Lipopolysaccharide induces DNA binding activity specific for the IFN-stimulated response element in murine peritoneal macrophages.

Several murine macrophage genes that exhibit transcriptional response to LPS (e.g., IP-10, D3) have IFN-stimulated response element (ISRE) sequences present in regions flanking the transcription start sites. In the present study, the ability of LPS to activate proteins in murine peritoneal macrophages capable of binding to the ISRE has been investigated. Nuclear extracts from both LPS-treated and untreated macrophages are capable of forming four distinct complexes with a radiolabeled oligonucleotide containing the ISRE sequence as detected by electrophoretic mobility shift assays. LPS-treated nuclei contained an additional ISRE binding activity (complex I) that was not found in unstimulated cells. The induction of the latter activity by LPS was sensitive to polymyxin B sulfate, a lipid A antagonist, demonstrating that LPS was the primary inducing activity. All five retarded protein-DNA complexes formed were specific for the ISRE sequence as shown by competition with a series of oligonucleotides containing either ISRE-related or -unrelated sequences. Complex I binding activity was dependent upon the concentration of LPS and the time of LPS treatment. Furthermore, complex I was similar to that induced in response to treatment with IFN-beta in terms of electrophoretic mobility and specificity for the ISRE. LPS-induced complex I formation was partially independent of protein synthesis and could not be blocked by including neutralizing antibody to IFN-alpha/beta in the culture medium. Thus, even though LPS is a potent inducer of IFN-beta in murine macrophages, class I IFN expression may not be an obligatory intermediate event in the LPS-driven activation of ISRE binding activity. These results suggest that induction of ISRE binding activity may be an important part of the signaling process initiated by LPS.