Platelet-derived growth factor induction of the immediate-early gene MCP-1 is mediated by NF-kappa B and a 90-kDa phosphoprotein coactivator

A broad panel of agents including serum, interleukin-1, double-stranded RNA, and platelet-derived growth factor (PDGF) stimulate transcription of the ''slow'' immediate-early gene MCP-1. These disparate inducers act through a tight cluster of regulatory elements in the distal 5'-flanking sequences of the MCP-1 gene, We describe a 22-base element in this cluster which, in single copy, confers PDGF-inducibility to a tagged MCP-1 reporter gene, In mobility shift assays, the element binds a PDGF-activated form of NF-kappa B, and a 90-kDa protein (p90) which binds constitutively, Antibody supershift and UV cross-linking experiments indicate that the PDGF-activated NF-kappa B species is a Rel A homodimer, The DNA binding form of p90 is a nuclear-restricted serine/threonine phosphoprotein. Mutagenesis of the 22-base element shows that the NF-kappa B and p90 binding sites overlap, but binding of the two species is mutually independent, Both sites, however, are required for optimum PDGF induction of MCP-1, Therefore, p90 appears to be a coactivator with NF-kappa B in PDGF-mediated induction of MCP-1.