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Tasuku Honjo - One of the best experts on this subject based on the ideXlab platform.
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rna binding motifs of hnrnp k are critical for induction of antibody diversification by activation induced Cytidine Deaminase
Proceedings of the National Academy of Sciences of the United States of America, 2020Co-Authors: Ziwei Yin, Maki Kobayashi, Nasim A Begum, Koichi Higashi, Ken Kurokawa, Tasuku HonjoAbstract:Activation-Induced Cytidine Deaminase (AID) is the key enzyme for class switch recombination (CSR) and somatic hypermutation (SHM) to generate antibody memory. Previously, heterogeneous nuclear ribonucleoprotein K (hnRNP K) was shown to be required for AID-dependent DNA breaks. Here, we defined the function of major RNA-binding motifs of hnRNP K, GXXGs and RGGs in the K-homology (KH) and the K-protein-interaction (KI) domains, respectively. Mutation of GXXG, RGG, or both impaired CSR, SHM, and cMyc/IgH translocation equally, showing that these motifs were necessary for AID-dependent DNA breaks. AID–hnRNP K interaction is dependent on RNA; hence, mutation of these RNA-binding motifs abolished the interaction with AID, as expected. Some of the polypyrimidine sequence-carrying prototypical hnRNP K-binding RNAs, which participate in DNA breaks or repair bound to hnRNP K in a GXXG and RGG motif-dependent manner. Mutation of the GXXG and RGG motifs decreased nuclear retention of hnRNP K. Together with the previous finding that nuclear localization of AID is necessary for its function, lower nuclear retention of these mutants may worsen their functional deficiency, which is also caused by their decreased RNA-binding capacity. In summary, hnRNP K contributed to AID-dependent DNA breaks with all of its major RNA-binding motifs.
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c terminal region of activation induced Cytidine Deaminase aid is required for efficient class switch recombination and gene conversion
Proceedings of the National Academy of Sciences of the United States of America, 2014Co-Authors: Somayeh Sabouri, Maki Kobayashi, Nasim A Begum, Kouji Hirota, Tasuku HonjoAbstract:Activation-Induced Cytidine Deaminase (AID) introduces single-strand breaks (SSBs) to initiate class switch recombination (CSR), gene conversion (GC), and somatic hypermutation (SHM). CSR is mediated by double-strand breaks (DSBs) at donor and acceptor switch (S) regions, followed by pairing of DSB ends in two S regions and their joining. Because AID mutations at its C-terminal region drastically impair CSR but retain its DNA cleavage and SHM activity, the C-terminal region of AID likely is required for the recombination step after the DNA cleavage. To test this hypothesis, we analyzed the recombination junctions generated by AID C-terminal mutants and found that 0- to 3-bp microhomology junctions are relatively less abundant, possibly reflecting the defects of the classical nonhomologous end joining (C-NHEJ). Consistently, the accumulation of C-NHEJ factors such as Ku80 and XRCC4 was decreased at the cleaved S region. In contrast, an SSB-binding protein, poly (ADP)-ribose polymerase1, was recruited more abundantly, suggesting a defect in conversion from SSB to DSB. In addition, recruitment of critical DNA synapse factors such as 53BP1, DNA PKcs, and UNG at the S region was reduced during CSR. Furthermore, the chromosome conformation capture assay revealed that DNA synapse formation is impaired drastically in the AID C-terminal mutants. Interestingly, these mutants showed relative reduction in GC compared with SHM in chicken DT40 cells. Collectively, our data indicate that the C-terminal region of AID is required for efficient generation of DSB in CSR and GC and thus for the subsequent pairing of cleaved DNA ends during recombination in CSR.
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rna editing of hepatitis b virus transcripts by activation induced Cytidine Deaminase
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: Tasuku Honjo, Guoxin Liang, Kouichi Kitamura, Sajeda Chowdhury, Miki Koura, Zhe Wang, Guangyan Liu, Kousho Wakae, Masamichi MuramatsuAbstract:Activation-Induced Cytidine Deaminase (AID) is essential for the somatic hypermutation (SHM) and class-switch recombination (CSR) of Ig genes. The mechanism by which AID triggers SHM and CSR has been explained by two distinct models. In the DNA deamination model, AID converts Cytidine bases in DNA into uridine. The uridine is recognized by the DNA repair system, which produces DNA strand breakages and point mutations. In the alternative model, RNA edited by AID is responsible for triggering CSR and SHM. However, RNA deamination by AID has not been demonstrated. Here we found that C-to-T and G-to-A mutations accumulated in hepatitis B virus (HBV) nucleocapsid DNA when AID was expressed in HBV-replicating hepatic cell lines. AID expression caused C-to-T mutations in the nucleocapsid DNA of RNase H-defective HBV, which does not produce plus-strand viral DNA. Furthermore, the RT-PCR products of nucleocapsid viral RNA from AID-expressing cells exhibited significant C-to-T mutations, whereas viral RNAs outside the nucleocapsid did not accumulate C-to-U mutations. Moreover, AID was packaged within the nucleocapsid by forming a ribonucleoprotein complex with HBV RNA and the HBV polymerase protein. The encapsidation of the AID protein with viral RNA and DNA provides an efficient environment for evaluating AID’s RNA and DNA deamination activities. A bona fide RNA-editing enzyme, apolipoprotein B mRNA editing catalytic polypeptide 1, induced a similar level of C-to-U mutations in nucleocapsid RNA as AID. Taken together, the results indicate that AID can deaminate the nucleocapsid RNA of HBV.
