title: The transcription factor RFX protects MHC class II genes against epigenetic silencing by DNA methylation.
abstract: Classical and nonclassical MHC class II (MHCII) genes are coregulated by the transcription factor RFX (regulatory factor X) and the transcriptional coactivator CIITA. RFX coordinates the assembly of a multiprotein "enhanceosome" complex on MHCII promoters. This enhanceosome serves as a docking site for the binding of CIITA. Whereas the role of the enhanceosome in recruiting CIITA is well established, little is known about its CIITA-independent functions. A novel role of the enhanceosome was revealed by the analysis of HLA-DOA expression in human MHCII-negative B cell lines lacking RFX or CIITA. HLA-DOA was found to be reactivated by complementation of CIITA-deficient but not RFX-deficient B cells. Silencing of HLA-DOA was associated with DNA methylation at its promoter, and was relieved by the demethylating agent 5-azacytidine. Surprisingly, DNA methylation was also established at the HLA-DRA and HLA-DQB loci in RFX-deficient cells. This was a direct consequence of the absence of RFX, as it could be reversed by restoring RFX function. DNA methylation at the HLA-DOA, HLA-DRA, and HLA-DQB promoters was observed in RFX-deficient B cells and fibroblasts, but not in CIITA-deficient B cells and fibroblasts, or in wild-type fibroblasts, which lack CIITA expression. These results indicate that RFX and/or enhanceosome assembly plays a key CIITA-independent role in protecting MHCII promoters against DNA methylation. This function is likely to be crucial for retaining MHCII genes in an open chromatin configuration permissive for activation in MHCII-negative cells, such as the precursors of APC and nonprofessional APC before induction with IFN-gamma.
authors.affiliation: Faculty of Medicine, University of Geneva, Geneva, Switzerland.
authors.forename: Queralt
authors.initials: Q
authors.lastname: Seguín-Estévez
authors.forename: Raffaele
authors.initials: R
authors.lastname: De Palma
authors.forename: Michal
authors.initials: M
authors.lastname: Krawczyk
authors.forename: Elisa
authors.initials: E
authors.lastname: Leimgruber
authors.forename: Jean
authors.initials: J
authors.lastname: Villard
authors.forename: Capucine
authors.initials: C
authors.lastname: Picard
authors.forename: Augusto
authors.initials: A
authors.lastname: Tagliamacco
authors.forename: Gianfranco
authors.initials: G
authors.lastname: Abbate
authors.forename: Jack
authors.initials: J
authors.lastname: Gorski
authors.forename: Arcangelo
authors.initials: A
authors.lastname: Nocera
authors.forename: Walter
authors.initials: W
authors.lastname: Reith
mesh_terms: D016175:B-Lymphocyte Subsets / Q000276:immunology / Q000378:metabolism; D002460:Cell Line; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D019175:DNA Methylation / Q000276:immunology*; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D004742:Enhancer Elements, Genetic / Q000276:immunology; D020868:Gene Silencing / Q000276:immunology*; D006681:HLA-D Antigens / Q000096:biosynthesis* / Q000235:genetics*; D006801:Humans; D009687:Nuclear Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D011401:Promoter Regions, Genetic / Q000276:immunology; D000071701:Regulatory Factor X Transcription Factors; D015534:Trans-Activators / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D014157:Transcription Factors / Q000172:deficiency / Q000235:genetics / Q000502:physiology*
chemical_list: D004268:DNA-Binding Proteins; D006681:HLA-D Antigens; C046148:HLA-DO antigens; C083728:MHC class II transactivator protein; D009687:Nuclear Proteins; D000071701:Regulatory Factor X Transcription Factors; D015534:Trans-Activators; D014157:Transcription Factors