AN S1 NUCLEASE-SENSITIVE REGION IN THE FIRST INTRON OF HUMAN PLATELET-DERIVED GROWTH-FACTOR A-CHAIN GENE CONTAINS A NEGATIVELY ACTING CELL-TYPE-SPECIFIC REGULATORY ELEMENT

The platelet-derived growth factor (PDGF) A-chain gene is expressed in a tissue- and developmental stage-specific manner. Here we identify a n S1 nuclease sensitive region within the first intron that functions as a negative regulatory element in HeLa but not in human glioblastoma (A172) cells in transient transfection assays. A 147 bp DNA fragment that contains this element functions in a position and orientation ind ependent manner to negatively regulate both the PDGF A-chain promoter and the heterologous herpes simplex virus thymidine kinase (TK) promot er. The cell-type specific effect of this 147 bp DNA fragment is seen when it is located downstream but not upstream of the reporter gene dr iven by either the PDGF A-chain or TK promoters. The negative regulato ry element has been localized to a 24 bp DNA sequence within the S1 se nsitive site that retains negative regulatory activity and recognizes a nuclear protein in HeLa but not in A172 cells. Furthermore, the 24 b p element functions as a cell type-specific negative element independe nt of its position. These results suggest that a functional silencer w ithin the first intron exhibits a non-B-form DNA structure under super helical stress in vitro and may contribute to the cell type-specific t ranscriptional regulation of PDGF A-chain gene in vivo.