scholarly journals Opposing roles for SNAP23 in secretion in exocrine and endocrine pancreatic cells

2016 ◽  
Vol 215 (1) ◽  
pp. 121-138 ◽  
Author(s):  
Masataka Kunii ◽  
Mica Ohara-Imaizumi ◽  
Noriko Takahashi ◽  
Masaki Kobayashi ◽  
Ryosuke Kawakami ◽  
...  
Keyword(s):  
Endocrine Cells ◽  
Plasma Membranes ◽  
Secretory Granules ◽  
Attachment Protein ◽  
Pancreatic Cells ◽  
Protein Receptor ◽  
Pancreatic Exocrine ◽  
Protein Attachment ◽  
Endocrine Pancreatic Cells

The membrane fusion of secretory granules with plasma membranes is crucial for the exocytosis of hormones and enzymes. Secretion disorders can cause various diseases such as diabetes or pancreatitis. Synaptosomal-associated protein 23 (SNAP23), a soluble N-ethyl-maleimide sensitive fusion protein attachment protein receptor (SNARE) molecule, is essential for secretory granule fusion in several cell lines. However, the in vivo functions of SNAP23 in endocrine and exocrine tissues remain unclear. In this study, we show opposing roles for SNAP23 in secretion in pancreatic exocrine and endocrine cells. The loss of SNAP23 in the exocrine and endocrine pancreas resulted in decreased and increased fusion of granules to the plasma membrane after stimulation, respectively. Furthermore, we identified a low molecular weight compound, MF286, that binds specifically to SNAP23 and promotes insulin secretion in mice. Our results demonstrate opposing roles for SNAP23 in the secretion mechanisms of the endocrine and exocrine pancreas and reveal that the SNAP23-binding compound MF286 may be a promising drug for diabetes treatment.

scholarly journals Localization of protein disulfide isomerase on plasma membranes of rat exocrine pancreatic cells.

1988 ◽  
Vol 36 (8) ◽  
pp. 1069-1074 ◽  
Author(s):  
S Akagi ◽  
A Yamamoto ◽  
T Yoshimori ◽  
R Masaki ◽  
R Ogawa ◽  
...  
Keyword(s):  
Protein Disulfide Isomerase ◽  
Plasma Membranes ◽  
Secretory Granules ◽  
Amorphous Material ◽  
Protein A ◽  
Disulfide Isomerase ◽  
Gold Particles ◽  
Pancreatic Cells ◽  
Acinar Lumen ◽  
Protein Disulfide

We investigated immunocytochemically the ultrastructural localization of protein disulfide isomerase (PDI) in rat pancreatic exocrine cells by use of the post-embedding protein A-gold technique. We found that not only the endoplasmic reticulum (ER) and nuclear envelope but also the trans-Golgi cisternae, secretory granules, and plasma membranes were heavily labeled with gold particles. Labeling density of the gold particles in the rough ER and plasma membranes of the exocrine pancreatic cells was twofold and twentyfold greater, respectively, than that of hepatocytes. In the acinar lumen, amorphous material presumably corresponding to the secreted zymogens was also labeled with gold particles. These results suggest that in rat exocrine pancreatic cells a significant amount of PDI is transported to the plasma membrane and secreted to the acinar lumen.

scholarly journals Comparative analysis of tandem C2 domains from the mammalian synaptotagmin family

2004 ◽  
Vol 378 (2) ◽  
pp. 681-686 ◽  
Author(s):  
Colin RICKMAN ◽  
Molly CRAXTON ◽  
Shona OSBORNE ◽  
Bazbek DAVLETOV
Keyword(s):  
Membrane Trafficking ◽  
Sequence Similarity ◽  
Attachment Protein ◽  
C2 Domains ◽  
Phospholipid Binding ◽  
Calcium Dependent ◽  
Functional Studies ◽  
Protein Receptor ◽  
High Degree ◽  
Protein Attachment

Intracellular membrane traffic is governed by a conserved set of proteins, including Syts (synaptotagmins). The mammalian Syt family includes 15 isoforms. Syts are membrane proteins that possess tandem C2 domains (C2AB) implicated in calcium-dependent phospholipid binding. We performed a pair-wise amino acid sequence comparison, together with functional studies of rat Syt C2ABs, to examine common and divergent properties within the mammalian family. Sequence analysis indicates three different C2AB classes, the members of which share a high degree of sequence similarity. All the other C2ABs are highly divergent in sequence. Nearly half of the Syt family does not exhibit calcium/phospholipid binding in comparison to Syt I, the major brain isoform. Syts do, however, possess a more conserved function, namely calcium-independent binding to target SNARE (soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor) heterodimers. All tested isoforms, except Syt XII and Syt XIII, bound the target SNARE heterodimer comprising syntaxin 1 and SNAP-25 (25 kDa synaptosome-associated protein). Our present study suggests that many Syt isoforms can function in membrane trafficking to interact with the target SNARE heterodimer on the pathway to calcium-triggered membrane fusion.

