The Experts below are selected from a list of 1746 Experts worldwide ranked by ideXlab platform
Fred S Gorelick - One of the best experts on this subject based on the ideXlab platform.
-
Activation of Soluble Adenylyl Cyclase Protects against Secretagogue Stimulated Zymogen Activation in Rat
2016Co-Authors: Pancreaic Acinar Cells, Edwin C Thrower, Thomas R. Kolodecik, Christine Shugrue, Lonny R Levin, Jochen Buck, Fred S GorelickAbstract:An early feature of acute pancreatitis is activation of Zymogens, such as trypsinogen, within the pancreatic acinar cell. Supraphysiologic concentrations of the hormone cholecystokinin (CCK; 100 nM), or its orthologue cerulein (CER), induce zymogen activation and elevate levels of cAMP in pancreatic acinar cells. The two classes of adenylyl cyclase, trans-membrane (tmAC) and soluble (sAC), are activated by distinct mechanisms, localize to specific subcellular domains, and can produce locally high concentrations of cAMP. We hypothesized that sAC activity might selectively modulate acinar cell zymogen activation. sAC was identified in acinar cells by PCR and immunoblot. It localized to the apical region of the cell under resting conditions and redistributed intracellularly after treatment with supraphysiologic concentrations of cerulein. In cerulein-treated cells, pre-incubation with a trans-membrane adenylyl cyclase inhibitor did not affect zymogen activation or amylase secretion. However, treatment with a sAC inhibitor (KH7), or inhibition of a downstream target of cAMP, protein kinase A (PKA), significantly enhanced secretagogue-stimulated zymogen activation and amylase secretion. Activation of sAC with bicarbonate significantly inhibited secretagogue-stimulated zymogen activation; this response was decreased by inhibition of sAC or PKA. Bicarbonate also enhanced secretagogue-stimulated cAMP accumulation; this effect was inhibited by KH7. Bicarbonate treatment reduced secretagogue-stimulated acinar cell vacuolization, an early marker of pancreatitis. These data suggest that activation of sAC in the pancreatic acinar cell has a protective effect and reduces the pathologi
-
Running Title: Reconstituted Zymogen Activation
2013Co-Authors: Cell System, Edwin C Thrower, Thomas R. Kolodecik, Fred S GorelickAbstract:Pathologic activation of digestive Zymogens within the pancreatic acinar cell initiates acute pancreatitis. Cytosolic events regulate this activation within intracellular compartments of unclear identity. In an in vivo model of acute pancreatitis, zymogen activation was detected in both zymogen granule-enriched and microsomal cellular fractions. To examine the mechanism of this activation in-vitro, a reconstituted system was developed using pancreatic cytosol, a zymogen granule-enriched fraction, and a microsomal fraction. Addition of cytosol to either particulate fraction resulted in a prominent increase in both trypsin and chymotrypsin activities. The percentage of the pool of trypsinogen and chymotrypsinogen activated was about 2-fold and 6-fold greater, respectively, in the microsomal than the zymogen granule-enriched fraction. Activation of chymotrypsinogen but not trypsinogen was significantly enhanced by ATP (5 mM) but not by the inactive ATP analogue, AMP-PNP. The processing of procarboxypeptidase-B to its mature form also demonstrated a requirement for ATP and cytosol. E64d, an inhibitor of cathepsin-B, a thiol protease that can activate trypsin, completely inhibited trypsin activity but did not affect chymotrypsin activity or carboxypeptidase-B generation
-
activation of soluble adenylyl cyclase protects against secretagogue stimulated zymogen activation in rat pancreaic acinar cells
PLOS ONE, 2012Co-Authors: Edwin C Thrower, Fred S Gorelick, Thomas R. Kolodecik, Christine Shugrue, Lonny R Levin, Jochen BuckAbstract:An early feature of acute pancreatitis is activation of Zymogens, such as trypsinogen, within the pancreatic acinar cell. Supraphysiologic concentrations of the hormone cholecystokinin (CCK; 100 nM), or its orthologue cerulein (CER), induce zymogen activation and elevate levels of cAMP in pancreatic acinar cells. The two classes of adenylyl cyclase, trans-membrane (tmAC) and soluble (sAC), are activated by distinct mechanisms, localize to specific subcellular domains, and can produce locally high concentrations of cAMP. We hypothesized that sAC activity might selectively modulate acinar cell zymogen activation. sAC was identified in acinar cells by PCR and immunoblot. It localized to the apical region of the cell under resting conditions and redistributed intracellularly after treatment with supraphysiologic