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Wang R, Wang H, Carrera I, Xu S, Lakshmana MK. COPS5 protein overexpression increases amyloid plaque burden, decreases spinophilin-immunoreactive puncta, and exacerbates learning and memory deficits in the mouse brain. J Biol Chem 2015; 290:9299-309. [PMID: 25713139 DOI: 10.1074/jbc.m114.595926] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [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: 02/10/2015] [Indexed: 01/05/2023] Open
Abstract
Brain accumulation of neurotoxic amyloid β (Aβ) peptide because of increased processing of amyloid precursor protein (APP), resulting in loss of synapses and neurodegeneration, is central to the pathogenesis of Alzheimer disease (AD). Therefore, the identification of molecules that regulate Aβ generation and those that cause synaptic damage is crucial for future therapeutic approaches for AD. We demonstrated previously that COPS5 regulates Aβ generation in neuronal cell lines in a RanBP9-dependent manner. Consistent with the data from cell lines, even by 6 months, COPS5 overexpression in APΔE9 mice (APΔE9/COPS5-Tg) significantly increased Aβ40 levels by 32% (p < 0.01) in the cortex and by 28% (p < 0.01) in the hippocampus, whereas the increases for Aβ42 were 37% (p < 0.05) and 34% (p < 0.05), respectively. By 12 months, the increase was even more robust. Aβ40 levels increased by 63% (p < 0.001) in the cortex and by 65% (p < 0.001) in the hippocampus. Similarly, Aβ42 levels were increased by 69% (p < 0.001) in the cortex and by 71% (p < 0.011) in the hippocampus. Increased Aβ levels were translated into an increased amyloid plaque burden both in the cortex (54%, p < 0.01) and hippocampus (64%, p < 0.01). Interestingly, COPS5 overexpression increased RanBP9 levels in the brain, which, in turn, led to increased amyloidogenic processing of APP, as reflected by increased levels of sAPPβ and decreased levels of sAPPα. Furthermore, COPS5 overexpression reduced spinophilin in both the cortex (19%, p < 0.05) and the hippocampus (20%, p < 0.05), leading to significant deficits in learning and memory skills. Therefore, like RanBP9, COPS5 also plays a pivotal role in amyloid pathology in vivo.
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Affiliation(s)
- Ruizhi Wang
- From the Section of Neurobiology, Torrey Pines Institute for Molecular Studies, Port Saint Lucie, Florida 34987
| | - Hongjie Wang
- From the Section of Neurobiology, Torrey Pines Institute for Molecular Studies, Port Saint Lucie, Florida 34987
| | - Ivan Carrera
- the Department of Neuroscience, Euroespes Biotechnology, Poligono de Bergondo, Nave F, 15165A, A Coruna, Spain, and
| | - Shaohua Xu
- the Florida Institute of Technology, Melbourne, Florida 32901
| | - Madepalli K Lakshmana
- From the Section of Neurobiology, Torrey Pines Institute for Molecular Studies, Port Saint Lucie, Florida 34987,
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2
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Machida K, Mikami S, Masutani M, Mishima K, Kobayashi T, Imataka H. A translation system reconstituted with human factors proves that processing of encephalomyocarditis virus proteins 2A and 2B occurs in the elongation phase of translation without eukaryotic release factors. J Biol Chem 2014; 289:31960-31971. [PMID: 25258322 PMCID: PMC4231674 DOI: 10.1074/jbc.m114.593343] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The genomic RNA of encephalomyocarditis virus (EMCV) encodes a single polyprotein, and the primary scission of the polyprotein occurs between nonstructural proteins 2A and 2B by an unknown mechanism. To gain insight into the mechanism of 2A-2B processing, we first translated the 2A-2B region in vitro with eukaryotic and prokaryotic translation systems. The 2A-2B processing occurred only in the eukaryotic systems, not in the prokaryotic systems, and the unprocessed 2A-2B protein synthesized by a prokaryotic system remained uncleaved when incubated with a eukaryotic cell extract. These results suggest that 2A-2B processing is a eukaryote-specific, co-translational event. To define the translation factors required for 2A-2B processing, we constituted a protein synthesis system with eukaryotic elongation factors 1 and 2, eukaryotic release factors 1 and 3 (eRF1 and eRF3), aminoacyl-tRNA synthetases, tRNAs, ribosome subunits, and a plasmid template that included the hepatitis C virus internal ribosome entry site. We successfully reproduced 2A-2B processing in the reconstituted system even without eRFs. Our results indicate that this unusual event occurs in the elongation phase of translation.
