CIITA is a transcriptional coactivator that is recruited to MHC class II promoters by multiple synergistic interactions with an enhanceosome complex.
By virtue of its control over major histocompatibility complex class II (MHC-II) gene expression, CIITA represents a key molecule in the regulation of adaptive immune responses. It was first identified as a factor that is defective in MHC-II deficiency, a hereditary disease characterized by the absence of MHC-II expression. CIITA is a highly regulated transactivator that governs all spatial, temporal, and quantitative aspects of MHC-II expression. It has been proposed to act as a non-DNA-binding transcriptional coactivator, but evidence that it actually functions at the level of MHC-II promoters was lacking. By means of chromatin immunoprecipitation assays, we show here for the first time that CIITA is physically associated with MHC-II, as well as HLA-DM, Ii, MHC-I, and beta(2)m promoters in vivo. To dissect the mechanism by which CIITA is recruited to the promoter, we have developed a DNA-dependent coimmunoprecipitation assay and a pull-down assay using immobilized promoter templates. We demonstrate that CIITA recruitment depends on multiple, synergistic protein-protein interactions with DNA-bound factors constituting the MHC-II enhanceosome. CIITA therefore represents a paradigm for a novel type of regulatory and gene-specific transcriptional cofactor.
Masternak
K
K
Department of Genetics and Microbiology, University of Geneva Medical School, 1211 Geneva, Switzerland.
Muhlethaler-Mottet
A
A
Villard
J
J
Zufferey
M
M
Steimle
V
V
Reith
W
W
D001402:B-Lymphocytes / Q000276:immunology*; D002460:Cell Line; D002843:Chromatin / Q000502:physiology; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000276:immunology*; D005802:Genes, MHC Class II; D006681:HLA-D Antigens / Q000235:genetics*; D006684:HLA-DR Antigens / Q000235:genetics; D059805:HLA-DR alpha-Chains; D006801:Humans; D009687:Nuclear Proteins; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000378:metabolism; D000071701:Regulatory Factor X Transcription Factors; D015534:Trans-Activators / Q000378:metabolism*; D014162:Transfection; D014407:Tumor Cells, Cultured
D002843:Chromatin; D004268:DNA-Binding Proteins; D006681:HLA-D Antigens; D006684:HLA-DR Antigens; D059805:HLA-DR alpha-Chains; C083728:MHC class II transactivator protein; D009687:Nuclear Proteins; C093524:RFX5 protein, human; D011994:Recombinant Proteins; D000071701:Regulatory Factor X Transcription Factors; D015534:Trans-Activators