1
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Li X, Mariappan M. Nascent Chain Ubiquitination is Uncoupled from Degradation to Enable Protein Maturation. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.10.09.561585. [PMID: 37873109 PMCID: PMC10592752 DOI: 10.1101/2023.10.09.561585] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2023]
Abstract
A significant proportion of nascent proteins undergo polyubiquitination on ribosomes in mammalian cells, yet the fate of these proteins remains elusive. The ribosome-associated quality control (RQC) is a mechanism that mediates the ubiquitination of nascent chains on stalled ribosomes. Here, we find that nascent proteins ubiquitinated on stalled ribosomes by the RQC E3 ligase LTN1 are insufficient for proteasomal degradation. Our biochemical reconstitution studies reveal that ubiquitinated nascent chains are promptly deubiquitinated in the cytosol upon release from stalled ribosomes, as they are no longer associated with LTN1 E3 ligase for continuous ubiquitination to compete with cytosolic deubiquitinases. These deubiquitinated nascent chains can mature into stable proteins. However, if they misfold and expose a degradation signal, the cytosolic quality control recognizes them for re-ubiquitination and subsequent proteasomal degradation. Thus, our findings suggest that cycles of ubiquitination and deubiquitination spare foldable nascent proteins while ensuring the degradation of terminally misfolded proteins.
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Affiliation(s)
- Xia Li
- Department of Cell Biology, Nanobiology Institute, Yale School of Medicine, Yale University West Campus, West Haven, CT 06516, USA
| | - Malaiyalam Mariappan
- Department of Cell Biology, Nanobiology Institute, Yale School of Medicine, Yale University West Campus, West Haven, CT 06516, USA
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2
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Turk SM, Indovina CJ, Miller JM, Overton DL, Runnebohm AM, Orchard CJ, Tragesser-Tiña ME, Gosser SK, Doss EM, Richards KA, Irelan CB, Daraghmi MM, Bailey CG, Niekamp JM, Claypool KP, Engle SM, Buchanan BW, Woodruff KA, Olesen JB, Smaldino PJ, Rubenstein EM. Lipid biosynthesis perturbation impairs endoplasmic reticulum-associated degradation. J Biol Chem 2023; 299:104939. [PMID: 37331602 PMCID: PMC10372827 DOI: 10.1016/j.jbc.2023.104939] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2023] [Revised: 06/02/2023] [Accepted: 06/09/2023] [Indexed: 06/20/2023] Open
Abstract
The relationship between lipid homeostasis and protein homeostasis (proteostasis) is complex and remains incompletely understood. We conducted a screen for genes required for efficient degradation of Deg1-Sec62, a model aberrant translocon-associated substrate of the endoplasmic reticulum (ER) ubiquitin ligase Hrd1, in Saccharomyces cerevisiae. This screen revealed that INO4 is required for efficient Deg1-Sec62 degradation. INO4 encodes one subunit of the Ino2/Ino4 heterodimeric transcription factor, which regulates expression of genes required for lipid biosynthesis. Deg1-Sec62 degradation was also impaired by mutation of genes encoding several enzymes mediating phospholipid and sterol biosynthesis. The degradation defect in ino4Δ yeast was rescued by supplementation with metabolites whose synthesis and uptake are mediated by Ino2/Ino4 targets. Stabilization of a panel of substrates of the Hrd1 and Doa10 ER ubiquitin ligases by INO4 deletion indicates ER protein quality control is generally sensitive to perturbed lipid homeostasis. Loss of INO4 sensitized yeast to proteotoxic stress, suggesting a broad requirement for lipid homeostasis in maintaining proteostasis. A better understanding of the dynamic relationship between lipid homeostasis and proteostasis may lead to improved understanding and treatment of several human diseases associated with altered lipid biosynthesis.
