Chk1 is dispensable for G2 arrest in response to sustained DNA damage when the ATM/p53/p21 pathway is functional
Abstract
In the presence of sustained DNA damage occurring in S-phase or G2, normal cells arrest before mitosis and eventually become senescent. The checkpoint kinases Chk1/Chk2 and the CDK inhibitor p21 are known to have important complementary roles in this process, in G2 arrest and cell cycle exit, respectively. However, additional checkpoint roles have been reported for these regulators and it is not clear to what extent their functions are redundant. Here we compared the respective roles of Chk1, Chk2 and p21 in DNA damage-induced G2 arrest in normal human fibroblasts, normal epithelial cells and frequently used p53 proficient cancer cells. We show that in normal cells, Chk1, but not Chk2, is involved in G2 arrest whereas neither are essential. In contrast, p21 is required. However, Chk1, but not Chk2, becomes necessary for arrest in U2OS osteosarcoma cells. We find that their ATM/p53/p21 response in G2 phase is defective, like in other cancer cells with wild-type p53, and conclude that cross-talk between the Chk1 and p21 pathways allows them to switch dependency for G2 arrest onto Chk1. Using the specific ATM inhibitor KU-55933 we confirm the essential role of ATM in the induction of p21 for G2 arrest of normal cells. Efficient p21 induction is required for nuclear sequestration of inactive cyclin B1-Cdk1 complexes preceding irreversible cell cycle exit in G2. Our results demonstrate that p21 is able to fulfill the Chk1 functions in G2 arrest under continuous genotoxic stress, which has important implications for cancer chemotherapy.
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Chk2 does not appear essential for G2 arrest; damaged cells more likely progress into mitosis because of inefficient Chk1 activation and/or weak p21 induction.
“A major caveat of this interpretation is that Chk2 does not seem to play an essential role in G2 arrest 84,85,72 and it is more likely that damaged cells progress into mitosis due to inefficient Chk1 activation 86 and/or lack of robust p21 induction.”
From Senescence from G2 arrest, revisited (2015) · cites this paper as [72]
In non-transformed cells, DNA damage-induced Chk2 phosphorylation at Thr68 is very transient and is not the best indicator of Chk2 activation.
“It should be noted that, at least in non-transformed cells, DNA damage-induced Chk2 phosphorylation at Thr68 is very transient 72 and hence not the best indicator of Chk2 activation (as opposed to SDS-PAGE shift).”
From Senescence from G2 arrest, revisited (2015) · cites this paper as [72]
In U2OS cells, p21 induction is impaired by an inefficient ATM response and probably by a Wip1 phosphatase mutation that interferes with p53 activation.
“In this p53/pRb proficient cell line, p21 induction is impaired due to inefficient ATM response 72 and, probably, mutation of the Wip1 phosphatase that interferes with p53 activation.97”
From Senescence from G2 arrest, revisited (2015) · cites this paper as [72]
p21-dependent sequestration of cyclin B1 does not occur in U2OS cells.
“In addition, by using fluorescent cyclin B1 and video-microscopy, they confirmed earlier observations 72 that p21-dependent sequestration of cyclin B1 does not take place in U2OS cells.”
From Senescence from G2 arrest, revisited (2015) · cites this paper as [72]
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- Authors
- Lossaint, G., Besnard, E., Fisher, D., Piette, J., & Dulić, V
- Affiliations
- Centre National de la Recherche Scientifique (FR)
- Corresponding author
- Piette, J
- Dulić, V
- Venue
- Oncogene
- Published
- 2011-05-02
- Volume
- 30
- Issue
- 41
- Pages
- 4261-4274
- ISSN
- 0950-9232 (ISSN-L)
- 1476-5594
- OpenAlex
- W2037532989
- Cited by
- 83
- References
- 10
- Citations by year
- 2025: 4 · 2024: 2 · 2023: 2 · 2022: 7 · 2021: 7 · 2020: 4 · 2019: 9 · 2018: 9 · 2017: 2 · 2016: 5 · 2015: 10 · 2014: 8 · 2013: 12 · 2012: 2
- FWCI
- 2.85
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Oncogene (publishedVersion)
- PubMed (publishedVersion)
- HAL (submittedVersion)
- Funders
- Israel Cancer Research Fund
- Versus Arthritis
- Topics
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › DNA Repair Mechanisms
- Health Sciences › Medicine › Oncology › Cancer-related Molecular Pathways
- Health Sciences › Medicine › Physiology › Telomeres, Telomerase, and Senescence
- Keywords
- Chk1, Chk2, p21, G2 cell cycle arrest, DNA damage response, ATM, p53, cell cycle checkpoints, CDK1-cyclin B1, cell cycle exit, senescence, KU55933, U2OS cells
- MeSH terms
- Checkpoint Kinase 1, Antineoplastic Agents, Bleomycin, Cells, Cultured, DNA Damage, DNA-Binding Proteins, Female, HeLa Cells, Humans, Male, Morpholines, Phosphorylation, Piperazines, Protein Kinases, Pyrones, Immunoblotting, Signal Transduction, Tumor Suppressor Protein p53, Protein Serine-Threonine Kinases, Cell Cycle Proteins, Tumor Suppressor Proteins, RNA Interference, HCT116 Cells, Cell Line, Tumor, Cyclin-Dependent Kinase Inhibitor p21, Diketopiperazines, Cyclin B1, G2 Phase Cell Cycle Checkpoints, Ataxia Telangiectasia Mutated Proteins, Checkpoint Kinase 2
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