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Mechanisms of synthetic lethality between BRCA1/2 and 53BP1 deficiencies and DNA polymerase theta targeting

George E Ronson1, Katarzyna Starowicz1,2, Elizabeth J Anthony1

  • 1Birmingham Centre for Genome Biology and Institute of Cancer and Genomic Sciences, College of Medical and Dental Sciences, University of Birmingham, Birmingham, B15 2TT, UK.

Nature Communications
|November 29, 2023
PubMed

Insights

Synthetic lethality between polymerase theta (Polθ) loss and DNA repair defects (like BRCA1 or 53BP1 loss) depends on RAD52 and cell genotype. Polθ inhibition reveals distinct genotype-specific mechanisms underlying this synthetic lethality.

Area of Science:

  • Molecular Biology
  • Genetics
  • Cancer Research

Background:

  • Synthetic lethality offers therapeutic strategies for cancer by exploiting dependencies between gene disruptions.
  • Polymerase theta (Polθ) plays a role in DNA repair, and its disruption shows synthetic letharilty with defects in 53BP1 or homologous recombination (HR) proteins like BRCA1.
  • The precise mechanisms driving these synthetic lethal interactions remain largely unelucidated.

Purpose of the Study:

  • To elucidate the distinct molecular mechanisms underlying the synthetic lethality between polymerase theta (Polθ) disruption and deficiencies in 53BP1 or BRCA1.
  • To investigate the influence of Polθ loss versus inhibition and the specific genetic background on these synthetic lethal phenotypes.

Main Methods:

  • Utilized cell-based assays to assess the sensitivity of BRCA1/2- and 53BP1-deficient cells to Polθ loss and inhibition (using ART558).
  • Investigated the role of RAD52 in mediating these synthetic lethal phenotypes.
  • Analyzed DNA single-stranded gap-filling processes and MRE11 nuclease accumulation in different genetic contexts.

Main Results:

  • Sensitivity to Polθ loss or inhibition in 53BP1-deficient cells, and Polθ loss in BRCA1/2-deficient cells, is dependent on RAD52.
  • RAD52 suppression can rescue synthetic lethality in 53BP1-deficient cells by preventing aberrant RAD52 accumulations and MRE11 nuclease activity.
  • In contrast, RAD52 suppression does not rescue BRCA1-deficient cells treated with a Polθ inhibitor, as the inhibited polymerase itself blocks DNA gap-filling.

Conclusions:

  • Identified two distinct mechanisms of Polθ synthetic lethality, dependent on whether Polθ is lost or inhibited, and the specific genotype.
  • Defined a novel role for Polθ in suppressing RAD52-mediated DNA repair intermediates.
  • These findings highlight genotype-specific mechanisms of Polθ inhibitor action and offer insights into targeted cancer therapies.

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