scholarly journals Cytosolic Proteins Regulate α-Synuclein Dissociation from Presynaptic Membranes

2006 ◽  
Vol 281 (43) ◽  
pp. 32148-32155 ◽  
Author(s):  
Sabine Wislet-Gendebien ◽  
Cheryl D'Souza ◽  
Toshitaka Kawarai ◽  
Peter St George-Hyslop ◽  
David Westaway ◽  
...  
Keyword(s):  
Lewy Bodies ◽  
Physiological Role ◽  
Normal Function ◽  
Vesicular Trafficking ◽  
Metabolic Energy ◽  
Cytosolic Proteins ◽  
Lewy Body Pathology ◽  
Cellular Factors ◽  
Membrane Bound ◽  
Biochemical Mechanisms

Intracellular accumulation of insoluble α-synuclein in Lewy bodies is a key neuropathological trait of Parkinson disease (PD). Neither the normal function of α-synuclein nor the biochemical mechanisms that cause its deposition are understood, although both are likely influenced by the interaction of α-synuclein with vesicular membranes, either for a physiological role in vesicular trafficking or as a pathological seeding mechanism that exacerbates the propensity of α-synuclein to self-assemble into fibrils. In addition to the α-helical form that is peripherally-attached to vesicles, a substantial portion of α-synuclein is freely diffusible in the cytoplasm. The mechanisms controlling α-synuclein exchange between these compartments are unknown and the possibility that chronic dysregulation of membrane-bound and soluble α-synuclein pools may contribute to Lewy body pathology led us to search for cellular factors that can regulate α-synuclein membrane interactions. Here we reveal that dissociation of membrane-bound α-synuclein is dependent on brain-specific cytosolic proteins and insensitive to calcium or metabolic energy. Two PD-linked mutations (A30P and A53T) significantly increase the cytosol-dependent α-synuclein off-rate but have no effect on cytosol-independent dissociation. These results reveal a novel mechanism by which cytosolic brain proteins modulate α-synuclein interactions with intracellular membranes. Importantly, our finding that α-synuclein dissociation is up-regulated by both familial PD mutations implicates cytosolic cofactors in disease pathogenesis and as molecular targets to influence α-synuclein aggregation.

scholarly journals Aberrant Regulation of Hematopoiesis by T Cells in BAZF-Deficient Mice

2007 ◽  
Vol 27 (15) ◽  
pp. 5275-5285 ◽  
Author(s):  
Hal E. Broxmeyer ◽  
Sarita Sehra ◽  
Scott Cooper ◽  
Lisa M. Toney ◽  
Saritha Kusam ◽  
...  
Keyword(s):  
T Cells ◽  
Cd8 T Cells ◽  
Physiological Role ◽  
Normal Function ◽  
Wild Type ◽  
Indirect Pathway ◽  
Hematopoietic Progenitor ◽  
Macrophage Colony Stimulating Factor ◽  
Macrophage Colony ◽  
Deficient Mice

ABSTRACTThe BAZF (BCL-6b) protein is highly similar to the BCL-6 transcriptional repressor. While BCL-6 has been characterized extensively, relatively little is known about the normal function of BAZF. In order to understand the physiological role of BAZF, we created BAZF-deficient mice. Unlike BCL-6-deficient mice, BAZF-deficient mice are healthy and normal in size. However, BAZF-deficient mice have a hematopoietic progenitor phenotype that is almost identical to that of BCL-6-deficient mice. Compared to wild-type mice, both BAZF-deficient and BCL-6-deficient mice have greatly reduced numbers of cycling hematopoietic progenitor cells (HPC) in the BM and greatly increased numbers of cycling HPC in the spleen. In contrast to HPC from wild-type mice, HPC from BAZF-deficient and BCL-6-deficient mice are resistant to chemokine-induced myelosuppression and do not show a synergistic growth response to granulocyte-macrophage colony-stimulating factor plus stem cell factor. Depletion of CD8 T cells in BAZF-deficient mice reverses several of the hematopoietic defects in these mice. Since both BAZF- and BCL-6-deficient mice have defects in CD8 T-cell differentiation, we hypothesize that both BCL-6 and BAZF regulate HPC homeostasis by an indirect pathway involving CD8 T cells.

