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

There is a developmental difference in the initial phase of compensatory renal growth (CRG) following unilateral nephrectomy (UNX), in that CRG is GH-dependent in adult rats and GH-independent in immature rats. Furthermore, CRG in immature rats is associated with an increase in renal IGF-I mRNA, an effect not seen in adult rats. In this study we have examined the age-related differences in expression of the insulin-like growth factor-I (IGF-I) and IGF-II genes as well as in IGF-I and IGF-II receptors and membrane binding after UNX. Immature (22-24 days of age) and adult (4 months of age) male Wistar rats underwent a sham operation or left UNX and were killed 24 or 48 h later. Levels of mRNA for IGF-I and IGF-II and their receptors were determined in the left (control) and right (compensated) remnant kidneys using solution hybridization/RNase protection assays. Steady state levels of IGF-I mRNA as well as IGF-I receptor and IGF-II/mannose-6-phosphate receptor mRNAs were increased 3- to 4-fold in immature remnant kidneys, but not in adult kidneys. The findings related to IGF-I gene expression were confirmed by in situ hybridization to immature and adult kidney slices. The increase in IGF-I gene expression in the immature remnant kidneys was localized to the thick ascending limbs of the loops of Henle. Furthermore, in concert with the changes in mRNA levels, membrane binding studies showed significant increases in specific binding to IGF-I in cortical membranes and increases in specific binding to IGF-II in whole kidney membranes from immature, but not adult, rats. Thus, these findings demonstrate that the initial phase of CRG in the immature rat is associated with increased renal IGF-I gene expression as well as enhanced specific renal binding of IGF-I and IGF-II to plasma membranes and support the notion that this period of rapid renal growth in the immature UNX rat may involve the paracrine influence of the IGFs.
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PMID:Altered expression of insulin-like growth factor-I (IGF-I) and IGF receptor genes after unilateral nephrectomy in immature rats. 130 31

We present evidence that insulin-like growth factor II (IGF-II) mediates growth in early mouse embryos and forms a pathway in which imprinted genes influence development during preimplantation stages. mRNA and protein for IGF-II were expressed in preimplantation mouse embryos, but the related factors IGF-I and insulin were not. IGF-I and insulin receptors and the IGF-II/mannose-6-phosphate receptor were expressed. Exogenous IGF-II or IGF-I increased the cell number in cultured blastocysts, but a mutant form of IGF-II that strongly binds only the IGF-II receptor did not. Reduction of IGF-II expression by antisense IGF-II oligonucleotides decreased the rate of progression to the blastocyst stage and decreased the cell number in blastocysts. Preimplantation parthenogenetic mouse embryos expressed mRNA for the IGF-II receptor but not for either IGF-II ligand or the IGF-I receptor, indicating that the latter genes are not expressed when inherited maternally. These data imply that some growth factors and receptors, regulated by genomic imprinting, may control cell proliferation from the earliest stages of embryonic development.
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PMID:Insulin-like growth factor II acts through an endogenous growth pathway regulated by imprinting in early mouse embryos. 131 21

Solution hybridization/RNase protection assays were used to study the developmental expression of the insulin-like growth factor-I (IGF-I), IGF-II, IGF-I receptor, and IGF-II/mannose-6-phosphate receptor genes in the rat ovary between postnatal days 1-80. Maximal IGF-I mRNA levels occurred during the 15- to 25-day postnatal period, and the level on day 20 represented a 9-fold increase over the baseline at earlier and later stages. IGF-II mRNA levels were maximal during the 1- to 5-day postnatal period and subsequently declined to undetectable levels after day 10. IGF-I receptor mRNA levels increased 10-fold to a maximum in the 20- to 25-day postnatal period. This pattern was similar to the developmental pattern of [125I]IGF-I binding in the ovary. Two apparent peaks of IGF-II/mannose-6-phosphate receptor mRNA levels were seen, on day 20 and between days 50-80. These specific and significant changes in the expression of the genes encoding the IGFs and their receptors suggest a role for the IGF system in postnatal ovarian development.
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PMID:Expression of the insulin-like growth factor (IGF)-I and -II and the IGF-I and -II receptor genes during postnatal development of the rat ovary. 132 54

