Effect of ligands that increase cAMP on caerulein-induced zymogen activation in pancreatic acini

Abstract

The pathological activation of proteases within the pancreatic acinar cell is critical to initiating pancreatitis. Stimulation of acinar cells with supraphysiological concentrations of the CCK analog caerulein (CER) leads to protease activation and pancreatitis. Agents that sensitize the acinar cell to the effects of CCK might contribute to disease. The effects of physiological ligands that increase acinar cell cAMP [secretin, VIP, and pituitary adenylate cyclase activating peptide (PACAP)] on CER-induced responses were examined in isolated rat pancreatic acini. Each ligand sensitized the acinar cell to zymogen activation by physiological concentrations of CER (0.1 nM). VIP and PACAP but not secretin also enhanced activation by supraphysiological concentrations of CER (0.1 μM). A cell-permeable cAMP analog also sensitized the acinar cell to CER-induced activation. The cAMP antagonist Rp-8-Br-cAMP inhibited these sensitizing effects. These findings suggest that ligands that increase acinar cell cAMP levels can sensitize the acinar cell to the effects of CCK-induced zymogen activation. Keywordscaerulein; chymotrypsin; secretin; trypsin THE PREMATURE ACTIVATION of digestive zymogens within the pancreatic acinar cell contributes to the initiation of pancreatitis. In the rodent pancreas, ligands such as CCK or the muscarinic agonist carbachol can cause zymogen activation in isolated pancreatic acini. These ligands activate specific G protein-linked receptors that stimulate phospholipase C and increase cytosolic Ca 2+ . Several reports (7,9) have observed that zymogen activation within the acinar cell requires an increase in cytosolic Ca 2+ . CCK-induced activation depends on the presence of extracellular Ca 2+ and an increase in cytosolic Ca 2+ (9). Removal of extracellular Ca 2+ or chelation of intracellular Ca 2+ blocks caerulein (a CCK homolog)-induced trypsin activation (7,9). Whether an increase in intracellular Ca 2+ alone is sufficient to cause activation is controversial. Increasing cytosolic Ca 2+ by thapsigargin was found to cause zymogen activation in one study but not in another (7,9). Thus additional signaling pathways may act independently or with Ca 2+ to cause zymogen activation.The pancreatic acinar cell has receptors for pathways that are coupled to increasing both cytosolic Ca 2+ and cAMP. Stimulation of acinar cell CCK or muscarinic receptors is linked to increased cytosolic Ca 2+ . Secretin, pituitary adenylate cyclase activating peptide (PACAP), and VIP stimulate receptors that are primarily coupled to cAMP generation. However, some 2+ and cAMP (5). Moreover, although physiological concentrations of CCK do not cause a measurable increase in cAMP, they do activate cAMP-dependent protein kinase (5). Similarly, secretin has been reported in some but not all studies to not only increase cellular cAMP, but to also stimulate phospholipase C activity causing an increase in cytosolic Ca 2+ in the acinar cell (10,12). Because ligands that increase both acinar cell Ca 2+ and cAMP are released in...

Extracellular Signal-Regulated Kinase 1/2 and c-Jun NH2-Terminal Kinase, through Nuclear Factor-κB and Activator Protein-1, Contribute to Caerulein-Induced Expression of Substance P and Neurokinin-1 Receptors in Pancreatic Acinar Cells

“…Intracellular signaling molecules such as the MAPKs, cAMP, protein kinase C, and NF-B are known to be activated upon induction of acute pancreatitis (Tando et al, 1999;Lu et al, 2003;Bi and Williams, 2004;Thrower et al, 2008). Previous studies showed that activation of ERK1/2 and JNK induced cytokine production, and inhibition of ERK1/2 and JNK showed protective effects (Samuel et al, 2006(Samuel et al, , 2008Namkung et al, 2008).…”

Over-Expression of Pancreatic Pituitary Adenylate Cyclase–Activating Polypeptide (PACAP) Aggravates Cerulein-Induced Acute Pancreatitis in Mice

“…Previous findings raise the possible concerns of PACAP in the pathophysiology of pancreatitis (12,14). Recently, it has been reported that development of human chronic pancreatitis is associated with intrapancreatic accumulation of PACAP (15).…”

“…2 and Table 1). PACAP or CCK alone has little effect on amylase secretion from pancreatic acinar cells, while in combination they markedly increase the amylase secretion by sensitizing the acinar cells to CCK-induced zymogen activation (12). Epac/Rap1 signals play an essential role as a common signal for both CCK-and cAMP-evoked amylase secretions in pancreatic acinar cells (24).…”

Blockade of Multidrug Resistance-Associated Proteins Aggravates Acute Pancreatitis and Blunts Atrial Natriuretic Factor’s Beneficial Effect in Rats: Role of MRP4 (ABCC4)

“…In pancreatic acinar cells, secretin as well as other agents that increase cAMP have little effect on zymogen activation alone but sensitize the response of agents that increase intracellular calcium such as cerulein or cholecystokinin (11,12). In pancreatic acini, it was reported that a cell-permeable cAMP inhibitor (Rp-8Br-cAMP) reduces the sensitization induced by vasoactive intestinal peptide and 8Br-cAMP to low and high doses of cerulein (11). It also reduces chymotrypsin activation induced by high doses of cerulein alone.…”