The effect of 5' and 3' non-translated regions on the expression of a transgene from a Newcastle disease virus vector.

Newcastle disease virus (NDV) is an avian virus and a promising vector for the development of vaccines for veterinary and human use. The optimal vaccine vector performance requires a stable high-level expression of a transgene. The foreign genes are usually incorporated in the genome of NDV as individual transcription units, whose transcription and subsequent translation of the mRNA are regulated by the 5' and 3' untranslated regions (UTRs) flanking the open reading frame of the transgene. Here, we investigated if the UTRs derived from the cognate NDV genes would increase the expression of a model protective antigene from an NDV vector. Our results show that in chicken DF1 cells, none of the UTRs tested significantly outperformed generic short sequences flanking the transgene, while in human HeLa cells, UTRs derived from the M gene of NDV statistically significantly increased the expression of the transgene. The UTRs derived from the HN gene significantly downregulated the transgene expression in both cell cultures. Further experiments demonstrated that NDV UTRs differently affect the mRNA abundance and translation efficacy. While both M and HN UTRs decreased the level of the transgene mRNA in infected cells compared to the mRNA flanked by generic UTRs, M, and particularly, HN UTRs strongly increased the mRNA translation efficacy. The major determinants of translation enhancement are localized in the 5'UTR of HN. Thus, our data reveal a direct role of NDV UTRs in translational regulation, and inform future optimization of NDV vectors for vaccine and therapeutic use.

The Arf-GEF GBF1 undergoes multi-domain structural shifts to activate Arf at the Golgi.

Golgi homeostasis require the activation of Arf GTPases by the guanine-nucleotide exchange factor requires GBF1, whose recruitment to the Golgi represents a rate limiting step in the process. GBF1 contains a conserved, catalytic, Sec7 domain (Sec7d) and five additional (DCB, HUS, HDS1-3) domains. Herein, we identify the HDS3 domain as essential for GBF1 membrane association in mammalian cells and document the critical role of HDS3 during the development of Drosophila melanogaster. We show that upon binding to Golgi membranes, GBF1 undergoes conformational changes in regions bracketing the catalytic Sec7d. We illuminate GBF1 interdomain arrangements by negative staining electron microscopy of full-length human GBF1 to show that GBF1 forms an anti-parallel dimer held together by the paired central DCB-HUS core, with two sets of HDS1-3 arms extending outward in opposite directions. The catalytic Sec7d protrudes from the central core as a largely independent domain, but is closely opposed to a previously unassigned α-helix from the HDS1 domain. Based on our data, we propose models of GBF1 engagement on the membrane to provide a paradigm for understanding GBF1-mediated Arf activation required for cellular and organismal function.

The development of resistance to an inhibitor of a cellular protein reveals a critical interaction between the enterovirus protein 2C and a small GTPase Arf1.

The cellular protein GBF1, an activator of Arf GTPases (ArfGEF: Arf guanine nucleotide exchange factor), is recruited to the replication organelles of enteroviruses through interaction with the viral protein 3A, and its ArfGEF activity is required for viral replication, however how GBF1-dependent Arf activation supports the infection remains enigmatic. Here, we investigated the development of resistance of poliovirus, a prototype enterovirus, to increasing concentrations of brefeldin A (BFA), an inhibitor of GBF1. High level of resistance required a gradual accumulation of multiple mutations in the viral protein 2C. The 2C mutations conferred BFA resistance even in the context of a 3A mutant previously shown to be defective in the recruitment of GBF1 to replication organelles, and in cells depleted of GBF1, suggesting a GBF1-independent replication mechanism. Still, activated Arfs accumulated on the replication organelles of this mutant even in the presence of BFA, its replication was inhibited by a pan-ArfGEF inhibitor LM11, and the BFA-resistant phenotype was compromised in Arf1-knockout cells. Importantly, the mutations strongly increased the interaction of 2C with the activated form of Arf1. Analysis of other enteroviruses revealed a particularly strong interaction of 2C of human rhinovirus 1A with activated Arf1. Accordingly, the replication of this virus was significantly less sensitive to BFA than that of poliovirus. Thus, our data demonstrate that enterovirus 2Cs may behave like Arf1 effector proteins and that GBF1 but not Arf activation can be dispensable for enterovirus replication. These findings have important implications for the development of host-targeted anti-viral therapeutics.

