scholarly journals Platelet-derived growth factor-BB represses smooth muscle cell marker genes via changes in binding of MKL factors and histone deacetylases to their promoters

2007 ◽  
Vol 292 (2) ◽  
pp. C886-C895 ◽  
Author(s):  
Tadashi Yoshida ◽  
Qiong Gan ◽  
Yueting Shang ◽  
Gary K. Owens
Keyword(s):  
Smooth Muscle ◽  
Growth Factor ◽  
Smooth Muscle Cell ◽  
Muscle Cell ◽  
Histone Deacetylases ◽  
Marker Gene ◽  
Platelet Derived Growth Factor ◽  
Phenotypic Switching ◽  
Marker Genes ◽  
Gene Promoters

A hallmark of smooth muscle cell (SMC) phenotypic switching is suppression of SMC marker gene expression. Although myocardin has been shown to be a key regulator of this process, the role of its related factors, MKL1 and MKL2, in SMC phenotypic switching remains unknown. The present studies were aimed at determining if: 1) MKL factors contribute to the expression of SMC marker genes in cultured SMCs; and 2) platelet-derived growth factor-BB (PDGF-BB)-induced repression of SMC marker genes is mediated by suppression of MKL factors. Results of gain- and loss-of-function experiments showed that MKL factors regulated the expression of single and multiple CArG [CC(AT-rich)6GG]-containing SMC marker genes, such as smooth muscle (SM) α-actin and telokin, but not CArG-independent SMC marker genes such as smoothelin-B. Treatment with PDGF-BB reduced the expression of CArG-containing SMC marker genes, as well as myocardin expression in cultured SMCs, while it had no effect on expression of MKL1 and MKL2. However, of interest, PDGF-BB induced the dissociation of MKL factors from the CArG-containing region of SMC marker genes, as determined by chromatin immunoprecipitation assays. This dissociation was caused by the competition between MKL factors and phosphorylated Elk-1 at early time points, but subsequently by the reduction in acetylated histone H4 levels at these promoter regions mediated by histone deacetylases, HDAC2, HDAC4, and HDAC5. Results provide novel evidence that PDGF-BB-induced repression of SMC marker genes is mediated through combinatorial mechanisms, including downregulation of myocardin expression and inhibition of the association of myocardin/MKL factors with CArG-containing SMC marker gene promoters.

Platelet-derived growth factor-BB and Ets-1 transcription factor negatively regulate transcription of multiple smooth muscle cell differentiation marker genes

2004 ◽  
Vol 286 (6) ◽  
pp. H2042-H2051 ◽  
Author(s):  
Frédéric Dandré ◽  
Gary K. Owens
Keyword(s):  
Transcription Factor ◽  
Smooth Muscle ◽  
Growth Factor ◽  
Tyrosine Phosphatase ◽  
Marker Gene ◽  
Platelet Derived Growth Factor ◽  
Phenotypic Switching ◽  
Marker Genes ◽  
Gene Promoters ◽  
Marker Expression

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 α-actin, SM myosin heavy chain (MHC), and SM22α 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 α-actin promoter in endothelial cells. PDGF-BB treatment increased expression of Ets-1 in cultured SMCs, and SM α-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.

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