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 serotonin transporter (SERT) is an N-glycosylated integral membrane protein that is predicted to contain 12 transmembrane regions. SERT is the major binding site in the brain for antidepressant drugs, and it also binds amphetamines and cocaine. The ability of various molecular chaperones to interact with a tagged version of SERT (Myc-SERT) was investigated using the baculovirus expression system. Overexpression of Myc-SERT using the baculovirus system led to substantial quantities of inactive transporter, together with small amounts of fully active and, therefore, correctly folded molecules. The high levels of inactive Myc-SERT probably arose because folding was rate-limiting due, perhaps, to insufficient molecular chaperones. Therefore, Myc-SERT was co-expressed with the endoplasmic reticulum (ER) molecular chaperones calnexin, calreticulin and immunoglobulin heavy chain binding protein (BiP), and the foldase, ERp57. The expression of functional Myc-SERT, as determined by an inhibitor binding assay, was enhanced nearly 3-fold by co-expressing calnexin, and to a lesser degree on co-expression of calreticulin and BiP. Co-expression of ERp57 did not increase the functional expression of Myc-SERT. A physical interaction between Myc-SERT-calnexin and Myc-SERT-calreticulin was demonstrated by co-immunoprecipitation. These associations were inhibited in vivo by deoxynojirimycin, an inhibitor of N-glycan precusor trimming that is known to prevent the calnexin/calreticulin-N-glycan interaction. Functional expression of the unglycosylated SERT mutant, SERT-QQ, was also increased on co-expression of calnexin, suggesting that the interaction between calnexin and SERT is not entirely dictated by the N-glycan. SERT is the first member of the neurotransmitter transporter family whose folding has been shown to be assisted by the molecular chaperones calnexin, calreticulin, and BiP.
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PMID:Molecular chaperones stimulate the functional expression of the cocaine-sensitive serotonin transporter. 1036 89

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

Glucose-regulated protein 58 (GRP58/ER-60/ERp57), best known as a chaperone in the endoplasmic reticulum lumen, was previously identified by us as one of several accessory proteins in the S100 cytosol fraction of human hepatoma Hep3B cells that was differentially coshifted by anti-Stat3 antibody in an antibody-subtracted differential protein display assay. In the present study, the association between GRP58 and Stat3 in different cytoplasmic compartments was evaluated using cross-immunoprecipitation and cell-fractionation techniques. In the S100 cytosol fraction, three different anti-GRP58 polyclonal antibodies (pAb) cross-immunoprecipitated Stat3 (but not Stat1), and, conversely, anti-Stat3 pAb cross-immunoprecipitated GRP58. Both cytosolic Stat3 and GRP58 eluted during Superose-6 gel-filtration chromatography in complexes of size 200-400 kDa (statosome I), and anti-Stat3 pAb cross-immunoprecipitated GRp58 from these FPLC elution fractions. Using differential sedimentation and density equilibrium flotation methods, Stat3 and GRP58 were observed to be coassociated with cytoplasmic membranes enriched for the plasma membrane marker 5' nucleotidase but not with those containing the endoplasmic reticulum marker BiP/GRP78. The Stat3 and GRP58-containing plasma membrane fraction also contained Stat1, Stat5b, and gp130. Stat activation by orthovanadate caused the accumulation of PY-Stat3 in the GRP58-containing plasma membrane fraction. However, this PY-Stat3 was DNA-binding deficient. Likewise, excess exogenous recombinant human GRP58 prepared using a baculovirus expression system preferentially inhibited Stat3 DNA-binding activity in the S100 cytosol, suggesting that GRP58 may sequester activated Stat3. The new data confirm the association between GRP58 and Stat3 in cytosolic 200-400-kDa statosome I complexes and show that both GRP58 and Stat family members coassociate in the plasma membrane compartment. We suggest that the chaperone GRP58 may regulate signaling by sequestering inactive and activated Stat3.
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PMID:Association of the chaperone glucose-regulated protein 58 (GRP58/ER-60/ERp57) with Stat3 in cytosol and plasma membrane complexes. 1206 Apr 94

