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Hwang S, Hartman IZ, Calhoun LN, Garland K, Young GA, Mitsche MA, McDonald J, Xu F, Engelking L, DeBose-Boyd RA. Contribution of Accelerated Degradation to Feedback Regulation of 3-Hydroxy-3-methylglutaryl Coenzyme A Reductase and Cholesterol Metabolism in the Liver. J Biol Chem 2016; 291:13479-94. [PMID: 27129778 DOI: 10.1074/jbc.m116.728469] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Indexed: 11/06/2022] Open
Abstract
Accumulation of sterols in endoplasmic reticulum membranes stimulates the ubiquitination of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR), which catalyzes a rate-limiting step in synthesis of cholesterol. This ubiquitination marks HMGCR for proteasome-mediated degradation and constitutes one of several mechanisms for feedback control of cholesterol synthesis. Mechanisms for sterol-accelerated ubiquitination and degradation of HMGCR have been elucidated through the study of cultured mammalian cells. However, the extent to which these reactions modulate HMGCR and contribute to control of cholesterol metabolism in whole animals is unknown. Here, we examine transgenic mice expressing in the liver the membrane domain of HMGCR (HMGCR (TM1-8)), a region necessary and sufficient for sterol-accelerated degradation, and knock-in mice in which endogenous HMGCR harbors mutations that prevent sterol-induced ubiquitination. Characterization of transgenic mice revealed that HMGCR (TM1-8) is appropriately regulated in the liver of mice fed a high cholesterol diet or chow diet supplemented with the HMGCR inhibitor lovastatin. Ubiquitination-resistant HMGCR protein accumulates in the liver and other tissues disproportionately to its mRNA, indicating that sterol-accelerated degradation significantly contributes to feedback regulation of HMGCR in vivo Results of these studies demonstrate that HMGCR is subjected to sterol-accelerated degradation in the liver through mechanisms similar to those established in cultured cells. Moreover, these studies designate sterol-accelerated degradation of HMGCR as a potential therapeutic target for prevention of atherosclerosis and associated cardiovascular disease.
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Affiliation(s)
- Seonghwan Hwang
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Isamu Z Hartman
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Leona N Calhoun
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Kristina Garland
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Gennipher A Young
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Matthew A Mitsche
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Jeffrey McDonald
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Fang Xu
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Luke Engelking
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Russell A DeBose-Boyd
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
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Kim A, Hartman IZ, Poore B, Boronina T, Cole RN, Song N, Ciudad MT, Caspi RR, Jaraquemada D, Sadegh-Nasseri S. Divergent paths for the selection of immunodominant epitopes from distinct antigenic sources. Nat Commun 2014; 5:5369. [PMID: 25413013 PMCID: PMC4241505 DOI: 10.1038/ncomms6369] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2014] [Accepted: 09/24/2014] [Indexed: 01/25/2023] Open
Abstract
Immunodominant epitopes are few selected epitopes from complex antigens that initiate T cell responses. Here, to provide further insights into this process, we use a reductionist cell-free antigen processing system composed of defined components. We use the system to characterize steps in antigen processing of pathogen-derived proteins or autoantigens and we find distinct paths for peptide processing and selection. Autoantigen-derived immunodominant epitopes are resistant to digestion by cathepsins, whereas pathogen-derived epitopes are sensitive. Sensitivity to cathepsins enforces capture of pathogen-derived epitopes by Major Histocompatibility Complex class II (MHC class II) prior to processing, and resistance to HLA-DM-mediated-dissociation preserves the longevity of those epitopes. We show that immunodominance is established by higher relative abundance of the selected epitopes, which survive cathepsin digestion either by binding to MHC class II and resisting DM-mediated-dissociation, or being chemically resistant to cathepsins degradation. Non-dominant epitopes are sensitive to both DM and cathepsins and are destroyed.