concentrations of cerulein. In cerulein-treated cells, pre-incubation with a trans-membrane adenylyl cyclase inhibitor did not affect zymogen activation or amylase secretion. However, treatment with a sAC inhibitor (KH7), or inhibition of a downstream target of cAMP, protein kinase A (PKA), significantly enhanced secretagogue-stimulated zymogen activation and amylase secretion. Activation of sAC with bicarbonate significantly inhibited secretagogue-stimulated zymogen activation; this response was decreased by inhibition of sAC or PKA. Bicarbonate also enhanced secretagogue-stimulated cAMP accumulation; this effect was inhibited by KH7. Bicarbonate treatment reduced secretagogue-stimulated acinar cell vacuolization, an early marker of pancreatitis. These data suggest that activation of sAC in the pancreatic acinar cell has a protective effect and reduces the pathologic activation of proteases during pancreatitis.
-
the acinar cell and early pancreatitis responses
Clinical Gastroenterology and Hepatology, 2009Co-Authors: Fred S Gorelick, Edwin C ThrowerAbstract:Pathologic responses arising from the pancreatic acinar cell appear to have a central role in initiating acute pancreatitis. Environmental factors that sensitize the acinar cell to harmful stimuli likely have a critical role in many forms of pancreatitis, including that induced by alcohol abuse. Activation of Zymogens within the acinar cell and an inhibition of secretion are critical, but poorly understood, early pancreatitis events. While there is firm evidence relating trypsinogen activation to pancreatitis, the importance of other Zymogens has been less studied. Preliminary studies suggest that trypsin may be activated by mechanisms that are distinct from other Zymogens. Further, unlike the small intestine, it may not catalyze the activation of other Zymogens. These features could affect strategies aimed at inhibiting proteases to treat pancreatitis. Specific intracellular signals are required to activate pancreatitis pathways in the acinar cell. The most important is calcium. Recent studies have suggested that calcium release through specific calcium channels in the endoplasmic reticulum is the means by which pathological elevations in cytosolic calcium occur. Although the targets of abnormal calcium signaling are unknown, calcineurin, a calcium-dependent phosphatase, may serve such a role. Finally, recent work suggests that an acute acid load might sensitize the acinar cell to pancreatitis responses. Therapies aimed at preventing or reversing the effects of an acid load on the pancreas may be important for treatment.
-
intracellular proteolysis of pancreatic Zymogens
Yale Journal of Biology and Medicine, 1992Co-Authors: Fred S Gorelick, Steven D Leach, Irvin M Modlin, R Carangelo, M KatzAbstract:Activation of pancreatic digestive Zymogens within the pancreatic acinar cell may be an early event in the development of pancreatitis. To detect such activation, an immunoblot assay has been developed that measures the relative amounts of inactive Zymogens and their respective active enzyme forms. Using this assay, high doses of cholecystokinin or carbachol were found to stimulate the intracellular conversion of at least three Zymogens (procarboxypeptidase A1, procarboxypeptidase B, and chymotrypsinogen 2) to their active forms. Thus, this conversion may be a generalized phenomenon of pancreatic Zymogens. The conversion is detected within ten minutes of treatment and is not associated with changes in acinar cell morphology; it has been predicted that the lysosomal thiol protease, cathepsin B, may initiate this conversion. Small amounts of cathepsin B are found in the secretory pathway, and cathepsin B can activate trypsinogen in vitro; however, exposure of acini to a thiol protease inhibitor (E64) did not block this conversion. Conversion was inhibited by the serine protease inhibitor, benzamidine, and by raising the intracellular pH, using chloroquine or monensin. This limited proteolytic conversion appears to require a low pH compartment and a serine protease activity. After long periods of treatment (60 minutes), the amounts of the active enzyme forms began to decrease; this observation suggested that the active enzyme forms were being degraded. Treatment of acini with E64 reduced this late decrease in active enzyme forms, suggesting that thiol proteases, including lysosomal hydrolases, may be involved in the degradation of the active enzyme forms. These findings indicate that pathways for zymogen activation as well as degradation of active enzyme forms are present within the pancreatic acinar cell.
