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Address correspondence to Antony A. Cooper, University of Missouri-Kansas City, Division of Cell Biology and Biophysics, School of Biological Sciences, 5100 Rockhill Rd., Kansas City, MO 64110. Tel.: (816) 235-2265. Fax: (816) 235-1503. E-mail: coopera{at}umkc.edu
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Abstract |
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Key Words: endoplasmic reticulum; ER-associated degradation; degradation; ubiquitin ligase; secretory pathway
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Introduction |
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ERQC contributes to the manifestation of a number of diseases by either depleting cells of essential proteins, or by the accumulation and aggregation of misfolded/mutant proteins it is incapable of degrading. Such substrates include the following: CFTR-F508 (Ward et al., 1995),
1-antitrypsin inhibitor (Teckman and Perlmutter, 1996), unassembled T cell receptor subunits (Bonifacino et al., 1989), and apoB under conditions of limited lipid availability (Fisher et al., 1997). Pathogens are able to promote or conceal their infection by manipulating the ERQC system to degrade CD4 or MHC class I heavy chain molecules (Margottin et al., 1996; Wiertz et al., 1996), whereas bacterial toxins usurp ERQC to access cytosolic targets (Simpson et al., 1999). ERQC substrates characterized in yeast include CPY* and PrA*, which are mutant forms of the yeast vacuolar carboxypeptidase Y (CPY) and proteinase A (PrA), respectively, that are retained in the ER (Knop et al., 1996), and Sec612p, which is a mutant subunit of the translocon (Biederer et al., 1996). Finally, the ERQC-degradative machinery also acts in a regulatory role to moderate the half-life of correctly folded proteins such as HMG-CoA reductase in response to cellular signals so as to modulate the sterol-synthesizing mevalonate pathway (Hampton et al., 1996).
The ERQC is intimately associated with the unfolded protein response (UPR), a wide-ranging cellular response to transcriptionally up-regulate a number of distinct mechanisms to cope with the ER stress encountered when increased amounts of misfolded proteins accumulate in the ER (Friedlander et al., 2000). ER stress is thought to be sensed by Ire1p and the chaperone Kar2p, which transduce the UPR signal from the ER to the nucleus where in yeast almost 400 genes are transcriptionally up-regulated, including those encoding molecular chaperones, components of the HRD/DER pathway, and machinery responsible for vesicular transport between the ER and Golgi apparatus (Travers et al., 2000).
The HRD/DER pathway is able to target a number of ERQC substrates for proteasomal degradation, yet CPY* turnover, while impaired in HRD/DER-deficient strains, still proceeds at a substantial rate (Hill and Cooper, 2000). This slowed, but not abolished, degradation in the absence of Hrd1p is also the case for a number of other substrates (Wilhovsky et al., 2000). Furthermore, the inactivation of the HRD/DER pathway has no effect on the degradation of unassembled Vph1p (Hill and Cooper, 2000) and Fur4430Np (Wilhovsky et al., 2000). This HRD/DER-independent means of degradation prompted the prediction of an additional degradative pathway (Hill and Cooper, 2000), or at a minimum an additional ubiquitin ligase (Wilhovsky et al., 2000).
Our interest in such an alternative degradative pathway resulted in the discovery of the requirement of ER-Golgi transport for efficient degradation of ERQC substrates (Caldwell et al., 2001). Inactivation of Sec12p (required for vesicle to exit the ER) or Sec18p (vesicle fusion with a post-ER compartment) significantly slowed the degradative rate of CPY* as did the absence of Erv29p (Caldwell et al., 2001). Erv29p is localized to the ER and Golgi apparatus, contains an ER-retrieval sequence, and behaves as a cargo loading/transport receptor that acts to transport a subset of lumenal proteins including CPY and PrA from the ER to the Golgi apparatus via COPII-coated vesicles (Belden and Barlowe, 2001; Caldwell et al., 2001). The absence of Erv29p severely retards the ER-Golgi transport of such ligands, yet the secretory pathway remains functional with invertase and alkaline phosphatase displaying normal transport kinetics (Caldwell et al., 2001). It is likely that CPY* also requires Erv29p to enter such transport vesicles and therefore, the absence of Erv29p severely impairs the transport of CPY* from the ER to the Golgi apparatus. This work investigates the role ER-Golgi trafficking plays in ERQC and resulted in the identification of an HRD/DER-independent ERQC mechanism capable of recognizing both lumenal and integral membrane substrates in the yeast Saccharomyces cerevisiae. This separate degradative mechanism requires ER-Golgi transport as evidenced by the requirement of Erv29p and Sec12p. We were able to directly observe this novel degradative mechanism by overexpressing CPY* because under these conditions the HRD/DER pathway appears saturated, causing CPY* degradation to be totally dependent on this novel mechanism. Substrates targeted for degradation through this mechanism are ubiquitinated, even in the absence of Hrd1p, by the ubiquitin ligase Rsp5p. Only by removing both ERQC pathways is CPY* degradation completely blocked. Our data call attention to the complexity of quality control in the ER and show that mechanisms in addition to the HRD/DER pathway are able to deliver misfolded proteins to the proteasome for degradation.
