ATM-Dependent Downregulation of USP7/HAUSP by PPM1G Activates p53 Response to DNA Damage

The peroxisome-proliferator receptor-γ (PPARγ) is expressed in multiple cancer types. Recently, our group has shown that PPARγ is phosphorylated on serine 273 (S273), which selectively modulates the transcriptional program controlled by this protein. PPARγ ligands, including thiazolidinediones (TZDs), block S273 phosphorylation. This activity is chemically separable from the canonical activation of the receptor by agonist ligands and, importantly, these noncanonical agonist ligands do not cause some of the known side effects of TZDs. Here, we show that phosphorylation of S273 of PPARγ occurs in cancer cells on exposure to DNA damaging agents. Blocking this phosphorylation genetically or pharmacologically increases accumulation of DNA damage, resulting in apoptotic cell death. A genetic signature of PPARγ phosphorylation is associated with worse outcomes in response to chemotherapy in human patients. Noncanonical agonist ligands sensitize lung cancer xenografts and genetically induced lung tumors to carboplatin therapy. Moreover, inhibition of this phosphorylation results in deregulation of p53 signaling, and biochemical studies show that PPARγ physically interacts with p53 in a manner dependent on S273 phosphorylation. These data implicate a role for PPARγ in modifying the p53 response to cytotoxic therapy, which can be modulated for therapeutic gain using these compounds.

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Butyrate modulates DNA-damage-induced p53 response by induction of p53-independent differentiation and apoptosis

Oncogene ◽

10.1038/sj.onc.1201304 ◽

1997 ◽

Vol 15 (12) ◽

pp. 1395-1406 ◽

Cited By ~ 42

Author(s):

Wiebke Janson ◽

Gerhard Brandner ◽

Johanna Siegel

Keyword(s):

Dna Damage ◽

P53 Response

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Supramolecular Complex Formation between Rad6 and Proteins of the p53 Pathway during DNA Damage-Induced Response

Molecular and Cellular Biology ◽

10.1128/mcb.23.7.2463-2475.2003 ◽

2003 ◽

Vol 23 (7) ◽

pp. 2463-2475 ◽

Cited By ~ 33

Author(s):

Alex Lyakhovich ◽

Malathy P. V. Shekhar

Keyword(s):

Dna Damage ◽

Complex Formation ◽

26S Proteasome ◽

Induced Response ◽

Postreplication Repair ◽

Protein Levels ◽

P53 Response ◽

Mcf10a Cells

ABSTRACT The HR6A and -B genes, homologues of the yeast Rad6 gene, encode ubiquitin-conjugating enzymes that are required for postreplication repair of DNA and damage-induced mutagenesis. Using surface plasmon resonance, we show here that HR6 protein (referred as Rad6) physically interacts with p53. Analysis of proteins coimmunoprecipitated with Rad6 antibody from metabolically labeled normal MCF10A human breast epithelial cells not only confirmed Rad6-p53 interactions in vivo but also demonstrated for the first time that exposure of MCF10A cells to cisplatin or adriamycin (ADR) induces recruitment of p14ARF into Rad6-p53 complexes. Further analysis of ADR-induced p53 response showed that stable Rad6-p53-p14ARF complex formation is associated with a parallel increase and decrease in monoubiquitinated and polyubiquitinated p53, respectively, and arrest in G2/M phase of the cell cycle. Interestingly, the ADR-induced suppression of p53 polyubiquitination correlated with a corresponding decline in intact Hdm2 protein levels. Treatment of MCF10A cells with MG132, a 26S proteasome inhibitor, effectively stabilized monoubiquitinated p53 and rescued ADR-induced downregulation of Hdm2. These data suggest that ADR-induced degradation of Hdm2 occurs via the ubiquitin-proteasome pathway. Rad6 is present in both the cytoplasmic and nuclear compartments of normal MCF10A cells, although in response to DNA damage it is predominantly found in the nucleus colocalizing with ubiquitinated p53, whereas Hdm2 is undetectable. Consistent with in vivo data, results from in vitro ubiquitination assays show that Rad6 mediates addition of one (mono-) to two (multimono-) ubiquitin molecules on p53 and that inclusion of Mdm2 is essential for its polyubiquitination. The data presented in the present study suggest that Rad6-p53-p14ARF complex formation and p53 ubiquitin modification are important damage-induced responses that perhaps determine the fidelity of DNA postreplication repair.

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p53 signaling in response to increased DNA damage sensitizes AML1-ETO cells to stress-induced death

Blood ◽

10.1182/blood-2007-06-093682 ◽

2008 ◽

Vol 111 (4) ◽

pp. 2190-2199 ◽

Cited By ~ 53

Author(s):

Ondrej Krejci ◽

Mark Wunderlich ◽

Hartmut Geiger ◽

Fu-Sheng Chou ◽

David Schleimer ◽

...

Keyword(s):

Dna Damage ◽

Dna Repair ◽

Acute Myeloid Leukemia ◽

Myeloid Leukemia ◽

Genetic Alterations ◽

P53 Pathway ◽

P53 Response ◽

Acute Myeloid

Chromosomal translocation (8;21) is present in 10% to 15% of patients with acute myeloid leukemia. Expression of the AML1-ETO (AE) fusion protein alone is not sufficient to induce leukemia, but the nature of the additional genetic alterations is unknown. It is unclear whether AE facilitates acquisition of these cooperating events. We show that AE down-regulates genes involved in multiple DNA repair pathways, potentially through a mechanism involving direct binding at promoter elements, and increases the mutation frequency in vivo. AE cells display increased DNA damage in vitro and have an activated p53 pathway. This results in increased basal apoptosis and enhanced sensitivity to DNA damaging agents. Intriguingly, microarray data indicate that t(8;21) patient samples exhibit decreased expression of DNA repair genes and increased expression of p53 response genes compared with other acute myeloid leukemia (AML) patient samples. Inhibition of the p53 pathway by RNAi increases the resistance of AE cells to DNA damage. We thus speculate that AML1-ETO may facilitate accumulation of genetic alterations by suppressing endogenous DNA repair. It is possible that the superior outcome of t(8;21) patients is partly due to an activated p53 pathway, and that loss of the p53 response pathway is associated with disease progression.

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