Department of Anatomy and Cell Biology, University of Kansas School of Medicine, Kansas City, Kansas
Submitted 4 March 2005 ; accepted in final form 23 June 2005
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
regulated secretion; protein sorting
By analogy to the sorting of lysosomal hydrolases to endosomes/lysosomes by the mannose 6-phosphate receptor (19), and protein traffic from the endoplasmic reticulum to the Golgi mediated by the p24 family of proteins (30), it has been proposed that Golgi cargo receptors are important in sorting of regulated proteins to secretory granules (11). Such receptors would be membrane proteins, or, at least, be membrane-associated. They are predicted to bind to the protein aggregates in the TGN lumen, thereby anchoring the cargo to the TGN membrane. This somehow identifies that patch of TGN membrane for the assembly of the other proteins and lipids needed to make a regulated secretory granule (RSG) {e.g., rabs, N-ethylmaleimide-sensitive factor attachment for protein receptor [vesicular soluble N-ethylmaleimide sensitive factor receptors (v-SNAREs)], and cholesterol-glycolipid rich rafts} (35).
The best characterized Golgi cargo receptor is carboxypeptidase E (CPE), which is expressed in neuronal and endocrine cells and has been shown to affect protein sorting to the regulated pathway (11). Cells or animals deficient in CPE show defects in sorting of neuropeptides/hormones to RSG (reviewed in Ref. 35). A complication of these studies is that CPE is a processing enzyme that normally modifies the cargo itself. In addition, the loss of CPE in knockout mice also decreases expression of other cargo-processing enzymes, the prohormone convertases. It is difficult to tell whether the effects of mutant or absent CPE are due to loss of the cargo receptor function or to an inability of unprocessed cargo to properly aggregate (35, 38). Nevertheless, the concept of TGN cargo receptors is attractive because of its potential to explain cargo selection and recruitment of accessory membrane and cytosolic proteins needed to make a functional RSG.
Muclin was discovered as an abundant component of the exocrine pancreatic RSG, the zymogen granule (12). Muclin was later shown to be derived from a precursor, a type I membrane protein called pro-Muclin, encoded by the dmbt1 gene (GenBank accession no. NM_007769) (16). As it passes through the secretory pathway, pro-Muclin becomes N- and O-glycosylated, and its O-linked sugars are sulfated in the TGN. After exiting the Golgi, pro-Muclin is cleaved to produce mature Muclin, which remains in the zymogen granule. The other product of pro-Muclin cleavage is an 80-kDa glycoprotein called apactin, which contains the transmembrane domain. Apactin is efficiently removed from the maturing RSG, and it is targeted to the actin cytoskeleton-rich apical plasma membrane (37). It was shown that purified Muclin directly associates with several of the zymogen granule content proteins at mildly acidic pH levels found in the TGN/RSG (4). It was further demonstrated in that work that the sulfated, O-linked oligosaccharides are the primary structure that mediate this pH-dependent interaction.
From these observations, it was proposed that pro-Muclin acts as a Golgi cargo receptor, which binds the RSG content proteins as they aggregate in the acidic environment of the TGN, and links the aggregate to the TGN membrane. The experiments in this article demonstrate that expression of pro-Muclin in a poorly differentiated pancreatic cell line is sufficient to induce functional RSGs. Furthermore, the efficiency of regulated secretion induced by pro-Muclin is synergized by concomitant treatment of the cells with the glucocorticoid analog dexamethasone. The experiments also test the importance of the cytosolic tail and transmembrane domains of pro-Muclin and show that the cytosolic tail is important to pro-Muclin's role in the regulated pathway.