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the histone chaperone spt6 is required for activation induced Cytidine Deaminase target determination through h3k4me3 regulation
Journal of Biological Chemistry, 2012Co-Authors: Nasim A Begum, Andre Stanlie, Mikiyo Nakata, Hideo Akiyama, Tasuku HonjoAbstract:H3K4me3 plays a critical role in the Activation-Induced Cytidine Deaminase (AID)-induced DNA cleavage of switch (S) regions in the immunoglobulin heavy chain (IgH) locus during class-switch recombination (CSR). The histone chaperone complex facilitates chromatin transcription (FACT) is responsible for forming H3K4me3 at AID target loci. Here we show that the histone chaperone suppressor of Ty6 (Spt6) also participates in regulating H3K4me3 for CSR and for somatic hypermutation in AID target loci. We found that H3K4me3 loss was correlated with defects in AID-induced DNA breakage and reduced mutation frequencies in IgH loci in both S and variable regions and in non-IgH loci such as metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) and small nucleolar RNA host gene 3 (SNHG3). Global gene expression analysis revealed that Spt6 can act as both a positive and negative transcriptional regulator in B cells, affecting ∼5% of the genes that includes suppressor of Ty4 (Spt4) and AID. Interestingly, Spt6 regulates CSR and AID expression through two distinct histone modification pathways, H3K4me3 and H3K36me3, respectively. Tandem SH2 domain of Spt6 plays a critical role in CSR and H3K4me3 regulation involving Set1 histone methyltransferase. We conclude that Spt6 is a unique histone chaperone capable of regulating the histone epigenetic state of both AID targets and the AID locus.
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decrease in topoisomerase i is responsible for activation induced Cytidine Deaminase aid dependent somatic hypermutation
Proceedings of the National Academy of Sciences of the United States of America, 2011Co-Authors: Maki Kobayashi, Yoko Kitawaki, Zahra Sabouri, Somayeh Sabouri, Takaya Abe, Hiroshi Kiyonari, Tasuku HonjoAbstract:Somatic hypermutation (SHM) and class-switch recombination (CSR) of the Ig gene require both the transcription of the locus and the expression of Activation-Induced Cytidine Deaminase (AID). During CSR, AID decreases the amount of topoisomerase I (Top1); this decrease alters the DNA structure and induces cleavage in the S region. Similarly, Top1 is involved in transcription-associated mutation at dinucleotide repeats in yeast and in triplet-repeat contraction in mammals. Here, we report that the AID-induced decrease in Top1 is critical for SHM. Top1 knockdown or haploinsufficiency enhanced SHM, whereas Top1 overexpression down-regulated it. A specific Top1 inhibitor, camptothecin, suppressed SHM, indicating that Top1's activity is required for DNA cleavage. Nonetheless, suppression of transcription abolished SHM, even in cells with Top1 knockdown, suggesting that transcription is critical. These results are consistent with a model proposed for CSR and triplet instability, in which transcription-induced non-B structure formation is enhanced by Top1 reduction and provides the target for irreversible cleavage by Top1. We speculate that the mechanism for transcription-coupled genome instability was adopted to generate immune diversity when AID evolved.
Masamichi Muramatsu - One of the best experts on this subject based on the ideXlab platform.
