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1-antitrypsin
1 Department of Molecular and Cellular Biology, Institute for Frontier Medical Sciences, Kyoto University, Kyoto 606-8397, Japan
2 CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
3 Department of Cell Sciences, Institute of Biomedical Sciences, Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan
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Abstract |
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1-antitrypsin variant, null (Hong Kong) (NHK), suggesting that EDEM may function as an acceptor of terminally misfolded glycoproteins. In this study, we constructed several genetically manipulated cell lines to test this hypothesis. EDEM expression did not alter the secretion rate of properly folded molecules and the forced retention of wild-type 1-antitrypsin in the ER did not cause its association with EDEM, suggesting that EDEM may function as a molecular chaperone. To examine this possibility, we analyzed the effect of EDEM over-expression on the structure of NHK, and found that the accumulation of covalent NHK dimers was selectively prevented by the over-expression of EDEM. Co-expression of NHK with two other ER membrane proteins, calnexin and H+/K+-ATPase (ß subunit), did not inhibit NHK dimer formation or accelerate NHK ERAD. These results indicate that EDEM may maintain the retrotranslocation competence of NHK by inhibiting aggregation so that unstable misfolded proteins can be accommodated by the dislocon for ERAD. |
Introduction |
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Many terminally misfolded glycoproteins that fail to fold correctly after several rounds of refolding through the calnexin cycle are transferred to the ERAD machinery. In this process, mannose trimming from the N-linked glycan functions as an important degradation signal (Cabral et al. 2001; Helenius & Aebi 2001), although precisely which oligosaccharide structures target the glycoproteins for ERAD remains to be clarified (Frenkel et al. 2003; Hosokawa et al. 2003; Kitzmuller et al. 2003). A mouse membrane protein, EDEM (ER-degradation enhancing -mannosidase-like protein) (Hosokawa et al. 2001) accelerates the ERAD of a terminally misfolded 1-anti-trypsin variant, null (Hong Kong) (NHK) (Sifers et al. 1988; Liu et al. 1999). EDEM is homologous to ER mannosidase I (ER ManI), but lacks the enzymatic activity to process 1,2-mannose. The effects of EDEM and ER ManI on glycoprotein ERAD are additive, and EDEM seems to act downstream of ER ManI after the mannose from the N-linked oligosaccharide of a misfolded protein is trimmed by this processing mannosidase (Hosokawa et al. 2003). It has been shown that yeast Htm1p/Mnl1p, a homolog of mouse EDEM, accelerates glycoprotein ERAD in yeast (Jakob et al. 2001; Nakatsukasa et al. 2001).
Because misfolded proteins are prone to aggregation due to the exposure of hydrophobic patches on their surfaces (Hartl 1996; Bukau et al. 2000), ER chaperone proteins such as BiP and PDI escort these polypeptides until they are retrotranslocated through the Sec61 channel (Tsai et al. 2001; Molinari et al. 2002). More recently, it was shown that misfolded glycoproteins bind calnexin, and then EDEM, before they are degraded (Molinari et al. 2003; Oda et al. 2003). In this report, we investigated whether EDEM affects the secretion or degradation of wild-type 1-antitrypsin (WT 1-AT) to address the possibility that EDEM discriminates misfolded glycoproteins from correctly folded proteins. We then examined whether EDEM interacts directly with the terminally misfolded NHK to change its structure, and found that EDEM maintains the degradation competency of misfolded glycoproteins.
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Results |
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1-AT
EDEM binds terminally misfolded NHK and accelerates its ERAD (Hosokawa et al. 2001). We used three approaches to examine whether EDEM also influences the fate of WT 1-AT. First, we transiently transfected WT 1-AT into HEK 293 cells with or without EDEM-HA and examined its secretion in a pulse-chase experiment (Fig. 1). Upon transport to the Golgi apparatus, WT 1-AT showed a decrease in electrophoretic mobility on SDS-PAGE due to the oligosaccharide modification (Fig. 1A) (Cox 1995). Almost no difference was observed in the kinetics of WT 1-AT secretion into the medium between cells co-transfected with mock vector or EDEM-HA (quantified in Fig. 1B), except for a small delay in the disappearance of the ER form of 1-AT in cells co-transfected with EDEM-HA at 1 h chase.