Frank Thevenod - One of the best experts on this subject based on the ideXlab platform.
-
channels and transporters in zymogen granule membranes and their role in granule function recent progress and a critical assessment
Pancreapedia: The Exocrine Pancreas Knowledge Base, 2015Co-Authors: Frank ThevenodAbstract:Secretory granules are located at the apex of pancreatic acinar cells. Secretagogues bind to their receptors at the basolateral membrane of acinar cells and trigger the activation of intracellular signaling pathways to elicit fusion of secretory granules with the apical plasma membrane that is followed by exocytosis of digestive pro-enzymes (the “Zymogens”) into the lumen. This regulated discharge of stored macromolecules is accompanied by the secretion of solutes and water to the cell exterior to hydrate these protein-rich secretory products. Previous functional and pharmacological studies in pancreatic acinar cells and zymogen granules (ZG) had suggested that ion channels and transporters are expressed in the membrane of ZG where they contribute to maturation, fusion, exocytosis and/or fluidization of Zymogens. This chapter reviews studies that have been largely published in the postgenomic era and combined biochemical, immunological, electrophysiological, pharmacological, and/or occasionally knockout methodologies to identify cloned transporters and ion channels in the membrane of ZG. Available experimental evidence indicates the presence of several ion channel and transporter proteins in ZG membranes (aquaporins, vacuolar-type HATPase, zinc influx transporter SLC30A2). The evidence for the K channels Kv7.1 and Kir6.1, for ClC Cl channels and the vesicular nucleotide transporter SLC17A9 in ZG is less strong. To better understand the function of these proteins in the secretory pathway further studies are needed. 1. Introductory Remarks A review on the topic of pancreatic zymogen granule (ZG) channels and transporters and their function is timely as the last exhaustive review appeared in 2002 (107) and is manageable because of the limited number of publications that had been published in the 12 years since then. These circumstances have allowed me to carry out an in-depth and critical analysis of the published data. The advent of the post-genomic era had raised hopes that – similar to other areas of cell biology – a large number of ZG transport proteins would be identified and their role in pancreatic secretion would be elucidated. Indeed, recent studies have combined functional and molecular approaches to characterize ZG channels and transporters and their role in pancreas physiology. Yet, the fact that only a very limited number of studies have been published in this area of research is surprising as there have been tremendous developments of knowledge and methodologies available to investigate the molecular and cellular biology and physiology of
-
expression of nhe1 and nhe4 in rat pancreatic zymogen granule membranes
Biochemical and Biophysical Research Communications, 1998Co-Authors: Ines Anderie, Winfried Haase, Robert Blum, Sergio Grinstein, Frank ThevenodAbstract:Abstract We previously characterized a Na + /H + exchange activity in rat pancreatic zymogen granules [Anderie, I., and Thevenod, F. (1996) J. Membrane Biol. 152, 195-205]. Here we have identified the Na + /H + exchanger (NHE) isoforms present in zymogen granules by functional studies with NHE inhibitors. The NHE1 specific blocker HOE 694 [3-(methylsulfonyl-4-piperidino-benzoyl)-guanidine methanesulfonate] inhibited zymogen granule Na + /H + exchange in a concentration dependent manner, maximally to 53 ± 5% of controls at 100nM. The remaining Na + /H + exchange activity was inhibitable by EIPA [5-(N-ethyl-N-isopropyl)amiloride] (EC 50 ∼ 25μM) or benzamil (EC 50 ∼ 100μM). Amiloride inhibited weakly suggesting that “amiloride-resistant” and “amiloride-sensitive” NHE are expressed in zymogen granules. cDNA sequences encoding NHE1- and NHE4-specific transmembrane domains were detected by RT-PCR in rat pancreatic tissue and in the rat pancreatic acinar cell line AR4-2J. The presence of NHE1 and NHE4 in zymogen granule membranes was confirmed by immunoblots of zymogen granule membranes and by pre-embedding immunogold labeling of purified rat pancreatic zymogen granules with polyclonal NHE1 and NHE4 antibodies. Therefore, we propose that NHE1 and NHE4 are expressed in zymogen granule membranes of rat exocrine pancreas.
