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Dong-er Zhang - One of the best experts on this subject based on the ideXlab platform.
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Identification and characterization of a novel ISG15-ubiquitin mixed chain and its role in regulating protein homeostasis
Scientific reports, 2015Co-Authors: Jun-bao Fan, Kei Lchiro Arimoto, Khatereh Motamedchaboki, Ming Yan, Dieter A. Wolf, Dong-er ZhangAbstract:As a ubiquitin-like modifier, ISG15 is conjugated to many cellular proteins in a process termed protein ISGylation. However, the crosstalk between protein ISGylation and the ubiquitin proteasome system is not fully understood. Here, we report that cellular ubiquitin is a substrate of ISG15 and Lys 29 on ubiquitin is the major ISG15 acceptor site. Using a model substrate, we demonstrate that ISG15 can modify ubiquitin, which is immobilized on its substrate, to form ISG15-ubiquitin mixed chains. Furthermore, our results indicate that ISG15-ubiquitin mixed chains do not serve as degradation signals for a ubiquitin fusion degradation substrate. Accordingly, an ISG15-ubiquitin fusion protein, which mimics an ISG15-ubiquitin mixed chain, negatively regulates cellular turnover of ubiquitylated proteins. In addition, ISG15-ubiquitin mixed chains, which are detectable on endogenously ubiquitylated proteins, dampen cellular turnover of these proteins. Thus, our studies unveil an unanticipated interplay between two protein modification systems and highlight its role in coordinating protein homeostasis.
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mice lacking the ISG15 e1 enzyme ube1l demonstrate increased susceptibility to both mouse adapted and non mouse adapted influenza b virus infection
Journal of Virology, 2009Co-Authors: Caroline Lai, Dong-er Zhang, Jessica J Struckhoff, Jana Schneider, Luis Martinezsobrido, Thorsten Wolff, Adolfo Garciasastre, Deborah J LenschowAbstract:ISG15 functions as a critical antiviral molecule against influenza virus, with infection inducing both the conjugation of ISG15 to target proteins and production of free ISG15. Here, we report that mice lacking the ISG15 E1 enzyme UbE1L fail to form ISG15 conjugates. Both UbE1L−/− and ISG15−/− mice display increased susceptibility to influenza B virus infection, including non-mouse-adapted strains. Finally, we demonstrate that ISG15 controls influenza B virus infection through its action within radioresistant stromal cells and not bone marrow-derived cells. Thus, the conjugation of ISG15 to target proteins within stromal cells is critical to its activity against influenza virus.
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Nitrosylation of ISG15 Prevents the Disulfide Bond-mediated Dimerization of ISG15 and Contributes to Effective ISGylation
The Journal of biological chemistry, 2008Co-Authors: Fumihiko Okumura, Deborah J Lenschow, Dong-er ZhangAbstract:The expression of the ubiquitin-like molecule ISG15 (UCRP) and protein modification by ISG15 (ISGylation) are strongly activated by interferon, genotoxic stress, and pathogen infection, suggesting that ISG15 plays an important role in innate immune responses. Inducible nitric-oxide synthase (iNOS) is induced by the similar stimuli as ISG15 and enhances the production of nitric oxide (NO), a pleiotropic free radical with antipathogen activity. Here, we report that cysteine residues (Cys-76 and -143 in mouse, Cys-78 in human) of ISG15 can be modified by NO, and the NO modification of ISG15 decreases the dimerization of ISG15. The mutation of the cysteine residue of ISG15 to serine improves total ISGylation. The NO synthase inhibitor S-ethylisothiourea reduces endogenous ISGylation. Furthermore, ectopic expression of iNOS enhanced total ISGylation. Together, these results suggest that nitrosylation of ISG15 enhances target protein ISGylation. This is the first report of a relationship between ISGylation and nitrosylation.
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Different roles for two ubiquitin-like domains of ISG15 in protein modification.
The Journal of biological chemistry, 2008Co-Authors: Yong-gang Chang, Xian Zhong Yan, Yuanyuan Xie, Xue Chao Gao, Ai Xin Song, Dong-er ZhangAbstract:ISG15 (interferon-stimulated gene 15) is a novel ubiquitin-like (UbL) modifier with two UbL domains in its architecture. We investigated different roles for the two UbL domains in protein modification by ISG15 (ISGylation) and the impact of Influenza B virus NS1 protein (NS1B) on regulation of the pathway. The results show that, although the C-terminal domain is sufficient to link ISG15 to UBE1L and UbcH8, the N-terminal domain is dispensable in the activation and transthiolation steps but required for efficient E3-mediated transfer of ISG15 from UbcH8 to its substrates. NS1B specifically binds to the N-terminal domain of ISG15 but does not affect ISG15 linkage via a thioester bond to its activating and conjugating enzymes. However, it does inhibit the formation of cellular ISG15 conjugates upon interferon treatment. We propose that the N-terminal UbL domain of ISG15 mainly functions in the ligation step and NS1B inhibits ISGylation by competing with E3 ligases for binding to the N-terminal domain.
