Tachykinin-1 receptor stimulates proinflammatory gene expression in lung epithelial cells through activation of NF-κB via a Gq-dependent pathway

The respiratory tract is innervated by irritant-responsive sensory nerves, which, on stimulation, release tachykinin neuropeptides in the lung. Tachykinins modulate inflammatory responses to injury by binding to tachykinin ( neurokinin) receptors present on various pulmonary cell types. In the present study, the activation of the proinflammatory transcription factor NF-kappa B in lung epithelial cells was investigated as a mechanism by which tachykinins stimulate inflammatory processes. In A549 human lung epithelial cells transfected with the tachykinin-1 receptor (Tacr1), treatment with the Tacr1 ligand substance P (SP) resulted in NF-kappa B activation, as judged by transcription of an NF-kappa B-luciferase reporter gene and production of interleukin-8, a chemokine whose expression is upregulated by NF-kappa B. SP caused a dose-dependent activation of NF-kappa B that was inhibited by the selective Tacr1 antagonist RP67580. Tacr1 is a G protein-coupled receptor capable of activating both the G(q) and G(s) families of G proteins. Expression of inhibitory peptides and constitutively active G protein mutants revealed that G(q) signaling was both necessary for Tacr1-induced NF-kappa B activation and sufficient for NF-kappa B activation in the absence of any other treatment. Treatment with pharmacological inhibitors to investigate events downstream of G(q) revealed that Tacr1-induced NF-kappa B activation proceeded through an intracellular signaling pathway that was dependent on phospholipase C, calcium, Ras, Raf-1, MEK, Erk, and proteasome function. These results identify intracellular signaling mechanisms that underlie the proinflammatory effects of tachykinins, which previously have been implicated in lung injury and disease.