scholarly journals MBD4 Facilitates Immunoglobulin Class Switch Recombination

2016 ◽  
Vol 37 (2) ◽  
Author(s):  
Fernando Grigera ◽  
Robert Wuerffel ◽  
Amy L. Kenter
Keyword(s):  
Excision Repair ◽  
Cytidine Deaminase ◽  
Ectopic Expression ◽  
Class Switch Recombination ◽  
Double Strand Breaks ◽  
Dna Double Strand Breaks ◽  
Strand Breaks ◽  
Class Switch ◽  
Activation Induced Cytidine Deaminase ◽  
Base Excision

ABSTRACT Immunoglobulin heavy chain class switch recombination (CSR) requires targeted formation of DNA double-strand breaks (DSBs) in repetitive switch region elements followed by ligation between distal breaks. The introduction of DSBs is initiated by activation-induced cytidine deaminase (AID) and requires base excision repair (BER) and mismatch repair (MMR). The BER enzyme methyl-CpG binding domain protein 4 (MBD4) has been linked to the MMR pathway through its interaction with MutL homologue 1 (MLH1). We find that when Mbd4 exons 6 to 8 are deleted in a switching B cell line, DSB formation is severely reduced and CSR frequency is impaired. Impaired CSR can be rescued by ectopic expression of Mbd4. Mbd4 deficiency yields a deficit in DNA end processing similar to that found in MutS homologue 2 (Msh2)- and Mlh1-deficient B cells. We demonstrate that microhomology-rich S-S junctions are enriched in cells in which Mbd4 is deleted. Our studies suggest that Mbd4 is a component of MMR-directed DNA end processing.

scholarly journals The ATPase activity of MLH1 is required to orchestrate DNA double-strand breaks and end processing during class switch recombination

2012 ◽  
Vol 209 (4) ◽  
pp. 671-678 ◽  
Author(s):  
Richard Chahwan ◽  
Johanna M.M. van Oers ◽  
Elena Avdievich ◽  
Chunfang Zhao ◽  
Winfried Edelmann ◽  
...  
Keyword(s):  
Atpase Activity ◽  
Somatic Hypermutation ◽  
Cytidine Deaminase ◽  
Point Mutations ◽  
Class Switch Recombination ◽  
Double Strand Breaks ◽  
Atpase Domain ◽  
Dna Double Strand Breaks ◽  
Strand Breaks ◽  
Class Switch

Antibody diversification through somatic hypermutation (SHM) and class switch recombination (CSR) are similarly initiated in B cells with the generation of U:G mismatches by activation-induced cytidine deaminase but differ in their subsequent mutagenic consequences. Although SHM relies on the generation of nondeleterious point mutations, CSR depends on the production of DNA double-strand breaks (DSBs) and their adequate recombination through nonhomologous end joining (NHEJ). MLH1, an ATPase member of the mismatch repair (MMR) machinery, is emerging as a likely regulator of whether a U:G mismatch progresses toward mutation or DSB formation. We conducted experiments on cancer modeled ATPase-deficient MLH1G67R knockin mice to determine the function that the ATPase domain of MLH1 mediates in SHM and CSR. Mlh1GR/GR mice displayed a significant decrease in CSR, mainly attributed to a reduction in the generation of DSBs and diminished accumulation of 53BP1 at the immunoglobulin switch regions. However, SHM was normal in these mice, which distinguishes MLH1 from upstream members of the MMR pathway and suggests a very specific role of its ATPase-dependent functions during CSR. In addition, we show that the residual switching events still taking place in Mlh1GR/GR mice display unique features, suggesting a role for the ATPase activity of MLH1 beyond the activation of the endonuclease functions of its MMR partner PMS2. A preference for switch junctions with longer microhomologies in Mlh1GR/GR mice suggests that through its ATPase activity, MLH1 also has an impact in DNA end processing, favoring canonical NHEJ downstream of the DSB. Collectively, our study shows that the ATPase domain of MLH1 is important to transmit the CSR signaling cascade both upstream and downstream of the generation of DSBs.

scholarly journals Involvement of Artemis in nonhomologous end-joining during immunoglobulin class switch recombination

2008 ◽  
Vol 205 (13) ◽  
pp. 3031-3040 ◽  
Author(s):  
Likun Du ◽  
Mirjam van der Burg ◽  
Sergey W. Popov ◽  
Ashwin Kotnis ◽  
Jacques J.M. van Dongen ◽  
...  
Keyword(s):  
Class Switch Recombination ◽  
Double Strand Breaks ◽  
Nonhomologous End Joining ◽  
Igg Subclass ◽  
Dna Double Strand Breaks ◽  
End Joining ◽  
Strand Breaks ◽  
Immunoglobulin Class ◽  
Class Switch ◽  
Human B Cells