![]() |
MATERIALS AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
Recombinant plasmids were screened for increased size compared with the parental Ad-Easy vector and then confirmed by restriction analysis. Recombinant plasmids were propagated in DH5 cells and transfected into the QBI-293A packaging cell line (QBiogene). Adenoviral plaques were picked using the GFP fluorescence signal to select strong expressors. For the full-length GFP-pro-Muclin, 10 clones were selected for characterization. By Western blot analysis for GFP-Muclin expression in infected QBI-293a cells, 8 of the 10 clones were correct (data not shown). Two clones were characterized with identical results and were used in the experiments presented here. For the other constructs, a single correct clone was used for each. As a control for effects of adenovirus infection, a recombinant adenovirus that expresses cytosolic GFP (Ad-GFP) was used (QBioGene). As a control for potential effects of GFP targeted to the secretory pathway, a secretory GFP cassette (sGFP) and an sGFP-transmembrane domain-cytosolic tail cassette (sGFP-TMD-Tail) (16) were used to prepare adenoviruses. Adenoviral titers were determined using the TCID50 technique according to the supplier's protocol (QBioGene).
Cell culture.
Rat pancreatic AR42J cells were purchased from the American Type Culture Collection (CRL-1492) and were maintained in Kaighn's modified Ham's F-12 medium (Sigma, St. Louis, MO) with 20% fetal bovine serum (FBS) and penicillin and streptomycin (34) in a 5% CO2 atmosphere. Cells were used between passages 25 and 71. AR42J cells were seeded at 1.25 x 105 cells/well in 24-well plates 1 day before infection with the replication-deficient adenovirus. The medium was removed, and adenovirus was added (0.2 ml/well; all adenoviruses were adjusted to 2 x 108 pfu/ml, resulting in a final multiplicity of infection of 150) and incubated for 90 min at 37°C, followed by addition of 0.8 ml Kaighn's medium with 10% FBS. When dexamethasone (Sigma) was used, it was added at this time at a final concentration of 100 nM. Cells were used 48 h later for analysis.
Amylase storage and release.
Amylase storage in AR42J cells was expressed as amylase activity in the cell pellet per microgram DNA. DNA was measured according to the method of Cesarone et al. (5). Amylase release was measured according to Ref. 27. Cells were washed twice in HEPES-buffered Ringer's solution supplemented with 0.5% bovine serum albumin. The cells were preincubated for 15 min at 37°C, after which time aliquots of the media were collected. The cells were incubated a further 40 min at 37°C in the absence or presence of the cholecystokinin analog caerulein (100 nM final) to stimulate secretion. The cells and the media were saved for amylase activity determination. Amylase release was calculated as media activity released during the 40 min period minus that released during the 15-min preincubation period and expressed as percentage of the total activity. Amylase enzyme activity was measured in a microtiter format at 405 nm with the use of 4,6-ethyldiene(glucose)7-p-nitrophenyl-glucose-,D-maltoheptaside, which liberates p-nitrophenol when hydrolyzed (no. 85305, Raichem, San Diego, CA).
Isolation of secretory granules from AR42J cells. Cells were washed and resuspended in 2 ml 0.3 M sucrose, 10 mM MOPS, pH 7.0, 0.1 mM MgSO4, and protease inhibitors, and pressurized to 500 psi in a nitrogen cavitation bomb (Parr, Moline, IL) for 5 min on ice. The bomb was depressurized and the disrupted cells were centrifuged at 450 g x 15 min to pellet nuclei and unbroken cells. The postnuclear supernatant was mixed with Percoll (Sigma; 40% final), 0.25 M sucrose, 50 mM MES, pH 5.5, 0.2 mM EGTA, 0.1 mM MgSO4, and protease inhibitors. The samples were centrifuged at 100,000 g x 15 min to form the gradient. Gradients were fractionated with an Auto-Densi Flow II (Labconco, Kansas City, MO).
Morphological analysis. For ultrastructural analysis, cells or subcellular fractions were fixed in 4% paraformaldehyde, 1.6% glutaraldehyde, and embedded in an epoxy resin, and sectioned for standard transmission electron microscopy. Electron microscope images were photographed at x7,200 magnification, and the negatives were digitized using a flatbed scanner (Hewlett-Packard, Palo Alto, CA). The percentage of the cell cytoplasm (excluding nuclear areas) occupied by zymogen granules was measured using the "magic wand" tool of PhotoShop software (Adobe, San Jose, CA). Granules were defined as being electron dense and circular or elliptical in shape. Analysis was performed by an individual unaware of the identity of the samples.
