GC factor 2 represses platelet-derived growth factor A-chain gene transcription and is itself induced by arterial injury

Platelet-derived growth factor (PDGF) is a mitogen and chemoattractant for a wide variety of cell types. The genes encoding PDGF A chain (PDGF-A) and PDGF B chain(PDGF-B) reside on separate chromosomes and are independently r egulated at the level of transcription. Regulatory events underlying induci ble PDCF-A expression have been the focus of much investigation However, me chanisms that inhibit transcription of this gene are not well understood. I n this study, we report the capacity of a newly cloned DNA binding factor, GC factor:! (GCF2), to repress expression driven by the human PDGF-A promot er. 5' Deletion and transient cotransfection analysis in vascular endotheli al cells revealed that GCF2 repression is mediated by a nucleotide region l ocated in the proximal region of the PDCF-A promoter. Electrophoretic mobil ity shift assays demonstrate that GCF2 binds to this region in a specific a nd dose-dependent manner. Interestingly, the site bound by GCF2 overlaps th ose for specificity protein-1 (Spl) and early growth response factor-1 (Egr -1), zinc finger transcription factors that direct basal and inducible expr ession of the PDGF-A gene. Gel shift experiments revealed that GCF2. compet es with these factors for interaction with the PDGF-A promoter. Overexpress ion of GCF2 suppressed endogenous PDGF-A expression in vascular endothelial cells and smooth muscle cells. GCF2 was induced on mechanical injury of ce lls in culture as well as after balloon injury of the rat carotid artery wa ll. Time course studies revealed the sustained induction of GCF2 after inju ry while PDGF-A levels sharply returned to baseline. Smooth muscle cell pro liferation was inhibited by GCF2, an effect reversed by the addition of exo genous PDGF-AA. These findings demonstrate negative regulation of PDGF-A ex pression by GCF2. This is the first report of the induction of an endogenou s transcriptional repressor in the rat vessel wall.