scholarly journals Chromatolysis: Do Injured Axons Regenerate Poorly when Ribonucleases Fragment or Degranulate Rough Endoplasmic Reticulum, Disaggregate Polyribosomes, Degrade Monoribosomes and Lyse RNA?

2018 ◽  
Author(s):  
Lawrence Moon
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Rough Endoplasmic Reticulum ◽  
Axon Regeneration ◽  
Axonal Injury ◽  
Rrna Synthesis ◽  
Autophagic Vacuoles ◽  
Protein Synthesis Machinery ◽  
Intrinsic Neurons ◽  
Nissl Substance

After axonal injury, chromatolysis (fragmentation of Nissl substance) occurs in both intrinsic neurons (whose processes are within the CNS) and extrinsic neurons (whose axons extend outside the CNS). Electron microscopy shows that chromatolysis involves fission of the rough endoplasmic reticulum. In intrinsic neurons (which do not regenerate axons) or in extrinsic neurons denied axon regeneration, chromatolysis is often accompanied by degranulation (loss of ribosomes from rough endoplasmic reticulum), disaggregation of polyribosomes and degradation of monoribosomes into dust-like particles. Ribosomes and rough endoplasmic reticulum may also be degraded in autophagic vacuoles by Ribophagy and Reticulophagy, respectively. In other words, chromatolysis is disruption of parts of the protein synthesis infrastructure. Whereas some neurons may show transient or no chromatolysis, severely injured neurons can remain chromatolytic and never again synthesise normal levels of protein; some may atrophy or die. What molecule(s) cause fragmentation or degranulation of rough endoplasmic reticulum, disaggregation of polyribosomes and degradation of monoribosomes? Ribonucleases can modify (and perhaps fragment) rough endoplasmic reticulum; various endoribonucleases can degrade mRNA causing polyribosomes to unchain and disperse; they can disassemble monoribosomes; Ribonuclease 5 can control rRNA synthesis and degrade tRNA; Ribonuclease T2 can degrade ribosomes, rough endoplasmic reticulum and RNA within autophagic vacuoles; and Ribonuclease IRE1α acts as a stress sensor within the endoplasmic reticulum. Regeneration might be improved after axonal injury by protecting the protein synthesis machinery from catabolism; targeting ribonucleases could be a profitable strategy.

scholarly journals Release of oligomannoside-type glycans as a marker of the degradation of newly synthesized glycoproteins

1994 ◽  
Vol 298 (1) ◽  
pp. 135-142 ◽  
Author(s):  
C Villers ◽  
R Cacan ◽  
A M Mir ◽  
O Labiau ◽  
A Verbert
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Cell Line ◽  
Rough Endoplasmic Reticulum ◽  
Major Part ◽  
Cho Cell ◽  
Glycosylation Pattern ◽  
Permeabilized Cells ◽  
Lysosomotropic Agents ◽  
Free Oligosaccharides

The N-glycosylation of proteins is accompanied by the release of soluble oligosaccharide material. Besides oligosaccharide phosphates originating from the cleavage of lipid intermediates, neutral free oligosaccharides represent the major part of this material and are heterogeneous depending on whether the reducing end has one or two N-acetylglucosamine residues. The present study focuses on the intracellular origin of neutral free oligosaccharides in a CHO cell line. Kinetic and pulse-chase experiments clearly indicate that oligosaccharides possessing a chitobiosyl unit are derived from oligosaccharide pyrophosphodolichol, whereas oligosaccharides possessing one N-acetyl-glucosamine residue are derived from newly synthesized glycoprotein. This relationship is confirmed by comparing the glycosylation pattern of lipid donors and glycoproteins with those of neutral free oligosaccharides under various incubation conditions (inhibition of protein synthesis, presence of processing inhibitors, presence or absence of glucose). Degradation of newly synthesized glycoprotein and formation of neutral oligosaccharides with one N-acetylglucosamine residue are inhibited at 16 degrees C but not affected by lysosomotropic agents such as leupeptin or NH4Cl. Together with the fact that the degradation of newly synthesized glycoproteins and the subsequent release of the glycan are recovered in permeabilized cells, these results suggest that this phenomenon occurs in the rough endoplasmic reticulum or in a closely related compartment.