DNA double-strand breaks (DSBs) introduced in the switch (S) regions are intermediates during immunoglobulin class switch recombination (CSR). These breaks are subsequently recognized, processed, and joined, leading to recombination of the two S regions. Nonhomologous end-joining (NHEJ) is believed to be the principle mechanism involved in DSB repair during CSR. One important component in NHEJ, Artemis, has however been considered to be dispensable for efficient CSR. In this study, we have characterized the S recombinational junctions from Artemis-deficient human B cells. Sμ–Sα junctions could be amplified from all patients tested and were characterized by a complete lack of “direct” end-joining and a remarkable shift in the use of an alternative, microhomology-based end-joining pathway. Sμ–Sγ junctions could only be amplified from one patient who carries “hypomorphic” mutations. Although these Sμ–Sγ junctions appear to be normal, a significant increase of an unusual type of sequential switching from immunoglobulin (Ig)M, through one IgG subclass, to a different IgG subclass was observed, and the Sγ–Sγ junctions showed long microhomologies. Thus, when the function of Artemis is impaired, varying modes of CSR junction resolution may be used for different S regions. Our findings strongly link Artemis to the predominant NHEJ pathway during CSR.

scholarly journals Nonhomologous end joining of complex DNA double-strand breaks with proximal thymine glycol and interplay with base excision repair

DNA Repair ◽  
2016 ◽  
Vol 41 ◽  
pp. 16-26 ◽  
Author(s):  
Mohammed Almohaini ◽  
Sri Lakshmi Chalasani ◽  
Duaa Bafail ◽  
Konstantin Akopiants ◽  
Tong Zhou ◽  
...  
Keyword(s):  
Base Excision Repair ◽  
Excision Repair ◽  
Double Strand Breaks ◽  
Nonhomologous End Joining ◽  
Dna Double Strand Breaks ◽  
End Joining ◽  
Strand Breaks ◽  
Thymine Glycol ◽  
Base Excision

scholarly journals DNA polymerase β is able to repair breaks in switch regions and plays an inhibitory role during immunoglobulin class switch recombination

2007 ◽  
Vol 204 (7) ◽  
pp. 1677-1689 ◽  
Author(s):  
Xiaoming Wu ◽  
Janet Stavnezer
Keyword(s):  
B Cells ◽  
Dna Polymerase ◽  
Excision Repair ◽  
Cytidine Deaminase ◽  
Class Switch Recombination ◽  
Strand Break ◽  
Dna Polymerase Β ◽  
Single Strand Break ◽  
Class Switch ◽  
Base Excision

Immunoglobulin (Ig) class switch recombination (CSR) is initiated by activation-induced cytidine deaminase (AID), which converts cytosines to uracils in switch (S) regions. Subsequent excision of dU by uracil DNA glycosylase (UNG) of the base excision repair (BER) pathway is required to obtain double-strand break (DSB) intermediates for CSR. Since UNG normally initiates faithful repair, it is unclear how the AID-instigated S region lesions are converted into DSBs rather than correctly repaired by BER. Normally, DNA polymerase β (Polβ) would replace the dC deaminated by AID, leading to correct repair of the single-strand break, thereby preventing CSR. We address the question of whether Polβ might be specifically down-regulated during CSR or inhibited from accessing the AID-instigated lesions, or whether the numerous AID-initiated S region lesions might simply overwhelm the BER capacity. We find that nuclear Polβ levels are induced upon activation of splenic B cells to undergo CSR. When Polβ−/− B cells are activated to switch in culture, they switch slightly better to IgG2a, IgG2b, and IgG3 and have more S region DSBs and mutations than wild-type controls. We conclude that Polβ attempts to faithfully repair S region lesions but fails to repair them all.

scholarly journals Molecular Mechanisms of H. pylori Induced DNA Double-Strand Breaks

2018 ◽  
Author(s):  
Dawit Kidane
Keyword(s):  
Genomic Instability ◽  
Oxidative Dna Damage ◽  
Molecular Mechanisms ◽  
Excision Repair ◽  
Current Knowledge ◽  
Double Strand Breaks ◽  
Dna Double Strand Breaks ◽  
Strand Breaks ◽  
Base Excision ◽  
H Pylori

Infections contribute to carcinogenesis through inflammation-related mechanisms. It is well established that H. pylori infection is an etiological factor in gastric carcinogenesis. However, the mechanism through which H. pylori infection contributes to the development of gastric cancer has not been fully elucidated. H. pylori-associated chronic inflammation is linked to genomic instability via reactive oxygen and nitrogen species (RONS). In this article, we summarize the current knowledge of H. pylori-induced double strand breaks (DSBs). Further, we will provide mechanistic insight into how processing of oxidative DNA damage via base excision repair (BER) leads to double strand breaks (DSBs). We review the recent progress how H. pylori infection triggers NF-kB /iNOS versus NF-kB/nucleotide excision repair (NER) axis mediated DSBs to drive genomic instability. Taken together, this review discusses current findings related to DSBs and their implications for the mechanisms of DSB repair.