Advantages and challenges of Newcastle disease virus as a vector for respiratory mucosal vaccines.

Newcastle disease virus (NDV) is an avian pathogen with an unsegmented negative-strand RNA genome. Properties such as the ease of genome modification, respiratory tract tropism, and self-limiting replication in mammals make NDV an attractive vector for vaccine development. Experimental NDV-based vaccines against multiple human and animal pathogens elicited both systemic and mucosal immune responses and were protective in preclinical animal studies, but their real-life efficacy remains to be demonstrated. Only recently, the first results of clinical trials of NDV-based vaccines against SARS-CoV-2 became available, highlighting the challenges that need to be overcome to fully realize the potential of NDV as a platform for the rapid development of economically affordable and effective mucosal vaccines.

A Proximity biotinylation assay with a host protein bait reveals multiple factors modulating enterovirus replication.

As ultimate parasites, viruses depend on host factors for every step of their life cycle. On the other hand, cells evolved multiple mechanisms of detecting and interfering with viral replication. Yet, our understanding of the complex ensembles of pro- and anti-viral factors is very limited in virtually every virus-cell system. Here we investigated the proteins recruited to the replication organelles of poliovirus, a representative of the genus Enterovirus of the Picornaviridae family. We took advantage of a strict dependence of enterovirus replication on a host protein GBF1, and established a stable cell line expressing a truncated GBF1 fused to APEX2 peroxidase that effectively supported viral replication upon inhibition of the endogenous GBF1. This construct biotinylated multiple host and viral proteins on the replication organelles. Among the viral proteins, the polyprotein cleavage intermediates were overrepresented, suggesting that the GBF1 environment is linked to viral polyprotein processing. The proteomics characterization of biotinylated host proteins identified multiple proteins previously associated with enterovirus replication, as well as more than 200 new factors recruited to the replication organelles. RNA metabolism proteins, many of which normally localize in the nucleus, constituted the largest group, underscoring the massive release of nuclear factors into the cytoplasm of infected cells and their involvement in viral replication. Functional analysis of several newly identified proteins revealed both pro- and anti-viral factors, including a novel component of infection-induced stress granules. Depletion of these proteins similarly affected the replication of diverse enteroviruses indicating broad conservation of the replication mechanisms. Thus, our data significantly expand the knowledge of the composition of enterovirus replication organelles, provide new insights into viral replication, and offer a novel resource for identifying targets for anti-viral interventions.

Encoding of a transgene in-frame with a Newcastle disease virus protein increases transgene expression and stability.

Newcastle disease virus (NDV) has been extensively explored as a vector for vaccine and oncolytic therapeutic development. In conventional NDV-based vectors, the transgene is arranged as a separate transcription unit in the NDV genome. Here, we expressed haemagglutinin protein (HA) of an avian influenza virus using an NDV vector design in which the transgene ORF is encoded in-frame with the ORF of an NDV gene. This arrangement does not increase the number of transcription units in the NDV genome, and imposes a selection pressure against mutations interrupting the transgene ORF. We placed the HA ORF upstream or downstream of N, M, F and HN ORFs of NDV so that both proteins are encoded in-frame and are separated by either a self-cleaving 2A peptide, furin cleavage site or both. Only constructs in which HA was placed downstream of the NDV HN were viable. These constructs expressed the transgene at a higher level compared to the vector encoding the same transgene in the same position in the NDV genome but as a separate transcription unit. Furthermore, the transgene expressed in one ORF with the NDV protein proved to be more stable over multiple passages. Thus, this design may be useful for applications where the stability of the transgene expression is highly important for a recombinant NDV vector.