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Affiliation(s)
- AeRyon Kim
- Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
| | - Isamu Z Hartman
- The Graduate Program in Immunology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
| | - Brad Poore
- Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
| | - Tatiana Boronina
- Department of Biological Chemistry, Mass Spectrometry and Proteomics Facility, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
| | - Robert N Cole
- Department of Biological Chemistry, Mass Spectrometry and Proteomics Facility, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
| | - Nianbin Song
- The Graduate Program in Immunology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
| | - M Teresa Ciudad
- Department of Cell Biology, Physiology and Immunology, Laboratori d'Immunologia Cellular, Institut de Biotecnologia i Biomedicina, Universitat Autònoma de Barcelona, 08193 Barcelona, Spain
| | - Rachel R Caspi
- Laboratory of Immunology, National Eye Institute, NIH, Bethesda, Maryland 20892, USA
| | - Dolores Jaraquemada
- Department of Cell Biology, Physiology and Immunology, Laboratori d'Immunologia Cellular, Institut de Biotecnologia i Biomedicina, Universitat Autònoma de Barcelona, 08193 Barcelona, Spain
| | - Scheherazade Sadegh-Nasseri
- 1] Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA [2] The Graduate Program in Immunology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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Morris LL, Hartman IZ, Jun DJ, Seemann J, DeBose-Boyd RA. Sequential actions of the AAA-ATPase valosin-containing protein (VCP)/p97 and the proteasome 19 S regulatory particle in sterol-accelerated, endoplasmic reticulum (ER)-associated degradation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase. J Biol Chem 2014; 289:19053-66. [PMID: 24860107 DOI: 10.1074/jbc.m114.576652] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Accelerated endoplasmic reticulum (ER)-associated degradation (ERAD) of the cholesterol biosynthetic enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase results from its sterol-induced binding to ER membrane proteins called Insig-1 and Insig-2. This binding allows for subsequent ubiquitination of reductase by Insig-associated ubiquitin ligases. Once ubiquitinated, reductase becomes dislocated from ER membranes into the cytosol for degradation by 26 S proteasomes through poorly defined reactions mediated by the AAA-ATPase valosin-containing protein (VCP)/p97 and augmented by the nonsterol isoprenoid geranylgeraniol. Here, we report that the oxysterol 25-hydroxycholesterol and geranylgeraniol combine to trigger extraction of reductase across ER membranes prior to its cytosolic release. This conclusion was drawn from studies utilizing a novel assay that measures membrane extraction of reductase by determining susceptibility of a lumenal epitope in the enzyme to in vitro protease digestion. Susceptibility of the lumenal epitope to protease digestion and thus membrane extraction of reductase were tightly regulated by 25-hydroxycholesterol and geranylgeraniol. The reaction was inhibited by RNA interference-mediated knockdown of either Insigs or VCP/p97. In contrast, reductase continued to become membrane-extracted, but not cytosolically dislocated, in cells deficient for AAA-ATPases of the proteasome 19 S regulatory particle. These findings establish sequential roles for VCP/p97 and the 19 S regulatory particle in the sterol-accelerated ERAD of reductase that may be applicable to the ERAD of other substrates.
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Affiliation(s)
| | | | | | | | - Russell A DeBose-Boyd
- From the Departments of Molecular Genetics and the Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9046
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Poluektov YO, Kim A, Hartman IZ, Sadegh-Nasseri S. HLA-DO as the optimizer of epitope selection for MHC class II antigen presentation. PLoS One 2013; 8:e71228. [PMID: 23951115 PMCID: PMC3738515 DOI: 10.1371/journal.pone.0071228] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Accepted: 06/28/2013] [Indexed: 11/18/2022] Open
Abstract
Processing of antigens for presentation to helper T cells by MHC class II involves HLA-DM (DM) and HLA-DO (DO) accessory molecules. A mechanistic understanding of DO in this process has been missing. The leading model on its function proposes that DO inhibits the effects of DM. To directly study DO functions, we designed a recombinant soluble DO and expressed it in insect cells. The kinetics of binding and dissociation of several peptides to HLA-DR1 (DR1) molecules in the presence of DM and DO were measured. We found that DO reduced binding of DR1 to some peptides, and enhanced the binding of some other peptides to DR1. Interestingly, these enhancing and reducing effects were observed in the presence, or absence, of DM. We found that peptides that were negatively affected by DO were DM-sensitive, whereas peptides that were enhanced by DO were DM-resistant. The positive and negative effects of DO could only be measured on binding kinetics as peptide dissociation kinetics were not affected by DO. Using Surface Plasmon Resonance, we demonstrate direct binding of DO to a peptide-receptive, but not a closed conformation of DR1. We propose that DO imposes another layer of control on epitope selection during antigen processing.
