title: Biased dA/dT somatic hypermutation as regulated by the heavy chain intronic iEmu enhancer and 3'Ealpha enhancers in human lymphoblastoid B cells.
abstract: Somatic hypermutation (SHM) in immunoglobulin gene (Ig) variable (V) regions is critical for the maturation of the antibody response. It is dependent on the expression of activation-induced cytidine deaminase (AID) and translesion DNA polymerases in germinal center B cells as well as Ig V transcription, as regulated by the Ig heavy chain (H) intronic enhancer (iEmu) and the 3' enhancer (3'Ealpha) region. We analyzed the role of these cis elements in SHM by stably transfecting Ramos human lymphoblastoid B cells with a rearranged human IgH chain VD (diversity) J (joining) DNA construct containing a V(H) promoter at the 5' end and C(H)1 and C(H)2 exons of Cgamma1 at the 3' end. In this construct, mutations preferentially targeted dA/dT basepairs in the RGYW/WRCY hotspot. Most of the dA/dT mutations and accompanying dC/dG mutations were transitions. Deletion of iEmu resulted in decreased SHM which could be partially restored by insertion of the IgH hs1,2 enhancer. Other two 3'Ealpha enhancers, hs3-hs4, did not significantly increase the mutation frequency, but further strengthened the dA/dT bias. The frequency and spectrum of the mutations were independent of the genomic integration of the transgene or V gene transcription level. Thus, we have established a novel in vitro system to analyze SHM and identify the role of multiple cis-regulatory elements in regulating dA/dT biased SHM. This model system will be useful to further address the role of other cis-regulating elements and recruited trans-acting factors in expressing the modalities of SHM.
authors.affiliation: Center for Immunology, School of Medicine and School of Biological Sciences, University of California, 3028 Hewitt Hall, Irvine, CA 92697-4120, USA.
authors.forename: Atsumasa
authors.initials: A
authors.lastname: Komori
authors.forename: Zhenming
authors.initials: Z
authors.lastname: Xu
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Wu
authors.forename: Hong
authors.initials: H
authors.lastname: Zan
authors.forename: Paolo
authors.initials: P
authors.lastname: Casali
mesh_terms: D001402:B-Lymphocytes / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D020029:Base Pairing; D001483:Base Sequence; D045744:Cell Line, Tumor; D002877:Chromosomes, Human / Q000235:genetics; D003564:Cytidine Deaminase / Q000235:genetics / Q000378:metabolism; D004742:Enhancer Elements, Genetic / Q000235:genetics*; D005786:Gene Expression Regulation; D006801:Humans; D017578:Immunoglobulin Class Switching / Q000235:genetics / Q000276:immunology; D007127:Immunoglobulin Constant Regions / Q000235:genetics / Q000276:immunology; D007142:Immunoglobulin gamma-Chains / Q000235:genetics / Q000276:immunology; D007148:Immunoglobulin mu-Chains / Q000235:genetics*; D007438:Introns / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D027041:Somatic Hypermutation, Immunoglobulin / Q000235:genetics*; D014158:Transcription, Genetic / Q000235:genetics; D050441:VDJ Exons / Q000235:genetics / Q000276:immunology; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
chemical_list: D007127:Immunoglobulin Constant Regions; D007142:Immunoglobulin gamma-Chains; D007148:Immunoglobulin mu-Chains; D012333:RNA, Messenger; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase