Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P20645 (mannose-6-phosphate receptor)
 320 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The intracellular and extracellular distribution of acid hydrolases in cultured retinal pigmented epithelium (RPE) was studied. Incubation of cultured RPE in medium containing 20 mM mannose-6-phosphate resulted in the extracellular release of approximately 15% of the cell-associated activity of several acid hydrolases. This represents an approximate 120% increase over control levels after 24 hr of culture with 20 mM mannose-6-phosphate. The extracellular release is not due to cell lysis, since no release of the cytoplasmic marker lactate dehydrogenase was seen. n-Acetyl-beta-glucosaminidase, alpha-mannosidase, and beta-glucuronidase were released into the extracellular medium, while acid phosphatase and beta-glucosidase were not. The release was specific for mannose-6-phosphate, and was dose-dependent. Inhibition of protein synthesis by treatment of RPE cells with cycloheximide (100 micrograms/ml) inhibited extracellular acid hydrolase release. RPE cells exhibited n-Acetyl-beta-glucosaminidase bound to the cell surface via a mannose-6-phosphate sensitive receptor. These results demonstrate a specific extracellular release of acid hydrolases by RPE and the presence of at least one acid hydrolase on the RPE cell surface. This may represent a mechanism for control of cell surface and extracellular levels of these enzymes in RPE via the mannose-6-phosphate receptor.
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PMID:Extracellular release of acid hydrolases from cultured retinal pigmented epithelium. 310 Apr 74

Highly purified cultures of rat astrocytes and oligodendrocytes were examined for their ability to bind and internalize lysosomal enzymes. Astrocytes displayed a saturable uptake of beta-glucosidase and beta-galactosidase. The uptake was specifically inhibited by mannose-6-phosphate but not by several other sugars or sugar phosphates, indicating that the process was mediated by mannose-6-phosphate receptors. When cells were allowed to take up 125I-beta-glucosidase for 1 hr at 37 degrees C and subcellular organelles were isolated, the enzyme was shown to comigrate with a lysosomal organelle marker enzyme, suggesting that the enzyme was targeted to lysosomes. Astrocyte receptors were probed directly by binding of 125I labeled beta-glucosidase to astrocyte membranes at 4 degrees C. Binding was saturable and competitively inhibited by mannose-6-phosphate. In contrast to the astrocytes, cultured oligodendrocytes showed no specific binding or uptake of the lysosomal enzymes. Immunocytochemical staining of mixed glial cultures supported the biochemical data; only the astrocytes stained positive with anti-mannose-6-phosphate receptor antibodies.
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PMID:Binding and internalization of lysosomal enzymes by primary cultures of rat glia. 316 Aug 66

We have studied estrogen-regulated proteins in an attempt to understand the mechanism by which estrogens stimulate cell proliferation and mammary carcinogenesis. In estrogen receptor positive human breast cancer cell lines (MCF7, ZR75-1) estrogens specifically increase the production into the culture medium of a 52,000 daltons (52K) glycoprotein. Several high affinity monoclonal antibodies to the partially purified secretory 52K protein have allowed to purify to homogeneity this protein and its cellular processed products. The 52K protein has been identified as the secreted precursor of a cathepsin-D like protease bearing mannose-6-phosphate signals and routed to lysosomes via mannose-6-phosphate receptor. The protease is mitogenic in vitro on estrogen deprived MCF7 cells and is able to degrade basement membrane and proteoglycans following its activation. The cellular related proteins, as detected by immunohistochemistry and immunoassay are more concentrated in proliferative mammary ducts than in resting ducts and their concentration in breast cancer cytosol appears to be more correlated with lymph nodes invasion and disease free survival (with S. Thorpe, Copenhagen) than with the estrogen receptor (RE) level. The protein is also produced constitutively by RE-negative cell lines, while in some antiestrogen resistant variants, it becomes inducible by tamoxifen, contrary to the wild type MCF7 cells. Cloning of its cDNA in lambda gt11 has allowed to show that the mRNA is rapidly induced by estrogens and to sequence the protein and compare it to that of the normal human kidney cathepsin-D.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The estrogen-regulated 52K-cathepsin-D in breast cancer: from biology to clinical applications. 365 55

Acid alpha-glucosidase (EC 3.2.1.20) was purified from human placenta and bovine testis by affinity chromatography using concanavalin A (conA) and Sephadex G 200. When added to the culture medium of human fibroblasts, the enzyme purified from bovine testis is taken up with a 200-fold higher efficiency than the enzyme from human placenta. Uptake of acid alpha-glucosidase from bovine testis is mediated by the mannose-6-phosphate receptor, whereas only a minor fraction of placental enzyme appears to be equipped with the mannose-6-phosphate recognition marker. Once internalized, both human and bovine acid alpha-glucosidase demonstrate a half-life of about 10 days in fibroblasts from control individuals and patients with different clinical forms of glycogenosis type II (Pompe's disease, acid alpha-glucosidase deficiency). Evidence is presented that the mannose-6-phosphate receptor is also present on the plasma membrane of the clonal myogenic skeletal muscle cell lines G8-1 and L6J1 (respectively from mouse and rat origin) and on cultured human skeletal muscle cells derived from a muscle biopsy. Addition of bovine testis acid alpha-glucosidase to skeletal muscle cell cultures from an adult patient with glycogenosis type II leads to complete correction of the enzyme deficiency.
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PMID:Uptake and stability of human and bovine acid alpha-glucosidase in cultured fibroblasts and skeletal muscle cells from glycogenosis type II patients. 623 28