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Affiliation(s)
- Yuri O. Poluektov
- Graduate Program in Immunology, Johns Hopkins School of Medicine, Baltimore, Maryland, United States of America
| | - AeRyon Kim
- Department of Pathology, Johns Hopkins School of Medicine, Baltimore, Maryland, United States of America
| | - Isamu Z. Hartman
- Graduate Program in Immunology, Johns Hopkins School of Medicine, Baltimore, Maryland, United States of America
| | - Scheherazade Sadegh-Nasseri
- Graduate Program in Immunology, Johns Hopkins School of Medicine, Baltimore, Maryland, United States of America
- Department of Pathology, Johns Hopkins School of Medicine, Baltimore, Maryland, United States of America
- * E-mail:
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Jo Y, Hartman IZ, DeBose-Boyd RA. Ancient ubiquitous protein-1 mediates sterol-induced ubiquitination of 3-hydroxy-3-methylglutaryl CoA reductase in lipid droplet-associated endoplasmic reticulum membranes. Mol Biol Cell 2012; 24:169-83. [PMID: 23223569 PMCID: PMC3564538 DOI: 10.1091/mbc.e12-07-0564] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Sterol-induced binding to Insigs in endoplasmic reticulum (ER) membranes triggers ubiquitination of the cholesterol biosynthetic enzyme 3-hydroxy-3-methylglutaryl CoA reductase. This ubiquitination, which is mediated by Insig-associated ubiquitin ligases gp78 and Trc8, is obligatory for extraction of reductase from lipid droplet-associated ER membranes into the cytosol for proteasome-mediated, ER-associated degradation (ERAD). In this study, we identify lipid droplet-associated, ancient, ubiquitous protein-1 (Aup1) as one of several proteins that copurify with gp78. RNA interference (RNAi) studies show that Aup1 recruits the ubiquitin-conjugating enzyme Ubc7 to lipid droplets and facilitates its binding to both gp78 and Trc8. The functional significance of these interactions is revealed by the observation that RNAi-mediated knockdown of Aup1 blunts sterol-accelerated ubiquitination of reductase, which appears to occur in lipid droplet-associated membranes and subsequent ERAD of the enzyme. In addition, Aup1 knockdown inhibits ERAD of Insig-1, another substrate for gp78, as well as that of membrane-bound precursor forms of sterol-regulatory, element-binding protein-1 and -2, transcription factors that modulate expression of genes encoding enzymes required for cholesterol synthesis. Considered together, these findings not only implicate a role for Aup1 in maintenance of intracellular cholesterol homeostasis, but they also highlight the close connections among ERAD, lipid droplets, and lipid droplet-associated proteins.
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Affiliation(s)
- Youngah Jo
- Howard Hughes Medical Institute and Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390-9046, USA
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Sadegh-Nasseri S, Chou CL, Hartman IZ, Kim A, Narayan K. How HLA-DM works: recognition of MHC II conformational heterogeneity. Front Biosci (Schol Ed) 2012; 4:1325-32. [PMID: 22652874 DOI: 10.2741/s334] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Helper T cells respond to peptide antigens derived from exogenous sources presented by MHC II on antigen presenting cells. Antigens from pathogens are internalized by professional antigen presenting cells (APC) and processed for presentation. Certain epitopes are selected during processing as the final peptides for stimulation of T cells and are termed "immunodominant". Understanding how selection of immunodominant epitopes takes place has been a difficult task because of the complexity of the mechanisms governing both antigen processing and T cell recognition. In this review, we discuss our current understanding of HLA-DM function in peptide exchange and selection and its relevance to epitope immunodominance.
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Sadegh-Nasseri S, Natarajan S, Chou CL, Hartman IZ, Narayan K, Kim A. Conformational heterogeneity of MHC class II induced upon binding to different peptides is a key regulator in antigen presentation and epitope selection. Immunol Res 2010; 47:56-64. [PMID: 20066513 DOI: 10.1007/s12026-009-8138-1] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
T cells bearing alphabeta receptors recognize antigenic peptides bound to class I and class II glycoproteins encoded in the major histocompatibility complex (MHC). Cytotoxic and helper T cells respond respectively to peptide antigens derived from endogenous sources presented by MHC class I, and exogenous sources presented by MHC II, on antigen presenting cells. Differences in the MHC class I and class II structures and their maturation pathways have evolved to optimize antigen presentation to their respective T cells. A main focus of our laboratory is on efforts to understand molecular events in processing of antigen for presentation by MHC class II. The different stages of MHC class II-interactions with molecular chaperons involved in folding and traffic from the ER through the antigen-loading compartments, peptide exchange, and transport to the cell surface have been investigated. Through intense research on biophysical and biochemical properties of MHC class II molecules, we have learned that the conformational heterogeneity of MHC class II induced upon binding to different peptides is a key regulator in antigen presentation and epitope selection, and a determinant of the ability of MHC class II to participate in peptide association or dissociation and interaction with the peptide editor HLA-DM.
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Hartman IZ, Liu P, Zehmer JK, Luby-Phelps K, Jo Y, Anderson RGW, DeBose-Boyd RA. Sterol-induced dislocation of 3-hydroxy-3-methylglutaryl coenzyme A reductase from endoplasmic reticulum membranes into the cytosol through a subcellular compartment resembling lipid droplets. J Biol Chem 2010; 285:19288-98. [PMID: 20406816 PMCID: PMC2885207 DOI: 10.1074/jbc.m110.134213] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Sterol-induced binding to Insigs in the endoplasmic reticulum (ER) allows for ubiquitination of 3-hydroxy-3-methylglutaryl coenzyme A reductase, the rate-limiting enzyme in cholesterol synthesis. This ubiquitination marks reductase for recognition by the ATPase VCP/p97, which mediates extraction and delivery of reductase from ER membranes to cytosolic 26 S proteasomes for degradation. Here, we report that reductase becomes dislocated from ER membranes into the cytosol of sterol-treated cells. This dislocation exhibits an absolute requirement for the actions of Insigs and VCP/p97. Reductase also appears in a buoyant fraction of sterol-treated cells that co-purifies with lipid droplets, cytosolic organelles traditionally regarded as storage depots for neutral lipids such as triglycerides and cholesteryl esters. Genetic, biochemical, and localization studies suggest a model in which reductase is dislodged into the cytosol from an ER subdomain closely associated with lipid droplets.
