PPM1D-truncating Mutations Confer Resistance to Chemotherapy and Sensitivity to PPM1D Inhibition in Hematopoietic Cells

Blood. 2018 Sep 13;132(11):1095-1105. doi: 10.1182/blood-2018-05-850339. Epub 2018 Jun 28.

Abstract

Truncating mutations in the terminal exon of protein phosphatase Mg2+/Mn2+ 1D (PPM1D) have been identified in clonal hematopoiesis and myeloid neoplasms, with a striking enrichment in patients previously exposed to chemotherapy. In this study, we demonstrate that truncating PPM1D mutations confer a chemoresistance phenotype, resulting in the selective expansion of PPM1D-mutant hematopoietic cells in the presence of chemotherapy in vitro and in vivo. Clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein-9 nuclease mutational profiling of PPM1D in the presence of chemotherapy selected for the same exon 6 mutations identified in patient samples. These exon 6 mutations encode for a truncated protein that displays elevated expression and activity due to loss of a C-terminal degradation domain. Global phosphoproteomic profiling revealed altered phosphorylation of target proteins in the presence of the mutation, highlighting multiple pathways including the DNA damage response (DDR). In the presence of chemotherapy, PPM1D-mutant cells have an abrogated DDR resulting in altered cell cycle progression, decreased apoptosis, and reduced mitochondrial priming. We demonstrate that treatment with an allosteric, small molecule inhibitor of PPM1D reverts the phosphoproteomic, DDR, apoptotic, and mitochondrial priming changes observed in PPM1D-mutant cells. Finally, we show that the inhibitor preferentially kills PPM1D-mutant cells, sensitizes the cells to chemotherapy, and reverses the chemoresistance phenotype. These results provide an explanation for the enrichment of truncating PPM1D mutations in the blood of patients exposed to chemotherapy and in therapy-related myeloid neoplasms, and demonstrate that PPM1D can be a targeted in the prevention of clonal expansion of PPM1D-mutant cells and the treatment of PPM1D-mutant disease.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence*
  • CRISPR-Cas Systems
  • Cell Line, Tumor
  • Drug Resistance, Neoplasm* / drug effects
  • Drug Resistance, Neoplasm* / genetics
  • Enzyme Inhibitors / pharmacology*
  • Hematologic Neoplasms* / drug therapy
  • Hematologic Neoplasms* / enzymology
  • Hematologic Neoplasms* / genetics
  • Hematologic Neoplasms* / pathology
  • Hematopoietic Stem Cells / enzymology*
  • Hematopoietic Stem Cells / pathology
  • Humans
  • Myeloproliferative Disorders* / drug therapy
  • Myeloproliferative Disorders* / enzymology
  • Myeloproliferative Disorders* / genetics
  • Myeloproliferative Disorders* / pathology
  • Neoplasm Proteins* / antagonists & inhibitors
  • Neoplasm Proteins* / genetics
  • Neoplasm Proteins* / metabolism
  • Neoplastic Stem Cells / enzymology*
  • Neoplastic Stem Cells / pathology
  • Protein Phosphatase 2C* / antagonists & inhibitors
  • Protein Phosphatase 2C* / genetics
  • Protein Phosphatase 2C* / metabolism
  • Sequence Deletion*

Substances

  • Enzyme Inhibitors
  • Neoplasm Proteins
  • PPM1D protein, human
  • Protein Phosphatase 2C