Interaction of Poliovirus Capsid Proteins with the Cellular Autophagy Pathway.

The capsid precursor P1 constitutes the N-terminal part of the enterovirus polyprotein. It is processed into VP0, VP3, and VP1 by the viral proteases, and VP0 is cleaved autocatalytically into VP4 and VP2. We observed that poliovirus VP0 is recognized by an antibody against a cellular autophagy protein, LC3A. The LC3A-like epitope overlapped the VP4/VP2 cleavage site. Individually expressed VP0-EGFP and P1 strongly colocalized with a marker of selective autophagy, p62/SQSTM1. To assess the role of capsid proteins in autophagy development we infected different cells with poliovirus or encapsidated polio replicon coding for only the replication proteins. We analyzed the processing of LC3B and p62/SQSTM1, markers of the initiation and completion of the autophagy pathway and investigated the association of the viral antigens with these autophagy proteins in infected cells. We observed cell-type-specific development of autophagy upon infection and found that only the virion signal strongly colocalized with p62/SQSTM1 early in infection. Collectively, our data suggest that activation of autophagy is not required for replication, and that capsid proteins contain determinants targeting them to p62/SQSTM1-dependent sequestration. Such a strategy may control the level of capsid proteins so that viral RNAs are not removed from the replication/translation pool prematurely.

Enterovirus Infection Induces Massive Recruitment of All Isoforms of Small Cellular Arf GTPases to the Replication Organelles.

Enterovirus replication requires the cellular protein GBF1, a guanine nucleotide exchange factor for small Arf GTPases. When activated, Arfs associate with membranes, where they regulate numerous steps of membrane homeostasis. The requirement for GBF1 implies that Arfs are important for replication, but which of the different Arfs function(s) during replication remains poorly understood. Here, we established cell lines expressing each of the human Arfs fused to a fluorescent tag and investigated their behavior during enterovirus infection. Arf1 was the first to be recruited to the replication organelles, where it strongly colocalized with the viral antigen 2B and mature virions but not double-stranded RNA. By the end of the infectious cycle, Arf3, Arf4, Arf5, and Arf6 were also concentrated on the replication organelles. Once on the replication membranes, all Arfs except Arf3 were no longer sensitive to inhibition of GBF1, suggesting that in infected cells they do not actively cycle between GTP- and GDP-bound states. Only the depletion of Arf1, but not other class 1 and 2 Arfs, significantly increased the sensitivity of replication to GBF1 inhibition. Surprisingly, depletion of Arf6, a class 3 Arf, normally implicated in plasma membrane events, also increased the sensitivity to GBF1 inhibition. Together, our results suggest that GBF1-dependent Arf1 activation directly supports the development and/or functioning of the replication complexes and that Arf6 plays a previously unappreciated role in viral replication. Our data reveal a complex pattern of Arf activation in enterovirus-infected cells that may contribute to the resilience of viral replication in different cellular environments.IMPORTANCE Enteroviruses include many known and emerging pathogens, such as poliovirus, enteroviruses 71 and D68, and others. However, licensed vaccines are available only against poliovirus and enterovirus 71, and specific anti-enterovirus therapeutics are lacking. Enterovirus infection induces the massive remodeling of intracellular membranes and the development of specialized domains harboring viral replication complexes, replication organelles. Here, we investigated the roles of small Arf GTPases during enterovirus infection. Arfs control distinct steps in intracellular membrane traffic, and one of the Arf-activating proteins, GBF1, is a cellular factor required for enterovirus replication. We found that all Arfs expressed in human cells, including Arf6, normally associated with the plasma membrane, are recruited to the replication organelles and that Arf1 appears to be the most important Arf for enterovirus replication. These results document the rewiring of the cellular membrane pathways in infected cells and may provide new ways of controlling enterovirus infections.