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Results |
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CPY* overexpression results in HRD/DER-independent degradation
In a separate project investigating the association between CPY* and the translocon in HRD/DER-deficient strains, CPY* was overexpressed approximately eightfold. Surprisingly, we observed that CPY* was now degraded with wild-type kinetics in a hrd1 strain instead of the expected slowed degradative rate (Fig. 2 A). The wild-type degradative rate caused by overexpression of CPY* was also observed in both der1
and hrd3
cells (unpublished data). This HRD/DER-independent degradation was further investigated using the ERQC substrate PrA*. PrA* was overexpressed in both wild-type and hrd1
strains, and the effect on the rate of single copy CPY* degradation was examined. Fig. 2 B shows that the overexpression of PrA*HA also resulted in CPY* being degraded with wild-type kinetics in a hrd1
strain. This suggests that this HRD/DER-independent degradative mechanism is not specific for CPY* and capable of recognizing and degrading a variety of lumenal ERQC substrates.
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To confirm that Rsp5p is a component of the HIP pathway instead of a potential third degradative pathway, we introduced the rsp52 mutation into a strain deficient for the HIP pathway (erv29). The stabilization of CPY* in an erv29
rsp52 double mutant was found to be no greater than either of the single mutants, indicating that Rsp5p is indeed a component of the HIP pathway (unpublished data). Furthermore, overexpression of CPY* in a hrd1
rsp52 strain does not suppress stabilization of CPY* (unpublished data).
The RING-H2 ubiquitin ligase Hrd1p has been demonstrated to use the ubiquitin-conjugating enzymes Ubc7p and Ubc1p (Friedlander et al., 2000; Bays et al., 2001) in the HRD/DER pathway. In contrast to Hrd1p, Rsp5p is a HECT domain ubiquitin ligase, and previous work has indicated that Rsp5p uses the ubiquitin-conjugating enzymes Ubc4p and Ubc5p (Gitan and Eide, 2000). If Ubc4p and Ubc5p act in concert with Rsp5p to mediate the degradation of ERQC substrates by the HIP pathway, then the absence of both Ubc4p and Ubc5p should impair the degradation of that substrate. The degradative rate of overexpressed CPY* was examined in both wild-type and ubc4 ubc5
cells, where it was found that the absence of Ubc4p and Ubc5p significantly slowed the degradation of CPY* (Fig. 6 D).
