title: The Werner syndrome protein confers resistance to the DNA lesions N3-methyladenine and O6-methylguanine: implications for WRN function.
abstract: The Werner syndrome (WS) protein (WRN), a DNA helicase/exonuclease, is required for genomic stability and avoidance of cancer. Current evidence suggests that WRN is involved in the resolution of stalled and/or collapsed replication forks. This function is indicated, in part, by replication defects in WS cells and by hypersensitivity to agents causing major structural aberrations in DNA that block replication. We show here that antisense suppression of WRN in two human glioma cell lines reproduces hallmarks of the drug cytotoxicity profile of WS cells, namely, hypersensitivity to 4-nitroquinoline 1-oxide, camptothecin and hydroxyurea. We also show that antisense-treated cells are hypersensitive to methyl-lexitropsin, a site-specific alkylating agent that produces mainly N3-methyladenine, a cytotoxic and replication-blocking lesion. Antisense-treated cells are hypersensitive to O(6)-methylguanine adducts as well, but only when repair by O(6)-methylguanine-DNA methyltransferase is lacking. Our results illustrate the drug sensitivity caused by deficiency of WRN in a uniform genetic background. They extend the WRN DNA damage sensitivity spectrum to methyl base adducts that can result in blocked replication, and suggest that WRN may be required for resumption of processive replication when incomplete repair of DNA damage leaves blocking lesions at forks. The evidence that highly disparate lesions fall within the purview of WRN, and that abrogating DNA repair can reveal dependence on WRN, suggests that WRN may protect the genome from the lethal, mutagenic and carcinogenic effects of widely diverse DNA damage arising from endogenous processes and environmental agents.
authors.affiliation: Department of Pathology, University of Washington, Seattle, WA 98195-7705, USA.
authors.forename: A
authors.initials: A
authors.lastname: Blank
authors.forename: Michael S
authors.initials: MS
authors.lastname: Bobola
authors.forename: Barry
authors.initials: B
authors.lastname: Gold
authors.forename: Sridhar
authors.initials: S
authors.lastname: Varadarajan
authors.forename: Douglas
authors.initials: D
authors.lastname: D  Kolstoe
authors.forename: Elizabeth H
authors.initials: EH
authors.lastname: Meade
authors.forename: Peter S
authors.initials: PS
authors.lastname: Rabinovitch
authors.forename: Lawrence A
authors.initials: LA
authors.lastname: Loeb
authors.forename: John R
authors.initials: JR
authors.lastname: Silber
mesh_terms: D015112:4-Nitroquinoline-1-oxide / Q000009:adverse effects; D000225:Adenine / Q000031:analogs & derivatives / Q000378:metabolism; D000477:Alkylating Agents / Q000009:adverse effects; D000970:Antineoplastic Agents / Q000009:adverse effects; D017209:Apoptosis / Q000187:drug effects*; D002166:Camptothecin / Q000009:adverse effects; D002273:Carcinogens / Q000009:adverse effects; D002478:Cells, Cultured; D004249:DNA Damage / Q000187:drug effects*; D004265:DNA Helicases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D004261:DNA Replication / Q000187:drug effects*; D004351:Drug Resistance; D005090:Exodeoxyribonucleases; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects; D005910:Glioma / Q000378:metabolism / Q000473:pathology*; D006147:Guanine / Q000009:adverse effects / Q000031:analogs & derivatives*; D006801:Humans; D006918:Hydroxyurea / Q000009:adverse effects; D009429:Netropsin / Q000009:adverse effects / Q000031:analogs & derivatives*; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000378:metabolism; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D053484:RecQ Helicases; D014898:Werner Syndrome; D000071657:Werner Syndrome Helicase
chemical_list: D000477:Alkylating Agents; D000970:Antineoplastic Agents; D002273:Carcinogens; D016376:Oligonucleotides, Antisense; C110963:methyl lexitropsin; D015112:4-Nitroquinoline-1-oxide; D006147:Guanine; D009429:Netropsin; D019853:O(6)-Methylguanine-DNA Methyltransferase; D005090:Exodeoxyribonucleases; D004265:DNA Helicases; D053484:RecQ Helicases; C098785:WRN protein, human; D000071657:Werner Syndrome Helicase; D000225:Adenine; D006918:Hydroxyurea; D002166:Camptothecin