Dynamic remodelling of the human host cell proteome and phosphoproteome upon enterovirus infection.

The group of enteroviruses contains many important pathogens for humans, including poliovirus, coxsackievirus, rhinovirus, as well as newly emerging global health threats such as EV-A71 and EV-D68. Here, we describe an unbiased, system-wide and time-resolved analysis of the proteome and phosphoproteome of human cells infected with coxsackievirus B3. Of the ~3,200 proteins quantified throughout the time course, a large amount (~25%) shows a significant change, with the majority being downregulated. We find ~85% of the detected phosphosites to be significantly regulated, implying that most changes occur at the post-translational level. Kinase-motif analysis reveals temporal activation patterns of certain protein kinases, with several CDKs/MAPKs immediately active upon the infection, and basophilic kinases, ATM, and ATR engaging later. Through bioinformatics analysis and dedicated experiments, we identify mTORC1 signalling as a major regulation network during enterovirus infection. We demonstrate that inhibition of mTORC1 activates TFEB, which increases expression of lysosomal and autophagosomal genes, and that TFEB activation facilitates the release of virions in extracellular vesicles via secretory autophagy. Our study provides a rich framework for a system-level understanding of enterovirus-induced perturbations at the protein and signalling pathway levels, forming a base for the development of pharmacological inhibitors to treat enterovirus infections.

A Redundant Mechanism of Recruitment Underlies the Remarkable Plasticity of the Requirement of Poliovirus Replication for the Cellular ArfGEF GBF1.

The replication of many positive-strand RNA viruses [(+)RNA viruses] depends on the cellular protein GBF1, but its role in the replication process is not clear. In uninfected cells, GBF1 activates small GTPases of the Arf family and coordinates multiple steps of membrane metabolism, including functioning of the cellular secretory pathway. The nonstructural protein 3A of poliovirus and related viruses has been shown to directly interact with GBF1, likely mediating its recruitment to the replication complexes. Surprisingly, viral mutants with a severely reduced level of 3A-GBF1 interaction demonstrate minimal replication defects in cell culture. Here, we systematically investigated the conserved elements of GBF1 to understand which determinants are important to support poliovirus replication. We demonstrate that multiple GBF1 mutants inactive in cellular metabolism could still be fully functional in the replication complexes. Our results show that the Arf-activating property, but not the primary structure of the Sec7 domain, is indispensable for viral replication. They also suggest a redundant mechanism of recruitment of GBF1 to the replication sites, which is dependent not only on direct interaction of the protein with the viral protein 3A but also on determinants located in the noncatalytic C-terminal domains of GBF1. Such a double-targeting mechanism explains the previous observations of the remarkable tolerance of different levels of GBF1-3A interaction by the virus and likely constitutes an important element of the resilience of viral replication.IMPORTANCE Enteroviruses are a vast group of viruses associated with diverse human diseases, but only two of them could be controlled with vaccines, and effective antiviral therapeutics are lacking. Here, we investigated in detail the contribution of a cellular protein, GBF1, in the replication of poliovirus, a representative enterovirus. GBF1 supports the functioning of cellular membrane metabolism and is recruited to viral replication complexes upon infection. Our results demonstrate that the virus requires a limited subset of the normal GBF1 functions and reveal the elements of GBF1 essential to support viral replication under different conditions. Since diverse viruses often rely on the same cellular proteins for replication, understanding the mechanisms by which these proteins support infection is essential for the development of broad-spectrum antiviral therapeutics.

Lipid Droplets Grease Enterovirus Replication.

Replication complexes of (+)RNA viruses of eukaryotes are associated with specialized membranous domains, termed replication organelles. How these structures develop is poorly understood. In a recent Cell paper, Laufman et al. (2019) reveal that enteroviruses recruit lipid droplets to support lipid synthesis required for the structural development of replication organelles.

Promiscuity of the catalytic Sec7 domain within the guanine nucleotide exchange factor GBF1 in ARF activation, Golgi homeostasis, and effector recruitment.

