Dislocation of Type I Membrane Proteins from the ER to the Cytosol Is Sensitive to Changes in Redox Potential

Tortorella, Domenico; Story, Craig M.; Huppa, Johannes B.; Wiertz, Emmanuel J. H. J.; Jones, Thomas R.; Ploegh, Hidde L.

doi:10.1083/jcb.142.2.365

Cited by 121 publications

(112 citation statements)

References 69 publications

(108 reference statements)

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“…By fractionating permeabilized proteasomeinhibited cells, we demonstrate that endogenous HMGR and a tagged version of its membrane region, as well as Insig-1-Myc, are released to the cytosol as full-length intact polypeptides. These results complement reports on the dislocation of luminal ERAD substrates (Rodighiero et al, 2002;Elkabetz et al, 2004;Afshar et al, 2005) and of membrane proteins with a single TMs (Huppa and Ploegh, 1997;Tortorella et al, 1998;Ye et al, 2003). Together with recent in vitro evidence for dislocation of ubiquitinated polytopic Ste6*p and Hmg2p (Garza et al, 2009) from yeast microsomes, it seems that, among the possible models suggested for dislocation of polytopic membrane ERAD substrates , complete extraction to the cytosol of intact polypeptide chains is a general feature of the delivery to the proteasome of this class of proteins.…”

Section: Discussionsupporting

confidence: 57%

Dislocation of HMG-CoA Reductase and Insig-1, Two Polytopic Endoplasmic Reticulum Proteins, En Route to Proteasomal Degradation

Leichner

Avner

Harats

et al. 2009

MBoC

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The endoplasmic reticulum (ER) glycoprotein HMG-CoA reductase (HMGR) catalyzes the rate-limiting step in sterols biosynthesis. Mammalian HMGR is ubiquitinated and degraded by the proteasome when sterols accumulate in cells, representing the best example for metabolically controlled ER-associated degradation (ERAD). This regulated degradation involves the short-lived ER protein Insig-1. Here, we investigated the dislocation of these ERAD substrates to the cytosol en route to proteasomal degradation. We show that the tagged HMGR membrane region, HMG 350 INTRODUCTIONA key mechanism for maintaining cholesterol homeostasis in mammalian cells involves modulating the stability of 3-hydroxy-3-methylglutaryl CoA reductase (HMGR). This enzyme catalyzes the rate-limiting step in the mevalonate (MVA) pathway in which essential sterols and nonsterol isoprenoids are synthesized (Goldstein and Brown, 1990). In cells deprived of sterols and/or MVA-derived isoprenoids, HMGR is a fairly stable protein that turns over with a half-life of 10 -14 h. Conversely, in cells replenished with MVA pathway products, HMGR degradation is accelerated severalfold and its half-life drops to 1-4 h (Faust et al., 1982;Edwards et al., 1983;Sinensky and Logel, 1983), reflecting one of the highly regulated processes that prevent accumulation of these metabolites to toxic levels.Similar to other proteins of the MVA pathway (Horton et al., 2002), HMGR is controlled also at the transcriptional level by the sterol regulatory element-binding protein (SREBP)-2, which binds to the promoter of the HMGR gene and activates transcription when demands for MVA-derived products increase (Osborne et al., 1985;Vallett et al., 1996). Like its closely related SREBP-1a and SREBP-1c factors, SREBP-2 is synthesized as a large endoplasmic reticulum (ER)-bound precursor whose transcription activation domain must be released from the membrane to function in the nucleus. On increased demand for MVA-derived metabolites, the SREBP precursor is transported by COP-II vesicles to the Golgi, where it is sequentially cleaved at two sites by resident site-1 and site-2 proteases. The liberated transcriptionally active domain enters the nucleus and stimulates the transcription of target genes, including HMGR (Sakai et al., 1996;Nohturfft et al., 1998aNohturfft et al., , 2000. When sterols are abundant and demand for MVA-derived products declines, the transport of the SREBP precursor out from the ER is prevented and transcription ceases (Nohturfft et al., 1999(Nohturfft et al., , 2000. This metabolically regulated traffic of the SREBP precursors critically depends on SREBP cleavage-activating protein (SCAP), a membrane protein with eight transmembranes spans (TMs), which tightly associates with the SREBP precursors and enables the packaging of both proteins in the COP-II vesicles and their transport from the ER to the Golgi Sakai et al., 1997;Nohturfft et al., 1998b Feramisco et al., 2004). This sterol-stimulated binding to Insig(s) masks the transport signal in SCAP and abrogates i...

