Differential activation of mitogen-activated protein kinase cascades and apoptosis by protein kinase C ε and δ in neonatal rat ventricular myocytes

Protein kinase C (PKC) epsilon and PKC delta 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 PKC epsilon and PKC delta were used to test if either or both of these PKCs are sufficient to activate ERKs, JNKs, and/or p38(MAPK) in NRVMs. Adv-caPKC epsilon infection (1 to 25 multiplicities of viral infection (MOI); 4 to 48 hours) increased total PKC epsilon levels in a time- and dose-dependent manner, with maximal expression observed 8 hours after Adv infection. Adv-caPKC epsilon induced a time- and dose-dependent increase in phosphorylated p42 and p44 ERKs, as compared with a control Adv encoding beta -galactosidase (Adv-ne beta gal). Maximal ERK phosphorylation occurred 8 hours after Adv infection. In contrast, JNK was only minimally activated, and p38(MAPK) was relatively unaffected. Adv-caPKC delta infection (2 to 25 MOI, 4 to 48 hours) increased total PKC delta levels in a similar fashion. Adv-caPKC delta (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-caPKC delta, but not Adv-caPKCE, induced NRVM apoptosis. We conclude that the novel PKCs differentially regulate MAPK cascades and apoptosis in an isoenzyme-specific and time-dependent manner.