scholarly journals NAD(P)H quinone oxidoreductase (NQO1): an enzyme which needs just enough mobility, in just the right places

2019 ◽  
Vol 39 (1) ◽  
Author(s):  
Angel L. Pey ◽  
Clare F. Megarity ◽  
David J. Timson
Keyword(s):  
Active Sites ◽  
Physiological Role ◽  
Polymorphic Form ◽  
Normal Function ◽  
Enzyme Mechanism ◽  
Quinone Oxidoreductase ◽  
Lower Stability ◽  
Increased Risk ◽  
Wide Range ◽  
The Right

AbstractNAD(P)H quinone oxidoreductase 1 (NQO1) catalyses the two electron reduction of quinones and a wide range of other organic compounds. Its physiological role is believed to be partly the reduction of free radical load in cells and the detoxification of xenobiotics. It also has non-enzymatic functions stabilising a number of cellular regulators including p53. Functionally, NQO1 is a homodimer with two active sites formed from residues from both polypeptide chains. Catalysis proceeds via a substituted enzyme mechanism involving a tightly bound FAD cofactor. Dicoumarol and some structurally related compounds act as competitive inhibitors of NQO1. There is some evidence for negative cooperativity in quinine oxidoreductases which is most likely to be mediated at least in part by alterations to the mobility of the protein. Human NQO1 is implicated in cancer. It is often over-expressed in cancer cells and as such is considered as a possible drug target. Interestingly, a common polymorphic form of human NQO1, p.P187S, is associated with an increased risk of several forms of cancer. This variant has much lower activity than the wild-type, primarily due to its substantially reduced affinity for FAD which results from lower stability. This lower stability results from inappropriate mobility of key parts of the protein. Thus, NQO1 relies on correct mobility for normal function, but inappropriate mobility results in dysfunction and may cause disease.

Role of an endoplasmic reticulum Ca2+-independent phospholipase A2 in oxidant-induced renal cell death

2002 ◽  
Vol 283 (3) ◽  
pp. F492-F498 ◽  
Author(s):  
Brian S. Cummings ◽  
Jane McHowat ◽  
Rick G. Schnellmann
Keyword(s):  
Lipid Peroxidation ◽  
Endoplasmic Reticulum ◽  
Subcellular Localization ◽  
Mammalian Cells ◽  
Cumene Hydroperoxide ◽  
Physiological Role ◽  
Antimycin A ◽  
Bacterial Cells ◽  
Tert Butylhydroperoxide ◽  
Membrane Bound

Phospholipase A2(PLA2) hydrolyzes the sn-2 ester bond in phospholipids, releasing a fatty acid and a lysophospholipid. Recently, a novel 85-kDa membrane-bound-Ca2+-independent PLA2 (iPLA2) was identified in insect and bacterial cells transfected with candidate PLA2 sequences. However, few data exist demonstrating a membrane-bound-iPLA2 in mammalian cells, its subcellular localization, or its physiological role. Herein, we demonstrate the expression of an 85-kDa endoplasmic reticulum (ER)-Ca2+-iPLA2 (ER-iPLA2) in rabbit renal proximal tubule cells (RPTC) that is plasmalogen selective and is inhibited by the specific Ca2+-iPLA2inhibitor bromoenol lactone (BEL). RPTC exposed to tert-butylhydroperoxide for 24 h exhibited 20% oncosis compared with 2% in controls. Inhibition of ER-iPLA2 with BEL before tert-butylhydroperoxide exposure resulted in 50% oncosis. To determine whether this effect was common to oxidants, we tested the ability of BEL to potentiate oncosis induced by cumene hydroperoxide, menadione, duraquinone, cisplatin, and the nonoxidant antimycin A. All oxidants tested produced oncosis after 24 h, and prior inhibition of ER-iPLA2 potentiated oncosis at least twofold. In contrast, inhibition of ER-iPLA2 did not alter antimycin A-induced oncosis. Lipid peroxidation increased from 1.4- to 5.2-fold in RPTC treated with BEL before oxidant exposure, whereas no change was seen in antimycin A-treated RPTC. These results are the first to demonstrate the expression and subcellular localization of an ER-iPLA2. These results also suggest that ER-iPLA2 functions to protect against oxidant-induced lipid peroxidation and oncosis.