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1-AT than for NHK (T1/2: < 30 min vs. 
1.5 h), we examined whether we had perhaps missed the effects of EDEM on WT 1-AT in Fig. 1A due to the short ER retention time. To test this, we added 0.6 M sorbitol to the chase medium to inhibit anterograde ER-Golgi transport (Lee & Linstedt 1999). As expected, WT 1-AT was retained in the ER and was not secreted into the medium either in the presence or absence of transfected EDEM-HA (Fig. 1C). However, the radioactivity of WT 1-AT at 1 h chase remained the same as that at 0 h chase regardless of the presence of co-expressed EDEM-HA (compare lanes 1 & 3 with 4 & 6), indicating that EDEM did not enhance the degradation of WT 1-AT. Importantly, no co-immunoprecipitation of WT 1-AT with EDEM-HA was observed even in cells treated with sorbitol (Fig. 1D, left panel), whereas misfolded NHK was efficiently co-immunoprecipitated with EDEM-HA (Fig. 1D, right panel).
EDEM accelerates ERAD of misfolded NHK, but does not affect WT 1-AT secretion in stable cell lines
To confirm that EDEM does not recognize WT 1-AT, we established a cell line that conditionally expresses EDEM-HA in the absence of tetracycline (293 Tet-Off EDEM-HA cells). Examination of the secretion rates revealed that the induction of EDEM-HA had no effect on the secretion of WT 1-AT (data not shown).
We also generated an EDEM-HA-expressing cell line, EDEM-HG, by retrovirus-mediated transgene integration of the parental human hepatoma HepG2 cell line. HepG2 cells secrete a variety of plasma proteins, including WT 1-AT. When NHK was transiently expressed, the rates of NHK disposal were faster in EDEM-HG cells than in the parental HepG2 cells (Fig. 2A, quantification in Fig. 2C), but WT 1-AT secretion was indistinguishable between these two cell lines (Fig. 2B,C).
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Terminally misfolded proteins are prone to expose hydrophobic patches on their surfaces, resulting in aggregation; this is prevented by the binding of molecular chaperone proteins in the cell (Hartl 1996; Bukau et al. 2000). Because EDEM bound to misfolded NHK but not to WT 1-AT, we examined the possibility that EDEM binding causes structural alteration of its ligands. 1-AT has one cysteine residue near its C-terminus, which is retained in the NHK variant (Sifers et al. 1988). We therefore used non-reducing SDS-PAGE to investigate the possibility that terminally misfolded NHK forms covalent dimers. As was expected, NHK synthesized in the absence of exogenous EDEM generated a slow-migrating band in non-reducing SDS-PAGE (Fig. 3A, lanes 7–9). Diagonal SDS-PAGE, which separates proteins under non-reducing conditions in the first dimension and then under reducing conditions in the second dimension (Molinari & Helenius 2002), identified the band as a covalent NHK homodimer (Fig. 3B). Interestingly, co-transfection of EDEM-HA markedly inhibited the formation of the disulfide-bonded NHK dimer (Fig. 3A, compare lanes 10–12 with 7–9).
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Because reduction of the disulfide bonds has been reported to accelerate the degradation of some ERAD substrates (Tortorella et al. 1998; Mancini et al. 2000; Fagioli et al. 2001), we next added DTT to the culture medium and examined the rate of NHK degradation. As expected, NHK dimer formation was greatly inhibited by adding DTT to the culture medium (Fig. 5A, compare lanes 1–3 with 4–6). Analysis of the other half of the cell lysate by reducing gel revealed that NHK degradation was accelerated by the addition of DTT into the culture medium (Fig. 5B, quantified in Fig. 5C).
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Enhanced degradation of NHK in the presence of DTT in the culture medium is most likely due to the inhibition of NHK disulfide-bonded dimer formation, but another possibility is that it results from the up-regulation of the ERAD machinery, because reducing reagents such as DTT or 2-mercaptoethanol are known to induce the UPR (unfolded protein response) (Kaufman 1999; Ma & Hendershot 2001; Patil & Walter 2001). Molecules involved in the ERAD machinery as well as ER chaperone proteins are induced by UPR (Casagrande et al. 2000; Travers et al. 2000). Because it is also possible that over-expression of EDEM-HA itself causes ER stress, we examined the effect of co-transfecting ER membrane proteins other than EDEM with NHK.