The integrity of the Golgi and trans-Golgi network (TGN) is disrupted by brefeldin A (BFA), which inhibits the Golgi-localized BFA-sensitive factor (GBF1) and brefeldin A-inhibited guanine nucleotide-exchange factors (BIG1 and BIG2). Using a cellular replacement assay to assess GBF1 functionality without interference from the BIGs, we show that GBF1 alone maintains Golgi architecture; facilitates secretion; activates ADP-ribosylation factor (ARF)1, 3, 4, and 5; and recruits ARF effectors to Golgi membranes. Unexpectedly, GBF1 also supports TGN integrity and recruits numerous TGN-localized ARF effectors. The impact of the catalytic Sec7 domain (Sec7d) on GBF1 functionality was assessed by swapping it with the Sec7d from ARF nucleotide-binding site opener (ARNO)/cytohesin-2, a plasma membrane GEF reported to activate all ARFs. The resulting chimera (GBF1-ARNO-GBF1 [GARG]) targets like GBF1, supports Golgi/TGN architecture, and facilitates secretion. However, unlike GBF1, GARG activates all ARFs (including ARF6) at the Golgi/TGN and recruits additional ARF effectors to the Golgi/TGN. Our results have general implications: 1) GEF's targeting is independent of Sec7d, but Sec7d influence the GEF substrate specificity and downstream effector events; 2) all ARFs have access to all membranes, but are restricted in their distribution by the localization of their activating GEFs; and 3) effector association with membranes requires the coincidental presence of activated ARFs and specific membrane identifiers.

Host Lipids in Positive-Strand RNA Virus Genome Replication.

Membrane association is a hallmark of the genome replication of positive-strand RNA viruses [(+)RNA viruses]. All well-studied (+)RNA viruses remodel host membranes and lipid metabolism through orchestrated virus-host interactions to create a suitable microenvironment to survive and thrive in host cells. Recent research has shown that host lipids, as major components of cellular membranes, play key roles in the replication of multiple (+)RNA viruses. This review focuses on how (+)RNA viruses manipulate host lipid synthesis and metabolism to facilitate their genomic RNA replication, and how interference with the cellular lipid metabolism affects viral replication.

Role of Host Cell Secretory Machinery in Zika Virus Life Cycle.

The high human cost of Zika virus infections and the rapid establishment of virus circulation in novel areas, including the United States, present an urgent need for countermeasures against this emerging threat. The development of an effective vaccine against Zika virus may be problematic because of the cross reactivity of the antibodies with other flaviviruses leading to antibody-dependent enhancement of infection. Moreover, rapidly replicating positive strand RNA viruses, including Zika virus, generate large spectrum of mutant genomes (quasi species) every replication round, allowing rapid selection of variants resistant to drugs targeting virus-specific proteins. On the other hand, viruses are ultimate cellular parasites and rely on the host metabolism for every step of their life cycle, thus presenting an opportunity to manipulate host processes as an alternative approach to suppress virus replication and spread. Zika and other flaviviruses critically depend on the cellular secretory pathway, which transfers proteins and membranes from the ER through the Golgi to the plasma membrane, for virion assembly, maturation and release. In this review, we summarize the current knowledge of interactions of Zika and similar arthropod-borne flaviviruses with the cellular secretory machinery with a special emphasis on virus-specific changes of the secretory pathway. Identification of the regulatory networks and effector proteins required to accommodate the trafficking of virions, which represent a highly unusual cargo for the secretory pathway, may open an attractive and virtually untapped reservoir of alternative targets for the development of superior anti-viral drugs.

Phospholipid synthesis fueled by lipid droplets drives the structural development of poliovirus replication organelles.