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interleukin 1 and tumor necrosis factor α trigger restriction of hepatitis b virus infection via a Cytidine Deaminase activation induced Cytidine Deaminase aid
Journal of Biological Chemistry, 2013Co-Authors: Koichi Watashi, Hiroyuki Marusawa, Masamichi Muramatsu, Guoxin Liang, Masashi Iwamoto, Nanako Uchida, Takuji Daito, Kouichi Kitamura, Hirofumi Ohashi, Tomoko KiyoharaAbstract:Virus infection is restricted by intracellular immune responses in host cells, and this is typically modulated by stimulation of cytokines. The cytokines and host factors that determine the host cell restriction against hepatitis B virus (HBV) infection are not well understood. We screened 36 cytokines and chemokines to determine which were able to reduce the susceptibility of HepaRG cells to HBV infection. Here, we found that pretreatment with IL-1β and TNFα remarkably reduced the host cell susceptibility to HBV infection. This effect was mediated by activation of the NF-κB signaling pathway. A Cytidine Deaminase, Activation-Induced Cytidine Deaminase (AID), was up-regulated by both IL-1β and TNFα in a variety of hepatocyte cell lines and primary human hepatocytes. Another Deaminase APOBEC3G was not induced by these proinflammatory cytokines. Knockdown of AID expression impaired the anti-HBV effect of IL-1β, and overexpression of AID antagonized HBV infection, suggesting that AID was one of the responsible factors for the anti-HBV activity of IL-1/TNFα. Although AID induced hypermutation of HBV DNA, this activity was dispensable for the anti-HBV activity. The antiviral effect of IL-1/TNFα was also observed on different HBV genotypes but not on hepatitis C virus. These results demonstrate that proinflammatory cytokines IL-1/TNFα trigger a novel antiviral mechanism involving AID to regulate host cell permissiveness to HBV infection. Background: Cytokines and host factors triggering innate immunity against hepatitis B virus (HBV) are not well understood. Results: IL-1 and TNFα induced Cytidine Deaminase AID, an anti-HBV host factor, and reduced HBV infection into hepatocytes. Conclusion: IL-1/TNFα reduced host susceptibility to HBV infection through AID up-regulation. Significance: Proinflammatory cytokines modulate HBV infection through a novel innate immune pathway involving AID.
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interleukin 1 and tumor necrosis factor α trigger restriction of hepatitis b virus infection via a Cytidine Deaminase activation induced Cytidine Deaminase aid
Journal of Biological Chemistry, 2013Co-Authors: Koichi Watashi, Hiroyuki Marusawa, Masamichi Muramatsu, Guoxin Liang, Masashi Iwamoto, Nanako Uchida, Takuji Daito, Kouichi Kitamura, Hirofumi Ohashi, Tomoko KiyoharaAbstract:Abstract Virus infection is restricted by intracellular immune responses in host cells and this is typically modulated by stimulation of cytokines. The cytokines and host factors which determine the host cell restriction against hepatitis B virus (HBV) infection are not well understood. We screened 36 cytokines and chemokines to determine which were able to reduce the susceptibility of HepaRG cells to HBV infection. Here, we found that pretreatment with IL-1β and TNFα remarkably reduced the host cell susceptibility to HBV infection. This effect was mediated by activation of the NF-κB signaling pathway. A Cytidine Deaminase, Activation-Induced Cytidine Deaminase (AID), was upregulated by both IL-1β and TNFα in a variety of hepatocyte cell lines and primary human hepatocytes. Another Deaminase APOBEC3G was not induced by these proinflammatory cytokines. Knocking down of AID expression impaired the anti-HBV effect of IL-1β, and overexpression of AID antagonized HBV infection, suggesting that AID was one of the responsible factors for the anti-HBV activity of IL-1/TNFα. Although AID induced hypermutation of HBV DNA, this activity was dispensable for the anti-HBV activity. The antiviral effect of IL-1/TNFα was also observed on different HBV genotypes, but not on hepatitis C virus. These results demonstrate that proinflammatory cytokines IL-1/TNFα trigger a novel antiviral mechanism involving AID to regulate host cell permissiveness to HBV infection.
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concerted action of activation induced Cytidine Deaminase and uracil dna glycosylase reduces covalently closed circular dna of duck hepatitis b virus
FEBS Letters, 2013Co-Authors: Sajeda Chowdhury, Kouichi Kitamura, Miyuki Simadu, Miki Koura, Masamichi MuramatsuAbstract:Covalently closed circular DNA (cccDNA) forms a template for the replication of hepatitis B virus (HBV) and duck HBV (DHBV). Recent studies suggest that Activation-Induced Cytidine Deaminase (AID) functions in innate immunity, although its molecular mechanism of action remains unclear, particularly regarding HBV restriction. Here we demonstrated that overexpression of chicken AID caused hypermutation and reduction of DHBV cccDNA levels. Inhibition of uracil-DNA glycosylase (UNG) by UNG inhibitor protein (UGI) abolished AID-induced cccDNA reduction, suggesting that the AID/UNG pathway triggers the degradation of cccDNA via cytosine deamination and uracil excision.
