Interferon-stimulated gene 15 (ISG15) is a member of the ubiquitin-like (Ubl) family. It is strongly induced upon exposure to type I Interferons (IFNs), viruses, bacterial LPS, and other stresses. Once released the mature ISG15 conjugates with an array of target proteins, a process termed ISGylation. ISGylation utilizes a mechanism similar to ubiquitination, requiring a three-step enzymatic cascade. UBE1L is the ISG15 E1 activating enzyme which specifically activates ISG15 at the expense of ATP. ISG15 is then transfered from E1 to the E2 conjugating enzyme UBCH8 and then to the target protein with the aid of an ISG15 E3 ligase, such as HERC5 and EFP. Hundreds of target proteins for ISGylation have been identified. Several proteins that are part of antiviral signaling pathways, such as RIG-I, MDA5, Mx1, PKR, filamin B, STAT1, IRF3 and JAK1, have been identified as targets for ISGylation. ISG15 also conjugates some viral proteins, inhibiting viral budding and release. ISGylation appears to act either by disrupting the activity of a target protein and/or by altering its localization within the cell.
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Cros JF, García-Sastre A, Palese P.; ''An unconventional NLS is critical for the nuclear import of the influenza A virus nucleoprotein and ribonucleoprotein.''; PubMedEurope PMCScholia
Kim KI, Giannakopoulos NV, Virgin HW, Zhang DE.; ''Interferon-inducible ubiquitin E2, Ubc8, is a conjugating enzyme for protein ISGylation.''; PubMedEurope PMCScholia
Lu G, Reinert JT, Pitha-Rowe I, Okumura A, Kellum M, Knobeloch KP, Hassel B, Pitha PM.; ''ISG15 enhances the innate antiviral response by inhibition of IRF-3 degradation.''; PubMedEurope PMCScholia
Okumura F, Zou W, Zhang DE.; ''ISG15 modification of the eIF4E cognate 4EHP enhances cap structure-binding activity of 4EHP.''; PubMedEurope PMCScholia
Jeon YJ, Choi JS, Lee JY, Yu KR, Kim SM, Ka SH, Oh KH, Kim KI, Zhang DE, Bang OS, Chung CH.; ''ISG15 modification of filamin B negatively regulates the type I interferon-induced JNK signalling pathway.''; PubMedEurope PMCScholia
Harty RN, Brown ME, Wang G, Huibregtse J, Hayes FP.; ''A PPxY motif within the VP40 protein of Ebola virus interacts physically and functionally with a ubiquitin ligase: implications for filovirus budding.''; PubMedEurope PMCScholia
Plafker SM, Plafker KS, Weissman AM, Macara IG.; ''Ubiquitin charging of human class III ubiquitin-conjugating enzymes triggers their nuclear import.''; PubMedEurope PMCScholia
Licata JM, Simpson-Holley M, Wright NT, Han Z, Paragas J, Harty RN.; ''Overlapping motifs (PTAP and PPEY) within the Ebola virus VP40 protein function independently as late budding domains: involvement of host proteins TSG101 and VPS-4.''; PubMedEurope PMCScholia
Skaug B, Chen ZJ.; ''Emerging role of ISG15 in antiviral immunity.''; PubMedEurope PMCScholia
Ott DE, Coren LV, Chertova EN, Gagliardi TD, Schubert U.; ''Ubiquitination of HIV-1 and MuLV Gag.''; PubMedEurope PMCScholia
Malakhova OA, Zhang DE.; ''ISG15 inhibits Nedd4 ubiquitin E3 activity and enhances the innate antiviral response.''; PubMedEurope PMCScholia
Kosinski J, Mosalaganti S, von Appen A, Teimer R, DiGuilio AL, Wan W, Bui KH, Hagen WJ, Briggs JA, Glavy JS, Hurt E, Beck M.; ''Molecular architecture of the inner ring scaffold of the human nuclear pore complex.''; PubMedEurope PMCScholia
