Dysregulated G2 phase checkpoint recovery pathway reduces DNA repair efficiency and increases chromosomal instability in a wide range of tumours

Madushan Fernando,Shivam Vora,Pascal H G Duijf,Martina Proctor,Brian Gabrielli,Alexander J Stevenson,Dubravka Skalamera,Mark Adams,Anna Ehmann

doi:10.1038/s41389-021-00329-8

Abstract

Defective DNA repair is being demonstrated to be a useful target in cancer treatment. Currently, defective repair is identified by specific gene mutations, however defective repair is a common feature of cancers without these mutations. DNA damage triggers cell cycle checkpoints that are responsible for co-ordinating cell cycle arrest and DNA repair. Defects in checkpoint signalling components such as ataxia telangiectasia mutated (ATM) occur in a low proportion of cancers and are responsible for reduced DNA repair and increased genomic instability. Here we have investigated the AURKA-PLK1 cell cycle checkpoint recovery pathway that is responsible for exit from the G2 phase cell cycle checkpoint arrest. We demonstrate that dysregulation of PP6 and AURKA maintained elevated PLK1 activation to promote premature exit from only ATM, and not ATR-dependent checkpoint arrest. Surprisingly, depletion of the B55α subunit of PP2A that negatively regulates PLK1 was capable of overcoming ATM and ATR checkpoint arrests. Dysregulation of the checkpoint recovery pathway reduced S/G2 phase DNA repair efficiency and increased genomic instability. We found a strong correlation between dysregulation of the PP6-AURKA-PLK1-B55α checkpoint recovery pathway with signatures of defective homologous recombination and increased chromosomal instability in several cancer types. This work has identified an unrealised source of G2 phase DNA repair defects and chromosomal instability that are likely to be sensitive to treatments targeting defective repair.

Highlights

Cells are constantly exposed to stresses that producedDNA damage such as single or double strand breaks
G2 phase checkpoint arrest To investigate the defective ataxia telangiectasia mutated (ATM) checkpoint function produced by dysregulated AURKA- PLK1 pathway, we stably over-expressed wild type AURKA in two ATM checkpoint functional melanoma cells lines, A2058 and A375
The effect of AURKA over-expression was restricted to G2 phase ATM-dependent checkpoint activated cells, with few obvious effects observed in normal cell cycle progression into mitosis

Summary

Introduction

Cells are constantly exposed to stresses that producedDNA damage such as single or double strand breaks. To ensure the fidelity and integrity of the genome, mechanisms to detect and repair DNA damage are co-ordinated by cell cycle checkpoints. These delay cell cycle progression to allow time for repair to occur before allowing cell division and regulate DNA repair processes. When DNA damage is detected during G2 phase ATM/ ATR kinases activate the checkpoint kinases CHK2 and Fernando et al Oncogenesis (2021)10:41. Once damage is repaired checkpoint signals are switched off to resume cell cycle; a process termed as checkpoint recovery. PLK1 is an essential mitotic kinase that regulates mitotic entry and progression[6], and plays a pivotal role in G2 phase checkpoint recovery[7]. BORA, which is an AURKA cofactor required to promote

Methods

Results

Conclusion