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Section: Discussionsupporting

confidence: 57%

Dislocation of HMG-CoA Reductase and Insig-1, Two Polytopic Endoplasmic Reticulum Proteins, En Route to Proteasomal Degradation

Leichner

Avner

Harats

et al. 2009

MBoC

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“…The fact that H-L disassembly requires energy might explain why the degradation of assembled s was facilitated by cytosolic factors and reducing agents to a greater extent than free chains (26,27). Our data do not allow us to establish whether also intrachain disulfides are reduced before dislocation of Ig subunits as suggested for major histocompatibility complex class I heavy chains (42).…”

Section: Discussionmentioning

confidence: 39%

Reduction of Interchain Disulfide Bonds Precedes the Dislocation of Ig-µ Chains from the Endoplasmic Reticulum to the Cytosol for Proteasomal Degradation

Fagioli¹,

Mezghrani²,

Sitia³

2001

Journal of Biological Chemistry

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Proteins that fail to fold or assemble in the endoplasmic reticulum (ER) are generally dislocated across the membrane to be degraded by cytosolic proteasomes. To investigate how the quality control machinery handles individual subunits that are part of covalent oligomers, we have analyzed the fate of transport-competent Ig light (L) chains that form disulfide bonds with shortlived heavy chains. When expressed alone, L chains are secreted. In cells producing excess , most L chains are retained in the ER as covalent ⅐L or 2 ⅐L 2 complexes. While chains present in these complexes are degraded by proteasomes, L chains are stable. Few L chains are secreted; most reassociate with newly synthesized chains. Therefore, interchain disulfide bonds are reduced in the ER lumen before the dislocation of chains in a site from which freed L chains can be rapidly reinserted in the assembly line. The ER can thus sustain the simultaneous formation and reduction of disulfide bonds.

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“…S1F). In contrast, diamide directly reacts with GSH and converts it to GSSG in the absence of any enzyme (25). Indeed, postlysis addition of diamide to HA-Urm1 WT lysates induces Urm1 conjugation almost as efficiently as does treatment of intact cells, whereas postlysis addition of H 2 O 2 has no effect (Fig.…”

Section: Urmylation Involves a Thioester Intermediate And Results In mentioning

confidence: 97%

Role of the ubiquitin-like protein Urm1 as a noncanonical lysine-directed protein modifier

Veen

Schorpp

Schlieker

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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171

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The ubiquitin (Ub)-related modifier Urm1 functions as a sulfur carrier in tRNA thiolation by means of a mechanism that requires the formation of a thiocarboxylate at the C-terminal glycine residue of Urm1. However, whether Urm1 plays an additional role as a Ublike protein modifier remains unclear. Here, we show that Urm1 is conjugated to lysine residues of target proteins and that oxidative stress enhances protein urmylation in both Saccharomyces cerevisiae and mammalian cells. Similar to ubiquitylation, urmylation involves a thioester intermediate and results in the formation of a covalent peptide bond between Urm1 and its substrates. In contrast to modification by canonical Ub-like modifiers, however, conjugation of Urm1 involves a C-terminal thiocarboxylate of the modifier. We have confirmed that the peroxiredoxin Ahp1 is such a substrate in S. cerevisiae and found that Urm1 targets a specific lysine residue of Ahp1 in vivo. In addition, we have identified several unique substrates in mammalian cells and show that Urm1 targets at least two pathways on oxidant treatment. First, Urm1 is appended to lysine residues of three components that function in its own pathway (i.e., MOCS3, ATPBD3, and CTU2). Second, Urm1 is conjugated to the nucleocytoplasmic shuttling factor cellular apoptosis susceptibility protein. Thus, Urm1 has a conserved dual role by integrating the functions of prokaryotic sulfur carriers with those of eukaryotic protein modifiers of the Ub family.posttranslational modification | hydrogen peroxide | nuclear transport | Uba4 | USP15

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Dislocation of Type I Membrane Proteins from the ER to the Cytosol Is Sensitive to Changes in Redox Potential

Cited by 121 publications

References 69 publications

Dislocation of HMG-CoA Reductase and Insig-1, Two Polytopic Endoplasmic Reticulum Proteins, En Route to Proteasomal Degradation

Dislocation of HMG-CoA Reductase and Insig-1, Two Polytopic Endoplasmic Reticulum Proteins, En Route to Proteasomal Degradation

Reduction of Interchain Disulfide Bonds Precedes the Dislocation of Ig-µ Chains from the Endoplasmic Reticulum to the Cytosol for Proteasomal Degradation

Role of the ubiquitin-like protein Urm1 as a noncanonical lysine-directed protein modifier

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