title: Oxaliplatin-induced gamma-H2AX activation via both p53-dependent and -independent pathways but is not associated with cell cycle arrest in human colorectal cancer cells.
abstract: Oxaliplatin, a chemotherapeutic drug, induces DNA double-strand breaks (DSBs) and apoptosis in colorectal cancer cells. It has been shown that gamma-H2AX acts as a marker of DSBs. However, the molecular events associated with oxaliplatin-mediated cell cycle arrest and cell death remain unclear. In this study, we investigated the roles of p53 and gamma-H2AX following oxaliplatin treatment, as they are important effector proteins for apoptosis and DSB repair, respectively. Both phosphorylated-p53 (Ser-15) and gamma-H2AX were up-regulated and accumulated in the nuclei of p53-wild type human colorectal cancer HCT116 cells after exposure to oxaliplatin. Concomitantly, oxaliplatin-induced G2/M arrest was associated with a reduction in both cyclin B1 expression and phosphorylated-CDC2 (Thr-161). Release of G2/M arrest by caffeine was accompanied by a decrease in the levels of p53/p21; however, gamma-H2AX levels were unchanged. Furthermore, inhibition of p53 phosphorylation by pifithrin-alpha was sufficient to reduce the oxaliplatin-induced up-regulation of gamma-H2AX and apoptosis. Oxaliplatin-induced gamma-H2AX via a p53-independent pathway but did not cause caspase-3 activation in p53-null HCT116 cells. Interestingly, no changes were observed in the H2AX gene knockdown with regards to oxaliplatin-induced G2/M arrest in p53-wild type and S phase arrest in p53-null HCT116 cells. Taken together, these data indicate that a molecular pathway involving p53, gamma-H2AX and cell cycle arrest plays a pivotal role in the cellular response to oxaliplatin.
authors.affiliation: Department of Life Science, Tzu Chi University, Hualien 970, Taiwan. chiusj@mail.tcu.edu.tw
authors.forename: Shu-Jun
authors.initials: SJ
authors.lastname: Chiu
authors.forename: Yi-Jang
authors.initials: YJ
authors.lastname: Lee
authors.forename: Tzu-Sheng
authors.initials: TS
authors.lastname: Hsu
authors.forename: Wen-Shu
authors.initials: WS
authors.lastname: Chen
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects; D016203:CDC2 Protein Kinase / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D015179:Colorectal Neoplasms / Q000188:drug therapy*; D019926:Cyclin B / Q000378:metabolism; D056744:Cyclin B1; D016195:G2 Phase / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006657:Histones / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D009944:Organoplatinum Compounds / Q000494:pharmacology* / Q000627:therapeutic use; D000077150:Oxaliplatin; D010766:Phosphorylation / Q000187:drug effects; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; C534699:CCNB1 protein, human; D019926:Cyclin B; D056744:Cyclin B1; C468783:H2AX protein, human; D006657:Histones; D009944:Organoplatinum Compounds; D016159:Tumor Suppressor Protein p53; D000077150:Oxaliplatin; D016203:CDC2 Protein Kinase