For GFP fluorescence and indirect immunofluorescence, cells were fixed in 2% paraformaldehyde containing 0.1% saponin (Sigma) to permeabilize cell membranes. Cells were immunostained with anti-amylase (sheep polyclonal, 1:500 dilution; The Binding Site, San Diego, CA) plus anti-sheep Ig coupled to Texas red (Jackson Immunoresearch, West Grove, PA) and anti-Muclin as described previously (4). Labeled cells were observed on a Nikon Diaphot using appropriate fluorescence filters, and imaged using a SPOT II digital camera (Diagnostic Instruments, Sterling Heights, MI).
Statistics. Data were analyzed using one-way ANOVA with appropriate post hoc tests or by t-test when comparing basal to stimulated release values. The specific statistical analyses used are given in the figure legends.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
AR42J cells lack endogenous Muclin expression and Ad-pro-Muclin infection results in robust expression.
We evaluated whether the AR42J cell is a suitable model in which to test the role of pro-Muclin in secretory protein storage and zymogen granule formation. By Western blot analysis, AR42J cells did not express detectable Muclin, either under standard culture conditions or after 48 h in the presence of dexamethasone (Fig. 2). Immunofluorescence for Muclin was also negative in cells grown in the presence of dexamethasone, whereas the cytosol was filled with fine amylase-positive vesicular structures (Fig. 1D,a). Muclin is a major protein of the mouse pancreas, accounting for 2% of the tissue protein (14). To express pro-Muclin to similar levels in AR42J cells, we used recombinant adenovirus with a CMV promoter-driven expression cassette. Cells that were infected with Ad-GFP-pro-Muclin express abundant Muclin, as detected by Western blot analysis (Fig. 2). By quantitative Western blot normalized to cell DNA content, GFP-pro-Muclin was expressed at 56 ± 14% of pancreatic levels in the absence of dexamethasone, and this increased to 90 ± 37% of pancreatic levels in the presence of dexamethasone (data not shown). The pro-Muclin adenovirus construct was tagged with GFP (Fig. 1A) and fluorescence was detected in virtually every cell after infection (Fig. 1B).
|
|
To see whether expression of pro-Muclin induced recognizable zymogen granules, AR42J cells were examined by electron microscopy. Uninduced cells, either without adenovirus infection (Fig. 4A) or with control Ad-GFP infection (Fig. 4B), had occasional small electron-dense granules. Infection with Ad-GFP-pro-Muclin caused the appearance of zymogen granule-like organelles (Fig. 4C). When cells were induced with dexamethasone, either without adenovirus infection (Fig. 4D) or with control Ad-GFP infection (Fig. 4E), they had a moderate number of small granules. In contrast, Ad-GFP-pro-Muclin infected cells in the presence of dexamethasone had more granules and those granules were of larger size (Fig. 4F).
|
|
|
|
|
|
It has been reported that GFP, when it is targeted to the secretory pathway of AtT-20 cells, oligomerizes and may behave as an RSP (21). Because the pro-Muclin constructs were expressed as GFP-fusion proteins in our experiments, an adenovirus expressing a secretory version of GFP (Ad-sGFP) was prepared to test whether the GFP affected storage of amylase. The fusion protein expressed by Ad-sGFP has previously been shown to be targeted to the secretory pathway of AtT-20 cells (16). Ad-sGFP infected cells did not exhibit any stimulated release when grown in the absence of dexamethasone (Fig. 8). When Ad-sGFP infected cells were treated with dexamethasone, they had a modest increase in stimulated secretion, similar to the control Ad-GFP infected cells (Figs. 8 and 7, respectively), and their storage efficiency was comparable to Ad-GFP infected cells (Fig. 10). An adenoviral construct was also prepared that had the C-Tail and TMD of pro-Muclin attached to the carboxyl terminus of sGFP, to test whether addition of the membrane anchor and cytosolic tail would allow GFP in the secretory pathway to affect amylase storage and release. When AR42J cells were infected with this adenovirus, there was no effect on constitutive or stimulated amylase secretion compared with cytosolic GFP expressing cells (data not shown).
