Mechanistic Analysis of VDR-Mediated Renin Suppression

BACKGROUND: The vitamin D receptor (VDR) is involved in the regulation of renin expression and vitamin D analogs down-regulated renin mRNA expression in As4.1 cells. METHODS: Microarray analysis was used to assess the VDR-mediated gene expression profile in As4.1 cells treated with paricalcitol, followed by real-time RT-PCR. Mechanistic analyses were done using siRNA, electrophoretic mobility shift assay (EMSA) and Western blotting. RESULTS: Microarray analysis shows that 709 target genes were affected by paricalcitol with 286 up- and 423 downregulated. A number of major pathways were impacted including transcription factors. Real-time RT-PCR confirmed the microarray results. Treatment of the cells with siRNA against nuclear receptor co-repressor (NCOR1) eliminated VDR-mediated renin suppression. Using EMSA, paricalcitol treatment reduced the level of protein complex binding to the cyclic AMP-responsive element (CRE)-like domain in the renin distal enhancer region. VDR, CRE-binding protein (CREB1) and NCOR1 were identified in the complex binding to the CRE-like domain by Western blot in the paricalcitol-treated cells. Paricalcitol treatment resulted in an increase in the VDR level, but no significant change in the CREB1 and NCOR1 levels. CONCLUSION: These results suggest that VDR-mediated renin suppression likely acts through a transcriptional regulatory complex including CREB1, NCOR1 and VDR that binds to the CRE-like domain in the renin enhancer region.