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Updated: Jun 17, 2026
Detection of DNA Double-Stranded Breaks in Mouse Oocytes
Published on: June 23, 2023
Defective DNA double-strand break repair underlies enhanced tumorigenesis and chromosomal instability in
W L See1, J P Miller, M Squatrito
1Program in Cell Biology, Memorial Sloan-Kettering Cancer Center, New York, NY 10021 USA.
Abstract:
The tumor suppressive activities of the Kip-family of cyclin-dependent kinase (cdk) inhibitors often go beyond their role directly regulating the cell cycle. In this study, we show that p27 enhances Rad51 accumulation during repair of double-strand DNA breaks. Progression of platelet-derived growth factor (PDGF)-induced oligodendrogliomas was accelerated in mice lacking the cyclin-cdk binding activities of p27(kip1). To understand how p27 deficiency contributes, cell lines were developed from RCAS-PDGF infection of nestin-tv-a brain progenitor cells in culture. p27 deficiency did not affect cell proliferation in early passage cell lines; however, the absence of p27 affected chromosomal stability. In p27-deficient cells, the activation of Atm and Chk2 and the accumulation of gamma-H2AX was unaffected when compared with wild-type cells, and the number of phospho-histone H3 staining mitotic cells was decreased, consistent with G2/M checkpoint activation. However, the percentage of Rad51 foci-positive cells was decreased, and the kinase activity that targets the C-terminus of BRCA2, regulating BRCA2/Rad51 interactions, was increased in lysates derived from p27-deficient cells. Increased numbers of chromatid breaks in p27-deficient cells that adapted to the checkpoint were also observed. These findings suggest that Rad51-dependent repair of double-stranded breaks was hindered in p27-deficient cells, leading to chromosomal instability, a hallmark of cancers with poor prognosis.
Insights
The tumor suppressor p27 aids in repairing DNA double-strand breaks by enhancing Rad51 accumulation. Its absence hinders this repair, causing chromosomal instability and accelerating tumor progression.
Area of Science:
- Cellular Biology
- Cancer Research
- Molecular Oncology
Background:
- The Kip-family of cyclin-dependent kinase (cdk) inhibitors, including p27, possess tumor-suppressive functions beyond cell cycle regulation.
- Platelet-derived growth factor (PDGF)-induced oligodendrogliomas in mice lacking p27's cyclin-cdk binding activities showed accelerated progression.
Purpose of the Study:
- To investigate the role of p27 in DNA double-strand break repair and its impact on chromosomal stability.
- To elucidate the mechanisms by which p27 deficiency contributes to tumor progression.
Main Methods:
- Development of cell lines from RCAS-PDGF infected nestin-tv-a brain progenitor cells.
- Analysis of cell proliferation, chromosomal stability, DNA damage response markers (Atm, Chk2, gamma-H2AX), and Rad51 foci in p27-deficient and wild-type cells.
- Assessment of kinase activity targeting BRCA2 and chromatid break frequency.
Main Results:
- p27 deficiency did not affect early cell proliferation but led to chromosomal instability.
- While DNA damage response activation (Atm, Chk2, gamma-H2AX) was unaffected, p27-deficient cells showed decreased Rad51 foci and increased BRCA2-targeting kinase activity.
- p27-deficient cells exhibited increased chromatid breaks, indicating hindered Rad51-dependent DNA repair.
Conclusions:
- p27 plays a crucial role in facilitating Rad51-dependent repair of double-strand DNA breaks.
- The absence of p27 impairs DNA repair, leading to chromosomal instability, a characteristic of aggressive cancers.
- These findings highlight p27's non-canonical function in maintaining genomic integrity and suggest its importance in cancer prognosis.
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