Submitted to: Keystone Symposia
Publication Type: Abstract Only
Publication Acceptance Date: 10/7/2005
Publication Date: 2/10/2006
Citation: Kogut, M.H., Genovese, K.J., He, H. 2006. Stimulation of avian heterophils by different toll-like agonists induce Ras-dependent and Ras-independent activation of ERK signaling [abstract]. Innate Immunity Keystone Symposia. p. 70.
Technical Abstract: We have recently shown that the TLR agonists, flagellin (FLG–TLR5) and LPS (TLR4), stimulate functional activation and cytokine gene expression via the extracellular signal regulated kinase 1/2 (ERK 1/2) MAP kinase cascade. However, the mechanism of these signaling events remains unknown. In mammals, the small GTP-binding protein Ras mediates ERK 1/2 activation through activation of downstream effectors Raf-MEK-ERK in response to a variety of stimuli. It is not clear whether the Ras cascade plays a role in TLR signaling. In the present study, we investigated the role of Ras in FLG and LPS-mediated signaling in ERK activation in chicken heterophils. Treatment of heterophils with LPS caused a time-dependent activation of RAS, Raf-1, and ERK. The LPS-induced increase in Ras activity was inhibited by a specific Ras inhibitor (FTI-277). Likewise, Raf-1 phosphorylation by LPS was inhibited by FTI-277 and a Raf-1 inhibitor (GW 5074). The LPS-induced increase in ERK activity was inhibited by FTI-277, GW 5074, and an MEK inhibitor (PD 098059). Treatment of the heterophils with FLG had no activating effect on Ras, but induced time-dependent activations of Raf-1 and ERK. These results were supported by the lack of inhibition of Ras activation, Raf-1 phosphorylation, and ERK activation by treatment with FTI-277. Treatment with GW 5074 and PD098059 inhibited the FLG-induced increase in ERK activity. The results demonstrate that for the first time that Ras is involved in LPS signaling as an early event by associating with TLR4 (Ras-dependent), but FLG signaling via TLR5 is a Ras-independent event.