We first co-transfected calnexin tagged with HA at its C-terminus (CNX-HA)(Wada et al. 1995), and examined its effect on NHK dimer formation in a pulse-chase experiment. In contrast to the result with EDEM-HA, co-expression of CNX-HA did not inhibit NHK disulfide-bonded dimer formation (Fig. 6A non-reducing gel, compare lanes 4–6 with 1–3). Although the total radioactivity of immunoprecipitated NHK increased when cells were co-transfected with CNX-HA (Fig. 6A, reducing gel), as we have reported previously (Oda et al. 2003), the ratio of NHK dimers to total NHK (dimer+monomer) was almost unchanged. We next co-transfected cells with the H+/K+-ATPase ß-subunit (Ma et al. 1991) tagged with YFP, and examined whether NHK covalent dimer formation was affected. As is shown in Fig. 6B, NHK degradation was not accelerated by the over-expression of this ATPase subunit, nor was NHK dimer formation inhibited.
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In the oxidative environment of the ER, several oxidoreductases function to edit disulfide bonds. Because PDI and ER60 (also called ERp57) are known to function in conjunction with Ero1L (Frand & Kaiser 1999) and calnexin (Zapun et al. 1998), respectively, we established cell lines stably over-expressing PDI or ER60 to examine whether over-expression of these oxidoreductases affects NHK dimer formation. The transgene-encoded proteins in 293+PDI-YFP and 293+ER60 cells were expressed at levels several-fold higher than the endogenous proteins (Fig. 7C). Examination of NHK turnover rates using pulse-chase experiments revealed that the degradation rates of NHK were slower in both 293+YFP-PDI and 293+ER60 cells than in the parental 293 cells (Fig. 7A, reducing). Dimer formation was enhanced in these cells, suggesting that the NHK dimer is more resistant to degradation than the monomer (Fig. 7A, non-reducing). Nevertheless, no disulfide-bonded dimer of WT 1-AT was detected in these cell lines over-expressing ER oxidoreductases (Fig. 7B). Co-expression of EDEM-HA eliminated the NHK covalent dimers in 293 cells over-expressing PDI-YFP and ER60 (data not shown).
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The NHK variant was previously reported to have higher solubility than another variant, 1-ATZ, which is known to make large aggregates in vivo (Lomas et al. 1992). Our results suggest that the covalent dimer represents the aggregated form of NHK. To confirm this, we fractionated the cell lysates based on NP-40 solubility (Fig. 8A). Most of the NHK was recovered in the 1% NP-40-soluble fraction, but some was retrieved from the insoluble fraction. In the latter, NHK was detected mostly as covalently bonded dimers, suggesting that these dimers were incorporated into NP-40-insoluble aggregates. A small population of monomers was recovered in the insoluble fraction. Co-expression of EDEM-HA markedly suppressed the intracellular accumulation of NHK (Fig. 8A, lanes 3, 5, 7 & 9).
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1-AT. To inhibit ERAD of NHK, we added the proteasome inhibitor lactacystin, which caused accumulation of NHK within the cells, as shown in the pulse-chase experiment (Fig. 4A). Under all the conditions examined, the NHK signal was detected mainly within the ER (Fig. 8B, insets), although some NHK can be observed in the ERGIC (ER-Golgi intermediate compartments) (Hosokawa et al. unpublished observation). The NHK signal was markedly weakened in cells co-transfected with EDEM-HA, but was restored by the addition of proteasome inhibitor. |
Discussion |
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1-AT. In contrast, EDEM binds to and accelerates the degradation of the terminally misfolded 1-AT variant NHK, as we have reported previously (Hosokawa et al. 2001), suggesting that EDEM discriminates correctly folded glycoproteins from misfolded polypeptides. We then examined whether EDEM alters the structure of terminally misfolded NHK, and found that EDEM inhibits covalent dimer formation and possibly the aggregation of misfolded 1-AT NHK, resulting in the accelerated degradation of the misfolded glycoproteins. Based on these data, we postulate that EDEM functions to maintain the retrotranslocation competence of terminally misfolded mutant proteins. In this model, the role of EDEM in ERAD resembles the role of calnexin in productive folding, in that calnexin maintains the folding competence of immature proteins. The direct binding of EDEM may sequester misfolded proteins to prevent intermolecular associations. This would be a prerequisite for ERAD because its substrates have to pass through a translocation channel. Recently, it was reported that PDI reduces the disulfide bonds of retrotranslocation substrates (Orlandi 1997; Tsai et al. 2001); however, it remains unknown how a massive aggregation of misfolded proteins is prevented. We also examined the effect of co-expressing ER membrane proteins other than EDEM on NHK dimer formation. We co-transfected HA-tagged calnexin and H+/K+-ATPase ß-subunit fused to YFP to address whether over-expression of ER membrane proteins can itself enhance NHK degradation by up-regulating the ERAD machinery through UPR. Calnexin is a well-characterized type I ER transmembrane protein that acts as a lectin-like chaperone involved in ER quality control, and H+/K+-ATPase ß-subunit is a type II ER membrane protein. Unlike EDEM, co-expression of CNX-HA or H+/K+-ATPase-YFP did not inhibit NHK disulfide-bonded dimer formation, and NHK degradation was not accelerated; instead, NHK degradation was delayed when cells were co-transfected with CNX-HA (Fig. 6). These results suggest that co-transfection of ER membrane proteins does not in itself accelerate NHK degradation by up-regulating the ERAD machinery.
We found here that the 1-AT mutant NHK can form covalent dimers, although another variant of ATZ (E342K) forms non-covalent dimers (Lomas et al. 1992). Since there is only one cysteine in this protein, the disulfide bond must be formed through Cys232, which is presumably located on the surface of the molecule. The disulfide bond would be formed spontaneously with a second molecule in the oxidative environment of the ER. Because disulfide bonds are generally strong structural constraints, NHK dimer needs to be reduced to monomer before retrotranslocation, as is reported on Ig-µ chains (Fagioli et al. 2001). Prevention or reduction of the disulfide bonds should lead to the effective disposal of misfolded proteins, although the molecule which reduces the disulfide bonds at the retrotranslocon remains elusive. Unlike the over-expression of EDEM, over-expression of oxidoreductases did not accelerate the degradation of NHK (Fig. 7A). This may be due to the different binding affinities of EDEM and oxidoreductases for NHK. The current data favor a model in which EDEM recognizes the misfolded conformations of proteins bearing specific oligosaccharides. At present, it is unclear whether EDEM recognizes both epitopes, i.e. the hydrophobic surface and the glycan structure, or only one. In the case of calnexin, either type of binding functions to reduce aggregates (Ellgaard et al. 1999; Schrag et al. 2003), but further analyses will be needed to distinguish between these two possibilities for EDEM. Nonetheless, we propose that EDEM may function as an effective chaperone of misfolded glycoproteins destined for retrotranslocation.
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Experimental procedures |
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293 cells (derived from human embryonic kidney, ATCC CRL 1573) and their derivative cells were cultured in DMEM supplemented with 10% fetal bovine serum and antibiotics (100 U/mL penicillin G and 100 ng/mL streptomycin), in humidified air containing 5% CO2 at 37 °C. Hep G2 cells (derived from human hepatocellular carcinoma, ATCC HB 8065) were cultured on poly L-lysine-coated dishes in DMEM supplemented with nonessential amino acids NHK, EDEM-HA, CNX-HA were constructed as described elsewhere (Wada et al. 1995; Hosokawa et al. 2001), and H+/K+-ATPase (ß subunit) (Ma et al. 1991) was tagged with YFP (Clontech) in its C-terminus. Plasmids were purified with a Plasmid Maxi Kit (Qiagen) and transfected using the FuGene6 transfection reagent (Roche) as previously described (Hosokawa et al. 2003).