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Affiliation(s)
- Samantha M Turk
- Department of Biology, Ball State University, Muncie, Indiana, USA
| | | | - Jacob M Miller
- Department of Biology, Ball State University, Muncie, Indiana, USA
| | | | | | - Cade J Orchard
- Department of Biology, Ball State University, Muncie, Indiana, USA
| | | | | | - Ellen M Doss
- Department of Biology, Ball State University, Muncie, Indiana, USA
| | - Kyle A Richards
- Department of Biology, Ball State University, Muncie, Indiana, USA
| | | | | | - Connor G Bailey
- Department of Biology, Ball State University, Muncie, Indiana, USA
| | - Julia M Niekamp
- Department of Biology, Ball State University, Muncie, Indiana, USA
| | | | - Sarah M Engle
- Department of Biology, Ball State University, Muncie, Indiana, USA
| | - Bryce W Buchanan
- Department of Biology, Ball State University, Muncie, Indiana, USA
| | | | - James B Olesen
- Department of Biology, Ball State University, Muncie, Indiana, USA
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3
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Ji C. Molecular Factors and Pathways of Hepatotoxicity Associated with HIV/SARS-CoV-2 Protease Inhibitors. Int J Mol Sci 2023; 24:ijms24097938. [PMID: 37175645 PMCID: PMC10178330 DOI: 10.3390/ijms24097938] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2023] [Revised: 04/21/2023] [Accepted: 04/25/2023] [Indexed: 05/15/2023] Open
Abstract
Antiviral protease inhibitors are peptidomimetic molecules that block the active catalytic center of viral proteases and, thereby, prevent the cleavage of viral polyprotein precursors into maturation. They continue to be a key class of antiviral drugs that can be used either as boosters for other classes of antivirals or as major components of current regimens in therapies for the treatment of infections with human immunodeficiency virus (HIV) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, sustained/lifelong treatment with the drugs or drugs combined with other substance(s) often leads to severe hepatic side effects such as lipid abnormalities, insulin resistance, and hepatotoxicity. The underlying pathogenic mechanisms are not fully known and are under continuous investigation. This review focuses on the general as well as specific molecular mechanisms of the protease inhibitor-induced hepatotoxicity involving transporter proteins, apolipoprotein B, cytochrome P450 isozymes, insulin-receptor substrate 1, Akt/PKB signaling, lipogenic factors, UDP-glucuronosyltransferase, pregnane X receptor, hepatocyte nuclear factor 4α, reactive oxygen species, inflammatory cytokines, off-target proteases, and small GTPase Rab proteins related to ER-Golgi trafficking, organelle stress, and liver injury. Potential pharmaceutical/therapeutic solutions to antiviral drug-induced hepatic side effects are also discussed.
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Affiliation(s)
- Cheng Ji
- Research Center for Liver Disease, GI/Liver Division, Department of Medicine, Keck School of Medicine of USC, University of Southern California, Los Angeles, CA 90089, USA
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4
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Daraghmi MM, Miller JM, Bailey CG, Doss EM, Kalinski AL, Smaldino PJ, Rubenstein EM. Macro-ER-phagy receptors Atg39p and Atg40p confer resistance to aminoglycoside hygromycin B in S. cerevisiae. MICROPUBLICATION BIOLOGY 2023; 2023:10.17912/micropub.biology.000738. [PMID: 36818312 PMCID: PMC9932795 DOI: 10.17912/micropub.biology.000738] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Figures] [Subscribe] [Scholar Register] [Received: 01/09/2023] [Revised: 01/24/2023] [Accepted: 01/26/2023] [Indexed: 02/24/2023]
Abstract
Receptor-mediated autophagic turnover of portions of the endoplasmic reticulum (ER) is mediated by macro-ER-phagy. We hypothesized macro-ER-phagy promotes proteotoxic stress resistance. We predicted Saccharomyces cerevisiae lacking macro-ER-phagy receptors would exhibit enhanced sensitivity to hygromycin B, which reduces translational fidelity and is expected to globally disrupt protein homeostasis, including at the ER. We observed that loss of either of two yeast macro-ER-phagy receptors (Atg39p or Atg40p) compromised cellular resistance to hygromycin B to a similar extent as loss of ER-associated degradation (ERAD) ubiquitin ligases Hrd1p and Doa10p. Our data are consistent with a model whereby macro-ER-phagy and ERAD collaborate to mediate ER protein quality control. Disruptions of macro-ER-phagy have been linked to neuropathy, dementia, and cancer. A dampened capacity to mediate protein quality control may contribute to these conditions.
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Affiliation(s)
| | | | | | | | | | | | - Eric M. Rubenstein
- Department of Biology, Ball State University
,
Correspondence to: Eric M. Rubenstein (
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5
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Singh S, Sharma A, Ahmad S, Guru B, Gulzar F, Kumar P, Ahmad I, Tamrakar AK. Convergence of Fructose-Induced NLRP3 Activation with Oxidative Stress and ER Stress Leading to Hepatic Steatosis. Inflammation 2023; 46:217-233. [PMID: 35941320 DOI: 10.1007/s10753-022-01727-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2022] [Revised: 07/18/2022] [Accepted: 08/03/2022] [Indexed: 11/05/2022]
Abstract
High fructose flux enhances hepatocellular triglyceride accumulation (hepatic steatosis), which is a prime trigger in the emergence of hepatic ailments. Nevertheless, the pathophysiology underlying the process is not completely understood. Emerging evidences have revealed the inputs from multiple cues including inflammation, oxidative stress, and endoplasmic reticulum (ER) stress in the development of hepatic steatosis. Here, we substantiated the role of NLRP3 inflammasome and its convergence with oxidative and ER stress leading to hepatic steatosis under high fructose diet feeding. Male SD rats were fed on 60% high fructose diet (HFrD) for 10 weeks and treated with antioxidant quercetin or NLRP3 inflammasome inhibitor glyburide during the last 6 weeks, followed by metabolic characterization and analysis of hepatic parameters. HFrD-induced hepatic steatosis was associated with the activation of NLRP3 inflammasome, pro-inflammatory response, oxidative, and ER stress in liver. Treatment with quercetin abrogated HFrD-induced oxidative stress, along with attenuation of NLRP3 activation in the liver. On the other hand, inhibition of NLRP3 signaling by glyburide suppressed HFrD-induced oxidative and ER stress. Both glyburide or quercetin treatment significantly attenuated hepatic steatosis, associated with mitigated expression of the lipogenic markers in liver. Our findings verified the association of NLRP3 inflammasome with oxidative and ER stress in fructose-induced lipogenic response and indicate that in addition to be a target of oxidative/ER stress, NLRP3 can act as a trigger for oxidative/ER stress to activate a vicious cycle where these cues act in a complex manner to propagate inflammatory response, leading to hepatic steatosis.
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Affiliation(s)
- Sushmita Singh
- Division of Biochemistry and Structural Biology, CSIR-Central Drug Research Institute, Sec-10, Jankipuram Extension, Sitapur Road, Lucknow, 226031, India.,Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
| | - Aditya Sharma
- Division of Biochemistry and Structural Biology, CSIR-Central Drug Research Institute, Sec-10, Jankipuram Extension, Sitapur Road, Lucknow, 226031, India
| | - Shadab Ahmad
- Division of Biochemistry and Structural Biology, CSIR-Central Drug Research Institute, Sec-10, Jankipuram Extension, Sitapur Road, Lucknow, 226031, India.,Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
| | - Bhavimani Guru
- Division of Biochemistry and Structural Biology, CSIR-Central Drug Research Institute, Sec-10, Jankipuram Extension, Sitapur Road, Lucknow, 226031, India
| | - Farah Gulzar
- Division of Biochemistry and Structural Biology, CSIR-Central Drug Research Institute, Sec-10, Jankipuram Extension, Sitapur Road, Lucknow, 226031, India
| | - Pawan Kumar
- Division of Biochemistry and Structural Biology, CSIR-Central Drug Research Institute, Sec-10, Jankipuram Extension, Sitapur Road, Lucknow, 226031, India.,Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
| | - Ishbal Ahmad
- Division of Biochemistry and Structural Biology, CSIR-Central Drug Research Institute, Sec-10, Jankipuram Extension, Sitapur Road, Lucknow, 226031, India
| | - Akhilesh K Tamrakar
- Division of Biochemistry and Structural Biology, CSIR-Central Drug Research Institute, Sec-10, Jankipuram Extension, Sitapur Road, Lucknow, 226031, India. .,Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India.
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6
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Mehrtash AB, Hochstrasser M. Ectopic RING activity at the ER membrane differentially impacts ERAD protein quality control pathways. J Biol Chem 2023; 299:102927. [PMID: 36682496 PMCID: PMC9950527 DOI: 10.1016/j.jbc.2023.102927] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2022] [Revised: 01/12/2023] [Accepted: 01/13/2023] [Indexed: 01/20/2023] Open
Abstract
Endoplasmic reticulum-associated degradation (ERAD) is a protein quality control pathway that ensures misfolded proteins are removed from the ER and destroyed. In ERAD, membrane and luminal substrates are ubiquitylated by ER-resident RING-type E3 ubiquitin ligases, retrotranslocated into the cytosol, and degraded by the proteasome. Overexpression of ERAD factors is frequently used in yeast and mammalian cells to study this process. Here, we analyze the impact of ERAD E3 overexpression on substrate turnover in yeast, where there are three ERAD E3 complexes (Doa10, Hrd1, and Asi1-3). Elevated Doa10 or Hrd1 (but not Asi1) RING activity at the ER membrane resulting from protein overexpression inhibits the degradation of specific Doa10 substrates. The ERAD E2 ubiquitin-conjugating enzyme Ubc6 becomes limiting under these conditions, and UBC6 overexpression restores Ubc6-mediated ERAD. Using a subset of the dominant-negative mutants, which contain the Doa10 RING domain but lack the E2-binding region, we show that they induce degradation of membrane tail-anchored Ubc6 independently of endogenous Doa10 and the other ERAD E3 complexes. This remains true even if the cells lack the Dfm1 rhomboid pseudoprotease, which is also a proposed retrotranslocon. Hence, rogue RING activity at the ER membrane elicits a highly specific off-pathway defect in the Doa10 pathway, and the data point to an additional ERAD E3-independent retrotranslocation mechanism.
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Affiliation(s)
- Adrian B Mehrtash
- Department of Molecular, Cellular, & Developmental Biology, Yale University, New Haven, Connecticut, USA
| | - Mark Hochstrasser
- Department of Molecular, Cellular, & Developmental Biology, Yale University, New Haven, Connecticut, USA; Department of Molecular Biophysics & Biochemistry, Yale University, New Haven, Connecticut, USA.
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7
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Mehrtash AB, Hochstrasser M. Elements of the ERAD ubiquitin ligase Doa10 regulating sequential poly-ubiquitylation of its targets. iScience 2022; 25:105351. [PMID: 36325070 PMCID: PMC9619350 DOI: 10.1016/j.isci.2022.105351] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2022] [Revised: 08/16/2022] [Accepted: 10/11/2022] [Indexed: 11/29/2022] Open
Abstract
In ER-associated degradation (ERAD), misfolded ER proteins are degraded by the proteasome after undergoing ubiquitylation. Yeast Doa10 (human MARCHF6/TEB4) is a membrane-embedded E3 ubiquitin ligase that functions with E2s Ubc6 and Ubc7. Ubc6 attaches a single ubiquitin to substrates, which is extended by Ubc7 to form a polyubiquitin chain. We show the conserved C-terminal element (CTE) of Doa10 promotes E3-mediated Ubc6 activity. Doa10 substrates undergoing an alternative ubiquitylation mechanism are still degraded in CTE-mutant cells. Structure prediction by AlphaFold2 suggests the CTE binds near the catalytic RING-CH domain, implying a direct role in substrate ubiquitylation, and we confirm this interaction using intragenic suppression. Truncation analysis defines a minimal E2-binding region of Doa10; structural predictions suggest that Doa10 forms a retrotranslocation channel and that E2s bind within the cofactor-binding region defined here. These results provide mechanistic insight into how Doa10, and potentially other ligases, interact with their cofactors and mediate ERAD. The conserved Doa10 C-terminus promotes E3-mediated activity of Ubc6 The minimal E2-binding region of Doa10 includes TMs 1–9 The N- and C-terminus of Doa10 interact, likely forming an ERAD protein channel