scholarly journals LYSOSOMES AND GERL IN NORMAL AND CHROMATOLYTIC NEURONS OF THE RAT GANGLION NODOSUM

1967 ◽  
Vol 33 (2) ◽  
pp. 419-435 ◽  
Author(s):  
Eric Holtzman ◽  
Alex B. Novikoff ◽  
Humberto Villaverde
Keyword(s):  
Endoplasmic Reticulum ◽  
Golgi Apparatus ◽  
Smooth Endoplasmic Reticulum ◽  
Cell Periphery ◽  
Electron Microscopic ◽  
Ganglion Nodosum ◽  
Autophagic Vacuoles ◽  
Inosine Diphosphatase ◽  
Nissl Substance ◽  
Membranous Material

The rat ganglion nodosum was used to study chromatolysis following axon section. After fixation by aldehyde perfusion, frozen sections were incubated for enzyme activities used as markers for cytoplasmic organelles as follows: acid phosphatase for lysosomes and GERL (a Golgi-related region of smooth endoplasmic reticulum from which lysosomes appear to develop) (31–33); inosine diphosphatase for endoplasmic reticulum and Golgi apparatus; thiamine pyrophosphatase for Golgi apparatus; acetycholinesterase for Nissl substance (endoplasmic reticulum); NADH-tetra-Nitro BT reductase for mitochondria. All but the mitochondrial enzyme were studied by electron microscopy as well as light microscopy. In chromatolytic perikarya there occur disruption of the rough endoplasmic reticulum in the center of the cell and segregation of the remainder to the cell periphery. Golgi apparatus, GERL, mitochondria and lysosomes accumulate in the central region of the cell. GERL is prominent in both normal and operated perikarya. Electron microscopic images suggest that its smooth endoplasmic reticulum produces a variety of lysosomes in several ways: (a) coated vesicles that separate from the reticulum; (b) dense bodies that arise from focal areas dilated with granular or membranous material; (c) "multivesicular bodies" in which vesicles and other material are sequestered; (d) autophagic vacuoles containing endoplasmic reticulum and ribosomes, presumably derived from the Nissl material, and mitochondria. The number of autophagic vacuoles increases following operation.

scholarly journals Binding of rat liver and hepatoma polyribosomes to stripped rough endoplasmic reticulum in vitro. Biological or an artifact?

1972 ◽  
Vol 130 (1) ◽  
pp. 19-25 ◽  
Author(s):  
A. A. Hochberg ◽  
F. W. Stratman ◽  
Rainer N. Zahlten ◽  
H. P. Morris ◽  
H. A. Lardy
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Rat Liver ◽  
Rough Endoplasmic Reticulum ◽  
Trichloroacetic Acid ◽  
Intact Cell ◽  
Biological Significance ◽  
Thiol Groups ◽  
Inhibition Of Protein Synthesis

Exposed thiol groups do not appear to be related to the binding of 32P-labelled polyribosomes to stripped rough endoplasmic reticulum in vitro. Treating stripped rough endoplasmic reticulum with GSSG did not diminish binding of polyribosomes, suggesting that binding in vitro has no correlation with the inhibition of protein synthesis in vitro reported by Kosower et al. (1971). Thiol reagents, which are known to dissociate ribosomes, did not significantly decrease binding of 32P-labelled polyribosomes to stripped rough endoplasmic reticulum. Denaturing the protein of 32P-labelled polyribosomes or stripped rough endoplasmic reticulum of liver or hepatoma with heat, trichloroacetic acid, or HClO4 did not alter the binding in vitro. Therefore, the practice of measuring the binding of 32P-labelled polyribosomes to stripped rough endoplasmic reticulum in vitro (Shires et al., 1971b) is an unsuitable indicator of biological significance in the intact cell.

scholarly journals ELECTRON MICROSCOPIC RADIOAUTOGRAPHIC DETECTION OF SITES OF PROTEIN SYNTHESIS AND MIGRATION IN LIVER

1969 ◽  
Vol 43 (2) ◽  
pp. 237-249 ◽  
Author(s):  
Charles A. Ashley ◽  
Theodore Peters
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Rough Endoplasmic Reticulum ◽  
Plasma Proteins ◽  
Liver Slice ◽  
Cell Periphery ◽  
Electron Microscopic ◽  
Golgi Bodies ◽  
And Migration ◽  
Electron Microscopic Radioautography

