Remodeling of the Actin Network Associated with the Non-Structural Protein 1 (NS1) of West Nile Virus and Formation of NS1-Containing Tunneling Nanotubes

Nuclear membrane protein SUN2 promotes replication of flaviviruses through modulating cytoskeleton reorganization mediated by NS1

Cytoskeleton is extensively recruited by flaviviruses for their infection. In this study, we uncovered an essential role of a nuclear membrane protein, SAD1/UNC84 domain protein 2 (SUN2) linking cytoskeleton and nucleoskeleton in the flavivirus replication. CRISPR/Cas9-mediated knockout of SUN2, but not SUN1, significantly reduces the replication of Zika virus (ZIKV), dengue virus (DENV), and Japanese encephalitis virus (JEV). In contrast, SUN2 does not affect the infection of non-flaviviridae RNA viruses. All three regions of SUN2 are required for its proviral effect. Mechanistically, SUN2 facilitates rearrangement of cytoskeleton and formation of replication organelles induced by viral infection, and hence promotes viral RNA synthesis. SUN2 is required for the interaction between cytoskeleton actin and ZIKV nonstructural protein 1 (NS1). Expression of dominant negative Nesprin-1 and Nesprin-2, which connect SUN2 to cytoskeleton proteins, alleviates the interaction between actin and NS1 and reduces viral replication levels. In a neonatal mouse infection model, SUN2 knockout dramatically alleviates the in vivo ZIKV replication and development of neuropathology. This work elucidates that recruitment of cytoskeleton proteins by flavivirus is coordinated by nuclear membrane proteins SUN2 and Nesprins, providing evidence for a link between nuclear membrane proteins and flavivirus infection.

Zika Virus NS1 Drives Tunneling Nanotube Formation for Mitochondrial Transfer, Enhanced Survival, Interferon Evasion, and Stealth Transmission in Trophoblasts

Zika virus (ZIKV) infection continues to pose a significant public health concern due to limited available preventive measures and treatments. ZIKV is unique among flaviviruses in its vertical transmission capacity (i.e., transmission from mother to fetus) yet the underlying mechanisms remain incompletely understood. Here, we show that both African and Asian lineages of ZIKV induce tunneling nanotubes (TNTs) in placental trophoblasts and multiple other mammalian cell types. Amongst investigated flaviviruses, only ZIKV strains trigger TNTs. We show that ZIKV-induced TNTs facilitate transfer of viral particles, proteins, and RNA to neighboring uninfected cells. ZIKV TNT formation is driven exclusively via its non-structural protein 1 (NS1); specifically, the N-terminal region (50 aa) of membrane-bound NS1 is necessary and sufficient for triggering TNT formation in host cells. Using affinity purification-mass spectrometry of cells infected with wild-type NS1 or non-TNT forming NS1 (pNS1ΔTNT) proteins, we found mitochondrial proteins are dominant NS1-interacting partners, consistent with the elevated mitochondrial mass we observed in infected trophoblasts. We demonstrate that mitochondria are siphoned via TNTs from healthy to ZIKV-infected cells, both homotypically and heterotypically, and inhibition of mitochondrial respiration reduced viral replication in trophoblast cells. Finally, ZIKV strains lacking TNT capabilities due to mutant NS1 elicited a robust antiviral IFN-λ 1/2/3 response, indicating ZIKV's TNT-mediated trafficking also allows ZIKV cell-cell transmission that is camouflaged from host defenses. Together, our findings identify a new stealth mechanism that ZIKV employs for intercellular spread among placental trophoblasts, evasion of antiviral interferon response, and the hijacking of mitochondria to augment its propagation and survival. Discerning the mechanisms of ZIKV intercellular strategies offers a basis for novel therapeutic developments targeting these interactions to limit its dissemination.

