Differential regulation of S-region hypermutation and class-switch recombination by noncanonical functions of uracil DNA glycosylase

Yousif, Ashraf S.; Stanlie, Andre; Mondal, Samiran; Honjo, Tasuku; Begum, Noorzahan

doi:10.1073/pnas.1402391111

Cited by 23 publications

(38 citation statements)

References 60 publications

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“…More importantly, APE1's endonuclease activity is not required for the AIDinduced DNA cleavage, in parallel with the findings that UNG is dispensable for the DNA cleavage step during SHM (56,57) and CSR (39,58). Recently, we reported that UNG enhances AIDdependent S-S synapse formation by recruiting p53-binding protein 1 and DNA-dependent protein kinase, catalytic subunit (49). We provide the evidence indicating that APE1 processes the broken ends of S-region DNA for the binding of Ku80 and mediates efficient S-S synapse formation during CSR.…”

Section: Discussionsupporting

confidence: 65%

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APE1 is dispensable for S-region cleavage but required for its repair in class switch recombination

Husain

et al. 2014

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

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Activation-induced cytidine deaminase (AID) is essential for antibody diversification, namely somatic hypermutation (SHM) and class switch recombination (CSR). The deficiency of apurinic/ apyrimidinic endonuclease 1 (Ape1) in CH12F3-2A B cells reduces CSR to ∼20% of wild-type cells, whereas the effect of APE1 loss on SHM has not been examined. Here we show that, although APE1's endonuclease activity is important for CSR, it is dispensable for SHM as well as IgH/c-myc translocation. Importantly, APE1 deficiency did not show any defect in AID-induced S-region break formation, but blocked both the recruitment of repair protein Ku80 to the S region and the synapse formation between Sμ and Sα. Knockdown of end-processing factors such as meiotic recombination 11 homolog (MRE11) and carboxy-terminal binding protein (CtBP)-interacting protein (CtIP) further reduced the remaining CSR in Ape1-null CH12F3-2A cells. Together, our results show that APE1 is dispensable for SHM and AID-induced DNA breaks and may function as a DNA end-processing enzyme to facilitate the joining of broken ends during CSR.class switch recombination | somatic hypermutation | DNA cleavage | DNA synapse formation | end processing

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Section: Discussionsupporting

confidence: 65%

“…UNG suppresses SHM by recruiting faithful BER pathway components at cleaved DNA loci, with competition against error-prone polymerases (49). In contrast, APE1 is not involved in the correct repair after cleavage during SHM because SHM occurs similarly between vector and WT transfectants of Ape1-null CH12F3-2A cells.…”

Section: Discussionmentioning

confidence: 99%

APE1 is dispensable for S-region cleavage but required for its repair in class switch recombination

Husain

et al. 2014

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

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“…In CSR, AID is targeted to an upstream (donor) S and a downstream (acceptor) S regions by 14-3-3 adaptors, which display high affinities for 5′-AGCT-3′ repeats, as recurring in all S regions, as well as for H3K9acS10ph histone posttranslational modifications, as induced specifically in the donor and acceptor S regions – these S regions also undergo germline I H -S-C H transcription initiated upon activation of their respective upstream intervening I H promoter (4, 5). High densities of deoxyuracils, as generated through AID-mediated DNA deamination, are processed by uracil DNA glycosylase (Ung) recruited by Rev1 (6-8), leading to the generation of S region (DSBs), which are obligatory CSR intermediates. Repair of such DSBs results in looping out of the intervening DNA as an S circle, formation of a S-S junction and juxtaposition of the expressed V H DJ H DNA to the downstream C H DNA.…”

Section: Introductionmentioning

confidence: 99%

B Cell Rab7 Mediates Induction of Activation-Induced Cytidine Deaminase Expression and Class-Switching in T-Dependent and T-Independent Antibody Responses

