title: Premature senescence in human breast cancer and colon cancer cells by tamoxifen-mediated reactive oxygen species generation.
abstract: OBJECTIVE
  Cellular senescence is an important tumor suppression process in vivo. Tamoxifen is a well-known anti-breast cancer drug; however, its molecular function is poorly understood. Here, we examined whether tamoxifen promotes senescence in breast cancer and colon cancer cells for the first time.
  
  
  METHODS
  Human breast cancer MCF-7, T47D, and MDA-MB-435 and colorectal cancer HCT116 cells were treated with tamoxifen. Cellular senescence was measured by SA-β-gal staining and based on the protein expression of p53 and p21(Cip1/WAF1). The production of reactive oxygen species (ROS) was determined by staining with CM-H2DCFDA and dihydroethidium (DHE). CK2 activity was assessed with a specific peptide substrate.
  
  
  RESULTS
  Tamoxifen promoted senescence phenotype and ROS generation in MCF-7 and HCT116 cells. The ROS scavenger, N-acetyl-l-cysteine (NAC), and the NADPH oxidase inhibitor, apocynin, almost completely abolished this event. Tamoxifen inhibited the catalytic activity of CK2. Overexpression of CK2α antagonized senescence mediated by tamoxifen, indicating that tamoxifen induced senescence via a CK2-dependent pathway. A well-known CK2 inhibitor, 5,6-dichloro-1-β-d-ribofuranosylbenzimidazole (DRB), also stimulated ROS production and senescence in MCF-7 cells. Finally, experiments using T47D (wild-type p53) and MDA-MB-435 (mutant p53) cell lines suggested that tamoxifen induces p53-independent ROS production as well as p53-dependent senescence in breast cancer cells.
  
  
  CONCLUSIONS
  These results demonstrate that tamoxifen promotes senescence through a ROS-p53-p21(Cip1/WAF1) dependent pathway by inhibiting CK2 activity in breast cancer and colon cancer cells.
authors.affiliation: School of Life Sciences and Biotechnology, College of Natural Sciences, Kyungpook National University, Daegu 702-701, Republic of Korea.
authors.forename: Young-Hoon
authors.initials: YH
authors.lastname: Lee
authors.affiliation: School of Life Sciences and Biotechnology, College of Natural Sciences, Kyungpook National University, Daegu 702-701, Republic of Korea.
authors.forename: Beom Sik
authors.initials: BS
authors.lastname: Kang
authors.affiliation: School of Life Sciences and Biotechnology, College of Natural Sciences, Kyungpook National University, Daegu 702-701, Republic of Korea. Electronic address: ysbae@knu.ac.kr.
authors.forename: Young-Seuk
authors.initials: YS
authors.lastname: Bae
mesh_terms: D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000473:pathology; D047390:Casein Kinase II / Q000378:metabolism; D045744:Cell Line, Tumor; D016922:Cellular Senescence / Q000187:drug effects; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000473:pathology; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D005260:Female; D045325:HCT116 Cells; D006801:Humans; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013629:Tamoxifen / Q000494:pharmacology*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D018931:Antineoplastic Agents, Hormonal; D050759:Cyclin-Dependent Kinase Inhibitor p21; D017382:Reactive Oxygen Species; D016159:Tumor Suppressor Protein p53; D013629:Tamoxifen; D047390:Casein Kinase II
keywords: Protein kinase CK2; ROS; Senescence; Tamoxifen; p53