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Affiliation(s)
- Kodai Machida
- Department of Materials Science and Chemistry and University of Hyogo, Himeji 671-2201, Japan; Molecular Nanotechnology Research Center, Graduate School of Engineering, University of Hyogo, Himeji 671-2201, Japan and
| | - Satoshi Mikami
- RIKEN Systems and Structural Biology Center, Yokohama 230-0045, Japan
| | - Mamiko Masutani
- Department of Materials Science and Chemistry and University of Hyogo, Himeji 671-2201, Japan
| | - Kurumi Mishima
- Department of Materials Science and Chemistry and University of Hyogo, Himeji 671-2201, Japan
| | - Tominari Kobayashi
- Department of Materials Science and Chemistry and University of Hyogo, Himeji 671-2201, Japan
| | - Hiroaki Imataka
- Department of Materials Science and Chemistry and University of Hyogo, Himeji 671-2201, Japan; Molecular Nanotechnology Research Center, Graduate School of Engineering, University of Hyogo, Himeji 671-2201, Japan and.
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3
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Song L, 宋 丽, Bachert C, Schjoldager KT, Clausen H, Linstedt AD. Development of isoform-specific sensors of polypeptide GalNAc-transferase activity. J Biol Chem 2014; 289:30556-30566. [PMID: 25225288 DOI: 10.1074/jbc.m114.599563] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [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: 01/11/2023] Open
Abstract
Humans express up to 20 isoforms of GalNAc-transferase (herein T1-T20) that localize to the Golgi apparatus and initiate O-glycosylation. Regulation of this enzyme family affects a vast array of proteins transiting the secretory pathway and diseases arise upon misregulation of specific isoforms. Surprisingly, molecular probes to monitor GalNAc-transferase activity are lacking and there exist no effective global or isoform-specific inhibitors. Here we describe the development of T2- and T3-isoform specific fluorescence sensors that traffic in the secretory pathway. Each sensor yielded little signal when glycosylated but was strongly activated in the absence of its glycosylation. Specificity of each sensor was assessed in HEK cells with either the T2 or T3 enzymes deleted. Although the sensors are based on specific substrates of the T2 and T3 enzymes, elements in or near the enzyme recognition sequence influenced their activity and required modification, which we carried out based on previous in vitro work. Significantly, the modified T2 and T3 sensors were activated only in cells lacking their corresponding isozymes. Thus, we have developed T2- and T3-specific sensors that will be valuable in both the study of GalNAc-transferase regulation and in high-throughput screening for potential therapeutic regulators of specific GalNAc-transferases.
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Affiliation(s)
- Lina Song
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 and
| | - 丽娜 宋
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 and
| | - Collin Bachert
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 and
| | - Katrine T Schjoldager
- Departments of Cellular and Molecular Medicine and School of Dentistry, Copenhagen Center for Glycomics, University of Copenhagen, DK-2200 Copenhagen, Denmark
| | - Henrik Clausen
- Departments of Cellular and Molecular Medicine and School of Dentistry, Copenhagen Center for Glycomics, University of Copenhagen, DK-2200 Copenhagen, Denmark
| | - Adam D Linstedt
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 and.