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rna editing of hepatitis b virus transcripts by activation induced Cytidine Deaminase
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: Tasuku Honjo, Guoxin Liang, Kouichi Kitamura, Sajeda Chowdhury, Miki Koura, Zhe Wang, Guangyan Liu, Kousho Wakae, Masamichi MuramatsuAbstract:Activation-Induced Cytidine Deaminase (AID) is essential for the somatic hypermutation (SHM) and class-switch recombination (CSR) of Ig genes. The mechanism by which AID triggers SHM and CSR has been explained by two distinct models. In the DNA deamination model, AID converts Cytidine bases in DNA into uridine. The uridine is recognized by the DNA repair system, which produces DNA strand breakages and point mutations. In the alternative model, RNA edited by AID is responsible for triggering CSR and SHM. However, RNA deamination by AID has not been demonstrated. Here we found that C-to-T and G-to-A mutations accumulated in hepatitis B virus (HBV) nucleocapsid DNA when AID was expressed in HBV-replicating hepatic cell lines. AID expression caused C-to-T mutations in the nucleocapsid DNA of RNase H-defective HBV, which does not produce plus-strand viral DNA. Furthermore, the RT-PCR products of nucleocapsid viral RNA from AID-expressing cells exhibited significant C-to-T mutations, whereas viral RNAs outside the nucleocapsid did not accumulate C-to-U mutations. Moreover, AID was packaged within the nucleocapsid by forming a ribonucleoprotein complex with HBV RNA and the HBV polymerase protein. The encapsidation of the AID protein with viral RNA and DNA provides an efficient environment for evaluating AID’s RNA and DNA deamination activities. A bona fide RNA-editing enzyme, apolipoprotein B mRNA editing catalytic polypeptide 1, induced a similar level of C-to-U mutations in nucleocapsid RNA as AID. Taken together, the results indicate that AID can deaminate the nucleocapsid RNA of HBV.
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activation induced Cytidine Deaminase aid promotes b cell lymphomagenesis in emu cmyc transgenic mice
Proceedings of the National Academy of Sciences of the United States of America, 2007Co-Authors: Ai Kotani, Kazuo Kinoshita, Ilmi Okazaki, Masamichi Muramatsu, Hitoshi Nagaoka, Naoki Kakazu, Tatsuaki Tsuruyama, Daisuke Yabe, Tasuku HonjoAbstract:Activation-Induced Cytidine Deaminase (AID), which is essential to both class switch recombination and somatic hypermutation of the Ig gene, is expressed in many types of human B cell lymphoma/leukemia. AID is a potent mutator because it is involved in DNA breakage not only of Ig but also of other genes, including proto-oncogenes. Recent studies suggest that AID is required for chromosomal translocation involving cmyc and Ig loci. However, it is unclear whether AID plays other roles in tumorigenesis. We examined the effect of AID deficiency on the generation of surface Ig-positive B cell lymphomas in Emu-cmyc transgenic mice. Almost all lymphomas that developed in AID-deficient transgenic mice were pre-B cell lymphomas, whereas control transgenic mice had predominantly B cell lymphomas, indicating that AID is required for development of B but not pre-B cell lymphomas from cmyc overexpressing tumor progenitors. Thus, AID may play multiple roles in B cell lymphomagenesis.
Kazuo Kinoshita - One of the best experts on this subject based on the ideXlab platform.
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chronic lung injury by constitutive expression of activation induced Cytidine Deaminase leads to focal mucous cell metaplasia and cancer
PLOS ONE, 2015Co-Authors: Jiro Kitamura, Munehiro Uemura, Mafumi Kurozumi, Toshiaki Manabe, Hiroshi Hiai, Makoto Sonobe, Hiroshi Date, Kazuo KinoshitaAbstract:Activation-Induced Cytidine Deaminase (AID) is an enzyme required for antibody diversification, and it causes DNA mutations and strand breaks. Constitutive AID expression in mice invariably caused lung lesions morphologically similar to human atypical adenomatous hyperplasia (AAH), which can be a precursor of bronchioloalveolar carcinoma. Similar to AAH, mouse AAH-like lesion (MALL) exhibited signs of alveolar differentiation, judging from the expression of alveolar type II (AT2) cell marker surfactant protein C (SP-C). However, electron microscopy indicated that MALL, which possessed certain features of a mucous cell, is distinct from an AAH or AT2 cell. Although MALL developed in all individuals within 30 weeks after birth, lung tumors occurred in only 10%; this suggests that the vast majority of MALLs fail to grow into visible tumors. MALL expressed several recently described markers of lung alveolar regeneration such as p63, keratin 5, keratin 14, leucine-rich repeat containing G protein-coupled receptor 5 (Lgr5), and Lgr6. Increased cell death was observed in the lungs of AID transgenic mice compared with wild-type mice. Based on these observations, we speculate that MALL is a regenerating tissue compensating for cellular loss caused by AID cytotoxicity. AID expression in such regenerating tissue should predispose cells to malignant transformation via its mutagenic activity.