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Ubp43 gene expression is required for normal ISG15 expression and fetal development.
Reproductive biology and endocrinology : RB&E, 2007Co-Authors: Lea A. Rempel, Kenneth J. Ritchie, Dong-er Zhang, Luiz E. Henkes, Ming Yan, Kathleen J. Austin, Mei-feng Shen, Thomas R. HansenAbstract:Background ISG15 covalently modifies murine endometrial proteins in response to early pregnancy. ISG15 can also be severed from targeted proteins by a specific protease called Ubp43 (Usp18). Mice lacking Ubp43 (null) form increased conjugated ISG15 in response to interferon. The ISG15 system has not been examined in chorioallantoic placenta (CP) or mesometrial (MM) components of implantation sites beyond 9.5 days post coitum (dpc). It was hypothesized that deletion of Ubp43 would cause disregulation of ISG15 in implantation sites, and that this would affect pregnancy rates.
Robert M. Krug - One of the best experts on this subject based on the ideXlab platform.
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Interferon-induced ISG15 pathway: An ongoing virus-host battle
Trends in microbiology, 2013Co-Authors: Chen Zhao, Tien Ying Hsiang, Mark N. Collins, Robert M. KrugAbstract:ISG15 is an interferon (IFN)-induced ubiquitin-like protein that is conjugated to target proteins via the sequential action of three enzymes that are also induced by IFN. Unlike ubiquitin, which is highly conserved, the sequence of ISG15 varies between species. ISG15 conjugation inhibits many viruses, and free (unconjugated) ISG15 can also act as an antiviral protein. In this review, we focus on the antiviral role of ISG15 conjugation and on countermeasures employed by several viruses. The countermeasure by influenza B virus is unique in that it exhibits species specificity. Only the antiviral activity of human and non-human primate ISG15s can be blocked, providing one possible explanation for the restriction of influenza B virus to humans.
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Structural basis for the sequence-specific recognition of human ISG15 by the NS1 protein of influenza B virus.
Proceedings of the National Academy of Sciences of the United States of America, 2011Co-Authors: Rongjin Guan, Robert M. Krug, Chen Zhao, Li Chung, Paul G. Leonard, Brendan R. Amer, Haripriya Sridharan, Gaetano T. MontelioneAbstract:Interferon-induced ISG15 conjugation plays an important antiviral role against several viruses, including influenza viruses. The NS1 protein of influenza B virus (NS1B) specifically binds only human and nonhuman primate ISG15s and inhibits their conjugation. To elucidate the structural basis for the sequence-specific recognition of human ISG15, we determined the crystal structure of the complex formed between human ISG15 and the N-terminal region of NS1B (NS1B-NTR). The NS1B-NTR homodimer interacts with two ISG15 molecules in the crystal and also in solution. The two ISG15-binding sites on the NS1B-NTR dimer are composed of residues from both chains, namely residues in the RNA-binding domain (RBD) from one chain, and residues in the linker between the RBD and the effector domain from the other chain. The primary contact region of NS1B-NTR on ISG15 is composed of residues at the junction of the N-terminal ubiquitin-like (Ubl) domain and the short linker region between the two Ubl domains, explaining why the sequence of the short linker in human and nonhuman primate ISG15s is essential for the species-specific binding of these ISG15s. In addition, the crystal structure identifies NS1B-NTR binding sites in the N-terminal Ubl domain of ISG15, and shows that there are essentially no contacts with the C-terminal Ubl domain of ISG15. Consequently, NS1B-NTR binding to ISG15 would not occlude access of the C-terminal Ubl domain of ISG15 to its conjugating enzymes. Nonetheless, transfection assays show that NS1B-NTR binding of ISG15 is responsible for the inhibition of interferon-induced ISG15 conjugation in cells.
