title: Hypersensitivity to chromium-induced DNA damage correlates with constitutive deregulation of upstream p53 kinases in p21-/- HCT116 colon cancer cells.
abstract: The cyclin-dependent kinase inhibitor p21(CIP1/WAF1) is a key component in cell cycle control and apoptosis, directing an anti-apoptotic response following DNA damage. Chromium exposure resulted in a 500-1000 fold increase in apoptosis-induced cell death in p21-/- HCT116 cells compared to wild-type or p53-/- cells. p53 shRNA (or transient p53 siRNA) into p21-/- HCT116 cells reduced Cr(VI) sensitivity, suggesting the enhanced apoptosis in p21-/- cells is p53-dependent. Under non-DNA damage conditions, the p53 level in p21-/- cells was significantly higher than in wild-type cells, due to enhanced p53 phosphorylation and stabilization rather than elevated p53 transcription. Wild-type cells showed significant p53 protein induction upon DNA damage whereas p21-/- cells showed no p53 increase. p21-/- cells display the constitutive activation of upstream p53 kinases (ATM, DNA-PK, ATR, AKT and p38). 2D gel analysis revealed p53 patterns in p21-/- cells were distinct from those in wild-type cells before and after chromium exposure. Our results suggest that p21 has an important role in the cellular response to normal replicative stress and its absence leads to a "chronic DNA damage" state that primes the cell for p53-dependent apoptosis.
authors.affiliation: Department of Microbiology & Immunology, Dalhousie University, Halifax, NS, Canada.
authors.forename: Richard
authors.initials: R
authors.lastname: Hill
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Leidal
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Madureira
authors.forename: Laura D
authors.initials: LD
authors.lastname: Gillis
authors.forename: Haley K
authors.initials: HK
authors.lastname: Cochrane
authors.forename: David M
authors.initials: DM
authors.lastname: Waisman
authors.forename: Arthur
authors.initials: A
authors.lastname: Chiu
authors.forename: Patrick W K
authors.initials: PW
authors.lastname: Lee
mesh_terms: D017304:Annexin A5; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D002453:Cell Cycle / Q000187:drug effects*; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D002857:Chromium / Q000633:toxicity; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics* / Q000378:metabolism; D004249:DNA Damage; D004305:Dose-Response Relationship, Drug; D015180:Electrophoresis, Gel, Two-Dimensional; D005786:Gene Expression Regulation / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
chemical_list: D017304:Annexin A5; D050759:Cyclin-Dependent Kinase Inhibitor p21; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; D002857:Chromium