1
|
Šenigl F, Soikkeli A, Prost S, Schatz DG, Slavková M, Hejnar J, Alinikula J. The SV40 virus enhancer functions as a somatic hypermutation-targeting element with potential oncogenic activity. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.09.574829. [PMID: 38260396 PMCID: PMC10802419 DOI: 10.1101/2024.01.09.574829] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2024]
Abstract
Simian virus 40 (SV40) is a monkey virus associated with several types of human cancers. SV40 is most frequently detected in mesotheliomas, brain and bone tumors and lymphomas, but the mechanism for SV40 tumorigenesis in humans is not clear. SV40 relative Merkel cell polyomavirus (MCPyV) causes Merkel cell carcinoma (MCC) in humans by expressing truncated large tumor antigen (LT) caused by APOBEC cytidine deaminase family enzymes induced mutations. AID (activation-induced cytidine deaminase), a member of the APOBEC family, is the initiator of the antibody diversification process known as somatic hypermutation (SHM) and its aberrant expression and targeting is a frequent source of lymphomagenesis. In this study, we investigated whether AID-induced mutations could cause truncation of SV40 LT. We demonstrate that the SV40 enhancer has strong SHM targeting activity in several cell types and that AID-induced mutations accumulate to SV40 LT in B cells and kidney cells and cause truncated LT expression in B cells. Our results argue that the ability of the SV40 enhancer to target SHM to LT is a potential source of LT truncation events in various cell types that could contribute to carcinogenesis.
Collapse
|
2
|
Masuda H, Sawada A, Hashimoto SI, Tamai K, Lin KY, Harigai N, Kurosawa K, Ohta K, Seo H, Itou H. Fast-tracking antibody maturation using a B cell-based display system. MAbs 2022; 14:2122275. [PMID: 36202784 PMCID: PMC9542628 DOI: 10.1080/19420862.2022.2122275] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Affinity maturation, an essential component of antibody engineering, is crucial for developing therapeutic antibodies. Cell display system coupled with somatic hypermutation (SHM) initiated by activation-induced cytidine deaminase (AID) is a commonly used technique for affinity maturation. AID introduces targeted DNA lesions into hotspots of immunoglobulin (Ig) gene loci followed by erroneous DNA repair, leading to biased mutations in the complementary determining regions. However, systems that use an in vivo mimicking mechanism often require several rounds of selection to enrich clones possessing accumulated mutations. We previously described the human ADLib® system, which features autonomous, AID-mediated diversification in Ig gene loci of a chicken B cell line DT40 and streamlines human antibody generation and optimization in one integrated platform. In this study, we further engineered DT40 capable of receiving exogenous antibody genes and examined whether the antibody could be affinity matured. The Ig genes of three representative anti-hVEGF-A antibodies originating from the human ADLib® were introduced; the resulting human IgG1 antibodies had up to 76.4-fold improvement in binding affinities (sub-picomolar KD) within just one round of optimization, owing to efficient accumulation of functional mutations. Moreover, we successfully improved the affinity of a mouse hybridoma-derived anti-hCDCP1 antibody using the engineered DT40, and the observed mutations remained effective in the post-humanized antibody as exhibited by an 8.2-fold increase of in vitro cytotoxicity without compromised physical stability. These results demonstrated the versatility of the novel B cell-based affinity maturation system as an easy-to-use antibody optimization tool regardless of the species of origin.Abbreviations: ADLib®: Autonomously diversifying library, ADLib® KI-AMP: ADLib® knock-in affinity maturation platform, AID: activation-induced cytidine deaminase, CDRs: complementary-determining regions, DIVAC: diversification activator, ECD: extracellular domain, FACS: fluorescence-activated cell sorting, FCM: flow cytometry, HC: heavy chainIg: immunoglobulin, LC: light chain, NGS: next-generation sequencing, PBD: pyrrolobenzodiazepine, SHM: somatic hypermutation, SPR: surface plasmon resonance.
