title: Identification of DNA cleavage- and recombination-specific hnRNP cofactors for activation-induced cytidine deaminase.
abstract: Activation-induced cytidine deaminase (AID) is essential for antibody class switch recombination (CSR) and somatic hypermutation (SHM). AID originally was postulated to function as an RNA-editing enzyme, based on its strong homology with apolipoprotein B mRNA-editing enzyme, catalytic polypeptide 1 (APOBEC1), the enzyme that edits apolipoprotein B-100 mRNA in the presence of the APOBEC cofactor APOBEC1 complementation factor/APOBEC complementation factor (A1CF/ACF). Because A1CF is structurally similar to heterogeneous nuclear ribonucleoproteins (hnRNPs), we investigated the involvement of several well-known hnRNPs in AID function by using siRNA knockdown and clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9-mediated disruption. We found that hnRNP K deficiency inhibited DNA cleavage and thereby induced both CSR and SHM, whereas hnRNP L deficiency inhibited only CSR and somewhat enhanced SHM. Interestingly, both hnRNPs exhibited RNA-dependent interactions with AID, and mutant forms of these proteins containing deletions in the RNA-recognition motif failed to rescue CSR. Thus, our study suggests that hnRNP K and hnRNP L may serve as A1CF-like cofactors in AID-mediated CSR and SHM.
authors.affiliation: Department of Immunology and Genomic Medicine, Graduate School of Medicine, Kyoto University, Yoshida Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Wenjun
authors.initials: W
authors.lastname: Hu
authors.affiliation: Department of Immunology and Genomic Medicine, Graduate School of Medicine, Kyoto University, Yoshida Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Nasim A
authors.initials: NA
authors.lastname: Begum
authors.affiliation: Department of Immunology and Genomic Medicine, Graduate School of Medicine, Kyoto University, Yoshida Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Samiran
authors.initials: S
authors.lastname: Mondal
authors.affiliation: Department of Immunology and Genomic Medicine, Graduate School of Medicine, Kyoto University, Yoshida Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Andre
authors.initials: A
authors.lastname: Stanlie
authors.affiliation: Department of Immunology and Genomic Medicine, Graduate School of Medicine, Kyoto University, Yoshida Sakyo-ku, Kyoto 606-8501, Japan honjo@mfour.med.kyoto-u.ac.jp.
authors.forename: Tasuku
authors.initials: T
authors.lastname: Honjo
mesh_terms: D000071479:APOBEC-1 Deaminase; D045744:Cell Line, Tumor; D002469:Cell Separation; D003564:Cytidine Deaminase / Q000737:chemistry* / Q000378:metabolism*; D004247:DNA / Q000737:chemistry*; D005434:Flow Cytometry; D005816:Genetic Complementation Test; D057809:HEK293 Cells; D034641:Heterogeneous-Nuclear Ribonucleoprotein K / Q000737:chemistry; D034664:Heterogeneous-Nuclear Ribonucleoprotein L / Q000737:chemistry; D034441:Heterogeneous-Nuclear Ribonucleoproteins / Q000737:chemistry*; D006801:Humans; D007070:Immunoglobulin A / Q000737:chemistry; D017578:Immunoglobulin Class Switching; D007143:Immunoglobulin Heavy Chains / Q000737:chemistry; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics; D034741:RNA, Small Interfering / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism*; D011995:Recombination, Genetic; D027041:Somatic Hypermutation, Immunoglobulin; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
chemical_list: C411647:A1CF protein, human; C000595707:BCL2 protein, human; D034641:Heterogeneous-Nuclear Ribonucleoprotein K; D034664:Heterogeneous-Nuclear Ribonucleoprotein L; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D007070:Immunoglobulin A; D007143:Immunoglobulin Heavy Chains; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D004247:DNA; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D000071479:APOBEC-1 Deaminase; C000605089:APOBEC1 protein, human; D003564:Cytidine Deaminase
keywords: B cell; IgH; activation-induced cytidine deaminase; class switch recombination; somatic hypermutation