AID expression levels determine the extent of <i>cMyc</i> oncogenic translocations and the incidence of B cell tumor development

Takizawa, Makiko; Tolarová, Helena; Li, Zhiyu; Dubois, Wendy; Lim, Susan E.; Callén, Elsa; Franco, Sonia; Mosaico, Maria; Feigenbaum, Lionel; Alt, Frederick W.; Nussenzweig, André; Potter, Michael; Casellas, Rafael

doi:10.1084/jem.20081007

Cited by 144 publications

(145 citation statements)

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“…MYC-IGH and BCL6-IGH translocations are found in a variety of human mature B cell lymphomas, such as Burkitt's lymphomas and DLBCL. AID initiates DSBs at the mouse MYC locus for the MYC-IGH translocation during the murine germinal-center B cell stage (23)(24)(25). It has recently become clear that AID targets DNA motifs in the human MYC-IGH and BCL6-IGH translocations as well (5).…”

Section: Resultsmentioning

confidence: 99%

Human Lymphoid Translocation Fragile Zones Are Hypomethylated and Have Accessible Chromatin

Lieber

Tsai

et al. 2015

Molecular and Cellular Biology

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Chromosomal translocations are a hallmark of hematopoietic malignancies. CG motifs within translocation fragile zones (typically 20 to 600 bp in size) are prone to chromosomal translocation in lymphomas. Here we demonstrate that the CG motifs in human translocation fragile zones are hypomethylated relative to the adjacent DNA. Using a methyltransferase footprinting assay on isolated nuclei (in vitro), we find that the chromatin at these fragile zones is accessible. We also examined in vivo accessibility using cellular expression of a prokaryotic methylase. Based on this assay, which measures accessibility over a much longer time interval than is possible with in vitro methods, these fragile zones were found to be more accessible than the adjacent DNA. Because DNA within the fragile zones can be methylated by both cellular and exogenous methyltransferases, the fragile zones are predominantly in a duplex DNA conformation. These observations permit more-refined models for why these zones are 100-to 1,000-fold more prone to undergo chromosomal translocation than the adjacent regions.C hromosomal translocations are seminal events in the development of many hematologic malignancies (1). Many hematopoietic malignancies are associated with recurrent reciprocal translocations and their resulting gene fusions or amplifications, which guide diagnosis, assessment of prognosis, and treatment. One example is the BCL2-IGH translocation, t(14;18)(q32;q21), observed in 85% of follicular lymphomas (FL) and 30% of diffuse large B cell lymphomas (DLBCL). A second example is the CCND1-IGH translocation, t(11;14)(q13;q32), observed in almost all mantle cell lymphomas (MCL). Oncogenes near sites of recurrent translocation often confer a selective growth advantage (2). For unknown reasons, human chromosomal translocation breakpoints near these oncogenes frequently cluster within tight DNA zones (often only 20 to 600 bp in length) known as fragile zones (see the green starbursts in the upper portion of Fig. 1A and 2A). These zones are 100-to 1,000-fold more sensitive to breakage than the adjacent DNA regions located, for example, only 20 bp to either side of the fragile zone (2-7). Hence, the DNA sequences surrounding each oncogene are not equally sensitive to breakage. The molecular basis for such an extreme breakage propensity within such a short zone of DNA is unknown, despite our progress on elucidation of other aspects of the mechanism described below (8).We have previously reported that breakpoints of human lymphoid translocation fragile zones are not randomly distributed (Fig. 1A and 2A). Pro-B/pre-B cell-stage translocations show a breakage propensity for the CG (commonly called CpG but designated CG in this paper) DNA sequence motif within the 20 to 600-bp fragile zones (3). We have proposed a model in which activation-induced deaminase (AID) initiates double-strand breaks (DSBs) by acting at the methylated form of these CG sites in single-stranded DNA (ssDNA) to deaminate the 5-methylcytosine to yield a T-G mismatch (3). The r...

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Section: Resultsmentioning

confidence: 99%

Human Lymphoid Translocation Fragile Zones Are Hypomethylated and Have Accessible Chromatin

Lieber

Tsai

et al. 2015

Molecular and Cellular Biology

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“…Indeed, it is possible that the diminished CSR obtained with some of the export-proficient mutant NESs might at least in part be the direct result of their diminished stability: the abundance of AID in normal B cells is known to be tightly controlled, with the efficiency of CSR being very sensitive to AID expression levels (15)(16)(17)(18)(19). Such a requirement for both export and abundance might nicely explain the CSR-deficiency exhibited by the AID P20 mutant (8), which carries a 34-aa insertion upstream of the NES, as we find that this mutant exhibits diminished stability although retaining a functional export sequence.…”

Section: Discussionmentioning

confidence: 99%

The stability of AID and its function in class-switching are critically sensitive to the identity of its nuclear-export sequence

Geisberger

Rada²,

Neuberger³

2009

Proc. Natl. Acad. Sci. U.S.A.

