Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P11021 (BiP)
 2,049 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The membrane glycoproteins G1 and G2 of Uukuniemi virus, a member of the Bunyaviridae family, are cotranslationally cleaved from a common precursor in the endoplasmic reticulum (ER). Here, we show that newly made G1 and G2 associate transiently with calnexin and calreticulin, two lectins involved in glycoprotein folding in the ER. Stable complexes between G1-G2 and calnexin or calreticulin could be immunoprecipitated after solubilization of virus-infected BHK21 cells with the detergents digitonin or Triton X-100. In addition, G1-G2-calnexin complexes could be recovered after solubilization with CHAPS (3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate), while G1-G2-calreticulin complexes were not readily detected by using this detergent. Only endoglycosidase H-sensitive forms of G1 were found complexed with calnexin. Pulse-chase experiments showed that G1 and G2 associated with both chaperones transiently for up to 120 min. Sequential immunoprecipitations with anticalreticulin and anticalnexin antisera indicated that about 50% of newly synthesized G1 and G2 was associated with either calnexin or calreticulin. Our previous results have shown that newly synthesized G1 and G2 transiently interact also with the ER chaperone BiP and with protein disulfide isomerase (R. Persson and R. F. Pettersson, J. Cell Biol. 112:257-266, 1991). Taking all of this into consideration, we conclude that the folding of G1 and G2 in the ER is catalyzed by at least four different folding factors.
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PMID:Transient association of calnexin and calreticulin with newly synthesized G1 and G2 glycoproteins of uukuniemi virus (family Bunyaviridae). 1036 70

To identify proteins that interact with alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors, we carried out coimmunoprecipitation analyses on detergent-solubilized rat forebrain membranes. Membranes were solubilized with Triton X-100, and immunoprecipitation was done using subunit-specific antibodies to GluR1, GluR2/3, and GluR4 attached to protein Aagarose. Proteins bound to the antibodies were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by silver staining and western blotting. With solubilization in low ionic strength buffer, several coimmunoprecipitating proteins, with Mr = 17,000-100,000, were identified in silver-stained gels. Western blots were then probed with antibodies to a series of candidate proteins that were chosen based on the molecular masses of the copurifying proteins. Two of these were identified as the molecular chaperones calnexin (90 kDa) and the immunoglobulin binding protein (BiP; 78 kDa). Immunoprecipitation with antibodies to calnexin and BiP demonstrated that glycosylated AMPA receptor subunits were associated. The relationship between AMPA receptors and calnexin and BiP was further studied with immunocytochemistry of the hippocampus. Both calnexin and BiP labeling was present not only in the cell body but also in dendrites of hippocampal pyramidal neurons, where double-label immunofluorescence also showed the presence of AMPA receptor subunits.
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PMID:Calnexin and the immunoglobulin binding protein (BiP) coimmunoprecipitate with AMPA receptors. 1046 83

Sendai virus envelope glycoproteins, F and HN, mature during their transport through the endoplasmic reticulum (ER) and Golgi complex. To better understand their maturation processes in the ER, we investigated the time course of their interactions with three ER- resident molecular chaperones, BiP, calnexin (CNX), and calreticulin (CRT), in Sendai virus-infected HeLa cells. Pulse-chase and immunoprecipitation analyses using antibodies against each virus glycoprotein or ER chaperone revealed that F precursor interacted with CNX transiently (t(1/2)=8 min), while HN protein displayed longer and sequential interactions with BiP (t(1/2)=8 min), CNX (t(1/2)=15 min), and CRT (t(1/2)=20 min). HN interacted with the three ER chaperones not only as a monomer but also as a tetramer for several hours, suggesting mechanism(s) to undergo chaperone-mediated quality control of an assembled HN oligomer in the ER. The kinetics of dissociation of the HN-chaperone complexes exhibited a marked delay in the presence of proteasome inhibitors, suggesting that a part of HN associated with BiP, CNX, and CRT is destined to be degraded in the proteasome-dependent pathway. Further, the associations between virus glycoproteins and CNX or CRT were impaired by castanospermine, an inhibitor of ER glucosidase I and II, confirming that these interactions require monoglucosylated oligosaccharide on F(0) and HN peptides. These findings together suggest that newly synthesized F protein undergoes rapid maturation in the ER through a transient interaction with CNX, whereas HN protein requires more complex processes involving prolonged association with BiP, CNX, and CRT for its quality control in the ER.
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PMID:Kinetics of interactions of sendai virus envelope glycoproteins, F and HN, with endoplasmic reticulum-resident molecular chaperones, BiP, calnexin, and calreticulin. 1057 61

We are studying endoplasmic reticulum-associated degradation (ERAD) with the use of a truncated variant of the type I ER transmembrane glycoprotein ribophorin I (RI). The mutant protein, RI(332), containing only the N-terminal 332 amino acids of the luminal domain of RI, has been shown to interact with calnexin and to be a substrate for the ubiquitin-proteasome pathway. When RI(332) was expressed in HeLa cells, it was degraded with biphasic kinetics; an initial, slow phase of approximately 45 min was followed by a second phase of threefold accelerated degradation. On the other hand, the kinetics of degradation of a form of RI(332) in which the single used N-glycosylation consensus site had been removed (RI(332)-Thr) was monophasic and rapid, implying a role of the N-linked glycan in the first proteolytic phase. RI(332) degradation was enhanced when the binding of glycoproteins to calnexin was prevented. Moreover, the truncated glycoprotein interacted with calnexin preferentially during the first proteolytic phase, which strongly suggests that binding of RI(332) to the lectin-like protein may result in the slow, initial phase of degradation. Additionally, mannose trimming appears to be required for efficient proteolysis of RI(332). After treatment of cells with the inhibitor of N-glycosylation, tunicamycin, destruction of the truncated RI variants was severely inhibited; likewise, in cells preincubated with the calcium ionophore A23187, both RI(332) and RI(332)-Thr were stabilized, despite the presence or absence of the N-linked glycan. On the other hand, both drugs are known to trigger the unfolded protein response (UPR), resulting in the induction of BiP and other ER-resident proteins. Indeed, only in drug-treated cells could an interaction between BiP and RI(332) and RI(332)-Thr be detected. Induction of BiP was also evident after overexpression of murine Ire1, an ER transmembrane kinase known to play a central role in the UPR pathway; at the same time, stabilization of RI(332) was observed. Together, these results suggest that binding of the substrate proteins to UPR-induced chaperones affects their half lives.
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PMID:Degradation of a short-lived glycoprotein from the lumen of the endoplasmic reticulum: the role of N-linked glycans and the unfolded protein response. 1058 43

A variety of molecular chaperones and folding enzymes assist the folding of newly synthesized proteins in the endoplasmic reticulum. Here we investigated why some glycoproteins interact with the molecular chaperone BiP, and others with the calnexin/calreticulin pathway. The folding of Semliki forest virus glycoproteins and influenza hemagglutinin was studied in living cells. The initial choice of chaperone depended on the location of N-linked glycans in the growing nascent chain. Direct interaction with calnexin and calreticulin without prior interaction with BiP occurred if glycans were present within about 50 residues of the protein's NH2-terminus.
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PMID:Chaperone selection during glycoprotein translocation into the endoplasmic reticulum. 1076 45

We have established a mammalian semipermeabilized cell system that faithfully reconstitutes the proteasome-mediated degradation of major histocompatibility complex Class I heavy chain. We show that degradation required unfolding of the protein and was cytosol- and ATP-dependent and that dislocation and degradation required proteasome activity. When the interaction of heavy chain with calnexin was prevented, the rate of degradation was accelerated, suggesting that an interaction with calnexin stabilized heavy chain. Stabilization of heavy chain to degradation was also achieved either by preventing mannose trimming or by removal of the N-linked glycosylation site. This demonstrates that glycosylation and mannose trimming are required to ensure degradation of heavy chain. When degradation or mannose trimming was inhibited, heavy chain formed a prolonged interaction with immunoglobulin heavy chain binding protein, ERp57, and protein disulfide isomerase. Taken together, these results indicate that calnexin association and mannose trimming provide a mechanism to regulate the folding, assembly, and degradation of glycoproteins entering the secretory pathway.
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PMID:Pivotal role of calnexin and mannose trimming in regulating the endoplasmic reticulum-associated degradation of major histocompatibility complex class I heavy chain. 1080 90

In this report we describe the molecular defect underlying partial and severe quantitative von Willebrand factor (VWF) deficiencies in 3 families previously diagnosed with types 1 and 3 Von Willebrand-disease. Analysis of the VWF gene in affected family members revealed a novel C to T transition at nucleotide 1067 of the VWF complemetary DNA (cDNA), predicting substitution of arginine by tryptophan at amino acid position 273 (R273W) of pre-pro-VWF. Two patients, homozygous for the R273W mutation, had a partial VWF deficiency (VWF:Ag levels of 0.06 IU/mL and 0.09 IU/mL) and lacked high-molecular weight VWF multimers in plasma. A third patient, also homozygous for the R273W mutation, had a severe VWF deficiency (VWF:Ag level of less than 0.01 IU/mL) and undetectable VWF multimers in plasma. Recombinant VWF having the R273W mutation was expressed in COS-7 cells. Pulse-chase experiments showed that secretion of rVWFR273W was severely impaired compared with wild-type rVWF. However, the mutation did not affect the ability of VWF to form dimers in the endoplasmic reticulum (ER). Multimer analysis showed that rVWFR273W failed to form high-molecular-weight multimers present in wild-type rVWF. We concluded that the R273W mutation is responsible for the quantitative VWF deficiencies and aberrant multimer patterns observed in the affected family members. To identify factors that may function in the intracellular retention of rVWFR273W, we investigated the interactions of VWF expressed in COS-7 cells with molecular chaperones of the ER. The R273W mutation did not affect the ability of VWF to bind to BiP, Grp94, ERp72, calnexin, and calreticulin in COS-7 cells. (Blood. 2000;96:560-568)
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PMID:A novel von Willebrand disease-causing mutation (Arg273Trp) in the von Willebrand factor propeptide that results in defective multimerization and secretion. 1088 19

