Ras controls tumor necrosis factor receptor-associated factor (TRAF)6-dependent induction of nuclear factor-kappa B - Selective regulation through receptor signaling components

In the present study, we show that Ras activity differentially controls int erleukin (IL)-1 induced transcription factor activation by selective regula tion of responses mediated by receptor complex components. Initial experime nts revealed that stimulation with IL-1 caused a rapid, matrix-dependent ac tivation of Ras. The effect was transient, peaking at 5 min and returning t o base levels after 30 min. Activation correlated with pronounced changes i n cell shape in EGFPH-Ras transfected cells. Transfection with the dominant negative mutant, Ras(Asn-17), inhibited IL-1 induced activation of the IL- 8 promoter as well as of NF-kappaB and AP-1 synthetic promoters in transien t transfection assays. Furthermore, overexpression of the IL-1 signaling pr oteins TRAF6 or MyD88 gave characteristic activation of IL-8, which was acc entuated in the presence of IL-1. Co-transfection with Ras(Asn-17) gave a d ose-dependent inhibition of TRAF6-induced responses in the presence and abs ence of IL-1, but had no effect on MyD88 mediated activity. Similarly, indu ction of NF-kappaB was abolished by Ras(Asn-17) only in TRAF6-transfected c ells. In contrast, inhibiting Ras activity limited AP-1-mediated responses through both receptor complex proteins. Constitutively active Ras(VaI-12) i ncreased the TRAF6 induced activity of the NF-kappaB pathway similar to the effect induced by IL-1, while the Ras(VaI-12) induced activity was not inh ibited by co-transfection with a dominant negative TRAF6. Our data show tha t activation of the Ras GTPase is an early, matrix-dependent response in IL -1 signaling which participates in structural regulation of IL-1-induced ge nes. In addition, they show that the Ras induced effect selectively regulat es TRAF6-mediated activation of the NF-kappaB pathway, suggesting that Ras GTPase represents a convergence point in structural and cytokine responses, with distinct effects on a subset of downstream signaling events.