title: Proteasomal degradation of myocardin is required for its transcriptional activity in vascular smooth muscle cells.
abstract: Myocardin is a transcriptional co-activator of serum response factor (SRF) and can be degraded through ubiquitin-proteasome system. Our preliminary studies unexpectedly revealed that accumulation of myocardin in response to proteasome inhibition by MG132 or lactacystin resulted in decrease of transcriptional activity of myocardin as indicated by reduced expression of SMC contractile marker genes (SM α-actin, SM22, and calponin) and muscle-enriched microRNAs (miR-143/145 and miR-1/133a), and reduced contractility of human vascular smooth muscle cells (SMCs) embedded in collagen gel lattices, suggesting that myocardin degradation is required for its transcriptional activity. Further studies using chromatin immunoprecipitation assay revealed that proteasome inhibition, although increased the occupancy of myocardin and SRF on the promoter of SM α-actin gene, abolished myocardin-dependent recruitment of RNA polymerase II. We further examined the degradation of myocardin in epithelioid and spindle-shaped SMCs and revealed that myocardin in more differentiated spindle-shaped SMCs was more quickly degraded and had shorter half-life than in epithelioid SMCs. In neointimal lesions, we found that stabilization of myocardin protein was companied by downregulation of transcripts of ubiquitin and proteasome subunits, further illustrating the mechanism underlying reduction of myocardin transcriptional activity. In summary, our results have suggested that proteasomal degradation of myocardin is required for its transcriptional activity.
authors.affiliation: Smooth Muscle Research Group, Department of Biochemistry & Molecular Biology, Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Hao
authors.initials: H
authors.lastname: Yin
authors.forename: Yulan
authors.initials: Y
authors.lastname: Jiang
authors.forename: Haijie
authors.initials: H
authors.lastname: Li
authors.forename: Jingjing
authors.initials: J
authors.lastname: Li
authors.forename: Yu
authors.initials: Y
authors.lastname: Gui
authors.forename: Xi-Long
authors.initials: XL
authors.lastname: Zheng
mesh_terms: D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D000199:Actins / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D020212:Carotid Artery Injuries / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D047369:Chromatin Immunoprecipitation; D003094:Collagen / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004257:DNA Polymerase II / Q000378:metabolism; D004195:Disease Models, Animal; D005782:Gels; D005786:Gene Expression Regulation; D005838:Genotype; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D035683:MicroRNAs / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000201:enzymology*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000201:enzymology*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D012694:Serine; D026362:Serum Response Factor / Q000235:genetics / Q000378:metabolism; D013997:Time Factors; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection; D014661:Vasoconstriction; D000099251:Myocardin
chemical_list: D000111:Acetylcysteine; D000199:Actins; D003094:Collagen; D015853:Cysteine Proteinase Inhibitors; D004257:DNA Polymerase II; D005782:Gels; D007976:Leupeptins; D035683:MicroRNAs; D009687:Nuclear Proteins; D046988:Proteasome Endopeptidase Complex; D061988:Proteasome Inhibitors; D012694:Serine; D026362:Serum Response Factor; D015534:Trans-Activators; D000099251:Myocardin; C067713:lactacystin; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde