Differential Activation of Mitogen-Activated Protein Kinase Cascades and Apoptosis by Protein Kinase C ε and δ in Neonatal Rat Ventricular Myocytes

Abstract

Protein kinase C (PKC) ε and PKCδ translocation in neonatal rat ventricular myocytes (NRVMs) is accompanied by subsequent activation of the ERK, JNK, and p38 MAPK cascades; however, it is not known if either or both novel PKCs are necessary for their downstream activation. Use of PKC inhibitors to answer this question is complicated by a lack of isoenzyme specificity, and the fact that many PKC inhibitors stimulate JNK and p38 MAPK activity. Therefore, replication-defective adenoviruses (Advs) encoding constitutively active (ca) mutants of PKCε and PKCδ were used to test if either or both of these PKCs are sufficient to activate ERKs, JNKs, and/or p38 MAPK in NRVMs. Adv-caPKCε infection (1 to 25 multiplicities of viral infection (MOI); 4 to 48 hours) increased total PKCε levels in a time- and dose-dependent manner, with maximal expression observed 8 hours after Adv infection. Adv-caPKCε induced a time- and dose-dependent increase in phosphorylated p42 and p44 ERKs, as compared with a control Adv encoding β-galactosidase (Adv-neβgal). Maximal ERK phosphorylation occurred 8 hours after Adv infection. In contrast, JNK was only minimally activated, and p38 MAPK was relatively unaffected. Adv-caPKCδ infection (1 to 25 MOI, 4 to 48 hours) increased total PKCδ levels in a similar fashion. Adv-caPKCδ (5 MOI) induced a 29-fold increase in phosphorylated p54 JNK, and a 15-fold increase in phosphorylated p38 MAPK 24 hours after Adv infection. In contrast, p42 and p44 ERK were only minimally activated. Whereas neither Adv induced NRVM hypertrophy, Adv-caPKCδ, but not Adv-caPKCε, induced NRVM apoptosis. We conclude that the novel PKCs differentially regulate MAPK cascades and apoptosis in an isoenzyme-specific and time-dependent manner.