Myocardin inhibits cellular proliferation by inhibiting NF- B(p65)-dependent cell cycle progression

Departments of Surgery and Cell and Developmental Biology, Carolina Cardiovascular Biology Center, and Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC 27599, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 04/2008; 105(9):3362-7. DOI: 10.1073/pnas.0705842105
Source: PubMed


We previously reported the importance of the serum response factor (SRF) cofactor myocardin in controlling muscle gene expression as well as the fundamental role for the inflammatory transcription factor NF-kappaB in governing cellular fate. Inactivation of myocardin has been implicated in malignant tumor growth. However, the underlying mechanism of myocardin regulation of cellular growth remains unclear. Here we show that NF-kappaB(p65) represses myocardin activation of cardiac and smooth muscle genes in a CArG-box-dependent manner. Consistent with their functional interaction, p65 directly interacts with myocardin and inhibits the formation of the myocardin/SRF/CArG ternary complex in vitro and in vivo. Conversely, myocardin decreases p65-mediated target gene activation by interfering with p65 DNA binding and abrogates LPS-induced TNF-alpha expression. Importantly, myocardin inhibits cellular proliferation by interfering with NF-kappaB-dependent cell-cycle regulation. Cumulatively, these findings identify a function for myocardin as an SRF-independent transcriptional repressor and cell-cycle regulator and provide a molecular mechanism by which interaction between NF-kappaB and myocardin plays a central role in modulating cellular proliferation and differentiation.

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Available from: William E Stansfield, Apr 15, 2015
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    • "Conditional cardiac ablation of Myocardin at late stages of development results in a postnatal cardiac physiology imbalance, an increase of fibrotic tissue and an increase of cell death leading to cardiac enlargement (Huang et al., 2009). Conversely, Myocardin over-expression in primary human mesenchymal stem cells or human vascular smooth muscle cells results in a reduction of cell proliferation and a forced expression of cardiac and smooth muscle molecular markers (Chen et al., 2011; Tang et al., 2008; Van Tuyn et al., 2005; Wang et al., 2003; Wystub et al., 2013). Furthermore, Myocardin over-expression induces cardiac hypertrophy in neonatal rat cardiomyocytes, as well as in transgenic mice (Wystub et al., 2013; Xing et al., 2006). "
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    ABSTRACT: The molecular events that control cell fate determination in cardiac and smooth muscle lineages remain elusive. Myocardin is an important transcription co-factor that regulates cell proliferation, differentiation and development of the cardiovascular system. Here, we describe the construction and analysis of a dual Cre and Enhanced Green Fluorescent Protein (EGFP) knock-in mouse line in the Myocardin locus (MyocdKI). We report that the MyocdKI allele expresses the Cre enzyme and the EGFP in a manner that recapitulates endogenous Myocardin expression patterns. We show that Myocardin expression marks the earliest cardiac and smooth muscle lineages. Furthermore, this genetic model allows for the identification of a cardiac cell population which maintains both Myocardin and Isl-1 expression, in E7.75 - E8.0 embryos, highlighting the contributions and merge of the first and second heart fields during cardiogenesis. Therefore, the MyocdKI allele is a unique tool for studying cardiovascular development and lineage-specific gene manipulation. © 2014 Wiley Periodicals, Inc.
    Full-text · Article · Oct 2014 · genesis
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    • "Regarding the underlying mechanisms, Zuckerbraun et al9 showed that the antiproliferative activity of IκB was related to cell‐cycle arrest through upregulation of the cyclin‐dependent kinase inhibitors p21WAF1/Cip1 and p27Kip1 in cultured SMCs. Moreover, of interest, myocardin has been shown to suppress SMC proliferation by inhibiting NF‐κB‐dependent cell‐cycle progression in cultured SMCs.40 Although the aforementioned mechanistic studies were mostly performed in cultured SMCs, it is highly possible that the decreased proliferation rate in our transgenic mice was also caused by these mechanisms. "
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    ABSTRACT: Background Vascular proliferative diseases such as atherosclerosis are inflammatory disorders involving multiple cell types including macrophages, lymphocytes, endothelial cells, and smooth muscle cells (SMCs). Although activation of the nuclear factor‐κB (NF‐κB) pathway in vessels has been shown to be critical for the progression of vascular diseases, the cell‐autonomous role of NF‐κB within SMCs has not been fully understood. Methods and Results We generated SMC‐selective truncated IκB expressing (SM22α‐Cre/IκBΔN) mice, in which NF‐κB was inhibited selectively in SMCs, and analyzed their phenotype following carotid injury. Results showed that neointima formation was markedly reduced in SM22α‐Cre/IκBΔN mice after injury. Although vascular injury induced downregulation of expression of SMC differentiation markers and myocardin, a potent activator of SMC differentiation markers, repression of these markers and myocardin was attenuated in SM22α‐Cre/IκBΔN mice. Consistent with these findings, NF‐κB activation by interleukin‐1β (IL‐1β) decreased expression of SMC differentiation markers as well as myocardin in cultured SMCs. Inhibition of NF‐κB signaling by BAY 11‐7082 attenuated repressive effects of IL‐1β. Of interest, Krüppel‐like factor 4 (Klf4), a transcription factor critical for regulating SMC differentiation and proliferation, was also involved in IL‐1β‐mediated myocardin repression. Promoter analyses and chromatin immunoprecipitation assays revealed that NF‐κB repressed myocardin by binding to the myocardin promoter region in concert with Klf4. Conclusions These results provide novel evidence that activation of the NF‐κB pathway cell‐autonomously mediates SMC phenotypic switching and contributes to neointima formation following vascular injury.
    Full-text · Article · Apr 2013 · Journal of the American Heart Association
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    • "Despite the popular assumption that MYOCD is expressed almost exclusively in cardiac and SM cells, MYOCD expression was also detected in human fibroblasts [65] where it is involved in functional differentiation and has a negative role in cell proliferation [66]. In fact, in model cell-based assays overexpression of Myocd resulted in inhibition of cell-cycle progression at the G2/M phase and formation of polyploidy cells [67]. MRTF-A and MRTF-B also exert antiproliferative effects on fibroblasts [68]. "
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    ABSTRACT: Growing evidence suggests that gene-regulatory networks, which are responsible for directing cardiovascular development, are altered under stress conditions in the adult heart. The cardiac gene regulatory network is controlled by cardioenriched transcription factors and multiple-cell-signaling inputs. Transcriptional coactivators also participate in gene-regulatory circuits as the primary targets of both physiological and pathological signals. Here, we focus on the recently discovered myocardin-(MYOCD) related family of transcriptional cofactors (MRTF-A and MRTF-B) which associate with the serum response transcription factor and activate the expression of a variety of target genes involved in cardiac growth and adaptation to stress via overlapping but distinct mechanisms. We discuss the involvement of MYOCD, MRTF-A, and MRTF-B in the development of cardiac dysfunction and to what extent modulation of the expression of these factors in vivo can correlate with cardiac disease outcomes. A close examination of the findings identifies the MYOCD-related transcriptional cofactors as putative therapeutic targets to improve cardiac function in heart failure conditions through distinct context-dependent mechanisms. Nevertheless, we are in support of further research to better understand the precise role of individual MYOCD-related factors in cardiac function and disease, before any therapeutic intervention is to be entertained in preclinical trials.
    Full-text · Article · May 2012
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