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 B cell antigen receptor (BCR) is comprised of four different polypeptides, immunoglobulin (Ig) heavy chain, Ig light chain, and the two signaling subunits of this receptor, Ig-alpha and Ig-beta. These four chains must assemble correctly in the endoplasmic reticulum (ER) before the BCR can be transported to the cell surface. The roles of the different chaperone proteins in mediating the assembly of mIg with the Ig-alpha/beta are not fully understood. To gain insights into the roles of chaperone proteins in BCR assembly, we have generated transfected non-lymphoid cell lines that express various intermediate assembled forms of the BCR and used them to examine the interactions of chaperone proteins with subunits of the BCR. We examined the interactions of BiP (GRP78), GRP94 and calnexin with the mu heavy chain, lambda light chain, Ig-alpha and Ig-beta. We report for the first time that Ig-alpha associates with GRP94 and that this interaction increases dramatically when other BCR chains are co-expressed. In contrast, the mu heavy chain interacts strongly with BiP (GRP78) when expressed by itself but this interaction is reduced when the lambda light chain is expressed, with the resulting mu(lambda) complexes interacting with GRP94 and calnexin. Thus, our data are consistent with the idea that there is an ordered association of BCR components with different protein chaperones during BCR assembly.
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PMID:Association of B lymphocyte antigen receptor polypeptides with multiple chaperone proteins. 1157 89

The hepatitis C virus (HCV) envelope proteins, E1 and E2, form noncovalent heterodimers and are leading candidate antigens for a vaccine against HCV. Studies in mammalian cell expression systems have focused primarily on E2 and its folding, whereas knowledge of E1 folding remains fragmentary. We used a cell-free in vitro translation system to study E1 folding and asked whether the flanking proteins, Core and E2, influence this process. We translated the polyprotein precursor, in which the Core is N-terminal to E1, and E2 is C-terminal, and found that when the core protein was present, oxidation of E1 was a slow, E2-independent process. The half-time for E1 oxidation was about 5 h in the presence or absence of E2. In contrast with previous reports, analysis of three constructs of different lengths revealed that the E2 glycoprotein undergoes slow oxidation as well. Unfolded or partially folded E1 bound to the endoplasmic reticulum chaperones calnexin and (with lower efficiency) calreticulin, whereas no binding to BiP/GRP78 or GRP94 could be detected. Release from calnexin and calreticulin was used to assess formation of mature E1. When E1 was expressed in the absence of Core and E2, its oxidation was impaired. We conclude that E1 folding is a process that is affected not only by E2, as previously shown, but also by the Core. The folding of viral proteins can thus depend on complex interactions between neighboring proteins within the polyprotein precursor.
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PMID:Folding of hepatitis C virus E1 glycoprotein in a cell-free system. 1160 60

Disruption of the calnexin gene in Saccharomyces cerevisiae did not lead to gross effects on the levels of cell growth and secretion of wild-type hen egg white lysozymes (HEWL). To investigate the function of calnexin in relation to the secretion of glycoproteins, we expressed both stable and unstable mutant glycosylated lysozymes in calnexin-disrupted S. cerevisiae. The secreted amounts of stable mutant glycosylated lysozymes (G49N and S91T/G49N) were almost the same in both wild-type and calnexin-disrupted S. cerevisiae. In contrast, the secretion of unstable mutant glycosylated lysozymes (K13D/G49N, C76A/G49N, and D66H/G49N) greatly increased in calnexin-disrupted S. cerevisiae, although their secretion was very low in the wild-type strain. This indicates that calnexin may act in the quality control of glycoproteins. We further investigated the expression level of the mRNA of the molecular chaperones BiP and PDI, which play a major role in the protein folding process in the ER, when glycosylated lysozymes were expressed in wild-type and calnexin-disrupted S. cerevisiae. The mRNA concentrations of BiP and PDI were evidently increased when the glycosylated lysozymes were expressed in calnexin-disrupted S. cerevisiae. This observation indicates that BiP and PDI may be induced by the accumulation of unfolded glycosylated lysozymes due to the deletion of calnexin.
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PMID:Effects of calnexin deletion in Saccharomyces cerevisiae on the secretion of glycosylated lysozymes. 1172 75

