title: Myocardin and Prx1 contribute to angiotensin II-induced expression of smooth muscle alpha-actin.
abstract: Previous studies demonstrated that angiotensin II (Ang II)-induced hypertrophy of smooth muscle cells (SMCs) was associated with increased transcription of SM alpha-actin gene. The aim of the present study was to determine whether myocardin, a SMC-selective cofactor of serum response factor (SRF), contributed to Ang II-induced increases in SM alpha-actin transcription. Results showed that Ang II increased myocardin mRNA expression as well as SM alpha-actin mRNA expression via the Ang II type 1 receptor in cultured rat aortic SMCs. Cotransfection studies revealed that CArG elements were required for Ang II-induced transcription of SM alpha-actin gene, and a dominant-negative form of myocardin or a short interfering RNA (siRNA) specific for myocardin decreased Ang II-induced SM alpha-actin transcription. Prx1, a homeodomain protein whose expression was increased by Ang II, also increased SM alpha-actin gene transcription in part via CArG elements, and siRNA specific for Prx1 markedly decreased basal and Ang II-induced SM alpha-actin transcription. Electrophoretic mobility shift assay showed that myocardin and Ang II, respectively, increased formation of a SMC-specific CArG-SRF-myocardin higher order complex. However, Ang II had no effect on binding between myocardin and SRF as determined by a mammalian two-hybrid assay, suggesting that Ang II-induced increases in formation of CArG-SRF-myocardin complex was the result of increased SRF binding to CArG elements and increased myocardin expression. Taken together, these results support a model in which Ang II-induced increases in expression of SM alpha-actin are mediated through Prx1-dependent increases in SRF binding to CArG elements and subsequent recruitment of myocardin.
authors.affiliation: Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Va 22908, USA.
authors.forename: Tadashi
authors.initials: T
authors.lastname: Yoshida
authors.forename: Mark H
authors.initials: MH
authors.lastname: Hoofnagle
authors.forename: Gary K
authors.initials: GK
authors.lastname: Owens
mesh_terms: D000199:Actins / Q000096:biosynthesis* / Q000235:genetics; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D001011:Aorta; D002478:Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology*; D017930:Genes, Reporter; D018398:Homeodomain Proteins / Q000235:genetics / Q000502:physiology*; D006984:Hypertrophy; D051379:Mice; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000235:genetics / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis; D034741:RNA, Small Interfering / Q000494:pharmacology; D051381:Rats; D044140:Receptor, Angiotensin, Type 1 / Q000187:drug effects; D011993:Recombinant Fusion Proteins / Q000502:physiology; D012045:Regulatory Sequences, Nucleic Acid; D026362:Serum Response Factor / Q000502:physiology; D015534:Trans-Activators / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic; D020798:Two-Hybrid System Techniques; D000099251:Myocardin
chemical_list: D000199:Actins; D000804:Angiotensin II; D018398:Homeodomain Proteins; D009687:Nuclear Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D044140:Receptor, Angiotensin, Type 1; D011993:Recombinant Fusion Proteins; D026362:Serum Response Factor; D015534:Trans-Activators; D000099251:Myocardin; C489936:Prrx1 protein, mouse