Activation of the Ras small guanine nucleotide-binding proteins upon IL-2 stimulation of T lymphocytes has been described previously. However, the relevance of the Ras molecules in the cellular events triggered by IL-2 still remained to be clarified. To analyze the effects of Ras inhibition in early proliferative responses to IL-2, we have transiently expressed a Ras dominant negative mutant carrying a point mutation in codon 17 (Ser17Asn or N17) under a tetracycline-controlled expression system. We have found that Ras has a crucial role in both proliferation and prevention of apoptosis through IL-2R, while IL-4 promotes proliferation and inhibits apoptosis by Ras-independent signals. The use of flow cytometry has allowed us to correlate the effects in proliferation and apoptosis with the expression level of the Ras mutant among the transfected population. Furthermore, the availability of a murine T cell line that can be maintained independently in the presence of IL-2 or IL-4 has provided specificity controls, since IL-4 does not trigger Ras activation.
Animals Apoptosis