Mechanism of glucocorticoid-induced increase in pancreatic amylase gene transcription

To determine the mechanism(s) responsible for glucocorticoid-induced increases in amylase content in pancreatic acinar AR42J cells, we examined the effects of dexamethasone on amylase protein biosynthesis, steady-state mRNA levels, and gene transcription. Dexamethasone treatment led to a dose-dependent increase in amylase synthesis which was one-half maximal at 2 nM and maximal at 100 nM where a 6-fold increase was achieved. This dexamethasone-induced increase in amylase synthesis was detectable after 12 h, one-half maximal after 19 h, and approached maximal after 72 h. Dexamethasone treatment also increased amylase mRNA levels in a time- and dose-dependent manner in parallel with the changes in amylase synthesis. Nuclear RNA transcript elongation (run-on) assays indicated that amylase gene transcription was also increased in a time- and dose-dependent manner. Glucocorticoid enhancement of amylase gene transcription occurred relatively slowly, with a 6-fold increase occurring after 48 h of treatment with 100 nM dexamethasone. Thus, the effects of glucocorticoids on pancreatic amylase gene transcription fully accounted for the increased levels of amylase mRNA, synthesis, and content. However, due to the slow time course of dexamethasone induction of amylase gene expression we evaluated the possibility of glucocorticoid induction of a regulatory protein. We found that inclusion of cycloheximide or puromycin during dexamethasone treatment blocked the induction of amylase mRNA. These data suggest that the glucocorticoid-induced increase in amylase gene transcription requires induction of an unidentified regulatory protein(s).