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up regulation of activation induced Cytidine Deaminase causes genetic aberrations at the cdkn2b cdkn2a in gastric cancer
Gastroenterology, 2010Co-Authors: Yuko Matsumoto, Kazuo Kinoshita, Hiroyuki Marusawa, Yoko Niwa, Yoshiharu Sakai, Tsutomu ChibaAbstract:Background & Aims The DNA/RNA editing enzyme Activation-Induced Cytidine Deaminase (AID) is mutagenic and has been implicated in human tumorigenesis. Helicobacter pylori infection of gastric epithelial cells leads to aberrant expression of AID and somatic gene mutations. We investigated whether AID induces genetic aberrations at specific chromosomal loci that encode tumor-related proteins in gastric epithelial cells. Methods Human gastric epithelial cell lines that express activated AID and gastric cells from AID transgenic mice were examined for DNA copy number changes and nucleotide alterations. Copy number aberrations in stomach cells of H pylori –infected mice and gastric tissues (normal and tumor) from H pylori –positive patients were also analyzed. Results In human gastric cells, aberrant AID activity induced copy number changes at various chromosomal loci. In AID-expressing cells and gastric mucosa of AID transgenic mice, point mutations and reductions in copy number were observed frequently in the tumor suppressor genes CDKN2A and CDKN2B . Oral infection of wild-type mice with H pylori reduced the copy number of the Cdkn2b - Cdkn2a locus, whereas no such changes were observed in the gastric mucosa of H pylori –infected AID-deficient mice. In human samples, the relative copy numbers of CDKN2A and CDKN2B were reduced in a subset of gastric cancer tissues compared with the surrounding noncancerous region. Conclusions H pylori infection leads to aberrant expression of AID and might be a mechanism of the accumulation of submicroscopic deletions and somatic mutations in gastric epithelial cells. AID-mediated genotoxic effects appear to occur frequently at the CDKN2b-CDKN2a locus and contribute to malignant transformation of the gastric mucosa.
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activation induced Cytidine Deaminase links between inflammation and the development of colitis associated colorectal cancers
Gastroenterology, 2008Co-Authors: Yoko Endo, Kazuo Kinoshita, Hiroyuki Marusawa, Tadayuki Kou, Tasuku Honjo, Hiroshi Nakase, Shigehiko Fujii, Takahiro Fujimori, Tsutomu ChibaAbstract:Background & Aims: Activation-Induced Cytidine Deaminase (AID) was originally identified as an inducer of somatic hypermutations in the immunoglobulin gene. We recently revealed that ectopic AID expression serves as a link between the cellular editing machinery and high mutation frequencies, leading to human cancer development. In the current study, we investigated whether AID might contribute to the development of colitis-associated colorectal cancers. Methods: The expression and regulation of AID in association with proinflammatory cytokine stimulation were investigated in cultured colonic cells. Genotoxic activity of AID in colonic cells was analyzed using retroviral system. Immunohistochemistry for AID was carried out on various human colonic tissues specimens. Results: Tumor necrosis factor-α induced aberrant AID expression via IκB kinase-dependent nuclear factor (NF)-κB-signaling pathways in human colonic epithelial cells. Moreover, AID expression was also induced in response to the T helper cell 2-driven cytokines interleukin-4 and interleukin-13, which are activated in human inflammatory bowel disease. Aberrant activation of AID in colonic cells preferentially induced genetic mutations in the TP53 gene, whereas there were no nucleotide alterations of the APC gene. Immunohistochemistry revealed enhanced expression of endogenous AID protein not only in the inflamed colonic mucosa of ulcerative colitis patients but also in tumor lesions of colitis-associated colorectal cancers. Conclusions: Our findings indicate that proinflammatory cytokine-mediated aberrant expression of AID in colonic epithelial cells is a genotoxic factor linking inflammation, somatic mutations, and colorectal cancer development.
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helicobacter pylori infection triggers aberrant expression of activation induced Cytidine Deaminase in gastric epithelium
Nature Medicine, 2007Co-Authors: Yuko Matsumoto, Kazuo Kinoshita, Hiroyuki Marusawa, Yoko Endo, Tadayuki Kou, Toshiyuki Morisawa, Takeshi Azuma, Ilmi Okazaki, Tasuku Honjo, Tsutomu ChibaAbstract:Infection with Helicobacter pylori (H. pylori) is a risk factor for the development of gastric cancer. Here we show that infection of gastric epithelial cells with 'cag' pathogenicity island (cagPAI)-positive H. pylori induced aberrant expression of Activation-Induced Cytidine Deaminase (AID), a member of the Cytidine-Deaminase family that acts as a DNA- and RNA-editing enzyme, via the IkappaB kinase-dependent nuclear factor-kappaB activation pathway. H. pylori-mediated upregulation of AID resulted in the accumulation of nucleotide alterations in the TP53 tumor suppressor gene in gastric cells in vitro. Our findings provide evidence that aberrant AID expression caused by H. pylori infection might be a mechanism of mutation accumulation in the gastric mucosa during H. pylori-associated gastric carcinogenesis.
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helicobacter pylori infection triggers aberrant expression of activation induced Cytidine Deaminase in gastric epithelium
Nature Medicine, 2007Co-Authors: Yuko Matsumoto, Kazuo Kinoshita, Hiroyuki Marusawa, Yoko Endo, Toshiyuki Morisawa, Takeshi Azuma, Ilmi Okazaki, Tasuku Honjo, Tsutomu ChibaAbstract:Helicobacter pylori infection triggers aberrant expression of Activation-Induced Cytidine Deaminase in gastric epithelium
Nasim A Begum - One of the best experts on this subject based on the ideXlab platform.
