Aims To examine the role of SNAP-23 in regulated exocytosis in acinar cells, we subcloned into adenoviral vectors SNAP-23, SNAP-25, and dominant negative mutants in which the C-terminal domains corresponding to the botulinum neurotoxin A cleavage sites are deleted.

Methodology and Results High-efficiency infection of rat pancreatic acini in culture with these adenoviruses by subcellular fractionation showed that the overexpressed SNAP-23, SNAP-25, and their truncated mutant proteins were uniformly targeted to the zymogen granules and plasma membrane. To maximally stimulate apical exocytosis from these infected acini, we used the cholecystokinin–phenylethyl ester analog (CCK-OPE), which does not show inhibition of secretion from maximal levels at high doses. CCK-OPE–stimulated amylase release from adenovirus–cytomegalovirus (AdCMV)–SNAP-23 or AdCMV–SNAP-25–infected acini to the same extent as from acini infected with the empty vector. In contrast, CCK-OPE–evoked enzyme secretion from AdCMV–SNAP-23ΔC8–and AdCMV–SNAP-25 1− 197–infected acini were inhibited by 60% and 40%, respectively. The identical targeting of the mutant SNAP-23 and SNAP-25 proteins to the same membrane compartments as SNAP-23 suggests that the inhibition of secretion was a result of their competition against endogenous SNAP-23. This is supported by the fact that this inhibition by the mutant proteins was partially reversed or rescued when the AdCMV–SNAP-25ΔC8–or AdCMV–SNAP-25 1− 197–infected acini were co-infected with wild-type SNAP-23 or SNAP-25.

Conclusion From these results, we conclude that SNAP-23 plays a role in CCK-evoked regulated exocytosis in the acinar cells.