Collapse
Affiliation(s)
- Hitomi Masuda
- Research Laboratories, Chiome Bioscience Inc, Tokyo, Japan,CONTACT Hitomi Masuda Research Laboratories, Chiome Bioscience Inc, Sumitomo-Fudosan Nishi-shinjuku bldg. No. 6, 3-12-1 Honmachi, Shibuya-ku, Tokyo151-0071, Japan
| | - Atsushi Sawada
- Research Laboratories, Chiome Bioscience Inc, Tokyo, Japan
| | | | - Kanako Tamai
- Research Laboratories, Chiome Bioscience Inc, Tokyo, Japan
| | - Ke-Yi Lin
- Research Laboratories, Chiome Bioscience Inc, Tokyo, Japan
| | - Naoto Harigai
- Research Laboratories, Chiome Bioscience Inc, Tokyo, Japan
| | - Kohei Kurosawa
- Research Laboratories, Chiome Bioscience Inc, Tokyo, Japan
| | - Kunihiro Ohta
- Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan
| | - Hidetaka Seo
- Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan
| | - Hiroshi Itou
- Research Laboratories, Chiome Bioscience Inc, Tokyo, Japan,Hiroshi Itou Research Laboratories, Chiome Bioscience Inc, Sumitomo-Fudosan Nishi-shinjuku bldg. No. 6, 3-12-1, Honmachi, Shibuya-ku, Tokyo 151-0071 Japan
| |
Collapse
|
3
|
Tarsalainen A, Maman Y, Meng FL, Kyläniemi MK, Soikkeli A, Budzynska P, McDonald JJ, Šenigl F, Alt FW, Schatz DG, Alinikula J. Ig Enhancers Increase RNA Polymerase II Stalling at Somatic Hypermutation Target Sequences. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2022; 208:143-154. [PMID: 34862258 PMCID: PMC8702490 DOI: 10.4049/jimmunol.2100923] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2021] [Accepted: 10/20/2021] [Indexed: 01/03/2023]
Abstract
Somatic hypermutation (SHM) drives the genetic diversity of Ig genes in activated B cells and supports the generation of Abs with increased affinity for Ag. SHM is targeted to Ig genes by their enhancers (diversification activators [DIVACs]), but how the enhancers mediate this activity is unknown. We show using chicken DT40 B cells that highly active DIVACs increase the phosphorylation of RNA polymerase II (Pol II) and Pol II occupancy in the mutating gene with little or no accompanying increase in elongation-competent Pol II or production of full-length transcripts, indicating accumulation of stalled Pol II. DIVAC has similar effect also in human Ramos Burkitt lymphoma cells. The DIVAC-induced stalling is weakly associated with an increase in the detection of ssDNA bubbles in the mutating target gene. We did not find evidence for antisense transcription, or that DIVAC functions by altering levels of H3K27ac or the histone variant H3.3 in the mutating gene. These findings argue for a connection between Pol II stalling and cis-acting targeting elements in the context of SHM and thus define a mechanistic basis for locus-specific targeting of SHM in the genome. Our results suggest that DIVAC elements render the target gene a suitable platform for AID-mediated mutation without a requirement for increasing transcriptional output.
Collapse
Affiliation(s)
- Alina Tarsalainen
- Unit of Infections and Immunity, Institute of Biomedicine, University of Turku, 20520 Turku, Finland
| | - Yaakov Maman
- The Azrieli Faculty of Medicine, Bar Ilan University, Safed, 1311502, Israel
| | - Fei-Long Meng
- Department of Genetics, Harvard Medical School and Program in Cellular and Molecular Medicine, HHMI, Boston Children’s Hospital, Boston, MA 02115, USA.,Current address: State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Shanghai 200031, China
| | - Minna K. Kyläniemi
- Unit of Infections and Immunity, Institute of Biomedicine, University of Turku, 20520 Turku, Finland,Current address: Turku Bioscience Centre, University of Turku and Åbo Akademi University, 20520 Turku, Finland
| | - Anni Soikkeli
- Unit of Infections and Immunity, Institute of Biomedicine, University of Turku, 20520 Turku, Finland
| | - Paulina Budzynska
- Unit of Infections and Immunity, Institute of Biomedicine, University of Turku, 20520 Turku, Finland
| | - Jessica J. McDonald
- Department of Immunobiology, Yale School of Medicine, New Haven, CT 06511, USA,Current address: The Annenberg Public Policy Center, Philadelphia, PA 19104-3806, USA
| | - Filip Šenigl
- Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, 142 20 Praha 4, Czech Republic
| | - Frederic W. Alt
- Department of Genetics, Harvard Medical School and Program in Cellular and Molecular Medicine, HHMI, Boston Children’s Hospital, Boston, MA 02115, USA
| | - David G. Schatz
- Department of Immunobiology, Yale School of Medicine, New Haven, CT 06511, USA,Correspondence should be addressed to and
| | - Jukka Alinikula
- Unit of Infections and Immunity, Institute of Biomedicine, University of Turku, 20520 Turku, Finland,Correspondence should be addressed to and
| |
Collapse
|
4
|
Senigl F, Maman Y, Dinesh RK, Alinikula J, Seth RB, Pecnova L, Omer AD, Rao SSP, Weisz D, Buerstedde JM, Aiden EL, Casellas R, Hejnar J, Schatz DG. Topologically Associated Domains Delineate Susceptibility to Somatic Hypermutation. Cell Rep 2020; 29:3902-3915.e8. [PMID: 31851922 PMCID: PMC6980758 DOI: 10.1016/j.celrep.2019.11.039] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2019] [Revised: 06/26/2019] [Accepted: 11/08/2019] [Indexed: 12/26/2022] Open
Abstract
Somatic hypermutation (SHM) introduces point mutations into immunoglobulin (Ig) genes but also causes mutations in other parts of the genome. We have used lentiviral SHM reporter vectors to identify regions of the genome that are susceptible (“hot”) and resistant (“cold”) to SHM, revealing that SHM susceptibility and resistance are often properties of entire topologically associated domains (TADs). Comparison of hot and cold TADs reveals that while levels of transcription are equivalent, hot TADs are enriched for the cohesin loader NIPBL, super-enhancers, markers of paused/stalled RNA polymerase 2, and multiple important B cell transcription factors. We demonstrate that at least some hot TADs contain enhancers that possess SHM targeting activity and that insertion of a strong Ig SHM-targeting element into a cold TAD renders it hot. Our findings lead to a model for SHM susceptibility involving the cooperative action of cis-acting SHM targeting elements and the dynamic and architectural properties of TADs. Senigl et al. show that genome susceptibility to somatic hypermutation (SHM) is confined within topologically associated domains (TADs) and is linked to markers of strong enhancers and stalled transcription and high levels of the cohesin loader NIPBL. Insertion of an ectopic SHM targeting element renders an entire TAD susceptible to SHM.
Collapse
Affiliation(s)
- Filip Senigl
- Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, Videnska 1083, 14220 Prague 4, Czech Republic.
| | - Yaakov Maman
- Laboratory of Genome Integrity, National Cancer Institute, NIH, Bethesda, MD 20892, USA
| | - Ravi K Dinesh
- Department of Immunobiology, Yale School of Medicine, 300 Cedar Street, Box 208011, New Haven, CT 06520-8011, USA
| | - Jukka Alinikula
- Institute of Biomedicine, University of Turku, Kiinamyllynkatu 10, 20520 Turku, Finland
| | - Rashu B Seth
- Department of Immunobiology, Yale School of Medicine, 300 Cedar Street, Box 208011, New Haven, CT 06520-8011, USA
| | - Lubomira Pecnova
- Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, Videnska 1083, 14220 Prague 4, Czech Republic
| | - Arina D Omer
- Center for Genome Architecture, Baylor College of Medicine, Houston, TX 77030, USA
| | - Suhas S P Rao
- Center for Genome Architecture, Baylor College of Medicine, Houston, TX 77030, USA
| | - David Weisz
- Center for Genome Architecture, Baylor College of Medicine, Houston, TX 77030, USA
| | | | - Erez Lieberman Aiden
- Center for Genome Architecture, Baylor College of Medicine, Houston, TX 77030, USA; Center for Theoretical Biological Physics, Rice University, Houston, TX 77005, USA
| | - Rafael Casellas
- Lymphocyte Nuclear Biology, NIAMS, NIH, Bethesda, MD 20892, USA; Center of Cancer Research, NCI, NIH, Bethesda, MD 20892, USA
| | - Jiri Hejnar
- Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, Videnska 1083, 14220 Prague 4, Czech Republic
| | - David G Schatz
- Department of Immunobiology, Yale School of Medicine, 300 Cedar Street, Box 208011, New Haven, CT 06520-8011, USA.
