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PPM1D suppresses p53-dependent transactivation and cell death by inhibiting the HRI-eIF2alpha-ATF4 pathway [RNA-seq]

ABSTRACT: The p53 transcription factor is a master regulator of cellular stress responses restrained by repressors such as MDM2 and the phosphatase PPM1D. Activation of p53 with pharmacological inhibitors of its repressors is being tested in clinical trials for cancer therapy, but efficacy has been limited by poor induction of tumor cell death. We demonstrate that dual inhibition of MDM2 and PPM1D induces cell death in multiple cancer cell types via amplification of the p53 transcriptional program through the eIF2alpha -ATF4 pathway. PPM1D inhibition induces phosphorylation of eIF2alpha, ATF4 accumulation, and ATF4-dependent enhancement of p53-dependent transactivation upon MDM2 inhibition. Dual inhibition of p53 repressors depletes heme and induces HRI-dependent eIF2alpha phosphorylation. Pharmacological induction of eIF2alpha phosphorylation synergizes with MDM2 inhibition to induce cell death and halt tumor growth in mice. These results demonstrate that PPM1D inhibits both the p53 network and the integrated stress response controlled by eIF2alpha, with clear therapeutic implications.

ORGANISM(S): Homo sapiens

PROVIDER: GSE191148 | GEO | 2022/11/01

REPOSITORIES: GEO

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PPM1D suppresses p53-dependent transactivation and cell death by inhibiting the HRI-eIF2alpha-ATF4 pathway [ChIP-seq]

Project description:The p53 transcription factor is a master regulator of cellular stress responses restrained by repressors such as MDM2 and the phosphatase PPM1D. Activation of p53 with pharmacological inhibitors of its repressors is being tested in clinical trials for cancer therapy, but efficacy has been limited by poor induction of tumor cell death. We demonstrate that dual inhibition of MDM2 and PPM1D induces cell death in multiple cancer cell types via amplification of the p53 transcriptional program through the eIF2alpha -ATF4 pathway. PPM1D inhibition induces phosphorylation of eIF2alpha, ATF4 accumulation, and ATF4-dependent enhancement of p53-dependent transactivation upon MDM2 inhibition. Dual inhibition of p53 repressors depletes heme and induces HRI-dependent eIF2alpha phosphorylation. Pharmacological induction of eIF2alpha phosphorylation synergizes with MDM2 inhibition to induce cell death and halt tumor growth in mice. These results demonstrate that PPM1D inhibits both the p53 network and the integrated stress response controlled by eIF2alpha, with clear therapeutic implications.

2022-09-01 | GSE191149 | GEO

PPM1D suppresses p53-dependent transactivation and cell death by inhibiting the HRI-eIF2alpha-ATF4 pathway.

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Project description:We investigate how modulation of the eIF2alpha-ATF4 stress pathway affects hepatoma cell response to bortezomib. Transcriptome profiling revealed that many ATF4 transcriptional target genes are among the highest upregulated genes in bortezomib-treated HepG2 human hepatoma cells. While pharmacological enhancement of the eIF2alpha-ATF4 pathway activity results in the elevation of the activities of all branches of the unfolded protein response (UPR) and sensitizes cells to bortezomib toxicity, the suppression of ATF4 induction delays bortezomib-induced cell death. The pseudokinase TRIB3, an inhibitor of ATF4, is expressed at a high basal level in hepatoma cells and is strongly upregulated in response to bortezomib. Bortezomib treatment leads to a robust enrichment of TRIB3 binding near genes induced by bortezomib and involved in the ER stress response and cell death. Disruption of TRIB3 increases C/EBP-ATF-driven transcription, augments ER stress and cell death in cells exposed to bortezomib, while TRIB3 overexpression enhances the cell survival. Thus, TRIB3, colocalizing with ATF4 and limiting its transcriptional activity, functions as a factor increasing resistance to bortezomib, while pharmacological over-activation of eIF2alpha-ATF4 can overcome the endogenous restraint mechanisms and sensitize cells to bortezomib.

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Substrate spectrum of PPM1D in the cellular response to DNA double strand breaks

Project description:PPM1D (also known as WIP1) is a p53-regulated protein phosphatase that modulates the DNA damage response (DDR) by dephosphorylation of DDR proteins. Amplification of PPM1D gene or gain-of-function mutations are commonly found in cancer. Here, we employed chemical inhibition of PPM1D and quantitative mass spectrometry-based phosphoproteomics to identify the substrates of PPM1D upon induction of DNA double strand breaks (DSBs) by topoisomerase II poison etoposide. We identified 73 putative PPM1D substrates that are involved in DNA repair, regulation of transcription and RNA processing. One third of DSB-induced S/TQ phosphorylation sites are dephosphorylated by PPM1D, demonstrating that PPM1D only partially counteracts ATM/ATR/DNA-PK signaling. PPM1D-targeted phosphorylation sites are found in a specific amino acid sequence motif that is characterized by glutamic acid residues, high intrinsic disorder and poor evolutionary conservation. We identified a functionally uncharacterized protein Kanadaptin as ATM and PPM1D substrate upon DSB induction. We propose that PPM1D plays a role during the response to DSBs formation by regulating the phosphorylation of DNA- and RNA-binding proteins in intrinsically disordered regions.

2022-09-06 | PXD035420 | Pride

Phosphorylation of TRF2 promotes its interaction with TIN2 and regulates DNA repair at damaged telomeres

Project description:Protein phosphatase magnesium-dependent 1 delta (PPM1D) is involved in termination of the cell cycle checkpoint by counteracting activity of the tumour suppressor protein p53. By dephosphorylating various proteins at chromatin, PPM1D contributes to the control of DNA damage response and DNA repair. Using proximity biotinylation followed by proteomic analysis, we identified interaction between PPM1D and the components of the shelterin complex that protects telomeric DNA. Interaction between PPM1D and TRF2 was confirmed by immunoprecipitation and proximity ligation assay. Confocal microscopy revealed colocalisation of the endogenous PPM1D with TRF2 at telomeres. Further, we found that TRF2 was phosphorylated by ATR at S410 after induction of DNA damage at telomeres and this modification was increased in cells lacking PPM1D or after PPM1D inhibition. Phosphorylation of TRF2 stimulated its interaction with TIN2 at telomeres and in vitro. Conversely, overexpression of PPM1D impaired localisation of TIN2 at telomeres. Finally, inhibition of PPM1D impaired recruitment of 53BP1 and RAD51 to DNA double strand breaks at telomeres. Expression of TRF2-S410A mutant fully rescued the recruitment of 53BP1 to telomeric breaks. These results suggest that TRF2 phosphorylation promotes association of TIN2 with the shelterin complex and regulates DNA repair at telomeres.

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