title: Constitutive Activation of DNA Damage Checkpoint Signaling Contributes to Mutant p53 Accumulation via Modulation of p53 Ubiquitination.
abstract: Many mutant p53 proteins exhibit an abnormally long half-life and overall increased abundance compared with wild-type p53 in tumors, contributing to mutant p53's gain-of-function oncogenic properties. Here, a novel mechanism is revealed for the maintenance of mutant p53 abundance in cancer that is dependent on DNA damage checkpoint activation. High-level mutant p53 expression in lung cancer cells was associated with preferential p53 monoubiquitination versus polyubiquitination, suggesting a role for the ubiquitin/proteasome system in regulation of mutant p53 abundance in cancer cells. Interestingly, mutant p53 ubiquitination status was regulated by ataxia-telangectasia mutated (ATM) activation and downstream phosphorylation of mutant p53 (serine 15), both in resting and in genotoxin-treated lung cancer cells. Specifically, either inhibition of ATM with caffeine or mutation of p53 (serine 15 to alanine) restored MDM2-dependent polyubiquitination of otherwise monoubiquitinated mutant p53. Caffeine treatment rescued MDM2-dependent proteasome degradation of mutant p53 in cells exhibiting active DNA damage signaling, and ATM knockdown phenocopied the caffeine effect. Importantly, in cells analyzed individually by flow cytometry, p53 levels were highest in cells exhibiting the greatest levels of DNA damage response, and interference with DNA damage signaling preferentially decreased the relative percentage of cells in a population with the highest levels of mutant p53. These data demonstrate that active DNA damage signaling contributes to high levels of mutant p53 via modulation of ubiquitin/proteasome activity toward p53.
  
  
  
  The ability of DNA damage checkpoint signaling to mediate accumulation of mutant p53 suggests that targeting this signaling pathway may provide therapeutic gain. Mol Cancer Res; 14(5); 423-36. ©2016 AACR.
authors.affiliation: Division of Hematology, Oncology, and Palliative Care, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Frum
authors.affiliation: Division of Hematology, Oncology, and Palliative Care, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: Ian M
authors.initials: IM
authors.lastname: Love
authors.affiliation: Division of Hematology, Oncology, and Palliative Care, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: Priyadarshan K
authors.initials: PK
authors.lastname: Damle
authors.affiliation: Department of Biostatistics, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: Nitai D
authors.initials: ND
authors.lastname: Mukhopadhyay
authors.affiliation: Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, Virginia. VCU Massey Cancer Center, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: Swati
authors.initials: S
authors.lastname: Palit Deb
authors.affiliation: Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, Virginia. VCU Massey Cancer Center, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: Sumitra
authors.initials: S
authors.lastname: Deb
authors.affiliation: Division of Hematology, Oncology, and Palliative Care, Virginia Commonwealth University, Richmond, Virginia. VCU Massey Cancer Center, Virginia Commonwealth University, Richmond, Virginia. steven.grossman@vcuhealth.org.
authors.forename: Steven R
authors.initials: SR
authors.lastname: Grossman
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D004249:DNA Damage; D015972:Gene Expression Regulation, Neoplastic; D018816:Genes, cdc; D006207:Half-Life; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000235:genetics* / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D012694:Serine; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D046988:Proteasome Endopeptidase Complex