| |
Collapse
|
5
|
Dinesh RK, Barnhill B, Ilanges A, Wu L, Michelson DA, Senigl F, Alinikula J, Shabanowitz J, Hunt DF, Schatz DG. Transcription factor binding at Ig enhancers is linked to somatic hypermutation targeting. Eur J Immunol 2019; 50:380-395. [PMID: 31821534 DOI: 10.1002/eji.201948357] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2019] [Revised: 10/05/2019] [Accepted: 12/02/2019] [Indexed: 01/15/2023]
Abstract
Secondary diversification of the Ig repertoire occurs through somatic hypermutation (SHM), gene conversion (GCV), and class switch recombination (CSR)-three processes that are initiated by activation-induced cytidine deaminase (AID). AID targets Ig genes at orders of magnitude higher than the rest of the genome, but the basis for this specificity is poorly understood. We have previously demonstrated that enhancers and enhancer-like sequences from Ig genes are capable of stimulating SHM of neighboring genes in a capacity distinct from their roles in increasing transcription. Here, we use an in vitro proteomics approach to identify E-box, MEF2, Ets, and Ikaros transcription factor family members as potential binders of these enhancers. ChIP assays in the hypermutating Ramos B cell line confirmed that many of these factors bound the endogenous Igλ enhancer and/or the IgH intronic enhancer (Eμ) in vivo. Further investigation using SHM reporter assays identified binding sites for E2A and MEF2B in Eμ and demonstrated an association between loss of factor binding and decreases in the SHM stimulating activity of Eμ mutants. Our results provide novel insights into trans-acting factors that dictate SHM targeting and link their activity to specific DNA binding sites within Ig enhancers.
Collapse
Affiliation(s)
- Ravi K Dinesh
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT, USA
| | - Benjamin Barnhill
- Department of Chemistry, University of Virginia, Charlottesville, VA, USA
| | - Anoj Ilanges
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT, USA
| | - Lizhen Wu
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT, USA
| | - Daniel A Michelson
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT, USA
| | - Filip Senigl
- Institute of Molecular Genetics, Czech Academy of Sciences, Videnska 1083, CZ-14220, Prague 4, Czech Republic
| | - Jukka Alinikula
- Institute of Biomedicine, University of Turku, Turku, Finland
| | | | - Donald F Hunt
- Department of Chemistry, University of Virginia, Charlottesville, VA, USA.,Department of Pathology, University of Virginia, Charlottesville, VA, USA
| | - David G Schatz
- Department of Immunobiology, Yale University School of Medicine, New Haven, CT, USA
| |
Collapse
|
6
|
Choudhary M, Tamrakar A, Singh AK, Jain M, Jaiswal A, Kodgire P. AID Biology: A pathological and clinical perspective. Int Rev Immunol 2017; 37:37-56. [PMID: 28933967 DOI: 10.1080/08830185.2017.1369980] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Activation-induced cytidine deaminase (AID), primarily expressed in activated mature B lymphocytes in germinal centers, is the key factor in adaptive immune response against foreign antigens. AID is responsible for producing high-affinity and high-specificity antibodies against an infectious agent, through the physiological DNA alteration processes of antibody genes by somatic hypermutation (SHM) and class-switch recombination (CSR) and functions by deaminating deoxycytidines (dC) to deoxyuridines (dU), thereby introducing point mutations and double-stranded chromosomal breaks (DSBs). The beneficial physiological role of AID in antibody diversification is outweighed by its detrimental role in the genesis of several chronic immune diseases, under non-physiological conditions. This review offers a comprehensive and better understanding of AID biology and its pathological aspects, as well as addresses the challenges involved in AID-related cancer therapeutics, based on various recent advances and evidence available in the literature till date. In this article, we discuss ways through which our interpretation of AID biology may reflect upon novel clinical insights, which could be successfully translated into designing clinical trials and improving patient prognosis and disease management.