The truncated -Tail and
-TMD pro-Muclin proteins had a similar labeling pattern to the full-length construct (Fig. 1D, c, d, and b, respectively). All three exhibited strong perinuclear labeling with a weaker signal near the cell periphery, and there was colocalization with amylase in both regions of the cell. By contrast, the sGFP construct exhibited a fine vesicular pattern that had a distribution similar to that of amylase (Fig. 1D,e), consistent with sGFP being fairly evenly distributed in the secretory pathway.
Increased cargo expression enhances regulated secretion.
It has been suggested that the ability of dexamethasone to induce regulated secretion in AR42J cells is due to the increased RSP expression that occurs (20). To test this idea more directly, an Ad-amylase construct was prepared and used to increase cargo without using dexamethasone. Infection of cells with Ad-amylase resulted in an increase in amylase synthesis by 30% as measured by [35S]met/cys pulse-labeling and phosphorimage quantitation (data not shown). When Ad-amylase infected cells were stimulated with caerulein there was a significant secretory response (Figs. 9 and 10), similar to Ad-pro-Muclin-infected cells (Fig. 7). However, Ad-amylase infected cells induced with dexamethasone did not exhibit a further enhancement of regulated secretion (Figs. 9 and 10), unlike that observed with Ad-pro-Muclin in the presence of dexamethasone (Figs. 7 and 10).
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Expression of pro-Muclin combined with dexamethasone-induction results in a strong reduction in constitutive release, resulting in much more efficient RSP storage (Fig. 10). Conceptual considerations and experimental work have provided a framework to investigate how RSGs are formed. There is evidence for two major mechanisms in RSG formation: 1) "sorting-for-entry" whereby RSPs are actively sorted into the pathway by a specific cargo receptor, or by cargo association with cholesterol-glycoplipid rich membrane domains in the TGN; and 2) "sorting-by-retention" mediated by the inherent propensity of RSG cargo proteins to aggregate with one another in the environment of the TGN and RSG, i.e., mildly acidic pH and high Ca2+ (for review, see Refs. 2, 3, 28, 35, 38). In addition to Muclin's role in RSP aggregation, the C-Tail of pro-Muclin further enhances the efficiency of the regulated pathway. Because -TMD-pro-Muclin and
-Tail-pro-Muclin were still able to enhance regulated secretion, but only half as well as the full-length protein, it is likely that induction of RSGs by pro-Muclin involves both sorting for entry as well as sorting by retention.
Expression of pro-Muclin without its membrane anchor enhanced RSP storage, and, therefore, Muclin in the lumen of the secretory pathway has an important function. We recently demonstrated pH-dependent interactions of purified Muclin with several isolated zymogen granule content proteins, including amylase, that were mediated by the sulfated, O-linked oligosaccharides of Muclin (4). Furthermore, aggregation of isolated granule content proteins was modestly enhanced in the presence of Muclin (13). On the basis of these observations, Muclin in the lumen is expected to help the aggregation of the RSPs, thereby acting in the "sorting-by-retention" mechanism. Several other proteins have been suggested to have a "helper" function in RSP aggregation, and many of them are acidic sulfated macromolecules, like Muclin (35). A striking example is serglycin, a sulfated proteoglycan that is essential for mast cell RSG maturation. In a serglycin knockout mouse, mast cell granules form but they are unable to condense properly and they fail to store their RSPs (1).
The C-Tail of pro-Muclin is important for the maximal effect on inducing regulated secretion, suggesting that the C-Tail interacts with cytosolic proteins, as fits the idea of a cargo receptor. One possibility is that the C-Tail is involved in the assembly of a novel coat structure to induce RSG formation. However, there is currently no evidence for such a coat in the regulated pathway at the TGN. A second possibility is that the C-Tail recruits to the forming RSG-specific proteins that are involved in targeting the granule and regulation of its fusion with the plasma membrane. For example, in neuronal cells, members of the Rab11 family regulate the balance between constitutive and regulated exocytosis (24). In pancreatic acinar cells, it has been recently shown that Rab3D and Rab27B positively regulate RSG exocytosis (6, 7). Also, Noc2, a regulatory protein that interacts with Rab3 and Rab27, has been shown in a knockout mouse to be essential for regulated pancreatic secretion (29). Other important proteins that must be incorporated into forming RSGs are v-SNAREs, which mediate the membrane fusion event of the RSG with the plasma membrane (36). Especially relevant to the acinar cell is the v-SNARE Vamp8/endobrevin, which is on pancreatic zymogen granules and was recently demonstrated in a knockout mouse to be required for stimulated release (39). It remains to be determined whether the C-Tail of pro-Muclin interacts with any of these proteins.
Induction of AR42J cells by dexamethasone combined with pro-Muclin expression achieves an efficiency of protein storage similar to that of freshly isolated pancreatic acini (40). The effects of dexamethasone on the AR42J cell are complex. Dexamethasone increases mRNA transcription for some RSPs (27), increases message stability for others (8), and can enhance protein translation (26). There is also an increase in rough endoplasmic reticulum (27) that is due to a structural reorganization of the protein translation machinery (32). In addition to increased amounts of cargo, there are changes in expression of proteins that control vesicular traffic and exocytosis. For example, the small GTPase Rab proteins Rab3A and Rab3C are downregulated, whereas Rab3B and Rab3D are upregulated, by dexamethasone (25, 31). Dynamin II, which is involved in the exit of vesicles from the TGN, is upregulated after dexamethasone induction (10). Several SNARE and SNARE-associated proteins are also upregulated in dexamethasone-induced AR42J cells, including Munc18b, syntaxins 14, and SNAP-23 and -25 (18).
Despite the numerous changes caused by dexamethasone, such induction results only in a modest regulated pathway. A robust regulated secretory pathway in AR42J cells was observed in the additional presence of full-length pro-Muclin. The data suggest that although dexamethasone induces expression of the protein machinery needed to assemble well-regulated and functional secretory granules, this machinery can only be fully utilized when the cells also express pro-Muclin. Because the C-Tail of pro-Muclin is needed for the maximal effect, it is consistent with the idea that the C-Tail is involved in recruiting the regulatory proteins to the forming RSG. The model system of pro-Muclin expression in dexamethasone-induced AR42J cells will be powerful for exploring how this machinery is put together and controlled to make the regulated secretory pathway in an exocrine cell. Future work will use Percoll-purified RSGs to determine whether expression of pro-Muclin enhances recruitment of such proteins to RSG and the mechanistic role of the C-Tail in these processes.
![]() |
GRANTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
ACKNOWLEDGMENTS |
---|
![]() |
FOOTNOTES |
---|
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
2. Arvan P and Castle D. Sorting and storage during secretory granule biogenesis: looking backward and looking forward. Biochem J 332: 593610, 1998.[ISI][Medline]
3. Arvan P, Zhang BY, Feng LJ, Liu M, and Kuliawat R. Lumenal protein multimerization in the distal secretory pathway/secretory granules. Curr Opin Cell Biol 14: 448453, 2002.[CrossRef][ISI][Medline]
4. Boulatnikov I and De Lisle RC. Binding of the Golgi sorting receptor Muclin to pancreatic zymogens through sulfated O-linked oligosaccharides. J Biol Chem 279: 4091840926, 2004.
5. Cesarone CF, Bolognesi C, and Santi L. Improved microfluorometric DNA determination in biological material using 33258 Hoechst. Anal Biochem 100: 188197, 1979.[CrossRef][ISI][Medline]
6. Chen X, Li C, Izumi T, Ernst SA, Andrews PC, and Williams JA. Rab27b localizes to zymogen granules and regulates pancreatic acinar exocytosis. Biochem Biophys Res Commun 323: 11571162, 2004.[CrossRef][ISI][Medline]
7. Chen XQ, Ernst SA, and Williams JA. Dominant negative Rab3D mutants reduce GTP-bound endogenous Rab3D in pancreatic acini. J Biol Chem 278: 5005350060, 2003.
