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)

Halothane causes an idiosyncratic hepatitis that is thought to result, in part, from immune reactions against one or more lumenal endoplasmic reticulum (ER) proteins that have been covalently modified by the trifluoroacetyl chloride metabolite of halothane. In this study, we have identified a 170 kDa protein target of halothane in the liver of rats. The 170 kDa protein was first detected when proteins in lysates of hepatocytes from halothane-treated rats were immunoprecipitated with antisera against several resident ER proteins. This 170 kDa protein was found to be associated with other protein targets of halothane, including protein disulfide isomerase, a protein disulfide isomerase isoform, a 59 kDa carboxylesterase, and 78 kDa glucose-regulated protein. Immunoblotting with antiserum directed against the trifluoroacetylated hapten indicated that the 170 kDa protein was trifluoroacetylated. Based upon its subcellular localization, molecular mass, N-terminal amino acid sequence, and antigenicity, the trifluoroacetylated 170 kDa protein was identified as UDP-glucose:glycoprotein glucosyltransferase (UGGT), a lumenal ER protein that is thought to have a role in the folding of N-linked glycoproteins. Moreover, treatment of rats with halothane caused a 44% decrease in the activity of liver microsomal UGGT, and at least 36% of the change in the activity of the enzyme could be due to a decrease in the level of the protein. The results suggest that the function of UGGT in folding of N-linked glycoproteins may be affected by other resident ER proteins or xenobiotics such as halothane.
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PMID:UDP-glucose:glycoprotein glucosyltransferase associates with endoplasmic reticulum chaperones and its activity is decreased in vivo by the inhalation anesthetic halothane. 907 3

The proper folding of newly synthesized membrane proteins in the endoplasmic reticulum (ER) is required for the formation of functional mature proteins. Calnexin is a ubiquitous ER chaperone that plays a major role in quality control by retaining incompletely folded or misfolded proteins. In contrast to other known chaperones such as heat-shock proteins, BiP and calreticulin, calnexin is an integral membrane protein. Calmegin is a testis-specific ER protein that is homologous to calnexin. Here we show that calmegin binds to nascent polypeptides during spermatogenesis, and have analysed its physiological function by targeted disruption of its gene. Homozygous-null male mice are nearly sterile even though spermatogenesis is morphologically normal and mating is normal. In vitro, sperm from homozygous-null males do not adhere to the egg extracellular matrix (zona pellucida), and this defect may explain the observed infertility. These results suggest that calmegin functions as a chaperone for one or more sperm surface proteins that mediate the interactions between sperm and egg. The defective zona pellucida-adhesion phenotype of sperm from calmegin-deficient mice is reminiscent of certain cases of unexplained infertility in human males.
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PMID:The putative chaperone calmegin is required for sperm fertility. 917 49

Eukaryotes respond to the presence of unfolded protein in the endoplasmic reticulum (ER) by up-regulating the transcription of genes encoding ER protein chaperones, such as BiP. We have isolated a novel human cDNA encoding a homolog to Saccharomyces cerevisiae Ire1p, a proximal sensor for this signal transduction pathway in yeast. The gene product hIre1p is a type 1 transmembrane protein containing a cytoplasmic domain that is highly conserved to the yeast counterpart having a Ser/Thr protein kinase domain and a domain homologous to RNase L. However, the luminal domain has extensively diverged from the yeast gene product. hIre1p expressed in mammalian cells displayed intrinsic autophosphorylation activity and an endoribonuclease activity that cleaved the 5' splice site of yeast HAC1 mRNA, a substrate for the endoribonuclease activity of yeast Ire1p. Overexpressed hIre1p was localized to the ER with particular concentration around the nuclear envelope and some colocalization with the nuclear pore complex. Expression of Ire1p mRNA was autoregulated through a process that required a functional hIre1p kinase activity. Finally, overexpression of wild-type hIre1p constitutively activated a reporter gene under transcriptional control of the rat BiP promoter, whereas expression of a catalytically inactive hIre1p acted in a trans-dominant-negative manner to prevent transcriptional activation of the BiP promoter in response to ER stress induced by inhibition of N-linked glycosylation. These results demonstrate that hIre1p is an essential proximal sensor of the unfolded protein response pathway in mammalian cells.
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PMID:A stress response pathway from the endoplasmic reticulum to the nucleus requires a novel bifunctional protein kinase/endoribonuclease (Ire1p) in mammalian cells. 963 83

