Expression of the Transcription Factor Egr-1 in Pancreatic Acinar Cells Following Stimulation of Cholecystokinin or Gαq-Coupled Designer Receptors

Abstract

Backgound/Aims: The injection of cerulein, an analogue of the pancreatic secretagogue cholecystokinin (CCK), induces acute pancreatitis in mice that is accompanied by the synthesis of the transcription factor Egr-1. The signaling cascade that connects cerulein stimulation with enhanced Egr-1 biosynthesis was analyzed. Methods: AR42J rat pancreatic acinar cells were used as a model system to measure cerulein-induced Egr-1 biosynthesis. For comparison, the signaling cascade induced by activation of Gαq-coupled designer receptors with the designer drug clozapine-N-oxide (CNO) was investigated. Results: Stimulation of AR42J cells with cerulein induced a robust and transient biosynthesis of Egr-1. The signaling cascade connecting cerulein stimulation with Egr-1 gene expression required elevated levels of cytosolic Ca²⁺ and the activation of the protein kinases PKC, Raf and ERK, while expression of MKP-1 prevented Egr-1 biosynthesis in cerulein-stimulated AR42J cells. In addition, ternary complex factors are required to connect cerulein stimulation with enhanced transcription of the Egr-1 gene. Egr-1 biosynthesis induced in CNO-stimulated AR42J pancreatic acinar cells expressing Gαq-coupled designer receptors required identical signaling molecules, although subtle differences were observed in comparison to cerulein/CCK receptor signaling. Conclusion: We propose that overstimulation of the canonical Gαq-induced signaling pathway may be crucial for inducing acute pancreatitis.