Antimetabolite Radiosensitizers

2007 ◽  
Vol 25 (26) ◽  
pp. 4043-4050 ◽  
Author(s):  
Donna S. Shewach ◽  
Theodore S. Lawrence
Keyword(s):  
Excision Repair ◽  
Growth Factor Receptor ◽  
Double Strand Breaks ◽  
Egfr Inhibitors ◽  
Dna Double Strand Breaks ◽  
Strand Breaks ◽  
Solid Malignancies ◽  
Target Dna ◽  
Epidermal Growth ◽  
Base Excision

Radiosensitization with antimetabolites has improved clinical outcome for patients with solid malignancies, especially cancers of the GI tract, cervix, and head and neck. Fluorouracil (FU) and hydroxyurea have been widely used clinically during the last four decades, and promising results have been observed more recently with gemcitabine. Although the antimetabolites all target DNA replication, they differ with respect to the mechanisms by which they produce radiosensitization. The antimetabolite radiosensitizers may inhibit thymidylate synthase (TS) or ribonucleotide reductase, and the nucleoside/nucleobase analogs can be incorporated into DNA. Radiosensitization can result from chemotherapy-induced increase in DNA double-strand breaks or inhibition of their repair. Studies of repair pathways involved in radiosensitization with antimetabolites implicate base excision repair with the TS inhibitors, homologous recombination with gemcitabine, and mismatch repair with FU and gemcitabine. Gemcitabine can also stimulate epidermal growth factor receptor (EGFR) phosphorylation; inhibiting this effect with EGFR inhibitors can potentiate cytotoxicity and radiosensitization. Additional work is necessary to determine more precisely the processes by which antimetabolites act as radiation sensitizers and to define the optimal sequencing of these agents with EGFR inhibitors to provide better guidance for clinical protocols combining these drugs with radiotherapy.

scholarly journals OGG1 Inhibitor TH5487 Alters OGG1 Chromatin Dynamics and Prevents Incisions

Biomolecules ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1483
Author(s):  
Bishoy M. F. Hanna ◽  
Thomas Helleday ◽  
Oliver Mortusewicz
Keyword(s):  
Excision Repair ◽  
Double Strand Breaks ◽  
Dna Glycosylase ◽  
Chromatin Binding ◽  
Dna Double Strand Breaks ◽  
Chromatin Dynamics ◽  
Strand Breaks ◽  
Pathological Conditions ◽  
Base Excision

8-oxoguanine DNA glycosylase (OGG1) is the main DNA glycosylase responsible for the excision of 7,8-dihydro-8-oxoguanine (8-oxoG) from duplex DNA to initiate base excision repair. This glycosylase activity is relevant in many pathological conditions including cancer, inflammation, and neurodegenerative diseases. To have a better understanding of the role of OGG1, we previously reported TH5487, a potent active site inhibitor of OGG1. Here, we further investigate the consequences of inhibiting OGG1 with TH5487. TH5487 treatment induces accumulation of genomic 8-oxoG lesions. Furthermore, it impairs the chromatin binding of OGG1 and results in lower recruitment of OGG1 to regions of DNA damage. Inhibiting OGG1 with TH5487 interferes with OGG1′s incision activity, resulting in fewer DNA double-strand breaks in cells exposed to oxidative stress. This study validates TH5487 as a potent OGG1 inhibitor that prevents the repair of 8-oxoG and alters OGG1–chromatin dynamics and OGG1′s recruitment kinetics.

scholarly journals DNA-PKcs and Artemis function in the end-joining phase of immunoglobulin heavy chain class switch recombination

2008 ◽  
Vol 205 (3) ◽  
pp. 557-564 ◽  
Author(s):  
Sonia Franco ◽  
Michael M. Murphy ◽  
Gang Li ◽  
Tiffany Borjeson ◽  
Cristian Boboila ◽  
...  
Keyword(s):  
B Cells ◽  
Cytidine Deaminase ◽  
Class Switch Recombination ◽  
Dna Double Strand Breaks ◽  
End Joining ◽  
Strand Breaks ◽  
Class Switch ◽  
Chromosomal Breaks ◽  
Dependent Protein ◽  
Activation Conditions

The DNA-dependent protein kinase catalytic subunit (DNA-PKcs) and Artemis are classical nonhomologous DNA end-joining (C-NHEJ) factors required for joining a subset of DNA double-strand breaks (DSB), particularly those requiring end processing. In mature B cells, activation-induced cytidine deaminase (AID) initiates class switch recombination (CSR) by introducing lesions into S regions upstream of two recombining CH exons, which are processed into DSBs and rejoined by C-NHEJ to complete CSR. The function of DNA-PKcs in CSR has been controversial with some reports but not others showing that DNA-PKcs–deficient mice are significantly impaired for CSR. Artemis-deficient B cells reportedly undergo CSR at normal levels. Overall, it is still not known whether there are any CSR-associated DSBs that require DNA-PKcs and/or Artemis to be joined. Here, we have used an immunoglobulin (Ig)H locus-specific fluorescent in situ hybridization assay to unequivocally demonstrate that both DNA-PKcs and, unexpectedly, Artemis are necessary for joining a subset of AID-dependent DSBs. In the absence of either factor, B cells activated for CSR frequently generate AID-dependent IgH locus chromosomal breaks and translocations. We also find that under specific activation conditions, DNA-PKcs−/− B cells with chromosomal breaks are eliminated or at least prevented from progressing to metaphase via a p53-dependent response.

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