Mechanisms and Effects on HBV Replication of the Interaction between HBV Core Protein and Cellular Filamin B

Filamin B restricts vaccinia virus spread and is targeted by vaccinia virus protein C4

Vaccinia virus (VACV) is a large DNA virus that encodes scores of proteins that modulate the host immune response. VACV protein C4 is one such immunomodulator known to inhibit the activation of both the NF-κB signaling cascade and the DNA-PK-mediated DNA sensing pathway. Here, we show that the N-terminal region of C4, which neither inhibits NF-κB nor mediates interaction with DNA-PK, still contributes to virus virulence. Furthermore, this domain interacts directly and with high affinity to the C-terminal domain of filamin B (FLNB). FLNB is a large actin-binding protein that stabilizes the F-actin network and is implicated in other cellular processes. Deletion of FLNB from cells results in larger VACV plaques and increased infectious viral yield, indicating that FLNB restricts VACV spread. These data demonstrate that C4 has a new function that contributes to virulence and engages the cytoskeleton. Furthermore, we show that the cytoskeleton performs further previously uncharacterized functions during VACV infection.

IMPORTANCE

Vaccinia virus (VACV), the vaccine against smallpox and monkeypox, encodes many proteins to counteract the host immune response. Investigating these proteins provides insights into viral immune evasion mechanisms and thereby indicates how to engineer safer and more immunogenic VACV-based vaccines. Here, we report that the N-terminal domain of VACV protein C4 interacts directly with the cytoskeletal protein filamin B (FLNB), and this domain of C4 contributes to virus virulence. Furthermore, VACV replicates and spreads better in cells lacking FLNB, thus demonstrating that FLNB has antiviral activity. VACV utilizes the cytoskeleton for movement within and between cells; however, previous studies show no involvement of C4 in VACV replication or spread. Thus, C4 associates with FLNB for a different reason, suggesting that the cytoskeleton has further uncharacterized roles during virus infection.

Detection of Tomato Spotted Wilt Virus (TSWV) Infection in Plants Using DAS-ELISA and Dot-ELISA

Plant viruses cause severe damages to crop productions each year worldwide. To prevent the losses caused by plant viruses, it is necessary to develop specific and efficient diagnostic tools to detect viruses. Among the current virus detection techniques, serological detection methods are considered to be rapid, simple, sensitive, and high throughput. Therefore, serological detection methods such as double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA), triple antibody sandwich ELISA (TAS-ELISA), antigen coated plate-ELISA (ACP-ELISA), Dot-ELISA and tissue print-ELISA as well as colloidal gold immunochromatographic strip are now wildly used to detect viruses in plants. In this chapter, we describe the DAS-ELISA and Dot-ELISA methods, and their applications in the detection of Tomato spotted wilt virus (TSWV) infection in plants. These two methods can be easily adapted for diagnosis of other plant viruses.

The Hepatitis B Virus Interactome: A Comprehensive Overview

Despite the availability of a prophylactic vaccine, chronic hepatitis B (CHB) caused by the hepatitis B virus (HBV) is a major health problem affecting an estimated 292 million people globally. Current therapeutic goals are to achieve functional cure characterized by HBsAg seroclearance and the absence of HBV-DNA after treatment cessation. However, at present, functional cure is thought to be complicated due to the presence of covalently closed circular DNA (cccDNA) and integrated HBV-DNA. Even if the episomal cccDNA is silenced or eliminated, it remains unclear how important the high level of HBsAg that is expressed from integrated HBV DNA is for the pathology. To identify therapies that could bring about high rates of functional cure, in-depth knowledge of the virus' biology is imperative to pinpoint mechanisms for novel therapeutic targets. The viral proteins and the episomal cccDNA are considered integral for the control and maintenance of the HBV life cycle and through direct interaction with the host proteome they help create the most optimal environment for the virus whilst avoiding immune detection. New HBV-host protein interactions are continuously being identified. Unfortunately, a compendium of the most recent information is lacking and an interactome is unavailable. This article provides a comprehensive review of the virus-host relationship from viral entry to release, as well as an interactome of cccDNA, HBc, and HBx.

The 3A protein of coxsackievirus B3 acts as a viral suppressor of RNA interference

RNA interference (RNAi) is a potent antiviral defence mechanism in eukaryotes, and numerous viruses have been found to encode viral suppressors of RNAi (VSRs). Coxsackievirus B3 (CVB3) belongs to the genus Enterovirus in the family Picornaviridae, and has been reported to be a major causative pathogen for viral myocarditis. Despite the importance of CVB3, it is unclear whether CVB3 can also encode proteins that suppress RNAi. Here, we showed that the CVB3 nonstructural protein 3A suppressed RNAi triggered by either small hairpin RNAs (shRNAs) or small interfering RNAs (siRNAs) in mammalian cells. We further uncovered that CVB3 3A interacted directly with double-stranded RNAs (dsRNAs) and siRNAs in vitro. Through mutational analysis, we found that the VSR activity of CVB3 3A was significantly reduced by mutations of D24A/L25A/L26A, Y37A/C38A and R60A in conserved residues. In addition, the 3A protein encoded by coxsackievirus B5 (CVB5), another member of Enterovirus, also showed VSR activity. Taken together, our findings showed that CVB3 3A has in vitro VSR activity, thereby providing insights into the pathogenesis of CVB3 and other enteroviruses.