The HIP pathway is also capable of degrading integral membrane ERQC substrates
The finding that the ERQC possesses an alternative degradative pathway capable of degrading lumenal ERQC substrates raised the issue of whether integral membrane ERQC proteins such as Sec612p might also be an alternative pathway substrate. The fact that Sec612p is not stabilized in a strain lacking Erv29p (Caldwell et al., 2001) does not exclude Sec612 from the alternative pathway because, Erv29p appears to act as a cargo receptor for a specific subset of ER lumenal proteins that would have no effect on integral membrane proteins. Sec612p seems likely to be a substrate of an alternative pathway as, analogous to CPY* in Fig. 1 A, the disabling of the HRD/DER pathway reduced, but did not abolish, the degradation of Sec612p (Fig. 7 A). Wild-type cells, hrd1, rsp52, or hrd1
rsp52 double mutants expressing Sec612p were radiolabeled at the restrictive temperature and the degradative kinetics of Sec612p were examined (Fig. 7 A). Even when the HRD/DER pathway is functional, Rsp5p contributes to the degradation of Sec612p as shown by the retarded degradative kinetics in the rsp52 strain. Second, the inactivation of Rsp5p in cells lacking HRD/DER components (rsp52 hrd1
) further stabilized Sec612p. The findings that Sec612p is not fully stabilized in HRD/DER- deficient cells and that inactivation of the Rsp5p further stabilizes Sec612p suggest that integral membrane ERQC substrates can be degraded by the HIP pathway. The ability of the alternative pathway to degrade Sec612p was further demonstrated by overexpressing CPY* in hrd1
cells also expressing Sec612p with the result that the retarded Sec612p degradation kinetics seen in hrd1
cells was accelerated to those of a wild-type cell (Fig. 7 B).
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Discussion |
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The ubiquitin ligase Rsp5p is a component of the HIP pathway and together with Hrd1p is responsible for the ubiquitination of CPY*. Only by inactivating both Rsp5p and Hrd1p does CPY* fail to be ubiquitinated and remains completely stable. Rsp5p-dependent ubiquitination involves the ubiquitin-conjugating enzymes Ubc4p and Ubc5p (Gitan and Eide, 2000), and these enzymes were also required by the HIP pathway to degrade overexpressed CPY*. In addition to its role in ERQC, Rsp5p is responsible for mediating ubiquitin-dependent protein sorting and trafficking within the secretory pathway. The ubiquitination of plasma membrane proteins by Rsp5p results in their internalization and subsequent transport to the vacuole for degradation (Galan et al., 1996; Hicke and Riezman, 1996). Rsp5p, acting in concert with Bul1p and Bul2p, can also ubiquitinate proteins such as Gap1p to direct them from the trans-Golgi compartment to the vacuole for degradation (Helliwell et al., 2001). However, the role of Rsp5p in ERQC is distinct from that involving vacuolar sorting, as the HIP pathway is independent of vacuolar proteases and instead utilizes the proteasome. Furthermore, the disruption of both BUL1 and BUL2 has no effect on the degradation rate of CPY* (unpublished data).
Examination of the mechanisms used by mammalian cells to degrade ERQC substrates suggests extensive overlap with the HIP pathway described here. This similarity includes the observation of the following ERQC substrates in post-ER compartments (ER-Golgi intermediate compartment and/or Golgi subcompartments): unassembled MHC class I molecules (Hsu et al., 1991), misfolded G protein of vesicular stomatitis virus (Hammond and Helenius, 1994), mutant forms of sucrase-isomaltase and lysosomal -glucosidase (Moolenaar et al., 1997), and precursors of human asialoglycoprotein receptor H2a (Kamhi-Nesher et al., 2001). The soluble secretory form of IgM molecules in differentiated B lymphocytes is degraded intracellularly in a manner completely dependent on transport to a post-ER compartment (Winitz et al., 1996), and truncated versions of CFTR reach the Golgi apparatus before degradation by the proteasome (Benharouga et al., 2001). Further evidence suggesting the involvement of post-ER compartment(s) is that some ERQC components are themselves found in post-ER locations: UDP-glucose:glycoprotein glucosyltransferase (UGGT), an important ERQC glycoprotein folding sensor, is found in post-ER vesicles (Zuber et al., 2001), whereas endo-
-mannosidase has been implicated in quality control and was localized to the cis/medial-Golgi apparatus (Zuber et al., 2000).
