A NEW PLATELET-DERIVED GROWTH FACTOR-REGULATED GENOMIC ELEMENT WHICH BINDS A SERINE THREONINE PHOSPHOPROTEIN MEDIATES INDUCTION OF THE SLOWIMMEDIATE-EARLY GENE MCP-1

The MCP-1 chemokine gene belongs to a cohort of immediate-early genes that are induced with slower kinetics than c-fos. In this study, we id entified a cluster of four platelet-derived growth factor (PDGF)-respo nsive elements within a 240-bp enhancer found in the distal 5' flankin g MCP-1 sequences. Two of the elements bind one or more forms of the t ranscription factor NF-kappa B. We focused on the other two elements w hich are hitherto unreported, PDGF-regulated genomic motifs. One of th ese novel elements, detected as a 28-mer by DNase I footprinting, rest ores PDGF inducibility when added in two copies to a 5' truncated MCP- 1 gene. A single copy of the second novel element, a 27-mer, restores PDGF inducibility to a 5' truncated MCP-1 gene. The 27-base element in teracts with a PDGP-activated serine/threonine phosphoprotein that is detected only within the nucleus of PDGF-treated 3T3 cells. DNA bindin g of this phosphoprotein is activated by PDGF treatment with slow kine tics that match the time course of MCP-1 gene expression, and activati on is not inhibited by cycloheximide. PDGP-activated binding to the 27 -mer is shown to involve a single 30-kDa protein by UV-cross-linking a nalysis.