TPL-2 INDUCES IL-2 EXPRESSION IN T-CELL LINES BY TRIGGERING MULTIPLE SIGNALING PATHWAYS THAT ACTIVATE NFAT AND NF-KAPPA-B

The Tpl-2 kinase activates the nuclear factor of activated T cells (NF AT) and induces IL-2 expression in T-cell lines. Here we show that the activation of the IL-2 promoter by Tpl-2 is inhibited by mutant signa ling molecules that inhibit the mitogen-activated protein kinase (MAPK ) or the calcineurin/NFAT pathways and is promoted by combinations of signaling molecules that activate these pathways, We, therefore, concl ude that signals generated by the convergence of the MAPK and the calc ineurin/NFAT pathway are necessary and sufficient for the activation o f the IL-2 promoter by Tpl-2. The activation of both the IL-2 promoter and an NEAT-driven minimal promoter were shown to depend on signals t ransduced by Raf1. However, it was only the IL-2 promoter whose activa tion by Tpl-2 was fully blocked by the dominant negative mutant MEK1S2 18/222A and the MEK1/MEK2 inhibitor PD098059, Since the activation of NEAT is MAPK-dependent these findings suggested that the activation of MAPK by Tpl-2 is either independent or only partially dependent on ME K1 and MEK2, In addition, they suggested that the activation of the IL -2 promoter is under the control of not only NFAT but also a second fa ctor whose activation is MEK-dependent. Experiments in COS-1 and EL-4 cells confirmed both hypotheses and revealed that the second factor ac tivated by Tpl-2 is NF-kappa B, While the activation of the IL-2 promo ter and an NEAT-driven minimal promoter by Tpl-2 was fully blocked by the dominant negative mutant NFAT Delta 418, it was only partially blo cked by the calcineurin inhibitor cyclosporin A suggesting that the Tp l-2-mediated NFAT activation is under the control of a combination of calcineurin-dependent and independent pathways. Both pathways were ful ly blocked by Bcl-2 or Bcl-X-L.