title: Activation-induced cytidine deaminase turns on somatic hypermutation in hybridomas.
abstract: The production of high-affinity protective antibodies requires somatic hypermutation (SHM) of the antibody variable (V)-region genes. SHM is characterized by a high frequency of point mutations that occur only during the centroblast stage of B-cell differentiation. Activation-induced cytidine deaminase (AID), which is expressed specifically in germinal-centre centroblasts, is required for this process, but its exact role is unknown. Here we show that AID is required for SHM in the centroblast-like Ramos cells, and that expression of AID is sufficient to induce SHM in hybridoma cells, which represent a later stage of B-cell differentiation that does not normally undergo SHM. In one hybridoma, mutations were exclusively in G*C base pairs that were mostly within RGYW or WRCY motifs, suggesting that AID has primary responsibility for mutations at these nucleotides. The activation of SHM in hybridomas indicates that AID does not require other centroblast-specific cofactors to induce SHM, suggesting either that it functions alone or that the factors it requires are expressed at other stages of B-cell differentiation.
authors.affiliation: Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue Chanin 403, Bronx, New York 10461, USA.
authors.forename: Alberto
authors.initials: A
authors.lastname: Martin
authors.forename: Philip D
authors.initials: PD
authors.lastname: Bardwell
authors.forename: Caroline J
authors.initials: CJ
authors.lastname: Woo
authors.forename: Manxia
authors.initials: M
authors.lastname: Fan
authors.forename: Marc J
authors.initials: MJ
authors.lastname: Shulman
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Scharff
mesh_terms: D001402:B-Lymphocytes / Q000166:cytology / Q000201:enzymology* / Q000276:immunology* / Q000378:metabolism; D001483:Base Sequence; D002454:Cell Differentiation; D002460:Cell Line; D018389:Codon, Nonsense / Q000235:genetics; D003564:Cytidine Deaminase / Q000378:metabolism*; D004252:DNA Mutational Analysis; D004790:Enzyme Induction; D020862:GC Rich Sequence / Q000235:genetics; D006801:Humans; D006825:Hybridomas / Q000166:cytology / Q000201:enzymology* / Q000276:immunology* / Q000378:metabolism; D007135:Immunoglobulin Variable Region / Q000235:genetics / Q000276:immunology; D008213:Lymphocyte Activation; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D027041:Somatic Hypermutation, Immunoglobulin / Q000235:genetics*; D014162:Transfection; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
chemical_list: D018389:Codon, Nonsense; D007135:Immunoglobulin Variable Region; D012333:RNA, Messenger; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase