MECHANISMS OF CCK REGULATION OF MONITOR PEPTIDE MESSENGER-RNA EXPRESSION IN PANCREATIC ACINAR AR42J CELLS

We explored the mechanism(s) by which cholecystokinin (CCK) stimulatio n of AR42J rat pancreatoma cells results in increased mRNA expression of a CCK-releasing peptide [monitor peptide (MP)]. With the use of a n ewly established reverse transcription-polymerase chain reaction assay system, CCK was shown to increase the level of MP mRNA by about ninef old. When protein synthesis was blocked by addition of cycloheximide, the MP mRNA level remained unchanged in the presence of CCK. Inhibitio n of transcription with actinomycin D resulted in a half-life for MP m RNA of similar to 17 h, and this rate remained unchanged after CCK tre atment, suggesting that CCK may regulate the MP mRNA level by influenc ing gene transcription. A-23187, bombesin, substance P, and carbachol increased the MP mRNA level. CoCl2 abolished actions of both CCK and A -23187 on MP mRNA expression. Dibutyryl-adenosine 3',5'-cyclic monopho sphate, forskolin, secretin, and vasoactive intestinal polypeptide had no effect on MP mRNA expression. 12-O-tetradecanoylphorbol-13-acetate and phorbol 12,13-dibutyrate also failed to increase MP mRNA. It was therefore proposed that CCK stimulates MP mRNA expression of AR42J cel ls in a Ca2+- dependent and protein kinase C-independent manner.