Establishment of stable cell lines
293 Tet-Off cells were purchased from Clontech. 293 Tet-Off EDEM-HA cells were established by transfecting cells with hemagglutinin (HA)-tagged EDEM subcloned in pTRE2hyg (Clontech) according to the protocol recommended by the manufacturer, and then selecting colonies resistant to hygromycin. To further analyze clones for the induction of EDEM-HA, doxycycline was removed from the culture medium, and EDEM-HA was measured by Western blotting. Eight clones were selected for detailed analysis, but none of the clones showed complete suppression of EDEM-HA expression in the presence of doxycycline. EDEM-HG2 cells, 293+PDI cells, and 293+ER60 cells were established using a retrovirus-mediated system. Genes of interest were subcloned into pCX4bsr, a plasmid bearing a retrovirus LTR, and amplified by transfection into 293 cells. pCX4bsr is a modified version of pCXbsr (Akagi et al. 2003) lacking the internal initiation codons within the gag region. For the construction of 293+PDI cells, PDI was tagged with YFP (Clontech) in its C-terminus. Cells were selected and maintained in medium containing 10 µg/mL blasticidin S (Funakoshi, Japan).
Metabolic labeling, immunoprecipitation, and SDS-PAGE
Metabolic labeling, cell lysis, immunoprecipitation, and SDS-PAGE were carried out as previously described (Hosokawa et al. 2003), except that DMEM lacking both methionine and cysteine was used instead of DMEM lacking only methionine. For the detection of disulfide-bonded dimers, cells were lyzed in a buffer containing 20 mM iodoacetamide (IA). Samples for non-reducing SDS-PAGE were supplemented with 5 mM IA prior to electrophoresis. Dithiothreitol (DTT) was added to the medium from 30 min before pulse-labeling at a concentration of 0.5 mM, and lactacystin was added from 4 h before at a concentration of 20 µM.
Antibodies
Antibodies against 1-AT were purchased from Cappel (goat polyclonal), DAKO (rabbit polyclonal), or MBL (goat polyclonal). The polyclonal antibody against the HA-tag was obtained from Santa Cruz Biotechnology, and the antibody against ER60 was from StressGen. The rabbit anti-PDI IgG fraction was kindly provided by Dr R. Masaki (Kansai Medical University, Japan).
Western blotting
Cell lysates were prepared as above in the presence of 20 mM IA, and the pellet insoluble in 1% NP-40 was recovered by sonication in 1 x Laemmli's buffer. The concentration of the cell lysates were adjusted to 1 x Laemmli's buffer, and 20 µg of NP-40-soluble protein and a cell-equivalent amount of the NP40-insoluble fraction were separated by 10% SDS-PAGE under reducing and non-reducing conditions. Proteins were blotted on to a nitrocellulose membrane in 5 mM sodium tetraborate buffer. After blocking in 5% skim milk, specific proteins recognized by each antibody were detected using ECL reagents and exposure to X-ray film (Fuji, Japan).
Diagonal 2-D SDS-PAGE
Cell lysates prepared as above were subjected to immunoprecipitation using an antibody against 1-AT (DAKO, rabbit polyclonal). The precipitated proteins were separated in a tube gel under non-reducing conditions, and then separated with reducing 10% SDS-PAGE as described (Molinari & Helenius 2002), except that the tube gels were immersed in Laemmli's buffer containing 5% 2-mercaptoethanol. The proteins in the gel were blotted on to a nitrocellulose membrane as above, and an antibody to 1-AT (MBL, goat polyclonal) was used to detect NHK.
Immunostaining
293 cells were plated on a poly L-lysine-coated cover glass placed in a 3.5-cm-diameter dish approximately 24 h prior to transfection. Twenty-four hours after transfection, the cells were fixed with 4% paraformaldehyde for 15 min at room temperature, and incubated first with an anti-1-AT antibody for 1 h, and then with an FITC-labeled anti-rabbit antibody for 1 h. Samples were examined with confocal microscopy (LSM 510 META, Carl-Zeiss, Germany).
