Bombesin receptor gene expression in rat pancreatic acinar AR42J cells: transcriptional regulation by glucocorticoids

BACKGROUND/AIMS: This study investigated the correlation between glucocorticoid-regulated gene expression of the bombesin receptor (BR) and cellular sensitivity to bombesin stimulation in the rat pancreatic acinar cell line AR42J. METHODS: BR gene expression was assessed using a cloned complementary DNA probe and radioligand binding assays. Intracellular Ca2+ mobilization was assessed by dual wavelength spectrophotometry using fura-2 in single cells. RESULTS: Dexamethasone resulted in a rapid dose- and time-dependent decrease of BR messenger RNA levels with maximal inhibition to 25% +/- 2% of controls (n = 4) after 6 hours of hormone treatment. BR messenger RNA half-life was approximately 120 minutes and was not affected by dexamethasone pretreatment; nuclear run-on analysis showed a decreased transcription rate of the BR to approximately 25% of control after hormonal treatment. Radioligand binding studies showed a time-dependent decrease of specific bombesin binding to 25% +/- 8% of control after 48 hours of hormone treatment. Down-regulation of BR gene expression by dexamethasone resulted in a time- and dose-dependent decrease of intracellular Ca2+ mobilization after bombesin stimulation compared with untreated controls. CONCLUSIONS: Glucocorticoids decrease BR gene transcription. The subsequent decrease in cellular BR number renders AR42J cells less sensitive for bombesin-stimulated intracellular Ca2+ mobilization