RSV-induced expanded ciliated cells contribute to bronchial wall thickening

Viral infection, particularly respiratory syncytial virus (RSV), causes inflammation in the bronchiolar airways (bronchial wall thickening, also known as bronchiolitis). This bronchial wall thickening is a common pathophysiological feature in RSV infection, but it causes more fatalities in infants than in children and adults. However, the molecular mechanism of RSV-induced bronchial wall thickening remains unknown, particularly in healthy adults. Using highly differentiated pseudostratified airway epithelium generated from primary human bronchial epithelial cells, we revealed RSV-infects primarily ciliated cells. The infected ciliated cells expanded substantially without compromising epithelial membrane integrity and ciliary functions and contributed to the increased height of the airway epithelium. Furthermore, we identified multiple factors, e.g., cytoskeletal (ARP2/3-complex-driven actin polymerization), immunological (IP10/CXCL10), and viral (NS2), contributing to RSV-induced uneven epithelium height increase in vitro. Thus, RSV-infected expanded cells contribute to a noncanonical inflammatory phenotype, which contributes to bronchial wall thickening in the airway, and is termed cytoskeletal inflammation.

RSV-induced Expanded Ciliated Cells Contribute to Bronchial Wall Thickening.. [DOI: 10.1101/2022.10.31.514471] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Viral infection, particularly respiratory syncytial virus (RSV), causes inflammation in the bronchiolar airways (bronchial wall thickening, also known as bronchiolitis), reducing airflow through the bronchioles. This bronchial wall thickening is a common pathophysiological feature in RSV infection, but it causes more fatalities in infants than in children and adults. However, the molecular mechanism of RSV-induced bronchial wall thickening remains unknown, particularly in healthy adults. RSV infection in the airway epithelium of healthy adult bronchial cells reveals RSV-infects primarily ciliated cells. RSV infection expands the cell cytoskeleton substantially without compromising epithelial membrane integrity and ciliary functions. The RSV-induced actin cytoskeleton expansion increases ununiformly epithelial height, and cytoskeletal (actin polymerization), immunological (INF-L1, TNF-α, IP10/CXCL10), and viral (NS2) factors are probably responsible. Interestingly, RSV-infected cell cytoskeleton’s expansion resembles a noncanonical inflammatory phenotype, which contributes to bronchial wall thickening, and is termed cytoskeletal inflammation.

Author Summary

RSV infects everyone. Although RSV-induced fatal pathophysiology (e.g., bronchiolitis) is more common in infants than adults, this bronchiolitis (or bronchial wall thickening) is common in the lower respiratory tract due to RSV infection in all ages. To determine the molecular mechanism of RSV-induced bronchial wall thickening, we infectedin vitroadult airway epithelium with RSV. We found that RSV-infection induced a substantial actin-cytoskeleton expansion, consequently increased the height of the epithelium. We identified actin polymerization, secretion of proinflammatory cytokines and chemokines, and viral proteins contribute to the RSV-induced cytoskeletal expansion. Our results suggest that RSV-induces a novel noncanonical epithelial host response termed cytoskeletal inflammation, which may contribute to bronchial wall thickening.

Opportunities and Challenges in Tunneling Nanotubes Research: How Far from Clinical Application?

Tunneling nanotubes (TNTs) are recognized long membrane nanotubes connecting distance cells. In the last decade, growing evidence has shown that these subcellular structures mediate the specific transfer of cellular materials, pathogens, and electrical signals between cells. As intercellular bridges, they play a unique role in embryonic development, collective cell migration, injured cell recovery, cancer treatment resistance, and pathogen propagation. Although TNTs have been considered as potential drug targets for treatment, there is still a long way to go to translate the research findings into clinical practice. Herein, we emphasize the heterogeneous nature of TNTs by systemically summarizing the current knowledge on their morphology, structure, and biogenesis in different types of cells. Furthermore, we address the communication efficiency and biological outcomes of TNT-dependent transport related to diseases. Finally, we discuss the opportunities and challenges of TNTs as an exciting therapeutic approach by focusing on the development of efficient and safe drugs targeting TNTs.

