Specific Activation of the Alternative Cardiac Promoter of Cacna1c by the Mineralocorticoid Receptor
Rationale: The mineralocorticoid receptor (MR) 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 are due to the regulation of L-type Cav1.2 Ca2+ channel expression, which is generated by tissue-specific alternative promoters as a long 'cardiac' (Cav1.2-LNT) or a short 'vascular' (Cav1.2-SNT) N-terminal transcripts.
Objective: To analyze the molecular mechanisms by which aldosterone, through MR, modulates Cav1.2 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 Cav1.2-LNT 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 Cav1.2-SNT is normally the major isoform, we found that MR signaling activates 'cardiac' Cav1.2-LNT 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 Cav1.2-LNT 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.
- Received November 24, 2017.
- Revision received February 15, 2018.
- Accepted February 19, 2018.