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Acknowledgements |
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Footnotes |
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* Correspondence: E-mail: nobuko{at}frontier.kyoto-u.ac.jp
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References |
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|---|
Bukau, B., Deuerling, E., Pfund, C. & Craig, E.A. (2000) Getting newly synthesized proteins into shape. Cell 101, 119–122.[CrossRef][Medline]
Cabral, C.M., Liu, Y. & Sifers, R.N. (2001) Dissecting glycoprotein quality control in the secretory pathway. Trends Biochem. Sci. 26, 619–624.[CrossRef][Medline]
Casagrande, R., Stern, P., Diehn, M., et al. (2000) Degradation of proteins from the ER of S. cerevisiae requires an intact unfolded protein response pathway. Mol. Cell 5, 729–735.[CrossRef][Medline]
Cox, D.W. (1995) A1-Antitrypsin Deficiency. New York: McGraw-Hill Inc.
Ellgaard, L., Molinari, M. & Helenius, A. (1999) Setting the standards: quality control in the secretory pathway. Science
286, 1882–1888.
Fagioli, C., Mezghrani, A. & Sitia, R. (2001) Reduction of interchain disulfide bonds precedes the dislocation of Ig-mu chains from the endoplasmic reticulum to the cytosol for proteasomal degradation. J. Biol. Chem.
276, 40962–40967.
Fewell, S.W., Travers, K.J., Weissman, J.S. & Brodsky, J.L. (2001) The action of molecular chaperones in the early secretory pathway. Annu. Rev. Genet. 35, 149–191.[CrossRef][Medline]
Frand, A.R. & Kaiser, C.A. (1999) Ero1p oxidizes protein disulfide isomerase in a pathway for disulfide bond formation in the endoplasmic reticulum. Mol. Cell 4, 469–477.[CrossRef][Medline]
Frenkel, Z., Gregory, W., Kornfeld, S. & Lederkremer, G.Z. (2003) Endoplasmic reticulum-associated degradation of mammalian glycoproteins involves sugar chain trimming to Man6–5GlcNAc2. J. Biol. Chem.
278, 34119–34124.
Hartl, F.U. (1996) Molecular chaperones in cellular protein folding. Nature 381, 571–579.[CrossRef][Medline]
Helenius, A. & Aebi, M. (2001) Intracellular functions of N-linked glycans. Science
291, 2364–2369.
Hosokawa, N., Tremblay, L.O., You, Z., et al. (2003) Enhancement of endoplasmic reticulum (ER) degradation of misfolded Null Hong Kong alpha1-antitrypsin by human ER mannosidase I. J. Biol. Chem.
278, 26287–26294.
Hosokawa, N., Wada, I., Hasegawa, K., et al. (2001) A novel ER alpha-mannosidase-like protein accelerates ER-associated degradation. EMBO Rep. 2, 415–422.[Medline]
Jakob, C.A., Bodmer, D., Spirig, U., et al. (2001) Htm1p, a mannosidase-like protein, is involved in glycoprotein degradation in yeast. EMBO Rep. 2, 423–430.[Medline]
Kaufman, R.J. (1999) Stress signaling from the lumen of the endoplasmic reticulum: coordination of gene transcriptional and translational controls. Genes Dev.
13, 1211–1233.
Kitzmuller, C., Caprini, A., Moore, S.E., et al. (2003) Processing of N-linked glycans during endoplasmic-reticulum-associated degradation of a short-lived variant of ribophorin I. Biochem. J. 376, 687–696.[CrossRef][Medline]
Kostova, Z. & Wolf, D.H. (2003) For whom the bell tolls: protein quality control of the endoplasmic reticulum and the ubiquitin-proteasome connection. EMBO J. 22, 2309–2317.[CrossRef][Medline]
Lee, T.H. & Linstedt, A.D. (1999) Osmotically induced cell Volume changes alter anterograde and retrograde transport, Golgi structure, and COPI dissociation. Mol. Biol. Cell
10, 1445–1462.
Liu, Y., Choudhury, P., Cabral, C.M. & Sifers, R.N. (1999) Oligosaccharide modification in the early secretory pathway directs the selection of a misfolded glycoprotein for degradation by the proteasome. J. Biol. Chem.
274, 5861–5867.