How far through the secretory pathway do ERQC substrates such as CPY* progress and what function would delivery of ERQC substrates to the Golgi apparatus serve? CPY* in either DER1-deficient cells (Knop et al., 1996) or those lacking an ER-localized proposed ERQC lectin (mnl1/htm1
) (Jakob et al., 2001; Nakatsukasa et al., 2001) received
1,6-mannose addition but not
1,3-mannose addition, indicating that CPY* reached the cis-Golgi but not the trans-Golgi compartment (Brigance et al., 2000). Similarly, we have also found that CPY* is delivered to the cis-Golgi compartment when overexpressed in hrd1
cells as evidenced by the addition of
1,6-mannose. A recent report has shown that a heterologously expressed fusion ERQC substrate Kar2 hemagglutinin neuraminidase receives O-linked glycosylation indicative of it reaching the yeast cis/medial-Golgi apparatus, whereas both KHN and CPY* can be found in in vitro ER-derived COPII vesicles (Vashist et al., 2001). Vashist et al. (2001) concluded that all the KHN is delivered to the Golgi apparatus, and then is returned to the ER where it is exported to the cytosol and likely ubiquitinated by Hrd1p. However, we suggest another possibility wherein KHN (much like CPY*) is degraded via two distinct pathways (HIP and HRD/DER), in which a portion of KHN is retained in the ER and is exported and ubiquitinated by Hrd1p while the remaining KHN is transported to the Golgi apparatus and eventually ubiquitinated by Rsp5p.
After transportation to the Golgi apparatus, CPY* must then be exported from within the secretory pathway to the cytosol to be accessible to the cytosolically located Rsp5p. Therefore CPY* is likely returned from the Golgi apparatus to the ER where it is exported to the cytosol, presumably through the translocon, and subsequently ubiquitinated by Rsp5p before proteasomal degradation. A highly speculative alternative model involves the export of CPY* directly from the cis-Golgi compartment to the cytosol by an unidentified mechanism before ubiquitination by Rsp5p. These two possibilities are presented in the model shown in Fig. 9. Unfortunately, the broad subcellular distribution of Rsp5p provides no indication as to which model is correct (Gajewska et al., 2001). Rsp5p can presumably associate with both the Golgi apparatus to mediate Gap1p sorting (Helliwell et al., 2001) and the ER, as evidenced by its ubiquitination of the nuclear membrane/ER-restrained transcription factor Spt23p (Hoppe et al., 2000). Although ERQC substrates are likely returned to the ER from the Golgi apparatus, such a requirement has yet to be definitely demonstrated. The use of Golgi to ER retrograde trafficking mutants is problematic as those mutants tested also show defects in forward transport over the time course required for the degradation experiments (unpublished data). The rationale for delivering ERQC substrates to the Golgi apparatus may be either to (a) access a mechanism responsible for exporting it directly from the Golgi apparatus to the cytosol, or (b) to receive a Golgi apparatus-based modification that signals either its efficient translocation to the cytosol on its return to the ER or its efficient ubiquitination by Rsp5p on its retrotranslocation from the ER to the cytosol. We favor an alternative model in which ERQC substrates are not actively targeted to the Golgi apparatus, but instead are inadequately retained in the ER by the relevant components of the HRD/DER pathway and are transported to the Golgi apparatus. The insufficient ER retention may be because certain individual ERQC substrates interact poorly with the HRD/DER components or due to saturation of this pathway. Therefore the cis-Golgi apparatus may act as a quality control catchment system to capture ERQC substrates that have "escaped" the ER before returning them by retrograde transport to the ER.
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The importance of preventing both the aggregation of misfolded proteins in the ER and the transport of these proteins to the cell surface is underscored by the fact that the cell uses at least two distinct mechanisms to effect their degradation. However, this apparent redundancy raises the question of why one would observe any stabilization of ERQC substrates in HRD/DER-deficient cells while the HIP pathway is functional. It is possible that the two systems complement each other, with the HRD/DER pathway comprising a low capacity system for contending with the nominal loads of misfolded proteins accruing in the ER under optimal growth conditions. The HIP pathway might act as a high capacity mechanism that is up-regulated, potentially by the UPR, to accommodate increased levels of ERQC substrates.
In summary, we have identified an HRD/DER-independent degradation mechanism in which ER-Golgi trafficking and Rsp5p-dependent ubiquitination is required before degradation by the proteasome. Further work will identify the purpose of delivering ERQC substrates to the Golgi apparatus, where in the cell ERQC substrate ubiquitination by Rsp5p occurs, and how such substrates gain access to the Rsp5p in the cytosol.
