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ATR and Chk1 suppress a caspase-3-dependent apoptotic response following DNA replication stress

Katie Myers1, Mary E Gagou, Pedro Zuazua-Villar

  • 1Institute for Cancer Studies, School of Medicine and Biomedical Sciences, University of Sheffield, Sheffield, United Kingdom.

Plos Genetics
|January 3, 2009
PubMed

Insights

The ATR-Chk1 pathway, not ATM, controls apoptosis during DNA replication stress. Depleting ATR or Chk1 enhances cell death, distinguishing this pathway from that responding to ionizing radiation.

Area of Science:

  • Cellular Biology
  • Molecular Biology
  • Genetics

Background:

  • Ataxia-Telangiectasia Mutated (ATM) and ATM- and Rad3-related (ATR) kinases regulate DNA damage responses.
  • The role of ATM in apoptosis after ionizing radiation (IR) is known, but less is understood about apoptosis control following DNA replication stress.
  • ATR's downstream target, Chk1, is implicated in protecting cells from apoptosis induced by replication inhibitors and IR.

Purpose of the Study:

  • To investigate the roles of ATM and ATR/Chk1 kinase cascades in apoptosis following replication stress.
  • To determine the relationship between Chk1-suppressed apoptotic pathways responding to replication stress and IR.

Main Methods:

  • Used siRNA-mediated depletions and specific inhibitors to manipulate ATM and ATR/Chk1 signaling pathways.
  • Studied two tumor cell lines and fibroblasts from patients with inherited mutations.
  • Assessed apoptosis, DNA replication stress markers (RPA foci, RPA34 hyperphosphorylation), and caspase 3 activation.

Main Results:

  • Depletion of ATM had minimal effect on apoptosis induced by replication inhibitors.
  • Depletion of ATR or Chk1 strongly enhanced cell death induced by replication inhibitors.
  • Early replication stress events in apoptosis-committed cells were absent in ATM-depleted cells but present in ATR/Chk1-depleted cells.
  • Replication stress-induced apoptosis did not require ATM and activated caspase 3 in both p53-proficient and -deficient cells.

Conclusions:

  • The ATR-Chk1 signaling pathway is crucial for regulating cell death in response to DNA replication stress.
  • The Chk1-suppressed pathway protecting cells from replication stress is distinct from the pathway protecting against IR.

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