8. Chobert MN, Grondin G, Brouillet A, Laperche Y, and Beaudoin AR. Control of -glutamyl transpeptidase expression by glucocorticoids in the rat pancreas. Correlation with granule formation. J Biol Chem 271: 1243112437, 1996.
9. Colomer V, Kicska GA, and Rindler MJ. Secretory granule content proteins and the luminal domains of granule membrane proteins aggregate in vitro at mildly acidic pH. J Biol Chem 271: 4855, 1996.
10. Cook TA, Mesa KJ, Gebelein BA, and Urrutia RA. Upregulation of dynamin II expression during the acquisition of a mature pancreatic acinar cell phenotype. J Histochem Cytochem 44: 13731378, 1996.[Abstract]
11. Cool DR, Normant E, Shen FS, Chen HC, Pannell L, Zhang Y, and Loh YP. Carboxypeptidase E is a regulated secretory pathway sorting receptor: Genetic obliteration leads to endocrine disorders in Cpefat mice. Cell 88: 7383, 1997.[CrossRef][ISI][Medline]
12. De Lisle RC. Characterization of the major sulfated protein of mouse pancreatic acinar cells: a high molecular weight peripheral membrane glycoprotein of zymogen granules. J Cell Biochem 56: 385396, 1994.[CrossRef][ISI][Medline]
13. De Lisle RC. Role of sulfated O-linked glycoproteins in zymogen granule formation. J Cell Sci 115: 29412952, 2002.
14. De Lisle RC, Petitt M, Huff J, Isom KS, and Agbas A. Muclin expression in the cystic fibrosis transmembrane conductance regulator knockout mouse. Gastroenterology 113: 521532, 1997.[CrossRef][ISI][Medline]
15. De Lisle RC, Schulz I, Tyrakowski T, Haase W, and Hopfer U. Isolation of stable pancreatic zymogen granules. Am J Physiol Gastrointest Liver Physiol 246: G411G418, 1984.
16. De Lisle RC and Ziemer D. Processing of pro-Muclin and divergent targeting of its products to zymogen granules and the apical plasma membrane of pancreatic acinar cells. Eur J Cell Biol 79: 892904, 2000.[CrossRef][ISI][Medline]
17. Doyon Y, Home W, Daull P, and LeBel D. Effect of C-domain N-glycosylation and deletion on rat pancreatic -amylase secretion and activity. Biochem J 362: 259264, 2002.[CrossRef][ISI][Medline]
18. Gaisano HY, Huang X, Sheu L, Ghai M, Newgard CB, Trinh KY, and Trimble WS. Snare protein expression and adenoviral transfection of amphicrine AR42J. Biochem Biophys Res Commun 260: 781784, 1999.[CrossRef][ISI][Medline]
19. Ghosh P and Kornfeld S. The GGA proteins: key players in protein sorting at the trans-Golgi network. Eur J Cell Biol 83: 257262, 2004.[ISI][Medline]
20. Gorr SU and Tseng SY. Aggregation and concentration-dependent sorting of exocrine regulated secretory proteins. Biochem Biophys Res Commun 215: 8288, 1995.[CrossRef][ISI][Medline]
21. Jain RK, Joyce PBM, Molinete M, Halban PA, and Gorr SU. Oligomerization of green fluorescent protein in the secretory pathway of endocrine cells. Biochem J 360: 645649, 2001.[CrossRef][ISI][Medline]
22. Jessop NW and Hay RJ. Characteristics of two rat pancreatic exocrine cell lines derived from transplantable tumors (Abstract). In Vitro 16: 212, 1980.[ISI]
23. Kelly RB. Pathways of protein secretion in eukaryotes. Science 230: 2532, 1985.[ISI][Medline]
24. Khvotchev MV, Ren M, Takamori S, Jahn R, and Sudhof TC. Divergent functions of neuronal Rab11b in Ca2+-regulated versus constitutive exocytosis. J Neurosci 23: 1053110539, 2003.
25. Klengel R, Piiper A, Pittelkow S, and Zeuzem S. Differential expression of Rab3 isoforms during differentiation of pancreatic acinar cell line AR42J. Biochem Biophys Res Commun 236: 719722, 1997.[CrossRef][ISI][Medline]
26. Kullman J, Gisi C, and Lowe ME. Dexamethasone-regulated expression of pancreatic lipase and two related proteins in AR42J cells. Am J Physiol Gastrointest Liver Physiol 270: G746G751, 1996.
27. Logsdon CD, Moessner J, Williams JA, and Goldfine ID. Glucocorticoids increase amylase mRNA levels, secretory organelles, and secretion in pancreatic acinar AR42J cells. J Cell Biol 100: 12001208, 1985.[Abstract]
28. Loh YP, Kim T, Rodriguez YM, and Cawley NX. Secretory granule biogenesis and neuropeptide sorting to the regulated secretory pathway in neuroendocrine cells. J Mol Neurosci 22: 6371, 2003.[ISI]
29. Matsumoto M, Miki T, Shibasaki T, Kawaguchi M, Shinozaki H, Nio J, Saraya A, Koseki H, Miyazaki M, Iwanaga T, and Seino S. Noc2 is essential in normal regulation of exocytosis in endocrine and exocrine cells. Proc Natl Acad Sci USA 101: 83138318, 2004.
30. Otte S and Barlowe C. Sorting signals can direct receptor-mediated export of soluble proteins into COPII vesicles. Nat Cell Biol 6: 11891194, 2004.[CrossRef][ISI][Medline]
31. Qiu X, Valentijn JA, and Jamieson JD. Carboxyl-methylation of rab3D in the rat pancreatic acinar tumor cell line AR42J. Biochem Biophys Res Commun 285: 708714, 2001.[CrossRef][ISI][Medline]
32. Rajasekaran AK, Morimoto T, Hanzel DK, Rodriguez-Boulan E, and Kreibich G. Structural reorganization of the rough endoplasmic reticulum without size expansion accounts for dexamethasone-induced secretory activity in AR42J cells. J Cell Sci 105: 333345, 1993.
33. Rosewicz S, Detjen K, Logsdon CD, Chen LM, Chao J, and Riecken EO. Glandular kallikrein gene expression is selectively down-regulated by glucocorticoids in pancreatic AR42J cells. Endocrinology 128: 22162222, 1991.[Abstract]
34. Schlegel A, Arvan P, and Lisanti MP. Caveolin-1 binding to endoplasmic reticulum membranes and entry into the regulated secretory pathway are regulated by serine phosphorylation. Protein sorting at the level of the endoplasmic reticulum. J Biol Chem 276: 43984408, 2001.
35. Schrader M. Membrane targeting in secretion. Subcell Biochem 37: 391421, 2004.[Medline]
36. Sollner TH. Intracellular and viral membrane fusion: a uniting mechanism. Curr Opin Cell Biol 16: 429435, 2004.[CrossRef][ISI][Medline]
37. Tandon C and De Lisle RC. Apactin is involved in remodeling of the actin cytoskeleton during regulated exocytosis. Eur J Cell Biol 83: 7989, 2004.[CrossRef][Medline]
38. Thiele C, Gerdes HH, and Huttner WB. Protein secretion: puzzling receptors. Curr Biol 7: R496R500, 1997.[CrossRef][ISI][Medline]
39. Wang CC, Ng CP, Lu L, Atlashkin V, Zhang W, Seet LF, and Hong W. A role of VAMP8/endobrevin in regulated exocytosis of pancreatic acinar cells. Dev Cell 7: 359371, 2004.[CrossRef][ISI][Medline]
40. Williams JA, Korc M, and Dormer RL. Action of secretagogues on a new preparation of functionally intact, isolated pancreatic acini. Am J Physiol Endocrinol Metab Gastrointest Physiol 235: E517E524, 1978.
41. Yu S, Hao Y, and Lowe AW. Effects of GP2 expression on secretion and endocytosis in pancreatic AR42J cells. Biochem Biophys Res Commun 322: 320325, 2004.[CrossRef][ISI][Medline]
|
HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Visit Other APS Journals Online |