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Affiliation(s)
- Adrian B. Mehrtash
- Department of Molecular, Cellular, & Developmental Biology, Yale University, New Haven, 06520 CT, USA
| | - Mark Hochstrasser
- Department of Molecular, Cellular, & Developmental Biology, Yale University, New Haven, 06520 CT, USA
- Department of Molecular Biophysics & Biochemistry, Yale University, New Haven, CT 06520, USA
- Corresponding author
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8
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Chen X, Gao K, Xiang Z, Zhang Y, Peng X. Identification and Validation of an Endoplasmic Reticulum Stress-Related lncRNA Signature for Colon Adenocarcinoma Patients. Int J Gen Med 2022; 15:4303-4319. [PMID: 35480990 PMCID: PMC9037931 DOI: 10.2147/ijgm.s358775] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2022] [Accepted: 04/12/2022] [Indexed: 11/23/2022] Open
Abstract
Purpose Methods Results Conclusion
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Affiliation(s)
- Xueru Chen
- Department of Pharmacy, The Third Xiangya Hospital, Central South University, Changsha, Hunan, 410013, People’s Republic of China
| | - Kai Gao
- Department of Gastrointestinal Surgery, The Third Xiangya Hospital of Central South University, Changsha, People’s Republic of China
| | - Zijin Xiang
- Department of Pharmacy, The Third Xiangya Hospital, Central South University, Changsha, Hunan, 410013, People’s Republic of China
| | - Yujun Zhang
- Department of Pharmacy, The Third Xiangya Hospital, Central South University, Changsha, Hunan, 410013, People’s Republic of China
| | - Xiangdong Peng
- Department of Pharmacy, The Third Xiangya Hospital, Central South University, Changsha, Hunan, 410013, People’s Republic of China
- Correspondence: Xiangdong Peng, Department of Pharmacy, The Third Xiangya Hospital, Central South University, 138 Tongzipo Road, Changsha, Hunan Province, 410013, People’s Republic of China, Email
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9
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Woodruff KA, Richards KA, Evans MD, Scott AR, Voas BM, Irelan CB, Olesen JB, Smaldino PJ, Rubenstein EM. Inner Nuclear Membrane Asi Ubiquitin Ligase Catalytic Subunits Asi1p and Asi3p, but not Asi2p, confer resistance to aminoglycoside hygromycin B in Saccharomyces cerevisiae. MICROPUBLICATION BIOLOGY 2021; 2021:10.17912/micropub.biology.000403. [PMID: 34095778 PMCID: PMC8170509 DOI: 10.17912/micropub.biology.000403] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The heterotrimeric Asi ubiquitin ligase (encoded by ASI1, ASI2, and ASI3) mediates protein degradation in the inner nuclear membrane in Saccharomyces cerevisiae. Asi1p and Asi3p possess catalytic domains, while Asi2p functions as an adaptor for a subset of Asi substrates. We hypothesized the Asi complex is an important mediator of protein quality control, and we predicted that Asi would be required for optimal growth in conditions associated with elevated abundance of aberrant proteins. Loss of Asi1p or Asi3p, but not Asi2p, sensitized yeast to hygromycin B, which promotes translational infidelity by distorting the ribosome A site. Surprisingly, loss of quality control ubiquitin ligase Hul5p did not sensitize yeast to hygromycin B. Our results are consistent with a prominent role for an Asi subcomplex that includes Asi1p and Asi3p (but not Asi2p) in protein quality control.