scholarly journals The yeast Batten disease orthologue Btn1 controls endosome–Golgi retrograde transport via SNARE assembly

2011 ◽  
Vol 195 (2) ◽  
pp. 203-215 ◽  
Author(s):  
Rachel Kama ◽  
Vydehi Kanneganti ◽  
Christian Ungermann ◽  
Jeffrey E. Gerst
Keyword(s):  
Disease Gene ◽  
Transmembrane Domain ◽  
Batten Disease ◽  
Retrograde Transport ◽  
Attachment Protein ◽  
Protein Receptor ◽  
Late Endosomes ◽  
Target Membrane ◽  
Opposing Effects ◽  
Protein Attachment

The human Batten disease gene CLN3 and yeast orthologue BTN1 encode proteins of unclear function. We show that the loss of BTN1 phenocopies that of BTN2, which encodes a retromer accessory protein involved in the retrieval of specific cargo from late endosomes (LEs) to the Golgi. However, Btn1 localizes to Golgi and regulates soluble N-ethyl-maleimide sensitive fusion protein attachment protein receptor (SNARE) function to control retrograde transport. Specifically, BTN1 overexpression and deletion have opposing effects on phosphorylation of the Sed5 target membrane SNARE, on Golgi SNARE assembly, and on Golgi integrity. Although Btn1 does not interact physically with SNAREs, it regulates Sed5 phosphorylation by modulating Yck3, a palmitoylated endosomal kinase. This may involve modification of the Yck3 lipid anchor, as substitution with a transmembrane domain suppresses the deletion of BTN1 and restores trafficking. Correspondingly, deletion of YCK3 mimics that of BTN1 or BTN2 with respect to LE–Golgi retrieval. Thus, Btn1 controls retrograde sorting by regulating SNARE phosphorylation and assembly, a process that may be adversely affected in Batten Disease patients.

The molecular mechanisms of the mammalian exocyst complex in exocytosis

2006 ◽  
Vol 34 (5) ◽  
pp. 687-690 ◽  
Author(s):  
S. Wang ◽  
S.C. Hsu
Keyword(s):  
Plasma Membrane ◽  
Molecular Mechanisms ◽  
Early Stage ◽  
Secretory Vesicles ◽  
Attachment Protein ◽  
Trafficking Pathway ◽  
Exocyst Complex ◽  
Protein Receptor ◽  
Associated Proteins ◽  
Protein Attachment

Exocytosis is a highly ordered vesicle trafficking pathway that targets proteins to the plasma membrane for membrane addition or secretion. Research over the years has discovered many proteins that participate at various stages in the mammalian exocytotic pathway. At the early stage of exocytosis, co-atomer proteins and their respective adaptors and GTPases have been shown to play a role in the sorting and incorporation of proteins into secretory vesicles. At the final stage of exocytosis, SNAREs (soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor) and SNARE-associated proteins are believed to mediate the fusion of secretory vesicles at the plasma membrane. There are multiple events that may occur between the budding of secretory vesicles from the Golgi and the fusion of these vesicles at the plasma membrane. The most obvious and best-known event is the transport of secretory vesicles from Golgi to the vicinity of the plasma membrane via microtubules and their associated motors. At the vicinity of the plasma membrane, however, it is not clear how vesicles finally dock and fuse with the plasma membrane. Identification of proteins involved in these events should provide important insights into the mechanisms of this little known stage of the exocytotic pathway. Currently, a protein complex, known as the sec6/8 or the exocyst complex, has been implicated to play a role at this late stage of exocytosis.

scholarly journals Quantitative analysis of the native presynaptic cytomatrix by cryoelectron tomography

2010 ◽  
Vol 188 (1) ◽  
pp. 145-156 ◽  
Author(s):  
Rubén Fernández-Busnadiego ◽  
Benoît Zuber ◽  
Ulrike Elisabeth Maurer ◽  
Marek Cyrklaff ◽  
Wolfgang Baumeister ◽  
...  
Keyword(s):  
Synaptic Vesicle ◽  
Neurotransmitter Release ◽  
Synaptic Vesicles ◽  
Attachment Protein ◽  
Readily Releasable Pool ◽  
Protein Receptor ◽  
Membrane Contact ◽  
Synaptic Vesicle Release ◽  
Protein Attachment

The presynaptic terminal contains a complex network of filaments whose precise organization and functions are not yet understood. The cryoelectron tomography experiments reported in this study indicate that these structures play a prominent role in synaptic vesicle release. Docked synaptic vesicles did not make membrane to membrane contact with the active zone but were instead linked to it by tethers of different length. Our observations are consistent with an exocytosis model in which vesicles are first anchored by long (>5 nm) tethers that give way to multiple short tethers once vesicles enter the readily releasable pool. The formation of short tethers was inhibited by tetanus toxin, indicating that it depends on soluble N-ethyl-maleimide sensitive fusion protein attachment protein receptor complex assembly. Vesicles were extensively interlinked via a set of connectors that underwent profound rearrangements upon synaptic stimulation and okadaic acid treatment, suggesting a role of these connectors in synaptic vesicle mobilization and neurotransmitter release.

