REDOX CONTROL OF RESISTANCE TO CIS-DIAMMINEDICHLOROPLATINUM-(II) (CDDP) - PROTECTIVE EFFECT OF HUMAN THIOREDOXIN AGAINST CDDP-INDUCED CYTOTOXICITY

Thioredoxin is a small ubiquitous protein with multiple biological fun ctions, including cellular defense mechanisms against oxidative stress . In the present study, we investigated the role of human thioredoxin (hTRX) in the acquisition of cellular resistance to cis-diamminedichlo roplatinum (II) (CDDP). The expression and activity of hTRX in Jurkat T cells was dose-dependently enhanced by exposure to CDDP, as determin ed by immunoblot analysis and insulin reducing assay. Furthermore, chl oramphenicol acetyltransferase analysis using the hTRX promoter-report er gene construct revealed that treatment of Jurkat cells with CDDP ca used transcriptional activation of the hTRX gene, which might be media ted through increased generation of intracellular reactive oxygen inte rmediates. To examine the biological significance of hTRX induction, w e established hTRX-overexpressing derivatives of L929 fibrosarcoma cel ls by stable transfection with the hTRX cDNA. The clones, which consti tutively expressed the exogenous hTRX, displayed increased resistance to CDDP-induced cytotoxicity, compared with the control clones. After exposure to CDDP, the control cells showed a significant increase in t he intracellular accumulation of peroxides, whereas the hTRX-transfect ed cells did not. Taken together, these results suggest that overexpre ssed hTRX is responsible for the development of cellular resistance to CDDP, possibly by scavenging intracellular toxic oxidants generated b y this anticancer agent.