The maturation of lipoprotein lipase (LPL) into a catalytically active enzyme was believed to occur only after its transport from the endoplasmic reticulum (ER) to the Golgi apparatus. To test this hypothesis, LPL located in these two subcellular compartments was separated and compared. Heparin affinity chromatography resolved low affinity, inactive LPL displaying ER characteristics from a high affinity, active fraction exhibiting both ER and Golgi forms. The latter forms were further separated by beta-ricin chromatography and were found to have comparable activities per unit of LPL mass. Thus, LPL must reach a functional conformation in the ER. Active LPL, regardless of its cellular location, exhibited the expected dimer conformation. However, inactive LPL, found only in the ER, was highly aggregated. Kinetic analysis indicated a concurrent formation of LPL dimer and aggregate and indicated that the two forms have dissimilar fates. Whereas the dimer remained stable even when confined to the ER, the aggregate was degraded. Degradation rates were not affected by proteasomal or lysosomal inhibitors but were markedly reduced by ATP depletion. Lowering the redox potential in the ER by dithiothreitol caused the dimer to associate with calnexin, BiP, and protein-disulfide isomerase to form large, inactive complexes; dithiothreitol removal induced complex dissociation with restoration of the functional LPL dimer. In contrast, the LPL aggregate was only poorly associated with ER chaperones, appearing to be trapped in an irreversible, inactive conformation destined for ER degradation.
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PMID:Maturation of lipoprotein lipase in the endoplasmic reticulum. Concurrent formation of functional dimers and inactive aggregates. 3142 May 23

Both glycosylated amyloidogenic lysozymes I55T/G49N and D66H/G49N were expressed in wild-type and calnexin-disrupted Saccharomyces cerevisiae. The secretion amounts of mutant I55T/G49N were almost similar in both wild-type and calnexin-disrupted S. cerevisiae. In contrast, the secretion of mutant D66H/G49N greatly increased in calnexin-disrupted S. cerevisiae, while the secretion was very low in the wild-type strain. In parallel, the induction level of the molecular chaperones BiP and PDI located in the endoplasmic reticulum (ER) was investigated when these glycosylated amyloidogenic lysozymes were expressed in wild-type and calnexin-disrupted S. cerevisiae. The mRNA concentrations of BiP and PDI were evidently increased when mutant lysozyme D66H/G49N was expressed in calnexin-disrupted S. cerevisiae, while they were not so increased when I55T/G49N mutant was expressed. This observation indicates that the conformation of mutant lysozyme D66H/G49N was less stable in the ER, thus leading to the higher-level expression of ER molecular chaperones via the unfolded protein response pathway. This suggests that glycosylated amyloidogenic lysozyme I55T/G49N may have a relatively stable conformation in the ER, thus releasing it from the quality control of calnexin compared with mutant lysozyme D66H/G49N.
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PMID:Different effects of calnexin deletion in Saccharomyces cerevisiae on the secretion of two glycosylated amyloidogenic lysozymes. 1185 82

Folding and post-translational modification of the thyroid hormone precursor, thyroglobulin (Tg), in the endoplasmic reticulum (ER) of the thyroid epithelial cells is facilitated by several molecular chaperones and folding enzymes, such as BiP, GRP94, calnexin, protein disulfide isomerase, ERp72, and others. They have been shown to associate simultaneously and/or sequentially with Tg in the course of its maturation, thus forming large heterocomplexes in the ER of thyrocytes. Here we present evidence that such complexes include a novel member, an ER-resident lumenal protein, ERp29, which is present in all mammalian tissues with exceptionally high levels of expression in the secretory cells. ERp29 was induced upon treatment of FRTL-5 rat thyrocytes with the thyroid-stimulating hormone, which is essential for the maintenance of thyroid cells and Tg biosynthesis. Chemical cross-linking followed by the cell lysis and immunoprecipitation of ERp29 or Tg revealed association of these proteins and additionally, immunocomplexes that also included major ER chaperones, BiP and GRP94. Sucrose density gradient analysis indicated co-localization of ERp29 with Tg and BiP in the fractions containing large macromolecular complexes. This was supported by immunofluorescent microscopy showing co-localization of ERp29 with Tg in the putative transport vesicular structures. Affinity chromatography using Tg as an affinity ligand demonstrated that ERp29 might be selectively isolated from the FRTL-5 cell lysate or purified lumenal fraction of rat liver microsomes along with the other ER chaperones. Preferential association with the urea-denatured Tg-Sepharose was indicative of either direct or circuitous ERp29/Tg interactions in a chaperone-like manner. Despite the presence of the C-terminal ER-retrieval signal, significant amounts of ERp29 were also recovered from the culture medium of stimulated thyrocytes, indicating ERp29 secretion. Based on these data, we suggest that the function of ERp29 in thyroid cells is connected with folding and/or secretion of Tg.
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PMID:Identification of ERp29, an endoplasmic reticulum lumenal protein, as a new member of the thyroglobulin folding complex. 1188 2

