Nup358 and Transportin 1 Cooperate in Adenoviral Genome Import

Nup358 and Nup153 Facilitate nuclear import of BmNPV nucleocapsids in Bombyx mori cells

Nuclear pore complexes (NPCs) are crucial for the nuclear import of viral genomes, serving as gateways for many viruses to deliver their genetic material into host cell nuclei. However, the role of NPCs in the entry of Bombyx mori nucleopolyhedrovirus (BmNPV) remains poorly understood. This study investigates the involvement of specific nucleoporins in the nuclear import of BmNPV nucleocapsids, a crucial step for viral replication in host cells. Using a combination of Importazole, wheat germ agglutinin (WGA), and small interfering RNAs (siRNAs), we demonstrate that BmNPV entry into BmN cells is mediated through the NPC. Importazole and WGA treatment significantly inhibited viral infection, highlighting the essential role of nucleoporins in BmNPV entry. Additionally, siRNA-mediated knockdown of Nup358 and Nup153 resulted in a marked accumulation of nucleocapsids in the cytoplasm. Overexpression of the N-terminal fragment of Nup358 (1-1127) enhanced nucleocapsid entry efficiency, whereas deletion of the phenylalanine-glycine (FG) repeats in Nup153 (Nup153ΔFG) reduced viral entry. These results confirm the pivotal roles of Nup358 and Nup153 in the nuclear import of BmNPV nucleocapsids. Our findings provide new insights into the molecular interactions between BmNPV and host NPCs, offering potential targets for controlling BmNPV infections in sericulture.

Role of Protein VII in the Production of Infectious Bovine Adenovirus-3 Virion

Bovine adenovirus (BAdV)-3 genome encodes a 26 kDa core protein designated as protein VII, which localizes to the nucleus/nucleolus. The requirement of a protein VII-complementing cell line for the replication of VII-deleted BAdV-3 suggests that protein VII is required for the production of infectious progeny virions. An analysis of the BAV.VIId+ virus (only phenotypically positive for protein VII) detected no noticeable differences in the expression and incorporation of viral proteins in the virions. Moreover, protein VII does not appear to be essential for the formation of mature BAV.VIId+. However, protein VII appeared to be required for the efficient assembly of mature BAV.VIId- virions. An analysis of the BAV.VIId- virus (genotypically and phenotypically negative for protein VII) in non-complementing cells detected the inefficient release of virions from endosomes, which affected the expression of viral proteins or DNA replication. Moreover, the absence of protein VII altered the proteolytic cleavage of protein VI of BAV.VIId-. Our results suggest that BAdV-3 protein VII appears to be required for efficient production of mature virions. Moreover, the absence of protein VII produces non-infectious BAdV-3 by altering the release of BAdV-3 from endosomes/vesicles.

Advances in the understanding of nuclear pore complexes in human diseases

BACKGROUND

Nuclear pore complexes (NPCs) are sophisticated and dynamic protein structures that straddle the nuclear envelope and act as gatekeepers for transporting molecules between the nucleus and the cytoplasm. NPCs comprise up to 30 different proteins known as nucleoporins (NUPs). However, a growing body of research has suggested that NPCs play important roles in gene regulation, viral infections, cancer, mitosis, genetic diseases, kidney diseases, immune system diseases, and degenerative neurological and muscular pathologies.

PURPOSE

In this review, we introduce the structure and function of NPCs. Then We described the physiological and pathological effects of each component of NPCs which provide a direction for future clinical applications.

METHODS

The literatures from PubMed have been reviewed for this article.

CONCLUSION

This review summarizes current studies on the implications of NPCs in human physiology and pathology, highlighting the mechanistic underpinnings of NPC-associated diseases.

