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 insulin-like growth factor-II/mannose-6-phosphate receptor binds two classes of ligands, IGF-II and lysosomal enzymes containing the mannose-6-phosphate recognition marker. To study the interaction of the two classes of ligands at the receptor level, we have isolated 'high uptake' forms of lysosomal enzymes containing mannose-6-phosphate that had been radiolabeled biosynthetically using a tissue culture model: Tay-Sachs disease fibroblasts were incubated in medium containing [3H]mannose, ammonium chloride and mannose-6-phosphate. Under the conditions of these experiments, the Tay-Sachs disease fibroblasts synthesized and secreted radiolabeled hexosaminidase B, as confirmed by measuring enzymatic activity of cell-conditioned medium. The enzyme secreted was recognized by antibodies raised against purified hexosaminidase A and B but not by nonimmune control sera in Western blotting and immunoprecipitation experiments. The radiolabeled cell-conditioned medium was partially purified by ion-exchange chromatography on a DEAE-Sephadex column. When partially purified [3H]hexosaminidase B was incubated with rat C6 glial cells which express large numbers of IGF-II/mannose-6-phosphate receptors, the enzyme was taken up specifically via the IGF-II/mannose-6-phosphate receptor as evidenced by carbohydrate competition experiments. The specific uptake of the radiolabeled lysosomal enzyme was partially inhibited by IGF-II and an antibody against the IGF-II/mannose-6-phosphate receptor (No. 3637). We conclude that the cellular uptake of a biosynthetically labeled lysosomal enzyme, hexosaminidase B, is partially inhibited by IGF-II. We hypothesize that IGF-II might be capable of modulating lysosomal pathways in vivo.
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PMID:Biosynthetic labeling of beta-hexosaminidase B: inhibition of the cellular uptake of lysosomal secretions containing [3H]hexosaminidase B by insulin-like growth factor-II in rat C6 glial cells. 130 95

MHC class II (MHC-II) molecules bind fragments of exogenous Ags in an intracellular endocytotic compartment. In view of divergent data on the MHC-II distribution in different cell lines, it was of interest to localize MHC-II molecules in a natural and the most potent APC type, the dendritic cell (DC). By using immunogold labeling of ultrathin cryosections of cultured mouse spleen DC, we found that MHC-II molecules were present abundantly at the plasma membrane and in intracellular compartments containing internal membrane vesicles and/or membrane sheets. The majority of these compartments was situated late in the endocytotic route, as demonstrated by the late appearance (after a lag of 30 min) of internalized exogenous tracer. These compartments contained the lysosomal enzymes cathepsin D and beta-hexosaminidase, but lacked the late endosomal marker cation-dependent mannose-6-phosphate receptor. We conclude that most of the intracellular MHC-II molecules in cultured spleen DC reside in a compartment with (pre)lysosomal characteristics, resembling the so-called MHC-II-enriched compartments (MIIC), originally described in B cells. We also investigated whether the presence of MHC-II molecules in endocytotic compartments was related to the kinetics of Ag processing and presentation by these cells. Pulse-chase endocytosis experiments with hen egg lysozyme (HEL) as a model Ag showed that activated spleen DC were able to efficiently process and present this Ag to an HEL-specific T hybridoma cell line. However, presentation started only after a lag of 2 h and was maximal after 6 h. The difference in time between the arrival of Ag in proteolytic endocytotic compartments, in particular MIIC, and effective Ag presentation is discussed in the context of DC maturation.
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PMID:MHC class II compartments and the kinetics of antigen presentation in activated mouse spleen dendritic cells. 775 23

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 intracellular transport of [125I]tyramine cellobiose low-density lipoprotein ([125ITC]LDL) and [131ITC]beta-very-low-density lipoprotein ([131ITC]beta-VLDL) in rat liver was studied by means of centrifugation in sucrose and Nycodenz gradients. At time-points up to 45 min after intravenous injection, the two ligands were found in endosomes with distinctly different buoyant densities. In the Nycodenz gradients [131ITC]beta-VLDL appeared at 1.08 g/ml partly coinciding with the distribution of the cation independent (alpha)mannose-6-phosphate receptor, whereas [125ITC]LDL was found at 1.13 mg/ml, where the degradation of [125ITC]LDL started. [131ITC]beta-VLDL, on the other hand, was transferred to denser vesicles, banding at 1.16 g/ml, and degradation started in these organelles, similar to that observed with asialoorosomucoid (ASOR) that was used as a control ligand. Since degradation products coincided with beta-N-acetylglucosaminidase we assume that these organelles are secondary lysosomes. [125ITC]LDL was subsequently also transferred to these dense secondary lysosomes, and the distribution of degraded [125ITC]LDL was therefore bimodal until [125ITC]LDL was completely cleared from the circulation. Furthermore our results show that the different intracellular pathways observed are not due to uptake in different liver cell types, since the bimodal distribution of [125ITC]LDL was also evident in purified liver parenchymal cells. The data suggest that LDL and beta-VLDL follow different endosomal pathways in the rat hepatocytes and that both pathways meet in a common final lysosome. The data also support the notion that LDL and beta-VLDL are taken up through different endocytic receptors. However, following estradiol treatment, both ligands seem to follow a common pathway. In this case the density distributions of the two ligands coincide and resemble the pathway of LDL observed in control animals. This may be due to a pronounced up-regulation of LDL receptors following estradiol treatment, and beta-VLDL may under these conditions be taken up via the LDL receptor.
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PMID:Endocytosed LDL and beta-VLDL follow different intracellular pathways in rat liver. 825 20