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species specificity of the ns1 protein of influenza b virus ns1 binds only human and non human primate ubiquitin like ISG15 proteins
Journal of Biological Chemistry, 2010Co-Authors: Haripriya Sridharan, Chen Zhao, Robert M. KrugAbstract:Influenza B viruses, which cause a highly contagious respiratory disease every year, are restricted to humans, but the basis for this restriction had not been determined. Here we provide one explanation for this restriction: the species specificity exhibited by the NS1 protein of influenza B virus (NS1B protein). This viral protein combats a major host antiviral response by binding the interferon-α/β-induced, ubiquitin-like ISG15 protein and inhibiting its conjugation to an array of proteins. We demonstrate that the NS1B protein exhibits species-specific binding; it binds human and non-human primate ISG15 but not mouse or canine ISG15. In both transfection assays and virus-infected cells, the NS1B protein binds and relocalizes only human and non-human primate ISG15 from the cytoplasm to nuclear speckles. Human and non-human primate ISG15 proteins consist of two ubiquitin-like domains separated by a short hinge linker of five amino acids. Remarkably, this short hinge plays a large role in the species-specific binding by the NS1B protein. The hinge of human and non-human primate ISG15, which has a sequence that differs from that of other mammalian ISG15 proteins, including mouse and canine ISG15, is absolutely required for binding the NS1B protein. Consequently, the ISG15 proteins of humans and non-human primates are the only mammalian ISG15 proteins that would bind NS1B.
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ISG15 conjugation system targets the viral ns1 protein in influenza a virus infected cells
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Chen Zhao, Tien Ying Hsiang, Robert M. KrugAbstract:ISG15 is an IFN-α/β–induced, ubiquitin-like protein that is conjugated to a wide array of cellular proteins through the sequential action of three conjugation enzymes that are also induced by IFN-α/β. Recent studies showed that ISG15 and/or its conjugates play an important role in protecting cells from infection by several viruses, including influenza A virus. However, the mechanism by which ISG15 modification exerts antiviral activity has not been established. Here we extend the repertoire of ISG15 targets to a viral protein by demonstrating that the NS1 protein of influenza A virus (NS1A protein), an essential, multifunctional protein, is ISG15 modified in virus-infected cells. We demonstrate that the major ISG15 acceptor site in the NS1A protein in infected cells is a critical lysine residue (K41) in the N-terminal RNA-binding domain (RBD). ISG15 modification of K41 disrupts the association of the NS1A RBD domain with importin-α, the protein that mediates nuclear import of the NS1A protein, whereas the RBD retains its double-stranded RNA-binding activity. Most significantly, we show that ISG15 modification of K41 inhibits influenza A virus replication and thus contributes to the antiviral action of IFN-β. We also show that the NS1A protein directly and specifically binds to Herc5, the major E3 ligase for ISG15 conjugation in human cells. These results establish a “loss of function” mechanism for the antiviral activity of the IFN-induced ISG15 conjugation system, namely, that it inhibits viral replication by conjugating ISG15 to a specific viral protein, thereby inhibiting its function.
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interferon induced ISG15 conjugation inhibits influenza a virus gene expression and replication in human cells
Journal of Virology, 2009Co-Authors: Tien Ying Hsiang, Chen Zhao, Robert M. KrugAbstract:Virus infection activates the synthesis of type I interferons (IFN-α and IFN-β), which induce the synthesis of a large array of proteins, many of which play crucial roles in the antiviral response (1). One of the most strongly induced proteins is ISG15, a 15-kDa ubiquitin-like protein that becomes conjugated to many cellular proteins (6, 8, 9, 12, 18, 22, 26, 30). Three of the human enzymes that catalyze this conjugation, the UbE1L E1 enzyme, the UbcH8 E2 enzyme, and the Herc5 E3 enzyme, are also induced by IFN-β (4, 10, 26, 27, 29). Although it had been reported that UbcH8 functions in both ISG15 and ubiquitin conjugation (3, 10, 13, 25, 28, 29), a recent study demonstrated that UbcH8 is unlikely to function in ubiquitin conjugation in vivo for two reasons: Km measurements revealed that the E1 ubiquitin-activating enzyme, unlike UbE1L, exhibits very low affinity for UbcH8, and UbcH8 is poorly, if not at all, expressed in the absence of IFN treatment, indicating that UbcH8 functions only during the IFN response (5). A large number of human proteins that are targets for ISG15 conjugation have been identified (22, 26, 30). Most of these targets are constitutively expressed proteins that function in diverse cellular pathways, but several of the targets are IFN-α/-β-induced antiviral proteins. Because