IP-10 gene transcription by virus in astrocytes requires cooperation of ISRE with adjacent κB site but not IRF-1 or viral transcription

Transcription of the IP-10 gene requires interferon (IFN)-stimulated response element (ISRE) and kappa B sites to be induced by lipopolysaccharide (LPS), IFN-gamma, virus, and poly(I:C), A requirement for Stat1 binding to ISRE for IFN-gamma and IFN regulatory factor-1 (IRF-1) binding to ISRE for LPS, poly(I:C), and virus has been reported. We investigated whether viral transcription is required for IP-10 induction and how ISRE interacts with IRF-1 and with two kappa B sites, IP-10 mRNA was induced by Newcastle disease virus and Sendai virus in rat astrocytes and the human astrocytoma U251 cell line. IF-10 was also induced by UV-irradiated virus, which is unable to carry out viral transcription. The minimal IF-10 virus response element (VRE) consists of an ISRE and adjacent kappa B site between -236 and -153, to which p50/p65 NF-kappa B proteins and IRF-like proteins bind. Virus induced NF-kappa B binding to an isolated kappa B sequence adjacent to ISRE, However, no protein binding to isolated ISRE was induced by virus. Virus also induced IF-10 in cells expressing a defective IRF-1 gene. Therefore, effective ISRE activity of IP-10 VRE may require an IRF-like protein binding, which is enhanced by an NF-kappa B heterodimer binding to an adjacent kappa B site. IRF-1 is not required for virus-induced IF-10 gene expression.