scholarly journals Endogenous alpha-synuclein monomers, oligomers and resulting pathology: let’s talk about the lipids in the room

2019 ◽  
Vol 5 (1) ◽  
Author(s):  
Bryan A. Killinger ◽  
Ronald Melki ◽  
Patrik Brundin ◽  
Jeffrey H. Kordower
Keyword(s):  
Lewy Bodies ◽  
Alpha Synuclein ◽  
Biological Origin ◽  
Lewy Pathology ◽  
Molecular Weights ◽  
Intrinsically Disordered ◽  
Bona Fide ◽  
Membrane Bound ◽  
Soluble Species ◽  
Alpha Synuclein Aggregation

Abstract Alpha-synuclein is an intrinsically disordered, highly dynamic protein that pathogenically aggregates into inclusion structures called Lewy bodies, in several neurogenerative diseases termed synucleinopathies. Despite its importance for understanding disease, the oligomerization status of alpha-synuclein in healthy cells remains unclear. Alpha-synuclein may exist predominantly as either a monomer or a variety of oligomers of different molecular weights. There is solid evidence to support both theories. Detection of apparent endogenous oligomers are intimately dependent on vesicle and lipid interactions. Here we consider the possibility that apparent endogenous alpha-synuclein oligomers are in fact conformations of membrane-bound alpha-synuclein and not a bona fide stable soluble species. This perspective posits that the formation of any alpha-synuclein oligomers within the cell is likely toxic and interconversion between monomer and oligomer is tightly controlled. This differs from the hypothesis that there is a continuum of endogenous non-toxic oligomers and they convert, through unclear mechanisms, to toxic oligomers. The distinction is important, because it clarifies the biological origin of synucleinopathy. We suggest that a monomer-only, lipid-centric view of endogenous alpha-synuclein aggregation can explain how alpha-synuclein pathology is triggered, and that the interactions between alpha-synuclein and lipids can represent a target for therapeutic intervention. This discussion is well-timed due to recent studies that show lipids are a significant component of Lewy pathology.

Prions: Protein Aggregation and Infectious Diseases

2009 ◽  
Vol 89 (4) ◽  
pp. 1105-1152 ◽  
Author(s):  
Adriano Aguzzi ◽  
Anna Maria Calella
Keyword(s):  
Protein Aggregation ◽  
Prion Diseases ◽  
Physiological Role ◽  
Infectious Agent ◽  
Normal Function ◽  
Cellular Prion Protein ◽  
Transmissible Spongiform Encephalopathies ◽  
Pathological Features ◽  
Spongiform Encephalopathies

Transmissible spongiform encephalopathies (TSEs) are inevitably lethal neurodegenerative diseases that affect humans and a large variety of animals. The infectious agent responsible for TSEs is the prion, an abnormally folded and aggregated protein that propagates itself by imposing its conformation onto the cellular prion protein (PrPC) of the host. PrPCis necessary for prion replication and for prion-induced neurodegeneration, yet the proximal causes of neuronal injury and death are still poorly understood. Prion toxicity may arise from the interference with the normal function of PrPC, and therefore, understanding the physiological role of PrPCmay help to clarify the mechanism underlying prion diseases. Here we discuss the evolution of the prion concept and how prion-like mechanisms may apply to other protein aggregation diseases. We describe the clinical and the pathological features of the prion diseases in human and animals, the events occurring during neuroinvasion, and the possible scenarios underlying brain damage. Finally, we discuss potential antiprion therapies and current developments in the realm of prion diagnostics.

scholarly journals Functional Analyses of a Putative, Membrane-Bound, Peroxisomal Protein Import Mechanism from the Apicomplexan Protozoan Toxoplasma gondii

