Kotlo KU, Hesabi B, Danziger RS. Implication of microRNAs in atrial natriuretic peptide and nitric oxide signaling in vascular smooth muscle cells. Am J Physiol Cell Physiol 301: C929 -C937, 2011. First published July 6, 2011; doi:10.1152/ajpcell.00088.2011 are endogenous small RNA molecules that suppress gene expression by binding to complementary sequences in the 3= untranslated regions of their target genes. miRs have been implicated in many diseases, including heart failure, ischemic heart disease, hypertension, cardiac hypertrophy, and cancers. Nitric oxide (NO) and atrial natriuretic peptide (ANP) are potent vasorelaxants whose actions are mediated through receptor guanylyl cyclases and cGMP-dependent protein kinase. The present study examines miRs in signaling by ANP and NO in vascular smooth muscle cells. miR microarray analysis was performed on human vascular smooth muscle cells (HVSMC) treated with ANP (10 nM, 4 h) and S-nitroso-N-acetylpenicillamine (SNAP) (100 M, 4 h), a NO donor. Twenty-two shared miRs were upregulated, and 21 shared miRs were downregulated, by both ANP and SNAP (P Ͻ 0.05). Expression levels of four miRs (miRs-21, -26b, -98, and -1826), which had the greatest change in expression, as determined by microarray analysis, were confirmed by quantitative RT-PCR. Rp-8-Br-PET-cGMPS, a cGMPdependent protein kinase-specific inhibitor, blocked the regulation of these miRs by ANP and SNAP. 8-bromo-cGMP mimicked the effect of ANP and SNAP on their expression. miR-21 was shown to inhibit HVSMC contraction in collagen gel lattice contraction assays. We also identified by computational algorithms and confirmed by Western blot analysis new intracellular targets of miR-21, i.e., cofilin-2 and myosin phosphatase and Rho interacting protein. Transfection with pre-miR-21 contracted cells and ANP and SNAP blocked miR-21-induced HVSMC contraction. Transfection with anti-miR-21 inhibitor reduced contractility of HVSMC (P Ͻ 0.05). The present results implicate miRs in NO and ANP signaling in general and miR-21 in particular in cGMP signaling and vascular smooth muscle cell relaxation. guanosine 3=,5=-cyclic monophosphate miR-21 MICRORNAS (MIRS) HAVE EMERGED as a novel class of endogenous small RNA molecules that negatively regulate ϳ30% of genes in the cell by annealing with complementary sequences in the 3= untranslated regions of their target mRNAs. More than 1,000 miRs have been identified in the human genome. A single miR can regulate hundreds of functional targets, and, similarly, a single mRNA can be targeted by multiple miRs in a cell (2). Recent evidence suggests roles for miRs in diverse processes including cell differentiation and proliferation (3,19,22). Aberrant expression of miRs has been linked to developmental abnormalities and pathologies, including cardiac hypertrophy, hypertension, ischemic heart disease, heart failure, and cancers (8,24,33,56,68,69).The potential role of miRs in vascular smooth muscle cell (VSMC) biology and blood pressure is just beginning to be appreciated. Both miR-143...