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TRICHOTHECENE EXPOSURE LEADS TO MITOCHONDRIAL ROS-MEDIATED CELL DEATH IN YEAST

We had previously identified several yeast deletion mutants that conferred resistance to trichothecin (Tcin), a type B trichothecene and DON congener, which revealed a critical role for mitochondria in trichothecene-toxicity (1). Mitochondrial translation was directly inhibited prior to damage to mitochondrial membrane integrity and independent of cytosolic translation inhibition (2). To further explore the molecular mechanism of trichothecene toxicity we screened the yeast diploid knockout (YKO) library to identify deletion mutants that exhibited increased sensitivity to Tcin at concentrations that are sublethal to nonlethal (0.5-2µM) to the wild-type parental strain BY4743. We identified 121 deletion mutants which were disrupted in functions involved in cellular damage control from the toxic effects of trichothecenes, including DNA repair and response (15.7%), RNA degradation and stability (29.8%), ribosome biogenesis and protein degradation (10.7%). Saccharomyces Genome Database (SGD) phenotypic analysis revealed that a large fraction (42%) of the Tcin-sensitive mutants exhibited high sensitivity to oxidative stress. Oxidant-sensitive 2’, 7’-dichlorofluorescin diacetate (DCFH-DA) staining of these mutants revealed that Tcin-induced ROS generation was up to 3-fold higher relative to BY4743. We observed a significant and dose-dependent increase in ROS levels (2-4 folds) in BY4743 treated with DON, T-2 and DAS and found a strong correlation between ROS generation and cell death. Moreover, treatment with antioxidants, such as ascorbic acid and vitamin E increased cell survival 3-4-fold in T-2 treated cells and 6-9-fold in Tcin treated cells, suggesting a direct role for ROS in trichothecene-mediated cell death. Trichothecenes failed to generate ROS in the petite strain lacking mitochondrial DNA (ρo) or when mitochondrial membrane potential (ψ mito ) was depolarized with the ionophore FCCP (carbonilcyanide p-triflouromethoxyphenylhydrazone), suggesting the mitochondrial origin of trichothecene-induced ROS. REFERENCES