title: The HoxC4 homeodomain protein mediates activation of the immunoglobulin heavy chain 3' hs1,2 enhancer in human B cells. Relevance to class switch DNA recombination.
abstract: The immunoglobulin heavy chain (IgH) 3' regulatory region modulates IgH locus transcription, upon induction by specific trans-acting factors, and plays a significant role in class switch DNA recombination (CSR) and, perhaps, somatic hypermutation (SHM). CSR and SHM are central to the maturation of the antibody response. In contrast to the single 5'-hs3a-hs1,2-hs3b-hs4-3 ' mouse IgH 3 ' regulatory region, the human IgH 3 ' regulatory region exists as a 5'-hs3-hs1,2-hs4-3' cluster duplicated 3 ' of Calpha1 and Calpha2. We show here that the human hs1,2 element is the strongest enhancer of transcription, as directed by a V(H)1 or the ECS-Igamma3 promoter, thereby suggesting a dominant role for hs1,2 over hs3 and hs4 in the overall activity of the 3 ' regulatory region. Within hs1,2, we identified three regions (1, 2, and 3) that are all necessary, but individually not sufficient, for enhancement of transcription. In region 2, a HoxC4 site and a HoxC4/embedded octamer (HoxC4/Oct) site are conserved across human, mouse, rat, and rabbit. These two sites recruit HoxC4 and Oct-1/Oct-2, which act synergistically with the Oca-B coactivator to effect the full hs1,2-enhancing activity. HoxC4, Oct-1/Oct-2, and Oca-B recruitment is negligible in pro-B cells, moderate in pre-B cells, and maximal in germinal center B cells and plasma cells, where HoxC4, Oct-2, and Oca-B expression correlates with hs1,2 activation and ongoing CSR. The hs1,2mediated enhancement of V(H) and C(H) promoter-driven transcription as induced by HoxC4 and Oct-1/Oct-2 suggests an important role of these homeodomain proteins in the overall regulation of the IgH locus expression.
authors.affiliation: Center for Immunology, College of Medicine and School of Biological Sciences, University of California, Irvine, California 92697-4120, USA.
authors.forename: Edmund C
authors.initials: EC
authors.lastname: Kim
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Edmonston
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Wu
authors.forename: András
authors.initials: A
authors.lastname: Schaffer
authors.forename: Paolo
authors.initials: P
authors.lastname: Casali
mesh_terms: D024509:3' Flanking Region; D001402:B-Lymphocytes / Q000276:immunology*; D017124:Conserved Sequence; D004268:DNA-Binding Proteins / Q000378:metabolism; D005809:Genes, Regulator; D018398:Homeodomain Proteins / Q000502:physiology*; D006801:Humans; D007143:Immunoglobulin Heavy Chains / Q000235:genetics*; D050811:Octamer Transcription Factor-1; D050813:Octamer Transcription Factor-2; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation
chemical_list: D004268:DNA-Binding Proteins; C098691:HOXC4 protein, human; D018398:Homeodomain Proteins; C490904:Hoxc4 protein, mouse; D007143:Immunoglobulin Heavy Chains; D050811:Octamer Transcription Factor-1; D050813:Octamer Transcription Factor-2; C091546:POU2AF1 protein, human; C494165:POU2F1 protein, human; C058435:POU2F2 protein, human; C490424:Pou2af1 protein, mouse; C489206:Pou2f2 protein, mouse; C489205:Pou2f2 protein, rat; D015534:Trans-Activators; D014157:Transcription Factors