A novel type of regulatory element is required for promoter-specific activity of the PDGF-B intronic enhancer region

We have previously described a non-classical, promoter-specific enhancer fo r the human Platelet-Derived Growth Factor B (PDGF-B) gene. In JEG-3 chorio carcinoma cells the activity of the enhancer depends upon co-operation with a sequence (the Enhancer-Dependent cis Go-activator "EDC" element) within the promoter. The PDGF-B enhancer fails to activate heterologous promoters, indicating that promoter-specificity depends on an element within the enha ncer that can recognise a target sequence within the promoter. Here we iden tify a sequence within the enhancer of the PDGF-B gene which directs activa tion of the PDGF-B promoter by distal cis-acting elements, This specifies t he wild-type PDGF-B promoter as the target for the enhancer and has been de signated the EDC specificity element (EDCse), The cell-type specific nature of this interaction is extended by the observation that the EDCse is also dispensable for enhancer activity in breast-cancer cells (ZR-75), Concomita nt to this observation, JEG-3 and ZR-75 cells differ in the binding of nucl ear factors to the EDCse, We discuss the relevance of the EDC/EDCse system in regulation of gene expression.