Phosphorylation of the rat pancreatic bile-salt-dependent lipase by casein kinase II is essential for secretion

Abstract

Bile-salt-dependent lipase (BSDL, EC 3.1.1.-) is an enzyme expressed by the pancreatic acinar cells and secreted as a component of the pancreatic juice of all examined species. During its secretion route BSDL is associated with intracellular membranes. This association allows the complete glycosylation of the enzyme or participates in the inhibition of the enzyme activity, which can deleterious for the acinar pancreatic cell. Thereafter, the human BSDL is phosphorylated by a serine/threonine protein kinase and released from intracellular membranes. In the present study, we show that the rat pancreatic BSDL, expressed by AR4-2J cells used as a model, is phosphorylated by a protein kinase that is insensitive to inhibitors of protein kinases A, C or G and that the phosphorylation process is favoured by okadaic acid (an inhibitor of protein phosphatases 1 and 2A). However, 5,6-dichloro-1-beta-d-ribofuranosylbenzimidazole (DRB), which is a specific inhibitor of casein kinase II, abolishes the phosphorylation in vitro of BSDL within micro- somes of AR4-2J pancreatic cells. We showed further that the alpha-subunit of casein kinase II co-locates with BSDL within the lumenal compartment of the Golgi. Genistein, which perturbs the trans-Golgi network, also inhibits the phosphorylation of BSDL, suggesting that this post-translational modification of BSDL probably occurred within this cell compartment. The inhibition of the phosphorylation of BSDL by DRB also decreases the rate at which the enzyme is secreted. Under the same conditions, the rate of alpha-amylase secretion was not modified. These data strongly suggest that phosphorylation is a post-translational event, which appears to be essential for the secretion of BSDL.

Endocytosis of Secreted Carboxyl Ester Lipase in a Syndrome of Diabetes and Pancreatic Exocrine Dysfunction

“…Moreover, O-glycosylation could be important for the solubility of the protein, protecting against self-association caused by exposed hydrophobic surfaces on the globular core of the enzyme (17). In the trans-Golgi area, phosphorylation releases CEL from the multiprotein folding complex, and the protein is concentrated and stored in zymogen granules before its secretion to the cell exterior upon stimulation (18).…”

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

“…Altogether, these results suggested that the dissociation of secretioncompetent molecules of BSDL from the folding complex occurs after the trans-Golgi compartment, probably in the transGolgi network, which is already known to segregate vesicle populations in cells [48]. However, the phosphorylation of BSDL and its release from intracellular membranes does not signify that all BSDL molecules dissociate from Grp94 [36], and two populations of BSDL seem to be secreted in the pancreatic juice [14]. The first population consists of monomeric BSDL, while the second population consists of BSDL complexed to Grp94.…”

“…from the folding complex) after phosphorylation of the enzyme [35]. This phosphorylation occurs within a genistein-sensitive compartment of AR4-2J cells [36]. Because genistein inhibits the formation and the release of cargo vesicles in the trans-Golgi network [47] one may suspect that the BSDL dissociates from the membrane folding complex in this latter compartment.…”

“…Once phosphorylated by casein kinase II, BSDL is released from intracellular membranes in the trans-Golgi network [35,36]. After this post-translational modification, soluble BSDL precipitates with other pancreatic enzymes in condensing vacuoles and finally follows the pancreatic secretion pathway until it reaches the duodenal lumen where it accomplishes its physiological role [1].…”

Monoclonal antibody 16D10 to the COOH-terminal domain of the feto-acinar pancreatic protein targets pancreatic neoplastic tissues

“…This Grp 94 controls the late folding steps and the sorting of the active enzyme toward secretion (8). Once in the trans-Golgi network and after completion of glycosylation (9,10), the complex is released from membranes on the phosphorylation of the threonine residue at position 340 (11) by a protein kinase CKII (12,13). Once released from intracellular membranes, BSDL enters into the secretion route until the duodenum where it accomplishes its physiologic role.…”