p21ras mediates control of IL‐2 gene promoter function in T cell activation.

It has been shown previously in T cells that stimulation of protein kinase C or the T cell antigen receptor leads to a rapid and persistent activation of p21ras as measured by a dramatic increase in the amount of bound GTP. These stimuli are also known to induce the expression of the T lymphocyte growth factor, interleukin‐2 (IL‐2), an essential growth factor for the immune system. Receptor induced activation of p21ras has been demonstrated in several cell types but involvement of protein kinase C as an upstream activator of p21ras appears to be unique to T cells. In this study we show that p21ras acts as a component of the protein kinase C and T cell antigen receptor downstream signalling pathway controlling IL‐2 gene expression. In the murine T cell line EL4, constitutively active p21ras greatly potentiates the phorbol ester and T cell receptor agonist induced production of IL‐2 as measured both by biological assay for the cytokine and by the use of a reporter construct. Active p21ras also partially replaces the requirement for protein kinase C activation in synergizing with a calcium ionophore to induce production of IL‐2. Furthermore, using a dominant negative mutant of ras, Ha‐rasN17, we show that endogenous ras function is essential for induction of IL‐2 expression in response to protein kinase C or T cell receptor stimulation. Activation of ras proteins is thus a necessary but not sufficient event in the induction of IL‐2 synthesis. Ras proteins are therefore pivotal signalling molecules in T cell activation.