EZH2 promotes degradation of stalled replication forks by recruiting MUS81 through histone H3 trimethylation

Nat Cell Biol. 2017 Nov;19(11):1371-1378. doi: 10.1038/ncb3626. Epub 2017 Oct 16.


The emergence of resistance to poly-ADP-ribose polymerase inhibitors (PARPi) poses a threat to the treatment of BRCA1 and BRCA2 (BRCA1/2)-deficient tumours. Stabilization of stalled DNA replication forks is a recently identified PARPi-resistance mechanism that promotes genomic stability in BRCA1/2-deficient cancers. Dissecting the molecular pathways controlling genomic stability at stalled forks is critical. Here we show that EZH2 localizes at stalled forks where it methylates Lys27 on histone 3 (H3K27me3), mediating recruitment of the MUS81 nuclease. Low EZH2 levels reduce H3K27 methylation, prevent MUS81 recruitment at stalled forks and cause fork stabilization. As a consequence, loss of function of the EZH2/MUS81 axis promotes PARPi resistance in BRCA2-deficient cells. Accordingly, low EZH2 or MUS81 expression levels predict chemoresistance and poor outcome in patients with BRCA2-mutated tumours. Moreover, inhibition of Ezh2 in a murine Brca2-/- breast tumour model is associated with acquired PARPi resistance. Our findings identify EZH2 as a critical regulator of genomic stability at stalled forks that couples histone modifications to nuclease recruitment. Our data identify EZH2 expression as a biomarker of BRCA2-deficient tumour response to chemotherapy.

MeSH terms

  • Animals
  • BRCA1 Protein / metabolism
  • BRCA2 Protein / metabolism
  • Biomarkers, Tumor / metabolism
  • Breast Neoplasms / genetics
  • Breast Neoplasms / metabolism
  • Cell Line
  • Cell Line, Tumor
  • DNA Replication / drug effects
  • DNA Replication / genetics*
  • DNA-Binding Proteins / metabolism*
  • Drug Resistance, Neoplasm / genetics
  • Endonucleases / metabolism*
  • Enhancer of Zeste Homolog 2 Protein / metabolism*
  • Female
  • Genomic Instability / drug effects
  • Genomic Instability / genetics
  • HEK293 Cells
  • HeLa Cells
  • Histones / metabolism*
  • Humans
  • Methylation / drug effects
  • Mice
  • Mice, Nude
  • Poly(ADP-ribose) Polymerase Inhibitors / pharmacology


  • BRCA1 Protein
  • BRCA1 protein, human
  • BRCA2 Protein
  • BRCA2 protein, human
  • Biomarkers, Tumor
  • DNA-Binding Proteins
  • Histones
  • Poly(ADP-ribose) Polymerase Inhibitors
  • EZH2 protein, human
  • Enhancer of Zeste Homolog 2 Protein
  • Endonucleases
  • MUS81 protein, human