The GM2 activator protein is a small monomeric protein containing a single site for Asn-linked glycosylation. Its only proven in vivo function is to act as a substrate specific cofactor for the hydrolysis of GM2 ganglioside by lysosomal beta-hexosaminidase A. However, we and others have shown it can act as a general glycolipid transporter at neutral pH in vitro. Any other possible in vivo functions would require that some of the newly synthesized activator molecules not be targeted to the lysosome. The lysosomal targeting mechanism for the activator has not been conclusively identified. While earlier reports suggested that it is likely through the mannose-6-phosphate receptor, another more recent report demonstrated that deficient human cells could recapture nonglycosylated, bacterially produced activator, suggesting its use of an alternate targeting pathway. Here, we demonstrate that the mannose-6-phosphate pathway is likely the major intracellular, biosynthetic route to the lysosome, as well as a high affinity recapture pathway for the endocytosis of activator protein from extracellular fluids. Additionally, we show that there exists a second lower affinity recapture pathway that requires its native protein structure, is carbohydrate independent, and likely does not involve its ability to bind glycosphingolipids in the plasma membrane. Finally, we document that the pool of newly synthesized precursor activator protein contains a majority of molecules with a complex-type oligosaccharide, which cannot contain a functional mannose-6-phosphate targeting signal. These molecules makeup the secreted forms of the protein in normal human fibroblasts.
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PMID:Two mechanisms for the recapture of extracellular GM2 activator protein: evidence for a major secretory form of the protein. 920 79

Tay-Sachs disease is a severe neurodegenerative disorder due to mutations in the HEXA gene coding for the alpha-chain of the alpha-beta heterodimeric lysosomal enzyme beta-hexosaminidase A (HexA). Because no treatment is available for this disease, we have investigated the possibility of enzymatic correction of HexA-deficient cells by HEXA gene transfer. Human HEXA cDNA was subcloned into a retroviral plasmid generating to G.HEXA vector. The best Psi-CRIP producer clone of G.HEXA retroviral particles was isolated, and murine HexA-deficient fibroblasts derived from hexa -/- mice were transduced with the G.HEXA vector. Transduced cells overexpressed the alpha-chain, resulting in the synthesis of interspecific HexA (human alpha-chain/murine beta-chain) and in a total correction of HexA deficiency. The alpha-chain was secreted in the culture medium and taken up by HexA-deficient cells via mannose-6-phosphate receptor binding, allowing for the restoration of intracellular HexA activity in non-transduced cells.
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PMID:Retrovirus-mediated enzymatic correction of Tay-Sachs defect in transduced and non-transduced cells. 953 87

Rab7b is a recently identified member of the Rab GTPase protein family and has high similarity to Rab7. It has been reported that Rab7b is lysosome associated, that it is involved in monocytic differentiation and that it promotes lysosomal degradation of TLR4 and TLR9. Here we investigated further the localization and function of this GTPase. We found that wild-type Rab7b is lysosome associated whereas an activated, GTP-bound form of Rab7b localizes to the Golgi apparatus. In contrast to Rab7, Rab7b is not involved in EGF and EGFR degradation. Depletion of Rab7b or expression of Rab7b T22N, a Rab7b dominant-negative mutant, impairs cathepsin-D maturation and causes increased secretion of hexosaminidase. Moreover, expression of Rab7b T22N or depletion of Rab7b alters TGN46 distribution, cation-independent mannose-6-phosphate receptor (CI-MPR) trafficking, and causes an increase in the levels of the late endosomal markers CI-MPR and cathepsin D. Vesicular stomatitis virus G protein (VSV-G) trafficking, by contrast, is normal in Rab7b-depleted or Rab7b-T22N-expressing cells. In addition, depletion of Rab7b prevents cholera toxin B-subunit from reaching the Golgi. Altogether, these data indicate that Rab7b is required for normal lysosome function, and, in particular, that it is an essential factor for retrograde transport from endosomes to the trans-Golgi network (TGN).
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PMID:Rab7b controls trafficking from endosomes to the TGN. 2037 62