A single amino acid change resulting in loss of fluorescence of eGFP in a viral fusion protein confers fitness and growth advantage to the recombinant vesicular stomatitis virus

Enteroviral 2B Interacts with VDAC3 to Regulate Reactive Oxygen Species Generation That Is Essential to Viral Replication

Enterovirus (EV) 71 caused episodes of outbreaks in China and Southeast Asia during the last few decades. We have previously reported that EV71 induces reactive oxygen species (ROS). However, the underlying mechanism remains elusive. Co-immunoprecipitation-proteomic analysis revealed that enteroviral 2B protein interacted with mitochondrial voltage-dependent anion channel 3 (VDAC3). Knockdown (KD) of VDAC3 expression specifically inhibited enteroviral replication. Single-round viral replication was also inhibited in KD cells, suggesting that VDAC3 plays an essential role in replication. Consistent with this, VDAC3 gene KD significantly reduced the EV71-induced mitochondrial ROS generation. Exogenous 2B expression could induce the mitochondrial ROS generation that was significantly reduced in VDAC3-KD cells or in the Mito-TEMPO-treated cells. Moreover, VDAC3 appears to be necessary for regulation of antioxidant metabolism. VDAC3 gene KD led to the enhancement of such pathways as hypotaurine/taurine synthesis in the infected cells. Taken together, these findings suggest that 2B and VDAC3 interact to enhance mitochondrial ROS generation, which promotes viral replication.

Experimental Evolution Generates Novel Oncolytic Vesicular Stomatitis Viruses with Improved Replication in Virus-Resistant Pancreatic Cancer Cells

Vesicular stomatitis virus (VSV)-based oncolytic viruses are promising agents against pancreatic ductal adenocarcinoma (PDAC). However, some PDAC cell lines are resistant to VSV. Here, using a directed viral evolution approach, we generated novel oncolytic VSVs with an improved ability to replicate in virus-resistant PDAC cell lines, while remaining highly attenuated in nonmalignant cells. Two independently evolved VSVs obtained 2 identical VSV glycoprotein mutations, K174E and E238K. Additional experiments indicated that these acquired G mutations improved VSV replication, at least in part due to improved virus attachment to SUIT-2 cells. Importantly, no deletions or mutations were found in the virus-carried transgenes in any of the passaged viruses. Our findings demonstrate long-term genomic stability of complex VSV recombinants carrying large transgenes and support further clinical development of oncolytic VSV recombinants as safe therapeutics for cancer.

Vesicular stomatitis virus (VSV) based oncolytic viruses are promising agents against various cancers. We have shown that pancreatic ductal adenocarcinoma (PDAC) cell lines exhibit great diversity in susceptibility and permissibility to VSV. Here, using a directed evolution approach with our two previously described oncolytic VSV recombinants, VSV-p53wt and VSV-p53-CC, we generated novel oncolytic VSVs with an improved ability to replicate in virus-resistant PDAC cell lines. VSV-p53wt and VSV-p53-CC encode a VSV matrix protein (M) with a ΔM51 mutation (M-ΔM51) and one of two versions of a functional human tumor suppressor, p53, fused to a far-red fluorescent protein, eqFP650. Each virus was serially passaged 32 times (which accounts for more than 60 viral replication cycles) on either the SUIT-2 (moderately resistant to VSV) or MIA PaCa-2 (highly permissive to VSV) human PDAC cell lines. While no phenotypic changes were observed for MIA PaCa-2-passaged viruses, both SUIT-2-passaged VSV-p53wt and VSV-p53-CC showed improved replication in SUIT-2 and AsPC-1, another human PDAC cell line also moderately resistant to VSV, while remaining highly attenuated in nonmalignant cells. Surprisingly, two identical VSV glycoprotein (VSV-G) mutations, K174E and E238K, were identified in both SUIT-2-passaged viruses. Additional experiments indicated that the acquired G mutations improved VSV replication, at least in part due to improved virus attachment to SUIT-2 cells. Importantly, no mutations were found in the M-ΔM51 protein, and no deletions or mutations were found in the p53 or eqFP650 portions of virus-carried transgenes in any of the passaged viruses, demonstrating long-term genomic stability of complex VSV recombinants carrying large transgenes.

IMPORTANCE Vesicular stomatitis virus (VSV)-based oncolytic viruses are promising agents against pancreatic ductal adenocarcinoma (PDAC). However, some PDAC cell lines are resistant to VSV. Here, using a directed viral evolution approach, we generated novel oncolytic VSVs with an improved ability to replicate in virus-resistant PDAC cell lines, while remaining highly attenuated in nonmalignant cells. Two independently evolved VSVs obtained 2 identical VSV glycoprotein mutations, K174E and E238K. Additional experiments indicated that these acquired G mutations improved VSV replication, at least in part due to improved virus attachment to SUIT-2 cells. Importantly, no deletions or mutations were found in the virus-carried transgenes in any of the passaged viruses. Our findings demonstrate long-term genomic stability of complex VSV recombinants carrying large transgenes and support further clinical development of oncolytic VSV recombinants as safe therapeutics for cancer.

