to that of the alphaPKC isozyme. Our studies suggest that the epsilonphi cannot be used as a selective inhibitor of the epsilonPKC isozyme in NCMs and that there are differences in the epsilonPKC and alphaPKC autoinhibitory pseudosubstrate mechanisms.
authors.affiliation: The Department of Pharmacology and Toxicology, School of Medicine and The Program in Cell Signaling, Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, GA 30912-2300, USA. jjohnson@mail.mcg.edu
authors.forename: John A
authors.initials: JA
authors.lastname: Johnson
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D007527:Isoenzymes / Q000502:physiology; D009200:Myocardial Contraction / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000201:enzymology*; D010446:Peptide Fragments / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000037:antagonists & inhibitors* / Q000378:metabolism; D051571:Protein Kinase C-alpha; D051744:Protein Kinase C-epsilon; D051381:Rats; D017207:Rats, Sprague-Dawley; D013379:Substrate Specificity
chemical_list: D004791:Enzyme Inhibitors; D007527:Isoenzymes; D010446:Peptide Fragments; C497257:Prkce protein, rat; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D051744:Protein Kinase C-epsilon