Induction of differentiation of HL-60 human myeloid cells profoundly affected expression of calreticulin, a Ca(2+)-binding endoplasmic reticulum chaperone. Induction with Me(2)SO or retinoic acid reduced levels of calreticulin protein by approximately 60% within 4 days. Pulse-chase studies indicated that labeled calreticulin decayed at similar rates in differentiated and undifferentiated cells (t(12) approximately 4.6 days), but the biosynthetic rate was <10% of control after 4 days. Differentiation also induced a rapid decline in calreticulin mRNA levels (90% reduction after 1 day) without a decrease in transcript stability (t(12) approximately 5 h). Nuclear run-on analysis demonstrated rapid down-regulation of gene transcription (21% of control at 2 h). Differentiation also greatly reduced the Ca(2+) content of the cells (25% of control), although residual Ca(2+) pools remained sensitive to thapsigargin, ionomycin, and inositol trisphosphate. Progressive decreases were also observed in levels of calnexin and ERp57, whereas BiP/GRP78 and protein disulfide isomerase were only modestly affected. Ultrastructural studies showed a substantial reduction in endoplasmic reticulum content of the cells. Thus, terminal differentiation of myeloid cells was associated with decreased endoplasmic reticulum content, selective reductions in molecular chaperones, and diminished intracellular Ca(2+) stores, perhaps reflecting an endoplasmic reticulum remodeling program as a prominent feature of granulocytic differentiation.
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PMID:Regulation of calreticulin expression during induction of differentiation in human myeloid cells. Evidence for remodeling of the endoplasmic reticulum. 1206 1

Sixteen clones, recently isolated from the PC12 nerve cell line, were analysed for a variety of markers and activities. Two endoplasmic reticulum (ER) luminal markers, the chaperone protein BiP and the major Ca2+ storage protein calreticulin, as well as the 40-kD rough ER membrane marker and the plus-end-directed mirotubule motor protein, kinesin, were found to be expressed at similar levels. These results suggest that the size of the ER, the function of microtubules and the capacity of the rapidly exchanging Ca2+ store do not change substantially among the clones. Other proteins expressed at comparable levels were synapsin I and IIa, members of a nerve cell-specific protein family known to bind synaptic vesicles to the cytoskeleton. In contrast, another ER membrane protein, calnexin, and the markers of secretory organelles were found to vary markedly. One clone (clone 27) completely lacked both chromogranin B and secretogranin II, the proteins contained within dense granules, and synaptophysin, a marker of clear vesicles. Other clones expressed these markers to variable and apparently mutually unrelated levels. Marked variability was observed also in the uptake of exogenous catecholamines, in their release both at rest and after stimulation, and in nerve growth factor-induced differentiation. These results provide indirect information about the mechanisms that regulate the expression of structures and activities in PC12 cells. Of particular interest is clone 27, which appears globally incompetent for regulated secretion and might therefore be a valuable tool for the study of this activity in a nerve cell.
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PMID:Differential Expression of Markers and Activities in a Group of PC12 Nerve Cell Clones. 1210 30

BACE457 is a recently identified pancreatic isoform of human beta-secretase. We report that this membrane glycoprotein and its soluble variant are characterized by inefficient folding in the ER, leading to proteasome-mediated ER-associated degradation (ERAD). Dissection of the degradation process revealed that upon release from calnexin, extensively oxidized BACE457 transiently entered in disulfide-bonded complexes associated with the lumenal chaperones BiP and protein disulfide isomerase (PDI) before unfolding and dislocation into the cytosol for degradation. BACE457 and its lumenal variant accumulated in disulfide-bonded complexes, in the ER lumen, also when protein degradation was inhibited. The complexes were disassembled and the misfolded polypeptides were cleared from the ER upon reactivation of the degradation machinery. Our data offer new insights into the mechanism of ERAD by showing a sequential involvement of the calnexin and BiP/PDI chaperone systems. We report the unexpected transient formation of covalent complexes in the ER lumen during the ERAD process, and we show that PDI participates as an oxidoreductase and a redox-driven chaperone in the preparation of proteins for degradation from the mammalian ER.
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PMID:Sequential assistance of molecular chaperones and transient formation of covalent complexes during protein degradation from the ER. 1211 63

Schwann cell-derived peripheral myelin protein-22 (PMP-22) when mutated or overexpressed causes heritable neuropathies with a previously unexplained "gain-of-function" endoplasmic reticulum (ER) retention phenotype. In wild-type sciatic nerves, PMP-22 associates in a specific, transient (t(1/2 ) approximately equal to 11 min), and oligosaccharide processing-dependent manner with the lectin chaperone calnexin (CNX), but not calreticulin nor BiP. In Trembler-J (Tr-J) sciatic nerves, prolonged association of mutant PMP-22 with CNX is found (t(1/2) > 60 min). In 293A cells overexpressing PMP-22(Tr-J), CNX and PMP-22 colocalize in large intracellular structures identified at the electron microscopy level as myelin-like figures with CNX localization in the structures dependent on PMP-22 glucosylation. Similar intracellular myelin-like figures were also present in Schwann cells of sciatic nerves from homozygous Trembler-J mice with no detectable activation of the stress response pathway as deduced from BiP and CHOP expression. Sequestration of CNX in intracellular myelin-like figures may be relevant to the autosomal dominant Charcot-Marie-Tooth-related neuropathies.
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PMID:Association of calnexin with mutant peripheral myelin protein-22 ex vivo: a basis for "gain-of-function" ER diseases. 1211 18


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