-
large scale purification of calf pancreatic zymogen granule membranes
Analytical Biochemistry, 1992Co-Authors: Frank Thevenod, Winfried Haase, Ulrich HopferAbstract:Abstract A protocol for isolating milligram quantities of highly purified zymogen granule membranes from calf pancreas was developed. The method provides a fivefold enriched zymogen granule fraction that is virtually free from major isodense contaminants, such as mitochondria and erythrocytes. Isolated granules are osmotically stable in isosmotic KCl buffers with half-lives between 90 and 120 min. They display specific ion permeabilities that can be demonstrated using ionophore probes to override intrinsic control mechanisms. A Cl− conductance, a Cl−/anion exchanger, and a K+ conductance are found in the zymogen granule membrane, as previously reported for rat pancreatic, rat parotid zymogen granules, and rabbit pepsinogen granules. Lysis of calf pancreatic secretory granules in hypotonic buffers and subsequent isolation of pure zymogen granule membranes yield about 5–10 mg membrane protein from ∼1000 ml pancreas homogenate. The purified zymogen granule membranes are a putative candidate for the rapid identification and purification of epithelial Cl− channels and regulatory proteins, since they contain fewer proteins than plasma membranes.
Ralf Kleene - One of the best experts on this subject based on the ideXlab platform.
-
regulated apical secretion of Zymogens in rat pancreas involvement of the glycosylphosphatidylinositol anchored glycoprotein gp 2 the lectin zg16p and cholesterol glycosphingolipid enriched microdomains
Journal of Biological Chemistry, 2001Co-Authors: Katja Schmidt, Michael Schrader, Horstfranz Kern, Ralf KleeneAbstract:Abstract We examined the role of glycosphingolipid- and cholesterol-enriched microdomains, or rafts, in the sorting of digestive enzymes into zymogen granules destined for apical secretion and in granule formation. Isolated membranes of zymogen granules from pancreatic acinar cells showed an enrichment in cholesterol and sphingomyelin and formed detergent-insoluble glycolipid-enriched complexes. These complexes floated to the lighter fractions of sucrose density gradients and contained the glycosylphosphatidylinositol (GPI)-anchored glycoprotein GP-2, the lectin ZG16p, and sulfated matrix proteoglycans. Morphological and pulse-chase studies with isolated pancreatic lobules revealed that after inhibition of GPI-anchor biosynthesis by mannosamine or the fungal metabolite YW 3548, granule formation was impaired leading to an accumulation of newly synthesized proteins in the Golgi apparatus and the rough endoplasmic reticulum. Furthermore, the membrane attachment of matrix proteoglycans was diminished. After cholesterol depletion or inhibition of glycosphingolipid synthesis by fumonisin B1, the formation of zymogen granules as well as the formation of detergent-insoluble complexes was reduced. In addition, cholesterol depletion led to constitutive secretion of newly synthesized proteins,e.g. amylase, indicating that Zymogens were missorted. Together, these data provide first evidence that in polarized acinar cells of the exocrine pancreas GPI-anchored proteins, e.g.GP-2, and cholesterol-sphingolipid-enriched microdomains are required for granule formation as well as for regulated secretion of Zymogens and may function as sorting platforms for secretory proteins destined for apical delivery.