Versteeg GA, Hale BG, van Boheemen S, Wolff T, Lenschow DJ, García-Sastre A.; ''Species-specific antagonism of host ISGylation by the influenza B virus NS1 protein.''; PubMedEurope PMCScholia
Ori A, Banterle N, Iskar M, Iskar M, Andrés-Pons A, Escher C, Khanh Bui H, Sparks L, Solis-Mezarino V, Rinner O, Bork P, Lemke EA, Beck M.; ''Cell type-specific nuclear pores: a case in point for context-dependent stoichiometry of molecular machines.''; PubMedEurope PMCScholia
Dastur A, Beaudenon S, Kelley M, Krug RM, Huibregtse JM.; ''Herc5, an interferon-induced HECT E3 enzyme, is required for conjugation of ISG15 in human cells.''; PubMedEurope PMCScholia
Lin DH, Stuwe T, Schilbach S, Rundlet EJ, Perriches T, Mobbs G, Fan Y, Thierbach K, Huber FM, Collins LN, Davenport AM, Jeon YE, Hoelz A.; ''Architecture of the symmetric core of the nuclear pore.''; PubMedEurope PMCScholia
Kabachinski G, Schwartz TU.; ''The nuclear pore complex--structure and function at a glance.''; PubMedEurope PMCScholia
Malakhov MP, Kim KI, Malakhova OA, Jacobs BS, Borden EC, Zhang DE.; ''High-throughput immunoblotting. Ubiquitiin-like protein ISG15 modifies key regulators of signal transduction.''; PubMedEurope PMCScholia
Zhao C, Beaudenon SL, Kelley ML, Waddell MB, Yuan W, Schulman BA, Huibregtse JM, Krug RM.; ''The UbcH8 ubiquitin E2 enzyme is also the E2 enzyme for ISG15, an IFN-alpha/beta-induced ubiquitin-like protein.''; PubMedEurope PMCScholia
Suntharalingam M, Wente SR.; ''Peering through the pore: nuclear pore complex structure, assembly, and function.''; PubMedEurope PMCScholia
Zhao C, Hsiang TY, Kuo RL, Krug RM.; ''ISG15 conjugation system targets the viral NS1 protein in influenza A virus-infected cells.''; PubMedEurope PMCScholia
Melén K, Kinnunen L, Fagerlund R, Ikonen N, Twu KY, Krug RM, Julkunen I.; ''Nuclear and nucleolar targeting of influenza A virus NS1 protein: striking differences between different virus subtypes.''; PubMedEurope PMCScholia
Takeuchi T, Yokosawa H.; ''ISG15 modification of Ubc13 suppresses its ubiquitin-conjugating activity.''; PubMedEurope PMCScholia
Giannakopoulos NV, Arutyunova E, Lai C, Lenschow DJ, Haas AL, Virgin HW.; ''ISG15 Arg151 and the ISG15-conjugating enzyme UbE1L are important for innate immune control of Sindbis virus.''; PubMedEurope PMCScholia
Shi HX, Yang K, Liu X, Liu XY, Wei B, Shan YF, Zhu LH, Wang C.; ''Positive regulation of interferon regulatory factor 3 activation by Herc5 via ISG15 modification.''; PubMedEurope PMCScholia
Yoneyama M, Kikuchi M, Natsukawa T, Shinobu N, Imaizumi T, Miyagishi M, Taira K, Akira S, Fujita T.; ''The RNA helicase RIG-I has an essential function in double-stranded RNA-induced innate antiviral responses.''; PubMedEurope PMCScholia
O'Neill RE, Jaskunas R, Blobel G, Palese P, Moroianu J.; ''Nuclear import of influenza virus RNA can be mediated by viral nucleoprotein and transport factors required for protein import.''; PubMedEurope PMCScholia
Goutagny N, Severa M, Fitzgerald KA.; ''Pin-ning down immune responses to RNA viruses.''; PubMedEurope PMCScholia
Giannakopoulos NV, Luo JK, Papov V, Zou W, Lenschow DJ, Jacobs BS, Borden EC, Li J, Virgin HW, Zhang DE.; ''Proteomic identification of proteins conjugated to ISG15 in mouse and human cells.''; PubMedEurope PMCScholia
Zou W, Papov V, Malakhova O, Kim KI, Dao C, Li J, Zhang DE.; ''ISG15 modification of ubiquitin E2 Ubc13 disrupts its ability to form thioester bond with ubiquitin.''; PubMedEurope PMCScholia
