Vascular smooth muscle cells (VSMCs) 3 are highly plastic cells that undergo phenotype modulation in response to physiological and pathological cues (1). In response to vascular injury or growth factors, such as platelet-derived growth factor (PDGF) (2), VSMCs dedifferentiate and adopt a highly migratory, proliferative phenotype known as a "synthetic" phenotype that is required for vascular injury repair or during angiogenesis (1). However, prolonged or deregulated dedifferentiation can cause occlusion of the vasculature and contributes to development of vascular proliferative disorders, such as atherosclerosis, restenosis following angioplasty, as well as both systemic and pulmonary hypertension (1). Unlike PDGF, the TGF-␤ family of growth factors, including TGF-␤ and BMP4, promote a less migratory and proliferative phenotype known as the "contractile" phenotype (3). Contractile VSMC phenotype is characterized by alterations in the gene expression profile of VSMC. In particular, high expression of VSMC-specific genes, such as smooth muscle ␣-actin (SMA), calponin1 (CNN), and SM22␣ (SM22) are associated with the contractile VSMC phenotype. Transcription of contractile genes is regulated by SRF through a DNA sequence motif known as the CArG box (CC(A/T) 6 GG), which is present in the promoters of VSMC-specific genes (1). A coactivator of SRF, Myocd, interacts with SRF and activates VSMC expression of contractile genes (4 -6). Similarly, the Myocd-related transcription factor (MRTF) family of proteins, MRTF-A and MRTF-B, are also involved in the transcriptional regulation of contractile gene markers as coactivators of SRF (7,8). Myocd is constitutively localized to the nucleus and its activity is regulated primarily at the level of expression. Conversely, MRTFs are sequestered in the cytoplasm through interaction with monomeric G-actin (9, 10). In response to BMP4 or other stimuli, Rho signaling promotes actin polymerization and MRTF translocation into the nucleus where MRTFs associate with SRF (3), resulting in the activation of contractile gene transcription. Unlike BMP4, TGF-␤ does not activate Rho signal-* This work was supported, in whole or in part, by National Institutes of Health 3 The abbreviations used are: VSMC, vascular smooth muscle cell; TGF-{␤}, transforming growth factor-{␤}; PDGF, platelet-derived growth factor; PAI-1, plasminogen activator inhibitor-1; PDCD4, programed cell death 4; BMP, bone morphogenetic protein; MRTF, Myocd-related transcription factor; PASMC, pulmonary artery smooth muscle cell; ESC, embryonic stem cell; SRF, serum response factor; Myocd, myocardin; miRNA, microRNA; pri-miRNA; primary miRNA; SBE, Smad-binding element; rAoSMC, rat aortic SMC; qRT, quantitative reverse transcriptase.