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

Some peptide hormones are associated with specific, high-affinity plasma proteins. The major binding protein (BP) for growth hormone (GH) in humans is a circulating fragment of the GH membrane receptor, consisting of the hydrophilic, extracellular portion of that transmembrane glycoprotein. The circulating levels of GH-BP mirror the levels of GH receptors. There are 4 well-characterized insulin-like growth factor (IGF)-BPs. One IGF-binding component in plasma is a fragment of the extracellular portion of the IGF-II/mannose-6-phosphate receptor, analogous to the GH-BP. The 3 other cloned IGF-BPs form a homologous family of proteins with differences in structure, glycosylation and hormonal control that suggest differences in function. The GH- and IGF-BPs play a major role in the metabolism and biological action of these peptide hormones.
 ...
PMID:Role of growth-hormone and insulin-like growth-factor-binding proteins. 169 1

The intraovarian insulin-like growth factor (IGF) system constitutes a triad composed of ligands, receptors, and binding proteins. Although conventional radioligand receptor assays have documented the presence of specific receptors for insulin and insulin-like peptides in some rat somatic ovarian cell types, the exact cellular localization and hormonal regulation of the receptors in question remain matters of inquiry. To reevaluate the very presence, cellular localization, and hormonal regulation of the IGF receptor gene family in the rat ovary, solution hybridization/RNase protection assays were used wherein ovarian total RNA (20 micrograms) from immature (21-23 days old) rats was hybridized with 32P-labeled type I IGF receptor, type II IGF/mannose-6-phosphate receptor, and insulin receptor riboprobes. Single protected fragments 261 (type I IGF receptor), 500 (type II IGF/mannose-6-phosphate receptor), and 478 (insulin receptor) bases long were evident in whole ovary, granulosa, and theca-interstitial cells. Hypophysectomy of immature rats led to significant (P less than 0.05) albeit variable decrements in the relative (densitometrically quantified) ovarian abundance of transcripts corresponding to the type I IGF (but not insulin or type II IGF/mannose-6-phosphate) receptor. Treatment of immature hypophysectomized rats with FSH (10 micrograms/rat.day x 2.5 days) resulted in a significant (P less than 0.05) increase (4-fold) in transcripts corresponding to the type I IGF receptor in both whole ovarian material and freshly isolated granulosa cells. Similar (3.7-fold) increments (P less than 0.05) were noted after treatment with a diethylstilbestrol-containing sc silastic implant applied for a total of 5 days.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Insulin-like growth factor receptor gene expression in the rat ovary: divergent regulation of distinct receptor species. 172 86

We have used endocytic and phagocytic tracers in an EM immunocytochemical study to define the compartments of the phagocytic and endocytic pathways in mouse peritoneal macrophages. Endocytosed BSA-gold appeared successively in early endosomes, spherical endosomal vesicles, a late endosomal tubuloreticular compartment (TC), and terminal lysosomes. The TC appeared as an elaborate structure enriched for the lysosomal membrane glycoproteins Lamp 1 and Lamp 2, and expressing significant levels of rab7, a late endosome-specific GTP-binding protein. The cation-independent mannose-6-phosphate receptor was restricted to specialized regions of the TC that were predominantly adjacent to the Golgi complex. Both the early endosome and the TC had coated bud structures whose composition and function are presently unknown. Phagolysosomes containing latex beads expressed the same membrane antigens and received endocytic tracers simultaneously with the TC. Since the membrane surrounding both organelles was also in direct continuity, we assume that both structures form one functional compartment. Macrosialin, an antigen confined to macrophages and dendritic cells, was heavily expressed in TC and phagolysosomal membranes with low levels being detected in other endosomal compartments and on the cell surface. Treatment of cells with wheat germ agglutinin drastically altered the morphology of the TC, giving rise to sheets of tightly adherent membrane and greatly expanded vesicles, in which cell-associated wheat germ agglutinin was concentrated. The spherical endosomal carrier vesicles loaded with internalized gold tracers clustered nearby, often making contact without fusing. Since the delivery of endocytic tracer to the TC was significantly delayed these experiments suggest that the lectin is somehow preventing the endosome vesicles from fusing with the TC. Collectively, our data argue first that the PLC is equivalent to the "tubular lysosomes" commonly described in macrophages, and second that the meeting of the phagocytic and endocytic pathway occurs in this compartment.
 ...
PMID:Immunocytochemical characterization of the endocytic and phagolysosomal compartments in peritoneal macrophages. 173 Jul 52

Bone resorption plays an important role in bone modeling and remodeling. Osteoclasts are the cells responsible for the bone resorption. Osteoclasts are located on endosteal bone surfaces and on the periosteal surface beneath the periosteum. They are multinucleated giant cells highly polarized in their morphology and function. Among the proximal surface, the membrane and the area of the cytoplasm directly oppose to the bone surface, which are specialized into two regions. A central region consisting of many irregular cytoplasmic processes and infoldings, the ruffled border, is known to be the active site of bone resorption. Surrounding the ruffled border, a second region, the clear zone provides an area of close attachment to the mineralized bone surface. The osteoclasts secrete a large amount of protons by the action of H(+)-pump on the ruffled border into the sealed resorption cavity, resulting in the acidified microenvironment under which condition the bone matrix is dissolved. Protons are provided by the intracellular action of carbonic anhydrase. Following the secretion of the protons, several ion-transporting systems, i.e., carbonate-chloride exchanger, chloride-channel, Ca(2+)-transport systems, Na+/K(+)-ATPase, and voltage-dependent Ca(2+)-channel, are sequentially operated on both apical and basolateral cytoplasmic membranes. In addition, osteoclasts contain a large amount of lysosomal enzymes (cathepsin C, beta-glycerophosphatase, beta-glucuronidase, etc.), which contribute to degrade the bone organic matrices exposed in the resorption cavity. These enzymes bind to the mannose-6-phosphate receptor on Golgi apparatus, are transported to the ruffled border and are secreted into the extracellular compartment in an exocytotic manner. Osteoclasts also have a high tartrate-resistant acid phosphatase activity which is currently used as a marker enzyme osteoclastic differentiation. Osteoclasts are considered to develop from hematopoietic stem cells. So far, the following four different pathways of the differentiation of osteoclast are proposed: The precursors of osteoclast develop (1) from multilineage hematopoietic cells via a completely separate differentiation line, (2) from granulocyte macrophage-colony forming cells, (3) from committed but proliferative monocyte-macrophage, and (4) from mature and unproliferative monocyte-macrophage. However, the differentiation line of the osteoclasts has still to be elucidated. The formation of osteoclasts as well as that of other hematopoietic cells is strongly regulated by many cytokines [interleukin (IL)-1,IL-3,IL-6, M-colony stimulating factor (CSF), and GM-CSF]. 1,25-Dihydroxyvitamin D3 and parathyroid hormone also stimulate the differentiation of osteoclast precursors. However, the mature osteoclasts do not possess the receptors for these hormones.(ABSTRACT TRUNCATED AT 400 WORDS)
 ...
PMID:[Osteoclasts in bone metabolism]. 175 56

Endogenous and exogenous phosphomannosyl ligands inhibit binding of insulin-like growth factor-II (IGF-II) to the IGF-II/mannose-6-phosphate receptor (IGF-II/Man-6-P receptor). In the present study, the mechanism of this antagonism was examined using a [125I]IGF-II cross-linking assay with disuccinimidyl suberate in cell membranes. Treatment with 5 mM Man-6-P enhanced [125I]IGF-II cross-linking to the receptor. The magnitude of the Man-6-P enhancement differed depending on the source of the membranes, ranging from a 30% increase in JEG-3 human choriocarcinoma up to a 560% increase in B16-F1 mouse melanoma. Man-6-P stimulated [125I]IGF-II-receptor cross-linking in H-35 hepatoma membranes by about 80%, even at concentrations of labeled IGF-II (greater than or equal to 10 nM) that nearly saturated the receptors. Thus, in addition to its effect on IGF-II-binding affinity, Man-6-P caused a 1.5- to 2-fold increase in cross-linking efficiency within the IGF-II-receptor complex. Furthermore, Man-6-P enhanced [125I]IGF-II cross-linking to the H-35 receptor by a constant (approximately 80%) increment 1) when the cross-linking reaction was conducted in buffers of different pH over the range 6.8-8.0, or 2) using cross-linking agents differing in spacer arm length from 6.4-16.1 A. Washing membranes before assay with either Man-6-P (pH 7.4) or 0.5 M NaCl (pH 4.5) reduced the subsequent Man-6-P enhancement of [125I]IGF-II-receptor cross-linking, suggesting that this phenomenon was actually due to displacement of inhibitory phosphomannosyl ligands bound endogenously to the Man-6-P sites of the receptor. In support of this hypothesis, Man-6-P produced a minimal (8-14%) enhancement of [125I]IGF-II-receptor cross-linking in membranes from I-cell fibroblasts lacking such phosphomannosyl ligands. Thus, phosphomannosyl ligands bound to the IGF-II/Man-6-P receptor decrease both IGF-II-binding affinity and IGF-II-receptor cross-linking efficiency. Membrane-associated receptors appear to exist in experimentally and perhaps functionally distinct populations, depending on occupancy of the Man-6-P-binding sites.
 ...
PMID:Mannose-6-phosphate enhances cross-linking efficiency between insulin-like growth factor-II (IGF-II) and IGF-II/mannose-6-phosphate receptors in membranes. 184 7

Latent recombinant transforming growth factor-beta 2 (LrTGF-beta 2) complex has been purified from serum-free media conditioned by Chinese hamster ovary cells transfected with a plasmid encoding the TGF-beta 2 (414) precursor. Under neutral conditions, LrTGF-beta 2 had an apparent molecular weight of 130 kDa. The complex contained both mature and pro-region sequences. Acidification of LrTGF-beta 2 resulted in the release of mature 24 kDa TGF-beta 2 from the high molecular weight pro-region-containing complex, suggesting that TGF-beta 2 was non-covalently associated with this complex. These results were confirmed by crosslinking experiments performed on partially purified LrTGF-beta 2. Protein sequence analysis of the purified TGF-beta 2 pro-region indicated that signal peptide cleavage occurred between ser(20) and leu(21). The pro-region, which previously was found to contain mannose-6-phosphate, bound to the mannose-6-phosphate receptor. Proteolytic cleavage of mature TGF-beta 2 from pro-TGF-beta 2 was inhibited by monensin and chloroquine suggesting that binding to this receptor and subsequent transport to acidic vesicles may be involved in the processing of rTGF-beta 2 precursor.
 ...
PMID:Characterization of latent recombinant TGF-beta 2 produced by Chinese hamster ovary cells. 184 62

We have tried to characterize the intracellular compartments involved in the traffic of the thyroid prohormone thyroglobulin (Tg) from the site of storage, the follicular lumen, to the expected site(s) of proteolytic degradation, lysosomes. Electron microscope immunogold labeling with antibodies against Tg, cation-independent mannose-6-phosphate receptor (MPR), or arylsulfatase-A (ArS-A) was used to identify endocytic structures. The implication of these structures in the transport of Tg was analyzed by following the internalization and intracellular fate of Tg-colloidal gold complexes microinjected into the thyroid follicular lumen. Immunogold labeling was performed on ultrathin cryosections of intact pig tissue, in vitro reconstituted thyroid follicles (RTF), and isolated vesicles prepared by differential and isopycnic centrifugation. Microinjection experiments were carried out on RTF. Using double labeling for MPR and ArS-A, we characterized three types of structures: those slightly positive for MPR and ArS-A, those strongly positive for both markers, and those only positive for ArS-A. These compartments exhibited the properties of early endosomes (EE), late endosomes (LE), and lysosomes (L), respectively. Tg immunoreactivity was high in EE, low in LE, and undetectable in L. Similar morphological and immunochemical characteristics of EE, LE, and L were found in intact tissue, RTF, and isolated vesicles. Tg-gold complexes microinjected into the lumen of RTF were efficiently internalized within 5 min into structures with the appearance of EE. Sixty minutes after the injection, Tg-gold complexes were detected into LE and L. We present here the first direct experimental evidence for an involvement of endosomal compartments in the Tg internalization/degradation pathway. The data indicate that internalized Tg molecules are transported to EE and then transferred from EE to LE.
 ...
PMID:Thyroglobulin internalized by thyrocytes passes through early and late endosomes. 191 1

The mouse insulin-like growth factor II (IGF-II) gene encodes a polypeptide that plays a role in embryonic growth. We have examined the temporal and spatial pattern of expression of this gene in sections of the mouse conceptus between embryonic days 4.0 and 8.5 by in situ hybridization. Abundant IGF-II transcripts were detected in all the trophectodermal derivatives, after implantation. Labeling was then observed in primitive endoderm, but was transient and disappeared after formation of the yolk sac. Expression was next detected in extraembryonic mesoderm at the early primitive streak stage. Labeling in the embryo proper appeared first at the late primitive streak/neural plate stage in lateral mesoderm and in anterior-proximal cells located between the visceral endoderm and the most cranial region of the embryonic ectoderm. The position of the latter cells suggests that their descendants are likely to participate in the formation of the heart and the epithelium of the ventral and lateral walls of the foregut, where intense labeling was observed at the neural fold stage. Hybridization was also detected in cranial mesenchyme, including neural crest cells. The intensity of hybridization signal increased progressively in paraxial (presomitic and somitic) mesoderm, while declining in the ectoplacental cone. The neuroectoderm and surface ectoderm did not exhibit hybridization at any stage. Immunohistochemical analysis indicated co-localization of IGF-II transcripts, translated pre-pro-IGF-II, and the cognate IGF-II/mannose-6-phosphate receptor. These correlations are consistent with the hypothesis that IGF-II has an autocrine function.
 ...
PMID:Pattern of the insulin-like growth factor II gene expression during early mouse embryogenesis. 196 8

The interaction between late endocytic structures and microtubules in polarized cells was studied using a procedure previously shown to cause microtubule-dependent redistribution of lysosomes in fibroblasts and macrophages (Heuser, J. 1989. J. Cell Biol. 108:855-864). In cultured rat hippocampal neurons, low cytoplasmic pH caused cation-independent mannose-6-phosphate receptor-enriched structures to move out of the cell body and into the processes. In filter grown MDCK cells lowering the cytosolic pH to approximately 6.5 caused late endosomes to move to the base of the cell and this process was shown to be microtubule dependent. Alkalinization caused a shift in distribution towards the apical pole of the cell. The results are consistent with low pH causing the redistribution of late endosomes towards the plus ends of the microtubules. In MDCK cells the microtubules orientated vertically in the cell may play a role in this process. The shape changes that accompanied the redistribution of the late endosomes in MDCK cells were examined by electron microscopy. On low pH treatment fragmentation of the late endosomes was observed whereas after microtubule depolymerization individual late endosomal structures appeared to fuse together. The late endosomes of the MDCK cell appear to be highly pleomorphic and dependent on microtubules for their form and distribution in the cell.
 ...
PMID:pH-induced microtubule-dependent redistribution of late endosomes in neuronal and epithelial cells. 201 Apr 63

Data presented in the accompanying paper suggests nascent autophagic vacuoles are formed from RER (Dunn, W. A. 1990. J. Cell Biol. 110:1923-1933). In the present report, the maturation of newly formed or nascent autophagic vacuoles into degradative vacuoles was examined using morphological and biochemical methods combined with immunological probes. Within 15 min of formation, autophagic vacuoles acquired acid hydrolases and lysosomal membrane proteins, thus becoming degradative vacuoles. A previously undescribed type of autophagic vacuole was also identified having characteristics of both nascent and degradative vacuoles, but was different from lysosomes. This intermediate compartment contained only small amounts of cathepsin L in comparison to lysosomes and was bound by a double membrane, typical of nascent vacuoles. However, unlike nascent vacuoles vet comparable to degradative vacuoles, these vacuoles were acidic and contained the lysosomal membrane protein, lgp120, at the outer limiting membrane. The results were consistent with the stepwise acquisition of lysosomal membrane proteins and hydrolases. The presence of mannose-6-phosphate receptor in autophagic vacuoles suggested a possible role of this receptor in the delivery of newly synthesized hydrolases from the Golgi apparatus. However, tunicamycin had no significant effect on the amount of mature acid hydrolases present in a preparation of autophagic vacuoles isolated from a metrizamide gradient. Combined, the results suggested nascent autophagic vacuoles mature into degradative vacuoles in a stepwise fashion: (a) acquisition of lysosomal membrane proteins by fusing with a vesicle deficient in hydrolytic enzymes (e.g., prelysosome); (b) vacuole acidification; and (c) acquisition of hydrolases by fusing with preexisting lysosomes or Golgi apparatus-derived vesicles.
 ...
PMID:Studies on the mechanisms of autophagy: maturation of the autophagic vacuole. 216 53


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>