Dietary and Hormonal Stimulation of Rat Exocrine Pancreatic Function Regulates CRHSP-28 Phosphorylation In Vivo

Abstract

Dietary regulation of digestive enzyme secretion from the pancreas is essential for the breakdown of macronutrients in the gastrointestinal tract. Ca(2+)-responsive heat stable protein (CRHSP)-28 is a regulatory protein that modulates the exocytosis of digestive enzymes from pancreatic acinar cells. In the present study, isoelectric focusing and immunoblotting were used to characterize CRHSP-28 phosphorylation in isolated rat acinar cells and also after hormonal and dietary stimulation of rat pancreas in vivo. CRHSP-28 was highly phosphorylated in isolated acini after stimulation with a physiologic range of concentrations of cholecystokinin-octapeptide (CCK-8). Activation of the high affinity state of the CCK-A receptor with the synthetic peptide JMV-180 confirmed the physiologic relevance of the response. CRHSP-28 phosphorylation was contingent on elevated cellular Ca2+ because it was maximally stimulated by Ca2+ ionophore, but unchanged after protein kinase C, cAMP or cyclic guanosine monophosphate activation. Intravenous infusion of rats with a secretory concentration of the CCK analog, caerulein, stimulated CRHSP-28 phosphorylation by 100% over control (P < 0.01) within 15 min of dosing. Moreover, CRHSP-28 phosphorylation was stimulated by 150% over control (P < 0.05) immediately after consumption of a semipurified AIN-93 diet. These data demonstrate that CRHSP-28 phosphorylation occurs in vivo and can be used as a functional indicator of nutrient-driven acinar cell activation.

Tumor protein D52 expression and Ca2+-dependent phosphorylation modulates lysosomal membrane protein trafficking to the plasma membrane

“…In accordance with the effects of physiological secretagogues to induce D52 phosphorylation in vivo (17,23,24), when transfected into CHO-K1 cells, D52 undergoes a robust Ca 2ϩ -sensitive phosphorylation that coincides with its rapid accumulation along the plasma membrane. Consistent with a recent report (11), site-specific mutational analysis indicated that D52 phosphorylation occurs at serine 136.…”