Chemokines are potent mediators of cell migration and activation and therefore play an essential role in early events of inflammation. In conjunction with cell adhesion molecules, chemokines help to localize cells to a specific site and enhance the inflammatory reaction at the site. Clinically, elevated levels of chemokines have been found in a variety of inflammatory diseases. The prototype C-C chemokine is monocyte chemoattractant protein-1 (MCP-1) which is synthesized by variety of cell types including endothelial cells in response to a variety of stimuli. MCP-1 is a major chemoattractant for monocytes, T lymphocytes, and basophils. In the present study, we investigated the factors involved in cytokine-induced MCP-1 gene expression in human endothelial cells. We present evidence that the nuclear factor (NF)-kappa B-like binding site and the AP-1 binding site located 90 and 68 base pairs upstream of the transcriptional start site, respectively, are required for maximal induction of the human MCP-1 promoter by interleukin-(IL)-1 beta. Site-directed mutagenesis or deletion of the NF-kappa B-like site decreased the cytokine-induced activity of the promoter. Site-directed mutagenesis of the AP-1 binding site also decreased the cytokine-induced activity of the promoter. We show that the NF-kappa B-like site located at-90 in the MCP-1 promoter binds to the p50/p65 heterodimer of the NF-kappa B/Rel family in IL-1 beta-stimulated human endothelial cells. Overexpression of p65 results in the transactivation of the MCP-1 promoter as well. The data presented in this study suggest that cytokine-induced MCP-1 gene expression in human endothelial cells depends on the cooperative action of NF-kappa B and AP-1.