Rapid development of complex membranous replication structures is a hallmark of picornavirus infections. However, neither the mechanisms underlying such dramatic reorganization of the cellular membrane architecture, nor the specific role of these membranes in the viral life cycle are sufficiently understood. Here we demonstrate that the cellular enzyme CCTα, responsible for the rate-limiting step in phosphatidylcholine synthesis, translocates from the nuclei to the cytoplasm upon infection and associates with the replication membranes, resulting in the rerouting of lipid synthesis from predominantly neutral lipids to phospholipids. The bulk supply of long chain fatty acids necessary to support the activated phospholipid synthesis in infected cells is provided by the hydrolysis of neutral lipids stored in lipid droplets. Such activation of phospholipid synthesis drives the massive membrane remodeling in infected cells. We also show that complex membranous scaffold of replication organelles is not essential for viral RNA replication but is required for protection of virus propagation from the cellular anti-viral response, especially during multi-cycle replication conditions. Inhibition of infection-specific phospholipid synthesis provides a new paradigm for controlling infection not by suppressing viral replication but by making it more visible to the immune system.

Newcastle Disease Virus-Based Vectored Vaccine against Poliomyelitis.

The poliovirus eradication initiative has spawned global immunization infrastructure and dramatically decreased the prevalence of the disease, yet the original virus eradication goal has not been met. The suboptimal properties of the existing vaccines are among the major reasons why the program has repeatedly missed eradication deadlines. Oral live poliovirus vaccine (OPV), while affordable and effective, occasionally causes the disease in the primary recipients, and the attenuated viruses rapidly regain virulence and can cause poliomyelitis outbreaks. Inactivated poliovirus vaccine (IPV) is safe but expensive and does not induce the mucosal immunity necessary to interrupt virus transmission. While the need for a better vaccine is widely recognized, current efforts are focused largely on improvements to the OPV or IPV, which are still beset by the fundamental drawbacks of the original products. Here we demonstrate a different design of an antipoliovirus vaccine based on in situ production of virus-like particles (VLPs). The poliovirus capsid protein precursor, together with a protease required for its processing, are expressed from a Newcastle disease virus (NDV) vector, a negative-strand RNA virus with mucosal tropism. In this system, poliovirus VLPs are produced in the cells of vaccine recipients and are presented to their immune systems in the context of active replication of NDV, which serves as a natural adjuvant. Intranasal administration of the vectored vaccine to guinea pigs induced strong neutralizing systemic and mucosal antibody responses. Thus, the vectored poliovirus vaccine combines the affordability and efficiency of a live vaccine with absolute safety, since no full-length poliovirus genome is present at any stage of the vaccine life cycle.IMPORTANCE A new, safe, and effective vaccine against poliovirus is urgently needed not only to complete the eradication of the virus but also to be used in the future to prevent possible virus reemergence in a postpolio world. Currently, new formulations of the oral vaccine, as well as improvements to the inactivated vaccine, are being explored. In this study, we designed a viral vector with mucosal tropism that expresses poliovirus capsid proteins. Thus, poliovirus VLPs are produced in vivo, in the cells of a vaccine recipient, and are presented to the immune system in the context of vector virus replication, stimulating the development of systemic and mucosal immune responses. Such an approach allows the development of an affordable and safe vaccine that does not rely on the full-length poliovirus genome at any stage.

Poliovirus Replicon RNA Generation, Transfection, Packaging, and Quantitation of Replication.

Poliovirus is a prototype member of the Enterovirus genus of the Picornaviridae family of small positive strand RNA viruses, which include important human and animal pathogens. Quantitative assessment of viral replication is very important for investigation of the virus biology and the development of anti-viral strategies. The poliovirus genome structure allows replacement of structural genes with a reporter protein, such as a luciferase or a fluorescent protein, whose signals can be detected and quantified in vivo, thus permitting observation of replication kinetics in live cells. This paper presents protocols for poliovirus replicon RNA production, purification, packaging and transfection, as well as techniques for monitoring Renilla luciferase replication signal in living cells. © 2018 by John Wiley & Sons, Inc.

