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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

Myeloperoxidase (MPO), a heme protein, is a major component of azurophilic granules of neutrophils. Optimal oxygen-dependent microbicidal activity depends on MPO as the critical enzyme for the generation of hypochlorous acid and other toxic oxygen products. MPO is synthesized during the promyelocytic stage of myeloid differentiation, the stage at which azurophilic granules are formed. Like other lysosomal enzymes, MPO is synthesized as a larger precursor which is subsequently processed and transported intracellularly to the lysosomes. The primary translation product is a single 80-kDa protein which undergoes cotranslational N-linked glycosylation to produce a 92-kDa glycoprotein. Glucosidases in the endoplasmic reticulum or early cis Golgi convert the proMPO to a 90-kDa form which is sorted into a prelysosomal compartment that undergoes final proteolytic maturation to native MPO, a pair of heavy-light protomers with subunits of 60 kDa and a 12 kDa. These events contrast with similar processes seen with other lysosomal enzymes in two ways. First, alkalinization of lysosomes with NH4+ does not alter processing or transport, in contrast to the pH dependence of these processes for other lysosomal enzymes. However, some studies indicate retardation of processing in the presence of the proton ionophore monensin. Second, intracellular transport of MPO is not apparently mediated by the mannose-6-phosphate receptor system. The gene for MPO is on the long arm of chromosome 17 (17q22, 23) near the breakpoint of the 15, 17 translocation of acute promyelocytic leukemia. The gene spans approximately 14 kb and contains 11 irons and 12 exons. The cloned full-length cDNA is approximately 2.2 kb and both normal bone marrow and cultured promyelocytic leukemia cells express two species of mRNA. Inherited MPO deficiency, a relatively common disorder, is associated with the absence of mature MPO but the presence of proMPO, consistent with a post-translational defect. Studies at the molecular level aimed at identifying the underlying genetic defect are thus far consistent with that hypothesis. In addition, the basis for the observed association between acquired MPO deficiency and some myeloid leukemias can now be studied at the molecular level using these probes.
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PMID:Biosynthesis and processing of myeloperoxidase--a marker for myeloid cell differentiation. 283 Oct 80

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

Mast cells play an important role at the early stages of immunological response to bacterial infections and parasite infestations. One of the major mast cell proinflammatory mediators is TNF-alpha. Mast cells are considered the only cells capable of storing TNF-alpha in cytoplasmic granules and rapidly releasing it upon activation. To determine what pathway is utilized to direct TNF-alpha to cytoplasmic granules and what motifs are responsible for the sorting process, we constructed a fusion protein covering the full sequence of TNF-alpha, N-terminally fused to enhanced green fluorescent protein (EGFP). In rodent mast cells, such protein was sorted to secretory granules, and this process was inhibited by both brefeldin A and monensin. Considering the relationship between lysosomes and secretory granules and following TNF-alpha sequence analysis, it was determined whether TNF-alpha is sorted through the mannose-6-phosphate receptor (MPR)-dependent pathway. We observed that ammonium chloride and tunicamycin blocked TNF-alpha-EGFP fusion protein delivery to secretory granules. In situ mutagenesis experiments confirmed the necessity of N-linked glycosylation for efficient sorting of TNF-alpha into rodent mast cell granules. In this work we established that TNF-alpha travels from the ER to mast cell granules via a brefeldin A- and monensin-sensitive route, utilizing the MPR-dependent pathway, although this dependency does not seem to be absolute.
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PMID:Efficient sorting of TNF-alpha to rodent mast cell granules is dependent on N-linked glycosylation. 1654 68