Immunoglobulin heavy-chain binding protein (BiP, GRP-78) associates tightly in the endoplasmic reticulum (ER) with newly synthesized proteins that are incompletely assembled, have mutant structures, or are incorrectly glycosylated. The function of BiP has been suggested to be to prevent secretion of incorrectly folded or incompletely assembled protein, to promote folding or assembly of proteins, or to solubilize protein aggregates within the ER lumen. Here we examine the interaction of BiP with newly synthesized polypeptides in an in vitro protein translation-translocation system. We find that BiP forms tight complexes with nonglycosylated yeast invertase and incorrectly disulphide-bonded prolactin, but does not associate detectably with either glycosylated invertase or correctly disulphide-bonded prolactin. Moreover, BiP associates detectably only with completed chains of prolactin, not with chains undergoing synthesis. We conclude that BiP recognizes and binds with high affinity in vitro to aberrantly folded or aberrantly glycosylated polypeptides, but not to all nascent chains as they are folding.
"In addition to TCR, many other cell surface receptors are multisubunit complexes and the assembly of these complexes occurs in the ER . Other early evidence indicated that the ER could expand if unfolded proteins accumulated, and that misfolded proteins associated with an Hsp70 in the ER, BiP       . Thus, the ER was now implicated as a potential site of general secretory protein quality control, and a factor that might mediate this event had been identified. "
[Show abstract][Hide abstract] ABSTRACT: All newly synthesized proteins are subject to quality control check-points, which prevent aberrant polypeptides from harming the cell. For proteins that ultimately reside in the cytoplasm, components that also reside in the cytoplasm were known for many years to mediate quality control. Early biochemical and genetic data indicated that misfolded proteins were selected by molecular chaperones and then targeted to the proteasome (in eukaryotes) or to proteasome-like particles (in bacteria) for degradation. What was less clear was how secreted and integral membrane proteins, which in eukaryotes enter the endoplasmic reticulum (ER), were subject to quality control decisions. In this review, we highlight early studies that ultimately led to the discovery that secreted and integral membrane proteins also utilize several components that constitute the cytoplasmic quality machinery. This component of the cellular quality control pathway is known as ER associated degradation, or ERAD.
"Under normal conditions, binding immunoglobulin protein (BiP) also known as 78 kDa glucose-regulated protein (GRP-78) physically interacts with the luminal domain of membrane-bound proteins, such as inositol-requiring enzyme 1 (IRE1) and protein kinase RNA-like endoplasmic reticulum kinase (PERK).12 Under stress conditions, BiP dissociates from the membrane-bound proteins and associates permanently with misfolded, under-glycosylated or incompletely assembled proteins.13,14 Since cigarette smoke exposure leads to increased ER stress markers in the lungs of patients with COPD,8 it is speculated that ER stress contributes to the pathogenesis of COPD. "
[Show abstract][Hide abstract] ABSTRACT: Cigarette smoke is the major risk factor associated with the development of chronic obstructive pulmonary disease (COPD). Recent studies propose a link between endoplasmic reticulum (ER) stress and emphysema, demonstrated by increased ER stress markers under smoking conditions. Here, we investigate whether cigarette smoke-induced ER stress is cell specific and correlates with acute and chronic cigarette smoke exposure.
Gene and protein expression changes in human primary lung cell cultures following cigarette smoke extract (CSE) exposure were monitored by qPCR and Western blot analysis. Mice and guinea pigs were exposed to cigarette smoke and ER stress markers examined in whole lung homogenates. Inflammatory cells from the bronchoalveolar lavage fluid of 10 days smoke exposed mice were also examined.
Cigarette smoke induced a trend increase in the ER stress response through an activating transcription factor 4 (ATF4) mediated induction of C/EBP homologous protein (CHOP) in primary small airway epithelial cells. Bronchial epithelial cells and macrophages responded similarly to CSE. Wild-type mice and guinea pigs exposed to acute levels of cigarette smoke exhibited increased levels of CHOP but not at significant levels. However, after long-term chronic cigarette smoke exposure, CHOP expression was reduced. Interestingly, inflammatory cells from smoke exposed mice had a significant increase in CHOP/ATF4 expression.
A trend increase in CHOP levels appear in multiple human lung cell types following acute cigarette smoke exposure in vitro. In vivo, inflammatory cells, predominately macrophages, demonstrate significant cigarette smoke-induced ER stress. Early induction of CHOP in cigarette smoke may play a pivotal role in early induction of lung disease, however in vivo long-term cigarette smoke exposure exhibited a reduction in the ER stress response.
International Journal of COPD 06/2011; 6(1):309-19. DOI:10.2147/COPD.S19599 · 3.14 Impact Factor
"equent folding of newly translocated secretory proteins ( Hurtley and Helenius , 1989 ) . Consistent with the proposed role of Hsp70s , BiP transiently binds and stabilizes partially folded intermediates , preventing irreversible formation of insoluble aggregates ( Knittler and Haas , 1992 ) . Misfolded proteins in mammalian cell culture systems ( Kassenbrock et al . , 1988 ; Hurtley et al . , 1989 ) and assembly - defective 75 phaseolin subunits ( Pedrazzini et al . , 1994 ) were demon - strated to be associated with BiP . Despite the suggestion that BiP may play a role in folding and oligomer assembly of secretory proteins , the precise protein - folding pathway that would occur in the ER via mediation b"
[Show abstract][Hide abstract] ABSTRACT: Seed protein proglobulins were synthesized from cDNAs in reticulocyte lysates. Most proglobulins were recovered as trimers when translation rates were low, but mostly monomers were recovered at high translation rates. The prevalence of monomers was accompanied by elevated amounts of insoluble protein recovered at the bottom of sucrose density gradients. Apyrase treatment of translation mixtures after synthesis, but before significant assembly occurred, drastically reduced trimer assembly and increased the proportion of insoluble aggregate. These observations indicated that ATP is required for protein folding and/or trimer assembly. The appearance of insoluble aggregated protein when rates of synthesis were elevated or when ATP was absent suggested that protein misfolding had occurred. Trimer assembly was stimulated when wheat germ translation mixtures defective in supporting efficient trimer assembly were supplemented with fractions isolated from endoplasmic reticula of developing pea (Pisum sativum) seeds. Molecular chaperones are likely involved in folding and/or assembly of proglobulin trimers both in reticulocyte lysates and in seeds. Consistent with this hypothesis, trimer formation was reduced when carboxymethylated bovine albumin and alpha-casein, considered to mimic proteins with extended chain and molten globular conformations and thereby compete for Hsp70- and Hsp60-type molecular chaperones, respectively, were introduced into translation mixtures.
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