The sites of synthesis of proteins and their subsequent migration in rat liver have been studied during a 75 min period after labeling of liver-slice proteins by exposure to leucine-H3 for 2 min. Incorporation of the label into protein began after 1 min and was maximal by 4 min. Electron microscopic radioautography showed that synthesis of proteins in hepatocytes occurs mainly on ribosomes, particularly those in rough endoplasmic reticulum and, to some extent, in nuclei and mitochondria. Most of the newly formed proteins leave the endoplasmic reticulum in the course of 40 min, and concurrently labeled proteins appear in Golgi bodies, smooth membranes, microbodies, and lysosomes. A likely pathway for the secretion of some or all plasma proteins is from typical rough endoplasmic reticulum to a zone of reticulum which is partially coated with ribosomes, to the Golgi apparatus, and thence to the cell periphery. The formation of protein by reticuloendothelial cells was measured and found to be about 5% of the total protein formed by the liver.

scholarly journals Dengue Virus Selectively Annexes Endoplasmic Reticulum-Associated Translation Machinery as a Strategy for Co-opting Host Cell Protein Synthesis

2018 ◽  
Vol 92 (7) ◽  
Author(s):  
David W. Reid ◽  
Rafael K. Campos ◽  
Jessica R. Child ◽  
Tianli Zheng ◽  
Kitti Wing Ki Chan ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Life Cycle ◽  
Stress Response ◽  
Dengue Virus ◽  
Host Cell ◽  
Denv Infection ◽  
Cell Protein ◽  
Host Cell Protein ◽  
Protein Synthesis Machinery

ABSTRACTA primary question in dengue virus (DENV) biology is the molecular strategy for recruitment of host cell protein synthesis machinery. Here, we combined cell fractionation, ribosome profiling, and transcriptome sequencing (RNA-seq) to investigate the subcellular organization of viral genome translation and replication as well as host cell translation and its response to DENV infection. We report that throughout the viral life cycle, DENV plus- and minus-strand RNAs were highly partitioned to the endoplasmic reticulum (ER), identifying the ER as the primary site of DENV translation. DENV infection was accompanied by an ER compartment-specific remodeling of translation, where ER translation capacity was subverted from host transcripts to DENV plus-strand RNA, particularly at late stages of infection. Remarkably, translation levels and patterns in the cytosol compartment were only modestly affected throughout the experimental time course of infection. Comparisons of ribosome footprinting densities of the DENV plus-strand RNA and host mRNAs indicated that DENV plus-strand RNA was only sparsely loaded with ribosomes. Combined, these observations suggest a mechanism where ER-localized translation and translational control mechanisms, likelycisencoded, are used to repurpose the ER for DENV virion production. Consistent with this view, we found ER-linked cellular stress response pathways commonly associated with viral infection, namely, the interferon response and unfolded protein response, to be only modestly activated during DENV infection. These data support a model where DENV reprograms the ER protein synthesis and processing environment to promote viral survival and replication while minimizing the activation of antiviral and proteostatic stress response pathways.IMPORTANCEDENV, a prominent human health threat with no broadly effective or specific treatment, depends on host cell translation machinery for viral replication, immune evasion, and virion biogenesis. The molecular mechanism by which DENV commandeers the host cell protein synthesis machinery and the subcellular organization of DENV replication and viral protein synthesis is poorly understood. Here, we report that DENV has an almost exclusively ER-localized life cycle, with viral replication and translation largely restricted to the ER. Surprisingly, DENV infection largely affects only ER-associated translation, with relatively modest effects on host cell translation in the cytosol. DENV RNA translation is very inefficient, likely representing a strategy to minimize disruption of ER proteostasis. Overall these findings demonstrate that DENV has evolved an ER-compartmentalized life cycle; thus, targeting the molecular signatures and regulation of the DENV-ER interaction landscape may reveal strategies for therapeutic intervention.

