scholarly journals An alternative hypothesis of cellular transport of lysosomal enzymes in fibroblasts. Effect of inhibitors of lysosomal enzyme endocytosis on intra- and extra-cellular lysosomal enzyme activities

1978 ◽  
Vol 176 (3) ◽  
pp. 943-950 ◽  
Author(s):  
Kurt Von Figura ◽  
Ernst Weber
Keyword(s):  
Cell Surface ◽  
Lysosomal Enzyme ◽  
Lysosomal Enzymes ◽  
Alternative Hypothesis ◽  
Fold Increase ◽  
Cellular Transport ◽  
Intracellular Enzyme ◽  
Surface Receptors ◽  
Mannose 6 Phosphate ◽  
A Minor

Recapture of lysosomal enzymes secreted by fibroblasts was inhibited by growing the cells in the presence of either free or immobilized antibodies against lysosomal enzymes or in the presence of phosphorylated carbohydrates known to interact with the cell-surface receptors for lysosomal enzymes. The following results were obtained. 1. Conditions that prevent recapture of released lysosomal enzymes increase the rate of extracellular accumulation of these enzymes up to twice that of controls. 2. Growing cells for 12 days in the presence of 0.5mm-mannose 6-phosphate, which decreases β-N-acetylglucosaminidase endocytosis to less than 10% of that of controls, has no effect on the intracellular activity of this and four other lysosomal enzymes. 3. Growing cells for 4 days in the presence of 50mm-mannose 6-phosphate, which is a 1000-fold higher concentration than that required for 50% inhibition of lysosomal enzyme endocytosis, leads to a 4-fold increase in extracellular β-N-acetylglucosaminidase accumulation and a decrease in intracellular enzyme. These results give evidence that, in fibroblasts, transfer of lysosomal enzymes into lysosomes does not require secretion before a receptor-mediated recapture [Hickman & Neufeld (1972) Biochem. Biophys. Res. Commun.49, 992–999]. We propose that (a) lysosomal enzymes are present in a receptor-bound form in those vesicles that fuse with the cell membrane, (b) the major part of the lysosomal enzyme cycles via the cell surface in a receptor-bound form and (c) only a minor part of the lysosomal enzyme is released into the extracellular space during its life cycle.

scholarly journals Is movement of mannose 6-phosphate-specific receptor triggered by binding of lysosomal enzymes?

1987 ◽  
Vol 104 (6) ◽  
pp. 1735-1742 ◽  
Author(s):  
T Braulke ◽  
C Gartung ◽  
A Hasilik ◽  
K von Figura
Keyword(s):  
Cell Surface ◽  
Lysosomal Enzymes ◽  
Free Cell ◽  
Cell Surface Receptors ◽  
Receptor Ligands ◽  
Receptor Ligand ◽  
Surface Receptors ◽  
Weak Bases ◽  
Specific Receptors ◽  
Mannose 6 Phosphate

Mannose 6-phosphate-specific receptors with an apparent molecular mass of 215,000 are present in fibroblasts at the cell surface and in intracellular membranes. The cell surface receptors mediate endocytosis of exogenous lysosomal enzymes and exchange with the intracellular receptors, which function in the sorting of endogenous lysosomal enzymes. In the present study, several methods independent of receptor ligands were designed in order to examine the exchange of receptors under conditions where receptor-ligand complexes do not dissociate (weak bases and monensin) or where receptor-ligand complexes are not formed due to absence of endogenous ligands as a result of inhibition of protein synthesis. Weak bases and monensin reduce the concentration of receptors at the cell surface by 20-30% and free cell surface receptors were replaced by occupied receptors. The latter continued to be exchanged with internal ligand-occupied receptors and the rates of the exchange were similar to the control values. The exchange of receptors between the cell surface and internal membranes was also not affected when the receptor ligands were depleted from the transport compartments by treating the cells with cycloheximide for up to 10 h. We conclude from these results that movement of mannose 6-phosphate-specific receptors along the endocytosis and sorting pathways is constitutive and not triggered by binding or dissociation of ligands.

Cobalamin transport proteins and their cell-surface receptors

2003 ◽  
Vol 5 (18) ◽  
pp. 1-18 ◽  
Author(s):  
Bellur Seetharam ◽  
Raghunatha R. Yammani
Keyword(s):  
Cell Surface ◽  
Blood Cells ◽  
Plasma Membranes ◽  
Intrinsic Factor ◽  
Transport Proteins ◽  
Cell Surface Receptors ◽  
Vitamin B ◽  
Cellular Transport ◽  
Surface Receptors ◽  
Molecular Aspects

The primary function of cobalamin (Cbl; vitamin B12) is the formation of red blood cells and the maintenance of a healthy nervous system. Before cells can utilise dietary Cbl, the vitamin must undergo cellular transport using two distinct receptor-mediated events. First, dietary Cbl bound to gastric intrinsic factor (IF) is taken up from the apical pole of ileal epithelial cells via a 460 kDa receptor, cubilin, and is transported across the cell bound to another Cbl-binding protein, transcobalamin II (TC II). Second, plasma TC II–Cbl is taken up by cells that need Cbl via the TC II receptor (TC II-R), a 62 kDa protein that is expressed as a functional dimer in cellular plasma membranes. Human Cbl deficiency can develop as a result of acquired or inherited dysfunction in either of these two transmembrane transport events. This review focuses on the biochemical, cellular and molecular aspects of IF and TC II and their cell-surface receptors.

scholarly journals Specific alterations in levels of mannose 6-phosphorylated glycoproteins in different neuronal ceroid lipofuscinoses

1998 ◽  
Vol 334 (3) ◽  
pp. 547-551 ◽  
Author(s):  
David E. SLEAT ◽  
Istvan SOHAR ◽  
Premila S. PULLARKAT ◽  
Peter LOBEL ◽  
Raju K. PULLARKAT
Keyword(s):  
Lysosomal Enzyme ◽  
Neurodegenerative Disorders ◽  
Enzyme Activities ◽  
Lysosomal Enzymes ◽  
Vesicular Transport ◽  
Cell Types ◽  
Neuronal Ceroid Lipofuscinoses ◽  
Mannose 6 Phosphate ◽  
Normal Controls ◽  
Lysosomal Proteins

Mannose 6-phosphate (Man-6-P) is a carbohydrate modification that is generated on newly synthesized lysosomal proteins. This modification is specifically recognized by two Man-6-P receptors that direct the vesicular transport of the lysosomal enzymes from the Golgi to a prelysosomal compartment. The Man-6-P is rapidly removed in the lysosome of most cell types; however, in neurons the Man-6-P modification persists. In this study we have examined the spectrum of Man-6-P-containing glycoproteins in brain specimens from patients with different neuronal ceroid lipofuscinoses (NCLs), which are progressive neurodegenerative disorders with established links to defects in lysosomal catabolism. We find characteristic alterations in the Man-6-P glycoproteins in specimens from late-infantile (LINCL), juvenile (JNCL) and adult (ANCL) patients. Man-6-P glycoproteins in LINCL patients were similar to controls, with the exception that the band corresponding to CLN2, a recently identified lysosomal enzyme whose deficiency results in this disease, was absent. In an ANCL patient, two Man-6-P glycoproteins were elevated in comparison with normal controls, suggesting that this disease also results from a perturbation in lysosomal hydrolysis. In JNCL, total levels of Man-6-P glycoproteins were 7-fold those of controls. In general this was reflected by increased lysosomal enzyme activities in JNCL but three Man-6-P glycoproteins were elevated to an even greater degree. These are CLN2 and the unidentified proteins that are also highly elevated in the ANCL.

scholarly journals Endocytosis of lysosomal enzymes by non-parenchymal rat liver cells. Comparative study of lysosomal-enzyme uptake by hepatocytes and non-parenchymal liver cells

1979 ◽  
Vol 182 (2) ◽  
pp. 329-335 ◽  
Author(s):  
Kurt Ullrich ◽  
Volkmar Gieselmann ◽  
Günther Mersmann ◽  
Kurt Von Figura
Keyword(s):  
Cell Surface ◽  
Rat Liver ◽  
Lysosomal Enzymes ◽  
High Efficiency ◽  
Indirect Evidence ◽  
Liver Cells ◽  
Cell Surface Receptors ◽  
Surface Receptors ◽  
Parenchymal Liver ◽  
Rat Liver Cells

Cultured non-parenchymal rat liver cells internalize human urine α-N-acetylglucosaminidase, human skin β-N-acetylglucosaminidase and pig kidney α-mannosidase. Different heat-stabilities of endocytosed and endogenous α-mannosidase activity provided indirect evidence that the increase in intracellular activity resulted from uptake. The high efficiency and the saturation kinetics of uptake indicated that these enzymes become internalized by adsorptive endocytosis. Competition experiments with glycoproteins bearing known carbohydrates at their non-reducing terminals, with mannans, methyl glycosides and monosaccharides, established that the uptake of these three lysosomal enzymes is mediated by the binding to cell-surface receptors that recognize mannose and N-acetylglucosamine residues. The decreased uptake after treatment of these enzymes with either β-N-acetylglucosaminidase or α-mannosidase was in accordance with the results of the inhibition experiments. Removal of oligosaccharides of the high-mannose type by treatment with endoglucosaminidase H inhibited uptake almost completely, suggesting that the sugars recognized by cell-surface receptors of non-parenchymal liver cells are located in the outer core of these oligosaccharides. A comparison of the uptake of these three lysosomal enzymes by parenchymal and non-parenchymal rat liver cells indicates that infused α-N-acetylglucosaminidase is taken up preferentially by hepatocytes, whereas α-mannosidase and β-N-acetylglucosaminidase are localized predominantly in non-parenchymal rat liver cells.