RANBP2 evolution and human disease

Ran-binding protein 2 (RANBP2)/Nup358 is a nucleoporin and a key component of the nuclear pore complex. Through its multiple functions (e.g., SUMOylation, regulation of nucleocytoplasmic transport) and subcellular localizations (e.g., at the nuclear envelope, kinetochores, annulate lamellae), it is involved in many cellular processes. RANBP2 dysregulation or mutation leads to the development of human pathologies, such as acute necrotizing encephalopathy 1, cancer, neurodegenerative diseases, and it is also involved in viral infections. The chromosomal region containing the RANBP2 gene is highly dynamic, with high structural variation and recombination events that led to the appearance of a gene family called RANBP2 and GCC2 Protein Domains (RGPD), with multiple gene loss/duplication events during ape evolution. Although RGPD homoplasy and maintenance during evolution suggest they might confer an advantage to their hosts, their functions are still unknown and understudied. In this review, we discuss the appearance and importance of RANBP2 in metazoans and its function-related pathologies, caused by an alteration of its expression levels (through promotor activity, post-transcriptional, or post-translational modifications), its localization, or genetic mutations.

Getting on the right track: Interactions between viruses and the cytoskeletal motor proteins

The cytoskeleton is an essential component of the cell and it is involved in multiple physiological functions, including intracellular organization and transport. It is composed of three main families of proteinaceous filaments; microtubules, actin filaments and intermediate filaments and their accessory proteins. Motor proteins, which comprise the dynein, kinesin and myosin superfamilies, are a remarkable group of accessory proteins that mainly mediate the intracellular transport of cargoes along with the cytoskeleton. Like other cellular structures and pathways, viruses can exploit the cytoskeleton to promote different steps of their life cycle through associations with motor proteins. The complexity of the cytoskeleton and the differences among viruses, however, has led to a wide diversity of interactions, which in most cases remain poorly understood. Unveiling the details of these interactions is necessary not only for a better comprehension of specific infections, but may also reveal new potential drug targets to fight dreadful diseases such as rabies disease and acquired immunodeficiency syndrome (AIDS). In this review, we describe a few examples of the mechanisms that some human viruses, that is, rabies virus, adenovirus, herpes simplex virus, human immunodeficiency virus, influenza A virus and papillomavirus, have developed to hijack dyneins, kinesins and myosins.

How viral proteins bind short linear motifs and intrinsically disordered domains

Viruses are the obligate intracellular parasites that exploit the host cellular machinery to replicate their genome. During the viral life cycle viruses manipulate the host cell through interactions with host proteins. Many of these protein-protein interactions are mediated through the recognition of host globular domains by short linear motifs (SLiMs), or longer intrinsically disordered domains (IDD), in the disordered regions of viral proteins. However, viruses also employ their own globular domains for binding to SLiMs and IDDs present in host proteins or virus proteins. In this review, we focus on the different strategies adopted by viruses to utilize proteins or protein domains for binding to the disordered regions of human or/and viral ligands. With a set of examples, we describe viral domains that bind human SLiMs. We also provide examples of viral proteins that bind to SLiMs, or IDDs, of viral proteins as a part of complex assembly and regulation of protein functions. The protein-protein interactions are often crucial for viral replication, and may thus offer possibilities for innovative inhibitor design.

Components of the LINC and NPC complexes coordinately target and translocate a virus into the nucleus to promote infection

Nuclear entry represents the final and decisive infection step for most DNA viruses, although how this is accomplished by some viruses is unclear. Polyomavirus SV40 transports from the cell surface through the endosome, the endoplasmic reticulum, and the cytosol from where it enters the nucleus to cause infection. Here we elucidate the nuclear entry mechanism of SV40. Our results show that cytosol-localized SV40 is targeted to the nuclear envelope by directly engaging Nesprin-2 of the linker of nucleoskeleton and cytoskeleton (LINC) nuclear membrane complex. Additionally, we identify the NUP188 subunit of the nuclear pore complex (NPC) as a new Nesprin-2-interacting partner. This physical proximity positions the NPC to capture SV40 upon release from Nesprin-2, enabling the channel to facilitate nuclear translocation of the virus. Strikingly, SV40 disassembles during nuclear entry, generating a viral genome-VP1-VP3 subcomplex that efficiently crosses the NPC to enter the nucleus. Our results reveal how two major nuclear membrane protein complexes are exploited to promote targeting and translocation of a virus into the nucleus.

