NFAT5 positively regulates SMαA gene expression in vascular smooth muscle

Abstract

Nuclear factor of activated T‐cells 5 (NFAT5) is a tonicity‐responsive transcription factor; however, NFAT5 function in vascular SMCs is unknown. The SM α‐actin (SMαA) gene contains an NFAT5 cis element overlapping the first intronic CArG. We hypothesized that NFAT5 positively regulates SMαA gene expression through binding to this consensus sequence. NFAT5 overexpression increased SMαA promoter‐reporter activity, which was attenuated by mutating the NFAT5 site. siRNA knockdown of endogenous NFAT5 inhibited an Ang II‐mediated upregulation of SMαA promoter activity. Conversely, platelet‐derived growth factor‐BB decreased SMαA expression concomitant with a 70% decrease in NFAT5 binding to the SMαA first intron. In the A404 SM precursor cell line, treatment with retinoic acid to induce SMαA mRNA was preceded by increased NFAT5 expression. Microarray analysis of NFAT5 null mouse embryonic fibroblasts indicated a 64% decrease in SMαA mRNA compared to WT. Additionally, aortas from heterozygous NFAT5 mice have a 41% decrease in SMαA protein at 5 wks of age, returning to WT levels by 20 wks. In the rat carotid artery balloon injury model, NFAT5 protein was upregulated at 7 and 21 days, corresponding with an increase in SMαA protein back to basal levels and resolution to the contractile phenotype. In conclusion, we have identified NFAT5 as a novel positive regulator of SMαA gene expression in vascular SMCs. (NIH HL81682)