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rna binding motifs of hnrnp k are critical for induction of antibody diversification by activation induced Cytidine Deaminase
Proceedings of the National Academy of Sciences of the United States of America, 2020Co-Authors: Ziwei Yin, Maki Kobayashi, Nasim A Begum, Koichi Higashi, Ken Kurokawa, Tasuku HonjoAbstract:Activation-Induced Cytidine Deaminase (AID) is the key enzyme for class switch recombination (CSR) and somatic hypermutation (SHM) to generate antibody memory. Previously, heterogeneous nuclear ribonucleoprotein K (hnRNP K) was shown to be required for AID-dependent DNA breaks. Here, we defined the function of major RNA-binding motifs of hnRNP K, GXXGs and RGGs in the K-homology (KH) and the K-protein-interaction (KI) domains, respectively. Mutation of GXXG, RGG, or both impaired CSR, SHM, and cMyc/IgH translocation equally, showing that these motifs were necessary for AID-dependent DNA breaks. AID–hnRNP K interaction is dependent on RNA; hence, mutation of these RNA-binding motifs abolished the interaction with AID, as expected. Some of the polypyrimidine sequence-carrying prototypical hnRNP K-binding RNAs, which participate in DNA breaks or repair bound to hnRNP K in a GXXG and RGG motif-dependent manner. Mutation of the GXXG and RGG motifs decreased nuclear retention of hnRNP K. Together with the previous finding that nuclear localization of AID is necessary for its function, lower nuclear retention of these mutants may worsen their functional deficiency, which is also caused by their decreased RNA-binding capacity. In summary, hnRNP K contributed to AID-dependent DNA breaks with all of its major RNA-binding motifs.
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c terminal region of activation induced Cytidine Deaminase aid is required for efficient class switch recombination and gene conversion
Proceedings of the National Academy of Sciences of the United States of America, 2014Co-Authors: Somayeh Sabouri, Maki Kobayashi, Nasim A Begum, Kouji Hirota, Tasuku HonjoAbstract:Activation-Induced Cytidine Deaminase (AID) introduces single-strand breaks (SSBs) to initiate class switch recombination (CSR), gene conversion (GC), and somatic hypermutation (SHM). CSR is mediated by double-strand breaks (DSBs) at donor and acceptor switch (S) regions, followed by pairing of DSB ends in two S regions and their joining. Because AID mutations at its C-terminal region drastically impair CSR but retain its DNA cleavage and SHM activity, the C-terminal region of AID likely is required for the recombination step after the DNA cleavage. To test this hypothesis, we analyzed the recombination junctions generated by AID C-terminal mutants and found that 0- to 3-bp microhomology junctions are relatively less abundant, possibly reflecting the defects of the classical nonhomologous end joining (C-NHEJ). Consistently, the accumulation of C-NHEJ factors such as Ku80 and XRCC4 was decreased at the cleaved S region. In contrast, an SSB-binding protein, poly (ADP)-ribose polymerase1, was recruited more abundantly, suggesting a defect in conversion from SSB to DSB. In addition, recruitment of critical DNA synapse factors such as 53BP1, DNA PKcs, and UNG at the S region was reduced during CSR. Furthermore, the chromosome conformation capture assay revealed that DNA synapse formation is impaired drastically in the AID C-terminal mutants. Interestingly, these mutants showed relative reduction in GC compared with SHM in chicken DT40 cells. Collectively, our data indicate that the C-terminal region of AID is required for efficient generation of DSB in CSR and GC and thus for the subsequent pairing of cleaved DNA ends during recombination in CSR.
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the histone chaperone spt6 is required for activation induced Cytidine Deaminase target determination through h3k4me3 regulation
Journal of Biological Chemistry, 2012Co-Authors: Nasim A Begum, Andre Stanlie, Mikiyo Nakata, Hideo Akiyama, Tasuku HonjoAbstract:H3K4me3 plays a critical role in the Activation-Induced Cytidine Deaminase (AID)-induced DNA cleavage of switch (S) regions in the immunoglobulin heavy chain (IgH) locus during class-switch recombination (CSR). The histone chaperone complex facilitates chromatin transcription (FACT) is responsible for forming H3K4me3 at AID target loci. Here we show that the histone chaperone suppressor of Ty6 (Spt6) also participates in regulating H3K4me3 for CSR and for somatic hypermutation in AID target loci. We found that H3K4me3 loss was correlated with defects in AID-induced DNA breakage and reduced mutation frequencies in IgH loci in both S and variable regions and in non-IgH loci such as metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) and small nucleolar RNA host gene 3 (SNHG3). Global gene expression analysis revealed that Spt6 can act as both a positive and negative transcriptional regulator in B cells, affecting ∼5% of the genes that includes suppressor of Ty4 (Spt4) and AID. Interestingly, Spt6 regulates CSR and AID expression through two distinct histone modification pathways, H3K4me3 and H3K36me3, respectively. Tandem SH2 domain of Spt6 plays a critical role in CSR and H3K4me3 regulation involving Set1 histone methyltransferase. We conclude that Spt6 is a unique histone chaperone capable of regulating the histone epigenetic state of both AID targets and the AID locus.
