Effects of T-2 toxin on induction of petite mutants and mitochondrial function in Saccharomyces cerevisiae

Trichothecene mycotoxins inhibit mitochondrial translation--implication for the mechanism of toxicity

Fusarium head blight (FHB) reduces crop yield and results in contamination of grains with trichothecene mycotoxins. We previously showed that mitochondria play a critical role in the toxicity of a type B trichothecene. Here, we investigated the direct effects of type A and type B trichothecenes on mitochondrial translation and membrane integrity in Saccharomyces cerevisiae. Sensitivity to trichothecenes increased when functional mitochondria were required for growth, and trichothecenes inhibited mitochondrial translation at concentrations, which did not inhibit total translation. In organello translation in isolated mitochondria was inhibited by type A and B trichothecenes, demonstrating that these toxins have a direct effect on mitochondrial translation. In intact yeast cells trichothecenes showed dose-dependent inhibition of mitochondrial membrane potential and reactive oxygen species, but only at doses higher than those affecting mitochondrial translation. These results demonstrate that inhibition of mitochondrial translation is a primary target of trichothecenes and is not secondary to the disruption of mitochondrial membranes.

Isolation and characterization of Saccharomyces cerevisiae mutants resistant to T-2 toxin

T-2 toxin, a trichothecene mycotoxin, inhibits the growth of Saccharomyces cerevisiae. We have isolated nine spontaneous S. cerevisiae mutants resistant to this toxin. The mutants were distinguished from the wild type according to their degree of resistance to T-2 toxin on media with dextrose or glycerol as the carbon source. Generation time, mutation stability and level of cross-resistance to roridin A, another trichothecene, were determined for each mutant. The T-2 toxin resistant mutants were further characterized by subsequent tests involving cross-resistance and collateral sensitivity to chlorampenicol, neomycin, paromomycin, ethidium bromide and thiolutin. Mutants have been placed into three subgroups and the mechanism of T-2 toxin resistance in each group has been postulated. Mutant HK1 is the first S. cerevisiae isolate resistant to roridin A. One particular isolate, mutant HK11, carries a single recessive nuclear mutation. This mutation was termed ttt (for T-2 toxin resistant).

Alteration of multiple cell membrane functions in L-6 myoblasts by T-2 toxin: an important mechanism of action

Recent studies suggest that T-2 toxin interacts with cell membranes and alters membrane function. This study was done to assess the effect of T-2 toxin on a broad range of cell membrane functions in L-6 myoblasts. The following parameters were assessed after exposure to T-2 toxin for 10 min: (1) the uptake of calcium, rubidium, and glucose; (2) the uptake of leucine and tyrosine and incorporation into protein; (3) the uptake of thymidine and incorporation into DNA; and (4) residual cellular lactate dehydrogenase (LDH) as a measure of cell membrane integrity. The effects of T-2 toxin on these parameters were: (1) The minimal effective concentration (MEC) of T-2 toxin that caused a reduction in the uptake of calcium and glucose was 4 pg/ml. The uptake of rubidium was increased at 0.4 pg/ml and then reduced at 4 pg/ml and higher concentrations. (2) The MEC for reduction of the uptake of leucine and tyrosine and their incorporation into protein was 4 pg/ml. (3) Thymidine uptake and incorporation into DNA showed a biphasic response with an increase at 0.4 pg/ml and a reduction at 4 pg for uptake and 40 pg/ml for incorporation. (4) Intracellular LDH was reduced at 4 ng/ml. (5) Calcium efflux was reduced after 1-, 5-, and 15-min exposures to T-2 toxin in a concentration of 40 ng/ml. All of the changes noted, including protein synthesis inhibition, were present to a significant degree within 10 min of exposure to T-2 toxin. This time interval is too short to attribute all of these effects directly to protein synthesis inhibition since most short-lived proteins have half-lives measured in hours. In conclusion, T-2 toxin appears to have multiple effects on cell membrane function at very low concentrations (0.4 pg/ml to 4 ng/ml), which are independent of protein synthesis inhibition. These likely include effects either direct or indirect on amino acid, nucleotide, and glucose transporters, as well as calcium and potassium (rubidium) channel activities.

Suppressive and enhancing effect of T-2 toxin on murine lymphocyte activation and interleukin 2 production

T-2 toxin, a fungal metabolite shown previously to exert potent immunosuppressive effects, was examined for its effects on activation and interleukin 2 (IL 2) production by murine and rat splenocytes. Splenocytes (1 X 10(6) cells/well) were incubated with 1 microgram Concanavalin A (Con A) for 48 h at which time cellular protein and DNA synthesis by these cells were ascertained using radiolabeled precursors. IL 2 synthesis was determined from the cell supernatant using the IL 2-requiring cell line CTLL. Spleen cells from mice treated for 4 consecutive days with 2 mg/kg toxin exhibited a 50% reduction in in vitro Con A activation but the supernatant IL 2 levels from these cells was 4-fold higher than cells from control mice. In vitro exposure of Con A-activated normal spleen cells to various toxin doses for 48 h resulted in diminished protein and DNA synthesis at 0.4 ng toxin with maximum inhibition at 1 ng (50% inhibition (TCID50) = 0.5 ng). Enhanced synthesis of both products was observed at lower toxin concentrations. IL 2 production by these cells followed a similar toxin dose response. Rat splenocytes were slightly more resistant and CTLL cells were slightly more sensitive to T-2 toxin than mouse splenocytes. These results indicate the variable effects a cytotoxic agent can have on lymphoid cells and that dosage is an important parameter for these effects.