Functional role of J domain of cysteine string protein in Ca2+-dependent secretion from acinar cells

Weng N, Baumler MD, Thomas DDH, Falkowski MA, Swayne LA, Braun JEA, Groblewski GE. Functional role of J domain of cysteine string protein in Ca2+-dependent secretion from acinar cells. Am J Physiol Gastrointest Liver Physiol 296: G1030-G1039, 2009. First published March 12, 2009; doi:10.1152/ajpgi.90592.2008.-The heat shock protein 70 family members Hsc70 and Hsp70 are known to play a protective role against the onset of experimental pancreatitis, yet their molecular function in acini is unclear. Cysteine string protein (CSP-alpha) is a zymogen granule (ZG) membrane protein characterized by an NH2-terminal J domain and a central palmitoylated string of cysteine residues. The J domain functions as a cochaperone by modulating the activity of Hsc70/Hsp70 family members. A role for CSP-alpha in regulating digestive enzyme exocytosis from pancreas was investigated by introducing CSP-alpha truncations into isolated acini following their permeabilization with Perfringolysin O. Incubation of acini with CSP-alpha(1-82), containing the J domain, significantly augmented Ca2+-stimulated amylase secretion. Effects of CSP-alpha(1-82) were concentration dependent, with a maximum 80% increase occurring at 200 mu g/ml of protein. Although CSP-alpha(1-82) had no effects on basal secretion measured in the presence of <10 nM free Ca2+, it did significantly augment GTP-gamma S-induced secretion under basal Ca2+ conditions by similar to 25%. Mutation of the J domain to abolish its cochaperone activity failed to augment Ca2+-stimulated secretion, implicating the CSP-alpha/Hsc70 cochaperone system as a regulatory component of the secretory pathway. CSP-alpha physically associates with vesicle-associated membrane protein 8 (VAMP 8) on ZGs, and the CSP-alpha-VAMP 8 interaction was dependent on amino acids 83-112 of CSP-alpha. Immunofluorescence analysis of acinar lobules or purified ZGs confirmed the CSP-alpha colocalization with VAMP 8. These data establish a role for CSP-alpha in regulating digestive enzyme secretion and suggest that CSP-alpha and Hsc70 modulate specific soluble N-ethylmaleimide-sensitive attachment receptor interactions necessary for exocytosis.