Low CDK Activity and Enhanced Degradation by APC/C<sup>CDH1</sup> Abolishes CtIP Activity and Alt-EJ in Quiescent Cells
Alt-EJ is an error-prone DNA double-strand break (DSBs) repair pathway coming to the fore when first-line repair pathways, c-NHEJ and HR, are defective or fail. It is thought to benefit from DNA end-resection—a process whereby 3′ single-stranded DNA-tails are generated—initiated by the CtIP/MRE11-RA...
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MDPI AG
2023-06-01
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| Series: | Cells |
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| Online Access: | https://www.mdpi.com/2073-4409/12/11/1530 |
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| author | Fanghua Li Emil Mladenov Yanjie Sun Aashish Soni Martin Stuschke Beate Timmermann George Iliakis |
| author_facet | Fanghua Li Emil Mladenov Yanjie Sun Aashish Soni Martin Stuschke Beate Timmermann George Iliakis |
| author_sort | Fanghua Li |
| collection | DOAJ |
| description | Alt-EJ is an error-prone DNA double-strand break (DSBs) repair pathway coming to the fore when first-line repair pathways, c-NHEJ and HR, are defective or fail. It is thought to benefit from DNA end-resection—a process whereby 3′ single-stranded DNA-tails are generated—initiated by the CtIP/MRE11-RAD50-NBS1 (MRN) complex and extended by EXO1 or the BLM/DNA2 complex. The connection between alt-EJ and resection remains incompletely characterized. Alt-EJ depends on the cell cycle phase, is at maximum in G<sub>2</sub>-phase, substantially reduced in G<sub>1</sub>-phase and almost undetectable in quiescent, G<sub>0</sub>-phase cells. The mechanism underpinning this regulation remains uncharacterized. Here, we compare alt-EJ in G<sub>1</sub>- and G<sub>0</sub>-phase cells exposed to ionizing radiation (IR) and identify CtIP-dependent resection as the key regulator. Low levels of CtIP in G<sub>1</sub>-phase cells allow modest resection and alt-EJ, as compared to G<sub>2</sub>-phase cells. Strikingly, CtIP is undetectable in G<sub>0</sub>-phase cells owing to APC/C-mediated degradation. The suppression of CtIP degradation with bortezomib or CDH1-depletion rescues CtIP and alt-EJ in G<sub>0</sub>-phase cells. CtIP activation in G<sub>0</sub>-phase cells also requires CDK-dependent phosphorylation by any available CDK but is restricted to CDK4/6 at the early stages of the normal cell cycle. We suggest that suppression of mutagenic alt-EJ in G<sub>0</sub>-phase is a mechanism by which cells of higher eukaryotes maintain genomic stability in a large fraction of non-cycling cells in their organisms. |
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| issn | 2073-4409 |
| language | English |
| last_indexed | 2024-03-11T03:09:59Z |
| publishDate | 2023-06-01 |
| publisher | MDPI AG |
| record_format | Article |
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| spelling | doaj.art-d417227a457c454ba99e032b1b5327122023-11-18T07:41:18ZengMDPI AGCells2073-44092023-06-011211153010.3390/cells12111530Low CDK Activity and Enhanced Degradation by APC/C<sup>CDH1</sup> Abolishes CtIP Activity and Alt-EJ in Quiescent CellsFanghua Li0Emil Mladenov1Yanjie Sun2Aashish Soni3Martin Stuschke4Beate Timmermann5George Iliakis6Institute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, GermanyInstitute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, GermanyInstitute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, GermanyInstitute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, GermanyDivision of Experimental Radiation Biology, Department of Radiation Therapy, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, GermanyDepartment of Particle Therapy, University Hospital Essen, West German Proton Therapy Centre Essen (WPE), West German Cancer Center (WTZ), German Cancer Consortium (DKTK), 45147 Essen, GermanyInstitute of Medical Radiation Biology, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, GermanyAlt-EJ is an error-prone DNA double-strand break (DSBs) repair pathway coming to the fore when first-line repair pathways, c-NHEJ and HR, are defective or fail. It is thought to benefit from DNA end-resection—a process whereby 3′ single-stranded DNA-tails are generated—initiated by the CtIP/MRE11-RAD50-NBS1 (MRN) complex and extended by EXO1 or the BLM/DNA2 complex. The connection between alt-EJ and resection remains incompletely characterized. Alt-EJ depends on the cell cycle phase, is at maximum in G<sub>2</sub>-phase, substantially reduced in G<sub>1</sub>-phase and almost undetectable in quiescent, G<sub>0</sub>-phase cells. The mechanism underpinning this regulation remains uncharacterized. Here, we compare alt-EJ in G<sub>1</sub>- and G<sub>0</sub>-phase cells exposed to ionizing radiation (IR) and identify CtIP-dependent resection as the key regulator. Low levels of CtIP in G<sub>1</sub>-phase cells allow modest resection and alt-EJ, as compared to G<sub>2</sub>-phase cells. Strikingly, CtIP is undetectable in G<sub>0</sub>-phase cells owing to APC/C-mediated degradation. The suppression of CtIP degradation with bortezomib or CDH1-depletion rescues CtIP and alt-EJ in G<sub>0</sub>-phase cells. CtIP activation in G<sub>0</sub>-phase cells also requires CDK-dependent phosphorylation by any available CDK but is restricted to CDK4/6 at the early stages of the normal cell cycle. We suggest that suppression of mutagenic alt-EJ in G<sub>0</sub>-phase is a mechanism by which cells of higher eukaryotes maintain genomic stability in a large fraction of non-cycling cells in their organisms.https://www.mdpi.com/2073-4409/12/11/1530ionizing radiationDNA repairrepair of DNA double-strand breaksalt-EJDNA end-resectionCtIP |
| spellingShingle | Fanghua Li Emil Mladenov Yanjie Sun Aashish Soni Martin Stuschke Beate Timmermann George Iliakis Low CDK Activity and Enhanced Degradation by APC/C<sup>CDH1</sup> Abolishes CtIP Activity and Alt-EJ in Quiescent Cells Cells ionizing radiation DNA repair repair of DNA double-strand breaks alt-EJ DNA end-resection CtIP |
| title | Low CDK Activity and Enhanced Degradation by APC/C<sup>CDH1</sup> Abolishes CtIP Activity and Alt-EJ in Quiescent Cells |
| title_full | Low CDK Activity and Enhanced Degradation by APC/C<sup>CDH1</sup> Abolishes CtIP Activity and Alt-EJ in Quiescent Cells |
| title_fullStr | Low CDK Activity and Enhanced Degradation by APC/C<sup>CDH1</sup> Abolishes CtIP Activity and Alt-EJ in Quiescent Cells |
| title_full_unstemmed | Low CDK Activity and Enhanced Degradation by APC/C<sup>CDH1</sup> Abolishes CtIP Activity and Alt-EJ in Quiescent Cells |
| title_short | Low CDK Activity and Enhanced Degradation by APC/C<sup>CDH1</sup> Abolishes CtIP Activity and Alt-EJ in Quiescent Cells |
| title_sort | low cdk activity and enhanced degradation by apc c sup cdh1 sup abolishes ctip activity and alt ej in quiescent cells |
| topic | ionizing radiation DNA repair repair of DNA double-strand breaks alt-EJ DNA end-resection CtIP |
| url | https://www.mdpi.com/2073-4409/12/11/1530 |
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