Loss of Ubr2, an E3 ubiquitin ligase, leads to chromosome fragility and impaired homologous recombinational repair

Yan Ouyang; Yong Tae Kwon; Jee Young An; Danny Eller; Shih Chang Tsai; Silvia Diaz-Perez; Joshua J. Troke; Michael A. Teitell; York Marahrens

doi:10.1016/j.mrfmmm.2005.12.016

Loss of Ubr2, an E3 ubiquitin ligase, leads to chromosome fragility and impaired homologous recombinational repair

Yan Ouyang, Yong Tae Kwon, Jee Young An, Danny Eller, Shih Chang Tsai, Silvia Diaz-Perez, Joshua J. Troke, Michael A. Teitell, York Marahrens

Genetics, Cell Biology and Development (CBS)

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Abstract

The N-end rule pathway of protein degradation targets proteins with destabilizing N-terminal residues. Ubr2 is one of the E3 ubiquitin ligases of the mouse N-end rule pathway. We have previously shown that Ubr2^-/- male mice are infertile, owing to the arrest of spermatocytes between the leptotene/zygotene and pachytene of meiosis I, the failure of chromosome pairing, and subsequent apoptosis. Here, we report that mouse fibroblast cells derived from Ubr2^-/- embryos display genome instability. The frequency of chromosomal bridges and micronuclei were much higher in Ubr2^-/- fibroblasts than in +/+ controls. Metaphase chromosome spreads from Ubr2^-/- cells revealed a high incidence of spontaneous chromosomal gaps, indicating chromosomal fragility. These fragile sites were generally replicated late in S phase. Ubr2^-/- cells were hypersensitive to mitomycin C, a DNA cross-linking agent, but displayed normal sensitivity to gamma-irradiation. A reporter assay showed that Ubr2^-/- cells are significantly impaired in the homologous recombination repair of a double strand break. In contrast, Ubr2^-/- cells appeared normal in an assay for non-homologous end joining. Our results therefore unveil the role of the ubiquitin ligase Ubr2 in maintaining genome integrity and in homologous recombination repair.

Original language	English (US)
Pages (from-to)	64-75
Number of pages	12
Journal	Mutation Research - Fundamental and Molecular Mechanisms of Mutagenesis
Volume	596
Issue number	1-2 SPEC. ISS.
DOIs	https://doi.org/10.1016/j.mrfmmm.2005.12.016
State	Published - Apr 11 2006

Bibliographical note

Funding Information:
We would like to thank Robert Schiestl (UCLA Department of Radiation Oncology) and Alexander Varshavsky (California Institute of Technology Division of Biology) for critically reading the manuscript. We also thank Rita Cantor (UCLA Department of Human Genetics) for help with the statistical analyses and Maria Jasin (Memorial Sloan-Kettering Cancer Center) for p59xDR-GFP6 and pCBASce. This work was supported by the National Institutes of Health R01 HD41451:01 (Y.M.), R01 GM61007-01A1 (Y.M.), R01 GM69482 (Y.T.K.), R01GM073981 (M.A.T), R01CA74929 (M.A.T.), R01CA107300 (M.A.T.), and CMISE, a NASA URETI Institute (NCC 2-1364: M.A.T.). M.A.T. is a Scholar of the Leukemia and Lymphoma Society.

Keywords

Fragile sites
Genome instability
Homologous recombination repair
Mitomycin C sensitivity
N-end rule proteolytic pathway
Ubr2 ubiquitin ligase

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Ouyang, Y., Kwon, Y. T., An, J. Y., Eller, D., Tsai, S. C., Diaz-Perez, S., Troke, J. J., Teitell, M. A., & Marahrens, Y. (2006). Loss of Ubr2, an E3 ubiquitin ligase, leads to chromosome fragility and impaired homologous recombinational repair. Mutation Research - Fundamental and Molecular Mechanisms of Mutagenesis, 596(1-2 SPEC. ISS.), 64-75. https://doi.org/10.1016/j.mrfmmm.2005.12.016

Ouyang, Y, Kwon, YT, An, JY, Eller, D, Tsai, SC, Diaz-Perez, S, Troke, JJ, Teitell, MA & Marahrens, Y 2006, 'Loss of Ubr2, an E3 ubiquitin ligase, leads to chromosome fragility and impaired homologous recombinational repair', Mutation Research - Fundamental and Molecular Mechanisms of Mutagenesis, vol. 596, no. 1-2 SPEC. ISS., pp. 64-75. https://doi.org/10.1016/j.mrfmmm.2005.12.016

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abstract = "The N-end rule pathway of protein degradation targets proteins with destabilizing N-terminal residues. Ubr2 is one of the E3 ubiquitin ligases of the mouse N-end rule pathway. We have previously shown that Ubr2-/- male mice are infertile, owing to the arrest of spermatocytes between the leptotene/zygotene and pachytene of meiosis I, the failure of chromosome pairing, and subsequent apoptosis. Here, we report that mouse fibroblast cells derived from Ubr2-/- embryos display genome instability. The frequency of chromosomal bridges and micronuclei were much higher in Ubr2-/- fibroblasts than in +/+ controls. Metaphase chromosome spreads from Ubr2-/- cells revealed a high incidence of spontaneous chromosomal gaps, indicating chromosomal fragility. These fragile sites were generally replicated late in S phase. Ubr2-/- cells were hypersensitive to mitomycin C, a DNA cross-linking agent, but displayed normal sensitivity to gamma-irradiation. A reporter assay showed that Ubr2-/- cells are significantly impaired in the homologous recombination repair of a double strand break. In contrast, Ubr2-/- cells appeared normal in an assay for non-homologous end joining. Our results therefore unveil the role of the ubiquitin ligase Ubr2 in maintaining genome integrity and in homologous recombination repair.",

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AU - Ouyang, Yan

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AU - An, Jee Young

AU - Eller, Danny

AU - Tsai, Shih Chang

AU - Diaz-Perez, Silvia

AU - Troke, Joshua J.

AU - Teitell, Michael A.

AU - Marahrens, York

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KW - Ubr2 ubiquitin ligase

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Loss of Ubr2, an E3 ubiquitin ligase, leads to chromosome fragility and impaired homologous recombinational repair

Abstract

Bibliographical note

Keywords

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