Sg. Li et al., SUPERINDUCTION OF IL-2 GENE-EXPRESSION BY VOMITOXIN (DEOXYNIVALENOL) INVOLVES INCREASED MESSENGER-RNA STABILITY, Toxicology and applied pharmacology, 147(2), 1997, pp. 331-342
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.