Regulation of human IP-10 gene expression in astrocytoma cells by inflammatory cytokines

Because of its prominent expression in central nervous system inflammatory pathology by astrocytes, we examined the mechanism of human IP-10 (hIP-10) gene induction by interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) in astrocytoma cells, When present together, IFN-gamma and TNF-alpha induced robust accumulation of hIP-10 mRNA, but hIP-10 mRNA was minimally induced when astrocytoma cells were treated with individual cytokines, This pattern of expression resembled that previously described for murine IP-10 (mIP-10) gene induction in fibroblasts and in rat astroglia, Nuclear run-on experiments showed that the synergistic effect of the cytokines resulted from an increased rate of IP-10 transcriptional initiation. Functional analysis of the hIP-10 promoter after deletion and substitution mutagenesis indicated that an interferon-stimulated response element (ISRE) governed both simple response to IFN-gamma and synergy with TNF-alpha. Synergistic induction of hIP-10 also required an ISRE-proximal nuclear factor kappa-B (NF kappa B) binding site. TNF-alpha-induced NF kappa B binding activity at this site was composed of RelA (p65) homodimers. Our results document that cis-elements through which cytokines mediate synergistic induction of IP-10 in mouse and human are strictly conserved despite divergence elsewhere within the proximal 5'-flanking region. J. Neurosci, Res. 54:169-180, 1998. (C) 1998 Wiley-Liss, Inc.