Interferon-γ-induced chromatin remodeling at the CIITA locus is BRG1 dependent

Abstract

SWI/SNF regulates growth control, differentiation and tumor suppression, yet few direct targets of this chromatin-remodeling complex have been identified in mammalian cells. We report that SWI/SNF is required for interferon (IFN)-γ induction of CIITA, the master regulator of major histocompatibility complex class II expression. Despite the presence of functional STAT1, IRF-1 and USF-1, activators implicated in CIITA expression, IFN-γ did not induce CIITA in cells lacking BRG1 and hBRM, the ATPase subunits of SWI/SNF. Reconstitution with BRG1, but not an ATPase-deficient version of this protein (K798R), rescued CIITA induction, and enhanced the rate of induction of the IFN-γ-responsive GBP-1 gene. Notably, BRG1 inhibited the CIITA promoter in transient transfection assays, underscoring the importance of an appropriate chromosomal environment. Chromatin immunoprecipitation revealed that BRG1 interacts directly with the endogenous CIITA promoter in an IFN-γ-inducible fashion, while in vivo DNase I footprinting and restriction enzyme accessibility assays showed that chromatin remodeling at this locus requires functional BRG1. These data provide the first link between a cytokine pathway and SWI/SNF, and suggest a novel role for this chromatin-remodeling complex in immune surveillance.