the NS1 protein of influenza B virus (NS1B) was shown to bind ISG15 and inhibit its conjugation to target proteins, it was proposed that ISG15 and/or its conjugation is inhibitory to the replication of influenza B virus (27). Subsequently, experiments using ISG15 knockout (ISG15−/−) mice established that ISG15 and/or its conjugation inhibits the replication of not only influenza B virus but also influenza A virus (16). For example, at one of the inoculum levels employed for influenza A virus, 52% of the ISG15−/− mice died, whereas a significantly smaller percentage, 23%, of the ISG15+/+ mice died. However, the effect of ISG15 and/or its conjugation on influenza A virus replication was not detected in mouse embryo fibroblasts (MEFs) in tissue culture. MEFs supported only very limited replication of influenza A virus, and there was no significant difference in virus replication between ISG15+/+ and ISG15−/− MEFs (16). These investigators postulated that influenza A virus replication was probably selectively spared in other cell types of the ISG15−/− mouse. A subsequent study showed that ISG15 conjugation exerts its antiviral action against influenza B virus (and presumably against influenza A virus) in radioresistant stromal cells of the mouse (14). However, an antiviral effect of ISG15 conjugation against influenza A virus has not yet been demonstrated in mouse cells in tissue culture. In the present study we focus on human tissue culture cells and on the effect of ISG15 and/or its conjugation on the replication of influenza A virus in such cells. We show that IFN-induced antiviral activity against influenza A virus in human cells is significantly alleviated by inhibiting ISG15 conjugation using small interfering RNAs (siRNAs) against ISG15-conjugating enzymes. Our results show that both the synthesis of viral proteins and the early rate of virus replication are inhibited by ISG15 conjugation. In contrast, we show that in MEFs ISG15 conjugation not only does not affect influenza A virus replication but also does not contribute to IFN-induced antiviral activity against influenza A virus gene expression.
Kenneth J. Ritchie - One of the best experts on this subject based on the ideXlab platform.
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Ubp43 gene expression is required for normal ISG15 expression and fetal development.
Reproductive biology and endocrinology : RB&E, 2007Co-Authors: Lea A. Rempel, Kenneth J. Ritchie, Dong-er Zhang, Luiz E. Henkes, Ming Yan, Kathleen J. Austin, Mei-feng Shen, Thomas R. HansenAbstract:Background ISG15 covalently modifies murine endometrial proteins in response to early pregnancy. ISG15 can also be severed from targeted proteins by a specific protease called Ubp43 (Usp18). Mice lacking Ubp43 (null) form increased conjugated ISG15 in response to interferon. The ISG15 system has not been examined in chorioallantoic placenta (CP) or mesometrial (MM) components of implantation sites beyond 9.5 days post coitum (dpc). It was hypothesized that deletion of Ubp43 would cause disregulation of ISG15 in implantation sites, and that this would affect pregnancy rates.
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Ubp43 gene expression is required for normal ISG15 expression and fetal development
Reproductive Biology and Endocrinology, 2007Co-Authors: Lea A. Rempel, Kenneth J. Ritchie, Dong-er Zhang, Luiz E. Henkes, Ming Yan, Kathleen J. Austin, Mei-feng Shen, Thomas R. HansenAbstract:Background ISG15 covalently modifies murine endometrial proteins in response to early pregnancy. ISG15 can also be severed from targeted proteins by a specific protease called Ubp43 (Usp18). Mice lacking Ubp43 (null) form increased conjugated ISG15 in response to interferon. The ISG15 system has not been examined in chorioallantoic placenta (CP) or mesometrial (MM) components of implantation sites beyond 9.5 days post coitum (dpc). It was hypothesized that deletion of Ubp43 would cause disregulation of ISG15 in implantation sites, and that this would affect pregnancy rates. Methods Heterozygous (het) Ubp43 mice were mated and MM and CP implantation sites were collected on 12.5 and 17.5 days post-coitum (dpc). Results Free and conjugated ISG15 were greater on 12.5 versus 17.5 dpc in MM. Free and conjugated ISG15 were also present in CP, but did not differ due to genotype on 12.5 dpc. However, null CP had greater free and conjugated ISG15 when compared to het/wt on 17.5 dpc. Null progeny died in utero with fetal genotype ratios (wt:het:null) of 2:5:1 on 12.5 and 2:2:1 on 17.5 dpc. Implantation sites were disrupted within the junctional zone and spongiotrophoblast, contained less vasculature based on lectin B4 staining and contained greater ISG15 mRNA and VEGF protein in Ubp43 null when compared to wt placenta. Conclusion It is concluded that ISG15 and its conjugates are present in implantation sites during mid to late gestation and that deletion of Ubp43 causes an increase in free and conjugated ISG15 at the feto-maternal interface. Also, under mixed genetic background, deletion of Ubp43 results in fetal death.