Takeuchi T, Kobayashi T, Tamura S, Yokosawa H.; ''Negative regulation of protein phosphatase 2Cbeta by ISG15 conjugation.''; PubMedEurope PMCScholia
Takeuchi T, Iwahara S, Saeki Y, Sasajima H, Yokosawa H.; ''Link between the ubiquitin conjugation system and the ISG15 conjugation system: ISG15 conjugation to the UbcH6 ubiquitin E2 enzyme.''; PubMedEurope PMCScholia
Zhao C, Denison C, Huibregtse JM, Gygi S, Krug RM.; ''Human ISG15 conjugation targets both IFN-induced and constitutively expressed proteins functioning in diverse cellular pathways.''; PubMedEurope PMCScholia
Malakhov MP, Malakhova OA, Kim KI, Ritchie KJ, Zhang DE.; ''UBP43 (USP18) specifically removes ISG15 from conjugated proteins.''; PubMedEurope PMCScholia
Saitoh T, Tun-Kyi A, Ryo A, Yamamoto M, Finn G, Fujita T, Akira S, Yamamoto N, Lu KP, Yamaoka S.; ''Negative regulation of interferon-regulatory factor 3-dependent innate antiviral response by the prolyl isomerase Pin1.''; PubMedEurope PMCScholia
Wong JJ, Pung YF, Sze NS, Chin KC.; ''HERC5 is an IFN-induced HECT-type E3 protein ligase that mediates type I IFN-induced ISGylation of protein targets.''; PubMedEurope PMCScholia
Ott DE, Coren LV, Copeland TD, Kane BP, Johnson DG, Sowder RC, Yoshinaka Y, Oroszlan S, Arthur LO, Henderson LE.; ''Ubiquitin is covalently attached to the p6Gag proteins of human immunodeficiency virus type 1 and simian immunodeficiency virus and to the p12Gag protein of Moloney murine leukemia virus.''; PubMedEurope PMCScholia
Fontoura BM, Blobel G, Matunis MJ.; ''A conserved biogenesis pathway for nucleoporins: proteolytic processing of a 186-kilodalton precursor generates Nup98 and the novel nucleoporin, Nup96.''; PubMedEurope PMCScholia
Rabut G, Doye V, Ellenberg J.; ''Mapping the dynamic organization of the nuclear pore complex inside single living cells.''; PubMedEurope PMCScholia
Cronshaw JM, Krutchinsky AN, Zhang W, Chait BT, Matunis MJ.; ''Proteomic analysis of the mammalian nuclear pore complex.''; PubMedEurope PMCScholia
Gottwein E, Jäger S, Habermann A, Kräusslich HG.; ''Cumulative mutations of ubiquitin acceptor sites in human immunodeficiency virus type 1 gag cause a late budding defect.''; PubMedEurope PMCScholia
Tsuchida T, Kawai T, Akira S.; ''Inhibition of IRF3-dependent antiviral responses by cellular and viral proteins.''; PubMedEurope PMCScholia
Zou W, Zhang DE.; ''The interferon-inducible ubiquitin-protein isopeptide ligase (E3) EFP also functions as an ISG15 E3 ligase.''; PubMedEurope PMCScholia
Durfee LA, Kelley ML, Huibregtse JM.; ''The basis for selective E1-E2 interactions in the ISG15 conjugation system.''; PubMedEurope PMCScholia
Yuan W, Krug RM.; ''Influenza B virus NS1 protein inhibits conjugation of the interferon (IFN)-induced ubiquitin-like ISG15 protein.''; PubMedEurope PMCScholia
Okumura A, Pitha PM, Harty RN.; ''ISG15 inhibits Ebola VP40 VLP budding in an L-domain-dependent manner by blocking Nedd4 ligase activity.''; PubMedEurope PMCScholia
Tang Y, Zhong G, Zhu L, Liu X, Shan Y, Feng H, Bu Z, Chen H, Wang C.; ''Herc5 attenuates influenza A virus by catalyzing ISGylation of viral NS1 protein.''; PubMedEurope PMCScholia
This CandidateSet contains sequences identified by William Pearson's analysis of Reactome catalyst entities. Catalyst entity sequences were used to identify analagous sequences that shared overall homology and active site homology. Sequences in this Candidate set were identified in an April 24, 2012 analysis.
