Protein kinase D₂ mediates lysophosphatidic acid-induced interleukin 8 production in nontransformed human colonic epithelial cells through NF-κB

The signaling pathways mediating lysophosphatidic acid (LPA)-stimulated PKD₂ activation and the potential contribution of PKD₂ in regulating LPA-induced interleukin 8 (IL-8) secretion in nontransformed, human colonic epithelial NCM460 cells were examined. Treatment of serum-deprived NCM460 cells with LPA led to a rapid and striking activation of PKD₂, as measured by in vitro kinase assay and phosphorylation at the activation loop (Ser706/710) and autophosphorylation site (Ser876). PKD₂ activation induced by LPA was abrogated by preincubation with selective PKC inhibitors GF-I and Ro-31-8220 in a dose-dependent manner. These inhibitors did not have any direct inhibitory effect on PKD₂ activity. LPA induced a striking increase in IL-8 production and stimulated NF-κB activation, as measured by NF-κB-DNA binding, NF-κB-driven luciferase reporter activity, and IκBα phosphorylation. PKD₂ gene silencing utilizing small interfering RNAs targeting distinct PKD₂ sequences dramatically reduced LPA-stimulated NF-κB promoter activity and IL-8 production. PKD₂ activation is a novel early event in the biological action of LPA and mediates LPA-stimulated IL-8 secretion in NCM460 cells through a NF-κB-dependent pathway. Our results demonstrate, for the first time, the involvement of a member of the PKD family in the production of IL-8, a potent proinflammatory chemokine, by epithelial cells.