The role of GRP78/BiP in coordinating endoplasmic reticular (ER) protein processing with mRNA translation was examined in GH3 pituitary cells. ADP-ribosylation of GRP78 and eukaryotic initiation factor (eIF)-2alpha phosphorylation were assessed, respectively, as indices of chaperone inactivation and the inhibition of translational initiation. Inhibition of protein processing by ER stress (ionomycin and dithiothreitol) resulted in GRP78 deribosylation and eIF-2 phosphorylation. Suppression of translation relative to ER protein processing (cycloheximide) produced approximately 50% ADP-ribosylation of GRP78 within 90 min without eIF-2 phosphorylation. ADP-ribosylation was reversed in 90 min by cycloheximide removal in a manner accelerated by ER stressors. Cycloheximide sharply reduced eIF-2 phosphorylation in response to ER stressors for about 30 min; sensitivity returned as GRP78 became increasingly ADP-ribosylated. Reduced sensitivity of eIF-2 to phosphorylation appeared to derive from the accumulation of free, unmodified chaperone as proteins completed processing without replacements. Prolonged (24 h) incubations with cycloheximide resulted in the selective loss of the ADP-ribosylated form of GRP78 and increased sensitivity of eIF-2 phosphorylation in response to ER stressors. Brefeldin A decreased ADP-ribosylation of GRP78 in parallel with increased eIF-2 phosphorylation. The cytoplasmic stressor, arsenite, which inhibits translational initiation through eIF-2 phosphorylation without affecting the ER, also produced ADP-ribosylation of GRP78.
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PMID:The dynamic role of GRP78/BiP in the coordination of mRNA translation with protein processing. 986 69

The yeast SAR1 gene encodes a low-molecular-weight GTPase which is essential for the formation of transport vesicles from the endoplasmic reticulum (ER). To understand how the Sar1p function is regulated in its GTPase cycle, we searched for multicopy suppressors of sar1 temperature-sensitive mutants and identified SEC12, SED4, truncated SEC16, and EKS1. EKS1 turns out to be identical to HRD3, which was independently isolated as a gene implicated in the degradation of an HMG-CoA reductase isozyme, Hmg2p. In this paper, we show that the product of EKS1/HRD3 is a type-I transmembrane glycoprotein and resides in the ER. The eks1/hrd3 disrupted cells are normal in growth and transport of cargo proteins, but missecrete BiP (Kar2p). The overexpression of EKS1/HRD3, which stabilizes Hmg2p, did not affect the stability of wild-type or mutant Sar1p or any early Sec proteins we examined. These results suggest that the role of Eks1p/Hrd3p is not involved in the ER protein degradation in general but rather required for the maintenance of the ER membrane functions. The novel genetic interactions unveiled between SAR1, SEC12, SEC16, and SED4 will provide useful information as to how the complex machinery of vesicle budding operates.
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PMID:Identification of SEC12, SED4, truncated SEC16, and EKS1/HRD3 as multicopy suppressors of ts mutants of Sar1 GTPase. 988 Aug 8

Polypeptide import into the yeast endoplasmic reticulum (ER) requires two hsp70s, Ssa1p in the cytosol and BiP (Kar2p) in the ER lumen. After import, aberrant polypeptides may be exported to the cytoplasm for degradation by the proteasome, and defects in the ER chaperone calnexin (Cne1p) compromise their degradation. Both import and export require BiP and the Sec61p translocation complex, suggesting that import and export may be mechanistically related. We now show that the cne1Delta and two kar2 mutant alleles exhibit a synthetic interaction and that the export and degradation of pro-alpha factor is defective in kar2 mutant microsomes. Pulse-chase analysis indicates that A1PiZ, another substrate for degradation, is stabilized in the kar2 strains at the restrictive temperature. Because two of the kar2 mutants examined are proficient for polypeptide import, the roles of BiP during ER protein export and import differ, indicating that these processes must be mechanistically distinct. To examine whether Ssa1p drives polypeptides from the ER and is also required for degradation, we assembled reactions using strains either containing a mutation in SSA1 or in which the level of Ssa1p could be regulated. We found that pro-alpha factor and A1PiZ were degraded normally, indicating further that import and export are distinct and that other cytosolic factors may pull polypeptides from the ER.
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PMID:The requirement for molecular chaperones during endoplasmic reticulum-associated protein degradation demonstrates that protein export and import are mechanistically distinct. 992 Aug 90

Hyperhomocysteinemia, a risk factor for vascular disease, injures endothelial cells through undefined mechanisms. We previously identified several homocysteine-responsive genes in cultured human vascular endothelial cells, including the endoplasmic reticulum (ER)-resident molecular chaperone GRP78/BiP. Here, we demonstrate that homocysteine induces the ER stress response and leads to the expression of a novel protein, Herp, containing a ubiquitin-like domain at the N terminus. mRNA expression of Herp was strongly up-regulated by inducers of ER stress, including mercaptoethanol, tunicamycin, A23187, and thapsigargin. The ER stress-dependent induction of Herp was also observed at the protein level. Immunochemical analyses using Herp-specific antibodies indicated that Herp is a 54-kDa, membrane-associated ER protein. Herp is the first integral membrane protein regulated by the ER stress response pathway. Both the N and C termini face the cytoplasmic side of the ER; this membrane topology makes it unlikely that Herp acts as a molecular chaperone for proteins in the ER, in contrast to GRP78 and other ER stress-responsive proteins. Herp may, therefore, play an unknown role in the cellular survival response to stress.
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PMID:Herp, a new ubiquitin-like membrane protein induced by endoplasmic reticulum stress. 1092 62

Subcellular localization of cyclic nucleotide phosphodiesterases (PDEs) may be important in compartmentalization of cAMP/cGMP signaling responses. In 3T3-L1 adipocytes, mouse (M) PDE3B was associated with the endoplasmic reticulum (ER) as indicated by its immunofluorescent colocalization with the ER protein BiP and subcellular fractionation studies. In transfected NIH 3006 or COS-7 cells, recombinant wild-type PDE3A and PDE3B isoforms were both found almost exclusively in the ER. The N-terminal portion of PDE3 can be arbitrarily divided into region 1 (aa 1-300), which contains a large hydrophobic domain with six predicted transmembrane helices, followed by region 2 (aa 301-500) containing a smaller hydrophobic domain (of approximately 50 aa). To investigate the role of regions 1 and 2 in membrane association, we examined the subcellular localization of a series of catalytically active, Flag-tagged N-terminal-truncated human (H) PDE3A and MPDE3B recombinants, as well as a series of fragments from regions 1 and 2 of MPDE3B synthesized as enhanced green fluorescent (EGFP) fusion proteins in COS-7 cells. In COS-7 cells, the localization of a mutant HPDE3A, lacking the first 189 amino acids (aa) and therefore four of the six predicted transmembrane helices (H3A-Delta189), was virtually identical to that of the wild type. M3B-Delta302 (lacking region 1) and H3A-Delta397 (lacking region 1 as well as part of region 2) retained, to different degrees, the ability to associate with membranes, albeit less efficiently than H3A-Delta189. Proteins that lacked both regions 1 and 2, H3A-Delta510 and M3B-Delta604, did not associate with membranes. Consistent with these findings, region 1 EGFP-MPDE3B fusion proteins colocalized with the ER, whereas region 2 EGFP fusion proteins were diffusely distributed. Thus, some portion of the N-terminal hydrophobic domain in region 1 plus a second domain in region 2 are important for efficient membrane association/targeting of PDE3.
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PMID:Membrane localization of cyclic nucleotide phosphodiesterase 3 (PDE3). Two N-terminal domains are required for the efficient targeting to, and association of, PDE3 with endoplasmic reticulum. 1095 71

Sec22p is an endoplasmic reticulum (ER)-Golgi v-SNARE protein whose retrieval from the Golgi compartment to the endoplasmic reticulum (ER) is mediated by COPI vesicles. Whether Sec22p exhibits its primary role at the ER or the Golgi apparatus is still a matter of debate. To determine the role of Sec22p in intracellular transport more precisely, we performed a synthetic lethality screen. We isolated mutant yeast strains in which SEC22 gene function, which in a wild type strain background is non-essential for cell viability, has become essential. In this way a novel temperature-sensitive mutant allele, dsl1-22, of the essential gene DSL1 was obtained. The dsl1-22 mutation causes severe defects in Golgi-to-ER retrieval of ER-resident SNARE proteins and integral membrane proteins harboring a C-terminal KKXX retrieval motif, as well as of the soluble ER protein BiP/Kar2p, which utilizes the HDEL receptor, Erd2p, for its recycling to the ER. DSL1 interacts genetically with mutations that affect components of the Golgi-to-ER recycling machinery, namely sec20-1, tip20-5, and COPI-encoding genes. Furthermore, we demonstrate that Dsl1p is a peripheral membrane protein, which in vitro specifically binds to coatomer, the major component of the protein coat of COPI vesicles.
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PMID:The coatomer-interacting protein Dsl1p is required for Golgi-to-endoplasmic reticulum retrieval in yeast. 1149 4

Endoplasmic reticulum (ER) stress elicits protective responses of chaperone induction and translational suppression and, when unimpeded, leads to caspase-mediated apoptosis. Alzheimer's disease-linked mutations in presenilin-1 (PS-1) reportedly impair ER stress-mediated protective responses and enhance vulnerability to degeneration. We used cleavage site-specific antibodies to characterize the cysteine protease activation responses of primary mouse cortical neurons to ER stress and evaluate the influence of a PS-1 knock-in mutation on these and other stress responses. Two different ER stressors lead to processing of the ER-resident protease procaspase-12, activation of calpain, caspase-3, and caspase-6, and degradation of ER and non-ER protein substrates. Immunocytochemical localization of activated caspase-3 and a cleaved substrate of caspase-6 confirms that caspase activation extends into the cytosol and nucleus. ER stress-induced proteolysis is unchanged in cortical neurons derived from the PS-1 P264L knock-in mouse. Furthermore, the PS-1 genotype does not influence stress-induced increases in chaperones Grp78/BiP and Grp94 or apoptotic neurodegeneration. A similar lack of effect of the PS-1 P264L mutation on the activation of caspases and induction of chaperones is observed in fibroblasts. Finally, the PS-1 knock-in mutation does not alter activation of the protein kinase PKR-like ER kinase (PERK), a trigger for stress-induced translational suppression. These data demonstrate that ER stress in cortical neurons leads to activation of several cysteine proteases within diverse neuronal compartments and indicate that Alzheimer's disease-linked PS-1 mutations do not invariably alter the proteolytic, chaperone induction, translational suppression, and apoptotic responses to ER stress.
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PMID:Endoplasmic reticulum stress-induced cysteine protease activation in cortical neurons: effect of an Alzheimer's disease-linked presenilin-1 knock-in mutation. 1157 34


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