Collapse
Affiliation(s)
- Meenal Choudhary
- a Centre for Biosciences and Biomedical Engineering , Indian Institute of Technology Indore , Simrol , Indore , Madhya Pradesh , India
| | - Anubhav Tamrakar
- a Centre for Biosciences and Biomedical Engineering , Indian Institute of Technology Indore , Simrol , Indore , Madhya Pradesh , India
| | - Amit Kumar Singh
- a Centre for Biosciences and Biomedical Engineering , Indian Institute of Technology Indore , Simrol , Indore , Madhya Pradesh , India
| | - Monika Jain
- a Centre for Biosciences and Biomedical Engineering , Indian Institute of Technology Indore , Simrol , Indore , Madhya Pradesh , India
| | - Ankit Jaiswal
- a Centre for Biosciences and Biomedical Engineering , Indian Institute of Technology Indore , Simrol , Indore , Madhya Pradesh , India
| | - Prashant Kodgire
- a Centre for Biosciences and Biomedical Engineering , Indian Institute of Technology Indore , Simrol , Indore , Madhya Pradesh , India
| |
Collapse
|
7
|
Williams AM, Maman Y, Alinikula J, Schatz DG. Bcl6 Is Required for Somatic Hypermutation and Gene Conversion in Chicken DT40 Cells. PLoS One 2016; 11:e0149146. [PMID: 26900682 PMCID: PMC4762950 DOI: 10.1371/journal.pone.0149146] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2015] [Accepted: 01/27/2016] [Indexed: 12/20/2022] Open
Abstract
The activation induced cytosine deaminase (AID) mediates diversification of B cell immunoglobulin genes by the three distinct yet related processes of somatic hypermutation (SHM), class switch recombination (CSR), and gene conversion (GCV). SHM occurs in germinal center B cells, and the transcription factor Bcl6 is a key regulator of the germinal center B cell gene expression program, including expression of AID. To test the hypothesis that Bcl6 function is important for the process of SHM, we compared WT chicken DT40 B cells, which constitutively perform SHM/GCV, to their Bcl6-deficient counterparts. We found that Bcl6-deficient DT40 cells were unable to perform SHM and GCV despite enforced high level expression of AID and substantial levels of AID in the nucleus of the cells. To gain mechanistic insight into the GCV/SHM dependency on Bcl6, transcriptional features of a highly expressed SHM target gene were analyzed in Bcl6-sufficient and -deficient DT40 cells. No defect was observed in the accumulation of single stranded DNA in the target gene as a result of Bcl6 deficiency. In contrast, association of Spt5, an RNA polymerase II (Pol II) and AID binding factor, was strongly reduced at the target gene body relative to the transcription start site in Bcl6-deficient cells as compared to WT cells. However, partial reconstitution of Bcl6 function substantially reconstituted Spt5 association with the target gene body but did not restore detectable SHM. Our observations suggest that in the absence of Bcl6, Spt5 fails to associate efficiently with Pol II at SHM targets, perhaps precluding robust AID action on the SHM target DNA. Our data also suggest, however, that Spt5 binding is not sufficient for SHM of a target gene even in DT40 cells with strong expression of AID.
Collapse
Affiliation(s)
- Alan M. Williams
- Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - Yaakov Maman
- Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - Jukka Alinikula
- Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - David G. Schatz
- Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut, United States of America
- Howard Hughes Medical Institute, Chevy Chase, Maryland, United States of America
- * E-mail:
| |
Collapse
|
8
|
Fowler T, Garruss AS, Ghosh A, De S, Becker KG, Wood WH, Weirauch MT, Smale ST, Aronow B, Sen R, Roy AL. Divergence of transcriptional landscape occurs early in B cell activation. Epigenetics Chromatin 2015; 8:20. [PMID: 25987903 PMCID: PMC4434543 DOI: 10.1186/s13072-015-0012-x] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2015] [Accepted: 05/01/2015] [Indexed: 12/15/2022] Open
Abstract
Background Signaling via B cell receptor (BCR) and Toll-like receptors (TLRs) results in activation of B cells with distinct physiological outcomes, but transcriptional regulatory mechanisms that drive activation and distinguish these pathways remain unknown. Results Two hours after ligand exposure RNA-seq, ChIP-seq and computational methods reveal that BCR- or TLR-mediated activation of primary resting B cells proceeds via a large set of shared and a smaller subset of distinct signal-selective transcriptional responses. BCR stimulation resulted in increased global recruitment of RNA Pol II to promoters that appear to transit slowly to downstream regions. Conversely, lipopolysaccharide (LPS) stimulation involved an enhanced RNA Pol II transition from initiating to elongating mode accompanied by greater H3K4me3 activation markings compared to BCR stimulation. These rapidly diverging transcriptomic landscapes also show distinct repressing (H3K27me3) histone signatures, mutually exclusive transcription factor binding in promoters, and unique miRNA profiles. Conclusions Upon examination of genome-wide transcription and regulatory elements, we conclude that the B cell commitment to different activation states occurs much earlier than previously thought and involves a multi-faceted receptor-specific transcriptional landscape. Electronic supplementary material The online version of this article (doi:10.1186/s13072-015-0012-x) contains supplementary material, which is available to authorized users.
