Two distinct gamma interferon-inducible promoters of the major histocompatibility complex class II transactivator gene are differentially regulated by STAT1, interferon regulatory factor 1, and transforming growth factor beta

The major histocompatibility complex (MRC) class II transactivator (CIITA) is the master regulatory factor required for appropriate expression of clas s II MHC genes. Understanding the expression of CIITA is key to understandi ng the regulation of class II MHC genes. This report describes the independ ent regulation of two distinct CIITA promoters by cytokines with opposing f unctions, gamma interferon (IFN-gamma) and transforming growth factor beta (TGF-beta). A functional analysis of deletion mutations of the upstream pro moter (promoter III) identified an IFN-gamma-responsive region located appr oximately 5 kb from the transcriptional start site. An in vivo DNase I hype rsensitivity analysis detected a hypersensitive site in this area which sup ports the relevance of this region. When the downstream promoter (promoter TV) was studied by in vivo genomic footprinting, IFN-gamma-induced changes at putative binding sites for STAT1, interferon regulatory factor 1 (IRF-1) , and E-box proteins were seen. Gel shift and supershift analyses for IRF-1 confirmed the in vivo footprint results. The role of the IFN-gamma-inducib le transcription factor STAT1 was examined functionally. Although both prom oters were controlled by STAT1, promoter-specific regulation was exhibited. The IFN-gamma response of promoter III was completely dependent on STAT1 a nd not IRF-1, while promoter IV was partially activated by IRF-1 in the tot al absence of STAT1 expression. While both promoters were affected by TGF-b eta, activation of promoter III by IFN-gamma was more severely diminished b y TGF-beta treatment. The differential control of CIITA promoters by TGF-be ta, IRF-1, and STAT1. may be important in refining regulation of class II M HC genes in different cell types and under different stimulatory conditions .