In this study we have explored the endoplasmic reticulum associated events accompanying the maturation of the tyrosinase-related protein-1 (TRP-1) nascent chain synthesized in mouse melanoma cells. We show that TRP-1 folding process occurs much more rapidly than for tyrosinase, a highly homologous protein, being completed post-translationally by the formation of critical disulfide bonds. In cells pretreated with dithiothreitol (DTT), unfolded TRP-1 is retained in the endoplasmic reticulum by a prolonged interaction with calnexin and BiP before being targeted for degradation. The TRP-1 chain was able to fold into DTT-resistant conformations both in the presence or absence of alpha-glucosidase inhibitors, but folding occurred through different pathways. During the normal folding pathway, TRP-1 interacts with calnexin. In the presence of alpha-glucosidase inhibitors, the interaction with calnexin is prevented, with TRP-1 folding being assisted by BiP. In this case, the process has similar kinetics to that of untreated TRP-1 and yields a compact form insensitive to DTT as well. However, this form has different thermal denaturation properties than the native conformation. We conclude that disulfide bridge burring is crucial for the TRP-1 export. This suggests that although various folding pathways may complete this process, the native form may be acquired only through the normal unperturbed pathway.
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PMID:Folding and maturation of tyrosinase-related protein-1 are regulated by the post-translational formation of disulfide bonds and by N-glycan processing. 1091 99

Respiratory syncytial virus (RSV) infection induced programmed cell death or apoptosis in the cultured lung epithelial cell line, A549. The apoptotic cells underwent multiple changes, including fragmentation and degradation of genomic DNA, consistent with the activation of the DNA fragmentation factor or caspase-activated DNase (DFF or CAD). The infection led to activation of FasL; however, a transdominant mutant of FAS-downstream death domain protein, FADD, did not inhibit apoptosis. Similarly, modest activation of cytoplasmic apoptotic caspases, caspase-3 and -8, were observed; however, only a specific inhibitor of caspases-3 inhibited apoptosis, while an inhibitor of caspase-8 had little effect. No activation of caspase-9 and -10, indicators of the mitochondrial apoptotic pathway, was observed. In contrast, RSV infection strongly activated caspase-12, an endoplasmic reticulum (ER) stress response caspase. Activation of the ER stress response was further evidenced by upregulation of ER chaperones BiP and calnexin. Antisense-mediated inhibition of caspase-12 inhibited apoptosis. Inhibitors of NF-kappa B had no effect on apoptosis. Thus, RSV-induced apoptosis appears to occur through an ER stress response that activates caspase-12, and is uncoupled from NF-kappa B activation.
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PMID:An endoplasmic reticulum-specific stress-activated caspase (caspase-12) is implicated in the apoptosis of A549 epithelial cells by respiratory syncytial virus. 1113 74

Degradation of proteins that, because of improper or suboptimal processing, are retained in the endoplasmic reticulum (ER) involves retrotranslocation to reach the cytosolic ubiquitin-proteasome machinery. We found that substrates of this pathway, the precursor of human asialoglycoprotein receptor H2a and free heavy chains of murine class I major histocompatibility complex (MHC), accumulate in a novel preGolgi compartment that is adjacent to but not overlapping with the centrosome, the Golgi complex, and the ER-to-Golgi intermediate compartment (ERGIC). On its way to degradation, H2a associated increasingly after synthesis with the ER translocon Sec61. Nevertheless, it remained in the secretory pathway upon proteasomal inhibition, suggesting that its retrotranslocation must be tightly coupled to the degradation process. In the presence of proteasomal inhibitors, the ER chaperones calreticulin and calnexin, but not BiP, PDI, or glycoprotein glucosyltransferase, concentrate in the subcellular region of the novel compartment. The "quality control" compartment is possibly a subcompartment of the ER. It depends on microtubules but is insensitive to brefeldin A. We discuss the possibility that it is also the site for concentration and retrotranslocation of proteins that, like the mutant cystic fibrosis transmembrane conductance regulator, are transported to the cytosol, where they form large aggregates, the "aggresomes."
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PMID:A novel quality control compartment derived from the endoplasmic reticulum. 1140 79


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