p21(ras) function is important for T cell antigen receptor and protein kinase C regulation of nuclear factor of activated T cells

In T cells, signals initiated at the TCR, and in particular activation of protein kinase C (PKC), can activate the p21(ras) proteins. Triggering of the TCR and PKC is required for the efficient production of the T cell growth factor, IL-2. IL-2 gene transcription is controlled by a 275-bp enhancer that is known to contain binding sites for many transcription factors including the octamer family of proteins, NFκB, AP-1, and a T cell-specific factor, NFAT (nuclear factor of activated T cells). NFAT binds to a region of the IL- 2 enhancer that has been defined as a TCR response element (ARRE-2), and is induced in response to increases in intracellular calcium, stimulation of PKC, or triggering of the TCR. To determine whether p21(ras) is involved in the signals that regulate NFAT, we examined the effect of expression of a constitutively active p21(ras) mutant, v-Ha-ras, and a dominant inhibitory mutant of p21(ras), c-Ha-ras(asn17), on the induction of a NFAT-driven reporter gene (NFAT CAT) during T cell activation. The constitutively active Ras mutant could synergize with the calcium ionophore ionomycin to induce NFAT. In addition, expression of p21(v-Ha-ras) could enhance NFAT CAT induction in response to TCR and PKC agonists. The dominant inhibitory mutant of p21(ras) could prevent NFAT CAT expression in response to PKC or TCR triggering. These data show that Ras regulates NFAT, and that p21(ras) function is important for the TCR- and PKC-regulated pathways that regulate NFAT.