Roles of Nucleoporin RanBP2/Nup358 in Acute Necrotizing Encephalopathy Type 1 (ANE1) and Viral Infection

Ran Binding Protein 2 (RanBP2 or Nucleoporin358) is one of the main components of the cytoplasmic filaments of the nuclear pore complex. Mutations in the RANBP2 gene are associated with acute necrotizing encephalopathy type 1 (ANE1), a rare condition where patients experience a sharp rise in cytokine production in response to viral infection and undergo hyperinflammation, seizures, coma, and a high rate of mortality. Despite this, it remains unclear howRanBP2 and its ANE1-associated mutations contribute to pathology. Mounting evidence has shown that RanBP2 interacts with distinct viruses to regulate viral infection. In addition, RanBP2 may regulate innate immune response pathways. This review summarizes recent advances in our understanding of how mutations in RANBP2 contribute to ANE1 and discusses how RanBP2 interacts with distinct viruses and affects viral infection. Recent findings indicate that RanBP2 might be an important therapeutic target, not only in the suppression of ANE1-driven cytokine storms, but also to combat hyperinflammation in response to viral infections.

SUMOylation in Viral Replication and Antiviral Defense

SUMOylation is a ubiquitination-like post-translational modification that plays an essential role in the regulation of protein function. Recent studies have shown that proteins from both RNA and DNA virus families can be modified by SUMO conjugation, which facilitates viral replication. Viruses can manipulate the entire process of SUMOylation through interplay with the SUMO pathway. By contrast, SUMOylation can eliminate viral infection by regulating host antiviral immune components. A deeper understanding of how SUMOylation regulates viral proteins and cellular antiviral components is necessary for the development of effective antiviral therapies. In the present review, the regulatory mechanism of SUMOylation in viral replication and infection and the antiviral immune response, and the consequences of this regulation for viral replication and engagement with antiviral innate immunity are summarized. The potential therapeutic applications of SUMOylation in diseases caused by viruses are also discussed.

CRM1 Promotes Capsid Disassembly and Nuclear Envelope Translocation of Adenovirus Independently of Its Export Function

After receptor-mediated endocytosis and endosomal escape, adenoviral capsids can travel via microtubule organizing centers to the nuclear envelope. Upon capsid disassembly, viral genome import into nuclei of interphase cells then occurs through nuclear pore complexes, involving the nucleoporins Nup214 and Nup358. Import also requires the activity of the classic nuclear export receptor CRM1, as it is blocked by the selective inhibitor leptomycin B. We have now used artificially enucleated as well as mitotic cells to analyze the role of an intact nucleus in different steps of the viral life cycle. In enucleated U2OS cells, viral capsids traveled to the microtubule organizing center, whereas their removal from this complex was blocked, suggesting that this step required nuclear factors. In mitotic cells, on the other hand, CRM1 promoted capsid disassembly and genome release, suggesting a role of this protein that does not require intact nuclear envelopes or nuclear pore complexes and is distinct from its function as a nuclear export receptor. Similar to enucleation, inhibition of CRM1 by leptomycin B also leads to an arrest of adenoviral capsids at the microtubule organizing center. In a small-scale screen using leptomycin B-resistant versions of CRM1, we identified a mutant, CRM1 W142A P143A, that is compromised with respect to adenoviral capsid disassembly in both interphase and mitotic cells. Strikingly, this mutant is capable of exporting cargo proteins out of the nucleus of living cells or digitonin-permeabilized cells, pointing to a role of the mutated region that is not directly linked to nuclear export. IMPORTANCE A role of nucleoporins and of soluble transport factors in adenoviral genome import into the nucleus of infected cells in interphase has previously been established. The nuclear export receptor CRM1 promotes genome import, but its precise function is not known. Using enucleated and mitotic cells, we showed that CRM1 does not simply function by exporting a crucial factor out of the nucleus that would then trigger capsid disassembly and genome import. Instead, CRM1 has an export-independent role, a notion that is also supported by a mutant, CRM1 W142A P143A, which is export competent but deficient in viral capsid disassembly, in both interphase and mitotic cells.

Adenovirus Core Proteins: Structure and Function

Adenoviruses have served as a model for investigating viral-cell interactions and discovering different cellular processes, such as RNA splicing and DNA replication. In addition, the development and evaluation of adenoviruses as the viral vectors for vaccination and gene therapy has led to detailed investigations about adenovirus biology, including the structure and function of the adenovirus encoded proteins. While the determination of the structure and function of the viral capsid proteins in adenovirus biology has been the subject of numerous reports, the last few years have seen increased interest in elucidating the structure and function of the adenovirus core proteins. Here, we provide a review of research about the structure and function of the adenovirus core proteins in adenovirus biology.

Transportin-1: A Nuclear Import Receptor with Moonlighting Functions

Transportin-1 (Trn1), also known as karyopherin-β2 (Kapβ2), is probably the best-characterized nuclear import receptor of the karyopherin-β family after Importin-β, but certain aspects of its functions in cells are still puzzling or are just recently emerging. Since the initial identification of Trn1 as the nuclear import receptor of hnRNP A1 ∼25 years ago, several molecular and structural studies have unveiled and refined our understanding of Trn1-mediated nuclear import. In particular, the understanding at a molecular level of the NLS recognition by Trn1 made a decisive step forward with the identification of a new class of NLSs called PY-NLSs, which constitute the best-characterized substrates of Trn1. Besides PY-NLSs, many Trn1 cargoes harbour NLSs that do not resemble the archetypical PY-NLS, which complicates the global understanding of cargo recognition by Trn1. Although PY-NLS recognition is well established and supported by several structures, the recognition of non-PY-NLSs by Trn1 is far less understood, but recent reports have started to shed light on the recognition of this type of NLSs. Aside from its principal and long-established activity as a nuclear import receptor, Trn1 was shown more recently to moonlight outside nuclear import. Trn1 has for instance been caught in participating in virus uncoating, ciliary transport and in modulating the phase separation properties of aggregation-prone proteins. Here, we focus on the structural and functional aspects of Trn1-mediated nuclear import, as well as on the moonlighting activities of Trn1.

E3 ubiquitin ligase Mindbomb 1 facilitates nuclear delivery of adenovirus genomes

The journey from plasma membrane to nuclear pore is a critical step in the lifecycle of DNA viruses, many of which must successfully deposit their genomes into the nucleus for replication. Viral capsids navigate this vast distance through the coordinated hijacking of a number of cellular host factors, many of which remain unknown. We performed a gene-trap screen in haploid cells to identify host factors for adenovirus (AdV), a DNA virus that can cause severe respiratory illness in immune-compromised individuals. This work identified Mindbomb 1 (MIB1), an E3 ubiquitin ligase involved in neurodevelopment, as critical for AdV infectivity. In the absence of MIB1, we observed that viral capsids successfully traffic to the proximity of the nucleus but ultimately fail to deposit their genomes within. The capacity of MIB1 to promote AdV infection was dependent on its ubiquitination activity, suggesting that MIB1 may mediate proteasomal degradation of one or more negative regulators of AdV infection. Employing complementary proteomic approaches to characterize proteins proximal to MIB1 upon AdV infection and differentially ubiquitinated in the presence or absence of MIB1, we observed an intersection between MIB1 and ribonucleoproteins (RNPs) largely unexplored in mammalian cells. This work uncovers yet another way that viruses utilize host cell machinery for their own replication, highlighting a potential target for therapeutic interventions that counter AdV infection.