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4
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Yamamoto-Tanaka M, Motoyama A, Miyai M, Matsunaga Y, Matsuda J, Tsuboi R, Hibino T. Mesotrypsin and caspase-14 participate in prosaposin processing: potential relevance to epidermal permeability barrier formation. J Biol Chem 2014; 289:20026-38. [PMID: 24872419 DOI: 10.1074/jbc.m113.543421] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [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: 12/29/2022] Open
Abstract
A proteomics-based search for molecules interacting with caspase-14 identified prosaposin and epidermal mesotrypsin as candidates. Prosaposin is a precursor of four sphingolipid activator proteins (saposins A-D) that are essential for lysosomal hydrolysis of sphingolipids. Thus, we hypothesized that caspase-14 and mesotrypsin participate in processing of prosaposin. Because we identified a saposin A sequence as an interactor with these proteases, we prepared a specific antibody to saposin A and focused on saposin A-related physiological reactions. We found that mesotrypsin generated saposins A-D from prosaposin, and mature caspase-14 contributed to this process by activating mesotrypsinogen to mesotrypsin. Knockdown of these proteases markedly down-regulated saposin A synthesis in skin equivalent models. Saposin A was localized in granular cells, whereas prosaposin was present in the upper layer of human epidermis. The proximity ligation assay confirmed interaction between prosaposin, caspase-14, and mesotrypsin in the granular layer. Oil Red staining showed that the lipid envelope was significantly reduced in the cornified layer of skin from saposin A-deficient mice. Ultrastructural studies revealed severely disorganized cornified layer structure in both prosaposin- and saposin A-deficient mice. Overall, our results indicate that epidermal mesotrypsin and caspase-14 work cooperatively in prosaposin processing. We propose that they thereby contribute to permeability barrier formation in vivo.
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Affiliation(s)
- Mami Yamamoto-Tanaka
- From the Shiseido Innovative Science Research Center, 2-2-1 Hayabuchi, Tsuzuki-ku, Yokohama 224-8558, the Department of Dermatology, Tokyo Medical University, 6-7-1 Nishishinjuku, Shinjuku-ku, Tokyo 160-0023, and
| | - Akira Motoyama
- From the Shiseido Innovative Science Research Center, 2-2-1 Hayabuchi, Tsuzuki-ku, Yokohama 224-8558
| | - Masashi Miyai
- From the Shiseido Innovative Science Research Center, 2-2-1 Hayabuchi, Tsuzuki-ku, Yokohama 224-8558
| | - Yukiko Matsunaga
- From the Shiseido Innovative Science Research Center, 2-2-1 Hayabuchi, Tsuzuki-ku, Yokohama 224-8558
| | - Junko Matsuda
- the Institute of Glycoscience, Tokai University, Kitakinnmoku 4-1-1, Hiratsuka, Kanagawa 259-1292, Japan
| | - Ryoji Tsuboi
- the Department of Dermatology, Tokyo Medical University, 6-7-1 Nishishinjuku, Shinjuku-ku, Tokyo 160-0023, and
| | - Toshihiko Hibino
- From the Shiseido Innovative Science Research Center, 2-2-1 Hayabuchi, Tsuzuki-ku, Yokohama 224-8558,
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5
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Abstract
Intein-mediated protein splicing raises questions and creates opportunities in many scientific areas. Evolutionary biologists question whether inteins are primordial enzymes or simply selfish elements, whereas biochemists seek to understand how inteins work. Synthetic chemists exploit inteins in the semisynthesis of proteins with or without nonribosomal modifications, whereas biotechnologists use modified inteins in an ever increasing variety of applications. The four minireviews in this series explore these themes. The first minireview focuses on the evolution and biological function of inteins, whereas the second describes the mechanisms that underlie the remarkable ability of inteins to perform complex sets of choreographed enzymatic reactions. The third explores the relationship between the three-dimensional structure and dynamics of inteins and their biochemical capabilities. The fourth describes intein applications that have moved beyond simple technology development to utilizing inteins in more sophisticated applications, such as biosensors for identifying ligands of human hormone receptors or improved methods of biofuel and plant-based sugar production.
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Affiliation(s)
| | - Norma M Allewell
- the Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, Maryland 20742
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6
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Abstract
The discovery of inteins in the early 1990s opened the door to a wide variety of new technologies. Early engineered inteins from various sources allowed the development of self-cleaving affinity tags and new methods for joining protein segments through expressed protein ligation. Some applications were developed around native and engineered split inteins, which allow protein segments expressed separately to be spliced together in vitro. More recently, these early applications have been expanded and optimized through the discovery of highly efficient trans-splicing and trans-cleaving inteins. These new inteins have enabled a wide variety of applications in metabolic engineering, protein labeling, biomaterials construction, protein cyclization, and protein purification.
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Affiliation(s)
- David W Wood
- From the Department of Chemical and Biomolecular Engineering, Ohio State University, Columbus, Ohio 43210 and
| | - Julio A Camarero
- the Departments of Pharmacology and Pharmaceutical Sciences and Department of Chemistry, University of Southern California, Los Angeles, California 90033
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7
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Lutz D, Loers G, Kleene R, Oezen I, Kataria H, Katagihallimath N, Braren I, Harauz G, Schachner M. Myelin basic protein cleaves cell adhesion molecule L1 and promotes neuritogenesis and cell survival. J Biol Chem 2014; 289:13503-18. [PMID: 24671420 DOI: 10.1074/jbc.m113.530238] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [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: 12/14/2022] Open
Abstract
The cell adhesion molecule L1 is a Lewis(x)-carrying glycoprotein that plays important roles in the developing and adult nervous system. Here we show that myelin basic protein (MBP) binds to L1 in a Lewis(x)-dependent manner. Furthermore, we demonstrate that MBP is released by murine cerebellar neurons as a sumoylated dynamin-containing protein upon L1 stimulation and that this MBP cleaves L1 as a serine protease in the L1 extracellular domain at Arg(687) yielding a transmembrane fragment that promotes neurite outgrowth and neuronal survival in cell culture. L1-induced neurite outgrowth and neuronal survival are reduced in MBP-deficient cerebellar neurons and in wild-type cerebellar neurons in the presence of an MBP antibody or L1 peptide containing the MBP cleavage site. Genetic ablation of MBP in shiverer mice and mutagenesis of the proteolytically active site in MBP or of the MBP cleavage site within L1 as well as serine protease inhibitors and an L1 peptide containing the MBP cleavage site abolish generation of the L1 fragment. Our findings provide evidence for novel functions of MBP in the nervous system.
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Affiliation(s)
- David Lutz
- From the Zentrum für Molekulare Neurobiologie, Universitätsklinikum Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany
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8
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Cebotaru V, Cebotaru L, Kim H, Chiaravalli M, Boletta A, Qian F, Guggino WB. Polycystin-1 negatively regulates Polycystin-2 expression via the aggresome/autophagosome pathway. J Biol Chem 2014; 289:6404-6414. [PMID: 24459142 DOI: 10.1074/jbc.m113.501205] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [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
Mutations of the PKD1 and PKD2 genes, encoding polycystin-1 (PC1) and polycystin-2 (PC2), respectively, lead to autosomal dominant polycystic kidney disease. Interestingly, up-regulation or down-regulation of PKD1 or PKD2 leads to polycystic kidney disease in animal models, but their interrelations are not completely understood. We show here that full-length PC1 that interacts with PC2 via a C-terminal coiled-coil domain regulates PC2 expression in vivo and in vitro by down-regulating PC2 expression in a dose-dependent manner. Expression of the pathogenic mutant R4227X, which lacks the C-terminal coiled-coil domain, failed to down-regulate PC2 expression, suggesting that PC1-PC2 interaction is necessary for PC2 regulation. The proteasome and autophagy are two pathways that control protein degradation. Proteins that are not degraded by proteasomes precipitate in the cytoplasm and are transported via histone deacetylase 6 (HDAC6) toward the aggresomes. We found that HDAC6 binds to PC2 and that expression of full-length PC1 accelerates the transport of the HDAC6-PC2 complex toward aggresomes, whereas expression of the R4227X mutant fails to do so. Aggresomes are engulfed by autophagosomes, which then fuse with the lysosome for degradation; this process is also known as autophagy. We have now shown that PC1 overexpression leads to increased degradation of PC2 via autophagy. Interestingly, PC1 does not activate autophagy generally. Thus, we have now uncovered a new pathway suggesting that when PC1 is expressed, PC2 that is not bound to PC1 is directed to aggresomes and subsequently degraded via autophagy, a control mechanism that may play a role in autosomal dominant polycystic kidney disease pathogenesis.