Highly conserved motifs within the large Sec7 ARF guanine nucleotide exchange factor GBF1 target it to the Golgi and are critical for GBF1 activity.

Cellular life requires the activation of the ADP-ribosylation factors (ARFs) by Golgi brefeldin A-resistant factor 1 (GBF1), a guanine nucleotide exchange factor (GEF) with a highly conserved catalytic Sec7 domain (Sec7d). In addition to the Sec7d, GBF1 contains other conserved domains whose functions remain unclear. Here, we focus on HDS2 (homology downstream of Sec7d 2) domain because the L1246R substitution within the HDS2 α-helix 5 of the zebrafish GBF1 ortholog causes vascular hemorrhaging and embryonic lethality (13). To dissect the structure/function relationships within HDS2, we generated six variants, in which the most conserved residues within α-helices 1, 2, 4, and 6 were mutated to alanines. Each HDS2 mutant was assessed in a cell-based "replacement" assay for its ability to support cellular functions normally supported by GBF1, such as maintaining Golgi homeostasis, facilitating COPI recruitment, supporting secretion, and sustaining cellular viability. We show that cells treated with the pharmacological GBF1 inhibitor brefeldin A (BFA) and expressing a BFA-resistant GBF1 variant with alanine substitutions of RDR1168 or LF1266 are compromised in Golgi homeostasis, impaired in ARF activation, unable to sustain secretion, and defective in maintaining cellular viability. To gain insight into the molecular mechanism of this dysfunction, we assessed the ability of each GBF1 mutant to target to Golgi membranes and found that mutations in RDR1168 and LF1266 significantly decrease targeting efficiency. Thus, these residues within α-helix 2 and α-helix 6 of the HDS2 domain in GBF1 are novel regulatory determinants that support GBF1 cellular function by impacting the Golgi-specific membrane association of GBF1.

Dynamic lipid landscape of picornavirus replication organelles.

Picornavirus infection induces rapid reorganization of the cellular membrane architecture and appearance of novel membranous structures associated with the viral RNA replication and virion assembly-replication organelles. Recent studies significantly advanced our understanding of their lipid composition and cellular mechanisms involved in their development. Picornaviruses activate synthesis of both structural and signaling lipids and reroute cellular cholesterol trafficking pathways to create unique membranous domains favoring viral replication. Rapidly replicating picornaviruses rely on posttranslational activation and/or specific recruitment of cellular proteins rather than on modulation of expression of cellular genes to create favorable membrane microenvironment. At the same time picornaviruses demonstrate remarkable adaptability to changes in the lipid landscape which should be taken into account when developing novel antiviral strategies.

Positive-strand RNA viruses stimulate host phosphatidylcholine synthesis at viral replication sites.

All positive-strand RNA viruses reorganize host intracellular membranes to assemble their viral replication complexes (VRCs); however, how these viruses modulate host lipid metabolism to accommodate such membrane proliferation and rearrangements is not well defined. We show that a significantly increased phosphatidylcholine (PC) content is associated with brome mosaic virus (BMV) replication in both natural host barley and alternate host yeast based on a lipidomic analysis. Enhanced PC levels are primarily associated with the perinuclear ER membrane, where BMV replication takes place. More specifically, BMV replication protein 1a interacts with and recruits Cho2p (choline requiring 2), a host enzyme involved in PC synthesis, to the site of viral replication. These results suggest that PC synthesized at the site of VRC assembly, not the transport of existing PC, is responsible for the enhanced accumulation. Blocking PC synthesis by deleting the CHO2 gene resulted in VRCs with wider diameters than those in wild-type cells; however, BMV replication was significantly inhibited, highlighting the critical role of PC in VRC formation and viral replication. We further show that enhanced PC levels also accumulate at the replication sites of hepatitis C virus and poliovirus, revealing a conserved feature among a group of positive-strand RNA viruses. Our work also highlights a potential broad-spectrum antiviral strategy that would disrupt PC synthesis at the sites of viral replication but would not alter cellular processes.