Five healthy related individuals in 3 generations of a Lebanese family have been found to have highly elevated plasma lysosomal enzyme levels inherited as a dominant Mendelian trait. The same enzymes in other extracellular fluids were within normal limits. While the pattern and extent of plasma enzyme elevation was similar to that found in mucolipidoses II and III, the physicochemical properties of the elevated enzymes were different from those of both control and I-cell disease plasma. Secretion of lysosomal hydrolases into cell media by fibroblasts from one of the individuals was increased two to seven times more than that from controls. The results suggest faulty recognition between lysosomal hydrolases and mannose-6-phosphate receptors. This could be caused by a defect either in the phosphodiesterase that normally uncovers mannose-6-phosphate hydrolase markers or in the mannose-6-phosphate receptor itself.
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PMID:Five related Lebanese individuals with high plasma lysosomal hydrolases: a new defect in mannose-6-phosphate receptor recognition? 623 28

In vitro human natural cell-mediated cytotoxicity (NCMC) to K-562, Molt-4, and F-265 cells is inhibited in a dose-dependent manner by mannose 6-phosphate, fructose 1-phosphate and fructose 6-phosphate. This inhibition is not observed with mannose, glucose, fucose, glucose 6-phosphate, mannose 1-phosphate, galactose 1-phosphate, or galactose 6-phosphate. Preincubation of the effector cells, obtained from fresh whole blood, with mannose-6-phosphate, fructose-1-phosphate, or fructose-6-phosphate did not inhibit cytotoxicity, which indicated that these hexose phosphates are not nonspecifically toxic towards the effector lymphocytes. Mannose-6-phosphate and the stereochemically similar fructose-1-phosphate are more potent inhibitors than fructose-6-phosphate in terms of concentration required and time of onset of effect. Inhibition of cytotoxicity by mannose-6-phosphate varied with target cell type: F-265 is protected at much lower concentrations of mannose-6-phosphate (less than 1 mM) than is either Molt-4 or K-562. The inhibition of NCMC is also observed with the inhibitors of lysosomal function, NH4Cl, and chloroquine. The presence of a functional mannose-6-phosphate receptor on target cells was demonstrated: (i) Gelonin, a seed protein that inactivates the eukaryotic ribosome but is nontoxic to intact cells, was covalently linked to monophosphopentamannose, and this conjugate ws toxic to both K-562 and F-265 target cells, the latter being by far the more sensitive; and (ii) chloroquine, NH4Cl, and mannose-6-phosphate all inhibited the toxicity of gelonin-monophosphopentamannose. These results suggest either that a cytolytic lymphokine contains a hexose phosphate residue and may be taken up by target cells through the lysosomal/mannose 6-phosphate pathway or that such a residue is involved in target cell-effector cell recognition.
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PMID:Mannose 6-, fructose 1-, and fructose 6-phosphates inhibit human natural cell-mediated cytotoxicity. 694 16

We cloned and sequenced the 8767-bp full-length cDNA for the chicken cation-independent mannose-6-phosphate receptor (CI-MPR), of interest because, unlike its mammalian homologs, it does not bind insulin-like growth factor II (IGF-II). The cDNA encodes a protein of 2470 aa that includes a putative signal sequence, an extracytoplasmic domain consisting of 15 homologous repeat sequences, a 23-residue transmembrane sequence, and a 161-residue cytoplasmic sequence. Overall, it shows 60% sequence identity with human and bovine CI-MPR homologs, and all but two of 122 cysteine residues are conserved. However, it shows much less homology in the N-terminal signal sequence, in repeat 11, which is proposed to contain the IGF-II-binding site in mammalian CI-MPR homologs, and in the 14-aa residue segment in the cytoplasmic sequence that has been proposed to mediate G-protein-coupled signal transduction in response to IGF-II binding by the human CI-MPR. Transient expression in COS-7 cells produced a functional CI-MPR which exhibited mannose-6-phosphate-inhibitable binding and mediated endocytosis of recombinant human beta-glucuronidase. Expression of the functional chicken CI-MPR in mice lacking the mammalian CI-MPR should clarify the controversy over the physiological role of the IGF-II-binding site in mammalian CI-MPR homologs.
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PMID:Cloning and expression of the cDNA of chicken cation-independent mannose-6-phosphate receptor. 756 13

