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Mismatch repair-mediated G2/M arrest by 6-thioguanine involves the ATR-Chk1 pathway

Kazuhiko Yamane1, Kerri Taylor, Timothy J Kinsella

  • 1Department of Radiation Oncology, Case Western Reserve University, Case Comprehensive Cancer Center/University Hospitals of Cleveland, Cleveland, OH 44106-4942, USA.

Biochemical and Biophysical Research Communications
|April 28, 2004
PubMed

Insights

DNA mismatch repair (MMR) deficiency causes chemotherapy resistance. 6-thioguanine (6-TG) triggers DNA mismatches, activating the ATR-Chk1 pathway, leading to cell cycle arrest and apoptosis in MMR-proficient cancer cells.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Cancer Research

Background:

  • DNA mismatch repair (MMR) deficiency is linked to resistance against chemotherapy drugs like 6-thioguanine (6-TG).
  • 6-TG induces DNA mismatches, causing G2/M cell cycle arrest and apoptosis in MMR-proficient (MMR(+)) cancer cells, but the underlying signaling is unclear.

Purpose of the Study:

  • To elucidate the signaling pathways involved in the G2/M cell cycle arrest and apoptosis induced by 6-TG in MMR(+) human cancer cells.

Main Methods:

  • MMR(+) HeLa cells were treated with 6-TG (3microM) for up to 4 days.
  • Phosphorylation of Chk1 and Chk2 was assessed.
  • Small interfering RNA (siRNA) was used to knock down ataxia telangiectasia-related (ATR) kinase and Chk1 kinase.
  • ATM(-/-) and ATM(+) human fibroblasts were used to evaluate the role of the ATM-Chk2 pathway.

Main Results:

  • Prolonged 6-TG treatment led to progressive phosphorylation of Chk1 and Chk2, correlating with G2/M arrest.
  • siRNA-mediated knockdown of ATR or Chk1 abolished the G2/M checkpoint and increased apoptosis.
  • The ATM-Chk2 pathway did not appear to play a significant role in the 6-TG response.

Conclusions:

  • 6-TG DNA mismatches activate the ATR-Chk1 pathway in MMR(+) cells.
  • This activation results in a G2/M checkpoint response, contributing to the observed cell cycle arrest and apoptosis.

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