Substance P-stimulated interleukin-8 expression in human colonic epithelial cells involves protein kinase Cδ activation

Substance P (SP) participates in acute intestinal inflammation via binding to the G-protein-coupled neurokinin-1 receptor (NK-1R) and release of nuclear factor κB (NF-κB)-driven proinflammatory cytokines from colonic epithelial cells. However, the signal transduction pathways by which SP-NK-1R interaction induces NF-κB activation and interleukin-8 (IL-8) production are not clear. Here, we examined participation of protein kinase C (PKC) in SP-induced IL-8 production in human nontransformed NCM460 colonocytes stably transfected with the human NK-1R (NCM460-NK-1R cells). SP (10^-7 M) induced an early (1 min) phosphorylation of the PKC isoforms PKCδ, PKCθ, and PKCε, followed by I-κB kinase, IκBα , and p65 phosphorylation. Depletion of PKC by phorbol-12-myristate-13-acetate (10 μM) blocked SP-induced IκBα and p65 phosphorylation and IL-8 production. The PKCδ inhibitor rottlerin at a low concentration (1 μM), but not pseudosubstrate PKCθ and PKCε inhibitors (10 μM), significantly reduced IL-8 secretion. PKCδ silencing by RNA interference reduced PKCδ protein expression and SP-induced PKCδ phosphorylation that was associated with diminished IL-8 promoter and NF-κB luciferase activities in response to SP. Moreover, overexpression of wildtype PKCδ increased SP-induced IL-8 promoter- and NF-κB-driven luciferase activities that were rottlerin-sensitive. We conclude that PKCδ plays an important role in SP-induced proinflammatory signaling in human colonocytes.