The secretion of pro-cathepsin D (pro-cath-D) in some human metastatic breast cancer cells (MCF7, MDA/MB231), contrary to normal mammary cells, is not increased by ammonium chloride treatment, indicating a mannose-6-phosphate-independent sorting to lysosomes. By studying a variety of cell lines and lysosomal enzymes, we show that secretion of newly synthesized pro-cath-D was not mediated by the 46-kDa mannose-6-phosphate receptor (MPR) and that its resistance to NH4Cl for secretion was specific to cath-D and not to other lysosomal enzymes. This resistance appeared to be correlated with the basal hypersecretion of pro-cath-D, but not with its overexpression. By contrast, pro-cath-D secretion was increased by NH4Cl in fibroblasts and nontumoral epithelial mammary cells, suggesting a specificity for cancer cells. Immunofluorescence staining showed that pro-cath-D, but neither cathepsin B nor beta-hexosaminidase, accumulated in intracytoplasmic vesicles of cells treated with ammonium chloride. In pulse--chase experiments and by subcellular fractionation on Percoll gradient, cath-D was found to be sorted into dense lysosomes whether cells were treated or not by NH4Cl. Treatment of cells with NH4Cl, however, inhibited processing and maturation of pro-cath-D, which was also observed in light vesicles in the absence of NH4Cl. Part of pro-cath-D, but not processed enzyme, was also found to be membrane associated in saponin-permeabilized cells. We conclude that in breast cancer cells, the MPR-independent pathway of pro-cath-D to lysosome is predominant compared to normal cells and other lysosomal enzymes. This alternative pathway should therefore be considered, in addition to MPR, to explain pro-cath-D sorting and activation in breast cancer cells.
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PMID:Specific mannose-6-phosphate receptor-independent sorting of pro-cathepsin D in breast cancer cells. 795 63

The receptor for insulin-like growth factor type 2, also known as the cation-independent mannose-6-phosphate receptor (Igf2/Mpr), is a multifunctional receptor thought to play a role in lysosomal targeting, cell growth and signal transduction. Igf2/Mpr has been mapped to the mouse Tme locus and shown to be an imprinted gene, which further suggests a role in embryonic growth regulation. To define the functions of Igf2/Mpr, we have generated mice lacking this gene. We report here that maternal inheritance of an Igf2/Mpr null allele (-/+) as well as homozygosity for the inactive allele (-/-) is generally lethal at birth and mutants are about 30% larger, indicating that maternal expression of Igf2/Mpr is essential for late embryonic development and growth regulation. The phenotype is probably caused by an excess of Igf2 because the introduction of an Igf2 null allele rescued the Igf2/Mpr mutant mice. Mutant mice also have organ and skeletal abnormalities and missort mannose-6-phosphate-tagged proteins. A few (-/+) mice reactivated their paternal Igf2/Mpr allele in some tissues and survived to adults. But no (-/-) mice survived, indicating a role for the reactivated paternal allele in postnatal survival.
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PMID:Regulation of embryonic growth and lysosomal targeting by the imprinted Igf2/Mpr gene. 798 40

beta-Glucuronidase undergoes proteolytic C-terminal processing during or after its transport to lysosomes or endosomes. We determined the C-terminal processing site for human placental beta-glucuronidase to be the peptide bond between Thr633-Arg634. To evaluate the role of the 18-amino acid peptide removed in C-terminal processing, we changed the codon for Arg634 to a stop codon by site-directed mutagenesis and studied expression of the truncated mutant enzyme in COS-7 cells. An increased fraction of newly synthesized enzyme from R634Stop cDNA was secreted. Pulse-chase experiments provided no evidence for increased degradation of the intracellular R634Stop enzyme. The total amount of catalytic activity expressed from the R634Stop mutant cDNA was only half that seen with the wild type cDNA, and the Kcat of the mutant enzyme was 52% that of wild type enzyme. These results indicate that the C-terminal propeptide in the precursor is important for beta-glucuronidase to achieve maximal activity. The truncated enzyme formed hybrid tetramers in cotransfection experiments with the cDNA for rat beta-glucuronidase. There appeared to be no decrease in stability of the R634Stop enzyme, since chaotropic agents, heat treatment, and pH had similar effects on the mutant and the wild type enzymes. The uptake rate of the truncated mutant (R634Stop) enzyme by beta-glucuronidase-deficient human fibroblast cells was only 55-60% that of the wild type enzyme. Binding to the immobilized cation-independent mannose-6-phosphate receptor and measurement of the 32P-labeled phosphorylated oligosaccharides revealed that the truncated mutant enzyme was 32-34% less phosphorylated and appeared to contain proportionately more covered phosphate groups than the wild type enzyme. These results suggest that the propeptide influences the accessibility to both processing enzymes that produce the mannose-6-phosphate recognition marker on beta-glucuronidase.
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PMID:C-terminal processing of human beta-glucuronidase. The propeptide is required for full expression of catalytic activity, intracellular retention, and proper phosphorylation. 822 71


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