Ozer U1, Barbour KW1, Clinton SA1, Berger FG2.[expand title=”Show Affiliations”]
- Department of Biological Sciences, and Center for Colon Cancer Research, University of South Carolina, Columbia, South Carolina.
- Department of Biological Sciences, and Center for Colon Cancer Research, University of South Carolina, Columbia, South Carolina [email protected]
Thymidylate synthase (TYMS; EC 188.8.131.52) catalyzes the reductive methylation of 2′-deoxyuridine-5′-monophosphate (dUMP) by N(5),N(10)-methyhlenetetrahydrofolate, forming dTMP for the maintenance of DNA replication and repair. Inhibitors of Thymidylate synthase have been widely used in the treatment of neoplastic disease. A number of fluoropyrimidine and folate analogs have been developed that lead to inhibition of the enzyme, resulting in dTMP deficiency and cell death. In the current study, we have examined the role of oxidative stress in response to TYMS inhibitors. We observed that intracellular reactive oxygen species (ROS) concentrations are induced by these inhibitors and promote apoptosis. Activation of the enzyme NADPH oxidase (NOX), which catalyzes one-electron reduction of O2 to generate superoxide (O2 (●-)), is a significant source of increased ROS levels in drug-treated cells. However, gene expression profiling revealed a number of other redox-related genes that may contribute to ROS generation. Thymidylate synthase inhibitors also induce a protective response, including activation of the transcription factor nuclear factor E2-related factor 2 (NRF2), a critical mediator of defense against oxidative and electrophilic stress. Our results show that exposure to Thymidylate synthase inhibitors induces oxidative stress that leads to cell death, while simultaneously generating a protective response that may underlie resistance against such death.
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