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Dysregulation of protein modification by ISG15 results in brain cell injury
Genes & Development, 2002Co-Authors: Kenneth J. Ritchie, Michael P. Malakhov, Oxana A. Malakhova, Marie-térèse Little, Christopher J. Hetherington, Jack C. Sipe, Stuart H Orkin, Liming Zhou, Dong-er ZhangAbstract:UBP43 (USP18) is a protease that removes the ubiquitin-like modifier ISG15 from conjugated proteins. Here we present the first report of dysregulation of protein ISG15 modification by the generation of UBP43 knockout mice. In the absence of UBP43, brain tissue showed an elevated level of ISG15 conjugates, and cellular necrosis was evident in the ependyma. Such disruption of the blood–brain barrier resulted in severe neurologic disorders. These results demonstrate that UBP43 plays a critical role in maintaining the homeostatic balance of ISG15-conjugated protein, and that regulation of cellular levels of ISG15 protein modification is essential for brain cell function.
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ubp43 usp18 specifically removes ISG15 from conjugated proteins
Journal of Biological Chemistry, 2002Co-Authors: Michael P. Malakhov, Oxana A. Malakhova, Kenneth J. Ritchie, Dong-er ZhangAbstract:Abstract UBP43 shows significant homology to well characterized ubiquitin-specific proteases and previously was shown to hydrolyze ubiquitin-β-galactosidase fusions in Escherichia coli. In our assays, the activity of UBP43 toward Ub fusions was undetectable in vitro directing us to investigate the possibility of Ub-like proteins such as SUMO, Nedd8, and ISG15 as probable substrates. We consequently demonstrate that UBP43 can efficiently cleave only ISG15 fusions including native ISG15 conjugates linked via isopeptide bonds. In addition to commonly used methods we introduce a new experimental design featuring ISG15-UBP43 fusion self-processing. Deletion of the UBP43 gene in mouse leads to a massive increase of ISG15 conjugates in tissues indicating that UBP43 is a major ISG15-specific protease. UBP43 is the first bona fide ISG15-specific protease reported. Both ISG15 andUBP43 genes are known to be strongly induced by interferon, genotoxic stress, and viral infection. We postulate that UBP43 is necessary to maintain a critical cellular balance of ISG15-conjugated proteins in both healthy and stressed organisms.
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UBP43 (USP18) specifically removes ISG15 from conjugated proteins
Journal of Biological Chemistry, 2002Co-Authors: Michael P. Malakhov, Oxana A. Malakhova, Kenneth J. Ritchie, Keun Kim, Dong-er ZhangAbstract:UBP43 shows significant homology to well characterized ubiquitin-specific proteases and previously was shown to hydrolyze ubiquitin-beta-galactosidase fusions in Escherichia coli. In our assays, the activity of UBP43 toward Ub fusions was undetectable in vitro directing us to investigate the possibility of Ub-like proteins such as SUMO, Nedd8, and ISG15 as probable substrates. We consequently demonstrate that UBP43 can efficiently cleave only ISG15 fusions including native ISG15 conjugates linked via isopeptide bonds. In addition to commonly used methods we introduce a new experimental design featuring ISG15-UBP43 fusion self-processing. Deletion of the UBP43 gene in mouse leads to a massive increase of ISG15 conjugates in tissues indicating that UBP43 is a major ISG15-specific protease. UBP43 is the first bona fide ISG15-specific protease reported. Both ISG15 and UBP43 genes are known to be strongly induced by interferon, genotoxic stress, and viral infection. We postulate that UBP43 is necessary to maintain a critical cellular balance of ISG15-conjugated proteins in both healthy and stressed organisms.
Michael P. Malakhov - One of the best experts on this subject based on the ideXlab platform.
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high throughput immunoblotting ubiquitin like protein ISG15 modifies key regulators of signal transduction
Journal of Biological Chemistry, 2003Co-Authors: Michael P. Malakhov, Oxana A. Malakhova, Ernest C Borden, Keun Il Kim, Barbara S Jacobs, Dong-er ZhangAbstract:ISG15 is a ubiquitin-like protein that conjugates to numerous proteins in cells treated with interferon or lipopolysaccharide. Dysregulation of protein ISG15 modification (ISGylation) in mice leads to decreased life expectancy, brain cell injury, and hypersensitivity to interferon. Although ISG15 was identified more than two decades ago, the exact biochemical and physiological functions of ISG15-modification remain unknown, and the proteins targeted by ISG15 have not been identified. The major purpose of this work was to identify ISG15 targets among well characterized proteins that could be used as models for biological studies. We purified ISGylated proteins from human thymus by immunoaffinity chromatography and analyzed ISG15 conjugates by a high-throughput Western blot screen (PowerBlotTM). We found that three key regulators of signal transduction, phospholipase Cγ1, Jak1, and ERK1 are modified by ISG15. In addition to that, we demonstrate that transcription factor Stat1, an immediate substrate of Jak1 kinase, is also ISGylated. Using whole cell protein extracts and phospholipase Cγ1 as an example we demonstrate that ISG15 conjugates are not accumulated in cells treated with specific inhibitors of proteasomes. Our work suggests a role for ISG15 in the regulation of multiple signal transduction pathways and offers attractive models to further elucidate the biochemical function of ISGylation.
