Regulation and rate limiting mechanisms of Ca2+ ATPase (SERCA2) expression in cardiac myocytes

Involvement of the calcineurin/NFAT pathway in transcription of cardiac sarcoplasmic reticulum Ca(2+) ATPase (SERCA2) was demonstrated (Prasad and Inesi, Am J Physiol Heart Circ Physiol 300(1):H173-H180, 2011) by upregulation of SERCA2 following calcineurin (CN) activation by cytosolic Ca(2+), and downregulation of SERCA2 following CN inhibition with cyclosporine (CsA) or CN subunits gene silencing. We show here that in cultured cardiac myocytes, competitive engagement of the CN/NFAT pathway is accompanied by downregulation of SERCA2 and Ca(2+) signaling alterations. In fact, SERCA2 downregulation occurs following infection of myocytes with adenovirus vectors carrying luciferase or SERCA1 cDNA under control of NFAT-dependent promoters, but not under control of CMV promoters that do not depend on NFAT. SERCA2 downregulation is demonstrated by comparison with endogenous transcription and protein expression standards such as GAPDH and actin, indicating prominent SERCA2 involvement by the CN/NFAT pathway. Transcription of genes involved in hypertrophy, triggered by adrenergic agonist or by direct protein kinase C (PKC) activation with phorbol 12-myristate 13-acetate (PMA), is also prominently dependent on CN/NFAT. This is demonstrated by CN inhibition with CsA, CN subunits gene silencing with siRNA, displacement of NFAT from CN with 9,10-Dihydro-9,10[1',2']-benzenoanthracene-1,4-dione (INCA-6), and myocyte infection with vectors carrying luciferase cDNA under control of NFAT-dependent promoter. We show here that competitive engagement of the CN/NFAT pathway by endogenous genes involved in hypertrophy produces downregulation of SERCA2, reduction of Ca(2+) transport and inadequate Ca(2+) signaling. It is most interesting that, in the presence of adrenergic agonist, specific protein kinase C (PKC) inhibition with 3-[1-[3-(dimethylamino)propyl]-5-methoxy-1H-indol-3-yl]-4-(1H-indol-3-yl)-1H-pyrrole-2,5-dione (Gö 6983) prevents development of hypertrophy and maintains adequate SERCA2 levels and Ca(2+) signaling.