Two factors, IRF1 and KBF1/NF-kappa B, cooperate during induction of MHC class I gene expression by interferon alpha beta or Newcastle disease virus.

The expression of class I genes of the Major Histocompatibility Complex is stimulated by IFN. The promoter of these genes contains an interferon response sequence (IRS) which overlaps the major enhancer. These elements are recognized by several protein factors, including IRF-1, which binds the IRS, and KBF1/NF-kappa B, which binds the enhancer. We demonstrate here that infection by Newcastle Disease Virus (NDV) results in an increased expression of class I genes, by a mechanism partially different from that of IFN, but that in both cases the cooperative action of IRF1 and KBF1/NF-kappa B is required. In F9 embryonal carcinoma cells, where KBF1/NF-kappa B activity cannot be detected, both types of stimuli are ineffective.