title: WRN protects against topo I but not topo II inhibitors by preventing DNA break formation.
abstract: The Werner syndrome helicase/3'-exonuclease (WRN) is a major component of the DNA repair and replication machinery. To analyze whether WRN is involved in the repair of topoisomerase-induced DNA damage we utilized U2-OS cells, in which WRN is stably down-regulated (wrn-kd), and the corresponding wild-type cells (wrn-wt). We show that cells not expressing WRN are hypersensitive to the toxic effect of the topoisomerase I inhibitor topotecan, but not to the topoisomerase II inhibitor etoposide. This was shown by mass survival assays, colony formation and induction of apoptosis. Upon topotecan treatment WRN deficient cells showed enhanced DNA replication inhibition and S-phase arrest, whereas after treatment with etoposide they showed the same cell cycle response as the wild-type. A considerable difference between WRN and wild-type cells was observed for DNA single- and double-strand break formation in response to topotecan. Topotecan induced DNA single-strand breaks 6h after treatment. In both wrn-wt and wrn-kd cells these breaks were repaired at similar kinetics. However, in wrn-kd but not wrn-wt cells they were converted into DNA double-strand breaks (DSBs) at high frequency, as shown by neutral comet assay and phosphorylation of H2AX. Our data provide evidence that WRN is involved in the repair of topoisomerase I, but not topoisomerase II-induced DNA damage, most likely via preventing the conversion of DNA single-strand breaks into DSBs during the resolution of stalled replication forks at topo I-DNA complexes. We suggest that the WRN status of tumor cells impacts anticancer therapy with topoisomerase I, but not topoisomerase II inhibitors.
authors.affiliation: Department of Toxicology, University of Mainz, Obere Zahlbacher Strasse 67, D-55131 Mainz, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Christmann
authors.forename: Maja T
authors.initials: MT
authors.lastname: Tomicic
authors.forename: Christopher
authors.initials: C
authors.lastname: Gestrich
authors.forename: Wynand P
authors.initials: WP
authors.lastname: Roos
authors.forename: Vilhelm A
authors.initials: VA
authors.lastname: Bohr
authors.forename: Bernd
authors.initials: B
authors.lastname: Kaina
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D001859:Bone Neoplasms / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D001973:Bromodeoxyuridine; D002453:Cell Cycle / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D003114:Colony-Forming Units Assay; D053960:DNA Breaks; D004260:DNA Repair / Q000502:physiology*; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005047:Etoposide / Q000494:pharmacology; D005090:Exodeoxyribonucleases / Q000502:physiology*; D006657:Histones; D006801:Humans; D012516:Osteosarcoma / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D034741:RNA, Small Interfering / Q000494:pharmacology; D053484:RecQ Helicases / Q000502:physiology*; D059004:Topoisomerase I Inhibitors; D059005:Topoisomerase II Inhibitors; D019772:Topotecan / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000187:drug effects; D000071657:Werner Syndrome Helicase
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D004791:Enzyme Inhibitors; C468783:H2AX protein, human; D006657:Histones; D034741:RNA, Small Interfering; D059004:Topoisomerase I Inhibitors; D059005:Topoisomerase II Inhibitors; D005047:Etoposide; D019772:Topotecan; D005090:Exodeoxyribonucleases; D053484:RecQ Helicases; C098785:WRN protein, human; D000071657:Werner Syndrome Helicase; D004264:DNA Topoisomerases, Type I; D004250:DNA Topoisomerases, Type II; D001973:Bromodeoxyuridine