Induction of MicroRNA-221 by Platelet-derived Growth Factor Signaling Is Critical for Modulation of Vascular Smooth Muscle Phenotype

Abstract

The platelet-derived growth factor (PDGF) signaling pathway is a critical regulator of animal development and homeostasis. Activation of the PDGF pathway leads to neointimal proliferative responses to artery injury; it promotes a switch of vascular smooth muscle cells (vSMC) to a less contractile phenotype by inhibiting the SMC-specific gene expression and increasing the rate of proliferation and migration. The molecular mechanism for these pleiotropic effects of PDGFs has not been fully described. Here, we identify the microRNA-221 (miR-221), a small noncoding RNA, as a modulator of the phenotypic change of vSMCs in response to PDGF signaling. We demonstrate that miR-221 is transcriptionally induced upon PDGF treatment in primary vSMCs, leading to down-regulation of the targets c-Kit and p27Kip1. Down-regulation of p27Kip1 by miR-221 is critical for PDGF-mediated induction of cell proliferation. Additionally, decreased c-Kit causes inhibition of SMC-specific contractile gene transcription by reducing the expression of Myocardin (Myocd), a potent SMC-specific nuclear coactivator. Our study demonstrates that PDGF signaling, by modulating the expression of miR-221, regulates two critical determinants of the vSMC phenotype; they are SMC gene expression and cell proliferation.Unlike many terminally differentiated cells, smooth muscle cells (SMCs) 3 can switch between differentiated and dedifferentiated phenotypes in response to changes in the local environment (2). In response to vascular injury, quiescent contractile vSMCs reduce the expression of SMC-specific genes such as ␣-smooth muscle actin (SMA), smooth muscle calponin (CNN), SM22␣ (SM22), and smooth muscle myosin heavy chain, increase proliferation, and synthesize collagens and matrix metalloproteinases (2, 9). Although this phenotype switch is believed to be essential for repair of vascular injury, deregulation of this process also plays a role in the pathogenesis of various human diseases, including atherosclerosis, hypertension, asthma, and cancer. Therefore, a complete understanding of the molecular mechanisms of vSMC phenotype regulation is essential for treatment or prevention of vascular disorders.PDGFs potently mediate the vSMC phenotype switch from a differentiated, contractile state to a dedifferentiated, synthetic state by repressing SMC marker gene expression as well as promoting vSMC proliferation and migration (2, 10). Consistent with the effect of PDGF on vSMC, up-regulation of molecules in the PDGF signaling pathway is found in various cardiovascular disorders and vascular injuries, including atherosclerosis and restenosis (1). PDGF released from platelets and endothelial cells at sites of vascular injury is thought to be a contributing factor to atherosclerosis (11). Inhibition of PDGF signaling by the PDGF receptor (PDGFR) kinase inhibitor imatinib mesylate (Gleevec) demonstrated a major protective effect on atherosclerosis development (1). It is of note that hyperactivation of the PDGFR pathway has been implicated in the pathogenesis of id...

Transforming Growth Factor-β1 (TGF-β1) Utilizes Distinct Pathways for the Transcriptional Activation of MicroRNA 143/145 in Human Coronary Artery Smooth Muscle Cells

“…For example, miR21 has been linked to the SMC proliferative phenotype in a balloon-injured rat carotid artery model (26). The miR221/222 gene is up-regulated after vascular injury and appears to mediate the SMC proliferative phenotype as well as intimal hyperplasia (27,28). miR26a was shown to be elevated with SMC differentiation, but it appears to negatively regulate expression of SMC contractile markers (29).…”

Functional Roles of microRNAs in Cancer: microRNomes and oncomiRs Connection

“…The majority of DNA-binding elements and transcription factors binding sites in microRNAs promoters largely overlap with those that control proteincoding genes, such as c-myc or p53. On the other hand, transcription of primary miRNA transcripts can be dynamically regulated in response to growth factor stimulation, including platelet-derived growth factor (PDGF), transforming growth factor beta (TGF-) and Smad [27]. Epigenetic control of microRNAs expression is another regulation level which includes DNA methylation and histones modifications.…”

Implication of MicroRNAs in the Pathophysiology of Cardiac and Vascular Smooth Muscle Cells

“…The critical target of miR-21 that is down-regulated in this process is programmed cell death 4 [22]. As a consequence, miR-21 induces VSMCs transdifferentiation to the contractile phenotype in response to BMP4 and TGF [31]. Additionally, miR-21 promotes VSMC proliferation and reduces apoptosis [32].…”