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nonimmunoglobulin target loci of activation induced Cytidine Deaminase aid share unique features with immunoglobulin genes
Proceedings of the National Academy of Sciences of the United States of America, 2012Co-Authors: Lucia Kato, Nasim A Begum, Maxwell A Burroughs, Tomomitsu Doi, Jun Kawai, Carsten O Daub, Takahisa Kawaguchi, Fumihiko Matsuda, Yoshihide HayashizakiAbstract:Activation-Induced Cytidine Deaminase (AID) is required for both somatic hypermutation and class-switch recombination in activated B cells. AID is also known to target nonimmunoglobulin genes and introduce mutations or chromosomal translocations, eventually causing tumors. To identify as-yet-unknown AID targets, we screened early AID-induced DNA breaks by using two independent genome-wide approaches. Along with known AID targets, this screen identified a set of unique genes (SNHG3, MALAT1, BCL7A, and CUX1) and confirmed that these loci accumulated mutations as frequently as Ig locus after AID activation. Moreover, these genes share three important characteristics with the Ig gene: translocations in tumors, repetitive sequences, and the epigenetic modification of chromatin by H3K4 trimethylation in the vicinity of cleavage sites.
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discovery of activation induced Cytidine Deaminase the engraver of antibody memory
Advances in Immunology, 2007Co-Authors: Masamichi Muramatsu, Nasim A Begum, Hitoshi Nagaoka, Reiko Shinkura, Tasuku HonjoAbstract:Discovery of activation‐induced Cytidine Deaminase (AID) paved a new path to unite two genetic alterations induced by antigen stimulation; class switch recombination (CSR) and somatic hypermutation (SHM). AID is now established to cleave specific target DNA and to serve as engraver of these genetic alterations. AID of a 198‐residue protein has four important domains: nuclear localization signal and SHM‐specific region at the N‐terminus; the α‐helical segment (residue 47–54) responsible for dimerization; catalytic domain (residues 56–94) shared by all the other Cytidine Deaminase family members; and nuclear export signal overlapping with class switch‐specific domain at the C‐terminus. Two alternative models have been proposed for the mode of AID action; whether AID directly attacks DNA or indirectly through RNA editing. Lines of evidence supporting RNA editing hypothesis include homology in various aspects with APOBEC1, a bona fide RNA editing enzyme as well as requirement of de novo protein synthesis for DNA cleavage by AID in CSR and SHM. This chapter critically evaluates DNA deamination hypothesis and describes evidence to indicate UNG is involved not in DNA cleavage but in DNA repair of CSR. In addition, UNG appears to have a noncanonical function through interaction with an HIV Vpr‐like protein at the WXXF motif. Taken together, RNA editing hypothesis is gaining the ground.
Tsutomu Chiba - One of the best experts on this subject based on the ideXlab platform.
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up regulation of activation induced Cytidine Deaminase causes genetic aberrations at the cdkn2b cdkn2a in gastric cancer
Gastroenterology, 2010Co-Authors: Yuko Matsumoto, Kazuo Kinoshita, Hiroyuki Marusawa, Yoko Niwa, Yoshiharu Sakai, Tsutomu ChibaAbstract:Background & Aims The DNA/RNA editing enzyme Activation-Induced Cytidine Deaminase (AID) is mutagenic and has been implicated in human tumorigenesis. Helicobacter pylori infection of gastric epithelial cells leads to aberrant expression of AID and somatic gene mutations. We investigated whether AID induces genetic aberrations at specific chromosomal loci that encode tumor-related proteins in gastric epithelial cells. Methods Human gastric epithelial cell lines that express activated AID and gastric cells from AID transgenic mice were examined for DNA copy number changes and nucleotide alterations. Copy number aberrations in stomach cells of H pylori –infected mice and gastric tissues (normal and tumor) from H pylori –positive patients were also analyzed. Results In human gastric cells, aberrant AID activity induced copy number changes at various chromosomal loci. In AID-expressing cells and gastric mucosa of AID transgenic mice, point mutations and reductions in copy number were observed frequently in the tumor suppressor genes CDKN2A and CDKN2B . Oral infection of wild-type mice with H pylori reduced the copy number of the Cdkn2b - Cdkn2a locus, whereas no such changes were observed in the gastric mucosa of H pylori –infected AID-deficient mice. In human samples, the relative copy numbers of CDKN2A and CDKN2B were reduced in a subset of gastric cancer tissues compared with the surrounding noncancerous region. Conclusions H pylori infection leads to aberrant expression of AID and might be a mechanism of the accumulation of submicroscopic deletions and somatic mutations in gastric epithelial cells. AID-mediated genotoxic effects appear to occur frequently at the CDKN2b-CDKN2a locus and contribute to malignant transformation of the gastric mucosa.