-
a submembranous matrix of proteoglycans on zymogen granule membranes is involved in granule formation in rat pancreatic acinar cells
Journal of Cell Science, 2000Co-Authors: K Schmidt, Heidrun Dartsch, Horstfranz Kern, D Linder, Ralf KleeneAbstract:The secretory lectin ZG16p mediated the binding of aggregated Zymogens to the granule membrane in pancreatic acinar cells. Using a recently established in vitro condensation-sorting assay, we now show that pretreatment of zymogen granule membranes (ZGM) with either sodium bicarbonate at pH 10 or with phosphatidyl inositol-specific phospholipase C (PI-PLC) reduced the binding efficiency of Zymogens to the same extent, as distinct components were liberated from ZGM. Analysis of the composition of the bicarbonate extract revealed the presence of the secretory lectin ZG16p, the serpin ZG46p and the GPI-linked glycoprotein GP-2, together with several unknown proteins, and small amounts of lipase and carboxylester lipase. The unknown proteins detected in 2-D gels represented a group of acidic and basic protein spots, which were positive in a glycan staining reaction and were soluble in methanol. One protein spot of the acidic group and several of the basic group reacted with a monoclonal antibody directed against chondroitin sulfate, indicating that the proteins represented proteoglycans. A staining pattern similar to the glycan reaction was observed in immunoblots using a polyclonal antibody directed against the whole bicarbonate extract. Immunogold electron microscopy revealed that this antibody reacted with components in the periphery of zymogen granules and strongly stained ZGM in the pellet fraction of a standard in vitro condensation-sorting assay. The amino acid composition of isolated components of both the acidic and basic group showed similarities to aggrecan, a cartilage-specific proteoglycan, and to glycine-rich glycoproteins, respectively. We therefore conclude that a submembranous matrix on the ZGM composed of proteoglycans and glycoproteins is involved in granule formation in pancreatic acinar cells.
Edwin C Thrower - One of the best experts on this subject based on the ideXlab platform.
-
Activation of Soluble Adenylyl Cyclase Protects against Secretagogue Stimulated Zymogen Activation in Rat
2016Co-Authors: Pancreaic Acinar Cells, Edwin C Thrower, Thomas R. Kolodecik, Christine Shugrue, Lonny R Levin, Jochen Buck, Fred S GorelickAbstract:An early feature of acute pancreatitis is activation of Zymogens, such as trypsinogen, within the pancreatic acinar cell. Supraphysiologic concentrations of the hormone cholecystokinin (CCK; 100 nM), or its orthologue cerulein (CER), induce zymogen activation and elevate levels of cAMP in pancreatic acinar cells. The two classes of adenylyl cyclase, trans-membrane (tmAC) and soluble (sAC), are activated by distinct mechanisms, localize to specific subcellular domains, and can produce locally high concentrations of cAMP. We hypothesized that sAC activity might selectively modulate acinar cell zymogen activation. sAC was identified in acinar cells by PCR and immunoblot. It localized to the apical region of the cell under resting conditions and redistributed intracellularly after treatment with supraphysiologic concentrations of cerulein. In cerulein-treated cells, pre-incubation with a trans-membrane adenylyl cyclase inhibitor did not affect zymogen activation or amylase secretion. However, treatment with a sAC inhibitor (KH7), or inhibition of a downstream target of cAMP, protein kinase A (PKA), significantly enhanced secretagogue-stimulated zymogen activation and amylase secretion. Activation of sAC with bicarbonate significantly inhibited secretagogue-stimulated zymogen activation; this response was decreased by inhibition of sAC or PKA. Bicarbonate also enhanced secretagogue-stimulated cAMP accumulation; this effect was inhibited by KH7. Bicarbonate treatment reduced secretagogue-stimulated acinar cell vacuolization, an early marker of pancreatitis. These data suggest that activation of sAC in the pancreatic acinar cell has a protective effect and reduces the pathologi