Cytosolic N-myristoyl Gag polyprotein is conjugated with a single molecule of ubiquitin. Conjugation is typically to one of two lysine residues in the p6 domain of Gag but can be to lysine residues in the MA, CA, NC, and SP2 domains of the protein. The specific host cell E2 and E3 proteins that mediate Gag ubiquitination have not been identified. The same studies that first identified the p6 ubiquitination sites in Gag also called the biological significance of Gag ubiquitination into question by demonstrating that Gag proteins in which the p6 ubiquitination sites had been removed by mutagenesis could still assemble efficiently into infectious viral particles (Ott et al. 1998, 2000). More recent work, however, has identified additional ubiquitination sites throughout the C-terminal region of the Gag polyprotein, and when all of these sites are removed by mutagenesis, both viral assembly involving the mutant Gag polyprotein and infectivity of the resulting viral particles are sharply reduced (Gottwein et al. 2006).
Note: Reactions directly involving interactions of human host proteins with foreign ones are highlighted in red.
The transcription factor IRF3 is a target for ISGylation. Conjugation of ISG15 positively regulates IRF3 and thereby promotes induction of type I interferons. ISGylation of IRF3 prevents the binding of PIN1, a protein that promotes IRF3 ubiquitination and subsequent degradation.
Some viral proteins are also targeted for ISGylation. The well studied viral protein ISGylation is the modification of the influenza A viral protein NS1, which functions as an IFN antagonist during viral infection. Studies identified seven lysine residues in NS1 as potential ISGylation sites among which K41 (Zhao et al. 2010), K126 and K217 (Tang et al. 2010) were found to be critical. ISGylation at these sites disrupts NS1 association with importin-alpha, a protein required for the nuclear import of NS1.
Ubiquitin ligase UBE1L is the ISG15 activating enzyme. UBE1L activates ISG15 in an ATP-dependent process that links UBE1L to ISG15 via a thioester bond. Arginine 153 (R153) in human ISG15 is identified as the key residue for ISG15 and UBE1L's interaction.
ISG15 negatively regulates the scaffold protein filamin B. In response to type I IFNs, filamin B recruits RAC1, MEKK1, and MKK4, enhancing their sequential activation and thereby promoting JNK activation and apoptosis. ISGylation of filamin B leads to the disassociation of RAC1, MEKK1, and MKK4 from the scaffold, preventing type I IFN dependent JNK activation and apoptosis. It has been suggested that this inhibition of apoptosis may protect uninfected bystander cells from IFN-mediated apoptosis (Jeon et al, 2009).
Ebola virus VP40 virus-like particles (VLPs) requires the interaction of overlapping L-domains in the VP40 protein with host NEDD4 protein for efficient budding. Mono-ubiquitination of VP40 mediated by the NEDD4 E3 ligase is thought to be required for virus budding and release. ISG15 interacts with NEDD4 and inhibits the transfer of ubiquitin from the E2 enzyme to NEDD4. This prevents NEDD4-mediated ubiquitination of Ebola virus VP40 which is required for virion release.
Ubiquitin conjugating E2 enzymes UBC13 and UBCH6 are targets for ISGylation. This suppresses the ubiquitin-conjugating activity of both UBC13 and UBCH6. This modification may play an important role in the control of signal transduction pathways, such as the NF-kB pathway, which are associated with K63-linked polyubiquitination (Takeuchi et al, 2005).
Ubiquitin ligase HERC5/CEB1 appears to be the predominant E3 ligase for ISGylation; EFP and HHARI/ARIH1 have also been reported as ISG15 E3 ligases. The E3 ligase recognizes specific target substrates and mediates the transfer of ISG15 from E2 to the substrate.
