SUPERINDUCTION OF IL-2 GENE-EXPRESSION BY VOMITOXIN (DEOXYNIVALENOL) INVOLVES INCREASED MESSENGER-RNA STABILITY

To better understand molecular mechanisms by which the trichothecene v omitoxin (VT) superinduces cytokine gene expression, we studied the po sttranscriptional effects of this mycotoxin on interleukin-2 (IL-2) ge ne expression in murine EL-4 thymoma cells stimulated with phorbol 12- myristate 13-acetate and ionomycin (PMA + ION). Northern analysis reve aled that doses of 50 to 500 ng/ml VT superinduced IL-2 mRNA expressio n in a dose-and time-dependent manner in a synchronous model where VT was added at onset of PMA + ION stimulation. In accordance with the mR NA levels, IL-2 production was significantly elevated in the presence of 50 to 250 ng/ml VT. Superinduction of IL-2 mRNA was also observed i n a delayed synchronous model (VT added 20 hr after PMA + ION stimulat ion) and an asynchronous model (VT added 20 hr after PIMA + ION stimul ation and removal). To assess the effects of VT (500 ng/ml) on IL-2 mR NA half-life, three transcriptional inhibitors were used in the delaye d synchronous model. Actinomycin D (ActD) had a pronounced stabilizing effect on IL-2 mRNA but not on mRNA for the housekeeping gene GAPDH. VT did not affect IL-2 mRNA levels in ActD-treated cells. Although 5,6 -dichloro-beta-D-ribofuranosyl-benzimidazole (DRB) also had a stabiliz ing effect on IL-2 mRNA, IL-2 mRNA half-life t(1/2) in VT-treated cell s was three times that of control. In contrast, inclusion of cyclospor in A (CsA) into the cultures specifically arrested IL-2 transcription in EL-4 cells without any stabilizing effect. VT exposure in the prese nce of CsA markedly prolonged the half-life of IL-2 mRNA in a dose-dep endent manner. The t(1/2) for IL-2 mRNA in the control culture was 2.1 hr, whereas t(1/2) was 3.1, 3.4, 4.2, and 10.5 hr in cultures contain ing 50, 100, 250, and 500 ng/ml VT, respectively, These results sugges t that VT can superinduce IL-2 at both the mRNA and the protein level and that this superinduction can be explained, in part, by posttranscr iptional mechanisms such as enhanced mRNA stability. (C) 1997 Academic Press.