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Affiliation(s)
- Valeriu Cebotaru
- Division of Nephrology, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Liudmila Cebotaru
- Departments of Ophthalmology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Hyunho Kim
- Division of Nephrology, Departments of Medicine, University of Maryland, Baltimore, Maryland 21201
| | - Marco Chiaravalli
- Division of Genetics and Cell Biology, San Raffaele Scientific Institute, 20132 Milan, Italy
| | - Alessandra Boletta
- Division of Genetics and Cell Biology, San Raffaele Scientific Institute, 20132 Milan, Italy
| | - Feng Qian
- Division of Nephrology, Departments of Medicine, University of Maryland, Baltimore, Maryland 21201
| | - William B Guggino
- Departments of Physiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
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9
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Ha SW, Ju D, Xie Y. Nuclear import factor Srp1 and its associated protein Sts1 couple ribosome-bound nascent polypeptides to proteasomes for cotranslational degradation. J Biol Chem 2013; 289:2701-10. [PMID: 24338021 DOI: 10.1074/jbc.m113.524926] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [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
Cotranslational protein degradation plays an important role in protein quality control and proteostasis. Although ubiquitylation has been suggested to signal cotranslational degradation of nascent polypeptides, cotranslational ubiquitylation occurs at a low level, suggesting the existence of an alternative route for delivery of nascent polypeptides to the proteasome. Here we report that the nuclear import factor Srp1 (also known as importin α or karyopherin α) is required for ubiquitin-independent cotranslational degradation of the transcription factor Rpn4. We further demonstrate that cotranslational protein degradation is generally impaired in the srp1-49 mutant. Srp1 binds nascent polypeptides emerging from the ribosome. The association of proteasomes with polysomes is weakened in srp1-49. The interaction between Srp1 and the proteasome is mediated by Sts1, a multicopy suppressor of srp1-49. The srp1-49 and sts1-2 mutants are hypersensitive to stressors that promote protein misfolding, underscoring the physiological function of Srp1 and Sts1 in degradation of misfolded nascent polypeptides. This study unveils a previously unknown role for Srp1 and Sts1 in cotranslational protein degradation and suggests a novel model whereby Srp1 and Sts1 cooperate to couple proteasomes to ribosome-bound nascent polypeptides.
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Affiliation(s)
- Seung-Wook Ha
- From the Karmanos Cancer Institute, Department of Oncology, and Department of Pathology, Wayne State University School of Medicine, Detroit, Michigan 48201
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10
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Chu BW, Kovary KM, Guillaume J, Chen LC, Teruel MN, Wandless TJ. The E3 ubiquitin ligase UBE3C enhances proteasome processivity by ubiquitinating partially proteolyzed substrates. J Biol Chem 2013; 288:34575-87. [PMID: 24158444 DOI: 10.1074/jbc.m113.499350] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [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: 01/10/2023] Open
Abstract
To maintain protein homeostasis, cells must balance protein synthesis with protein degradation. Accumulation of misfolded or partially degraded proteins can lead to the formation of pathological protein aggregates. Here we report the use of destabilizing domains, proteins whose folding state can be reversibly tuned using a high affinity ligand, as model substrates to interrogate cellular protein quality control mechanisms in mammalian cells using a forward genetic screen. Upon knockdown of UBE3C, an E3 ubiquitin ligase, a reporter protein consisting of a destabilizing domain fused to GFP is degraded more slowly and incompletely by the proteasome. Partial proteolysis is also observed when UBE3C is present but cannot ubiquitinate substrates because its active site has been mutated, it is unable to bind to the proteasome, or the substrate lacks lysine residues. UBE3C knockdown also results in less substrate polyubiquitination. Finally, knockdown renders cells more susceptible to the Hsp90 inhibitor 17-AAG, suggesting that UBE3C protects against the harmful accumulation of protein fragments arising from incompletely degraded proteasome substrates.
