Abstract
MicroRNAs are involved in phenotypic switching of smooth muscle cells (SMCs). Brg1-containing SWI/SNF chromatin-remodeling complexes also play an important role in controlling the phenotype of SMCs. We thus determined whether Brg1 influences the transcription of microRNAs in SMCs. Microarray and quantitative RT-PCR analysis of smooth muscle from mice harboring smooth muscle-specific deletion of Brg1 revealed altered expression of several microRNAs, including miRs-143/145 and miR-133. Ablation of Brg1 in SMCs in vitro either by expression of dominant negative Brg1 or Brg1 knock-out attenuated miRs-143/145 expression. Knockdown of serum response factor (SRF) in SMCs significantly reduced the expression levels of miRs-143/145 and miR-133, whereas knockdown of myocardin only attenuated miRs-143/145 expression. Myocardin induced expression of miRs-143/145 and miR-133a and increased SRF binding to these genes in 10T1/2 cells. This myocardin-mediated induction was attenuated by dominant negative Brg1. In Brg1-null SW13 cells, miRs-143/145 were dramatically induced by myocardin only in the presence of Brg1, whereas miR-133 was not induced by myocardin in a Brg1-dependent manner. Chromatin immunoprecipitation assays demonstrated that in the presence of Brg1, myocardin increased SRF binding to both the miRs-143/145 and miR-133a loci. Together, these data suggest a mechanism in which Brg1-containing SWI/SNF complexes are required for myocardin to induce expression of miRs-143/145 in smooth muscle cells. In contrast, miR-133 expression appears to be regulated by Brg1-containing chromatin remodeling complexes in a partially SRF-dependent, although largely myocardin-independent manner. SWI/SNF-mediated chromatin remodeling thus regulates the phenotype of smooth muscle by affecting expression of protein-coding genes and microRNAs.
Highlights
It is unknown whether Brg1 regulates microRNA expression during smooth muscle differentiation
Our current results demonstrate that the SWI/SNF chromatin remodeling complex acts together with transcription factors and cofactors to regulate the expression of microRNAs in smooth muscle cells
Brg1 is required for miR-133 expression in vivo and serum response factor (SRF) is involved in the regulation of miR-133 expres
Summary
It is unknown whether Brg regulates microRNA expression during smooth muscle differentiation. Chromatin immunoprecipitation assays demonstrated that in the presence of Brg, myocardin increased SRF binding to both the miRs-143/145 and miR-133a loci Together, these data suggest a mechanism in which Brg1-containing SWI/ SNF complexes are required for myocardin to induce expression of miRs-143/145 in smooth muscle cells. Postnatal deletion of Dicer in smooth muscle cells using a tamoxifen-regulated smMHCCre transgene resulted in a dramatic reduction of blood pressure and loss of contractile proteins within the vasculature [3] These studies demonstrate that microRNAs play a key role in the development and maintenance of smooth muscle cells in both vascular and gastrointestinal tissues. The Brg ATPase subunit of the SWI/ SNF chromatin remodeling complex has been shown to be required for MyoD to activate transcription of both skeletal muscle contractile protein genes and miR-133a [16]. The regulation of miR-133 expression by Brg requires other factors to cooperate with SRF to activate transcription
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