Stimulated human monocytes release several proteins thought to play a role in inflammation, including interleukin 1, tumor necrosis factor, and plasminogen activator. We have purified another proinflammatory protein that is chemotactic for human neutrophils from conditioned medium of lipopolysaccharide-stimulated monocytes. After a series of steps that included anion-exchange chromatography, gel filtration, and HPLC on cation-exchange and reverse-phase columns, an apparently pure protein was obtained that migrated as a single 7-kDa band on NaDodSO4/polyacrylamide gels under reducing or nonreducing conditions. The amino acid composition of this monocyte-derived neutrophil chemotactic factor was different from that of interleukin 1 and tumor necrosis factor. N-terminal amino acid sequence of the first 42 residues was determined. This portion of the molecule has up to 56% sequence similarity with several proteins that may be involved in host responses to infection or tissue injury. It is identical to a portion of a sequence deduced from an mRNA induced by staphylococcal enterotoxin treatment of human leukocytes. At the optimal concentration of 10 nM, 50% of neutrophils added to chemotaxis assay wells migrated toward the pure attractant. Potency and efficacy are comparable to that of fMet-Leu-Phe, which is often used as a reference. In contrast to many attractants, the protein was not chemotactic for human monocytes.

Human monocyte chemoattractant protein-1 (human MCP-1) mRNA accumulated in THP-1 cells 2 h after lipopolysaccharide (LPS) stimulation. DNase I footprinting revealed that LPS stimulation induced protein binding to the two closely located NF-κB sites, A1 and A2. By electrophoretic gel mobility shift assay and supershift assay, the binding of (p65)₂, c-Rel/p65, p50/p65, and p50/c-Rel to the A2 oligonucleotide probe was detected after LPS stimulation. In contrast, 12-o-tetradecanoylphorbol 13-acetate did not induce a significant amount of MCP-1 mRNA in THP-1 cells 2 h after stimulation, and only p50/p65 bound to the A2 probe.trans-Activity of each NF-κB/Rel dimer was investigated by transfecting P19 cells with p65, p50, and/or c-Rel expression vectors, and a luciferase construct containing the enhancer region of the human MCP-1 gene. Expression of recombinant p65 or p65 and c-Rel resulted in elevated luciferase activities, indicating that (p65)₂ and c-Rel/p65 had trans-activity. The binding of (p65)₂ and/or c-Rel/p65 to the A2 probe was also detected from 12-o-tetradecanoylphorbol 13-acetate-stimulated HeLa, HOS, and A172 cells in which expression of MCP-1 mRNA was elevated. Finally, the role of the A1 site was investigated. Both (p65)₂ and c-Rel/p65 bound to the A1 probe by electrophoretic mobility shift assay and a mutation in the A1 or A2 site resulted in a loss of the enhancer activity. These results suggest that the binding of (p65)₂ and c-Rel/p65 to the A1 and A2 sites of this gene is important for the tissue- and stimulus-specific transcription of the human MCP-1gene.