Control of pancreatic bile-salt-dependent-lipase secretion by the glucose-regulated protein of 94 kDa (Grp94)

Bile-salt-dependent lipase (BSDL; EC 3.1.1.13) is an enzyme expressed by th e pancreatic acinar cell and secreted as a component of the pancreatic juic e. During its route towards secretion, BSDL is associated with intracellula r membranes by means of a multiprotein folding complex, which includes the glucose-regulated protein of 94 kDa (Grp94). We have postulated that the as sociation of BSDL with membranes is required for the complete O-glycosylati on of the protein, which diverts BSDL from a degradation route and conseque ntly allows its secretion. To further characterize the role of Grp94 in BSD L secretion, we have studied the effect of a ribozyme specifically targeted to Grp94 mRNA, This ribozyme has been transfected into AR4-2J cells, and w e have shown that a decrease in Grp94 expression leads to a concomitant dec rease in BSDL secretion and expression. Geldanamycin (GA), which alters Grp 94 functions, also affects the release of BSDL into the culture medium of A R4-2J cells. BSDL expressed in GA-treated AR4-2J cells is unstable. Further more, under conditions that decrease the level of BSDL secretion, no intrac ellular accumulation of the enzyme was observed. suggesting that BSDL that cannot associate with (or be structured by) Grp94 could be rapidly degraded . We have further shown that this degradation probably occurs via the ubiqu itin-dependent pathway. Altogether, these results indicate that Grp94 has a pivotal role in BSDL folding and in the sorting of this pancreatic enzyme.