Differential activation of mitogen-activated protein kinase cascades and apoptosis by protein kinase C epsilon and delta 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 bo th novel PKCs are necessary for their downstream activation. Use of PKC inh ibitors to answer this question is complicated by a lack of isoenzyme speci ficity, and the fact that many PKC inhibitors stimulate JNK and p38(MAPK) a ctivity. Therefore, replication-defective adenoviruses (Advs) encoding cons titutively active (ca) mutants of PKC epsilon and PKC delta were used to te st if either or both of these PKCs are sufficient to activate ERKs, JNKs, a nd/or p38(MAPK) in NRVMs. Adv-caPKC epsilon infection (1 to 25 multipliciti es of viral infection (MOI); 4 to 48 hours) increased total PKC epsilon lev els in a time- and dose-dependent manner, with maximal expression observed 8 hours after Adv infection. Adv-caPKC epsilon induced a time- and dose-dep endent increase in phosphorylated p42 and p44 ERKs, as compared with a cont rol Adv encoding beta -galactosidase (Adv-ne beta gal). Maximal ERK phospho rylation occurred 8 hours after Adv infection. In contrast, JNK was only mi nimally 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 p hosphorylated p54 JNK, and a 15-fold increase in phosphorylated p38(MAPK) 2 4 hours after Adv infection. In contrast, p42 and p44 ERK were only minimal ly activated. Whereas neither Adv induced NRVM hypertrophy, Adv-caPKC delta , but not Adv-caPKCE, induced NRVM apoptosis. We conclude that the novel PK Cs differentially regulate MAPK cascades and apoptosis in an isoenzyme-spec ific and time-dependent manner.