The mismatch repair-mediated cell cycle checkpoint response to fluorodeoxyuridine

Area of Science:

• Molecular Biology
• Cancer Research
• Genetics

Background:

• DNA mismatch repair (MMR) deficiency is linked to hereditary nonpolyposis colorectal cancer and drug resistance.
• 5-Fluorouracil (FU) is a chemotherapy drug whose mechanism of cell killing, especially in MMR-deficient cells, is not fully understood.
• Understanding FdU's cellular response and MMR's role is crucial for optimizing colorectal cancer treatment.

Purpose of the Study:

• To investigate the cellular response to fluorodeoxyuridine (FdU) and elucidate the role of the DNA mismatch repair (MMR) system.
• To determine how MMR deficiency influences cell sensitivity and response to FdU.
• To identify the specific DNA damage signaling pathways involved in FdU treatment.

Main Methods:

• Exposure of cells to varying doses of FdU.
• Analysis of cell cycle progression and DNA damage signaling.
• In vitro binding assays using MutSalpha and FdU:G mispairs.
• Assessment of MMR status and its impact on cellular response.

Main Results:

• MMR mediates DNA damage signaling during S-phase and G2/M arrest in response to low FdU doses, requiring MutSalpha, MutLalpha, and DNA replication.
• ATR kinase, Chk1, and SMC1 phosphorylation are involved in MMR-mediated cell cycle arrest.
• MutSalpha binds FdU:G mispairs, indicating its role as a DNA damage sensor.
• Prolonged FdU treatment leads to MMR-independent G2 arrest and DNA lesion accumulation targeted by the base excision repair (BER) pathway.

Conclusions:

• MMR functions as a direct sensor of FdU-induced DNA lesions, initiating cell cycle arrest via the ATR/Chk1 pathway.
• While MMR is critical for sensing initial FdU damage, other pathways like BER become important for managing higher levels of DNA damage.
• These findings clarify the mechanism of FdU-induced cell killing and highlight the complex interplay of DNA repair pathways in cancer therapy.