Protein kinase D1 mediates NF-κB activation induced by cholecystokinin and cholinergic signaling in pancreatic acinar cells

Abstract

The transcription factor NF-κB plays a critical role in inflammatory and cell death responses during acute pancreatitis. Previous studies in our laboratory demonstrated that protein kinase C (PKC) isoforms PKCδ and ε are key regulators of NF-κB activation induced by cholecystokinin-8 (CCK-8), tumor necrosis factor-α, and ethanol. However, the downstream participants in regulating NF-κB activation in exocrine pancreas remain poorly understood. Here, we demonstrate that protein kinase D1 (PKD1) is a key downstream target of PKCδ and PKCε in pancreatic acinar cells stimulated by two major secretagogues, CCK-8 and the cholinergic agonist carbachol (CCh), and that PKD1 is necessary for NF-κB activation induced by CCK-8 and CCh. Both CCK-8 and CCh dose dependently induced a rapid and striking activation of PKD1 in rat pancreatic acinar cells, as measured by in vitro kinase assay and by phosphorylation at PKD1 activation loop (Ser744/748) or autophosphorylation site (Ser916). The phosphorylation and activation of PKD1 correlated with NF-κB activity stimulated by CCK-8 or CCh, as measured by NF-κB DNA binding. Either inhibition of PKCδ or ε by isoform-specific inhibitory peptides, genetic deletion of PKCδ and ε in pancreatic acinar cells, or knockdown of PKD1 by using small interfering RNAs in AR42J cells resulted in a marked decrease in PKD1 and NF-κB activation stimulated by CCK-8 or CCh. Conversely, overexpression of PKD1 resulted in augmentation of CCK-8- and CCh-stimulated NF-κB activation. Finally, the kinetics of PKD1 and NF-κB activation during cerulein-induced rat pancreatitis showed that both PKD1 and NF-κB activation were early events during acute pancreatitis and that their time courses of response were similar. Our results identify PKD1 as a novel early convergent point for PKCδ and ε in the signaling pathways mediating NF-κB activation in pancreatitis.