The F-Box Domain-Dependent Activity of EMI1 Regulates PARPi Sensitivity in Triple-Negative Breast Cancers

Mol Cell. 2019 Jan 17;73(2):224-237.e6. doi: 10.1016/j.molcel.2018.11.003. Epub 2018 Dec 13.

Abstract

The BRCA1-BRCA2-RAD51 axis is essential for homologous recombination repair (HRR) and is frequently disrupted in breast cancers. PARP inhibitors (PARPis) are used clinically to treat BRCA-mutated breast tumors. Using a genetic screen, we identified EMI1 as a modulator of PARPi sensitivity in triple-negative breast cancer (TNBC) cells. This function requires the F-box domain of EMI1, through which EMI1 assembles a canonical SCF ubiquitin ligase complex that constitutively targets RAD51 for degradation. In response to genotoxic stress, CHK1-mediated phosphorylation of RAD51 counteracts EMI1-dependent degradation by enhancing RAD51's affinity for BRCA2, leading to RAD51 accumulation. Inhibition of RAD51 degradation restores HRR in BRCA1-depleted cells. Human breast cancer samples display an inverse correlation between EMI1 and RAD51 protein levels. A subset of BRCA1-deficient TNBC cells develop resistance to PARPi by downregulating EMI1 and restoring RAD51-dependent HRR. Notably, reconstitution of EMI1 expression reestablishes PARPi sensitivity both in cellular systems and in an orthotopic mouse model.

Keywords: BRCA1; CHK1; DNA damage; EMI1; HRR; PARPi resistance; RAD51; breast cancer; proteolysis; ubiquitin.

Publication types

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

MeSH terms

  • Animals
  • BRCA1 Protein / deficiency
  • BRCA1 Protein / genetics
  • BRCA2 Protein / genetics
  • BRCA2 Protein / metabolism
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism*
  • Cell Line, Tumor
  • Checkpoint Kinase 1 / genetics
  • Checkpoint Kinase 1 / metabolism
  • DNA Damage
  • Drug Resistance, Neoplasm* / genetics
  • F-Box Proteins / genetics
  • F-Box Proteins / metabolism*
  • Female
  • Gene Expression Regulation, Neoplastic
  • HEK293 Cells
  • Humans
  • Mice, Inbred NOD
  • Mice, SCID
  • Phosphorylation
  • Phthalazines / pharmacology*
  • Piperazines / pharmacology*
  • Poly(ADP-ribose) Polymerase Inhibitors / pharmacology*
  • Proteolysis
  • Rad51 Recombinase / genetics
  • Rad51 Recombinase / metabolism
  • Recombinational DNA Repair
  • Signal Transduction / drug effects
  • Triple Negative Breast Neoplasms / drug therapy*
  • Triple Negative Breast Neoplasms / genetics
  • Triple Negative Breast Neoplasms / metabolism
  • Triple Negative Breast Neoplasms / pathology
  • Tumor Burden / drug effects
  • Xenograft Model Antitumor Assays

Substances

  • BRCA1 Protein
  • BRCA1 protein, human
  • BRCA2 Protein
  • BRCA2 protein, human
  • Cell Cycle Proteins
  • F-Box Proteins
  • FBXO5 protein, human
  • Phthalazines
  • Piperazines
  • Poly(ADP-ribose) Polymerase Inhibitors
  • CHEK1 protein, human
  • Checkpoint Kinase 1
  • RAD51 protein, human
  • Rad51 Recombinase
  • olaparib