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European Masters Program Language & Communication Technologies

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Epic Meeting On Photonics At The Final Frontier At European Space Agency (esa)

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Department of Microbiology, Immunology and Genetics, University of North Texas Health Science Center, Fort Worth, TX 76107, USA

Received: 31 March 2021 / Revised: 20 April 2021 / Accepted: 21 April 2021 / Published: 23 April 2021

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The ubiquitin (Ub) proteasome system (UPS) plays a central role in the regulation of many cellular processes, including innate and adaptive immune responses, which are important in limiting the life cycle of the virus in infected cells. Deubiquitination by the deubiquitinating enzyme deubiquitinase (DUB) is a reversible molecular process to remove Ub or Ub chains from target proteins. Deubiquitination is an integral strategy of the UPS that regulates the survival and proliferation of the infecting virus and cells invaded by the virus. Many viruses in infected cells encode viral DUBs, and these DUBs in vials actively interfere with cellular Ub-dependent processes to suppress the host’s antiviral immune response, increasing viral replication and thus proliferation. This review examines the types of DUBs encoded by different viruses and their molecular processes to see how infectious viruses use the DUB system to evade the host immune response and accelerate their replication.

Post-translational modifications of ubiquitin (Ub) proteins and Ub-like modifiers (Ubl) such as Nedd8, interferon-stimulated gene 15 (ISG15) and small Ub-like modifier (SUMO) have emerged as key regulatory mechanisms. various aspects of cellular activity, including signaling, transcription, membrane protein trafficking, autophagy, nuclear transport, and immune responses [ 1 , 2 , 3 , 4 , 5 ]. The binding of Ub and Ubl to target proteins is achieved by successive cascades of three enzymatic actions: those of the activating enzyme (E1), conjugating enzymes (E2) and ligases (E3), which specifically define the target molecules [2, 6]. These sequential enzymatic actions promote protein degradation by the Ub-proteasome system (UPS), which is the most important mechanism for the degradation of cytoplasmic and nuclear proteins [ 5 , 7 ].

Deubiquitination is the reverse process of ubiquitination and is catalyzed by the deubiquitinating enzymes deubiquitinases (DUBs), which remove Ub from proteins by cleaving peptide or isopeptide bonds between Ub and its substrate proteins as well as between Ub molecules in the fate chain to reverse the ubiquitinated proteins and thus the aforementioned molecular and cellular functions of proteins [8, 9, 10, 11, 12]. The human genome encodes nearly 100 DUBs, which are divided into two main groups: cysteine ​​proteases and metalloproteases. Cysteine ​​protease DUBs consist of four major groups of subfamilies: (1) Ub-specific protease (USP/UBP), the largest superfamily of DUBs (various USPs such as USP1, USP2, etc.); (2) ovarian tumor superfamily (OTU); (3) Machado–Josephine superfamily (MJD); and (4) the Ub C-terminal hydrolase (UCH) superfamily [ 13 , 14 ]. Meanwhile, the Jab1/Mov34/Mpr1 metalloproteases comprise the Pad1 N-terminal (MPN+) (JAMM) domain superfamily of zinc-binding proteins and are thus metalloproteases [ 14 ]. These DUBs contain a catalytic domain surrounded by one or more additional domains, such as a Ub-specific protease domain, a Ubl domain, a meprin and receptor-related factor (TNF) factor (TRAF) homology (MATH) domain, a zinc finger Ub-domain. specific protease (ZnF-UBP) etc. [13, 15]. The conserved amino acid sequence motifs around the catalytically active amino acid residues of these classes of DUBs and protein structures have been extensively reviewed for mechanisms and interactional specificity [14].

Eukaryotic viruses use post-translational modifications to degrade various viral and cellular proteins to overcome host defense mechanisms at various stages of the infection cycle. In these processes, both DNA and RNA viruses use the cellular UPS for degradation [16, 17, 18, 19], while many viruses also express their E3 to degrade cellular proteins such as p53, major histocompatibility complex class I (MHC) . -I) etc. [20, 21]. Thus, it is well known that viruses and their infected hosts use the proteasome degradation system to promote efficient viral replication or, respectively, to limit viral invasion of the infected host. Figure 1 provides an overview of how ubiquitination and host and viral DUBs regulate protein fate.

