title: Tipin functions in the protection against topoisomerase I inhibitor.
abstract: The replication fork temporarily stalls when encountering an obstacle on the DNA, and replication resumes after the barrier is removed. Simultaneously, activation of the replication checkpoint delays the progression of S phase and inhibits late origin firing. Camptothecin (CPT), a topoisomerase I (Top1) inhibitor, acts as a DNA replication barrier by inducing the covalent retention of Top1 on DNA. The Timeless-Tipin complex, a component of the replication fork machinery, plays a role in replication checkpoint activation and stabilization of the replication fork. However, the role of the Timeless-Tipin complex in overcoming the CPT-induced replication block remains elusive. Here, we generated viable TIPIN gene knock-out (KO) DT40 cells showing delayed S phase progression and increased cell death. TIPIN KO cells were hypersensitive to CPT. However, homologous recombination and replication checkpoint were activated normally, whereas DNA synthesis activity was markedly decreased in CPT-treated TIPIN KO cells. Proteasome-dependent degradation of chromatin-bound Top1 was induced in TIPIN KO cells upon CPT treatment, and pretreatment with aphidicolin, a DNA polymerase inhibitor, suppressed both CPT sensitivity and Top1 degradation. Taken together, our data indicate that replication forks formed without Tipin may collide at a high rate with Top1 retained on DNA by CPT treatment, leading to CPT hypersensitivity and Top1 degradation in TIPIN KO cells.
authors.affiliation: Molecular Cell Biology Laboratory, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba 6-3, Aramaki, Aoba-ku, Sendai 980-8578, Japan.
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Hosono
authors.affiliation: Instituto FIRC di Oncologia Molecolare (IFOM), Fondazione Italiana per la Ricerca sul Cancro (FIRC) Institute for Molecular Oncology Foundation, IFOM-Istituto Europeo di Oncologia Campus, Via Adamello 16, 20139 Milan, Italy.
authors.forename: Takuya
authors.initials: T
authors.lastname: Abe
authors.affiliation: Molecular Cell Biology Laboratory, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba 6-3, Aramaki, Aoba-ku, Sendai 980-8578, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Higuchi
authors.affiliation: Department of Biochemistry, Tohoku Pharmaceutical University, 4-4-1 Komatsushima, Aoba-ku, Sendai, Miyagi 981-8558, Japan.
authors.forename: Kosa
authors.initials: K
authors.lastname: Kajii
authors.affiliation: Molecular Cell Biology Laboratory, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba 6-3, Aramaki, Aoba-ku, Sendai 980-8578, Japan.
authors.forename: Shuichi
authors.initials: S
authors.lastname: Sakuraba
authors.affiliation: Faculty of Pharmaceutical Sciences, Teikyo Heisei University, 4-21-2 Nakano, Nakano-ku, Tokyo 164-8530, Japan, and.
authors.forename: Shusuke
authors.initials: S
authors.lastname: Tada
authors.affiliation: Molecular Cell Biology Laboratory, Research Institute of Pharmaceutical Sciences, Faculty of Pharmacy, Musashino University, 1-1-20 Shinmachi, Nishitokyo-shi, Tokyo 202-8585, Japan.
authors.forename: Takemi
authors.initials: T
authors.lastname: Enomoto
authors.affiliation: Department of Biochemistry, Tohoku Pharmaceutical University, 4-4-1 Komatsushima, Aoba-ku, Sendai, Miyagi 981-8558, Japan,. Electronic address: seki@tohoku-pharm.ac.jp.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Seki
mesh_terms: D000818:Animals; D030161:Avian Proteins / Q000235:genetics / Q000378:metabolism*; D002166:Camptothecin / Q000494:pharmacology*; D016923:Cell Death / Q000187:drug effects / Q000235:genetics; D002460:Cell Line; D002645:Chickens; D004247:DNA / Q000096:biosynthesis / Q000235:genetics; D004261:DNA Replication / Q000187:drug effects* / Q000502:physiology; D004264:DNA Topoisomerases, Type I / Q000235:genetics / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D059748:Proteolysis / Q000187:drug effects; D016196:S Phase / Q000187:drug effects / Q000502:physiology; D059004:Topoisomerase I Inhibitors / Q000494:pharmacology*
chemical_list: D030161:Avian Proteins; D009687:Nuclear Proteins; D059004:Topoisomerase I Inhibitors; D004247:DNA; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin
keywords: Anticancer Drug; Camptothecin; DNA Repair; DNA Replication; DNA Topoisomerase; DT40; Molecular Cell Biology; Replication Fork; Tipin; Top1