A role for WRN in telomere-based DNA damage responses

doi:10.1073/pnas.0607332103

A role for WRN in telomere-based DNA damage responses

*Department of Dermatology, Boston University School of Medicine, 609 Albany Street, Boston, MA 02118;
^‡Department of Environmental and Occupational Health, University of Pittsburgh, 100 Technology Drive, Cellomics Building, Suite 350, Pittsburgh, PA 15219; and
^§Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, 5600 Nathan Shock Drive, Baltimore, MD 21224-6825

Communicated by Philip Leder, Harvard Medical School, Boston, MA, August 23, 2006 (received for review June 14, 2006)

Abstract

Telomeres cap the ends of eukaryotic chromosomes and prevent them from being recognized as DNA breaks. We have shown that certain DNA damage responses induced during senescence and, at times of telomere uncapping, also can be induced by treatment of cells with small DNA oligonucleotides homologous to the telomere 3′ single-strand overhang (T-oligos), implicating this overhang in generation of these telomere-based damage responses. Here, we show that T-oligo-treated fibroblasts contain γH2AX foci and that these foci colocalize with telomeres. T-oligos with nuclease-resistant 3′ ends are inactive, suggesting that a nuclease initiates T-oligo responses. We therefore examined WRN, a 3′ → 5′ exonuclease and helicase mutated in Werner syndrome, a disorder characterized by aberrant telomere maintenance, premature aging, chromosomal rearrangements, and predisposition to malignancy. Normal fibroblasts and U20S osteosarcoma cells rendered deficient in WRN showed reduced phosphorylation of p53 and histone H2AX in response to T-oligo treatment. Together, these data demonstrate a role for WRN in processing of telomeric DNA and subsequent activation of DNA damage responses. The T-oligo model helps define the role of WRN in telomere maintenance and initiation of DNA damage responses after telomere disruption.

Footnotes

^¶To whom correspondence should be addressed. E-mail: bgilchre{at}bu.edu
Author contributions: M.S.E. and B.A.G. designed research; X.L., S.L., K.H., H.B., and B.A.G. performed research; M.S.E., H.B., P.L.O., V.A.B., and B.A.G. analyzed data; and M.S.E. and B.A.G. wrote the paper.
↵ ^†Present address: Dana–Farber Cancer Institute, 44 Binney Street, Boston, MA 02115.
Conflict of interest statement: Portions of the work reported in this article pertain to a patent application for which M.S.E. and B.A.G. are coinventors and, if awarded, will be assigned to the Trustees of Boston University (their employer) and then licensed to Semaco, Inc., a for-profit company created to commercialize intellectual property arising out of their laboratory. M.S.E. and B.A.G. both hold equity in Semaco, and B.A.G. is Semaco's Chief Scientific Officer.
Abbreviations:

PS,

phosphorothioate;

TRF,

telomere repeat-binding factor;

WS,

Werner syndrome.
Freely available online through the PNAS open access option.