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Volume 271, Number 33, Issue of August 16, 1996 pp. 19877-19882
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.

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Calcineurin Mediates Calcium-induced Potentiation of Adenylyl Cyclase Activity in Dispersed Chief Cells from Guinea Pig Stomach
FURTHER EVIDENCE FOR CROSS-TALK BETWEEN SIGNAL TRANSDUCTION PATHWAYS THAT REGULATE PEPSINOGEN SECRETION

(Received for publication, April 19, 1996, and in revised form, June 5, 1996)

Jean-Pierre Raufman ^§ , Junying Lin ^§ and Robert D. Raffaniello ^§

From the  Division of Gastroenterology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205-7199 and the ^§ Gastrointestinal Cell Biology Laboratory, Department of Medicine, State University of New York, Health Science Center at Brooklyn, Brooklyn, New York 11203-2098

In cholera toxin-treated gastric chief cells, incubation with a cholinergic agonist (carbamylcholine), a regulatory peptide (cholecystokinin), or a calcium ionophore (A23187) causes a dose- and time-dependent potentiation of cAMP levels. Because this augmented response is calcium/calmodulin-dependent, we hypothesized that it was mediated by calcineurin (protein phosphatase 2B). To test this hypothesis, we examined the actions of calcineurin inhibitors on secretagogue-induced potentiation of cAMP levels in guinea pig chief cells. Preincubation of cells with 0.1 µM FK-506 completely prevented carbachol-induced augmentation of cAMP levels and pepsinogen secretion from cholera toxin-treated cells. Cyclosporin-A, another calcineurin inhibitor, also prevented the augmented cAMP response. FK-506 and cyclosporin inhibited augmentation of cAMP levels following treatment with cholecystokinin(26-33) and A23187, but not the smaller increase in cAMP following treatment with a phorbol ester that activates protein kinase C. Hence, the actions of calcineurin inhibitors were limited to secretagogues that increase cellular calcium. Rapamycin, an agent that competes with FK-506 for the immunophilin, FK binding protein 12, does not inhibit calcineurin. In the present study, preincubation with rapamycin did not prevent carbachol-induced augmentation of cAMP levels in cholera toxin-treated chief cells. However, a molar excess of rapamycin reversed the inhibitory actions of FK-506. These experiments provide further evidence that the actions of FK-506 on cholera toxin-treated gastric chief cells are caused by its inhibitory actions on calcineurin. FK-506 also inhibited potentiation of cAMP levels when carbachol was added to cells that were preincubated with forskolin, an agent that directly activates adenylyl cyclase. We conclude that, in gastric chief cells, calcineurin mediates cross-talk between the calcium/calmodulin and adenylyl cyclase signaling pathways.

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