Angiotensin II activates p44/42 MAP kinase partly through PKCepsilon in H295R cells

Using pharmaceutical and overexpression approaches we have previously reported that in H295R cells, (a) angiotensin II (AII) activates PKCepsilon, PKCalpha and p44/42 MAPK pathway, (b) PKCepsilon, PKCalpha and p44/42 MAPK overexpression inhibits AII-induced CYP11B2 gene transcription and (c) overexpression of PKCepsilon inhibits CYP11B2 gene transcription through p44/42 MAPK activation [LeHoux, J.G., Dupuis, G., Lefebvre, A., 2001. Control of CYP11B2 gene expression through differential regulation of its promoter by atypical and conventional protein kinase C isoforms. J. Biol. Chem. 276 (11), 8021-8028; LeHoux, J.G., Lefebvre, A., 2006. Novel protein kinase C-epsilon inhibits human CYP11B2 gene expression through ERK1/2 signalling pathway and JunB. J. Mol. Endocrinol. 36 (1), 51-64]. The aim of the present work was to evaluate the physiological role of endogenous PKCepsilon and PKCalpha isoforms in the activation of p44/42 MAPK by AII. A 50% reduction of PKCepsilon protein by siRNA-PKCepsilon resulted in 35% inhibition of AII-induced p44/42 MAPK activation. Knockdown of PKCepsilon stimulated AII-induced CYP11B2 transcription indicating that the PKCepsilon is not involved in the activation of CYP11B2 gene expression by AII. Furthermore, knockdown of PKCalpha enhanced AII-stimulated CYP11B2 transcription without altering p44/42 MAPK indicating that inhibition of AII-stimulated CYP11B2 gene by PKCalpha does not involve the p44/42 MAPK signalling pathway. These results thus establish that physiologically, PKCepsilon and PKCalpha act through different signalling pathways to inhibit AII-stimulated CYP11B2 gene expression.