The diacylglycerol kinase inhibitor, R59022, potentiates cholecystokinin-induced enzyme secretion from rabbit pancreatic acini.
The putative inhibitor of diacylglycerol kinase activity, 6-(2-[(4-fluorophenyl)phenylmethylene]-1-piperidinyl)-ethyl-7-meth yl-5H- thiazolo[3,2-a]pyrimidin-5-one (R59022), markedly potentiated cholecystokinin-C-terminal-octapeptide(CCK-8-)stimulated enzyme secretion from isolated rabbit pancreatic acini. Maximal potentiation occurred when acini were stimulated in the presence of 5-10 microM R59022. Potentiation depended both on the concentration of R59022 and CCK-8. No potentiation was observed when acini were half-maximally stimulated, whereas the secretory response to maximal and supramaximal concentrations of secretagogue was increased by 50-60%. R59022 alone had no effect on basal enzyme secretion and the drug did not potentiate the secretory response to the Ca2+ ionophore A23187 or to the phorbol ester, 12-O-tetradecanoylphorbol 13-acetate. Moreover, no increase in basal secretion was observed when acini were incubated in the presence of both R59022 and forskolin. These observations strongly suggest that receptor-mediated activation of the inositol phospholipid pathway is required for R59022-induced potentiation. R59022 inhibited the CCK-8-stimulated incorporation of 32Pi into phosphatidic acid dose dependently, without affecting the CCK-8-stimulated hydrolysis of 32P-labelled phosphatidylinositol 4,5-bisphosphate. This is consistent with an inhibitory effect of R59022 on acinar cell diacylglycerol kinase activity. The potentiating effect of R59022 was mimicked by 12-O-tetradecanoylphorbol 13-acetate added simultaneously with CCK-8. Therefore, it is concluded that in the presence of 5-10 microM R59022 the receptor-mediated increase in acinar cell diacylglycerol content is enhanced leading to enhanced activation of protein kinase C and to potentiation of the secretory response. The fact that the secretory response to maximal and supramaximal concentrations of CCK-8 is potentiated by R59022 suggests that at these concentrations of secretagogue the diacylglycerol/protein kinase C branch of the signal-transduction route is rate-limiting.
Department of Biochemistry, University of Nijmegen, The Netherlands.
A G
AG
Ederveen
S E
SE
van Emst-de Vries
J J
JJ
De Pont
P H
PH
Willems
D000681:Amylases / Q000378:metabolism; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002766:Cholecystokinin / Q000494:pharmacology*; D019852:Diacylglycerol Kinase; D004075:Diglycerides / Q000378:metabolism / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D006868:Hydrolysis; D010179:Pancreas / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D010703:Phorbol Esters / Q000494:pharmacology; D010712:Phosphatidic Acids / Q000096:biosynthesis; D010770:Phosphotransferases / Q000037:antagonists & inhibitors*; D011493:Protein Kinase C / Q000378:metabolism*; D011744:Pyrimidinones / Q000494:pharmacology*; D011817:Rabbits; D013844:Thiazoles / Q000494:pharmacology*
D004075:Diglycerides; D010703:Phorbol Esters; D010712:Phosphatidic Acids; D011744:Pyrimidinones; D013844:Thiazoles; D000001:Calcimycin; D002766:Cholecystokinin; C047505:R 59022; D010770:Phosphotransferases; D019852:Diacylglycerol Kinase; D011493:Protein Kinase C; D000681:Amylases