The mechanisms of enzyme delivery to and acidification of early autophagic vacuoles in cultured fibroblasts were elucidated by cryoimmunoelectron microscopic methods. The cation-independent mannose-6-phosphate receptor (MPR) was used as a marker of the pre-lysosomal compartment, and cathepsin L and an acidotropic amine (3-(2,4-dinitroanilino)-3'-amino-N-methyl-dipropylamine (DAMP), a cytochemical probe for low-pH organelles) as markers of both pre-lysosomal and lysosomal compartments. In addition, cationized ferritin was used as an endocytic marker. In ultrastructural double labeling experiments, the bulk of all the antigens was found in vesicles containing tightly packed membrane material. These vesicles also contained small amounts of endocytosed ferritin and probably correspond to the MPR-enriched pre-lysosomal compartment. Some immunolabeling was also visible in the trans-Golgi network. In addition, cathepsin L, DAMP, and large amounts of ferritin were found in smaller vesicles which can be classified as mature lysosomes. Early autophagic vacuoles were defined as vesicles containing recognizable cytoplasm. MPR, cathepsin L, and DAMP, but not ferritin, were detected in the early vacuoles. Inhibition of the acidification in the early vacuoles by monensin did not prevent the delivery of MPR and cathepsin L. The presence of MPR in the vacuoles suggests that cathepsin L is not delivered to early autophagic vacuoles solely by fusion with mature, MPR-deficient lysosomes. Furthermore, although lysosomes were loaded with endocytosed ferritin, it was not detected in autophagic vacuoles. Either the trans-Golgi network or the MPR-enriched pre-lysosomes may be the main source of enzymes and acidification machinery for the autophagic vacuoles in fibroblasts.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Autophagy, cathepsin L transport, and acidification in cultured rat fibroblasts. 132 77

Biosynthesis of myeloperoxidase (MPO), a myeloid lysosomal hemoprotein critical for the optimal oxygen-dependent microbicidal activity of human neutrophils, is incompletely understood. The primary translation product undergoes cotranslational N-linked glycosylation with subsequent insertion of the Fe-containing prosthetic group into the peptide backbone, thereby converting the enzymatically inactive, heme-free apoproMPO into the peroxidatively active precursor, proMPO. Eventually, proMPO undergoes proteolytic processing into native, lysosomal MPO, with subunits of 59 and 13.5 Kd. We studied three unanswered questions regarding MPO biosynthesis: (1) At what point during MPO biosynthesis is the heme moiety inserted into the apoenzyme? (2) What consequences does heme-insertion have on subsequent processing events? (3) What role does the mannose-6-phosphate receptor (M6PR) system play in the delivery of MPO to the lysosome? Disruption of Golgi by brefeldin A (BFA) produced two major changes in MPO biosynthesis: (1) processing of the 89-Kd precursor to mature MPO was blocked and (2) constitutive secretion of the MPO precursor was inhibited. Inhibition of heme synthesis with succinyl acetone (SA) reduced peroxidase activity and profoundly blocked processing of proMPO to mature MPO. This inhibition of processing was not a generalized effect on all lysosomal enzymes, because the maturation of a non-heme-containing lysosomal enzyme, beta-glucuronidase, was not altered. Electron microscopy showed that, although the normal peroxidase staining of endoplasmic reticulum was absent in SA-treated cells, there were MPO-related peptides in the ER. The role of the M6PR system was assessed by immunoprecipitating fractions obtained from M6PR affinity column chromatography. The 89-Kd proMPO failed to adhere to the M6PR affinity column, whereas the 59-Kd heavy subunit of mature MPO was specifically eluted from the column. We interpret these data to indicate that: (1) processing of proMPO to mature MPO occurs in a post-ER compartment that is itself BFA-sensitive or is distal to a BFA-sensitive compartment and (2) heme insertion into apoproMPO precedes and may be a prerequisite for proteolytic processing to enzymatically active mature MPO. Our analysis of the M6PR system in MPO biosynthesis led to the unanticipated finding that there were phosphomannosyl residues on mature MPO, but none on proMPO. We suggest that the bulk of proMPO at any time is not phosphorylated, but, when generated, the phosphorylated proMPO is quickly processed to the phosphorylated 59-Kd subunit of mature MPO. Thus, if the M6PR is important in the intracellular transport of MPO, it is the phosphorylated mature MPO that is directed to the lysosomal compartment by this system.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Roles of heme insertion and the mannose-6-phosphate receptor in processing of the human myeloid lysosomal enzyme, myeloperoxidase. 133 78

Human lysosomal alpha-galactosidase A (alpha-Gal A) was stably overexpressed in CHO cells and its biosynthesis and targeting were investigated. Clone AGA5.3-1000Mx, which was the highest enzyme overexpressor, produced intracellular alpha-Gal A levels of 20,900 U/mg (approximately 100 micrograms of enzyme/10(7) cells) and secreted approximately 13,000 U (or 75 micrograms/10(7) cells) per day. Ultrastructural examination of these cells revealed numerous 0.25-1.5 microns crystalline structures in dilated trans-Golgi network (TGN) and in lysosomes which stained with immunogold particles using affinity-purified anti-human alpha-Gal A antibodies. Pulse-chase studies revealed that approximately 65% of the total enzyme synthesized was secreted, while endogenous CHO lysosomal enzymes were not, indicating that the alpha-Gal A secretion was specific. The recombinant intracellular and secreted enzyme forms were normally processed and phosphorylated; the secreted enzyme had mannose-6-phosphate moieties and bound the immobilized 215-kD mannose-6-phosphate receptor (M6PR). Thus, the overexpressed enzyme's selective secretion did not result from oversaturation of the M6PR-mediated pathway or abnormal binding to the M6PR. Of note, the secreted alpha-Gal A was sulfated and the percent of enzyme sulfation decreased with increasing amplification, presumably due to the inaccessibility of the enzyme's tyrosine residues for the sulfotransferase in the TGN. Overexpression of human lysosomal alpha-N-acetylgalactosaminidase and acid sphingomyelinase in CHO cell lines also resulted in their respective selective secretion. In vitro studies revealed that purified secreted alpha-Gal A was precipitated as a function of enzyme concentration and pH, with 30% of the soluble enzyme being precipitated when 10 mg/ml of enzyme was incubated at pH 5.0. Thus, it is hypothesized that these overexpressed lysosomal enzymes are normally modified until they reach the TGN where the more acidic environment of this compartment causes the formation of soluble and particulate enzyme aggregates. A significant proportion of these enzyme aggregates are unable to bind the M6PR and are selectively secreted via the constitutive secretory pathway, while endogenous lysosomal enzymes bind the M6PRs and are transported to lysosomes.
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PMID:Overexpression of human alpha-galactosidase A results in its intracellular aggregation, crystallization in lysosomes, and selective secretion. 133 79

