Abstract
Telomeres allow cells to distinguish natural chromosome ends from damaged DNA and protect the ends from degradation and fusion. In human cells, telomere protection depends on the TTAGGG repeat binding factor, TRF2 (refs 1–4), which has been proposed to remodel telomeres into large duplex loops5 (t-loops). Here we show by nanoelectrospray tandem mass spectrometry that RAD50 protein is present in TRF2 immunocomplexes. Protein blotting showed that a small fraction of RAD50, MRE11 and the third component of the MRE11 double-strand break (DSB) repair complex, the Nijmegen breakage syndrome protein (NBS1), is associated with TRF2. Indirect immunofluorescence demonstrated the presence of RAD50 and MRE11 at interphase telomeres. NBS1 was associated with TRF2 and telomeres in S phase, but not in G1 or G2. Although the MRE11 complex accumulated in irradiation-induced foci (IRIFs) in response to γ-irradiation, TRF2 did not relocate to IRIFs and irradiation did not affect the association of TRF2 with the MRE11 complex, arguing against a role for TRF2 in DSB repair. Instead, we propose that the MRE11 complex functions at telomeres, possibly by modulating t-loop formation.
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Acknowledgements
We thank N. Heintz and W. Lee for HeLa nuclear extract; J. Karlseder for help with FACS analysis, pCDNA3-TRF2ΔBΔM and comments on the manuscript; A. Smogorzewska for HeLa cells infected with TRF2ΔBΔM retrovirus and comments on the manuscript; and B. Li, G. Celli, S. Smith and J. Ye for discussion. X.-D.Z. is supported by a Canadian MRC postdoctoral fellowship. B.K. was supported (in part) by a long-term post-doctoral fellowship from the EMBO. The laboratory of M.M. at the University of Southern Denmark is supported by a grant from the Danish National Research Foundation to the Center of Experimental BioInformatics (CEBI). J.H.J.P. is supported by NIH/NCI GM56888, GM59413 and the Milwaukee Foundation. This work was supported by a grant from the NIH (GM49046) to T.d.L.
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Zhu, XD., Küster, B., Mann, M. et al. Cell-cycle-regulated association of RAD50/MRE11/NBS1 with TRF2 and human telomeres. Nat Genet 25, 347–352 (2000). https://doi.org/10.1038/77139
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DOI: https://doi.org/10.1038/77139
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