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a novel mechanism for inflammation associated carcinogenesis an important role of activation induced Cytidine Deaminase aid in mutation induction
Journal of Molecular Medicine, 2009Co-Authors: Tsutomu Chiba, Hiroyuki MarusawaAbstract:Inflammation is a risk for cancer development; however, its mechanism is unknown. Recent studies have revealed that Activation-Induced Cytidine Deaminase (AID), which plays essential roles in both class-switch recombination and somatic hypermutation of immunoglobulin gene in B lymphocytes, is aberrantly expressed in non-lymphoid cells not only by H.pylori and HCV infection but also by various proinflammatory cytokines, leading to the generation of gene mutations. These findings not only suggested a new mechanism of inflammation-associated carcinogenesis but has also opened up a new field of tumor biology.
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activation induced Cytidine Deaminase links between inflammation and the development of colitis associated colorectal cancers
Gastroenterology, 2008Co-Authors: Yoko Endo, Kazuo Kinoshita, Hiroyuki Marusawa, Tadayuki Kou, Tasuku Honjo, Hiroshi Nakase, Shigehiko Fujii, Takahiro Fujimori, Tsutomu ChibaAbstract:Background & Aims: Activation-Induced Cytidine Deaminase (AID) was originally identified as an inducer of somatic hypermutations in the immunoglobulin gene. We recently revealed that ectopic AID expression serves as a link between the cellular editing machinery and high mutation frequencies, leading to human cancer development. In the current study, we investigated whether AID might contribute to the development of colitis-associated colorectal cancers. Methods: The expression and regulation of AID in association with proinflammatory cytokine stimulation were investigated in cultured colonic cells. Genotoxic activity of AID in colonic cells was analyzed using retroviral system. Immunohistochemistry for AID was carried out on various human colonic tissues specimens. Results: Tumor necrosis factor-α induced aberrant AID expression via IκB kinase-dependent nuclear factor (NF)-κB-signaling pathways in human colonic epithelial cells. Moreover, AID expression was also induced in response to the T helper cell 2-driven cytokines interleukin-4 and interleukin-13, which are activated in human inflammatory bowel disease. Aberrant activation of AID in colonic cells preferentially induced genetic mutations in the TP53 gene, whereas there were no nucleotide alterations of the APC gene. Immunohistochemistry revealed enhanced expression of endogenous AID protein not only in the inflamed colonic mucosa of ulcerative colitis patients but also in tumor lesions of colitis-associated colorectal cancers. Conclusions: Our findings indicate that proinflammatory cytokine-mediated aberrant expression of AID in colonic epithelial cells is a genotoxic factor linking inflammation, somatic mutations, and colorectal cancer development.
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helicobacter pylori infection triggers aberrant expression of activation induced Cytidine Deaminase in gastric epithelium
Nature Medicine, 2007Co-Authors: Yuko Matsumoto, Kazuo Kinoshita, Hiroyuki Marusawa, Yoko Endo, Tadayuki Kou, Toshiyuki Morisawa, Takeshi Azuma, Ilmi Okazaki, Tasuku Honjo, Tsutomu ChibaAbstract:Infection with Helicobacter pylori (H. pylori) is a risk factor for the development of gastric cancer. Here we show that infection of gastric epithelial cells with 'cag' pathogenicity island (cagPAI)-positive H. pylori induced aberrant expression of Activation-Induced Cytidine Deaminase (AID), a member of the Cytidine-Deaminase family that acts as a DNA- and RNA-editing enzyme, via the IkappaB kinase-dependent nuclear factor-kappaB activation pathway. H. pylori-mediated upregulation of AID resulted in the accumulation of nucleotide alterations in the TP53 tumor suppressor gene in gastric cells in vitro. Our findings provide evidence that aberrant AID expression caused by H. pylori infection might be a mechanism of mutation accumulation in the gastric mucosa during H. pylori-associated gastric carcinogenesis.
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helicobacter pylori infection triggers aberrant expression of activation induced Cytidine Deaminase in gastric epithelium
Nature Medicine, 2007Co-Authors: Yuko Matsumoto, Kazuo Kinoshita, Hiroyuki Marusawa, Yoko Endo, Toshiyuki Morisawa, Takeshi Azuma, Ilmi Okazaki, Tasuku Honjo, Tsutomu ChibaAbstract:Helicobacter pylori infection triggers aberrant expression of Activation-Induced Cytidine Deaminase in gastric epithelium