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10
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Runnebohm AM, Richards KA, Irelan CB, Turk SM, Vitali HE, Indovina CJ, Rubenstein EM. Overlapping function of Hrd1 and Ste24 in translocon quality control provides robust channel surveillance. J Biol Chem 2020; 295:16113-16120. [PMID: 33033070 DOI: 10.1074/jbc.ac120.016191] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Revised: 10/06/2020] [Indexed: 12/20/2022] Open
Abstract
Translocation of proteins across biological membranes is essential for life. Proteins that clog the endoplasmic reticulum (ER) translocon prevent the movement of other proteins into the ER. Eukaryotes have multiple translocon quality control (TQC) mechanisms to detect and destroy proteins that persistently engage the translocon. TQC mechanisms have been defined using a limited panel of substrates that aberrantly occupy the channel. The extent of substrate overlap among TQC pathways is unknown. In this study, we found that two TQC enzymes, the ER-associated degradation ubiquitin ligase Hrd1 and zinc metalloprotease Ste24, promote degradation of characterized translocon-associated substrates of the other enzyme in Saccharomyces cerevisiae Although both enzymes contribute to substrate turnover, our results suggest a prominent role for Hrd1 in TQC. Yeast lacking both Hrd1 and Ste24 exhibit a profound growth defect, consistent with overlapping function. Remarkably, two mutations that mildly perturb post-translational translocation and reduce the extent of aberrant translocon engagement by a model substrate diminish cellular dependence on TQC enzymes. Our data reveal previously unappreciated mechanistic complexity in TQC substrate detection and suggest that a robust translocon surveillance infrastructure maintains functional and efficient translocation machinery.
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Affiliation(s)
| | - Kyle A Richards
- Department of Biology, Ball State University, Muncie, Indiana, USA
| | | | - Samantha M Turk
- Department of Biology, Ball State University, Muncie, Indiana, USA
| | - Halie E Vitali
- Department of Biology, Ball State University, Muncie, Indiana, USA
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11
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Croft T, Venkatakrishnan P, James Theoga Raj C, Groth B, Cater T, Salemi MR, Phinney B, Lin SJ. N-terminal protein acetylation by NatB modulates the levels of Nmnats, the NAD + biosynthetic enzymes in Saccharomyces cerevisiae. J Biol Chem 2020; 295:7362-7375. [PMID: 32299909 PMCID: PMC7247314 DOI: 10.1074/jbc.ra119.011667] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2019] [Revised: 04/14/2020] [Indexed: 12/13/2022] Open
Abstract
NAD+ is an essential metabolite participating in cellular biochemical processes and signaling. The regulation and interconnection among multiple NAD+ biosynthesis pathways are incompletely understood. Yeast (Saccharomyces cerevisiae) cells lacking the N-terminal (Nt) protein acetyltransferase complex NatB exhibit an approximate 50% reduction in NAD+ levels and aberrant metabolism of NAD+ precursors, changes that are associated with a decrease in nicotinamide mononucleotide adenylyltransferase (Nmnat) protein levels. Here, we show that this decrease in NAD+ and Nmnat protein levels is specifically due to the absence of Nt-acetylation of Nmnat (Nma1 and Nma2) proteins and not of other NatB substrates. Nt-acetylation critically regulates protein degradation by the N-end rule pathways, suggesting that the absence of Nt-acetylation may alter Nmnat protein stability. Interestingly, the rate of protein turnover (t½) of non-Nt-acetylated Nmnats did not significantly differ from those of Nt-acetylated Nmnats. Accordingly, deletion or depletion of the N-end rule pathway ubiquitin E3 ligases in NatB mutants did not restore NAD+ levels. Next, we examined whether the status of Nt-acetylation would affect the translation of Nmnats, finding that the absence of Nt-acetylation does not significantly alter the polysome formation rate on Nmnat mRNAs. However, we observed that NatB mutants have significantly reduced Nmnat protein maturation. Our findings indicate that the reduced Nmnat levels in NatB mutants are mainly due to inefficient protein maturation. Nmnat activities are essential for all NAD+ biosynthesis routes, and understanding the regulation of Nmnat protein homeostasis may improve our understanding of the molecular basis and regulation of NAD+ metabolism.
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Affiliation(s)
- Trevor Croft
- Department of Microbiology and Molecular Genetics, College of Biological Sciences, University of California, Davis, California 95616
| | - Padmaja Venkatakrishnan
- Department of Microbiology and Molecular Genetics, College of Biological Sciences, University of California, Davis, California 95616
| | - Christol James Theoga Raj
- Department of Microbiology and Molecular Genetics, College of Biological Sciences, University of California, Davis, California 95616
| | - Benjamin Groth
- Department of Microbiology and Molecular Genetics, College of Biological Sciences, University of California, Davis, California 95616
| | - Timothy Cater
- Department of Microbiology and Molecular Genetics, College of Biological Sciences, University of California, Davis, California 95616
| | - Michelle R Salemi
- Proteomic Core Facility, University of California, Davis, California 95616
| | - Brett Phinney
- Proteomic Core Facility, University of California, Davis, California 95616
| | - Su-Ju Lin
- Department of Microbiology and Molecular Genetics, College of Biological Sciences, University of California, Davis, California 95616.
