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Mismatch repair, G(2)/M cell cycle arrest and lethality after DNA damage

G Aquilina1, M Crescenzi, M Bignami

  • 1Laboratory of Comparative Toxicology and Ecotoxicology, Section of Chemical Carcinogenesis, Istituto Superiore di Sanita', Viale Regina Elena 299, 00161 Roma, Italy.

Carcinogenesis
|December 11, 1999
PubMed

Insights

The mismatch repair (MMR) pathway is not essential for activating the G(2)/M checkpoint after DNA damage from CCNU or gamma radiation. However, MMR is crucial for G(2) arrest following N-methyl-N-nitrosourea exposure.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Genetics

Background:

  • The mismatch repair (MMR) pathway is critical for DNA replication fidelity.
  • Its role in processing DNA damage from external agents and activating cell cycle checkpoints is less understood.
  • DNA repair and cell cycle control are interconnected, with MMR potentially influencing the G(2)/M checkpoint.

Purpose of the Study:

  • To investigate the role of mismatch repair (MMR) in activating the G(2)/M cell cycle checkpoint after exposure to DNA-damaging agents.
  • To compare the cellular response of MMR-proficient and MMR-deficient cells to various DNA-damaging agents.

Main Methods:

  • Utilized MMR-proficient HeLa and Raji cells alongside isogenic MMR-defective variants (deficient in hMutLalpha or hMutSalpha).
  • Exposed cells to DNA-damaging agents: N-(2-chloroethyl)-N'-cyclohexyl-N-nitrosourea (CCNU), gamma-radiation, and N-methyl-N-nitrosourea (MNU).
  • Assessed cell survival and analyzed cell cycle distribution to evaluate G(2)/M checkpoint activation.

Main Results:

  • MMR-defective cells showed sensitivity to CCNU but not gamma-radiation.
  • G(2) arrest occurred efficiently in MMR-defective cells exposed to CCNU or gamma-radiation.
  • MNU did not induce G(2) accumulation in MMR-defective cells, indicating MMR's dependence for MNU-induced alterations.
  • G(2)/M checkpoint activation by CCNU and gamma-radiation is independent of functional MMR.
  • No direct correlation between G(2) arrest extent and cell killing suggests MMR processes both lethal and non-lethal DNA damage.

Conclusions:

  • Functional mismatch repair (MMR) is not required for G(2)/M checkpoint activation following CCNU or gamma-radiation exposure.
  • MMR is essential for inducing G(2) arrest in response to methylating agents like MNU.
  • The G(2) arrest observed reflects the processing of diverse DNA damages by MMR, not solely lethal lesions.

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