N-ras mRNA expression is unaffected in glutathione-depleted cells of hematopoietic origin

Glutathione (GSH) depletion in mitogen-stimulated T lymphocytes has been shown to markedly inhibit their proliferative response. This block in proliferation is associated with a significant reduction in total RNA and DNA synthesis; however, the specific mechanism involved in this inhibition of proliferation is unknown. Miller et al. have reported that lowering intracellular GSH levels by greater than 30%, in murine and human tumor cell lines of non-hematopoietic origin, leads to down-regulation of Ha-, Ki-, and N-ras oncogene expression [Miller, A.C., Gafner, J., Clark, E.P. and Samid, D. (1993) Mol. Cell Biol., 13, 4416–4422]. The reduction in ras transcript levels correlated with the extent of GSH depletion and was independent of the specific mode of oncogene activation. Since the activity of p21ras is thought to be involved in pathways of T cell activation, we set out to determine whether down-regulation of ras expression in T cells could be the mechanism by which T cell proliferation was inhibited in GSH-depleted T lymphocytes. Despite reducing the GSH level of concanavalin A-activated human peripheral blood mononuclear cells by 66%, no effect on ras mRNA expression was observed. Similarly, no reduction of ras transcript levels were detected in a human T cell line (Jurkat) or in a human monocytic cell line (THP-1) depleted of glutathione. Our results demonstrate that the mechanism by which GSH depletion inhibits T cell proliferation does not appear to involve a decrease in ras mRNA expression. In addition, our results suggest that differences in the regulation of ras mRNA expression may exist between lymphoid/monocytic cells and cells of non-hematopoietic origin.