Lomas, D.A., Evans, D.L., Finch, J.T. & Carrell, R.W. (1992) The mechanism of Z alpha 1-antitrypsin accumulation in the liver. Nature 357, 605–607.[CrossRef][Medline]
Ma, Y. & Hendershot, L.M. (2001) The unfolding tale of the unfolded protein response. Cell 107, 827–830.[CrossRef][Medline]
Ma, J.-Y., Song, Y.-H., Sjöstrand, S.E., Rask, L. & Mårdh, S. (1991) cDNA cloning of the ß-subunit of the human gastric H,K-ATPase. Biochem. Biophys. Res. Commun. 180, 39–45.[CrossRef][Medline]
Mancini, R., Fagioli, C., Fra, A.M., Maggioni, C. & Sitia, R. (2000) Degradation of unassembled soluble Ig subunits by cytosolic proteasomes: evidence that retrotranslocation and degradation are coupled events. FASEB J.
14, 769–778.
Molinari, M., Calanca, V., Galli, C., Lucca, P. & Paganetti, P. (2003) Role of EDEM in the release of misfolded glycoproteins from the calnexin cycle. Science
299, 1397–1400.
Molinari, M., Galli, C., Piccaluga, V., Pieren, M. & Paganetti, P. (2002) Sequential assistance of molecular chaperones and transient formation of covalent complexes during protein degradation from the ER. J. Cell Biol.
158, 247–257.
Molinari, M. & Helenius, A. (2002) Analyzing cotranslational protein folding and disulfide formation by diagonal sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Methods Enzymol. 348, 35–42.[Medline]
Nakatsukasa, K., Nishikawa, S., Hosokawa, N., Nagata, K. & Endo, T. (2001) Mnl1p, an alpha-mannosidase-like protein in yeast Saccharomyces cerevisiae, is required for endoplasmic reticulum-associated degradation of glycoproteins. J. Biol. Chem.
276, 8635–8638.
Oda, Y., Hosokawa, N., Wada, I. & Nagata, K. (2003) EDEM as an acceptor of terminally misfolded glycoproteins released from calnexin. Science
299, 1394–1397.
Orlandi, P.A. (1997) Protein-disulfide isomerase-mediated reduction of the A subunit of cholera toxin in a human intestinal cell line. J. Biol. Chem.
272, 4591–4599.
Parodi, A.J. (2000) Protein glucosylation and its role in protein folding. Annu. Rev. Biochem. 69, 69–93.[CrossRef][Medline]
Patil, C. & Walter, P. (2001) Intracellular signaling from the endoplasmic reticulum to the nucleus: the unfolded protein response in yeast and mammals. Curr. Opin. Cell Biol. 13, 349–355.[CrossRef][Medline]
Schrag, J.D., Procopio, D.O., Cygler, M., Thomas, D.Y. & Bergeron, J.J. (2003) Lectin control of protein folding and sorting in the secretory pathway. Trends Biochem. Sci. 28, 49–57.[CrossRef][Medline]
Sifers, R.N., Brashears-Macatee, S., Kidd, V.J., Muensch, H. & Woo, S.L. (1988) A frameshift mutation results in a truncated alpha 1-antitrypsin that is retained within the rough endoplasmic reticulum. J. Biol. Chem.
263, 7330–7335.
Tortorella, D., Story, C.M., Huppa, J.B., et al. (1998) Dislocation of type I membrane proteins from the ER to the cytosol is sensitive to changes in redox potential. J. Cell Biol.
142, 365–376.
Travers, K.J., Patil, C.K., Wodicka, L., Lockhart, D.J., Weissman, J.S. & Walter, P. (2000) Functional and genomic analyses reveal an essential coordination between the unfolded protein response and ER-associated degradation. Cell 101, 249–258.[CrossRef][Medline]
Tsai, B., Rodighiero, C., Lencer, W.I. & Rapoport, T.A. (2001) Protein disulfide isomerase acts as a redox-dependent chaperone to unfold cholera toxin. Cell 104, 937–948.[CrossRef][Medline]
Tsai, B., Ye, Y. & Rapoport, T.A. (2002) Retro-translocation of proteins from the endoplasmic reticulum into the cytosol. Nature Rev. Mol. Cell. Biol. 3, 246–255.[CrossRef][Medline]
Wada, I., Imai, S., Kai, M., Sakane, F. & Kanoh, H. (1995) Chaperone function of calreticulin when expressed in the endoplasmic reticulum as the membrane-anchored and soluble forms. J. Biol. Chem.
