Small GTP-binding protein, Rab6, is associated with secretory granules in atrial myocytes

1997 ◽  
Vol 272 (5) ◽  
pp. C1594-C1601 ◽  
Author(s):  
H. Iida ◽  
S. Tanaka ◽  
Y. Shibata
Keyword(s):  
Electron Microscopy ◽  
Intracellular Transport ◽  
Binding Proteins ◽  
Secretory Granules ◽  
Immunogold Electron Microscopy ◽  
Rab Proteins ◽  
Atrial Myocytes ◽  
Vesicular Traffic ◽  
Gtp Binding Proteins ◽  
Gtp Binding

Rab proteins, a subfamily of small GTP-binding proteins, have been shown to play key roles in regulation of vesicular traffic in eukaryotic cells. In this study, we have intended to identify, the atrial granule-associated Rab proteins that seem to be required for formation or intracellular transport of the granules. Atrial granules contained at least four small GTP-binding proteins, and we have demonstrated by biochemical analysis that one of the small GTP-binding proteins associated with the atrial granules is a Rab6 protein (Rab6p). Rab6p was also detected in highly purified zymogen granules of pancreatic exocrine gland. Immunogold electron microscopy performed on ultrathin cryosections of rat auricle revealed that Rab6p was associated with the atrial granule membranes. Association of Rab6p with the atrial granule membranes was also confirmed by immunodiffusion electron microscopy in agarose-embedded atrial granules. These data indicate that Rab6p is associated with the atrial granules and that it might function in the intracellular traffic of the secretory granules in the atrial myocytes.

scholarly journals Retrograde transport from the Golgi region to the endoplasmic reticulum is sensitive to GTP gamma S.

1992 ◽  
Vol 116 (6) ◽  
pp. 1357-1367 ◽  
Author(s):  
A Tan ◽  
J Bolscher ◽  
C Feltkamp ◽  
H Ploegh
Keyword(s):  
Hepg2 Cells ◽  
Intracellular Transport ◽  
Secretory Pathway ◽  
Binding Proteins ◽  
Brefeldin A ◽  
Retrograde Transport ◽  
Gtp Binding Proteins ◽  
Gtp Binding ◽  
Streptolysin O ◽  
Gamma S

The involvement of GTP-binding proteins in the intracellular transport of the secretory glycoprotein alpha 1-antitrypsin was investigated in streptolysin O-permeabilized HepG2 cells. This permeabilization procedure allows ready access to the intracellular milieu of the membrane-impermeant, nonhydrolyzable GTP analog GTP gamma S. In streptolysin O-permeabilized HepG2 cells, the constitutive secretory pathway remains functional and is sensitive to GTP gamma S. Exposure of HepG2 cells to brefeldin A resulted in redistribution of Golgi-resident glycosyltransferases (including both alpha 2----3 and alpha 2----6 sialyltransferases) to the ER. This redistribution was sensitive to GTP gamma S. Our results suggest that GTP-binding proteins are involved in the regulation not only of the anterograde, but also of the retrograde, pathway.

scholarly journals GTP-Binding Proteins and Regulated Exocytosis

1999 ◽  
Vol 10 (3) ◽  
pp. 284-306 ◽  
Author(s):  
E.L. Watson
Keyword(s):  
Membrane Trafficking ◽  
Binding Proteins ◽  
Molecular Mechanisms ◽  
Secretory Granules ◽  
Vesicular Trafficking ◽  
Snare Complex ◽  
Secretory Vesicles ◽  
Regulated Exocytosis ◽  
Gtp Binding Proteins ◽  
Gtp Binding

Regulated exocytosis, which occurs in response to stimuli, is a two-step process involving the docking of secretory granules (SGs) at specific sites on the plasma membrane (PM), with subsequent fusion and release of granule contents. This process plays a crucial role in a number of tissues, including exocrine glands, chromaffin cells, platelets, and mast cells. Over the years, our understanding of the proteins involved in vesicular trafficking has increased dramatically. Evidence from genetic, biochemical, immunological, and functional assays supports a role for ras-like monomeric GTP-binding proteins (smgs) as well as heterotrimeric GTP-binding protein (G-protein) subunits in various steps of the vesicular trafficking pathway, including the transport of secretory vesicles to the PM. Data suggest that the function of GTP-binding proteins is likely related to their localization to specific cellular compartments. The presence of both G-proteins and smgs on secretory vesicles/granules implicates a role for these proteins in the final stages of exocytosis. Molecular mechanisms of exocytosis have been postulated, with the identification of a number of proteins that modify, regulate, and interact with GTP-binding proteins, and with the advent of approaches that assess the functional importance of GTP-binding proteins in downstream, exocytotic events. Further, insight into vesicle targeting and fusion has come from the characterization of a SNAP receptor (SNARE) complex composed of vesicle, PM, and soluble membrane trafficking components, and identification of a functional linkage between GTP-binding and SNARES.

scholarly journals A rab protein regulates the localization of secretory granules in AtT-20 cells.