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Dysregulation of protein modification by ISG15 results in brain cell injury
Genes & Development, 2002Co-Authors: Kenneth J. Ritchie, Michael P. Malakhov, Oxana A. Malakhova, Marie-térèse Little, Christopher J. Hetherington, Jack C. Sipe, Stuart H Orkin, Liming Zhou, Dong-er ZhangAbstract:UBP43 (USP18) is a protease that removes the ubiquitin-like modifier ISG15 from conjugated proteins. Here we present the first report of dysregulation of protein ISG15 modification by the generation of UBP43 knockout mice. In the absence of UBP43, brain tissue showed an elevated level of ISG15 conjugates, and cellular necrosis was evident in the ependyma. Such disruption of the blood–brain barrier resulted in severe neurologic disorders. These results demonstrate that UBP43 plays a critical role in maintaining the homeostatic balance of ISG15-conjugated protein, and that regulation of cellular levels of ISG15 protein modification is essential for brain cell function.
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ubp43 usp18 specifically removes ISG15 from conjugated proteins
Journal of Biological Chemistry, 2002Co-Authors: Michael P. Malakhov, Oxana A. Malakhova, Kenneth J. Ritchie, Dong-er ZhangAbstract:Abstract UBP43 shows significant homology to well characterized ubiquitin-specific proteases and previously was shown to hydrolyze ubiquitin-β-galactosidase fusions in Escherichia coli. In our assays, the activity of UBP43 toward Ub fusions was undetectable in vitro directing us to investigate the possibility of Ub-like proteins such as SUMO, Nedd8, and ISG15 as probable substrates. We consequently demonstrate that UBP43 can efficiently cleave only ISG15 fusions including native ISG15 conjugates linked via isopeptide bonds. In addition to commonly used methods we introduce a new experimental design featuring ISG15-UBP43 fusion self-processing. Deletion of the UBP43 gene in mouse leads to a massive increase of ISG15 conjugates in tissues indicating that UBP43 is a major ISG15-specific protease. UBP43 is the first bona fide ISG15-specific protease reported. Both ISG15 andUBP43 genes are known to be strongly induced by interferon, genotoxic stress, and viral infection. We postulate that UBP43 is necessary to maintain a critical cellular balance of ISG15-conjugated proteins in both healthy and stressed organisms.
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UBP43 (USP18) specifically removes ISG15 from conjugated proteins
Journal of Biological Chemistry, 2002Co-Authors: Michael P. Malakhov, Oxana A. Malakhova, Kenneth J. Ritchie, Keun Kim, Dong-er ZhangAbstract:UBP43 shows significant homology to well characterized ubiquitin-specific proteases and previously was shown to hydrolyze ubiquitin-beta-galactosidase fusions in Escherichia coli. In our assays, the activity of UBP43 toward Ub fusions was undetectable in vitro directing us to investigate the possibility of Ub-like proteins such as SUMO, Nedd8, and ISG15 as probable substrates. We consequently demonstrate that UBP43 can efficiently cleave only ISG15 fusions including native ISG15 conjugates linked via isopeptide bonds. In addition to commonly used methods we introduce a new experimental design featuring ISG15-UBP43 fusion self-processing. Deletion of the UBP43 gene in mouse leads to a massive increase of ISG15 conjugates in tissues indicating that UBP43 is a major ISG15-specific protease. UBP43 is the first bona fide ISG15-specific protease reported. Both ISG15 and UBP43 genes are known to be strongly induced by interferon, genotoxic stress, and viral infection. We postulate that UBP43 is necessary to maintain a critical cellular balance of ISG15-conjugated proteins in both healthy and stressed organisms.
Chen Zhao - One of the best experts on this subject based on the ideXlab platform.