270, 20298–20304.
Zapun, A., Darby, N.J., Tessier, D.C., Michalak, M., Bergeron, J.J. & Thomas, D.Y. (1998) Enhanced catalysis of ribonuclease B folding by the interaction of calnexin or calreticulin with ERp57. J. Biol. Chem.
273, 6009–6012.
Received: 13 July 2005
Accepted: 29 January 2006
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 Y. Ishida, A. Yamamoto, A. Kitamura, S. R. Lamande, T. Yoshimori, J. F. Bateman, H. Kubota, and K. Nagata Autophagic Elimination of Misfolded Procollagen Aggregates in the Endoplasmic Reticulum as a Means of Cell Protection Mol. Biol. Cell, June 1, 2009; 20(11): 2744 - 2754. [Abstract] [Full Text] [PDF]
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D. J. Termine, K. W. Moremen, and R. N. Sifers The mammalian UPR boosts glycoprotein ERAD by suppressing the proteolytic downregulation of ER mannosidase I J. Cell Sci., April 1, 2009; 122(7): 976 - 984. [Abstract] [Full Text] [PDF]
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 R. Ushioda, J. Hoseki, K. Araki, G. Jansen, D. Y. Thomas, and K. Nagata ERdj5 Is Required as a Disulfide Reductase for Degradation of Misfolded Proteins in the ER Science, July 25, 2008; 321(5888): 569 - 572. [Abstract] [Full Text] [PDF]
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 N. Hosokawa, I. Wada, K. Nagasawa, T. Moriyama, K. Okawa, and K. Nagata Human XTP3-B Forms an Endoplasmic Reticulum Quality Control Scaffold with the HRD1-SEL1L Ubiquitin Ligase Complex and BiP J. Biol. Chem., July 25, 2008; 283(30): 20914 - 20924. [Abstract] [Full Text] [PDF]
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 C. M. Wilson, Q. Roebuck, and S. High Ribophorin I regulates substrate delivery to the oligosaccharyltransferase core PNAS, July 15, 2008; 105(28): 9534 - 9539. [Abstract] [Full Text] [PDF]
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S. Granell, G. Baldini, S. Mohammad, V. Nicolin, P. Narducci, B. Storrie, and G. Baldini Sequestration of Mutated {alpha}1-Antitrypsin into Inclusion Bodies Is a Cell-protective Mechanism to Maintain Endoplasmic Reticulum Function Mol. Biol. Cell, February 1, 2008; 19(2): 572 - 586. [Abstract] [Full Text] [PDF]
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E. Avezov, Z. Frenkel, M. Ehrlich, A. Herscovics, and G. Z. Lederkremer Endoplasmic Reticulum (ER) Mannosidase I Is Compartmentalized and Required for N-Glycan Trimming to Man5 6GlcNAc2 in Glycoprotein ER-associated Degradation Mol. Biol. Cell, January 1, 2008; 19(1): 216 - 225. [Abstract] [Full Text] [PDF]
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J. Fort, L. R. de la Ballina, H. E. Burghardt, C. Ferrer-Costa, J. Turnay, C. Ferrer-Orta, I. Uson, A. Zorzano, J. Fernandez-Recio, M. Orozco, et al. The Structure of Human 4F2hc Ectodomain Provides a Model for Homodimerization and Electrostatic Interaction with Plasma Membrane J. Biol. Chem., October 26, 2007; 282(43): 31444 - 31452. [Abstract] [Full Text] [PDF]
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 D. N. Hebert and M. Molinari In and Out of the ER: Protein Folding, Quality Control, Degradation, and Related Human Diseases Physiol Rev, October 1, 2007; 87(4): 1377 - 1408. [Abstract] [Full Text] [PDF]
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L. W. Ruddock and M. Molinari N-glycan processing in ER quality control J. Cell Sci., November 1, 2006; 119(21): 4373 - 4380. [Abstract] [Full Text] [PDF]
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