Kruppel-like factor 4 abrogates myocardin-induced activation of smooth muscle gene expression.
Platelet-derived growth factor BB (PDGF-BB) has been shown to be an extremely potent negative regulator of smooth muscle cell (SMC) differentiation. Moreover, previous studies have demonstrated that the Kruppel-like transcription factor (KLF) 4 potently represses the expression of multiple SMC genes. However, the mechanisms whereby KLF4 suppresses SMC gene expression are not known, nor is it clear whether KLF4 contributes to PDGF-BB-induced down-regulation of SMC genes. The goals of the present studies were to determine the molecular mechanisms by which KLF4 represses expression of SMC genes and whether it contributes to PDGF-BB-induced suppression of these genes. Results demonstrated that KLF4 markedly repressed both myocardin-induced activation of SMC genes and expression of myocardin. KLF4 was rapidly up-regulated in PDGF-BB-treated, cultured SMC, and a small interfering RNA to KLF4 partially blocked PDGF-BB-induced SMC gene repression. Both PDGF-BB and KLF4 markedly reduced serum response factor binding to CArG containing regions within intact chromatin. Finally, KLF4, which is normally not expressed in differentiated SMC in vivo, was rapidly up-regulated in vivo in response to vascular injury. Taken together, results indicate that KLF4 represses SMC genes by both down-regulating myocardin expression and preventing serum response factor/myocardin from associating with SMC gene promoters, and suggest that KLF4 may be a key effector of PDGF-BB and injury-induced phenotypic switching of SMC.
Liu
Yan
Y
Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia 22908, USA.
Sinha
Sanjay
S
McDonald
Oliver G
OG
Shang
Yueting
Y
Hoofnagle
Mark H
MH
Owens
Gary K
GK
D016475:3T3 Cells; D000818:Animals; D001011:Aorta; D000077214:Becaplermin; D019556:COS Cells; D002522:Chlorocebus aethiops; D002843:Chromatin / Q000235:genetics; D004268:DNA-Binding Proteins / Q000502:physiology*; D005786:Gene Expression Regulation / Q000187:drug effects; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors; D051379:Mice; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics*; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D020574:Proto-Oncogene Proteins c-sis; D051381:Rats; D015534:Trans-Activators / Q000037:antagonists & inhibitors* / Q000235:genetics*; D014157:Transcription Factors / Q000502:physiology*; D014162:Transfection; D000099251:Myocardin
D000077214:Becaplermin; D002843:Chromatin; D004268:DNA-Binding Proteins; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors; D009687:Nuclear Proteins; D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; D015534:Trans-Activators; D014157:Transcription Factors; D000099251:Myocardin; C000715468:Klf4 protein, mouse; C000715469:Klf4 protein, rat