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Affiliation(s)
- Bernard W Chu
- From the Department of Chemical and Systems Biology, Stanford University, Stanford, California 94305
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11
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Zhu H, Xu BL, Liang X, Yang YR, Tang XF, Tang B. Molecular basis for auto- and hetero-catalytic maturation of a thermostable subtilase from thermophilic Bacillus sp. WF146. J Biol Chem 2013; 288:34826-38. [PMID: 24145031 DOI: 10.1074/jbc.m113.498774] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [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
The proform of the WF146 protease, an extracellular subtilase produced by thermophilic Bacillus sp. WF146, matures efficiently at high temperatures. Here we report that the proform, which contains an N-terminal propeptide composed of a core domain (N*) and a linker peptide, is intrinsically able to mature via multiple pathways. One autocatalytic pathway is initiated by cis-processing of N* to generate an autoprocessed complex N*-I(WT), and this step is followed by truncation of the linker peptide and degradation of N*. Another autocatalytic pathway is initiated by trans-processing of the linker peptide followed by degradation of N*. Unlike most reported subtilases, the maturation of the WF146 protease occurs not only autocatalytically but also hetero-catalytically whereby heterogeneous proteases accelerate the maturation of the WF146 protease via trans-processing of the proform and N*-I(WT). Although N* acts as an intramolecular chaperone and an inhibitor of the mature enzyme, the linker peptide is susceptible to proteolysis, allowing the trans-processing reaction to occur auto- and hetero-catalytically. These studies also demonstrate that the WF146 protease undergoes subtle structural adjustments during the maturation process and that the binding of Ca(2+) is required for routing the proform to mature properly at high temperatures. Interestingly, under Ca(2+)-free conditions, the proform is cis-processed into a unique propeptide-intermediate complex (N*-I(E)) capable of re-synthesis of the proform. Based on the basic catalytic principle of serine proteases and these experimental results, a mechanism for the cis-processing/re-synthesis equilibrium of the proform and the role of the linker peptide in regulation of this equilibrium has been proposed.
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Affiliation(s)
- Hui Zhu
- From the State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, China
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12
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Humbard MA, Surkov S, De Donatis GM, Jenkins LM, Maurizi MR. The N-degradome of Escherichia coli: limited proteolysis in vivo generates a large pool of proteins bearing N-degrons. J Biol Chem 2013; 288:28913-24. [PMID: 23960079 DOI: 10.1074/jbc.m113.492108] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [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
The N-end rule is a conserved mechanism found in Gram-negative bacteria and eukaryotes for marking proteins to be degraded by ATP-dependent proteases. Specific N-terminal amino acids (N-degrons) are sufficient to target a protein to the degradation machinery. In Escherichia coli, the adaptor ClpS binds an N-degron and delivers the protein to ClpAP for degradation. As ClpS recognizes N-terminal Phe, Trp, Tyr, and Leu, which are not found at the N terminus of proteins translated and processed by the canonical pathway, proteins must be post-translationally modified to expose an N-degron. One modification is catalyzed by Aat, an enzyme that adds leucine or phenylalanine to proteins with N-terminal lysine or arginine; however, such proteins are also not generated by the canonical protein synthesis pathway. Thus, the mechanisms producing N-degrons in proteins and the frequency of their occurrence largely remain a mystery. To address these issues, we used a ClpS affinity column to isolate interacting proteins from E. coli cell lysates under non-denaturing conditions. We identified more than 100 proteins that differentially bound to a column charged with wild-type ClpS and eluted with a peptide bearing an N-degron. Thirty-two of 37 determined N-terminal peptides had N-degrons. Most of the proteins were N-terminally truncated by endoproteases or exopeptidases, and many were further modified by Aat. The identities of the proteins point to possible physiological roles for the N-end rule in cell division, translation, transcription, and DNA replication and reveal widespread proteolytic processing of cellular proteins to generate N-end rule substrates.