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Materials and methods |
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KHY163 was constructed as described previously (Caldwell et al., 2001). KHY171 was created by repairing the vma22 locus of KHY140 (Hill and Cooper, 2000). The prc1
::KAN allele was amplified by PCR and inserted into pTOPO 2.1 (Invitrogen) to create pAC550. A 0.9-kb ClaI-SalI fragment from pAC550 was replaced with the HIS3-containing ClaI-SalI fragment from pJJ217 to create pAC556. The prc1
::HIS3 allele from pAC556 was amplified by and transformed into KHY163 and KHY171, creating strains KHY298 and KHY299, respectively. The disruption was confirmed by PCR and Western blot (Caldwell et al., 2001). The pep4
::TRP1 allele from SacI-XhoIdigested pLS110 (provided by Dr. Steven Nothwehr, University of Missouri, Columbia, MO) was introduced into KHY171 to create KHY265. The ubc6
::HIS3 allele was amplified by from RH3140 (provided by Dr. Linda Hicke, Northwestern University, Evanston, IL), and transformed into KHY313, creating KHY333.
The hrd1::TRP1 allele was constructed by inserting a TRP1-containing BglII-NsiI fragment from pJJ248 into BglII-NsiIdigested pAC370 (Hill and Cooper, 2000) creating pAC401. The hrd1
::TRP1 allele from DraI-digested pAC401 was introduced into KHY127 (Hill and Cooper, 2000) and KHY270 (Caldwell et al., 2001) to create strains KHY158 and KHY279, respectively. KHY237 was created by repairing the vma22
locus in KHY158.
To introduce the sec124 allele and create KHY306 and KHY308, SalI-digested pAC559, was transformed into KHY163 and KHY171, and Ura+ prototrophs were placed on 5-FOA. Ura- colonies were screened by failure to grow at 38°C. pAC559 was created by ligating a sec124 containing 3.4-kb XhoI-XbaI from pSHf21 (provided by Dr. Akihiko Nakano, RIKEN, Wako, Saitama, Japan) into XhoI-SpeI-digested pRS306. The rsp52 allele was introduced by transforming KHY163 with StuI-digested pKM017 (provided by Dr. Stefan Jentsch, Max Plank Institute of Biochemistry, Martinsried, Germany). RSP5 was then deleted by transforming the rsp5::HIS3-containing fragment from SacI-SphIdigested pKM017.
Strains deleted for potential ubiquitin ligase genes were transformed with pAC578, radiolabeled, and CPYHA was immunoprecipitated at various times (Hill and Cooper, 2000). Potential RING-H2containing proteins were as follows: YFL010C, YMR075C-A, YKR073C, YKL034W, YDR128W, YOL138C, YCR066W, YHL010C, YOL054W, YLR247C, YLR024C, YGR184C, YHR115C, YDR265W, YDR266C, YOR191W, YOR027W, YLR427W, YMR247C, YDR143C, YLR032W, YPR093C, YNL116W, YBR114W, YLR148W, YER068W, YIL030C (DOA10/SSM4), YER116C, YDL074C, YBR062C, and YDL013W; and strains deleted/temperature sensitive allele for HECT domaincontaining proteins are YJR036C, YDR457W, YKL010C, YGL141W, and YER125W.
pAC453 and pAC519 are 2-µm plasmids and pAC446 is a CEN plasmid in which a prc11-containing 2.8-kb SacI-SalI fragment from pAC356 (Hill and Cooper, 2000) was ligated into the SacI-SalI sites of pTV3,YEp352, and pRS315, respectively. pAC578 was created by ligating a CPY3XHAcontaining 4.3-kb SacI-XhoI fragment from pBG15 (provided by Dr. Scott Moye-Rowley, University of Iowa, Iowa City, IO) into SacI-SalIdigested YEp352. pAC540 is a 2-µm plasmid in which the 1.9-kb SacI-BglII fragment containing PrA3XHA from pAC535 (Caldwell et al., 2001) was ligated in SacI-BamHIdigested YEp352.
Radiolabeling, immunoprecipitation, and antibodies
Radiolabeling and immunoprecipitation were performed as described previously (Hill and Cooper, 2000). Samples were resolved by SDS-PAGE, the gels were fixed, dried, and exposed either to a phosphor cassette (Molecular Dynamics) or to X-ray film. Quantification of gels was performed as described previously (Hill and Cooper, 2000).
