Multiple regulation of proenkephalin gene expression by protein kinase C.
In the present study we investigated the role of protein kinase C (Ca2+/phospholipid-dependent enzyme)-mediated processes in the regulation of proenkephalin gene expression in primary cultures of bovine adrenal chromaffin cells. Activators of protein kinase C such as 1-oleoyl-2-acetylglycerol, mezerein, and the phorbol esters phorbol 12-myristate 13-acetate (PMA) and phorbol 12,13-didecanoate induced a time-dependent increase in proenkephalin mRNA levels, whereas the inactive phorbol ester 4 alpha-phorbol 12,13-didecanoate had no effect. The increase in phorbol ester-induced proenkephalin mRNA was potentiated by low concentrations of the Ca2+ ionophore A23187, suggesting an interaction between protein kinase- and Ca2+-mediated processes in the regulation of proenkephalin mRNA. The phorbol ester-induced stimulation does not appear to be mediated by an interaction with the cAMP-generating system or increases in Ca2+ uptake. However, when proenkephalin mRNA levels were stimulated by KCl (10 mM) and the dihydropyridine BayK8644, PMA exhibited an inhibitory effect on proenkephalin mRNA, which was detectable at a 10-fold lower concentration of PMA than the stimulatory effect. This inhibitory effect appears to be mediated by an inhibition of Ca2+ entry through voltage-dependent Ca2+ channels, as suggested by 45Ca2+ uptake experiments. Thus, the net effect of PMA depends on and varies with the state of voltage-dependent Ca2+ channel activity. A third mode of action by protein kinase C to modulate proenkephalin gene expression is by interaction with the phosphatidylinositol second messenger system. Stimulation of phosphoinositide hydrolysis and proenkephalin mRNA by histaminic H1-receptor activation was inhibited by low concentrations of PMA. We suggest that protein kinase C may act as a positive and negative regulator of proenkephalin gene expression by interacting with at least three receptor-coupled second messenger systems.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002417:Cattle; D002837:Chromaffin Granules / Q000201:enzymology; D004745:Enkephalins / Q000235:genetics*; D005786:Gene Expression Regulation / Q000187:drug effects*; D007473:Ion Channels / Q000378:metabolism; D010703:Phorbol Esters / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism*; D011498:Protein Precursors / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism
D004745:Enkephalins; D007473:Ion Channels; D010703:Phorbol Esters; D010716:Phosphatidylinositols; D011498:Protein Precursors; D012333:RNA, Messenger; C029992:proenkephalin; D011493:Protein Kinase C; D002118:Calcium