Pone

Lam

Lou

et al. 2015

The Journal of Immunology

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Class switch DNA recombination (CSR) is central to the maturation of the antibody response, as it diversifies antibody effector functions. Like somatic hypermutation, CSR requires AID, whose expression is restricted to B cells, as induced by CD40 engagement or dual TLR-BCR engagement (primary CSR-inducing stimuli). By constructing conditional knockout Igh+/Cγ1-creRab7fl/fl mice, we identified a B cell-intrinsic role for Rab7, a small GTPase involved in intracellular membrane functions, in mediating AID induction and CSR. Igh+/Cγ1-creRab7fl/fl mice displayed normal B and T cell development, and were deficient in Rab7 only in B cells undergoing IghCγ1-cre Iγ1-Sγ1-Cγ1-cre transcription, as induced – like Igh germline Iγ1-Sγ1-Cγ1 and Iε-Sε-Cε transcription – by IL-4 in conjunction with a primary CSR-inducing stimulus. These mice could not mount T-independent or T-dependent class-switched IgG1 or IgE responses, while maintaining normal IgM levels. Igh+/Cγ1-creRab7fl/fl B cells showed, in vivo and in vitro, normal proliferation and survival, normal Blimp-1 expression and plasma cell differentiation, as well as intact activation of the non-canonical NF-κB, p38 kinase and ERK1/2 kinase pathways. They, however, were defective in AID expression and CSR in vivo and in vitro, as induced by CD40 engagement or dual TLR1/2-, TLR4-, TLR7- or TLR9-BCR engagement. In Igh+/Cγ1-creRab7fl/fl B cells, CSR was rescued by enforced AID expression. These findings, together with our demonstration that Rab7 mediated canonical NF-κB activation, as critical to AID induction, outline a novel role of Rab7 in signaling pathways that lead to AID expression and CSR, likely by promoting assembly of signaling complexes along intracellular membranes.

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“…AID induces DNA breaks at the variable (V) and switch (S) regions during SHM and CSR, respectively. Most of the mutations produced during SHM are introduced by errorprone DNA synthesis during single-strand break (SSB) repair (3,4). In contrast, CSR requires the conversion of SSBs to doublestrand breaks (DSBs), followed by recombination between two DSB ends located in the donor and acceptor S regions (5,6).…”

mentioning

confidence: 99%

Identification of DNA cleavage- and recombination-specific hnRNP cofactors for activation-induced cytidine deaminase

Begum

Mondal

et al. 2015

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

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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 RNAediting 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.class switch recombination | somatic hypermutation | activation-induced cytidine deaminase | B cell | IgH A ntigen-stimulated mature B cells express activation-induced cytidine deaminase (AID), an essential enzyme for somatic hypermutation (SHM) and class switch recombination (CSR) at the Ig locus (1, 2). AID induces DNA breaks at the variable (V) and switch (S) regions during SHM and CSR, respectively. Most of the mutations produced during SHM are introduced by errorprone DNA synthesis during single-strand break (SSB) repair (3, 4). In contrast, CSR requires the conversion of SSBs to doublestrand breaks (DSBs), followed by recombination between two DSB ends located in the donor and acceptor S regions (5, 6). The entire process of CSR is accomplished through elaborate DNArepair processes involving S-S synapse formation and end-joining.The mechanism by which AID functions differently in DNA cleavage and recombination at different loci remains unclear. Functional studies of a large number of AID mutants revealed that the N-terminal AID mutations impair SHM and CSR, indicating that the AID N terminus, which also possesses a bipartite nuclear-localization signal, is required for DNA cleavage in both SHM and CSR (7-9). On the other hand, C-terminal AID mutations suppressed the recombination activity of CSR but had no effect on SHM, indicating that the C terminus of AID, which contains a nuclear-export signal, is required for the recombination activity associated specifically with CSR (7, 9, 10). Indeed, recent studies showed that defects in the AID C terminus compromise DNA end-joining and S-S synapse formation without perturbing DNA breakage at either the V or S region (11, 12), also suggesting a specific role for the AID C terminus in the recombination step of CSR. Given AID's small size (198 resi...

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Differential regulation of S-region hypermutation and class-switch recombination by noncanonical functions of uracil DNA glycosylase

Cited by 23 publications

References 60 publications

APE1 is dispensable for S-region cleavage but required for its repair in class switch recombination

APE1 is dispensable for S-region cleavage but required for its repair in class switch recombination

B Cell Rab7 Mediates Induction of Activation-Induced Cytidine Deaminase Expression and Class-Switching in T-Dependent and T-Independent Antibody Responses

Identification of DNA cleavage- and recombination-specific hnRNP cofactors for activation-induced cytidine deaminase

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