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

FrCas(E) is a mouse retrovirus that causes a fatal noninflammatory spongiform neurodegenerative disease with pathological features strikingly similar to those induced by transmissible spongiform encephalopathy (TSE) agents. Neurovirulence is determined by the sequence of the viral envelope protein, though the specific role of this protein in disease pathogenesis is not known. In the present study, we compared host gene expression in the brain stems of mice infected with either FrCas(E) or the avirulent virus F43, differing from FrCas(E) in the sequence of the envelope gene. Four of the 12 disease-specific transcripts up-regulated during the preclinical period represent responses linked to the accumulation of unfolded proteins in the endoplasmic reticulum (ER). Among these genes was CHOP/GADD153, which is induced in response to conditions that perturb endoplasmic reticulum function. In vitro studies with NIH 3T3 cells revealed up-regulation of CHOP as well as BiP, calreticulin, and Grp58/ERp57 in cells infected with FrCas(E) but not with F43. Immunoblot analysis of infected NIH 3T3 cells demonstrated the accumulation of uncleaved envelope precursor protein in FrCas(E)- but not F43-infected cells, consistent with ER retention. These results suggest that retrovirus-induced spongiform neurodegeneration represents a protein-folding disease and thus may provide a useful tool for exploring the causal link between protein misfolding and the cytopathology that it causes.
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PMID:Endoplasmic reticulum stress is a determinant of retrovirus-induced spongiform neurodegeneration. 1461 Jan 84

Most loss-of-function mutations of the glycoprotein hormone receptors have been found to be due to the misfolding of the receptor, resulting in its intracellular retention and, therefore, decreased cell surface expression. Chaperone proteins within the endoplasmic reticulum play an essential role in facilitating the folding of newly synthesized proteins and in recognizing and segregating misfolded proteins, thereby preventing their transit to the Golgi. The present study was conducted to begin to elucidate the role of chaperone proteins in the folding of the glycoprotein hormone receptors and misfolded mutants thereof. Toward this end, we examined the potential associations of calnexin, calreticulin, Grp94, BiP, ERp57, and protein disulfide-isomerase with each of the three glycoprotein hormone receptors. Calnexin, calreticulin, and protein disulfide-isomerase were found to associate with the immature forms of all three wild-type (wt) glycoprotein hormone receptors. As examples of misfolded glycoprotein hormone receptors, we studied two human LH receptor (hLHR) loss-of-function mutants that we show to be expressed predominantly as immature forms that are retained intracellularly. Significantly, the patterns of chaperone protein associations with the misfolded hLHR mutants differ from that observed with the wt hLHR. Furthermore, and unexpectedly, the chaperone protein associations were found to differ between the two misfolded hLHR mutants. Altogether, our studies show that although the same chaperone proteins are used by the three wt glycoprotein hormone receptors, different chaperone proteins associate with misfolded mutants thereof, and the specificity of interactions can vary between mutants, most likely reflecting the different stages of folding they achieve before being targeted for degradation.
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PMID:Intracellularly located misfolded glycoprotein hormone receptors associate with different chaperone proteins than their cognate wild-type receptors. 1510 36

Oxidation and folding of secretory proteins in the endoplasmic reticulum (ER) depends on the presence of chaperones and oxidoreductases. Two of the oxidoreductases present in the ER of mammalian cells are protein disulfide isomerase (PDI) and ERp57. In this study, we investigated the influence of ERp57 on the in vitro reoxidation and refolding of an antibody Fab fragment. Our results show that ERp57 shares functional properties with PDI and that both are clearly different from other oxidoreductases. The reactivation of the denatured and reduced Fab fragment was enhanced significantly in the presence of ERp57 with kinetics and redox dependence of the reactivation reaction comparable to those obtained for PDI. These properties were not influenced by the presence of calnexin. Furthermore, whereas PDI cooperates with the immunoglobulin heavy chain binding protein (BiP), no synergistic effect could be observed for BiP and ERp57. These results indicate that the cooperation of the two oxidoreductases with different partner proteins may explain their different roles in the folding of proteins in the ER.
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PMID:Influence of the oxidoreductase ER57 on the folding of an antibody fab fragment. 1532 18