Genes ◽  
2018 ◽  
Vol 9 (9) ◽  
pp. 434
Author(s):  
Alison Mbekeani ◽  
Will Stanley ◽  
Vishal Kalel ◽  
Noa Dahan ◽  
Einat Zalckvar ◽  
...  
Keyword(s):  
Toxoplasma Gondii ◽  
Protein Import ◽  
Fluorescent Protein ◽  
Metabolic Energy ◽  
Peroxisomal Protein ◽  
Genes Encoding ◽  
Peroxisomal Targeting ◽  
Membrane Bound ◽  
Green Fluorescent

Peroxisomes are central to eukaryotic metabolism, including the oxidation of fatty acids—which subsequently provide an important source of metabolic energy—and in the biosynthesis of cholesterol and plasmalogens. However, the presence and nature of peroxisomes in the parasitic apicomplexan protozoa remains controversial. A survey of the available genomes revealed that genes encoding peroxisome biogenesis factors, so-called peroxins (Pex), are only present in a subset of these parasites, the coccidia. The basic principle of peroxisomal protein import is evolutionarily conserved, proteins harbouring a peroxisomal-targeting signal 1 (PTS1) interact in the cytosol with the shuttling receptor Pex5 and are then imported into the peroxisome via the membrane-bound protein complex formed by Pex13 and Pex14. Surprisingly, whilst Pex5 is clearly identifiable, Pex13 and, perhaps, Pex14 are apparently absent from the coccidian genomes. To investigate the functionality of the PTS1 import mechanism in these parasites, expression of Pex5 from the model coccidian Toxoplasma gondii was shown to rescue the import defect of Pex5-deleted Saccharomyces cerevisiae. In support of these data, green fluorescent protein (GFP) bearing the enhanced (e)PTS1 known to efficiently localise to peroxisomes in yeast, localised to peroxisome-like bodies when expressed in Toxoplasma. Furthermore, the PTS1-binding domain of Pex5 and a PTS1 ligand from the putatively peroxisome-localised Toxoplasma sterol carrier protein (SCP2) were shown to interact in vitro. Taken together, these data demonstrate that the Pex5–PTS1 interaction is functional in the coccidia and indicate that a nonconventional peroxisomal import mechanism may operate in the absence of Pex13 and Pex14.

scholarly journals Podocyte Lysosome Dysfunction in Chronic Glomerular Diseases

2020 ◽  
Vol 21 (5) ◽  
pp. 1559 ◽  
Author(s):  
Guangbi Li ◽  
Jason Kidd ◽  
Pin-Lan Li
Keyword(s):  
Structural Integrity ◽  
Hydrolytic Enzymes ◽  
Therapeutic Strategies ◽  
Normal Function ◽  
Current Evidence ◽  
Autophagic Flux ◽  
Glomerular Diseases ◽  
Podocyte Injury ◽  
Membrane Bound

Podocytes are visceral epithelial cells covering the outer surface of glomerular capillaries in the kidney. Blood is filtered through the slit diaphragm of podocytes to form urine. The functional and structural integrity of podocytes is essential for the normal function of the kidney. As a membrane-bound organelle, lysosomes are responsible for the degradation of molecules via hydrolytic enzymes. In addition to its degradative properties, recent studies have revealed that lysosomes may serve as a platform mediating cellular signaling in different types of cells. In the last decade, increasing evidence has revealed that the normal function of the lysosome is important for the maintenance of podocyte homeostasis. Podocytes have no ability to proliferate under most pathological conditions; therefore, lysosome-dependent autophagic flux is critical for podocyte survival. In addition, new insights into the pathogenic role of lysosome and associated signaling in podocyte injury and chronic kidney disease have recently emerged. Targeting lysosomal functions or signaling pathways are considered potential therapeutic strategies for some chronic glomerular diseases. This review briefly summarizes current evidence demonstrating the regulation of lysosomal function and signaling mechanisms as well as the canonical and noncanonical roles of podocyte lysosome dysfunction in the development of chronic glomerular diseases and associated therapeutic strategies.

scholarly journals Identification of a rabbit liver cytosolic binding protein for human growth hormone

