Site-specific methylation inhibits transcriptional activity of platelet-derived growth factor A-chain promoter

Expression of the platelet-derived growth factor (PDGF) A-chain gene is temporally and spatially restricted in development and highly regulated in selected normal and tumor cell lines. Because DNA methylation appears to be important in regulating tissue specific gene expression, we tested the influence of in vitro methylation of the human PDGF A-chain promotor on its activity in vivo in transient transfection assays. We now report that PDGF A-chain promoter activity is strongly repressed by DNA methylation in a DNA sequence-specific manner and that the repression of promoter activity by methylation requires a methyl CpG-binding protein(s). We also report that incubation of HeLa cells with 5-azacytidine sharply increases levels of endogenous PDGF A-chain gene transcripts. These results indicate that the promoter activity of the PDGF A-chain gene is sharply and selectively reduced by in vitro DNA methylation and that DNA methylation in vivo also may reduce its function in selected cell lines.