Zika virus is transmitted in neural progenitor cells via cell-to-cell spread and infection is inhibited by the autophagy inducer trehalose

Zika virus (ZIKV) is a mosquito-borne human pathogen that causes congenital Zika syndrome and neurological symptoms in some adults. There are currently no approved treatments or vaccines for ZIKV, and exploration of therapies targeting host processes could avoid viral development of drug resistance. The purpose of our study was to determine if the non-toxic and widely used disaccharide trehalose, which showed antiviral activity against Human Cytomegalovirus (HCMV) in our previous work, could restrict ZIKV infection in clinically relevant neural progenitor cells (NPCs). Trehalose is known to induce autophagy, the degradation and recycling of cellular components. Whether autophagy is proviral or antiviral for ZIKV is controversial and depends on cell type and specific conditions used to activate or inhibit autophagy. We show here that trehalose treatment of NPCs infected with recent ZIKV isolates from Panama and Puerto Rico significantly reduces viral replication and spread. In addition, we demonstrate that ZIKV infection in NPCs spreads primarily cell-to-cell as an expanding infectious center, and NPCs are infected via contact with infected cells far more efficiently than by cell-free virus. Importantly, ZIKV was able to spread in NPCs in the presence of neutralizing antibody.Importance Zika virus causes birth defects and can lead to neurological disease in adults. While infection rates are currently low, ZIKV remains a public health concern with no treatment or vaccine available. Targeting a cellular pathway to inhibit viral replication is a potential treatment strategy that avoids development of antiviral resistance. We demonstrate in this study that the non-toxic autophagy-inducing disaccharide trehalose reduces spread and output of ZIKV in infected neural progenitor cells (NPCs), the major cells infected in the fetus. We show that ZIKV spreads cell-to-cell in NPCs as an infectious center and that NPCs are more permissive to infection by contact with infected cells than by cell-free virus. We find that neutralizing antibody does not prevent the spread of the infection in NPCs. These results are significant in demonstrating anti-ZIKV activity of trehalose and in clarifying the primary means of Zika virus spread in clinically relevant target cells.

Viral and host heterogeneity and their effects on the viral life cycle

Traditionally, the viral replication cycle is envisioned as a single, well-defined loop with four major steps: attachment and entry into a target cell, replication of the viral genome, maturation of viral proteins and genome packaging into infectious progeny, and egress and dissemination to the next target cell. However, for many viruses, a growing body of evidence points towards extreme heterogeneity in each of these steps. In this Review, we reassess the major steps of the viral replication cycle by highlighting recent advances that show considerable variability during viral infection. First, we discuss heterogeneity in entry receptors, followed by a discussion on error-prone and low-fidelity polymerases and their impact on viral diversity. Next, we cover the implications of heterogeneity in genome packaging and assembly on virion morphology. Last, we explore alternative egress mechanisms, including tunnelling nanotubes and host microvesicles. In summary, we discuss the implications of viral phenotypic, morphological and genetic heterogeneity on pathogenesis and medicine. This Review highlights common themes and unique features that give nuance to the viral replication cycle.

Bridging the Gap: Virus Long-Distance Spread via Tunneling Nanotubes

Tunneling nanotubes (TNTs) are actin-based intercellular conduits that connect distant cells and allow intercellular transfer of molecular information, including genetic information, proteins, lipids, and even organelles. Besides providing a means of intercellular communication, TNTs may also be hijacked by pathogens, particularly viruses, to facilitate their spread. Viruses of many different families, including retroviruses, herpesviruses, orthomyxoviruses, and several others have been reported to trigger the formation of TNTs or TNT-like structures in infected cells and use these structures to efficiently spread to uninfected cells. In the current review, we give an overview of the information that is currently available on viruses and TNT-like structures, and we discuss some of the standing questions in this field.