DNA fragmentation and cytotoxicity from increased cellular deoxyuridylate

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Thymidylate deprivation leads to increased intracellular deoxyuridine triphosphate (dUTP) and deoxyuridine monophosphate (dUMP) incorporation into DNA.
• Cytotoxicity from thymidylate deprivation, known as thymineless death, is typically attributed to reduced intracellular thymidine triphosphate (dTTP).

Purpose of the Study:

• To investigate if elevated dUTP levels contribute to the cytotoxicity observed during thymidylate deprivation.
• To determine the role of dUTP accumulation in cell death, independent of dTTP reduction.

Main Methods:

• Cells were exposed to deoxyuridine in HAT medium to increase intracellular dUTP without decreasing dTTP.
• Cell viability and DNA fragmentation were assessed.
• DNA polymerase assays were used to measure nucleotide pools, including distinguishing dUTP from dTTP.

Main Results:

• Exposure to deoxyuridine led to significant dUTP accumulation, reaching levels comparable to or exceeding dTTP.
• Cells exposed to deoxyuridine exhibited decreased viability and DNA fragmentation, mirroring effects of thymidylate depletion.
• A significant portion of the measured "dTTP" in methotrexate-treated cells was actually dUTP, explaining prior observations.

Conclusions:

• Elevated intracellular dUTP is a significant contributor to the cytotoxicity of thymidine starvation.
• The findings suggest that dUTP accumulation, not solely dTTP reduction, drives thymineless death.
• This work clarifies the role of dUTP in drug-induced cytotoxicity and may explain previous experimental findings.