scholarly journals Biosynthesis of intestinal microvillar proteins. Pulse-chase labelling studies on aminopeptidase N and sucrase-isomaltase

1982 ◽  
Vol 204 (3) ◽  
pp. 639-645 ◽  
Author(s):  
E M Danielsen
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Plasma Membrane ◽  
Aminopeptidase N ◽  
Secretory Proteins ◽  
Oligosaccharide Structure ◽  
Membrane Flow ◽  
Polypeptide Synthesis ◽  
High Mannose ◽  
Small Intestinal

The biogenesis of two microvillar enzymes, aminopeptidase N (EC 3.4.11.2) and sucrase (EC 3.2.1.48)-isomaltase (EC 3.2.1.10), was studied by pulse-chase labelling of pig small-intestinal explants kept in organ culture. Both enzymes became inserted into the membrane during or immediately after polypeptide synthesis, indicating that translation takes place on ribosomes attached to the rough endoplasmic reticulum. The earliest detectable forms of aminopeptidase and sucrase-isomaltase were polypeptides of Mr 140 000 and 240 000 respectively. These polypeptides were susceptible to treatment with endo-β-N-acetylglucosaminidiase H (EC 3.2.1.96), suggesting that the microvillar enzymes during or immediately after completion of protein synthesis become glycosylated with a ‘high-mannose’ oligosaccharide structure similarly to other plasma-membrane and secretory proteins. After 20-40 min or 60-90 min of chase, respectively, aminopeptidase N and sucrase-isomaltase were reglycosylated to give the polypeptides of Mr 166 000 (aminopeptidase N) and 265 000 (sucrase-isomaltase). These were expressed at the microvillar membrane after 60-90 min. During the entire process of synthesis and transport to the microvillar membrane the enzymes were bound to membranes, indicating that the biogenesis of aminopeptidase N and sucrase-isomaltase occurs in accordance with the membrane flow hypothesis.

Cleavage of SNAP-25 and VAMP-2 impairs store-operated Ca2+entry in mouse pancreatic acinar cells

2005 ◽  
Vol 288 (1) ◽  
pp. C214-C221 ◽  
Author(s):  
Juan A. Rosado ◽  
Pedro C. Redondo ◽  
Ginés M. Salido ◽  
Stewart O. Sage ◽  
Jose A. Pariente
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Secretory Cell ◽  
Botulinum Toxin A ◽  
Acinar Cells ◽  
Pancreatic Acinar Cells ◽  
Secretory Proteins ◽  
Amylase Secretion ◽  
Cell Type ◽  
Store Depletion

We recently reported that store-operated Ca2+entry (SOCE) in nonexcitable cells is likely to be mediated by a reversible interaction between Ca2+channels in the plasma membrane and the endoplasmic reticulum, a mechanism known as “secretion-like coupling.” As for secretion, in this model the actin cytoskeleton plays a key regulatory role. In the present study we have explored the involvement of the secretory proteins synaptosome-associated protein (SNAP-25) and vesicle-associated membrane protein (VAMP) in SOCE in pancreatic acinar cells. Cleavage of SNAP-25 and VAMPs by treatment with botulinum toxin A (BoNT A) and tetanus toxin (TeTx), respectively, effectively inhibited amylase secretion stimulated by the physiological agonist CCK-8. BoNT A significantly reduced Ca2+entry induced by store depletion using thapsigargin or CCK-8. In addition, treatment with BoNT A once SOCE had been activated reduced Ca2+influx, indicating that SNAP-25 is needed for both the activation and maintenance of SOCE in pancreatic acinar cells. VAMP-2 and VAMP-3 are expressed in mouse pancreatic acinar cells. Both proteins associate with the cytoskeleton upon Ca2+store depletion, although only VAMP-2 seems to be sensitive to TeTx. Treatment of pancreatic acinar cells with TeTx reduced the activation of SOCE without affecting its maintenance. These findings support a role for SNAP-25 and VAMP-2 in the activation of SOCE in pancreatic acinar cells and show parallels between this process and secretion in a specialized secretory cell type.

scholarly journals The selective recruitment of mRNA to the ER and an increase in initiation are important for glucose-stimulated proinsulin synthesis in pancreatic β-cells

2005 ◽  
Vol 391 (2) ◽  
pp. 291-300 ◽  
Author(s):  
Isabel C. Greenman ◽  
Edith Gomez ◽  
Claire E. J. Moore ◽  
Terence P. Herbert
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Regulatory Mechanism ◽  
De Novo ◽  
Secretory Protein ◽  
Secretory Proteins ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Large Pool ◽  
Proinsulin Synthesis

Glucose acutely stimulates proinsulin synthesis in pancreatic β-cells through a poorly understood post-transcriptional mechanism. In the present study, we demonstrate in pancreatic β-cells that glucose stimulates the recruitment of ribosome-associated proinsulin mRNA, located in the cytoplasm, to the ER (endoplasmic reticulum), the site of proinsulin synthesis, and that this plays an important role in glucose-stimulated proinsulin synthesis. Interestingly, glucose has greater stimulatory effect on the recruitment of proinsulin mRNA to the ER compared with other mRNAs encoding secretory proteins. This, as far as we are aware, is the first example whereby mRNAs encoding secretory proteins are selectively recruited to the ER and provides a novel regulatory mechanism for secretory protein synthesis. Contrary to previous reports, and importantly in understanding the mechanism by which glucose stimulates proinsulin synthesis, we demonstrate that there is no large pool of ‘free’ proinsulin mRNA in the cytoplasm and that glucose does not increase the rate of de novo initiation on the proinsulin mRNA. However, we show that glucose does stimulate the rate of ribosome recruitment on to ribosome-associated proinsulin mRNA. In conclusion, our results provide evidence that the selective recruitment of proinsulin mRNA to the ER, together with increases in the rate of initiation are important mediators of glucose-stimulated proinsulin synthesis in pancreatic β-cells.

scholarly journals Biosynthesis of intestinal microvillar proteins. The effect of swainsonine on post-translational processing of aminopeptidase N

1983 ◽  
Vol 216 (2) ◽  
pp. 325-331 ◽  
Author(s):  
E M Danielsen ◽  
G M Cowell ◽  
O Norén ◽  
H Sjöström ◽  
P R Dorling
Keyword(s):  
Palmitic Acid ◽  
Golgi Complex ◽  
Alkaline Hydrolysis ◽  
Considerable Increase ◽  
Aminopeptidase N ◽  
Final Destination ◽  
High Mannose ◽  
Small Intestinal ◽  
Mucosal Explants

The post-translational processing of pig small-intestinal aminopeptidase N (EC 3.4.11.2) was studied in organ-cultured mucosal explants. Exposure of the explants to swainsonine, an inhibitor of Golgi mannosidase II, resulted in the formation of a Mr-160000 polypeptide, still sensitive to endo-beta-N-acetylglucosaminidase H. Swainsonine caused only a moderate inhibition of transport of the enzyme through the Golgi complex and the subsequent expression in the microvillar membrane. This may imply that the trimming of the high-mannose core and complex glycosylation of N-linked oligosaccharides is not essential for the transport of aminopeptidase N to its final destination. A different type of processing was observed to take place in the presence of swainsonine, resulting in a considerable increase in apparent Mr (from 140000 to 160000). This processing could not be ascribed to N-linked glycosylation, since treatment of the Mr-160000 polypeptide with endo-beta-N-acetylglucosaminidase H only decreased its apparent Mr by 15000. The susceptibility of the mature Mr-166000 polypeptide, but not the Mr-140000 polypeptide, to mild alkaline hydrolysis suggests that aminopeptidase N becomes glycosylated with O-linked oligosaccharides during its passage through the Golgi complex. Aminopeptidase N was not labelled by [3H]palmitic acid, indicating that the processing of the enzyme does not include acylation.

scholarly journals Cryo–electron microscopy structures of human oligosaccharyltransferase complexes OST-A and OST-B

Science ◽  
2019 ◽  
Vol 366 (6471) ◽  
pp. 1372-1375 ◽  
Author(s):  
Ana S. Ramírez ◽  
Julia Kowal ◽  
Kaspar P. Locher
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Secretory Proteins ◽  
Catalytic Subunits ◽  
Protein Substrates ◽  
Cryo Electron Microscopy ◽  
Structural Differences ◽  
High Mannose ◽  
Equivalent Region ◽  
High Mannose Glycan

Oligosaccharyltransferase (OST) catalyzes the transfer of a high-mannose glycan onto secretory proteins in the endoplasmic reticulum. Mammals express two distinct OST complexes that act in a cotranslational (OST-A) or posttranslocational (OST-B) manner. Here, we present high-resolution cryo–electron microscopy structures of human OST-A and OST-B. Although they have similar overall architectures, structural differences in the catalytic subunits STT3A and STT3B facilitate contacts to distinct OST subunits, DC2 in OST-A and MAGT1 in OST-B. In OST-A, interactions with TMEM258 and STT3A allow ribophorin-I to form a four-helix bundle that can bind to a translating ribosome, whereas the equivalent region is disordered in OST-B. We observed an acceptor peptide and dolichylphosphate bound to STT3B, but only dolichylphosphate in STT3A, suggesting distinct affinities of the two OST complexes for protein substrates.

scholarly journals The rough endoplasmic reticulum and the Golgi apparatus visualized using specific antibodies in normal and tumoral prolactin cells in culture.

1983 ◽  
Vol 96 (5) ◽  
pp. 1197-1207 ◽  
Author(s):  
C Tougard ◽  
D Louvard ◽  
R Picart ◽  
A Tixier-Vidal
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Golgi Apparatus ◽  
Rough Endoplasmic Reticulum ◽  
Primary Cultures ◽  
Gh3 Cells ◽  
Membrane Flow ◽  
Golgi Membranes ◽  
Membrane Components ◽  
Golgi Zone

Antibodies directed against membrane components of dog pancreas rough endoplasmic reticulum (A-RER) and rat liver Golgi apparatus (A-Golgi) (Louvard, D., H. Reggio, and G. Warren, 1982, J. Cell Biol. 92:92-107) have been applied to cultured rat prolactin (PRL) cells, either normal cells in primary cultures, or clonal GH3 cells. In normal PRL cells, the A-RER stained the membranes of the perinuclear cisternae as well as those of many parallel RER cisternae. The A-Golgi stained part of the Golgi membranes. In the stacks it stained the medial saccules and, with a decreasing intensity, the saccules of the trans side, as well as, in some cells, a linear cisterna in the center of the Golgi zone. It also stained the membrane of many small vesicles as well as that of lysosomelike structures in all cells. In contrast, it never stained the secretory granule membrane, except at the level of very few segregating granules on the trans face of the Golgi zone. In GH3 cells the A-RER stained the membrane of the perinuclear cisternae, as well as that of short discontinuous flat cisternae. The A-Golgi stained the same components of the Golgi zone as in normal PRL cells. In some cells of both types the A-Golgi also stained discontinuous patches on the plasma membrane and small vesicles fusing with the plasma membrane. Immunostaining of Golgi membranes revealed modifications of membrane flow in relation to either acute stimulation of PRL release by thyroliberin or inhibition of basal secretion by monensin.

Synthesis and Turnover of Membrane Proteins in Rat Liver: An Examination of the Membrane Flow Hypothesis

1971 ◽  
Vol 26 (10) ◽  
pp. 1031-1039 ◽  
Author(s):  
Werner W. Franke ◽  
D. James Morre ◽  
Barbara Deumling ◽  
Ronald D. Cheetham ◽  
Jürgen Kartenbeck ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Membrane Proteins ◽  
Golgi Apparatus ◽  
Plasma Membranes ◽  
Degradation Kinetics ◽  
Specific Radioactivity ◽  
Membrane Flow ◽  
Rapid Turnover ◽  
Associated Proteins

The kinetics of synthesis and degradation of the protein constituents of nuclear membranes, endoplasmic reticulum membranes (rough-surfaced microsomes), Golgi apparatus membranes and plasma membranes were determined following a single administration of L- [guanido-14C] arginine by intraperitoneal injection. Membrane protein was determined as the fraction which resists sonication and sequential extrations with 1.5 M KCl, 0.1% deoxycholate and water to remove intravesicular, intracisternal (secretory), nucleo-, adsorbed and ribosome-associated proteins.The order of maximum labeling of membrane proteins was a) endoplasmic reticulum (nuclear membrane), b) Golgi apparatus, and c) plasma membrane. Rapid decreases in specific radioactivity followed maximal labeling of endoplasmic reticulum and Golgi apparatus membranes. These rapid turnover components of endoplasmic reticulum and Golgi apparatus were sufficient to account for labeling of plasma membranes via a flow mechanism.Incorporation of radioactivity into plasma membranes showed two distinct phases. The ultrastructural features underlying the biphasic pattern of incorporation into plasma membranes are discussed.Following initial incorporation and rapid turnover, membrane proteins were characterized by degradation kinetics approximating 1st order. Rates of degradation for Golgi apparatus and plasma membranes were faster than those for nuclear envelope and endoplasmic reticulum membranes.Assuming steady state conditions, an absolute synthetic rate of 7.1 mpg/min/avergage hepatocyte was calculated for membrane proteins of the plasma membrane.The results are compatible with intracellular movement and conversion of rough endoplasmic reticulum to plasma membrane via the membranes of the Golgi apparatus, i. e., membrane flow. Additionally, the kinetics indicate that membrane synthesis and transfer is restricted to specific parts of the endoplasmic reticulum and Golgi apparatus.

Golgi Apparatus Function in Membrane Flow and Differentiation: Origin of Plasma Membrane from Endoplasmic Reticulum

Biomembranes ◽  
1971 ◽  
pp. 95-104 ◽  
Author(s):  
D. James Morré ◽  
W. W. Franke ◽  
B. Deumling ◽  
S. E. Nyquist ◽  
L. Ovtracht
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Golgi Apparatus ◽  
Membrane Flow ◽  
Apparatus Function

scholarly journals Intracellular localization of fibronectin by immunoelectron microscopy.

1980 ◽  
Vol 28 (9) ◽  
pp. 953-960 ◽  
Author(s):  
S S Yamada ◽  
K M Yamada ◽  
M C Willingham
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Plasma Membrane ◽  
Golgi Apparatus ◽  
Intracellular Localization ◽  
Ultrastructural Localization ◽  
Ultrastructural Level ◽  
Protein Synthesis Inhibitors ◽  
Cultured Fibroblasts ◽  
Extracellular Glycoprotein

We have localized fibronectin, a major extracellular glycoprotein of cultured fibroblasts, in chick embryo fibroblasts at the ultrastructural level using affinity-purified antibodies to fibronectin. The use of a ferritin bridge procedure permitted quantitation of localization in various organelles. These results provide the first intracellular ultrastructural localization of fibronectin. Extracellular labeling was confined to aggregates and fibrils, with little or no labeling of the plasma membrane. The principal sites of intracellular localization were the rough endoplasmic reticulum and the Golgi apparatus. Treatment of cells with the protein synthesis inhibitors cycloheximide and pactamycin reduced fibronectin localization in the endoplasmic reticulum to 50% of normal levels. Removal of cycloheximide permitted recovery of labeling to 85% of control levels in the endoplasmic reticulum. Similar, but much reduced, changes also occurred in the Golgi apparatus.

scholarly journals Assistance for Folding of Disease-Causing Plasma Membrane Proteins

Biomolecules ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 728
Author(s):  
Karina Juarez-Navarro ◽  
Victor M. Ayala-Garcia ◽  
Estela Ruiz-Baca ◽  
Ivan Meneses-Morales ◽  
Jose Luis Rios-Banuelos ◽  
...  
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Plasma Membrane ◽  
Small Molecule ◽  
Protein Quality ◽  
Therapeutic Strategies ◽  
Protein Processing ◽  
Small Molecule Drugs ◽  
Different Types

An extensive catalog of plasma membrane (PM) protein mutations related to phenotypic diseases is associated with incorrect protein folding and/or localization. These impairments, in addition to dysfunction, frequently promote protein aggregation, which can be detrimental to cells. Here, we review PM protein processing, from protein synthesis in the endoplasmic reticulum to delivery to the PM, stressing the main repercussions of processing failures and their physiological consequences in pathologies, and we summarize the recent proposed therapeutic strategies to rescue misassembled proteins through different types of chaperones and/or small molecule drugs that safeguard protein quality control and regulate proteostasis.

scholarly journals Translational control of an intestinal microvillar enzyme

1986 ◽  
Vol 235 (2) ◽  
pp. 447-451 ◽  
Author(s):  
E M Danielsen ◽  
G M Cowell ◽  
H Sjöström ◽  
O Norén
Keyword(s):  
Translational Control ◽  
Aminopeptidase N ◽  
Total Rna ◽  
Membrane Bound ◽  
High Mannose ◽  
Small Intestinal ◽  
Adult Rate ◽  
Foetal Intestine ◽  
Translational Level

The rates of biosynthesis of adult and foetal pig small-intestinal aminopeptidase N (EC 3.4.11.2) were compared to determine at which level the expression of the microvillar enzyme is developmentally controlled. In organ-cultured explants, the rate of biosynthesis of foetal aminopeptidase N is only about 3% of the adult rate. The small amount synthesized occurs in a high-mannose-glycosylated, membrane-bound, form that is processed to the mature, complex-glycosylated, form at a markedly slower rate than that of the adult enzyme. Extracts of total RNA from adult and foetal intestine contained comparable amounts of aminopeptidase N mRNA, encoding gel-electrophoretically identical primary translation products. Together, these data indicate that the expression of aminopeptidase N is controlled at a translational level.

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