Ultrastructural localization of cytoskeletal proteins in pancreatic secretory cells

1985 ◽  
Vol 63 (6) ◽  
pp. 680-690 ◽  
Author(s):  
Moïse Bendayan
Keyword(s):  
Secretory Granules ◽  
Protein A ◽  
Ultrastructural Localization ◽  
Cytoskeletal Proteins ◽  
Secretory Cells ◽  
Secretory Proteins ◽  
Protein Maturation ◽  
Pancreatic Cells ◽  
Pancreatic Exocrine ◽  
Cell Web

Actin, myosin, and keratin immunoreactive sites have been localized with high resolution in pancreatic exocrine cells, by applying the protein A – gold technique on tissues processed at low temperature conditions. The labeling by gold particles was found at the level of the cell web and closely associated with the limiting membranes of the immature and mature secretory granules, as well as those of the "trans" cisternae of the Golgi apparatus. These results, together with those obtained in the study on the localization of secretory proteins in exocrine pancreatic cells, demonstrate that cytoskeletal proteins are present at sites where maturation and (or) concentration of the secretory proteins occur. Thus, besides the role that cytoskeletal proteins must play in the transport of the secretory granules from the Golgi to the plasma membrane, they may also be involved in the process of protein maturation and (or) concentration.

scholarly journals A Novel Site of Action for α-SNAP in the SNARE Conformational Cycle Controlling Membrane Fusion

2008 ◽  
Vol 19 (3) ◽  
pp. 776-784 ◽  
Author(s):  
Marcin Barszczewski ◽  
John J. Chua ◽  
Alexander Stein ◽  
Ulrike Winter ◽  
Rainer Heintzmann ◽  
...  
Keyword(s):  
Membrane Fusion ◽  
Plasma Membranes ◽  
Secretory Granules ◽  
Neuroendocrine Cells ◽  
Snare Complex ◽  
Protein Receptor ◽  
Sensitive Factor ◽  
Site Of Action ◽  
Snare Motif ◽  
Liposome Fusion

Regulated exocytosis in neurons and neuroendocrine cells requires the formation of a stable soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex consisting of synaptobrevin-2/vesicle-associated membrane protein 2, synaptosome-associated protein of 25 kDa (SNAP-25), and syntaxin 1. This complex is subsequently disassembled by the concerted action of α-SNAP and the ATPases associated with different cellular activities-ATPase N-ethylmaleimide-sensitive factor (NSF). We report that NSF inhibition causes accumulation of α-SNAP in clusters on plasma membranes. Clustering is mediated by the binding of α-SNAP to uncomplexed syntaxin, because cleavage of syntaxin with botulinum neurotoxin C1 or competition by using antibodies against syntaxin SNARE motif abolishes clustering. Binding of α-SNAP potently inhibits Ca2+-dependent exocytosis of secretory granules and SNARE-mediated liposome fusion. Membrane clustering and inhibition of both exocytosis and liposome fusion are counteracted by NSF but not when an α-SNAP mutant defective in NSF activation is used. We conclude that α-SNAP inhibits exocytosis by binding to the syntaxin SNARE motif and in turn prevents SNARE assembly, revealing an unexpected site of action for α-SNAP in the SNARE cycle that drives exocytotic membrane fusion.

scholarly journals The human SNARE protein Ykt6 mediates its own palmitoylation at C-terminal cysteine residues

2004 ◽  
Vol 384 (2) ◽  
pp. 233-237 ◽  
Author(s):  
Michael VEIT
Keyword(s):  
Fusion Protein ◽  
Binding Site ◽  
Covalent Attachment ◽  
Receptor Protein ◽  
Cysteine Residues ◽  
Snare Protein ◽  
Attachment Protein ◽  
Present Evidence ◽  
Protein Receptor ◽  
Protein Attachment

The yeast SNARE (soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor) protein Ykt6 was shown to mediate palmitoylation of the fusion factor Vac8 in a reaction essential for the fusion of vacuoles. Here I present evidence that hYkt6 (human Ykt6) has self-palmitoylating activity. Incubation of recombinant hYkt6 with [3H]Pal-CoA ([3H]palmitoyl-CoA) leads to covalent attachment of palmitate to C-terminal cysteine residues. The N-terminal domain of human Ykt6 contains a Pal-CoA binding site and is required for the reaction.

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