1993 ◽  
Vol 4 (7) ◽  
pp. 747-756 ◽  
Author(s):  
J K Ngsee ◽  
A M Fleming ◽  
R H Scheller
Keyword(s):  
Mammalian Cells ◽  
Binding Proteins ◽  
Secretory Granules ◽  
Release Site ◽  
Secretory Vesicles ◽  
Gtp Binding Proteins ◽  
Rab Protein ◽  
Gtp Binding ◽  
Cell Processes ◽  
Intracellular Vesicles

Low molecular weight (LMW) GTP-binding proteins are hypothesized to play a role in the vectorial transport of intracellular vesicles. Mutational studies in yeast and subcellular localization in mammalian cells suggest that a family of LMW GTP-binding proteins, termed rab, target intracellular vesicles to their appropriate acceptor compartment. In this report, we demonstrate that an elasmobranch homologue of rab3A, o-rab3, plays a significant role in the sequestration of regulated secretory vesicles. When transfected into the murine endocrine cell line AtT-20, the wild-type o-rab3 protein is localized exclusively to the tips of the processes, a region of the cell known to accumulate proteins associated with regulated secretory vesicles. Two mutations, Gln81 to Leu (Q81L) and Asn135 Ile (N135I), which alter GTP binding or rate of hydrolysis, blocked the localization of the o-rab3 protein to the tips of cell processes. These mutations also hindered the sequestration of ACTH-containing secretory vesicles to the process tips but did not affect the basal or stimulated release of ACTH. Moreover, the sequestration of the protein VAMP to the process tip was also hindered by the mutation. The results demonstrate a role for the rab3 proteins in localization, sequestration, and storage of secretory vesicles near their release site.

scholarly journals Multiple GTP-binding proteins regulate vesicular transport from the ER to Golgi membranes.

1992 ◽  
Vol 119 (5) ◽  
pp. 1077-1096 ◽  
Author(s):  
R Schwaninger ◽  
H Plutner ◽  
G M Bokoch ◽  
W E Balch
Keyword(s):  
G Protein ◽  
Secretory Pathway ◽  
Binding Proteins ◽  
Protein S ◽  
Rab Proteins ◽  
Heterotrimeric G Protein ◽  
Gtp Binding Proteins ◽  
Initial Event ◽  
Gtp Binding ◽  
Transport Vesicle

Using indirect immunofluorescence we have examined the effects of reagents which inhibit the function of ras-related rab small GTP-binding proteins and heterotrimeric G alpha beta gamma proteins in ER to Golgi transport. Export from the ER was inhibited by an antibody towards rab1B and an NH2-terminal peptide which inhibits ARF function (Balch, W. E., R. A. Kahn, and R. Schwaninger. 1992. J. Biol. Chem. 267:13053-13061), suggesting that both of these small GTP-binding proteins are essential for the transport vesicle formation. Export from the ER was also potently inhibited by mastoparan, a peptide which mimics G protein binding regions of seven transmembrane spanning receptors activating and uncoupling heterotrimeric G proteins from their cognate receptors. Consistent with this result, purified beta gamma subunits inhibited the export of VSV-G from the ER suggesting an initial event in transport vesicle assembly was regulated by a heterotrimeric G protein. In contrast, incubation in the presence of GTP gamma S or AIF(3-5) resulted in the accumulation of transported protein in different populations of punctate pre-Golgi intermediates distributed throughout the cytoplasm of the cell. Finally, a peptide which is believed to antagonize the interaction of rab proteins with putative downstream effector molecules inhibited transport at a later step preceding delivery to the cis Golgi compartment, similar to the site of accumulation of transported protein in the absence of NSF or calcium (Plutner, H., H. W. Davidson, J. Saraste, and W. E. Balch. 1992. J. Cell Biol. 119:1097-1116). These results are consistent with the hypothesis that multiple GTP-binding proteins including a heterotrimeric G protein(s), ARF and rab1 differentially regulate steps in the transport of protein between early compartments of the secretory pathway. The concept that G protein-coupled receptors gate the export of protein from the ER is discussed.

scholarly journals Rabs and EHDs: alternate modes for traffic control

2011 ◽  
Vol 32 (1) ◽  
pp. 17-23 ◽  
Author(s):  
Jing Zhang ◽  
Naava Naslavsky ◽  
Steve Caplan
Keyword(s):  
Membrane Transport ◽  
Traffic Control ◽  
Binding Proteins ◽  
Endocytic Trafficking ◽  
Rab Proteins ◽  
Protein Families ◽  
Vesicle Budding ◽  
Gtp Binding Proteins ◽  
Gtp Binding ◽  
Key Aspects

Endocytic trafficking is a highly organized process regulated by a network of proteins, including the Rab family of small GTP-binding proteins and the C-terminal EHDs (Eps15 homology-domain-containing proteins). Central roles for Rab proteins have been described in vesicle budding, delivery, tethering and fusion, whereas little is known about the functions of EHDs in membrane transport. Common effectors for these two protein families have been identified, and they facilitate regulation of sequential steps in transport. By comparing and contrasting key aspects in their modes of function, we shall promote a better understanding of how Rab proteins and EHDs regulate endocytic trafficking.

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