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12
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Richards KA, Rubenstein EM. Endoplasmic reticulum stress-regulated degradation of a translocon-associated protein is independent of integrated stress response transcription factor Gcn4p. MICROPUBLICATION BIOLOGY 2020; 2020:10.17912/micropub.biology.000239. [PMID: 32550483 PMCID: PMC7252232 DOI: 10.17912/micropub.biology.000239] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Kyle A Richards
- Ball State University, Department of Biology, Muncie, IN 47306
| | - Eric M Rubenstein
- Ball State University, Department of Biology, Muncie, IN 47306,
Correspondence to: Eric M Rubenstein ()
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13
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Xu Y, Fang D. Endoplasmic reticulum-associated degradation and beyond: The multitasking roles for HRD1 in immune regulation and autoimmunity. J Autoimmun 2020; 109:102423. [PMID: 32057541 DOI: 10.1016/j.jaut.2020.102423] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Revised: 02/01/2020] [Accepted: 02/04/2020] [Indexed: 12/19/2022]
Abstract
Endoplasmic reticulum (ER)-associated degradation (ERAD) is a mechanism against ER stress, wherein unfolded/misfolded proteins accumulated in the ER are transported to the cytosol for degradation by the ubiquitin-proteasome system. The ER resident E3 ubiquitin ligase HRD1 has been identified as a key ERAD factor that directly catalyzes ubiquitin conjugation onto the unfolded or misfolded proteins for proteasomal degradation. The abnormally increased HRD1 expression was discovered in rheumatoid synovial cells, providing the first evidence for HRD1 dysregulation involved in human inflammatory pathogenesis. Further studies shown that inflammatory cytokines involved in rheumatoid pathogenesis including IL-1β, TNF-α, IL-17 and IL-26 induce HRD1 expression. Recent studies using mice with tissue-specific targeted deletion of HRD1 gene have revealed important functions of HRD1 in immune regulation and inflammatory diseases. HRD1 has been shown critical for dendritic cell expression of antigens to both CD4 and CD8 T cells. Both TCR and costimulatory receptor CD28 signaling induces HRD1 expression, which promotes T cell clonal expansion and IL-2 production. Together with the fact that HRD1 is required for maintaining the stability of regulatory T cell (Treg) stability, HRD1 appears to fine tone T cell immunity. In addition, HRD1 is involved in humoral immune response by regulating early B cell development and maintaining B cell survival upon recognition of specific antigen. HRD1 appears to target its substrates for ubiquitination through, either ERAD-dependent or -independent, at least two distinct molecular mechanisms in a cell or tissue specific manner to achieve its physiological functions. Dysregulation of HRD1 expression and/or it functions are involved in autoimmune inflammatory diseases in particular rheumatoid arthritis and lupus. Here, we review current findings on the mechanism of HRD1 protein in immune regulation and the involvement of HRD1 in the pathogenesis of autoimmune inflammatory diseases.
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Affiliation(s)
- Yuanming Xu
- Department of Pathology, Northwestern University Feinberg School of Medicine, 303 E. Chicago Ave, Chicago, IL, 60611, USA
| | - Deyu Fang
- Department of Pathology, Northwestern University Feinberg School of Medicine, 303 E. Chicago Ave, Chicago, IL, 60611, USA.
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14
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Broshar CL, Rubenstein EM. Glucose concentration does not affect degradation of a protein that aberrantly engages the endoplasmic reticulum translocon. MICROPUBLICATION BIOLOGY 2020; 2020:248. [PMID: 32548573 PMCID: PMC7295686] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
| | - Eric M Rubenstein
- Ball State University, Department of Biology, Muncie, IN 47306,To whom correspondence should be addressed:
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