Ubiquitin experiment
Yeast strains overexpressing HA-tagged ubiquitin from the CUP1 promoter (YEp112, provided by Dr. Mark Hochstrasser, Yale University, New Haven, CT) were grown overnight in 0.2% oleic acid minimal media containing 150 µM CuSO4. Cells were radiolabeled, spheroplasted, and lysed in buffer containing 10 mM NEM. Immunoprecipitation of CPY* was as described previously (Hill and Cooper, 2000), except with subsaturating amounts of antibody. A sequential immunoprecipitation was performed with HA antibodies. Samples were loaded on a 10% SDS-PAGE.
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Footnotes |
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Acknowledgments |
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This work was supported by the National Institutes of Health grant GM55848.
Submitted: 11 January 2002
Revised: 14 May 2002
Accepted: 16 May 2002
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References |
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![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Altschul, S.F., T.L. Madden, A.A. Schaffer, J. Zhang, Z. Zhang, W. Miller, and D.J. Lipman. 1997. Gapped BLAST and PSI-BLAST: a new generation of protein database search programs. Nucleic Acids Res. 25:33893402.
Baba, M., M. Osumi, S.V. Scott, D.J. Klionsky, and Y. Ohsumi. 1997. Two distinct pathways for targeting proteins from the cytoplasm to the vacuole/lysosome. J. Cell Biol. 139:16871695.
Belden, W.J., and C. Barlowe. 2001. Role of Erv29p in collecting soluble secretory proteins into ER-derived transport vesicles. Science. 294:15281531.
Benharouga, M., M. Haardt, N. Kartner, and G.L. Lukacs. 2001. COOH-terminal truncations promote proteasome-dependent degradation of mature cystic fibrosis transmembrane conductance regulator from post-Golgi compartments. J. Cell Biol. 153:957970.
Biederer, T., C. Volkwein, and T. Sommer. 1996. Degradation of subunits of the Sec61p complex, an integral component of the ER membrane, by the ubiquitin-proteasome pathway. EMBO J. 15:20692076.[Abstract]
Bonifacino, J.S., C.K. Suzuki, J. Lippincott-Schwartz, A.M. Weissman, and R.D. Klausner. 1989. Pre-Golgi degradation of newly synthesized T-cell antigen receptor chains: intrinsic sensitivity and the role of subunit assembly. J. Cell Biol. 109:7383.[Abstract]
Bordallo, J., R.K. Plemper, A. Finger, and D.H. Wolf. 1998. Der3p/Hrd1p is required for endoplasmic reticulum-associated degradation of misfolded lumenal and integral membrane proteins. Mol. Biol. Cell. 9:209222.
Brigance, W.T., C. Barlowe, and T.R. Graham. 2000. Organization of the yeast Golgi complex into at least four functionally distinct compartments. Mol. Biol. Cell. 11:171182.
Brodsky, J.L., E.D. Werner, M.E. Dubas, J.L. Goeckeler, K.B. Kruse, and A.A. McCracken. 1999. The requirement for molecular chaperones during endoplasmic reticulum-associated protein degradation demonstrates that protein export and import are mechanistically distinct. J. Biol. Chem. 274:34533460.
Caldwell, S.R., K.J. Hill, and A.A. Cooper. 2001. Degradation of endoplasmic reticulum (ER) quality control substrates requires transport between the ER and Golgi. J. Biol. Chem. 276:2329623303.
Cooper, A.A., and T.H. Stevens. 1996. Vps10p cycles between the late-Golgi and prevacuolar compartments in its function as the sorting receptor for multiple yeast vacuolar hydrolases. J. Cell Biol. 133:529541.[Abstract]
Deak, P.M., and D.H. Wolf. 2001. Membrane topology and function of Der3/Hrd1p as a ubiquitin-protein ligase (E3) involved in endoplasmic reticulum degradation. J. Biol. Chem. 276:1066310669.
Ellgaard, L., M. Molinari, and A. Helenius. 1999. Setting the standards: quality control in the secretory pathway. Science. 286:18821888.
