Specific Activation of the Alternative Cardiac Promoter of Cacna1c by the Mineralocorticoid Receptor

Abstract

Rationale: The MR (mineralocorticoid receptor) antagonists belong to the current therapeutic armamentarium for the management of cardiovascular diseases, but the mechanisms conferring their beneficial effects are poorly understood. Part of the cardiovascular effects of MR is because of the regulation of L-type Ca_v1.2 Ca²⁺ channel expression, which is generated by tissue-specific alternative promoters as a long cardiac or short vascular N-terminal transcripts.

Objective: To analyze the molecular mechanisms by which aldosterone, through MR, modulates Ca_v1.2 expression and function in a tissue-specific manner.

Methods and results: In primary cultures of neonatal rat ventricular myocytes, aldosterone exposure for 24 hours increased in a concentration-dependent manner long cardiac Ca_v1.2 N-terminal transcripts expression at both mRNA and protein levels, correlating with enhanced concentration-, time-, and MR-dependent P1-promoter activity. In silico analysis and mutagenesis identified MR interaction with both specific activating and repressing DNA-binding elements on the P1-promoter. The relevance of this regulation is confirmed both ex and in vivo in transgenic mice harboring the luciferase reporter gene under the control of the cardiac P1-promoter. Moreover, we show that this cis-regulatory mechanism is not limited to the heart. Indeed, in smooth muscle cells from different vascular beds, in which the short vascular Cav1.2 N-terminal transcripts is normally the major isoform, we found that MR signaling activates long cardiac Ca_v1.2 N-terminal transcripts expression through P1-promoter activation, leading to vascular contractile dysfunction. These results were further corroborated in hypertensive aldosterone/salt rodent models, showing notably a positive correlation between blood pressure and cardiac P1-promoter activity in aorta. This new vascular long cardiac Ca_v1.2 N-terminal transcripts molecular signature reduced sensitivity to the Ca²⁺ channel blocker, nifedipine, in aldosterone-treated vessels.

Conclusions: Our results reveal that MR acts as a transcription factor to translate aldosterone signal into specific cardiac P1-promoter activation that might influence the therapeutic outcome of cardiovascular diseases.

Keywords: aldosterone; blood pressure; calcium channels, L-type; cardiovascular diseases; nifedipine; receptors, mineralocorticoid.