Platelet-derived growth factor-BB and Ets-1 transcription factor negatively regulate transcription of multiple smooth muscle cell differentiation marker genes.
Platelet-derived growth factor (PDGF)-BB, a potent mitogen for mesenchymal cells, also downregulates expression of multiple smooth muscle (SM) cell (SMC)-specific markers. However, there is conflicting evidence whether PDGF-BB represses SMC marker expression at a transcriptional or posttranscriptional level, and little is known regarding the mechanisms responsible for these effects. Results of the present studies provide clear evidence that PDGF-BB treatment strongly repressed SM alpha-actin, SM myosin heavy chain (MHC), and SM22alpha promoters in SMCs. Of major significance for resolving previous controversies in the field, we found PDGF-BB-induced repression of SMC marker gene promoters in subconfluent, but not postconfluent, cultures. Treatment of postconfluent SMCs with a tyrosine phosphatase inhibitor restored PDGF-BB-induced repression, whereas treatment of subconfluent SMCs with a tyrosine kinase blocker abolished PDGF-BB-induced repression, suggesting that a tyrosine phosphorylation event mediates cell density-dependent effects. On the basis of previous observations that Ets-1 transcription factor is upregulated within phenotypically modulated neointimal SMCs, we tested whether Ets-1 would repress SMC marker expression. Consistent with this hypothesis, results of cotransfection experiments indicated that Ets-1 overexpression reduced transcriptional activity of SMC marker promoter constructs in SMCs, whereas it increased activity of SM alpha-actin promoter in endothelial cells. PDGF-BB treatment increased expression of Ets-1 in cultured SMCs, and SM alpha-actin mRNA expression was reduced in multiple independent clones of SMCs stably transfected with an Ets-1-overexpressing construct. Taken together, results of these experiments provide novel insights regarding possible mechanisms whereby PDGF-BB and Ets-1 may contribute to SMC phenotypic switching associated with vascular injury.
Dandré
Frédéric
F
Cardiovascular Research Center, University of Virginia, PO Box 801394, Charlottesville, VA 22908-1394, USA.
Owens
Gary K
GK
D000199:Actins / Q000235:genetics; D000818:Animals; D000925:Anticoagulants / Q000494:pharmacology*; D001013:Aorta, Thoracic / Q000166:cytology; D000077214:Becaplermin; D015415:Biomarkers; D002452:Cell Count; D002454:Cell Differentiation / Q000502:physiology; D002478:Cells, Cultured; D008156:Luciferases / Q000235:genetics; D008840:Microfilament Proteins / Q000235:genetics; D009124:Muscle Proteins / Q000235:genetics; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000235:genetics; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D050784:Proto-Oncogene Protein c-ets-1; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D050783:Proto-Oncogene Proteins c-ets; D020574:Proto-Oncogene Proteins c-sis; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects*; D015854:Up-Regulation / Q000187:drug effects
D000199:Actins; D000925:Anticoagulants; D015415:Biomarkers; C494042:Ets1 protein, mouse; C494043:Ets1 protein, rat; D008840:Microfilament Proteins; D009124:Muscle Proteins; D010982:Platelet-Derived Growth Factor; D050784:Proto-Oncogene Protein c-ets-1; D011518:Proto-Oncogene Proteins; D050783:Proto-Oncogene Proteins c-ets; D020574:Proto-Oncogene Proteins c-sis; C058992:Tagln protein, mouse; D014157:Transcription Factors; C051615:transgelin; D000077214:Becaplermin; D008156:Luciferases; D018995:Myosin Heavy Chains