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Interferon-induced ISG15 pathway: An ongoing virus-host battle
Trends in microbiology, 2013Co-Authors: Chen Zhao, Tien Ying Hsiang, Mark N. Collins, Robert M. KrugAbstract:ISG15 is an interferon (IFN)-induced ubiquitin-like protein that is conjugated to target proteins via the sequential action of three enzymes that are also induced by IFN. Unlike ubiquitin, which is highly conserved, the sequence of ISG15 varies between species. ISG15 conjugation inhibits many viruses, and free (unconjugated) ISG15 can also act as an antiviral protein. In this review, we focus on the antiviral role of ISG15 conjugation and on countermeasures employed by several viruses. The countermeasure by influenza B virus is unique in that it exhibits species specificity. Only the antiviral activity of human and non-human primate ISG15s can be blocked, providing one possible explanation for the restriction of influenza B virus to humans.
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Structural basis for the sequence-specific recognition of human ISG15 by the NS1 protein of influenza B virus.
Proceedings of the National Academy of Sciences of the United States of America, 2011Co-Authors: Rongjin Guan, Robert M. Krug, Chen Zhao, Li Chung, Paul G. Leonard, Brendan R. Amer, Haripriya Sridharan, Gaetano T. MontelioneAbstract:Interferon-induced ISG15 conjugation plays an important antiviral role against several viruses, including influenza viruses. The NS1 protein of influenza B virus (NS1B) specifically binds only human and nonhuman primate ISG15s and inhibits their conjugation. To elucidate the structural basis for the sequence-specific recognition of human ISG15, we determined the crystal structure of the complex formed between human ISG15 and the N-terminal region of NS1B (NS1B-NTR). The NS1B-NTR homodimer interacts with two ISG15 molecules in the crystal and also in solution. The two ISG15-binding sites on the NS1B-NTR dimer are composed of residues from both chains, namely residues in the RNA-binding domain (RBD) from one chain, and residues in the linker between the RBD and the effector domain from the other chain. The primary contact region of NS1B-NTR on ISG15 is composed of residues at the junction of the N-terminal ubiquitin-like (Ubl) domain and the short linker region between the two Ubl domains, explaining why the sequence of the short linker in human and nonhuman primate ISG15s is essential for the species-specific binding of these ISG15s. In addition, the crystal structure identifies NS1B-NTR binding sites in the N-terminal Ubl domain of ISG15, and shows that there are essentially no contacts with the C-terminal Ubl domain of ISG15. Consequently, NS1B-NTR binding to ISG15 would not occlude access of the C-terminal Ubl domain of ISG15 to its conjugating enzymes. Nonetheless, transfection assays show that NS1B-NTR binding of ISG15 is responsible for the inhibition of interferon-induced ISG15 conjugation in cells.
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species specificity of the ns1 protein of influenza b virus ns1 binds only human and non human primate ubiquitin like ISG15 proteins
Journal of Biological Chemistry, 2010Co-Authors: Haripriya Sridharan, Chen Zhao, Robert M. KrugAbstract:Influenza B viruses, which cause a highly contagious respiratory disease every year, are restricted to humans, but the basis for this restriction had not been determined. Here we provide one explanation for this restriction: the species specificity exhibited by the NS1 protein of influenza B virus (NS1B protein). This viral protein combats a major host antiviral response by binding the interferon-α/β-induced, ubiquitin-like ISG15 protein and inhibiting its conjugation to an array of proteins. We demonstrate that the NS1B protein exhibits species-specific binding; it binds human and non-human primate ISG15 but not mouse or canine ISG15. In both transfection assays and virus-infected cells, the NS1B protein binds and relocalizes only human and non-human primate ISG15 from the cytoplasm to nuclear speckles. Human and non-human primate ISG15 proteins consist of two ubiquitin-like domains separated by a short hinge linker of five amino acids. Remarkably, this short hinge plays a large role in the species-specific binding by the NS1B protein. The hinge of human and non-human primate ISG15, which has a sequence that differs from that of other mammalian ISG15 proteins, including mouse and canine ISG15, is absolutely required for binding the NS1B protein. Consequently, the ISG15 proteins of humans and non-human primates are the only mammalian ISG15 proteins that would bind NS1B.