Common pathways for cellular transport of steroid sulfatase, lysosomal enzymes and the mannose 6-phosphate receptor: An immunocytochemical appraisal

1987 ◽  
Vol 21 (2) ◽  
pp. 205
Author(s):  
Rob Willemsen ◽  
Marian Kroos ◽  
AndréT. Hoogeveen ◽  
JohanM. van Dongen ◽  
ArnoldJ.J. Reuser
Keyword(s):  
Lysosomal Enzymes ◽  
Cellular Transport ◽  
Steroid Sulfatase ◽  
Mannose 6 Phosphate

scholarly journals Cellular transport of lysosomal enzymes: an alternative hypothesis

1977 ◽  
Vol 164 (1) ◽  
pp. 281-282 ◽  
Author(s):  
J B Lloyd
Keyword(s):  
Lysosomal Enzymes ◽  
Alternative Explanation ◽  
Alternative Hypothesis ◽  
Cellular Transport ◽  
Membrane Recycling

Hickman & Neufeld [(1972) Biochem, Biophys. Res. Commun. 49, 992-999] have proposed that lysosomal enzymes reach the lysosomes by means of exocytosis and subsequent pinocytic reincorporation. The results leading to this conclusion are re-assessed and an alternative explanation is advanced that relates to the necessity for membrane recycling in endocytic cells.

scholarly journals Effect of monensin on intracellular transport and receptor-mediated endocytosis of lysosomal enzymes

1984 ◽  
Vol 217 (3) ◽  
pp. 649-658 ◽  
Author(s):  
R Pohlmann ◽  
S Krüger ◽  
A Hasilik ◽  
K von Figura
Keyword(s):  
Golgi Apparatus ◽  
Lysosomal Enzyme ◽  
Cathepsin D ◽  
Lysosomal Enzymes ◽  
Intracellular Transport ◽  
Human Fibroblasts ◽  
Free Medium ◽  
Intracellular Enzyme ◽  
Cultured Human Fibroblasts ◽  
Monensin A

In cultured human fibroblasts we observed that monensin, a Na+/H+-exchanging ionophore, (i) inhibits mannose 6-phosphate-sensitive endocytosis of a lysosomal enzyme, (ii) enhances secretion of the precursor of cathepsin D, while inhibiting secretion of the precursors of beta-hexosaminidase, (iii) induces secretion of mature beta-hexosaminidase and mature cathepsin D, and (iv) inhibits carbohydrate processing in and proteolytic maturation of the precursors remaining within the cells; this last effect appears to be secondary to an inhibition of the transport of the precursors. If the treated cells are transferred to a monensin-free medium, about half of the accumulated precursors are secreted, and the intracellular enzyme is converted into the mature form. Monensin blocks formation of complex oligosaccharides in lysosomal enzymes. In the presence of monensin, total phosphorylation of glycoproteins is partially inhibited, whereas the secreted glycoproteins are enriched in the phosphorylated species. The suggested inhibition by monensin of the transport within the Golgi apparatus [Tartakoff (1980) Int. Rev. Exp. Pathol. 22, 227-250] may be the cause of some of the effects observed in the present study (iv). Other effects (i, ii) are rather explained by interference by monensin with the acidification in the lysosomal and prelysosomal compartments, which appears to be necessary for the transport of endocytosed and of newly synthesized lysosomal enzymes.

scholarly journals Recognition of human urine α-N-acetylglucosaminidase by rat hepatocytes. Involvement of receptors specific for galactose, mannose 6-phosphate and mannose

1979 ◽  
Vol 180 (2) ◽  
pp. 413-419 ◽  
Author(s):  
K Ullrich ◽  
R Basner ◽  
V Gieselmann ◽  
K Von Figura
Keyword(s):  
Cell Surface ◽  
Human Urine ◽  
Rat Hepatocytes ◽  
Cell Surface Receptor ◽  
Cell Surface Receptors ◽  
Minor Role ◽  
Isolated Rat Hepatocytes ◽  
Surface Receptors ◽  
Terminal Galactose ◽  
Mannose 6 Phosphate

Adsorptive endocytosis of alpha-N-acetylglucosaminidase from human urine by isolated rat hepatocytes is inhibited by glycoproteins, polysaccharides and sugars that are known to bind to cell-surface receptors specific for either terminal galactose/N-acetylgalactosamine residues, terminal mannose residues or mannose 6-phosphate residues. Recognition of alpha-N-acetylglucosaminidase by a cell-surface receptor specific for terminal galactose/N-acetylgalactosamine residues is supported by the observations (a) that neuraminidase pretreatment of the enzyme enhances endocytosis, (b) that beta-galactosidase treatment decreases endocytosis and (c) that neuraminidase pretreatment of hepatocytes decreases alpha-N-acetylglucosaminidase endocytosis. Recognition of alpha-N-acetylglucosaminidase via receptors recognizing mannose 6-phosphate residues is lost after treatment of the enzyme with alkaline phosphatase and endoglucosaminidase H. The effect of endoglucosaminidase H supports the view that the mannose 6-phosphate residues reside in N-glycosidically linked oligosaccharide side chains of the high-mannose type. The weak inhibition of endocytosis produced by compounds known to interact with cell-surface receptors specific for mannose residues suggests that this recognition system plays only a minor role in the endocytosis of lysosomal alpha-N-acetylglucosaminidase by hepatocytes.

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