1984 ◽  
Vol 221 (3) ◽  
pp. 617-622 ◽  
Author(s):  
S I Ymer ◽  
J L Stevenson ◽  
A C Herington
Keyword(s):  
Growth Hormone ◽  
Binding Affinity ◽  
Binding Protein ◽  
Physiological Role ◽  
Rabbit Liver ◽  
Precipitation Method ◽  
Affinity Column ◽  
Separation Procedure ◽  
Binding Characteristics ◽  
Membrane Bound

A specific growth hormone (GH) binding protein of Mr approx. 100000 has been demonstrated in the cytosolic fraction (200000g supernatant) of pregnant-rabbit liver by gel filtration techniques. This binding species was detectable by a standard charcoal separation procedure but not by the widely used poly(ethylene glycol) precipitation method. The GH binding protein had similar binding characteristics to those of classical membrane-bound GH receptors. The kinetics of association and dissociation, binding affinity (2.56×10(9)1/mol) and hormonal specificity have been established. There appears to be equal or greater amounts of GH binding protein in the cytosol than in the membrane fraction. The presence of the GH binding protein in rabbit liver cytosol was substantiated by its selective purification on a GH-Affigel 15 affinity column. This technique has resulted in a 200-300-fold purification with no substantial change in binding affinity. The ability of a concanavalin A-Sepharose affinity column to also bind the cytosolic binding protein indicates that, like the membrane-bound GH receptor, it is a glycoprotein. This is the first report of a cytosolic binding protein for GH and raises important questions regarding its potential physiological role in the mechanism of action of GH.

scholarly journals The differential degradation of two cytosolic proteins as a tool to monitor autophagy in hepatocytes by immunocytochemistry.

1993 ◽  
Vol 120 (4) ◽  
pp. 897-908 ◽  
Author(s):  
C Rabouille ◽  
G J Strous ◽  
J D Crapo ◽  
H J Geuze ◽  
J W Slot
Keyword(s):  
Cathepsin D ◽  
Rat Hepatocytes ◽  
Autophagic Vacuole ◽  
Male Rat ◽  
Major Pathway ◽  
Cytosolic Proteins ◽  
Autophagic Vacuoles ◽  
Subsequent Elimination ◽  
Membrane Bound

The major pathway for cytosolic constituents to enter lysosomes is by autophagy. We used two cytosolic proteins, CuZn superoxide dismutase (SOD) and carbonic anhydrase III (CAIII), as autophagic markers in male rat hepatocytes. We took advantage of the differential presence of the two proteins in autophagic vacuoles because of the high resistance of SOD to lysosomal degradation as compared with CAIII. This allows us to determine the sequence of autophagic vacuole formation. We have double immunogold-labeled SOD and CAIII in cryosections of fasted rat liver and calculated the ratios of SOD over CAIII labeling densities (SOD/CAIII) in autophagic vacuoles (AV), as compared with the cytoplasm. Different classes of AV were defined according to their SOD/CAIII, their morphology, and their additional immunolabeling for the lysosomal markers lgp120 and cathepsin D. Of all AV, 15% exhibited a cytosol-like SOD/CAIII, indicating that degradation had not yet begun. Most of these initial AV (AVi) showed two enveloping membranes. The formation of AVi was prevented by 3-methyladenine, a potent inhibitor of autophagy. Of all AV, 85% showed a SOD/CAIII that exceeded the cytosolic ratio. These single membrane-bound vacuoles were called degradative AV (AVd). Labeling for lysosomal markers allowed the characterization of AV that shared features with both AVi and AVd. These AVi/d had a cytosol-like SOD/CAIII and a double membrane, but showed some labeling for lysosomal markers. Probably these AVi/d represent the recipient compartment for lysosomal components. AVd were positive for cathepsin D and lgp120. We discerned two AVd subclasses. Early AVd with cytosol-like SOD labeling density while CAIII labeling density was consistently lower than in the cytosol. Their size was similar to AVi and AVi/d. Late AVd contained higher SOD concentrations and were mostly larger. Our findings suggest that AV acquire lysosomal constituents by fusion with small nonautophagic structures and that after subsequent elimination of the inner membrane of AVi, degradation starts resulting in the formation of early AVd and late AVd.

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