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The carboxyterminal region of activation-induced deaminase (AID) is required for its function in Ig class switch recombination (CSR) and also contains a nuclear-export sequence (NES). Here, based on an extensive fine-structure mutation analysis of the AID NES, as well as from AID chimeras bearing heterologous NESs, we show that while a functional NES is indeed essential for CSR, it is not sufficient. The precise nature of the NES is critical both for AID stabilization and CSR function: minor changes in the NES can perturb stabilization and CSR without jeopardizing nuclear export. The results indicate that the AID NES fulfills a function beyond simply providing a signal for nuclear export and suggest the possibility that the quality of exportin-binding may be critical to the stabilization of AID and its activity in CSR.activation-induced deaminase ͉ antibody diversification ͉ immunoglobulin class switching ͉ exportin ͉ nuclear transport A ctivation-induced deaminase (AID) plays a central role in antibody gene-diversification, triggering both somatic hypermutation (SHM) and class-switch recombination (CSR) by deaminating deoxycytidine residues within the Ig locus to yield deoxyuridine (1, 2).AID is largely found in the cytoplasm of activated B cells but shuttles between cytoplasm and nucleus (3-6). The C-terminal amino acids of AID comprise a nuclear-export sequence (NES): removal of this NES causes AID to be restricted to the nucleus, whereas its addition to a heterologous nuclear protein drives export of the fusion protein into the cytoplasm (3-5). The sequence of the AID C-terminus conforms well to the consensus established for substrates of the Crm1-dependent export machinery: in keeping with this, export mediated by the AID NES is sensitive to leptomycin B.Analysis of both clinical and contrived mutations in AID have revealed that the AID C-terminal region is also essential for its function in CSR, although not in SHM (7-9). The C-terminal mutations that interfere with AID's ability to potentiate CSR do not compromise its ability to deaminate deoxycytidine in biochemical or bacterial genetic assays. Thus, as previously suggested by others, either the nuclear/cytoplasmic shuttling of AID must be specifically required for CSR or, alternatively, factors specific for CSR must interact with the C-terminal region of AID in an area overlapping the NES (4, 5, 7-9).It was with a view to discriminating these possibilities that we embarked on a refined mutagenic dissection of the AID NES and investigated the ability of heterologous NESs to substitute for the AID NES. Our results suggest that although nuclear export is likely necessary for CSR, this is not the sole function of the AID C-terminal region, with the data raising the possibility that successful CSR depends on the precise quality of AID binding to exportin or a related protein. Results NES Function and CSR Correlate in Alanine-Scanning Mutagenesis.To ascertain whether there was a correlation between export activity and CSR, we performed an alanine-scanning mut...

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“…3E) also raised the question of whether UNG could be limiting for CSR. AID haploinsufficient mice show reduced preimmune serum Ig accumulation (37,38). However, Ung +/2 mice did not show any differences compared with wt for any Ig subclass (Fig.…”

Section: Ung Is Not Limiting For Csrmentioning

confidence: 99%

Separation of Function between Isotype Switching and Affinity Maturation In Vivo during Acute Immune Responses and Circulating Autoantibodies in UNG-Deficient Mice

Zahn

Daugan

Safavi

et al. 2013

The Journal of Immunology

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Activation-induced deaminase converts deoxycytidine to deoxyuridine at the Ig loci. Complementary pathways, initiated by the uracil-DNA glycosylase (UNG) or the mismatch repair factor MSH2/MSH6, must process the deoxyuridine to initiate class-switch recombination (CSR) and somatic hypermutation. UNG deficiency most severely reduces CSR efficiency and only modestly affects the somatic hypermutation spectrum in vitro. This would predict isotype-switching deficiency but normal affinity maturation in Ung−/− mice in vivo, but this has not been tested. Moreover, puzzling differences in the amount of circulating Ig between UNG-deficient humans and mice make it unclear to what extent MSH2/MSH6 can complement for UNG in vivo. We find that Ab affinity maturation is indeed unaffected in Ung−/− mice, even allowing IgM responses with higher than normal affinity. Ung−/− mice display normal to only moderately reduced basal levels of most circulating Ig subclasses and gut-associated IgA, which are elicited in response to chronically available environmental Ag. In contrast, their ability to produce switched Ig in response to immunization or vesicular stomatitis virus infection is strongly impaired. Our results uncover a specific need for UNG in CSR for timely and efficient acute Ab responses in vivo. Furthermore, Ung−/− mice provide a novel model for separating isotype switching and affinity maturation during acute (but not chronic) Ab responses, which could be useful for dissecting their relative contribution to some infections. Interestingly, Ung−/− mice present with circulating autoantibodies, suggesting that UNG may impinge on tolerance.

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AID expression levels determine the extent of cMyc oncogenic translocations and the incidence of B cell tumor development

Cited by 144 publications

References 35 publications

Human Lymphoid Translocation Fragile Zones Are Hypomethylated and Have Accessible Chromatin

Human Lymphoid Translocation Fragile Zones Are Hypomethylated and Have Accessible Chromatin

The stability of AID and its function in class-switching are critically sensitive to the identity of its nuclear-export sequence

Separation of Function between Isotype Switching and Affinity Maturation In Vivo during Acute Immune Responses and Circulating Autoantibodies in UNG-Deficient Mice

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