We have examined the subcellular localization of p60c-src in mammalian fibroblasts. Analysis of indirect immunofluorescence by three-dimensional optical sectioning microscopy revealed a granular cytoplasmic staining that co-localized with the microtubule organizing center. Immunofluorescence experiments with antibodies against a number of membrane markers demonstrated a striking co-localization between p60c-src and the cation-dependent mannose-6-phosphate receptor (CI-MPR), a marker that identifies endosomes. Both p60c-src and the CI-MPR were found to cluster at the spindle poles throughout mitosis. In addition, treatment of interphase and mitotic cells with brefeldin A resulted in a clustering of p60c-src and CI-MPR at a peri-centriolar position. Biochemical fractionation of cellular membranes showed that a major proportion of p60c-src co-enriched with endocytic membranes. Treatment of membranes containing HRP to alter their apparent density also altered the density of p60c-src-containing membranes. Similar density shift experiments with total cellular membranes revealed that the majority of membrane-associated p60c-src in the cell is associated with endosomes, while very little is associated with plasma membranes. These results support a role for p60c-src in the regulation of endosomal membranes and protein trafficking.
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PMID:Association of p60c-src with endosomal membranes in mammalian fibroblasts. 137 46

The insulin-like growth factors (IGFs) have important roles in normal cellular growth and development. The IGFs have also been implicated in regulation of tumor cell growth. Two ligands, IGF-I and IGF-II, have been identified that are expressed in both fetal and adult tissues. They interact with at least two specific cell surface receptors. The type I IGF receptor is homologous to the insulin receptor in structure and has tyrosine kinase activity. The type II receptor is identical to the mannose-6-phosphate receptor known to be important in the trafficking of lysosomal enzymes; its role in IGF signal transduction is not clear. Furthermore, a hybrid receptor composed of subunits from the insulin receptor and the type I IGF receptor have been identified. In addition to these receptors, six different IGF binding proteins have been identified, which modulate the activity of the IGFs in various ways. Thus, there is great potential for complex interactions between the family members that could ultimately regulate normal and neoplastic cell growth.
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PMID:The insulin-like growth factor family of ligands, receptors, and binding proteins. 138 4

We prepared a mouse monoclonal antibody, 2D5, which recognized a highly glycosylated human lysosomal membrane antigen. The apparent molecular mass of this antigen was cell type dependent and ranged between 100 kDa and 130 kDa. The difference was due to a variation in the carbohydrate moiety, since upon removal of the N-linked oligosaccharides the size of the glycoprotein was reduced to approximately 50 kDa in all cases. The high carbohydrate contents, subcellular localization and N-terminal sequence indicated a high similarity or identity of this antigen with the lamp-2 protein. In U937 cells several agents known to elicit differentiation induced synthesis of a larger form of the lamp antigen. Thus, treatment of cells with calcitriol resulted in a shift in its average molecular mass from 115 kDa to 130 kDa. The difference was due to an increase in the contents of lactosamine repeats. In subcellular membranes from calcitriol-treated cells the specific activity of the UDP-N-acetylglucosamine: N-acetyllactosamine N-acetylglucosaminyltransferase was enhanced 3-fold. The enhancement was accompanied with an elongation of lactosamine repeats in N-linked oligosaccharides in the 46 kDa mannose 6-phosphate receptor and the homing receptor, the leucocyte antigen CD44. In contrast, the apparent size of the leucocyte antigen CD43 which bears numerous O-linked oligosaccharides was not changed indicating a selectivity in the modulation of the formation of lactosamine repeats in N- and O-linked carbohydrates. It is shown further that the synthesis of lactosamine repeats in U937 cells is impeded in the presence of NH4Cl.
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PMID:Stimulation of the biosynthesis of lactosamine repeats in glycoproteins in differentiating U937 cells and its suppression in the presence of NH4Cl. 138 63


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