Collapse
Affiliation(s)
- Trent Fowler
- Department of Developmental, Chemical and Molecular Biology, Sackler School of Biomedical Science, Tufts University School of Medicine, 150 Harrison Avenue, Boston, MA 02111 USA
| | - Alexander S Garruss
- Wyss Institute for Biologically Inspired Engineering, Harvard University and Department of Genetics, Harvard Medical School, Boston, MA 02115 USA
| | - Amalendu Ghosh
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, Baltimore, MD 21224 USA
| | - Supriyo De
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, Baltimore, MD 21224 USA ; Gene Expression Unit, Laboratory of Genetics, National Institute on Aging, Baltimore, MD 21224 USA
| | - Kevin G Becker
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, Baltimore, MD 21224 USA ; Gene Expression Unit, Laboratory of Genetics, National Institute on Aging, Baltimore, MD 21224 USA
| | - William H Wood
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, Baltimore, MD 21224 USA ; Gene Expression Unit, Laboratory of Genetics, National Institute on Aging, Baltimore, MD 21224 USA
| | - Matthew T Weirauch
- Center for Autoimmune Genomics and Etiology (CAGE) and Divisions of Biomedical Informatics and Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229 USA
| | - Stephen T Smale
- Department of Microbiology, Immunology, and Molecular Genetics, UCLA, Los Angeles, CA 90095 USA
| | - Bruce Aronow
- Center for Autoimmune Genomics and Etiology (CAGE) and Divisions of Biomedical Informatics and Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229 USA
| | - Ranjan Sen
- Laboratory of Molecular Biology and Immunology, National Institute on Aging, Baltimore, MD 21224 USA
| | - Ananda L Roy
- Department of Developmental, Chemical and Molecular Biology, Sackler School of Biomedical Science, Tufts University School of Medicine, 150 Harrison Avenue, Boston, MA 02111 USA
| |
Collapse
|
9
|
Chen Z, Ranganath S, Viboolsittiseri SS, Eder MD, Chen X, Elos MT, Yuan S, Yuan S, Hansen E, Wang JH. AID-initiated DNA lesions are differentially processed in distinct B cell populations. THE JOURNAL OF IMMUNOLOGY 2014; 193:5545-56. [PMID: 25339658 DOI: 10.4049/jimmunol.1401549] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Activation-induced deaminase (AID) initiates U:G mismatches, causing point mutations or DNA double-stranded breaks at Ig loci. How AID-initiated lesions are prevented from inducing genome-wide damage remains elusive. A differential DNA repair mechanism might protect certain non-Ig loci such as c-myc from AID attack. However, determinants regulating such protective mechanisms are largely unknown. To test whether target DNA sequences modulate protective mechanisms via altering the processing manner of AID-initiated lesions, we established a knock-in model by inserting an Sγ2b region, a bona fide AID target, into the first intron of c-myc. Unexpectedly, we found that the inserted S region did not mutate or enhance c-myc genomic instability, due to error-free repair of AID-initiated lesions, in Ag-stimulated germinal center B cells. In contrast, in vitro cytokine-activated B cells display a much higher level of c-myc genomic instability in an AID- and S region-dependent manner. Furthermore, we observe a comparable frequency of AID deamination events between the c-myc intronic sequence and inserted S region in different B cell populations, demonstrating a similar frequency of AID targeting. Thus, our study reveals a clear difference between germinal center and cytokine-activated B cells in their ability to develop genomic instability, attributable to a differential processing of AID-initiated lesions in distinct B cell populations. We propose that locus-specific regulatory mechanisms (e.g., transcription) appear to not only override the effects of S region sequence on AID targeting frequency but also influence the repair manner of AID-initiated lesions.
