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

Biochem Biophys Res Commun. 2004 May 21;318(1):297-302. doi: 10.1016/j.bbrc.2004.04.030.


DNA mismatch repair (MMR) deficiency in human cancers is associated with resistance to a spectrum of clinically active chemotherapy drugs, including 6-thioguanine (6-TG). We and others have shown that 6-TG-induced DNA mismatches result in a prolonged G2/M cell cycle arrest followed by apoptosis in MMR(+) human cancer cells, although the signaling pathways are not clearly understood. In this study, we found that prolonged (up to 4 days) treatment with 6-TG (3microM) resulted in a progressive phosphorylation of Chk1 and Chk2 in MMR(+) HeLa cells, correlating temporally with a drug-induced G2/M arrest. Transfection of HeLa cells with small interfering RNA (siRNA) against the ataxia telangiectasia-related (ATR) kinase or against the Chk1 kinase destroyed the G2/M checkpoint and enhanced the apoptosis following 6-TG treatment. On the other hand, the induction of a G2/M population by 6-TG was similar in ATM(-/-) and ATM(+) human fibroblasts, suggesting that the ATM-Chk2 pathway does not play a major role in this 6-TG response. Our results indicate that 6-TG DNA mismatches activate the ATR-Chk1 pathway in the MMR(+) cells, resulting in a G2/M checkpoint response

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Antimetabolites, Antineoplastic / pharmacology
  • Apoptosis / drug effects
  • Ataxia Telangiectasia Mutated Proteins
  • Base Pair Mismatch / genetics*
  • Blotting, Western
  • Cell Cycle Proteins / metabolism*
  • Checkpoint Kinase 1
  • Checkpoint Kinase 2
  • DNA Repair / genetics*
  • G2 Phase / drug effects*
  • G2 Phase / physiology
  • HeLa Cells
  • Humans
  • In Situ Nick-End Labeling
  • Mitosis / drug effects*
  • Mitosis / physiology
  • Phosphorylation
  • Protein Kinases / metabolism*
  • Protein Serine-Threonine Kinases / metabolism*
  • RNA, Small Interfering / genetics
  • Signal Transduction
  • Thioguanine / pharmacology*
  • Transfection


  • Antimetabolites, Antineoplastic
  • Cell Cycle Proteins
  • RNA, Small Interfering
  • Protein Kinases
  • Checkpoint Kinase 2
  • ATR protein, human
  • Ataxia Telangiectasia Mutated Proteins
  • CHEK1 protein, human
  • CHEK2 protein, human
  • Checkpoint Kinase 1
  • Protein Serine-Threonine Kinases
  • Thioguanine