title: Smooth muscle-specific genes are differentially sensitive to inhibition by Elk-1.
abstract: Understanding the mechanism of smooth muscle cell (SMC) differentiation will provide the foundation for elucidating SMC-related diseases, such as atherosclerosis, restenosis, and asthma. In the current study, overexpression of Elk-1 in SMCs down-regulated expression of several endogenous smooth muscle-restricted proteins, including telokin, SM22alpha, and smooth muscle alpha-actin. In contrast, down-regulation of endogenous Elk-1 in smooth muscle cells increased the expression of only telokin and SM22alpha, suggesting that smooth muscle-specific promoters are differentially sensitive to the inhibitory effects of Elk-1. Consistent with this, overexpression of the DNA binding domain of Elk-1, which acts as a dominant-negative protein by displacing endogenous Elk-1, enhanced the expression of telokin and SM22alpha without affecting expression of smooth muscle alpha-actin. Elk-1 suppressed the activity of smooth muscle-restricted promoters, including the telokin promoter that does not contain a consensus Elk-1 binding site, through its ability to block myocardin-induced activation of the promoters. Gel mobility shift and chromatin immunoprecipitation assays revealed that Elk-1 binds to a nonconsensus binding site in the telokin promoter and Elk-1 binding is dependent on serum response factor (SRF) binding to a nearby CArG box. Although overexpression of the SRF-binding B-box domain of Elk-1 is sufficient to repress the myocardin activation of the telokin promoter, this repression is not as complete as that seen with an Elk-1 fragment that includes the DNA binding domain. In addition, reporter gene assays demonstrate that an intact Elk-1 binding site in the telokin promoter is required for Elk-1 to maximally inhibit promoter activity. Together, these data suggest that the differential sensitivity of smooth muscle-specific genes to inhibition by Elk-1 may play a role in the complex changes in smooth muscle-specific protein expression that are observed under pathological conditions.
authors.affiliation: Department of Cellular and Integrative Physiology, Indiana University School of Medicine, 635 Barnhill Drive, Indianapolis, Indiana 46202-5120, USA.
authors.forename: Jiliang
authors.initials: J
authors.lastname: Zhou
authors.forename: Guoqing
authors.initials: G
authors.lastname: Hu
authors.forename: B Paul
authors.initials: BP
authors.lastname: Herring
mesh_terms: D000199:Actins / Q000096:biosynthesis; D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D015153:Blotting, Western; D002454:Cell Differentiation; D002460:Cell Line; D002843:Chromatin / Q000737:chemistry; D047369:Chromatin Immunoprecipitation; D004247:DNA / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D005786:Gene Expression Regulation; D005799:Genes, Dominant; D017930:Genes, Reporter; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D008840:Microfilament Proteins / Q000096:biosynthesis; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000096:biosynthesis; D009130:Muscle, Smooth / Q000166:cytology*; D009154:Mutation; D009219:Myosin-Light-Chain Kinase / Q000096:biosynthesis / Q000235:genetics; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism; D010446:Peptide Fragments; D010455:Peptides / Q000235:genetics; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D026362:Serum Response Factor / Q000378:metabolism; D015534:Trans-Activators / Q000737:chemistry / Q000378:metabolism; D014162:Transfection; D020798:Two-Hybrid System Techniques; D050807:ets-Domain Protein Elk-1 / Q000378:metabolism*; D000099251:Myocardin
chemical_list: D000199:Actins; D002843:Chromatin; D004247:DNA; D008156:Luciferases; D008840:Microfilament Proteins; D009124:Muscle Proteins; D009219:Myosin-Light-Chain Kinase; D009687:Nuclear Proteins; D010446:Peptide Fragments; D010455:Peptides; D016760:Proto-Oncogene Proteins c-fos; D034741:RNA, Small Interfering; D026362:Serum Response Factor; D015534:Trans-Activators; D050807:ets-Domain Protein Elk-1; D000099251:Myocardin; C051615:transgelin; C060640:telokin