Abstract 5247: MiR-132 Regulates Angiotensin II Type 1 Receptor Expression Through a Protein Coding Region Binding Site

Abstract

Most of the known physiological and pathophysiological effects of angiotensin II (Ang II) are mediated via the angiotensin II type 1 receptor (AT1R). A number of studies suggest that AT1R expression levels are predominantly regulated by post-transcriptional mechanisms. Recently, it has been suggested that 30% of human genes may be regulated, by a novel post-transcriptional mechanism involving microRNAs (miRNAs). MiRNAs are natural, single-stranded, small RNA molecules that regulate gene expression by binding to target mRNAs and suppressing its translation or initiating its degradation. Our previous studies demonstrated that miR-155 can bind to the 3′-untranslated region (3′-UTR) of human AT1R mRNAs and translationally repress the expression of this protein. In this study, we demonstrate, for the first time, that miRNAs can also bind to sequence recognition sites harbored in the coding region of the human AT1R mRNA and suppress its translation. Specifically, i n situ hybridization experiments demonstrate that, like the AT1R, miR-132 is abundantly expressed in vascular smooth muscle cells (VSMCs) in vivo . Further, we show that over-expression of miR-132 (“gain-of function”) represses human AT1R expression in VSMCs. In contrast, “loss-of-function” experiments demonstrate that transfection of the miR-132 antisense inhibitor results in augmented AT1R protein levels. Importantly, miR-132 regulation of AT1R expression was abolished by mutating the putative miR-132 target site harbored in the AT1R mRNA open reading frame. Taken together, our study demonstrates that the AT1R and miR-132 are co-expressed and that miR-132 translationally represses the expression of AT1R in vivo . Our data support the hypothesis that Ang II responsiveness is “fine-tuned” by exquisitely regulating the expression levels of the AT1R by a number of distinct mechanisms including miRNA regulation.