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Platelet‐derived growth factor induces p21/WAF1 promoter in vascular smooth muscle cells via activation of an Sp1 site
Author(s) -
Moon Sung-Kwon,
Jung Sun-Young,
Choi Yung-Hyun,
Lee Young-Choon,
Kim Cheorl-Ho
Publication year - 2003
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(03)00935-9
Subject(s) - platelet derived growth factor receptor , cyclin dependent kinase , microbiology and biotechnology , vascular smooth muscle , biology , retinoblastoma protein , platelet derived growth factor , sp1 transcription factor , transcription factor , growth factor , cyclin d1 , gene expression , promoter , cancer research , gene , cell cycle , biochemistry , endocrinology , receptor , smooth muscle
Many studies suggested that cyclin‐dependent kinase inhibitor (CDKI) p21 acts as a universal inhibitor of cyclin/CDK catalytic activity. This protein has also been shown to be a component of active cyclin/CDK complexes. In addition, it has recently been suggested that p21 serves as an assembly factor in platelet‐derived growth factor (PDGF)‐stimulated vascular smooth muscle cells (VSMC). However, little is known concerning the molecular mechanisms by which PDGF induces p21 gene expression in VSMC. In this report we demonstrate that PDGF induces the p21 expression at both the mRNA and protein levels. This increase in p21 gene expression was due to activation of the p21 promoter by PDGF. Through both deletion and mutation analysis of the p21 promoter, we defined a 10‐bp sequence that is required for the activation of the p21 promoter by PDGF. In addition, gel shift and supershift assays demonstrated that this PDGF‐responsive element binds specifically to the transcription factor Sp1. These results demonstrate that Sp1 mediates PDGF‐induced p21 gene expression in VSMC. Moreover, immunoblot and immonoprecipitation analysis showed that the level of hyperphosphorylated retinoblastoma protein (Rb) is increased and the protein is physically associated with Sp1 in PDGF‐treated cells, indicating that phosphorylated Rb may play a role in regulating Sp1 to activate p21 expression.