Transcriptional Up-Regulation by Aldosterone of the Cardiac Cav1.2 Encoding Gene CACNA1C

Abstract

Although the effect of aldosterone beyond the epithelia is now well recognized, specific action through the mineralocorticoid receptor (MR) in heart is still matter of debate. In the past decade, we have accumulated evidence, both ex vivo and in vivo, that modulation of Ca2+ signaling, especially Ca2+ influx via L-type Ca2+ channel (Cav1.2), is a central factor in the cardiac action of aldosterone. Even if our results established that a specific transcriptional upregulation is involved in the effect of aldosterone on Cav1.2, it cannot be concluded whether this genomic effect is direct or indirect. The effect of the mineralocorticoid, aldosterone, on the regulation of the cardiac Cav1.2 expression was investigated in primary cultures of neonatal rat ventricular myocytes (nRVM). By use of quantitative real time RT-PCR, we found that aldosterone increased the Cav1.2 mRNA amount in time- and dose-dependent manner. This up-regulation appeared as early as 1hour of incubation even with 1 nM aldosterone. Inspection of the upstream promoter region from rat Cav1.2 encoding gene, revealed one putative hormone response element, GRE. The activity of the promoter-luciferase reporter gene constructs in transfected nRVMs showed similar time- and dose-dependent stimulation with aldosterone. We will examine the intracellular trafficking of MR in nRVMs using a fusion protein of green fluorescent protein and human MR. Selectivity of these effects will be tested as well as electrophoretic mobility shift assays to identify the region of the cacna1c promoter that can bind MRs. The data will provide new insights in the molecular mechanisms underlying the regulation of Cav1.2 channel expression by mineralocorticoids.