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ISG15 conjugation system targets the viral ns1 protein in influenza a virus infected cells
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Chen Zhao, Tien Ying Hsiang, Robert M. KrugAbstract:ISG15 is an IFN-α/β–induced, ubiquitin-like protein that is conjugated to a wide array of cellular proteins through the sequential action of three conjugation enzymes that are also induced by IFN-α/β. Recent studies showed that ISG15 and/or its conjugates play an important role in protecting cells from infection by several viruses, including influenza A virus. However, the mechanism by which ISG15 modification exerts antiviral activity has not been established. Here we extend the repertoire of ISG15 targets to a viral protein by demonstrating that the NS1 protein of influenza A virus (NS1A protein), an essential, multifunctional protein, is ISG15 modified in virus-infected cells. We demonstrate that the major ISG15 acceptor site in the NS1A protein in infected cells is a critical lysine residue (K41) in the N-terminal RNA-binding domain (RBD). ISG15 modification of K41 disrupts the association of the NS1A RBD domain with importin-α, the protein that mediates nuclear import of the NS1A protein, whereas the RBD retains its double-stranded RNA-binding activity. Most significantly, we show that ISG15 modification of K41 inhibits influenza A virus replication and thus contributes to the antiviral action of IFN-β. We also show that the NS1A protein directly and specifically binds to Herc5, the major E3 ligase for ISG15 conjugation in human cells. These results establish a “loss of function” mechanism for the antiviral activity of the IFN-induced ISG15 conjugation system, namely, that it inhibits viral replication by conjugating ISG15 to a specific viral protein, thereby inhibiting its function.
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interferon induced ISG15 conjugation inhibits influenza a virus gene expression and replication in human cells
Journal of Virology, 2009Co-Authors: Tien Ying Hsiang, Chen Zhao, Robert M. KrugAbstract:Virus infection activates the synthesis of type I interferons (IFN-α and IFN-β), which induce the synthesis of a large array of proteins, many of which play crucial roles in the antiviral response (1). One of the most strongly induced proteins is ISG15, a 15-kDa ubiquitin-like protein that becomes conjugated to many cellular proteins (6, 8, 9, 12, 18, 22, 26, 30). Three of the human enzymes that catalyze this conjugation, the UbE1L E1 enzyme, the UbcH8 E2 enzyme, and the Herc5 E3 enzyme, are also induced by IFN-β (4, 10, 26, 27, 29). Although it had been reported that UbcH8 functions in both ISG15 and ubiquitin conjugation (3, 10, 13, 25, 28, 29), a recent study demonstrated that UbcH8 is unlikely to function in ubiquitin conjugation in vivo for two reasons: Km measurements revealed that the E1 ubiquitin-activating enzyme, unlike UbE1L, exhibits very low affinity for UbcH8, and UbcH8 is poorly, if not at all, expressed in the absence of IFN treatment, indicating that UbcH8 functions only during the IFN response (5). A large number of human proteins that are targets for ISG15 conjugation have been identified (22, 26, 30). Most of these targets are constitutively expressed proteins that function in diverse cellular pathways, but several of the targets are IFN-α/-β-induced antiviral proteins. Because the NS1 protein of influenza B virus (NS1B) was shown to bind ISG15 and inhibit its conjugation to target proteins, it was proposed that ISG15 and/or its conjugation is inhibitory to the replication of influenza B virus (27). Subsequently, experiments using ISG15 knockout (ISG15−/−) mice established that ISG15 and/or its conjugation inhibits the replication of not only influenza B virus but also influenza A virus (16). For example, at one of the inoculum levels employed for influenza A virus, 52% of the ISG15−/− mice died, whereas a significantly smaller percentage, 23%, of the ISG15+/+ mice died. However, the effect of ISG15 and/or its conjugation on influenza A virus replication was not detected in mouse embryo fibroblasts (MEFs) in tissue culture. MEFs supported only very limited replication of influenza A virus, and there was no significant difference in virus replication between ISG15+/+ and ISG15−/− MEFs (16). These investigators postulated that influenza A virus replication was probably selectively spared in other cell types of the ISG15−/− mouse. A subsequent study showed that ISG15 conjugation exerts its antiviral action against influenza B virus (and presumably against influenza A virus) in radioresistant stromal cells of the mouse (14). However, an antiviral effect of ISG15 conjugation against influenza A virus has not yet been demonstrated in mouse cells in tissue culture. In the present study we focus on human tissue culture cells and on the effect of ISG15 and/or its conjugation on the replication of influenza A virus in such cells. We show that IFN-induced antiviral activity against influenza A virus in human cells is significantly alleviated by inhibiting ISG15 conjugation using small interfering RNAs (siRNAs) against ISG15-conjugating enzymes. Our results show that both the synthesis of viral proteins and the early rate of virus replication are inhibited by ISG15 conjugation. In contrast, we show that in MEFs ISG15 conjugation not only does not affect influenza A virus replication but also does not contribute to IFN-induced antiviral activity against influenza A virus gene expression.