-
Running Title: Reconstituted Zymogen Activation
2013Co-Authors: Cell System, Edwin C Thrower, Thomas R. Kolodecik, Fred S GorelickAbstract:Pathologic activation of digestive Zymogens within the pancreatic acinar cell initiates acute pancreatitis. Cytosolic events regulate this activation within intracellular compartments of unclear identity. In an in vivo model of acute pancreatitis, zymogen activation was detected in both zymogen granule-enriched and microsomal cellular fractions. To examine the mechanism of this activation in-vitro, a reconstituted system was developed using pancreatic cytosol, a zymogen granule-enriched fraction, and a microsomal fraction. Addition of cytosol to either particulate fraction resulted in a prominent increase in both trypsin and chymotrypsin activities. The percentage of the pool of trypsinogen and chymotrypsinogen activated was about 2-fold and 6-fold greater, respectively, in the microsomal than the zymogen granule-enriched fraction. Activation of chymotrypsinogen but not trypsinogen was significantly enhanced by ATP (5 mM) but not by the inactive ATP analogue, AMP-PNP. The processing of procarboxypeptidase-B to its mature form also demonstrated a requirement for ATP and cytosol. E64d, an inhibitor of cathepsin-B, a thiol protease that can activate trypsin, completely inhibited trypsin activity but did not affect chymotrypsin activity or carboxypeptidase-B generation
-
activation of soluble adenylyl cyclase protects against secretagogue stimulated zymogen activation in rat pancreaic acinar cells
PLOS ONE, 2012Co-Authors: Edwin C Thrower, Fred S Gorelick, Thomas R. Kolodecik, Christine Shugrue, Lonny R Levin, Jochen BuckAbstract:An early feature of acute pancreatitis is activation of Zymogens, such as trypsinogen, within the pancreatic acinar cell. Supraphysiologic concentrations of the hormone cholecystokinin (CCK; 100 nM), or its orthologue cerulein (CER), induce zymogen activation and elevate levels of cAMP in pancreatic acinar cells. The two classes of adenylyl cyclase, trans-membrane (tmAC) and soluble (sAC), are activated by distinct mechanisms, localize to specific subcellular domains, and can produce locally high concentrations of cAMP. We hypothesized that sAC activity might selectively modulate acinar cell zymogen activation. sAC was identified in acinar cells by PCR and immunoblot. It localized to the apical region of the cell under resting conditions and redistributed intracellularly after treatment with supraphysiologic concentrations of cerulein. In cerulein-treated cells, pre-incubation with a trans-membrane adenylyl cyclase inhibitor did not affect zymogen activation or amylase secretion. However, treatment with a sAC inhibitor (KH7), or inhibition of a downstream target of cAMP, protein kinase A (PKA), significantly enhanced secretagogue-stimulated zymogen activation and amylase secretion. Activation of sAC with bicarbonate significantly inhibited secretagogue-stimulated zymogen activation; this response was decreased by inhibition of sAC or PKA. Bicarbonate also enhanced secretagogue-stimulated cAMP accumulation; this effect was inhibited by KH7. Bicarbonate treatment reduced secretagogue-stimulated acinar cell vacuolization, an early marker of pancreatitis. These data suggest that activation of sAC in the pancreatic acinar cell has a protective effect and reduces the pathologic activation of proteases during pancreatitis.
