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Telomere dysfunction impairs DNA repair and enhances sensitivity to ionizing radiation

Abstract

Telomeres are specialized nucleoprotein complexes that serve as protective caps of linear eukaryotic chromosomes. Loss of telomere function is associated with rampant genetic instability and loss of cellular viability and renewal potential. The telomere also participates in processes of chromosomal repair, as evidenced by the ‘capture’ or de novo synthesis of telomere repeats at double-stranded breaks1,2,3,4 and by the capacity of yeast telomeres to serve as repositories of essential components of the DNA repair machinery, particularly those involved in non-homologous end-joining5,6,7 (NHEJ). Here we used the telomerase-deficient mouse, null for the essential telomerase RNA gene (Terc), to assess the role of telomerase and telomere function on the cellular and organismal response to ionizing radiation. Although the loss of telomerase activity per se had no discernable impact on the response to ionizing radiation, the emergence of telomere dysfunction in late-generation Terc−/− mice imparted a radiosensitivity syndrome associated with accelerated mortality. On the cellular level, the gastrointestinal crypt stem cells and primary thymocytes showed increased rates of apoptosis, and mouse embryonic fibroblasts (MEFs) showed diminished dose-dependent clonogenic survival. The radiosensitivity of telomere dysfunctional cells correlated with delayed DNA break repair kinetics, persistent chromosomal breaks and cytogenetic profiles characterized by complex chromosomal aberrations and massive fragmentation. Our findings establish a intimate relationship between functionally intact telomeres and the genomic, cellular and organismal response to ionizing radiation.

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Figure 1: Decreased survival of late generation Terc−/− mice after exposure to ionizing irradiation.
Figure 2: Late-generation Terc−/− intestinal cells, thymocytes and MEFs exhibit enhanced radiosensitivity in vivo and in vitro.
Figure 3: G6 Terc−/− MEFs exhibit persistent cytogenetic aberrations after exposures to ionizing irradiation.
Figure 4: Late-generation Terc−/− MEFs exhibit impaired double-strand DNA break repair kinetics after exposure to ionizing radiation, but exhibit an intact NHEJ pathway.

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Acknowledgements

We thank D. Livingston's laboratory for advice on the double-strand DNA break repair assay; W. Swat for advice on the thymocyte assays; and J. Sekiguchi, K. Mills, Y. Gu and D. Fergueson for critically reading the manuscript. This work was supported by grants from the National Institutes of Health (R01HD34880, R01HD28317). K.L.R. is supported by a grant of the Deutsche Forschungsgemeinschaft (Ru 745/1-1). F.W.A. is an Investigator of the Howard Hughes Medical Institute. L.C. is supported by grant from the National Institutes of Health (K08AR02104-01) and is a foundation scholar. S.E.A., K.K.W., S.C. and S.G. are Howard Hughes Physican Postdoctoral fellows. C.Z. is a Cancer Research Institute Fellow. J.C. is a Walter Winchell Damon Runyon Cancer Research fellow. Support from the DFCI/HCC Cancer Core grant to R.A.D. and L.C. is acknowledged. R.A.D. is an American Cancer Society Research Professor.

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Correspondence to Ronald A. DePinho.

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Wong, KK., Chang, S., Weiler, S. et al. Telomere dysfunction impairs DNA repair and enhances sensitivity to ionizing radiation. Nat Genet 26, 85–88 (2000). https://doi.org/10.1038/79232

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