DSB repair pathway choice is regulated by recruitment of 53BP1 through cell cycle-dependent regulation of Sp1

Loss of p53, a transcription factor activated by cellular stress, is a frequent event in cancer. The role of p53 in tumour suppression is largely attributed to cell fate decisions. Here, we provide evidence supporting a novel role for p53 in the regulation of DNA double-strand break (DSB) repair pathway choice. 53BP1, another tumour suppressor, was initially identified as p53 Binding Protein 1, and has been shown to inhibit DNA end resection, thereby stimulating non-homologous end joining (NHEJ). Yet another tumour suppressor, BRCA1, reciprocally promotes end resection and homologous recombination (HR). Here, we show that in both human and mouse cells, the absence of p53 results in impaired 53BP1 focal recruitment to sites of DNA damage induced by ionizing radiation. This effect is largely independent of cell cycle phase and the extent of DNA damage. In p53-deficient cells, diminished localization of 53BP1 is accompanied by a reciprocal increase in BRCA1 recruitment to DSBs. Consistent with these findings, we demonstrate that DSB repair via NHEJ is abrogated, while repair via homology-directed repair (HDR) is stimulated. Overall, we propose that in addition to its role as an ‘effector’ protein in the DNA damage response, p53 plays a role in the regulation of DSB repair pathway choice.

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Importance of the cell cycle phase for the choice of the appropriate DSB repair pathway, for genome stability mintenance: the trans-S double-strand break repair model

Cell Cycle ◽

10.4161/cc.7.1.5149 ◽

2008 ◽

Vol 7 (1) ◽

pp. 33-38 ◽

Cited By ~ 64

Author(s):

Fabien Delacôte ◽

Bernard S. Lopez

Keyword(s):

Cell Cycle ◽

Genome Stability ◽

Strand Break ◽

Double Strand Break ◽

Cell Cycle Phase ◽

Double Strand Break Repair ◽

Cycle Phase ◽

Repair Pathway ◽

Dsb Repair ◽

Break Repair

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ATM and CDK2 control chromatin remodeler CSB to inhibit RIF1 in DSB repair pathway choice

Nature Communications ◽

10.1038/s41467-017-02114-x ◽

2017 ◽

Vol 8 (1) ◽

Cited By ~ 18

Author(s):

Nicole L. Batenburg ◽

John R. Walker ◽

Sylvie M. Noordermeer ◽

Nathalie Moatti ◽

Daniel Durocher ◽

...

Keyword(s):

Repair Pathway ◽

Chromatin Remodeler ◽

Dsb Repair ◽

Pathway Choice

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The Impact of Nuclear Organization and Homolgous Recombination in Repair of DNA Damage Introduced By Aid during Class Switch Recombination

Blood ◽

10.1182/blood.v124.21.2738.2738 ◽

2014 ◽

Vol 124 (21) ◽

pp. 2738-2738

Author(s):

Pedro P Rocha ◽

Yi Fu ◽

JungHyun Kim ◽

Jane Skok

Keyword(s):

Cell Cycle ◽

Mouse Model ◽

B Cell ◽

Class Switch Recombination ◽

Enzyme Activation ◽

G1 Phase ◽

Repair Pathway ◽

Class Switch ◽

Igh Locus ◽

Pathway Choice

Abstract Class Switch Recombination (CSR) involves the introduction of double stranded breaks (DSBs) at the switch regions of the immunoglulin heavy chain (Igh) locus by the enzyme Activation Cytidine Deaminse (AID). AID can also act as a general mutator targeting other loci in the genome which can then either be repaired faithfully or in an error-prone fashion introducing mutations and potentially initiating B cell lymphoma. The factors contributing to the choice of repair pathway are not fully understood. Here we tested the hypothesis that repair pathway choice is influenced by differential accessibility and expression levels of target loci across cell cycle. More specifically in the context of CSR we tested whether differential regulation of gene accessibility across cell cycle is an important determinant for AID binding and subsequent repair pathway choice as different repair pathways predominate at different stages of cell cycle. Using 3D-FISH in conjunction with Immunofluorescence we observed that AID target genes that are faithfully repaired are more accessible (found in euchromatic regions) in the G2 phase of the cell cycle then genes that are frequently mutated. In contrast, those genes which are repaired in an error prone fashion are more accessible in the G1 phase of cell cycle. Since Homologous Recombination mediated repair (HR), which is a faithful repair mechanism, occurs in G2 we speculate that accessibility of these genes at this stage of cell cycle facilitates action by this repair pathway. Conversely, genes that are more accessible during the G1 phase of cell cycle will be repaired by the non-homologous end joining (NHEJ) repair pathway and therefore are more likely to be mutated. Thus, HR could be the pathway by which faithful repair is accomplished and use of the NHEJ pathway on the other hand could contribute to the introduction of dangerous DNA mutations that might lead to B cell transformation and cancer. To connect differences in accessibility with repair pathway usage, we used a mouse model carrying a hypomorphic mutation in BRCA2, a protein involved in HR. This is the first mouse model impaired in HR that eludes embryonic lethality and allows inspection of the role of this pathway in maintaining genomic stability in splenocytes undergoing CSR. Our preliminary investigations indicate that in Brca2 mutant B cells not only is the integrity of fathfully repaired loci compromised, but the Igh locus is also damaged. Taken together these results support our hypothesis and further indicate that the HR pathway is involved in repairing Igh. Given that approximately 95% of lymphomas are of B cell origin and many of these are associated with AID mediated breaks, it is crucial for us to understand the factors that influence targeting and repair. Disclosures No relevant conflicts of interest to declare.

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SCFSKP2 regulates APC/CCDH1-mediated degradation of CTIP to adjust DNA-end resection in G2-phase

Cell Death and Disease ◽

10.1038/s41419-020-02755-9 ◽

2020 ◽

Vol 11 (7) ◽

Author(s):

Fanghua Li ◽

Emil Mladenov ◽

Sharif Mortoga ◽

George Iliakis

Keyword(s):

Cell Cycle ◽

Cell Survival ◽

S Phase ◽

Repair Pathway ◽

End Joining ◽

Alternative End Joining ◽

G2 Phase ◽

Dna End Resection ◽

Cycle Dependent ◽

End Resection

Abstract The cell cycle-dependent engagement of DNA-end resection at DSBs is regulated by phosphorylation of CTIP by CDKs, the central regulators of cell cycle transitions. Cell cycle transitions are also intimately regulated by protein degradation via two E3 ubiquitin ligases: SCFSKP2 and APC/CCDH1 complex. Although APC/CCDH1 regulates CTIP in G1– and G2-phase, contributions by SCFSKP2 have not been reported. We demonstrate that SCFSKP2 is a strong positive regulator of resection. Knockdown of SKP2, fully suppresses resection in several cell lines. Notably, this suppression is G2-phase specific and is not observed in S-phase or G1–phase cells. Knockdown of SKP2 inactivates SCFSKP2 causing APC/CCDH1 activation, which degrades CTIP. The stabilizing function of SCFSKP2 on CTIP promotes resection and supports gene conversion (GC), alternative end joining (alt-EJ) and cell survival. We propose that CDKs and SCFSKP2-APC/CCDH1 cooperate to regulate resection and repair pathway choice at DSBs in G2-phase.

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