Transient Agonist-Induced Regulation of the Cholecystokinin-A and Cholecystokinin-B Receptor mRNA Levels in Rat Pancreatic Acinar AR42J Cells

Abstract

Background: CCK-8 and gastrin exert multiple effects in the gastrointestinal tract and the nervous system. Their actions are mediated via the G-protein coupled CCK-A and CCK-B receptors. Methods: Rat pancreatic acinar tumor AR42J cells express both CCK receptor subtypes. This cell line was used to characterize the agonist-dependent regulation of CCK-A and CCK-B receptor gene expression. Results: CCK-8 (10 nM) or gastrin (10 nM) reduced CCK-A receptor mRNA expression to 56% and 53%, respectively 2 h after hormonal exposure. In contrast, the level of CCK-B receptor gene expression was upregulated to 157% and 153%, respectively. These effects are most probably linked to the CCK-B receptor in AR42J cells. The phorbolester PMA (100 nM), a protein kinase C activator, downregulated CCK-A receptor expression but did not affect CCK-B receptor gene transcription. Activation of protein kinase A by forskolin (10 µM) or Bt₂cAMP (100 µM) is not involved in the transient regulation of CCK receptor mRNA expression. Both elevated CCK-B and decreased CCK-A receptor mRNA expression returned to basal levels 6 h after continuous stimulation. Conclusion: These results demonstrate that CCK-A and CCK-B receptor mRNA levels are differentially regulated by their agonists via distinct signal transduction mechanisms in AR42J cells.