Heterotrimeric Gi/Goproteins modulate endothelial TLR signaling independent of the MyD88-dependent pathway

Abstract

The innate immune recognition of bacterial lipopolysaccharide (LPS) is mediated by Toll-like receptor 4 (TLR4) and results in activation of proinflammatory signaling including NF-κB and MAPK pathways. Heterotrimeric G proteins have been previously implicated in LPS signaling in macrophages and monocytes. In the present study, we show that pertussis toxin sensitive heterotrimeric G proteins (Gαi/o) are involved in the activation of MAPK and Akt downstream of TLR2, TLR3, and TLR4 in endothelial cells. Gαi/oare also required for full activation of interferon signaling downstream of TLR3 and TLR4 but are not required for the activation of NF-κB. We find that Gαi/o-mediated activation of the MAPK is independent of the canonical MyD88, interleukin-1 receptor-associated kinase, and tumor necrosis factor receptor-associated factor 6 signaling cascade in LPS-stimulated cells. Taken together, the data presented here suggest that heterotrimeric G proteins are widely involved in TLR pathways along a signaling cascade that is distinct from MyD88-TRAF6.