title: Gambogic acid triggers DNA damage signaling that induces p53/p21(Waf1/CIP1) activation through the ATR-Chk1 pathway.
abstract: Gambogic acid (GA) has been wildly studied to show potent anti-tumor effects in vivo and in vitro. We have confirmed that GA stabilized and activated p53 through down-regulating the expression of MDM2 in variety of cancer cell lines. However, GA-induced p53 activation could be partially reversed by caffeine, a PI3k inhibitor. Therefore, questions of whether GA induces post-translational modifications of p53 and subsequent activation of p53; and if that is the case, which upstream signaling pathway(s) is (are) responsible for that are proposed. Here, the relationship between p53 activation and its post-translational modifications was investigated in the human cancer cell lines HepG2 and A549 in response to GA or adriamycin treatment. GA induces p53 phosphorylation at sites Ser15 and Ser20 in a concentration- or time-dependent way, which was a direct result of DNA damage, as gamma-HA2X foci and 'comet' DNA fragments were detected. GA induces p53 phosphorylation through activation of an ATM- and Rad3-related pathway, and GA-induced phosphorylation of Chk1 is also involved. Upon treatment with GA, ATR activation is clearly associated with p53 phosphorylation, as well as activation of its target gene p21(Waf/CIP1). Furthermore, we found the dephosphorylation of Cdk1 at Thr161 induced by GA was abrogated, followed by a remarkable disruption of G2/M arrest when the cells were pre-incubated with caffeine. Interestingly, the sensitivity to caffeine enhanced the cytotoxicity of GA as well. Taken together, these data showed an important role of the DNA damage response mediated by ATR-Chk1 in p53/p21(Waf/CIP1) activation and downstream G2/M arrest during GA treatment.
authors.affiliation: Jiangsu Key Laboratory of Carcinogenesis and Intervention, China Pharmaceutical University, Nanjing 210009, China.
authors.forename: Jing-Jing
authors.initials: JJ
authors.lastname: Rong
authors.forename: Rong
authors.initials: R
authors.lastname: Hu
authors.forename: Xiu-Ming
authors.initials: XM
authors.lastname: Song
authors.forename: Jun
authors.initials: J
authors.lastname: Ha
authors.forename: Na
authors.initials: N
authors.lastname: Lu
authors.forename: Qi
authors.initials: Q
authors.lastname: Qi
authors.forename: Lei
authors.initials: L
authors.lastname: Tao
authors.forename: Qi-Dong
authors.initials: QD
authors.lastname: You
authors.forename: Qing-Long
authors.initials: QL
authors.lastname: Guo
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology; D001859:Bone Neoplasms / Q000235:genetics / Q000378:metabolism; D016203:CDC2 Protein Kinase / Q000187:drug effects / Q000378:metabolism; D002110:Caffeine / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D020552:Comet Assay; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics*; D004249:DNA Damage / Q000187:drug effects*; D015536:Down-Regulation / Q000187:drug effects; D004317:Doxorubicin / Q000494:pharmacology; D056945:Hep G2 Cells / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D006801:Humans; D012516:Osteosarcoma / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D010769:Phosphothreonine / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013912:Threonine / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D000077191:Wortmannin; D044004:Xanthones / Q000494:pharmacology*
chemical_list: D000730:Androstadienes; D000970:Antineoplastic Agents; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016159:Tumor Suppressor Protein p53; D044004:Xanthones; D010769:Phosphothreonine; D013912:Threonine; D002110:Caffeine; D004317:Doxorubicin; C052659:gambogic acid; D016203:CDC2 Protein Kinase; D000077191:Wortmannin