MORPHOLOGICAL ASPECTS OF PROTEIN SYNTHESIS

1973 ◽  
Vol 74 (Suppl) ◽  
pp. S13-S32
Author(s):  
Bernard Droz ◽  
Monique Pisam ◽  
Monique Chrétien
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Rough Endoplasmic Reticulum ◽  
Secretory Granules ◽  
Great Majority ◽  
Cell Organelles ◽  
Differentiated Cells ◽  
Morphological Aspects ◽  
Cellular Machinery ◽  
Secretory Products

ABSTRACT Morphological aspects of protein synthesis have been mainly investigated by means of high resolution radioautography. Most of the cellular proteins are synthesized in the rough endoplasmic reticulum and on free cytoplasmic polysomes. Only few structural proteins (sedentary protein) remain in the vicinity of their sites of synthesis. The great majority of the newlysynthesized proteins move away (migratory protein). One portion of the migratory proteins is redistributed to various cell organelles and is referred to as "non exportable" protein. The migration of polypeptide chains from cytoplasmic polysomes ensures the renewal of protein in mitochondria, nucleus, and specialized membranes, in spite of the capacity of these organelles to incorporate slightly labelled amino acids. Plasma membrane precursors undergo a series of intracellular translocations and molecular complexification by adding carbohydrate groups before they reach the cell surface. Another portion of the migratory proteins, which includes secretory products, is referred to as "exportable" proteins. These exportable proteins are conveyed from the rough endoplasmic reticulum to the Golgi apparatus, then either stored and condensed in secretory granules or directly released by exocytosis. In some differentiated cells, the development of the cellular machinery for the synthesis of protein is triggered and maintained by the level of steroid hormones which controls both the quality and the quantity of secreted proteins.

scholarly journals Cytosolic deglycosylation process of newly synthesized glycoproteins generates oligomannosides possessing one GlcNAc residue at the reducing end

1998 ◽  
Vol 335 (2) ◽  
pp. 389-396 ◽  
Author(s):  
Sandrine DUVET ◽  
Odette LABIAU ◽  
Anne-Marie MIR ◽  
Daniel KMIÉCIK ◽  
Sharon S. KRAG ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Rough Endoplasmic Reticulum ◽  
Chinese Hamster Ovary Cells ◽  
Chinese Hamster ◽  
Ovary Cells ◽  
Glcnac Residue ◽  
Chase Period ◽  
Mechanism Of Degradation ◽  
Inhibitor Of Protein Synthesis

Recent studies on the mechanism of degradation of newly synthesized glycoproteins suggest the involvement of a retrotranslocation of the glycoprotein from the lumen of the rough endoplasmic reticulum into the cytosol, where a deglycosylation process takes place. In the studies reported here, we used a glycosylation mutant of Chinese hamster ovary cells that does not synthesize mannosylphosphoryldolichol and has an increased level of soluble oligomannosides originating from glycoprotein degradation. In the presence of anisomycin, an inhibitor of protein synthesis, we observed an accumulation of glucosylated oligosaccharide-lipid donors (Glc3Man5GlcNAc2-PP-Dol), which are the precursors of the soluble neutral oligosaccharide material. Inhibition of rough endoplasmic reticulum glucosidase(s) by castanospermine led to the formation of Glc3Man5GlcNAc2(OSGn2) (in which OSGn2 is an oligomannoside possessing two GlcNAc residues at its reducing end), which was then retained in the lumen of intracellular vesicles. Thus they were protected during an 8 h chase period from the action of cytosolic chitobiase, which is responsible for the conversion of OSGn2 to oligomannosides possessing one GlcNAc residue at the reducing end (OSGn1). In contrast, when protein synthesis was maintained in the presence of castanospermine, glucosylated oligomannosides (Glc1–3Man5GlcNAc1) were recovered in cytosol. Except for monoglucosylated Man5 species, which are potential substrates for luminal calnexin and calreticulin, the pattern of oligomannosides was similar to that observed on glycoproteins. The occurrence in the cytosol of glucosylated species with one GlcNAc residue at the reducing end implies that the deglycosylation process that generates glucosylated OSGn1 from glycoproteins occurs in the cytosol.

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