Abstract
Myocardin (MYOCD) is a critical regulator of smooth muscle cell (SMC) differentiation, but its transcriptional targets remain to be exhaustively characterized, especially at the protein level. Here we leveraged human RNA and protein expression data to identify novel potential MYOCD targets. Using correlation analyses we found several targets that we could confirm at the protein level, including SORBS1, SLMAP, SYNM, and MCAM. We focused on SYNM, which encodes the intermediate filament protein synemin. SYNM rivalled smooth muscle myosin (MYH11) for SMC specificity and was controlled at the mRNA and protein levels by all myocardin-related transcription factors (MRTFs: MYOCD, MRTF-A/MKL1, and MRTF-B/MKL2). MRTF activity is regulated by the ratio of filamentous to globular actin, and SYNM was accordingly reduced by interventions that depolymerize actin, such as latrunculin treatment and overexpression of constitutively active cofilin. Many MRTF target genes depend on serum response factor (SRF), but SYNM lacked SRF-binding motifs in its proximal promoter, which was not directly regulated by MYOCD. Furthermore, SYNM resisted SRF silencing, yet the time course of induction closely paralleled that of the SRF-dependent target gene ACTA2. SYNM was repressed by the ternary complex factor (TCF) FLI1 and was increased in mouse embryonic fibroblasts lacking three classical TCFs (ELK1, ELK3, and ELK4). Imaging showed colocalization of SYNM with the intermediate filament proteins desmin and vimentin, and MRTF-A/MKL1 increased SYNM-containing intermediate filaments in SMCs. These studies identify SYNM as a novel SRF-independent target of myocardin that is abundantly expressed in all SMCs.
Keywords:
CFL2; DSTN; actin dynamics; lineage markers; phenotypic modulation.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Actins / genetics
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Actins / metabolism
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Animals
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Bridged Bicyclo Compounds, Heterocyclic / pharmacology
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CD146 Antigen / genetics
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CD146 Antigen / metabolism
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Cell Line
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Cofilin 2 / genetics*
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Cofilin 2 / metabolism
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Coronary Vessels / cytology
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Coronary Vessels / drug effects
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Coronary Vessels / metabolism
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Desmin / genetics
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Desmin / metabolism
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Gene Expression Regulation
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Humans
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Intermediate Filament Proteins / genetics*
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Intermediate Filament Proteins / metabolism
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Membrane Proteins / genetics
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Membrane Proteins / metabolism
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Mice
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Microfilament Proteins / genetics
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Microfilament Proteins / metabolism
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Myocytes, Smooth Muscle / cytology
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Myocytes, Smooth Muscle / drug effects
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Myocytes, Smooth Muscle / metabolism*
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Myosin Heavy Chains / genetics
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Myosin Heavy Chains / metabolism
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Nuclear Proteins / genetics*
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Nuclear Proteins / metabolism
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Primary Cell Culture
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Proto-Oncogene Protein c-fli-1 / genetics
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Proto-Oncogene Protein c-fli-1 / metabolism
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Serum Response Factor / genetics
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Serum Response Factor / metabolism
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Signal Transduction
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Thiazolidines / pharmacology
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Trans-Activators / genetics*
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Trans-Activators / metabolism
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Transcription Factors / genetics*
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Transcription Factors / metabolism
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Urinary Bladder / cytology
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Urinary Bladder / drug effects
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Urinary Bladder / metabolism
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Vimentin / genetics
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Vimentin / metabolism
Substances
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ACTA2 protein, human
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Actins
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Bridged Bicyclo Compounds, Heterocyclic
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CD146 Antigen
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CFL2 protein, human
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Cofilin 2
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Desmin
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FLI1 protein, human
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Intermediate Filament Proteins
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MCAM protein, human
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MRTFA protein, human
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MRTFB protein, human
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MYH11 protein, human
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Membrane Proteins
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Microfilament Proteins
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Nuclear Proteins
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Proto-Oncogene Protein c-fli-1
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SLMAP protein, human
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SORBS1 protein, human
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SRF protein, human
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Serum Response Factor
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Thiazolidines
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Trans-Activators
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Transcription Factors
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VIM protein, human
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Vimentin
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desmuslin
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myocardin
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Myosin Heavy Chains
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latrunculin A