Collapse
Affiliation(s)
- Zhangguo Chen
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045; Department of Biomedical Research, National Jewish Health, Denver, CO 80206; and
| | - Sheila Ranganath
- Boston Children's Hospital, Howard Hughes Medical Institute, Harvard Medical School, Boston, MA 02115
| | - Sawanee S Viboolsittiseri
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045
| | - Maxwell D Eder
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045
| | - Xiaomi Chen
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045; Department of Biomedical Research, National Jewish Health, Denver, CO 80206; and
| | - Mihret T Elos
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045
| | - Shunzong Yuan
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045
| | | | - Erica Hansen
- Boston Children's Hospital, Howard Hughes Medical Institute, Harvard Medical School, Boston, MA 02115
| | - Jing H Wang
- Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO 80045; Department of Biomedical Research, National Jewish Health, Denver, CO 80206; and
| |
Collapse
|
10
|
Chen Z, Wang JH. Generation and repair of AID-initiated DNA lesions in B lymphocytes. Front Med 2014; 8:201-16. [PMID: 24748462 PMCID: PMC4039616 DOI: 10.1007/s11684-014-0324-4] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2013] [Accepted: 12/30/2013] [Indexed: 01/12/2023]
Abstract
Activation-induced deaminase (AID) initiates the secondary antibody diversification process in B lymphocytes. In mammalian B cells, this process includes somatic hypermutation (SHM) and class switch recombination (CSR), both of which require AID. AID induces U:G mismatch lesions in DNA that are subsequently converted into point mutations or DNA double stranded breaks during SHM/CSR. In a physiological context, AID targets immunoglobulin (Ig) loci to mediate SHM/CSR. However, recent studies reveal genome-wide access of AID to numerous non-Ig loci. Thus, AID poses a threat to the genome of B cells if AID-initiated DNA lesions cannot be properly repaired. In this review, we focus on the molecular mechanisms that regulate the specificity of AID targeting and the repair pathways responsible for processing AID-initiated DNA lesions.
Collapse
Affiliation(s)
- Zhangguo Chen
- Integrated Department of Immunology, University of Colorado Anschutz Medical Campus and National Jewish Health, Denver, CO 80206
| | - Jing H. Wang
- Integrated Department of Immunology, University of Colorado Anschutz Medical Campus and National Jewish Health, Denver, CO 80206
| |
Collapse
|
11
|
Targeting of somatic hypermutation by immunoglobulin enhancer and enhancer-like sequences. PLoS Biol 2014; 12:e1001831. [PMID: 24691034 PMCID: PMC3972084 DOI: 10.1371/journal.pbio.1001831] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2013] [Accepted: 02/21/2014] [Indexed: 11/19/2022] Open
Abstract
Immunoglobulin gene enhancers have a conserved function in targeting somatic hypermutation to immunoglobulin genes, thereby supporting the production of high affinity antibodies. Somatic hypermutation (SH) generates point mutations within rearranged immunoglobulin (Ig) genes of activated B cells, providing genetic diversity for the affinity maturation of antibodies. SH requires the activation-induced cytidine deaminase (AID) protein and transcription of the mutation target sequence, but how the Ig gene specificity of mutations is achieved has remained elusive. We show here using a sensitive and carefully controlled assay that the Ig enhancers strongly activate SH in neighboring genes even though their stimulation of transcription is negligible. Mutations in certain E-box, NFκB, MEF2, or Ets family binding sites—known to be important for the transcriptional role of Ig enhancers—impair or abolish the activity. Full activation of SH typically requires a combination of multiple Ig enhancer and enhancer-like elements. The mechanism is evolutionarily conserved, as mammalian Ig lambda and Ig heavy chain intron enhancers efficiently stimulate hypermutation in chicken cells. Our results demonstrate a novel regulatory function for Ig enhancers, indicating that they either recruit AID or alter the accessibility of the nearby transcription units. During the B cell immune response, immunoglobulin (Ig) genes are subject to a unique mutation process known as somatic hypermutation that allows the immune system to generate high-affinity antibodies. Somatic hypermutation preferentially affects Ig genes, relative to other genes, and this is important in preventing catastrophic levels of general genomic mutations that could lead to B cell cancers. We hypothesized that this preferential targeting of somatic hypermutation is assisted by specific DNA sequences in or near Ig genes that focus the action of the mutation machinery on those genes. In this study, we show that Ig genes across species—from human, mouse, and chicken—do indeed contain such mutation targeting sequences and that they coincide with transcriptional regulatory regions known as enhancers. We show that combinations of Ig enhancers cooperate to achieve strong mutation targeting and that this action depends on well-known transcription factor binding sites in these enhancer elements. Our findings establish an evolutionarily conserved function for enhancers in somatic hypermutation targeting, which operates by a mechanism distinct from the conventional enhancer function of increasing levels of transcription. We propose that combinations of Ig enhancers target somatic mutation to Ig genes by recruiting the mutation machinery and/or by making the Ig genes better substrates for mutation.
Collapse
|