title: Y-box binding protein 1 enhances DNA topoisomerase 1 activity and sensitivity to camptothecin via direct interaction.
abstract: BACKGROUND
  The Y-box binding protein 1 (YB-1) possesses pleiotropic functions through its interactions with various cellular proteins, and its high expression levels make it a potential useful prognostic biomarker for cancer cells. Eukaryotic DNA topoisomerases, such as DNA topoisomerase 1 (TOPO1) and DNA topoisomerase 2 (TOPO2), are the essential DNA metabolism regulators that usually overexpressed in cancer cells, and multiple proteins have been reported to regulate the enzyme activity and the clinical efficacy of their inhibitors. The present study unraveled the interaction of YB-1 with TOPO1, and further investigated the related function and potential mechanisms during the interaction.
  
  
  METHODS
  The direct association of TOPO1 with specific domain of YB-1 was explored by co-immunoprecipitation and GST pull-down assays. The interaction function was further clarified by DNA relaxation assays, co-immunoprecipitation and WST-8 assays with in vitro gain- and loss- of function models.
  
  
  RESULTS
  We found that YB-1 interacts directly with TOPO1 (but not with TOPO2) and promotes TOPO1 catalytic activity. Interactions between YB-1 and TOPO1 increased when cancer cells were treated with the TOPO1 inhibitor, camptothecin (CPT), but not with the TOPO2 inhibitor, adriamycin (ADM). Furthermore, we found that the interaction is prevented by pretreatment with the antioxidant agent, N-acetyl cysteine, and that YB-1 downregulation renders cells resistant to CPT.
  
  
  CONCLUSIONS
  Our findings suggest that nuclear YB-1 serves as an intracellular promoter of TOPO1 catalytic activity that enhances CPT sensitivity through its direct interaction with TOPO1.
authors.affiliation: Department of Medical Oncology, the First Hospital, China Medical University, Shenyang, China. cmuwuying@hotmail.co.|The President Laboratory, University of Occupational and Environmental Health, Kitakyushu, Fukuoka, Japan. cmuwuying@hotmail.co.
authors.forename: Ying
authors.initials: Y
authors.lastname: Wu
authors.affiliation: Shared-Use Research Center, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Fukuoka, Japan. kywang@med.uoeh-u.ac.jp.
authors.forename: Ke-yong
authors.initials: KY
authors.lastname: Wang
authors.affiliation: Department of Medical Oncology, the First Hospital, China Medical University, Shenyang, China. lancetgemini@gmail.com.
authors.forename: Zhi
authors.initials: Z
authors.lastname: Li
authors.affiliation: Department of Medical Oncology, the First Hospital, China Medical University, Shenyang, China. cmuliuyunpeng@hotmail.com.
authors.forename: Yun-peng
authors.initials: YP
authors.lastname: Liu
authors.affiliation: Department of Occupational Pneumology, Institute of Industrial Ecological Science, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Fukuoka, Japan. h-izumi@med.uoeh-u.ac.jp.
authors.forename: Hiroto
authors.initials: H
authors.lastname: Izumi
authors.affiliation: Department of Surgery, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Fukuoka, Japan. hidetaka@med.uoeh-u.ac.jp.
authors.forename: Hidetaka
authors.initials: H
authors.lastname: Uramoto
authors.affiliation: Department of Surgery, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Fukuoka, Japan. nakayama@med.uoeh-u.ac.jp.
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Nakayama
authors.affiliation: Department of Surgery, School of Medicine, Shinshu University, Matsumoto, Nagano, Japan. kenito@shinshu-u.ac.jp.
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Ito
authors.affiliation: The President Laboratory, University of Occupational and Environmental Health, Kitakyushu, Fukuoka, Japan. k-kohno@med.uoeh-u.ac.jp.
authors.forename: Kimitoshi
authors.initials: K
authors.lastname: Kohno
mesh_terms: D000111:Acetylcysteine / Q000494:pharmacology; D000975:Antioxidants / Q000494:pharmacology; D001665:Binding Sites; D002166:Camptothecin / Q000494:pharmacology*; D002384:Catalysis; D045744:Cell Line, Tumor; D004264:DNA Topoisomerases, Type I / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D009690:Nucleic Acid Conformation; D018384:Oxidative Stress / Q000187:drug effects; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D034622:RNA Interference; D059004:Topoisomerase I Inhibitors / Q000494:pharmacology*; D014162:Transfection; D051840:Y-Box-Binding Protein 1 / Q000235:genetics / Q000378:metabolism*
chemical_list: D000975:Antioxidants; D059004:Topoisomerase I Inhibitors; D051840:Y-Box-Binding Protein 1; C070856:YBX1 protein, human; D004264:DNA Topoisomerases, Type I; C528909:TOP1 protein, human; D000111:Acetylcysteine; D002166:Camptothecin