title: Bortezomib induces G2-M arrest in human colon cancer cells through ROS-inducible             phosphorylation of ATM-CHK1.
abstract: Colorectal cancer (CRC) is one of the most common cancers; however, the development of drugs to treat the condition has reached a plateau. Bortezomib (PS-341, Velcade®) is a proteasome inhibitor approved for the treatment of hematological malignancies, including multiple myeloma. A few trials of bortezomib, alone or in combination chemotherapy, for CRC patients have been reported; however, the results were largely inconclusive. This may be related to a lack of understanding of the drug's mechanism of action. Although bortezomib is reported to induce apoptosis and cell cycle arrest in various human cancer cells, the inhibitory mechanism involved is not clear. In this study, the effect of bortezomib as a treatment for human CRC was examined in vitro using three CRC cell lines. Bortezomib induced G2-M arrest in CRC cells. Investigation of G2-M phase-related cell cycle proteins involved in the response to bortezomib revealed that the ataxia telangiectasia mutated (ATM)-cell cycle checkpoint kinase 1 (CHK1) pathway, but not ATM and Rad3-related (ATR), was activated, resulting in the inactivation of cdc2. Bortezomib caused an increase in intracellular reactive oxygen species (ROS) and treatment with the ROS scavenger NAC inhibited phosphorylation of ATM leading to a decrease in the number of cells in G2-M phase. Thus, increased ROS levels after exposure to bortezomib resulted in ATM phosphorylation. In addition, knockdown of endogenous ATM by RNA interference resulted in decreased sensitivity to bortezomib. These results suggest that bortezomib induces G2-M arrest through ROS-inducible ATM phosphorylation and demonstrate that bortezomib is a potential candidate for further investigations in the treatment for CRC patients.
authors.affiliation: Department of Oncology, Asan Medical Center, University of Ulsan                     College of Medicine, Seoul, Republic of Korea.
authors.forename: Yong Sang
authors.initials: YS
authors.lastname: Hong
authors.forename: Seung-Woo
authors.initials: SW
authors.lastname: Hong
authors.forename: Seung-Mi
authors.initials: SM
authors.lastname: Kim
authors.forename: Dong-Hoon
authors.initials: DH
authors.lastname: Jin
authors.forename: Jae-Sik
authors.initials: JS
authors.lastname: Shin
authors.forename: Dok Hyun
authors.initials: DH
authors.lastname: Yoon
authors.forename: Kyu-Pyo
authors.initials: KP
authors.lastname: Kim
authors.forename: Jae-Lyun
authors.initials: JL
authors.lastname: Lee
authors.forename: Dae Seog
authors.initials: DS
authors.lastname: Heo
authors.forename: Jung Shin
authors.initials: JS
authors.lastname: Lee
authors.forename: Tae Won
authors.initials: TW
authors.lastname: Kim
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D064007:Ataxia Telangiectasia Mutated Proteins; D001897:Boronic Acids / Q000494:pharmacology*; D000069286:Bortezomib; D016203:CDC2 Protein Kinase; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D000071877:Checkpoint Kinase 1; D003110:Colonic Neoplasms; D019926:Cyclin B / Q000378:metabolism; D018844:Cyclin-Dependent Kinases; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D059565:G2 Phase Cell Cycle Checkpoints / Q000187:drug effects*; D006801:Humans; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011719:Pyrazines / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D001897:Boronic Acids; D018797:Cell Cycle Proteins; D019926:Cyclin B; D004268:DNA-Binding Proteins; D011719:Pyrazines; D017382:Reactive Oxygen Species; D025521:Tumor Suppressor Proteins; D000069286:Bortezomib; D011494:Protein Kinases; C576324:ATM protein, human; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D017346:Protein Serine-Threonine Kinases; D016203:CDC2 Protein Kinase; C528899:CDK1 protein, human; D018844:Cyclin-Dependent Kinases