Fisher, E.A., M. Zhou, D.M. Mitchell, X. Wu, S. Omura, H. Wang, A.L. Goldberg, and H.N. Ginsberg. 1997. The degradation of apolipoprotein B100 is mediated by the ubiquitin-proteasome pathway and involves heat shock protein 70. J. Biol. Chem. 272:2042720434.
Gajewska, B., J. Kaminska, A. Jesionowska, N.C. Martin, A.K. Hopper, and T. Zoladek. 2001. WW domains of Rsp5p define different functions: determination of roles in fluid phase and uracil permease endocytosis in Saccharomyces cerevisiae. Genetics. 157:91101.
Galan, J.M., V. Moreau, B. Andre, C. Volland, and R. Haguenauer-Tsapis. 1996. Ubiquitination mediated by the Npi1p/Rsp5p ubiquitin-protein ligase is required for endocytosis of the yeast uracil permease. J. Biol. Chem. 271:1094610952.
Gardner, R.G., G.M. Swarbrick, N.W. Bays, S.R. Cronin, S. Wilhovsky, L. Seelig, C. Kim, and R.Y. Hampton. 2000. Endoplasmic reticulum degradation requires lumen to cytosol signaling. Transmembrane control of Hrd1p by Hrd3p. J. Cell Biol. 151:6982.
Hammond, C., and A. Helenius. 1994. Quality control in the secretory pathway: retention of a misfolded viral membrane glycoprotein involves cycling between the ER, intermediate compartment, and Golgi apparatus. J. Cell Biol. 126:4152.[Abstract]
Hampton, R.Y., R.G. Gardner, and J. Rine. 1996. Role of 26S proteasome and HRD genes in the degradation of 3-hydroxy-3-methylglutaryl-CoA reductase, an integral endoplasmic reticulum membrane protein. Mol. Biol.Cell. 7:20292044.[Abstract]
Helliwell, S.B., S. Losko, and C.A. Kaiser. 2001. Components of a ubiquitin ligase complex specify polyubiquitination and intracellular trafficking of the general amino acid permease. J. Cell Biol. 153:649662.
Hill, K., and A.A. Cooper. 2000. Degradation of unassembled Vph1p reveals novel aspects of the yeast ER quality control system. EMBO J. 19:550561.
Hill, K.J., and T.H. Stevens. 1994. Vma21p is a yeast membrane protein retained in the endoplasmic reticulum by a di-lysine motif and is required for the assembly of the vacuolar H(+)-ATPase complex. Mol. Biol. Cell. 5:10391050.[Abstract]
Hiller, M.M., A. Finger, M. Schweiger, and D.H. Wolf. 1996. ER degradation of a misfolded luminal protein by the cytosolic ubiquitin-proteasome pathway. Science. 273:17251728.
Hong, E., A.R. Davidson, and C.A. Kaiser. 1996. A pathway for targeting soluble misfolded proteins to the yeast vacuole. J. Cell Biol. 135:623633.[Abstract]
Hsu, V.W., L.C. Yuan, J.G. Nuchtern, J. Lippincott-Schwartz, G.J. Hammerling, and R.D. Klausner. 1991. A recycling pathway between the endoplasmic reticulum and the Golgi apparatus for retention of unassembled MHC class I molecules. Nature. 352:441444.[CrossRef][Medline]
Jakob, C.A., P. Burda, J. Roth, and M. Aebi. 1998. Degradation of misfolded endoplasmic reticulum glycoproteins in Saccharomyces cerevisiae is determined by a specific oligosaccharide structure. J. Cell Biol. 142:12231233.
Jakob, C.A., D. Bodmer, U. Spirig, P. Battig, A. Marcil, D. Dignard, J.J. Bergeron, D.Y. Thomas, and M. Aebi. 2001. Htm1p, a mannosidase-like protein, is involved in glycoprotein degradation in yeast. EMBO Rep. 2:423430.
Jones, E.W., G.S. Zubenko, and R.R. Parker. 1982. PEP4 gene function is required for expression of several vacuolar hydrolases in Saccharomyces cerevisiae. Genetics. 102:665677.
Kamhi-Nesher, S., M. Shenkman, S. Tolchinsky, S.V. Fromm, R. Ehrlich, and G.Z. Lederkremer. 2001. A novel quality control compartment derived from the endoplasmic reticulum. Mol. Biol. Cell. 12:17111723.
