Cholesterol esterase biosynthesis in rat pancreatic AR42J cells. Post-transcriptional activation by gastric hormones

This study used the rat pancreatoma AR42J as a model system to investigate the possible regulation of cholesterol esterase biosynthesis in pancreas. Initial experiments were performed to verify the synthesis of pancreatic cholesterol esterase by the AR42J cells. Results indicated that this pancreatoma cell line synthesized two forms of cholesterol esterase (Mr = 71,000 and 74,000). The 74-kDa protein is most likely the precursor protein, and the 71-kDa protein is the matured enzyme secreted by the AR42J cells. The synthesis and secretion of cholesterol esterase were stimulated 2-5-fold by incubating the cells with 0.5-4 nM of cholecystokinin or 0.5-2 nM of secretin. Analysis of the RNA isolated from the hormone-stimulated cells revealed that stimulation of cholesterol esterase biosynthesis was not due to an increase in cholesterol esterase mRNA. Furthermore, inhibition of transcription with actinomycin D has no effect on the hormone-induced cholesterol esterase biosynthesis. Therefore, the mechanism of hormone stimulation was not dependent on de novo RNA synthesis. In vitro translation studies showed that the cholesterol esterase mRNA isolated from stimulated AR42J cells were translated more efficiently than those from control cells. Thus, the increased cholesterol esterase biosynthesis induced by gastric hormones was most likely mediated by posttranscriptional modification of the cholesterol esterase mRNA.