Kinetics of a Gamma Interferon Response: Expression and Assembly of CIITA Promoter IV and Inhibition by Methylation

Abstract

Chromatin immunoprecipitation assays were employed to assess the kinetics of transcription factor assembly and histone modifications that occur during gamma interferon (IFN-␥) induction of CIITA gene expression. CIITA is the master regulator of major histocompatibility complex class II transcription. Promoter IV (PIV), the major IFN-␥ responsive promoter for CIITA expression, requires both STAT1 and IFN regulatory factor 1 (IRF-1) for induction by IFN-␥. STAT1 binding to PIV was detected first and was accompanied by a modest acetylation of histones H3 and H4 that were associated with the region. Despite these changes, which occurred within 30 min of IFN-␥ treatment, CIITA mRNA was not detected until IRF-1 protein was synthesized and bound to its site, a process that required >120 min. In contrast to these events, fetal trophoblast-like cell lines, which are refractory to CIITA induction by IFN-␥, failed to assemble the above factors or modify their chromatin, suggesting that accessibility to the promoter is blocked. Bisulfite sequencing of PIV showed strong hypermethylation of PIV, providing a link between methylation, chromatin structure, and factor binding. Together, this analysis provides a kinetic view of the activation of the CIITA gene in response to IFN-␥ and shows that regulatory factor assembly, chromatin modification, and gene expression proceed in discrete steps.

Inactivation of class II transactivator by DNA methylation and histone deacetylation associated with absence of HLA-DR induction by interferon-γ in haematopoietic tumour cells

“…The methylation around the transcription start site, which silenced CIITA-PIV gene expression, was in turn inversely related to histone acetylation, indicating a possible role for histone deacetylation in the gene silencing. This would be consistent with the findings of Morris et al (2002), who reported histone acetylation to be involved in the transcriptional regulation of CIITA.…”

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.…”

“…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.…”

HLA class II antigen-processing pathway in tumors: Molecular defects and clinical relevance

“…In addtion, to promote the binding of TF to CIITA-PIV, IFNg also includes the acetylation of histones leading to an accessibility of CIITA-PIV. 28 Furthermore, a variety of signal transduction pathways, such as PKA, upregulates CIITA expression, which, in turn, enhances HLA class II antigen cell surface expression. 29 …”