title: PU.1 binds to a distal regulatory element that is necessary for B cell-specific expression of CIITA.
abstract: The transcriptional coactivator CIITA regulates MHC class II genes. In the mouse, CIITA is expressed from three distinct promoters (pI, pIII, and pIV) in a developmental and cell type-specific manner with pIII being responsible for B lymphocyte-specific expression. Although the promoter proximal sequences that regulate CIITA in B cells have been described, nothing is known about additional distal elements that may regulate its expression in B cells. Sequence homology comparisons, DNase I hypersensitivity assays, and histone modification analysis revealed a potential regulatory element located 11 kb upstream of pIII. Deletion of this element, termed hypersensitive site 1 (HSS1), in a bacterial artificial chromosome encoding the entire CIITA locus and surrounding genes, resulted in a complete loss of CIITA expression from the bacterial artificial chromosome following transfection into B cells. HSS1 and pIII displayed open chromatin architecture features in B cell but not in plasma cell lines, which are silenced for CIITA expression. PU.1 was found to bind HSS1 and pIII in B cells but not in plasma cells. Depletion of PU.1 by short hairpin RNA reduced CIITA expression. Chromatin conformation capture assays showed that HSS1 interacted directly with pIII in B cells and that PU.1 was important for this interaction. These results provide evidence that HSS1 is required for B cell-specific expression of CIITA and that HSS1 functions by interacting with pIII, forming a long-distance chromatin loop that is partly mediated through PU.1.
authors.affiliation: Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, GA 30322, USA.
authors.forename: Hyesuk
authors.initials: H
authors.lastname: Yoon
authors.forename: Jeremy M
authors.initials: JM
authors.lastname: Boss
mesh_terms: D000818:Animals; D017951:Antigen Presentation / Q000235:genetics / Q000276:immunology; D016175:B-Lymphocyte Subsets / Q000276:immunology* / Q000378:metabolism*; D002460:Cell Line; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D002843:Chromatin / Q000378:metabolism; D017124:Conserved Sequence / Q000276:immunology; D003850:Deoxyribonuclease I / Q000032:analysis / Q000378:metabolism / Q000502:physiology; D018985:Epitopes, B-Lymphocyte / Q000276:immunology* / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000276:immunology; D006801:Humans; D007371:Interferon-gamma / Q000502:physiology; D016393:Lymphoma, B-Cell / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D009687:Nuclear Proteins / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics / Q000276:immunology; D011485:Protein Binding / Q000235:genetics / Q000276:immunology; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D050436:Regulatory Elements, Transcriptional / Q000276:immunology*; D017422:Sequence Analysis, DNA; D015534:Trans-Activators / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism*; D000099232:Proto-Oncogene Protein Spi-1
chemical_list: D002843:Chromatin; D003850:Deoxyribonuclease I; D018985:Epitopes, B-Lymphocyte; D007371:Interferon-gamma; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D015534:Trans-Activators; D000099232:Proto-Oncogene Protein Spi-1; C083728:MHC class II transactivator protein