Wirtschaftsuniversität Wien: Structure & Content

DUBs are also used by viruses and virus-infected cells to reverse the biological effects of ubiquitinated proteins by removing Ub from target proteins during viral infection of the host, as reviewed [ 1 , 2 ]. In contrast to ubiquitination, not many examples of virus-targeted protein deubiquitination have been reported to date, leaving researchers without a relatively detailed molecular understanding of either the viral hijacking of deubiquitination or the blockade of the host infection response. This review focuses on how infecting viruses and invading cells use deubiquitination systems to achieve the competing biological goals of viral proliferation and host cell maintenance.

Upon viral infection, the invaded host activates antiviral innate immune signaling pathways to prevent virus replication [22]. Activation of innate immune responses begins with the recognition of pathogen-associated molecular patterns (PAMPs; conserved components of microbes) by a large repertoire of pattern recognition receptors (PRRs) [ 23 , 24 ]. The best characterized PRRs for recognizing different types of PAMPs are toll-like receptors (TLRs), retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs), NOD-like receptors and C-type lectin receptors. CLR) [22]. Recognition of PAMPs by specific PRRs activates their specific downstream signaling pathways, inducing the synthesis of various antiviral molecules such as interferons (IFNs) and proinflammatory cytokines [ 25 , 26 , 27 , 28 ]. During these processes, host DUBs play a central role in the regulation of antiviral innate immune signaling pathways. For example, USP7, a host DUB, prevents degradation of the nuclear factor kappa light chain enhancer of activated B cells (NF-κB) by deubiquitination by K48 of the p65 subunit of NF-κB in the TLR pathway (TLR3 and TLR9). increases the stability of NF-kB, which up-regulates the transcription of pro-inflammatory cytokines [29]. The USP7-mediated increase in NF-κB activity is then counterbalanced by another DUB known as A20 in the TLR pathway, where A20 down-regulates NF-κB activity by deubiquitinating TRAF6 [ 29 , 30 ]. In the immune signaling cascade, DUBs such as USP3 [31], USP15 [32], USP21 [33], cylindromatosis (CYLD) [34, 35], etc., directly target the receptor RIG-I, a cytosolic RNA sensor, for K63 -deubiquitination and I to inhibit type I IFN, while USP4 stabilizes RIG-I by removing the K-48 poly-Ub chain, positively regulating RIG-I-mediated antiviral responses [36]. USP17 and USP25 also deubiquitinate RIG-I in different ways; that is, USP17 stabilizes RIG-I through K48-deubiquitination, while USP25 inhibits RIG-I degradation through K63-deubiquitination [ 37 , 38 ].

In addition to regulating the innate immune system, cellular DUBs play important roles in modulating viral infectivity, replication, and pathogenicity. USP11 inhibits influenza virus infection [ 39 ], while USP14 enhances the replication of viruses including norovirus, encephalomyocarditis virus, Sindbis virus, and La Crosse virus [ 40 ]. USP7, also known as herpesvirus-associated Ub-specific protease (HAUSP), is known to interact with the ICP0 protein of herpes simplex virus type 1 (HSV-1), and interactions between these two proteins have been implicated in viral infectivity [41] . Epstein-Barr virus (EBV) Epstein-Barr nuclear antigen 1 (EBNA1) also uses USP7 to initiate the destruction of PML nuclear bodies to contribute to nasopharyngeal carcinoma [ 42 ]. USP7 is also important for EBNA1-mediated recruitment of histone H2B deubiquitination complex to EBV latency to stimulate EBNA1 DNA binding activity to enhance viral replication [ 43 ]. Other reports have further shown that USP7 can interact with the Kaposi’s sarcoma-associated herpesvirus (KSHV) latency-associated nuclear antigen (LANA) to regulate replication of the latent viral genome [ 44 ]. A Gaussia princeps luciferase protein complementation assay showed that USP15 interacts with the human papillomavirus (HPV) E6 major oncoprotein, while USP29 and USP33 bind to the E7 protein, suggesting that cellular DUBs influence HPV tumorigenesis by regulating the stability of viral proteins [45] . USP15 is also known to be a critical factor in the observed stability

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