Down-regulation of Kruppel-like Factor-4 (KLF4) by MicroRNA-143/145 Is Critical for Modulation of Vascular Smooth Muscle Cell Phenotype by Transforming Growth Factor-β and Bone Morphogenetic Protein 4

In the postnatal vasculature, fully differentiated and quiescent vascular smooth muscle cells (VSMCs) in a contractile phenotype are required for the normal regulation of vascular tone. The transforming growth factor-beta (TGF-beta) superfamily of growth factors (TGF-beta s and bone morphogenetic proteins (BMPs)) are potent inducers of contractile phenotype and mediate (i) induction of contractile genes, and (ii) inhibition of VSMC growth and migration. Transcription of contractile genes is positively regulated by a regulatory DNA element called a CArG box. The CArG box is activated by the binding of serum response factor and its coactivators, myocardin (Myocd) or Myocd-related transcription factors (MRTFs). Kruppel-like factor-4 (KLF4) is known to inhibit activation of the CArG box. However, the potential role of KLF4 in the contractile activities of TGF-beta or BMP has not been explored. Here, we demonstrate that TGF-beta and BMP4 rapidly down-regulate KLF4 through induction of microRNA-143 (miR-143) and miR-145, which leads to a reduction of KLF4 transcripts and decreased KLF4 protein expression. Inhibition of miR-145 prevents down-regulation of KLF4 and activation of contractile genes by TGF-beta or BMP4, suggesting that modulation of KLF4 is a prerequisite for induction of contractile genes by TGF-beta and BMP4. Interestingly, both TGF-beta and BMP4 activate transcription of the miR-143/145 gene cluster through the CArG box, however, TGF-beta mediates this effect through induction of Myocd expression, whereas BMP4 utilizes nuclear translocation of MRTF-A. Thus, this study sheds light on both the similarities and the differences of TGF-beta and BMP4 signaling in the regulation of KLF4 and contractile genes.