Knop, M., A. Finger, T. Braun, K. Hellmuth, and D.H. Wolf. 1996. Der1, a novel protein specifically required for endoplasmic reticulum degradation in yeast. EMBO J. 15:753763.[Abstract]
Margottin, F., S. Benichou, H. Durand, V. Richard, L.X. Liu, E. Gomas, and R. Benarous. 1996. Interaction between the cytoplasmic domains of HIV-1 Vpu and CD4: role of Vpu residues involved in CD4 interaction and in vitro CD4 degradation. Virology. 223:381386.[CrossRef][Medline]
Moolenaar, C.E., J. Ouwendijk, M. Wittpoth, H.A. Wisselaar, H.P. Hauri, L.A. Ginsel, H.Y. Naim, and J.A. Fransen. 1997. A mutation in a highly conserved region in brush-border sucrase-isomaltase and lysosomal alpha-glucosidase results in Golgi retention. J. Cell Sci. 110:557567.
Nakatsukasa, K., S. Nishikawa, N. Hosokawa, K. Nagata, and T. Endo. 2001. Mnl1p, an alpha -mannosidase-like protein in yeast Saccharomyces cerevisiae, is required for endoplasmic reticulum-associated degradation of glycoproteins. J. Biol. Chem. 276:86358638.
Plemper, R.K., S. Bohmler, J. Bordallo, T. Sommer, and D.H. Wolf. 1997. Mutant analysis links the translocon and BiP to retrograde protein transport for ER degradation. Nature. 388:891895.[CrossRef][Medline]
Simpson, J.C., L.M. Roberts, K. Romisch, J. Davey, D.H. Wolf, and J.M. Lord. 1999. Ricin A chain utilises the endoplasmic reticulum-associated protein degradation pathway to enter the cytosol of yeast. FEBS Lett. 459:8084.[CrossRef][Medline]
Swanson, R., M. Locher, and M. Hochstrasser. 2001. A conserved ubiquitin ligase of the nuclear envelope/endoplasmic reticulum that functions in both ER-associated and Matalpha2 repressor degradation. Genes Dev. 15:26602674.
Teckman, J.H., and D.H. Perlmutter. 1996. The endoplasmic reticulum degradation pathway for mutant secretory proteins alpha1-antitrypsin Z and S is distinct from that for an unassembled membrane protein. J. Biol. Chem. 271:1321513220.
Vashist, S., W. Kim, W.J. Belden, E.D. Spear, C. Barlowe, and D.T. Ng. 2001. Distinct retrieval and retention mechanisms are required for the quality control of endoplasmic reticulum protein folding. J. Cell Biol. 155:355368.
Wiertz, E.J., T.R. Jones, L. Sun, M. Bogyo, H.J. Geuze, and H.L. Ploegh. 1996. The human cytomegalovirus US11 gene product dislocates MHC class I heavy chains from the endoplasmic reticulum to the cytosol. Cell. 84:769779.[Medline]
Wilhovsky, S., R. Gardner, and R. Hampton. 2000. HRD gene dependence of endoplasmic reticulum-associated degradation. Mol. Biol. Cell. 11:16971708.
Winitz, D., I. Shachar, Y. Elkabetz, R. Amitay, M. Samuelov, and S. Bar-Nun. 1996. Degradation of distinct assembly forms of immunoglobulin M occurs in multiple sites in permeabilized B cells. J. Biol. Chem. 271:2764527651.
Zuber, C., M.J. Spiro, B. Guhl, R.G. Spiro, and J. Roth. 2000. Golgi apparatus immunolocalization of endomannosidase suggests post-endoplasmic reticulum glucose trimming: implications for quality control. Mol. Biol. Cell. 11:42274240.
Zuber, C., J.Y. Fan, B. Guhl, A. Parodi, J.H. Fessler, C. Parker, and J. Roth. 2001. Immunolocalization of UDP-glucose:glycoprotein glucosyltransferase indicates involvement of pre-Golgi intermediates in protein quality control. Proc. Natl. Acad. Sci. USA. 98:1071010715.
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