title: Angiotensin II-induced stimulation of smooth muscle alpha-actin expression by serum response factor and the homeodomain transcription factor MHox.
abstract: The objective of the present study was to examine the molecular mechanisms whereby angiotensin II (Ang II) stimulates smooth muscle (SM) alpha-actin expression in rat aortic smooth muscle cells (SMCs). Nuclear run-on analysis and transfection studies indicated that the effects of Ang II on SM alpha-actin were mediated at least in part at the transcriptional level. Transfection of various rat SM alpha-actin promoter/chloramphenicol acetyltransferase (CAT) constructs into SMCs demonstrated that the first 155 bp of the SM alpha-actin promoter was sufficient to confer maximal Ang II responsiveness, conferring an approximately 4-fold increase in reporter activities in these SMCs compared with vehicle-treated SMCs. Mutation of either of two highly conserved CArG elements, designated A (-62) and B (-112), completely abolished Ang II-induced increases in reporter activity, whereas mutation of a homeodomain-like binding sequence at -145 (ATTA) reduced reporter activity by half. Results of EMSAs showed that nuclear extracts from Ang II-treated SMCs exhibited enhanced binding activity of serum response factor (SRF) to the CArG elements and of a homeodomain factor, MHox, to the ATTA element. Northern analyses showed that Ang II also stimulated marked increases in MHox mRNA levels. Western analyses demonstrated that Ang II-induced increases in SRF binding were not due to increased SRF protein expression. Recombinant MHox markedly enhanced binding activity of SRF in EMSAs. Finally, MHox overexpression transactivated a SM alpha-actin promoter/CAT reporter construct by approximately 3.5-fold in transient cotransfection studies. These results provide evidence for involvement of a homeodomain transcription factor, MHox, in Ang II-mediated stimulation of SM alpha-actin via a CArG/SRF-dependent mechanism.
authors.affiliation: Department of Molecular Physiology and Biological Physics, University of Virginia Health Sciences Center, Charlottesville 22908, USA.
authors.forename: M B
authors.initials: MB
authors.lastname: Hautmann
authors.forename: M M
authors.initials: MM
authors.lastname: Thompson
authors.forename: E A
authors.initials: EA
authors.lastname: Swartz
authors.forename: E N
authors.initials: EN
authors.lastname: Olson
authors.forename: G K
authors.initials: GK
authors.lastname: Owens
mesh_terms: D000199:Actins / Q000235:genetics / Q000378:metabolism*; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D001483:Base Sequence; D017124:Conserved Sequence; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D005786:Gene Expression Regulation; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism / Q000494:pharmacology; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000494:pharmacology; D026362:Serum Response Factor; D014157:Transcription Factors / Q000235:genetics / Q000494:pharmacology*; D014158:Transcription, Genetic / Q000187:drug effects; D015533:Transcriptional Activation
chemical_list: D000199:Actins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D026362:Serum Response Factor; D014157:Transcription Factors; D000804:Angiotensin II