Protein phosphatase 1 beta (PPM1B/PP2CB) is a target for ISG15. PP2CB dephosphorylates TAK1 and suppresses TAK1/TAB1-mediated IkB alpha degradation and thereby controls the NF-kB signaling pathway, which plays a critical role in innate and adaptive immunity and cancer. ISGylation of PP2CB may block the suppressive function of the phosphatase against TAK1/TAB1 mediated NF-kB activation.
Many host proteins are targets for ISGylation including constitutively expressed proteins involved in various cellular pathways such as immunity, RNA splicing, chromatin remodeling/polymerase II transcription, stress responses and translation. Many ISG15 target proteins are IFN alpha/beta-induced antiviral proteins such as PKR, MxA, IRF3, and RIG-I, also included are several key regulators of signal transduction such as PLC gamma1, JAK1, STAT1 and ERK1. The contribution of most of these modified proteins to antiviral activity is unclear because the fate of the vast majority of ISGylated target proteins is unknown.
Influenza A virus nonstructural protein 1 (NS1A) is a multifunctional protein that exists as a dimer and is involved in the inhibition of host cell antiviral pre-mRNA processing and counteracts host cell antiviral responses. Unlike most other RNA viruses, influenza viruses replicate in the nucleus of the host cells. NS1A protein carries two nuclear localization signal (NLS) elements and these sequence elements are recognized by importin-alpha/beta. In the cytoplasm NS1A binds to importin-alpha/beta and these protein complexes are then translocated into the nucleus through the nuclear pore complex (NPC).
Note:Reactions directly involving interactions of human host proteins with foreign ones are highlighted in red.
Ubiquitin specific protease 18 (USP18/UBP43) is the major ISG15 deconjugating enzyme. It removes ISG15 from ISGylated proteins. ISG15-specific protease activity of this enzyme is crucial for proper cellular balance of ISG15-conjugated proteins. However, it is not required for processing pre-ISG15 to the mature form. Furthermore, USP18 inhibits type I interferon signaling independent of its ISG15 deconjugating enzyme activity. Several viral proteins were also reported with de-ISGylation activity.
Eukaryotic translation initiation factor 4F (eIF4F) is a protein complex that mediates recruitment of ribosomes to mRNA (Gingras et al. 1999). eIF4F contains complex of cap-binding protein eIF4E, scaffold protein eIF4G, and RNA helicase eIF4A. There are three eIF4E-family members in mammals termed eIF4E-1 (eIF4E), eIF4E2 (4EHP), and eIF4E3, of which both eIF4E and eIF4E3 are able to bind to eIF4G to facilitate translation initiation. However, 4EHP does not interact with eIF4G and thus cannot function in ribosome recruitment. 4EHP competes with eIF4E or eIF4E3 for binding to the RNA 5? cap structure and prevents translation initiation. ISGylated 4EHP has a much higher cap structure binding activity, suggesting a regulatory function of ISGylation in protein translation during immune responses (Okumura et al. 2007, Joshi et al. 2004).
4EHP is a member of eukaryotic translation initiation factor 4E (eIF4E) family that acts as an mRNA 5' cap structure-binding protein and suppresses translation. 4EHP is one of the targets of ISG15 and ISGylated 4EHP has a much higher cap structure-binding activity.
PIN1 acts as a negative regulator of IFN induction. Its association with IRF3 leads to ubiquitin-mediated proteosomal degradation of IRF3. PIN1 on its own does not have ubiquitin activation, transfer or ligase activities. Exactly how this IRF3 degradation is achieved is unclear at present. Immunoprecipitation of ubiquitin followed by immunoblot analysis for IRF3 demonstrated that polyubiquitination of IRF3 was induced by RNA stimulation and that polyubiquitination was augmented by PIN1 expression and abrogated by expression of PIN1-specific shRNA.
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N-myristoyl GAG
(P12493) proteinAnnotated Interactions
N-myristoyl GAG
(P12493) protein