Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.1.4.3 (phospholipase C)
18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The prion protein (PrP) gene on chromosome 20 encodes a protein designated PrPC. An abnormal, protease-resistant isoform of PrPC, denoted PrPCJD or PrPSc, is present in the brains of patients with Creutzfeldt-Jakob disease (CJD). In Libyan Jews, CJD segregates with a point mutation at codon 200 of the PrP gene, resulting in the substitution of lysine for glutamate. In the present study, we examined the presence of PrP in fibroblasts and leukocytes derived from eight CJD patients with the codon 200 mutation. In cultured fibroblasts as well as in leukocytes, there was a significant increase in PrP as judged by immunocytochemistry in addition to immunoblotting. Most of the PrP in fibroblasts and leukocytes could be released from the external surface by phosphatidylinositol-specific phospholipase C, a property characteristic of PrPC. In leukocytes only, part of the protein was protease resistant, resembling PrPCJD. The concentration of PrP mRNA was similar in fibroblast lines derived from controls and CJD patients. These results suggest that in CJD patients carrying a mutation at codon 200 of the PrP gene, the metabolism of PrP, rather than PrP synthesis, is abnormal.
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PMID:Presence of prion protein in peripheral tissues of Libyan Jews with Creutzfeldt-Jakob disease. 841 96

Infectious scrapie prions are composed largely, if not entirely, of an abnormal isoform of the prion protein (PrP) which is designated PrPSc. A chromosomal gene encodes both the cellular prion protein (PrPC) as well as PrPSc. Pulse-chase experiments with scrapie-infected cultured cells indicate that PrPSc is formed by a post-translational process. PrP is translated in the endoplasmic reticulum, modified as it passes through the Golgi, and is transported to the cell surface. Release of nascent PrP from the cell surface by phosphatidylinositol-specific phospholipase C or hydrolysis with dispase prevented PrPSc synthesis. At 18 degrees C, the synthesis of PrPSc was inhibited under conditions that other investigators report a blockage of endosomal fusion with lysosomes. Our results suggest that PrPSc synthesis occurs after PrP transits from the cell surface. Whether all of the PrP molecules have an equal likelihood to be converted into PrPSc or only a distinct subset is eligible for conversion remains to be established. Identifying the subcellular compartment(s) of PrPSc synthesis should be of considerable importance in defining the molecular changes that distinguish PrPSc from PrPC.
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PMID:Evidence for synthesis of scrapie prion proteins in the endocytic pathway. 135 61

The cellular prion protein (PrPC) is a sialoglycoprotein anchored to the external surface of cells by a glycosyl phosphatidylinositol moiety. During scrapie, an abnormal PrP isoform designated PrPSc accumulates, and much evidence argues that it is a major and necessary component of the infectious prion. Based on the resistance of native PrPSc to proteolysis and to digestion with phosphatidylinositol-specific phospholipase C as well as the enhancement of PrPSc immunoreactivity after denaturation, we devised in situ immunoassays for the detection of PrPSc in cultured cells. Using these immunoassays, we identified the sites of PrPSc accumulation in scrapie-infected cultured cells. We also used these immunoassays to isolate PrPSc-producing clones from a new hamster brain cell line (HaB) and found an excellent correlation between their PrPSc content and prion infectivity titers. In scrapie-infected HaB cells as well as in scrapie-infected mouse neuroblastoma cells, most PrPSc was found to be intracellular and most localized with ligands of the Golgi marker wheat germ agglutinin. In one scrapie-infected HaB clone, PrPSc also localized extensively with MG-160, a protein resident of the medial-Golgi stack whereas this colocalization was not observed in another subclone of these cells. Whether the sites of intracellular accumulation of PrPSc are limited to a few subcellular organelles or they are highly variable remains to be determined. If the intracellular accumulation of PrPSc is found in the cells of the central nervous system, then it might be responsible for the neuronal dysfunction and degeneration which are cardinal features of prion diseases.
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PMID:Scrapie prion proteins accumulate in the cytoplasm of persistently infected cultured cells. 169 23

The cellular prion protein (PrPc) is a host-encoded sialoglycoprotein bound to the external surface of the cell membrane by a glycosyl phosphatidylinositol anchor. A posttranslationally modified PrP isoform (PrPSc) is a component of the infectious particle causing scrapie and the other prion diseases. mAb have been raised against the protease-resistant core of Syrian hamster (SHa) PrPSc designated PrP 27-30. To map the epitopes within PrP reacting to these antibodies, we have expressed wild-type, chimeric mouse (Mo)/SHa and mutant MoPrP genes using recombinant vaccinia virus systems. The fidelity of the expression of recombinant PrPC was examined using vaccinia viruses expressing SHa-PrPC. It is full length, possesses Asn-linked carbohydrates and is attached to the external surface of the cell membrane by a glycosyl phosphatidylinositol anchor that is sensitive to cleavage by phosphatidylinositol-specific phospholipase C. We have tested 18 mAb for their ability to bind to chimeric prion proteins on immunoblots. Three distinct epitopes were identified that mapped to amino acid differences between SHa and MoPrP sequences. The first epitope, recognized by three of the antibodies tested, was defined by methionines at amino acids 108 and 111 in the mouse protein. The second epitope was dependent upon the presence of asparagines at positions 154 and 174 in MoPrP and was recognized by four of the antibodies tested. The third epitope mapped to a single amino acid substitution at residue 138 in MoPrP. mAb raised against SHaPrP 27-30 specific for this epitope are able to bind MoPrPC which has a single amino acid change (Ile to Met) at position 138. Eleven of the 18 antibodies tested mapped to this immunodominant epitope. It is located within a postulated amphipathic helix, a structure associated with immunodominant Ag. Inasmuch as PrPC, in its native form on the cell surface, is detected by the mAb 13A5 (a prototypic antibody of the immunodominant third epitope class), it is likely that this epitope is accessible in the native conformation of this protein.
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PMID:Epitope mapping of the Syrian hamster prion protein utilizing chimeric and mutant genes in a vaccinia virus expression system. 171 82

Previous studies have indicated that scrapie infection results in the accumulation of a proteinase K-resistant form of an endogenous brain protein generally referred to as prion protein (PrP). The molecular nature of the scrapie-associated modification of PrP accounting for proteinase K resistance is not known. As an approach to understanding the cellular events associated with the PrP modification in brain tissue, we sought to identify proteinase K-resistant PrP (PrP-res) in scrapie-infected neuroblastoma cells in vitro and to compare properties of PrP-res with those of its normal proteinase K-sensitive homolog, PrP-sen. PrP-res was detected by immunoblot in scrapie-infected but not uninfected neuroblastoma clones. Densitometry of immunoblots indicated that there was two- to threefold more PrP-res than PrP-sen in one infected clone. Metabolic labeling and membrane immunofluorescence experiments indicated that PrP-sen was located on the cell surface and could be removed from intact cells by phosphatidylinositol-specific phospholipase C and proteases. In contrast, PrP-res was not removed after reaction with these enzymes. Thus, either the scrapie-associated PrP-res was not on the cell surface or it was there in a form that is resistant to these hydrolytic enzymes. Attempts to detect intracellular PrP-res by immunofluorescent staining of fixed and permeabilized cells revealed that PrP was present in discrete perinuclear Golgi-like structures. However, the staining pattern was similar in both scrapie-infected and uninfected clones, and thus the intracellular staining may have represented only PrP-sen. Analysis of scrapie infectivity in cells treated with extracellular phospholipase, proteinase K, and trypsin indicated that, like PrP-res, the scrapie agent was not removed from the infected cells by any of these enzymes.
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PMID:Normal and scrapie-associated forms of prion protein differ in their sensitivities to phospholipase and proteases in intact neuroblastoma cells. 196 4

Both the cellular and scrapie isoforms of the prion protein (PrP) designated PrPc and PrPSc are encoded by a single-copy chromosomal gene and appear to be translated from the same 2.1-kb mRNA. PrPC can be distinguished from PrPSc by limited proteolysis under conditions where PrPC is hydrolyzed and PrPSc is resistant. We report here that PrPC can be released from the surface of both normal-control and scrapie-infected murine neuroblastoma (N2a) cells by phosphatidylinositol-specific phospholipase C (PIPLC) digestion and it can be selectively labeled with sulfo-NHS-biotin, a membrane impermeant reagent. In contrast, PrPSc was neither released by PIPLC nor labeled with sulfo-NHS-biotin. Pulse-chase experiments showed that [35S]methionine was incorporated almost immediately into PrPC while incorporation into PrPSc molecules was observed only during the chase period. While PrPC is synthesized and degraded relatively rapidly (t1/2 approximately 5 h), PrPSc is synthesized slowly (t1/2 approximately 15 h) and appears to accumulate. These results are consistent with several observations previously made on rodent brains where PrP mRNA and PrPC levels did not change throughout the course of scrapie infection, yet PrPSc accumulated to levels exceeding that of PrPC. Our kinetic studies demonstrate that PrPSc is derived from a protease-sensitive precursor and that the acquisition of proteinase K resistance results from a posttranslational event. Whether or not prolonged incubation periods, which are a cardinal feature of prion diseases, reflect the slow synthesis of PrPSc remains to be established.
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PMID:Scrapie and cellular prion proteins differ in their kinetics of synthesis and topology in cultured cells. 196 66

Numerous studies have indicated that a modified proteinase K-resistant form of an endogenous brain protein, prion protein (PrP), is associated with scrapie infection in animals. This scrapie-associated PrP modification appears to occur posttranslationally in brain, but its molecular nature is not known. To learn about the normal PrP biosynthesis and whether it is altered by scrapie infection in vitro, we did metabolic labeling experiments with uninfected and scrapie-infected mouse neuroblastoma tissue culture cells. Pulse-chase labeling experiments indicated that, in both cell types, two major PrP precursors of 28 and 33 kilodaltons (kDa) were processed to mature 30- and 35- to 41-kDa forms. Endoglycosidase H, tunicamycin, and phospholipase treatments revealed that the 28- and 33-kDa precursors resulted from the addition of high-mannose glycans to a 25-kDa polypeptide containing a phosphatidylinositol moiety and that maturation of the precursors involved the conversion of the high-mannose glycans to hybrid or complex glycans. Treatments of the live cells with trypsin and phosphatidylinositol-specific phospholipase C indicated that the mature PrP species were expressed solely on the cell surface, where they were anchored by covalent linkage to phosphatidylinositol. Once on the cell surface, the major PrP forms had half-lives of 3 to 6 h. No differences in PrP biosynthesis were observed between the scrapie-infected versus uninfected neuroblastoma cells.
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PMID:Prion protein biosynthesis in scrapie-infected and uninfected neuroblastoma cells. 256 14

Secreted forms of the sialoglycoprotein designated cellular prion protein (PrPC) have been identified that cannot be explained by alternative splicing. We report that secreted forms of PrPC derive from precursors that are bound to the plasma membrane by glycoinositol phospholipid (GPI) anchors. Secreted PrPC slowly appeared in the culture medium of metabolically radiolabelled cells after incubations of 8-24 h. Digestion of nascent PrPC with phosphatidylinositol-specific phospholipase C (PIPLC) prevented the appearance of secreted PrPC. Secreted PrPC partitioned into the aqueous phase of Triton X-114 like PrpC-released PrPC. While the M(r) of PIPLC-released PrPC was reduced 2-4 kDa after treatment with aqueous hydroflouric acid, which removes the entire GPI anchor modification, the M(r) of secreted PrPC was unchanged. Both PIPLC-released and secreted PrPC were recognized by antiserum raised against a synthetic C-terminal peptide corresponding to residues 220-233 (amino acid 231 is the site of GPI attachment). We conclude that GPI-anchored PrPC is post-translationally processed to remove most, if not all, of the GPI modification and then shed into culture medium. Whether PrPC is shed after proteolysis near the C-terminus remains to be established. A minority of PrPC in normal Syrian hamster brain partitioned into the aqueous phase of Triton X-114 like shed PrPC, suggesting physiological significance.
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PMID:Release of the cellular prion protein from cultured cells after loss of its glycoinositol phospholipid anchor. 769 Dec 78

ChPrP is the chicken homologue of PrPC, the cellular isoform of the mammalian prion protein. We have used sequence-specific antibodies to immunoprecipitate and immunoblot chPrP derived from stably transfected cultures of neuroblastoma cells, as well as from chicken brain and cerebrospinal fluid. We have also used mass spectrometry to characterize fragments of the protein purified from conditioned medium. The majority of chPrP protein present in neuroblastoma cells and on isolated brain membranes can be released by incubation with phosphatidylinositol-specific phospholipase C, indicating that these molecules are attached to the cell surface by a glycosylphosphatidylinositol anchor. Surprisingly, most of the surface-anchored molecules are truncated at their N-terminus distal to the proline/glycine-rich repeats. The corresponding N-terminal fragments are found in medium conditioned by neuroblastoma cells, as well as in cerebrospinal fluid and a postmicrosomal supernatant of brain. One of these fragments extends from Lys25 to Phe116. 35-45-kDa forms of chPrP that can be metabolically labeled with [3H]ethanolamine can also be found in extracellular media. We propose that the chPrP molecule undergoes at least two cleavages as part of its normal metabolism: one within the glycosylphosphatidylinositol anchor and one within or just N-terminal to the central hydrophobic domain. The second cleavage lies within a region of 24 amino acids that is identical in chPrP and mammalian PrP, and represents a major processing event that may have physiological as well as pathological significance.
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PMID:Processing of a cellular prion protein: identification of N- and C-terminal cleavage sites. 809 41

Syrian hamster prion protein (PrPC) and a truncated Syrian hamster prion protein lacking the glycosylphosphatidylinositol (GPI) anchor C-terminal signal sequence (GPI-) were expressed in Chinese hamster ovary cells using a glutamine synthetase selection and amplification system. The CHO cell clones expressing the GPI- PrP secreted the majority of the protein into the media, whereas most of the PrP produced by clones expressing the full-length protein with the GPI anchor was located on the cell surface, as demonstrated by its release upon treatment with phosphatidylinositol-specific phospholipase C (PIPLC). A cell clone that expressed the highest levels of full length PrP was subcloned to obtain clone 30C3-1. PrP from clone 30C3-1 was shown to be sensitive to proteolysis by proteinase K and to react with monoclonal and polyclonal antibodies that recognize native PrPC. The recombinant PrP migrated as a diffuse band of 19-40 kDa but removal of the N-linked oligosaccharides with peptide N-glycosidase F (PNGase F) revealed three protein species of 19, 17 and 15 kDa. The 19 kDa band corresponding to deglycosylated full-length PrP was quantified and found to be expressed at a level approximately 14-fold higher than that of PrPC found in Syrian hamster brain.
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PMID:Prion protein expression in Chinese hamster ovary cells using a glutamine synthetase selection and amplification system. 954 9


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