The maturation of eukaryotic secretory cargo initiates cotranslationally and cotranslocationally as the polypeptide chain emerges into the endoplasmic reticulum lumen. Here, we characterized the cotranslational maturation pathway for the human type I membrane glycoprotein tyrosinase. To recapitulate the cotranslational events, including glycosylation, signal sequence cleavage, chaperone binding, and oxidation, abbreviated transcripts lacking a stop codon were in vitro translated in the presence of semipermeabilized melanocyte membranes. This created a series of ribosome/translocon-arrested chains of increasing lengths, simulating intermediates in the cotranslational folding process. Initially, nascent chains were found to associate with the heat shock protein (Hsp) 70 family member BiP. As the nascent chains elongated and additional glycans were transferred, BiP binding rapidly decreased and the lectin-based chaperone system was recruited in its place. The lectin chaperone calnexin bound to the nascent chain after the addition of two glycans, and calreticulin association followed upon the addition of a third. The glycan-specific oxidoreductase ERp57 was cross-linked to tyrosinase when calnexin and calreticulin were associated. This timing coincided with the formation of disulfide bonds within tyrosinase and the cleavage of its signal sequence. Therefore, tyrosinase maturation initiates cotranslationally with the Hsp70 system and is handed off to the lectin chaperone system that first uses calnexin before calreticulin. Interestingly, divergence in the maturation pathways of wild-type and mutant albino tyrosinase can already be observed for translocon-arrested nascent chains.
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PMID:The cotranslational maturation of the type I membrane glycoprotein tyrosinase: the heat shock protein 70 system hands off to the lectin-based chaperone system. 1595 86

We present the first identification of transient folding intermediates of endogenous thyroglobulin (Tg; a large homodimeric secretory glycoprotein of thyrocytes), which include mixed disulfides with endogenous oxidoreductases servicing Tg folding needs. Formation of disulfide-linked Tg adducts with endoplasmic reticulum (ER) oxidoreductases begins cotranslationally. Inhibition of ER glucosidase activity blocked formation of a subgroup of Tg adducts containing ERp57 while causing increased Tg adduct formation with protein disulfide isomerase (PDI), delayed adduct resolution, perturbed oxidative folding of Tg monomers, impaired Tg dimerization, increased Tg association with BiP/GRP78 and GRP94, activation of the unfolded protein response, increased ER-associated degradation of a subpopulation of Tg, partial Tg escape from ER quality control with increased secretion of free monomers, and decreased overall Tg secretion. These data point towards mixed disulfides with the ERp57 oxidoreductase in conjunction with calreticulin/calnexin chaperones acting as normal early Tg folding intermediates that can be "substituted" by PDI adducts only at the expense of lower folding efficiency with resultant ER stress.
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PMID:Mixed-disulfide folding intermediates between thyroglobulin and endoplasmic reticulum resident oxidoreductases ERp57 and protein disulfide isomerase. 1626 May 97

The endoplasmic reticulum (ER) chaperones are highly conserved proteins that catalyze the posttranslational processing of all secretory and membrane proteins. Our studies suggest that chaperone declines are one of the two central defects in Alzheimer's disease. We propose that similar declines in other organ systems underlie the physiological deficits of aging. Rats were maintained in a colony from age 21 days to death. Animals were killed at regular intervals, and hepatic, ER chaperone contents were determined by immunoblotting. ERp55, ERp57, ERp72, BiP, and calnexin constitutive levels declined 30%-50% with age. Calreticulin was unaffected. BiP (also known as GRP78), ERp55, and ERp57 showed marked swings with peaks occurring in midwinter and midsummer. This cyclics declined 73% with age. Considering the role of the ER chaperones in membrane and secretory protein posttranslational processing, these data support the concept that their loss could lead to many of the physiological declines associated with aging.
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PMID:The effect of aging on the chaperone concentrations in the hepatic, endoplasmic reticulum of male rats: the possible role of protein misfolding due to the loss of chaperones in the decline in physiological function seen with age. 1672 Jul 39


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