-
the acinar cell and early pancreatitis responses
Clinical Gastroenterology and Hepatology, 2009Co-Authors: Fred S Gorelick, Edwin C ThrowerAbstract:Pathologic responses arising from the pancreatic acinar cell appear to have a central role in initiating acute pancreatitis. Environmental factors that sensitize the acinar cell to harmful stimuli likely have a critical role in many forms of pancreatitis, including that induced by alcohol abuse. Activation of Zymogens within the acinar cell and an inhibition of secretion are critical, but poorly understood, early pancreatitis events. While there is firm evidence relating trypsinogen activation to pancreatitis, the importance of other Zymogens has been less studied. Preliminary studies suggest that trypsin may be activated by mechanisms that are distinct from other Zymogens. Further, unlike the small intestine, it may not catalyze the activation of other Zymogens. These features could affect strategies aimed at inhibiting proteases to treat pancreatitis. Specific intracellular signals are required to activate pancreatitis pathways in the acinar cell. The most important is calcium. Recent studies have suggested that calcium release through specific calcium channels in the endoplasmic reticulum is the means by which pathological elevations in cytosolic calcium occur. Although the targets of abnormal calcium signaling are unknown, calcineurin, a calcium-dependent phosphatase, may serve such a role. Finally, recent work suggests that an acute acid load might sensitize the acinar cell to pancreatitis responses. Therapies aimed at preventing or reversing the effects of an acid load on the pancreas may be important for treatment.
Denis Lebel - One of the best experts on this subject based on the ideXlab platform.
-
development of gp 2 and five Zymogens in the fetal and young pig biochemical and immunocytochemical evidence of an atypical zymogen granule composition in the fetus
Journal of Histochemistry and Cytochemistry, 1996Co-Authors: Jean Laine, G Pelletier, G Grondin, Manli Peng, Denis LebelAbstract:To uncover the mechanisms involved in the biogenesis of secretory granules, we studied development of the exocrine pancreas in the pig from the fetus up to the mature animal by following the enzyme activities and expression (Northern blot) of five Zymogens and GP-2, the major protein of the granule membrane. Fetal pancreas mainly contained chymotrypsinogen and barely detectable amounts of amylase, trypsin, lipase, and elastase. GP-2 was not notably expressed before the Day 21 of life. Ultrastructural examination of the fetal tissue embedded in Epon with osmium postfixation or in Lowicryl at -20 degrees C without postfixation showed dense granules with an irregular shape but also showed that most granules had uncondensed contents, with the aspect of immature granules, or had a dense core surrounded by light material. With immunogold cytochemistry, the concentration of chymotrypsinogen was directly associated with the acquisition of electron density by the granule matrix. These observations suggest that fetal granules have a slower rhythm of zymogen condensation and an irregular shape that could be due to the particular composition of the matrix and the absence of GP-2. We conclude that, in the exocrine pancreas, secretory granules can be formed under various conditions, even with a matrix containing a ratio of components very different from that of the normal mature animal.
-
reconstitution in vitro of the ph dependent aggregation of pancreatic Zymogens en route to the secretory granule implication of gp 2
Biochemical Journal, 1993Co-Authors: F A Leblond, G Viau, Jean Laine, Denis LebelAbstract:Regulated secretory proteins are thought to be sorted in the trans-Golgi network (TGN) via selective aggregation. To elucidate the biogenesis of the secretory granule in the exocrine pancreas, we reconstituted in vitro the conditions of pH and ions believed to exist in the TGN using the end product of this sorting process, the zymogen granule contents. Protein aggregation was dependent on pH (acidic) and on the presence of cations (10 mM Ca2+, 150 mM K+) to reproduce the pattern of proteins found in the granule. The constitutive secretory protein IgG was excluded from these aggregates. Zymogen aggregation correlated with the relative proportion of the major granule membrane protein GP-2 in the assay. These results show that the glycosylphosphatidylinositol-anchored protein GP-2 co-aggregates with Zymogens in the acidic environment believed to exist in the pancreatic TGN, and thus suggest that GP-2 would function as a membrane anchor for zymogen aggregates, facilitating their entrapment in budding vesicles directed towards the regulated secretory pathway.
