Fibroblast growth factor-2 represses platelet-derived growth factor receptor-alpha (PDGFR-alpha) transcription via ERK1/2-dependent Sp1 phosphorylation and an atypical cis-acting element in the proximal PDGFR-alpha promoter.
Platelet-derived growth factor (PDGF) is a potent mitogen and chemoattractant for vascular smooth muscle cells (SMCs) whose biological activity is mediated via its high affinity interaction with specific cell surface receptors. The molecular mechanisms governing the expression of PDGF receptor-alpha (PDGFR-alpha) are poorly understood. Here we demonstrate that PDGFR-alpha protein and transcriptional regulation in SMCs is under the positive regulatory influence of the zinc finger nuclear protein, Sp1. Electrophoretic mobility shift, competition, and supershift analysis revealed the existence of an atypical G-rich Sp1-binding element located in the PDGFR-alpha promoter -61 to -52 bp upstream of the transcriptional start site. Mutation of this sequence ablated endogenous Sp1 binding and activation of the PDGFR-alpha promoter. PDGFR-alpha transcription, mRNA, and protein expression were repressed in SMCs exposed to fibroblast growth factor-2 (FGF-2). This inhibition was rescued by the blockade of extracellular signal-regulated kinase-1/2 (ERK1/2). FGF-2 repression of PDGFR-alpha transcription was abrogated upon mutation of this Sp1-response element. FGF-2 stimulated Sp1 phosphorylation in an ERK1/2- but not p38-dependent manner, the growth factor enhancing Sp1 interaction with the PDGFR-alpha promoter. Mutation of residues Thr(453) and Thr(739) in Sp1 (amino acids phosphorylated by ERK) blocked FGF-2 repression of PDGFR-alpha transcription. These findings, taken together, demonstrate that FGF-2 stimulates ERK1/2-dependent Sp1 phosphorylation, thereby repressing PDGFR-alpha transcription via the -61/-52 element in the PDGFR-alpha promoter. Phosphorylation triggered by FGF-2 switches Sp1 from an activator to a repressor of PDGFR-alpha transcription, a finding previously unreported in any Sp1-dependent gene.
Bonello
Michelle R
MR
Centre for Vascular Research, The University of New South Wales and Department of Haematology, The Prince of Wales Hospital, Sydney New South Wales 2052, Australia.
Khachigian
Levon M
LM
D000818:Animals; D002478:Cells, Cultured; D004742:Enhancer Elements, Genetic / Q000235:genetics; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology / Q000502:physiology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000502:physiology; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000502:physiology; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000235:genetics*; D051381:Rats; D020796:Receptor, Platelet-Derived Growth Factor alpha / Q000235:genetics*; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics; D016329:Sp1 Transcription Factor / Q000502:physiology; D014158:Transcription, Genetic / Q000187:drug effects
D016329:Sp1 Transcription Factor; D016222:Fibroblast Growth Factor 2; D020796:Receptor, Platelet-Derived Growth Factor alpha; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases