Endothelin-converting Enzyme 1 and β-Arrestins Exert Spatiotemporal Control of Substance P-induced Inflammatory Signals

Although the intracellular trafficking of G protein-coupled receptors controls specific signaling events, it is unclear how the spatiotemporal control of signaling contributes to complex pathophysiological processes such as inflammation. By using bioluminescence resonance energy transfer and superresolution microscopy, we found that substance P (SP) induces the association of the neurokinin 1 receptor(NK1R) with two classes of proteins that regulate SP signaling from plasma and endosomal membranes: the scaffolding proteins beta-arrestin (beta ARRs) 1 and 2 and the transmembrane metallopeptidases ECE-1c and ECE-1d. In HEK293 cells and non-transformed human colonocytes, we observed that G protein-coupled receptor kinase 2 and beta ARR1/2 terminate plasma membrane Ca2+ signaling and initiate receptor trafficking to endosomes that is necessary for sustained activation of ERKs in the nucleus. beta ARRs deliver the SP-NK1R endosomes, where ECE-1 associates with the complex, degrades SP, and allows the NK1R, freed from beta ARRs, to recycle. Thus, both ECE-1 and beta ARRs mediate the resensitization of NK1R Ca2+ signaling at the plasma membrane. Sustained exposure of colonocytes to SP activates NF-kappa B and stimulates IL-8 secretion. This proinflammatory signaling is unaffected by inhibition of the endosomal ERK pathway but is suppressed by ECE-1 inhibition or beta ARR2 knockdown. Inhibition of protein phosphatase 2A, which also contributes to sustained NK1R signaling at the plasma membrane, similarly attenuates IL-8 secretion. Thus, the primary function of beta ARRs and ECE-1 in SP-dependent inflammatory signaling is to promote resensitization, which allows the sustained NK1R signaling from the plasma membrane that drives inflammation.