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Affiliation(s)
- Isamu Z Hartman
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 74390-9046, USA
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Narayan K, Chou CL, Kim A, Hartman IZ, Dalai S, Khoruzhenko S, Sadegh-Nasseri S. HLA-DM targets the hydrogen bond between the histidine at position beta81 and peptide to dissociate HLA-DR-peptide complexes. Nat Immunol 2006; 8:92-100. [PMID: 17143275 PMCID: PMC3019572 DOI: 10.1038/ni1414] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2006] [Accepted: 10/24/2006] [Indexed: 11/08/2022]
Abstract
The peptide editor HLA-DM (DM) mediates exchange of peptides bound to major histocompatibility (MHC) class II molecules during antigen processing; however, the mechanism by which DM displaces peptides remains unclear. Here we generated a soluble mutant HLA-DR1 with a histidine-to-asparagine substitution at position 81 of the beta-chain (DR1betaH81N) to perturb an important hydrogen bond between MHC class II and peptide. Peptide-DR1betaH81N complexes dissociated at rates similar to the dissociation rates of DM-induced peptide-wild-type DR1, and DM did not enhance the dissociation of peptide-DR1betaH81N complexes. Reintroduction of an appropriate hydrogen bond (DR1betaH81N betaV85H) restored DM-mediated peptide dissociation. Thus, DR1betaH81N might represent a 'post-DM effect' conformation. We suggest that DM may mediate peptide dissociation by a 'hit-and-run' mechanism that results in conformational changes in MHC class II molecules and disruption of hydrogen bonds between betaHis81 and bound peptide.
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Affiliation(s)
- Kedar Narayan
- Graduate Program in Immunology, Johns Hopkins University Baltimore, Maryland 21205, USA
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Brown ST, Miranda GA, Galic Z, Hartman IZ, Lyon CJ, Aguilera RJ. Regulation of the RAG-1 promoter by the NF-Y transcription factor. J Immunol 1997; 158:5071-4. [PMID: 9164918] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
We have cloned the RAG-1 promoter region and have determined that almost all detectable promoter activity resides within a 208-bp fragment. Sequence analysis of this promoter region has identified potential recognition motifs for a number of lymphocyte-restricted and ubiquitous transcription factors. Subsequent assays have revealed that the NF-Y transcription factor interacts with a CCAAT site within the RAG-1 promoter and appears to play an important role in the positive transcriptional regulation of this gene.
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Affiliation(s)
- S T Brown
- Department of Molecular, Cell, and Developmental Biology, Molecular Biology Institute, University of California at Los Angeles, 90095, USA
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Brown ST, Miranda GA, Galic Z, Hartman IZ, Lyon CJ, Aguilera RJ. Regulation of the RAG-1 promoter by the NF-Y transcription factor. The Journal of Immunology 1997. [DOI: 10.4049/jimmunol.158.11.5071] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Abstract
We have cloned the RAG-1 promoter region and have determined that almost all detectable promoter activity resides within a 208-bp fragment. Sequence analysis of this promoter region has identified potential recognition motifs for a number of lymphocyte-restricted and ubiquitous transcription factors. Subsequent assays have revealed that the NF-Y transcription factor interacts with a CCAAT site within the RAG-1 promoter and appears to play an important role in the positive transcriptional regulation of this gene.
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Affiliation(s)
- S T Brown
- Department of Molecular, Cell, and Developmental Biology, Molecular Biology Institute, University of California at Los Angeles, 90095, USA
| | - G A Miranda
- Department of Molecular, Cell, and Developmental Biology, Molecular Biology Institute, University of California at Los Angeles, 90095, USA
| | - Z Galic
- Department of Molecular, Cell, and Developmental Biology, Molecular Biology Institute, University of California at Los Angeles, 90095, USA
| | - I Z Hartman
- Department of Molecular, Cell, and Developmental Biology, Molecular Biology Institute, University of California at Los Angeles, 90095, USA
| | - C J Lyon
- Department of Molecular, Cell, and Developmental Biology, Molecular Biology Institute, University of California at Los Angeles, 90095, USA
| | - R J Aguilera
- Department of Molecular, Cell, and Developmental Biology, Molecular Biology Institute, University of California at Los Angeles, 90095, USA
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