Regulation of the initiation of pancreatic digestive enzyme protein synthesis by cholecystokinin in rat pancreas in vivo

Background & Aims: Cholecystokinin (CCK) is known to stimulate the synthesi s of digestive enzymes in the pancreas at the translational level. We inves tigated in vivo the biochemical regulation of initiation factors important for the stimulation of translation of digestive enzyme protein in rat pancr eas by CCH. Methods: Intraperitoneal injection of CCK or intragastric admin istration of a trypsin inhibitor to elicit endogenous CCK release was follo wed by removal and preparation of pancreas for protein evaluation. Isoelect ric focusing was used to evaluate the phosphorylation of the initiation fac tor eIF4E, and Western blotting and immunoprecipitation followed by Western blotting were used to study the phosphorylation state and amount of other interacting factors. Results: CCK treatment induced a time- and dose-depend ent phosphorylation of pancreatic eIF4E and its binding protein (PHAS-I). B ecause the release of eIF4E from its binding protein as a result of phospho rylation is followed by formation of a messenger RNA cap-binding complex th at includes the initiation factor eIF4G, we evaluated the association of eI F4G with released eIF4E and showed that it was increased by CCK. These even ts occurred over a range of CCK doses from 0.2 to 5 mug/kg. We also evaluat ed the effect of endogenous CCH by administering a synthetic trypsin inhibi tor, camostat (100 mg/kg). Camostat treatment markedly increased the phosph orylation of both PHAS-I and eIF4E and the formation of eIF4E-eIF4G complex . Thus, both exogenous and endogenous CCK activate translational initiation factors in vivo. Conclusions: Activation of translational machinery necess ary for initiation of protein synthesis likely contributes to the normal po stprandial synthesis of pancreatic digestive enzymes.