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 β

Abstract

The major histocompatibility complex (MHC) class II transactivator (CIITA) is the master regulatory factor required for appropriate expression of class II MHC genes. Understanding the expression of CIITA is key to understanding the regulation of class II MHC genes. This report describes the independent regulation of two distinct CIITA promoters by cytokines with opposing functions, gamma interferon (IFN-gamma) and transforming growth factor beta (TGF-beta). A functional analysis of deletion mutations of the upstream promoter (promoter III) identified an IFN-gamma-responsive region located approximately 5 kb from the transcriptional start site. An in vivo DNase I hypersensitivity analysis detected a hypersensitive site in this area which supports the relevance of this region. When the downstream promoter (promoter IV) 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-inducible transcription factor STAT1 was examined functionally. Although both promoters were controlled by STAT1, promoter-specific regulation was exhibited. The IFN-gamma response of promoter III was completely dependent on STAT1 and not IRF-1, while promoter IV was partially activated by IRF-1 in the total absence of STAT1 expression. While both promoters were affected by TGF-beta, activation of promoter III by IFN-gamma was more severely diminished by TGF-beta treatment. The differential control of CIITA promoters by TGF-beta, IRF-1, and STAT1 may be important in refining regulation of class II MHC genes in different cell types and under different stimulatory conditions.

Role of PKCδ in IFN-γ-inducible CIITA gene expression☆

“…The activation of the IFN-γ inducible CIITA promoter requires Stat1 and IRF-1 (MuhlethalerMottet et al, 1997;Piskurich et al, 1999;Morris et al, 2002). Based on our data and published studies, IFN-γ stimulation activates PKCδ, which in turn leads phosphorylation of Stat1 at serine 727.…”

“…Key transcription factors necessary for IFN-γ inducible expression of the CIITA gene are Stat1 and IRF-1 (Muhlethaler-Mottet et al, 1998;Piskurich et al, 1999). Therefore, we investigated whether the inhibition of PKCδ affects the recruitment of Stat1 and IRF-1.…”

“…Activated Stat1 dimerizes and translocates to the nucleus, where it binds to the GAS element in pIV (Shuai et al, 1994;Wen et al, 1995;Vinkemeier et al, 1996;Mowen et al, 2000;Darnell, 1997). Stat1 also controls IRF-1 expression, which in turn activates the CIITA promoter (Piskurich et al, 1999;Morris et al, 2002). Therefore, IFN-γ mediated activation of pIV requires both Stat1 and IRF-1.…”

Regulation of the Class II MHC Pathway in Primary Human Monocytes by Granulocyte-Macrophage Colony-Stimulating Factor

“…The cis regions important for activation of PIII have been identified in B and T cells (15,35,36,39). In addition, a region upstream of PIII responsible for CIITA expression in response to IFN-␥ has been identified and involves binding of STAT-1, but not IRF-1 (40). GM-CSF binding to the GM-CSF receptor results in the activation of Janus kinase 2, which in turn activates STAT5 (41,42).…”

Methylation of Class IItrans-Activator Promoter IV: A Novel Mechanism of MHC Class II Gene Control

“…Promoter III drives constitutive expression of CIITA, such as that observed in B cells, and promoter IV controls the IFN-␥-inducible expression of CIITA seen in most other cell types (20). There has also been a report that promoter III contributes to IFN-␥-inducible CIITA expression (21).…”