Role for ribosome-associated complex and stress-seventy subfamily B (RAC-Ssb) in integral membrane protein translation

Targeting of most integral membrane proteins to the endoplasmic reticulum is controlled by the signal recognition particle, which recognizes a hydrophobic signal sequence near the protein N terminus. Proper folding of these proteins is monitored by the unfolded protein response and involves protein degradation pathways to ensure quality control. Here, we identify a new pathway for quality control of major facilitator superfamily transporters that occurs before the first transmembrane helix, the signal sequence recognized by the signal recognition particle, is made by the ribosome. Increased rates of translation elongation of the N-terminal sequence of these integral membrane proteins can divert the nascent protein chains to the ribosome-associated complex and stress-seventy subfamily B chaperones. We also show that quality control of integral membrane proteins by ribosome-associated complex-stress-seventy subfamily B couples translation rate to the unfolded protein response, which has implications for understanding mechanisms underlying human disease and protein production in biotechnology.

Deep Sequencing Details the Cross-over Map of Chimeric Genes in Two Porcine Reproductive and Respiratory Syndrome Virus Infectious Clones

BACKGROUND

Recombination is an important contributor to the genetic diversity of most viruses. A reverse genetics system using green fluorescence protein (GFP)- and enhanced GFP (EGFP)-expressing infectious clones was developed to study the requirements for recombination. However, it is still unclear what types of cross-over events occurred to produce the viable offspring.

OBJECTIVE

We utilized 454 sequencing to infer recombination events in this system.

METHOD

Two porcine reproductive and respiratory syndrome virus (PRRSV) infectious clones, P129-EGFP-97C and P129-GFPm-d (2-6), were co-transfected into HEK-293T cells. P129-EGFP-97C is a fully functional virus that contains a non-fluorescent EGFP. P129-GFPm-d (2-6) is a defective virus but contains a fluorescent GFPm. Successful recombination was evident by the appearance of fully functional progeny virus that expresses fluorescence. Total RNA was extracted from infected cells expressing fluorescence, and the entire fluorescent gene was amplified to prepare an amplicon library for 454 sequencing.

RESULTS

Deep sequencing showed that the nucleotide identities changed from ~37% (in the variable region from 21nt to 165nt) to 20% (T₂₈₉C) to ~38% (456-651nt) then to 100% (672-696nt) when compared to EGFP. The results indicated that cross-over events occurred in three conserved regions (166-288nt, 290-455nt, 652-671nt), which were also supported by sequence alignments. Remarkably, the short conserved region (652-671nt) showed to be a cross-over hotspot. In addition, four cross-over patterns (two single and two double cross-over) might be used to produce viable recombinants.

CONCLUSION

The reverse genetics system incorporating the use of high throughput sequencing creates a genetic platform to study the generation of viable recombinant viruses.

Oncolytic viruses: From bench to bedside with a focus on safety

Oncolytic viruses are a relatively new class of anti-cancer immunotherapy agents. Several viruses have undergone evaluation in clinical trials in the last decades, and the first agent is about to be approved to be used as a novel cancer therapy modality. In the current review, an overview is presented on recent (pre)clinical developments in the field of oncolytic viruses that have previously been or currently are being evaluated in clinical trials. Special attention is given to possible safety issues like toxicity, environmental shedding, mutation and reversion to wildtype virus.

Applications of Replicating-Competent Reporter-Expressing Viruses in Diagnostic and Molecular Virology

Commonly used tests based on wild-type viruses, such as immunostaining, cannot meet the demands for rapid detection of viral replication, high-throughput screening for antivirals, as well as for tracking viral proteins or virus transport in real time. Notably, the development of replicating-competent reporter-expressing viruses (RCREVs) has provided an excellent option to detect directly viral replication without the use of secondary labeling, which represents a significant advance in virology. This article reviews the applications of RCREVs in diagnostic and molecular virology, including rapid neutralization tests, high-throughput screening systems, identification of viral receptors and virus-host interactions, dynamics of viral infections in vitro and in vivo, vaccination approaches and others. However, there remain various challenges associated with RCREVs, including pathogenicity alterations due to the insertion of a reporter gene, instability or loss of the reporter gene expression, or attenuation of reporter signals in vivo. Despite all these limitations, RCREVs have become powerful tools for both basic and applied virology with the development of new technologies for generating RCREVs, the inventions of novel reporters and the better understanding of regulation of viral replication.

Development and application of reporter-expressing mononegaviruses: current challenges and perspectives

Reverse genetics allows the generation of recombinant viruses entirely from cDNA. One application of this technology is the creation of reporter-expressing viruses, which greatly increase the detail and ease with which these viruses can be studied. However, there are a number of challenges when working with reporter-expressing viruses. Both the reporter protein itself as well as the genetic manipulations within the viral genome required for expression of this reporter can result in altered biological properties of the recombinant virus, and lead to attenuation in vitro and/or in vivo. Further, instability of reporter expression and purging of the genetic information encoding for the reporter from the viral genome can be an issue. Finally, a practical challenge for in vivo studies lies in the attenuation of light signals when traversing tissues. Novel expression strategies and the continued development of brighter, red and far-red shifted reporters and the increased use of bioluminescent reporters for in vivo applications promise to overcome some of these limitations in future. However, a "one size fits all" approach to the design of reporter-expressing viruses has thus far not been possible. Rather, a reporter suited to the intended application must be selected and an appropriate expression strategy and location for the reporter in the viral genome chosen. Still, attenuating effects of the reporter on viral fitness are difficult to predict and have to be carefully assessed with respect to the intended application. Despite these limitations the generation of suitable reporter-expressing viruses will become more common as technology and our understanding of the intricacies of viral gene expression and regulation improves, allowing deeper insight into virus biology both in living cells and in animals.