Ac. Miller et al., POSTTRANSCRIPTIONAL DOWN-REGULATION OF RAS ONCOGENE EXPRESSION BY INHIBITORS OF CELLULAR GLUTATHIONE, Molecular and cellular biology, 13(7), 1993, pp. 4416-4422
Alterations in intracellular glutathione (GSH) content are known to af
fect intrinsic responses to ionizing radiation. More recently, it beca
me apparent that radiation responses may depend also on the expression
of specific oncogenes, including ras. These findings, suggesting a po
ssible link between GSH and ras, led us to examine the effect of vario
us GSH modulators on ras expression. Treatment of c-Ha-ras-transformed
NIH 3T3 cells with L-buthionine S'R'-sulfoximine, dimethylfumarate, o
r -1,3-bis(trans-4-hydroxycyclohexyl)-N'-nitrosourea resulted in dose-
and time-dependent reduction in ras mRNA steady-state levels followed
by a decrease in ras-encoded p21 protein production. The effect on ra
s correlated with the extent of GSH decline, was common to different m
embers of the ras family, and was independent of the mode of oncogene
activation or cell phenotype. Indeed, similar drug effects were observ
ed with murine cells in which overexpression of the c-Ha-ras proto-onc
ogene was due to transcriptional activation (PR4, nontumorigenic) or g
ene amplification (NIH 136, tumorigenic) and with malignant cells expr
essing a mutated Ha-ras (RS504). Moreover, N-ras, EJras, and Ki-ras in
human tumor cells were similarly affected. Molecular analysis reveale
d a significant decrease in ras mRNA half-life in cells subjected to G
SH inhibition, an effect that required de novo protein synthesis, but
there was no change in the rate of gene transcription. These results i
ndicate that pharmacological manipulation of cellular GSH content can
down-regulate ras expression at the posttranscriptional level by desta
bilizing ras transcripts. The potential clinical implications are disc
ussed.