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Németh BC, Wartmann T, Halangk W, Sahin-Tóth M. Autoactivation of mouse trypsinogens is regulated by chymotrypsin C via cleavage of the autolysis loop. J Biol Chem 2013; 288:24049-62. [PMID: 23814066 DOI: 10.1074/jbc.m113.478800] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [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: 12/31/2022] Open
Abstract
Chymotrypsin C (CTRC) is a proteolytic regulator of trypsinogen autoactivation in humans. CTRC cleavage of the trypsinogen activation peptide stimulates autoactivation, whereas cleavage of the calcium binding loop promotes trypsinogen degradation. Trypsinogen mutations that alter these regulatory cleavages lead to increased intrapancreatic trypsinogen activation and cause hereditary pancreatitis. The aim of this study was to characterize the regulation of autoactivation of mouse trypsinogens by mouse Ctrc. We found that the mouse pancreas expresses four trypsinogen isoforms to high levels, T7, T8, T9, and T20. Only the T7 activation peptide was cleaved by mouse Ctrc, causing negligible stimulation of autoactivation. Surprisingly, mouse Ctrc poorly cleaved the calcium binding loop in all mouse trypsinogens. In contrast, mouse Ctrc readily cleaved the Phe-150-Gly-151 peptide bond in the autolysis loop of T8 and T9 and inhibited autoactivation. Mouse chymotrypsin B also cleaved the same peptide bond but was 7-fold slower. T7 was less sensitive to chymotryptic regulation, which involved slow cleavage of the Leu-149-Ser-150 peptide bond in the autolysis loop. Modeling indicated steric proximity of the autolysis loop and the activation peptide in trypsinogen, suggesting the cleaved autolysis loop may directly interfere with activation. We conclude that autoactivation of mouse trypsinogens is under the control of mouse Ctrc with some notable differences from the human situation. Thus, cleavage of the trypsinogen activation peptide or the calcium binding loop by Ctrc is unimportant. Instead, inhibition of autoactivation via cleavage of the autolysis loop is the dominant mechanism that can mitigate intrapancreatic trypsinogen activation.
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Affiliation(s)
- Balázs Csaba Németh
- Department of Molecular and Cell Biology, Boston University Henry M. Goldman School of Dental Medicine, Boston, Massachusetts 02118, USA
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14
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Cakir I, Cyr NE, Perello M, Litvinov BP, Romero A, Stuart RC, Nillni EA. Obesity induces hypothalamic endoplasmic reticulum stress and impairs proopiomelanocortin (POMC) post-translational processing. J Biol Chem 2013; 288:17675-88. [PMID: 23640886 DOI: 10.1074/jbc.m113.475343] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.6] [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: 01/20/2023] Open
Abstract
It was shown previously that abnormal prohormone processing or inactive proconverting enzymes that are responsible for this processing cause profound obesity. Our laboratory demonstrated earlier that in the diet-induced obesity (DIO) state, the appetite-suppressing neuropeptide α-melanocyte-stimulating hormone (α-MSH) is reduced, yet the mRNA of its precursor protein proopiomelanocortin (POMC) remained unaltered. It was also shown that the DIO condition promotes the development of endoplasmic reticulum (ER) stress and leptin resistance. In the current study, using an in vivo model combined with in vitro experiments, we demonstrate that obesity-induced ER stress obstructs the post-translational processing of POMC by decreasing proconverting enzyme 2, which catalyzes the conversion of adrenocorticotropin to α-MSH, thereby decreasing α-MSH peptide production. This novel mechanism of ER stress affecting POMC processing in DIO highlights the importance of ER stress in regulating central energy balance in obesity.
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Affiliation(s)
- Isin Cakir
- Division of Endocrinology, Department of Medicine, Warren Alpert Medical School of Brown University/Rhode Island Hospital, Providence, Rhode Island 02907, USA
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