Porcine Sapovirus Protease Controls the Innate Immune Response and Targets TBK1.

Human sapoviruses (HuSaVs) and noroviruses are considered the leading cause of acute gastroenteritis worldwide. While extensive research has focused on noroviruses, our understanding of sapoviruses (SaVs) and their interactions with the host's immune response remains limited. HuSaVs have been challenging to propagate in vitro, making the porcine sapovirus (PSaV) Cowden strain a valuable model for studying SaV pathogenesis.

An optimized protocol for the extraction and quantification of cytosolic DNA in mammalian cells.

Leakage of mitochondrial or nuclear DNA into the cytosol can occur following viral infections, radiation damage, and some cancers. Here, we present an optimized protocol for isolating and quantifying cytosolic DNA from mammalian cells. We describe steps for collecting cytosolic fractions from cells, extracting DNA using columns, and quantifying extracted DNA using qPCR.

Leaked genomic and mitochondrial DNA contribute to the host response to noroviruses in a STING-dependent manner.

The cGAS-STING pathway is central to the interferon response against DNA viruses. However, recent studies are increasingly demonstrating its role in the restriction of some RNA viruses. Here, we show that the cGAS-STING pathway also contributes to the interferon response against noroviruses, currently the commonest causes of infectious gastroenteritis worldwide.

Cardiovirus leader proteins retarget RSK kinases toward alternative substrates to perturb nucleocytoplasmic traffic.

Proteins from some unrelated pathogens, including small RNA viruses of the family Picornaviridae, large DNA viruses such as Kaposi sarcoma-associated herpesvirus and even bacteria of the genus Yersinia can recruit cellular p90-ribosomal protein S6 kinases (RSKs) through a common linear motif and maintain the kinases in an active state. On the one hand, pathogens' proteins might hijack RSKs to promote their own phosphorylation (direct target model). On the other hand, some data suggested that pathogens' proteins might dock the hijacked RSKs toward a third interacting partner, thus redirecting the kinase toward a specific substrate.

A case of convergent evolution: Several viral and bacterial pathogens hijack RSK kinases through a common linear motif.

Microbes have been coevolving with their host for millions of years, exploiting host resources to their own benefit. We show that viral and bacterial pathogens convergently evolved to hijack cellular mitogen-activated protein kinase (MAPK) p90-ribosomal S6-kinases (RSKs). Theiler's virus leader (L) protein binds RSKs and prevents their dephosphorylation, thus maintaining the kinases active.

Murine norovirus virulence factor 1 (VF1) protein contributes to viral fitness during persistent infection.

Murine norovirus (MNV) is widely used as a model for studying norovirus biology. While MNV isolates vary in their pathogenesis, infection of immunocompetent mice mostly results in persistent infection. The ability of a virus to establish a persistent infection is dependent on its ability to subvert or avoid the host immune response.

Murine Norovirus Infection Results in Anti-inflammatory Response Downstream of Amino Acid Depletion in Macrophages.

Murine norovirus (MNV) infection results in a late translation shutoff that is proposed to contribute to the attenuated and delayed innate immune response observed both and Recently, we further demonstrated the activation of the α subunit of eukaryotic initiation factor 2 (eIF2α) kinase GCN2 during MNV infection, which has been previously linked to immunomodulation and resistance to inflammatory signaling during metabolic stress. While viral infection is usually associated with activation of double-stranded RNA (dsRNA) binding pattern recognition receptor PKR, we hypothesized that the establishment of a metabolic stress in infected cells is a proviral event, exploited by MNV to promote replication through weakening the activation of the innate immune response. In this study, we used multi-omics approaches to characterize cellular responses during MNV replication.

Norovirus Replication in Human Intestinal Epithelial Cells Is Restricted by the Interferon-Induced JAK/STAT Signaling Pathway and RNA Polymerase II-Mediated Transcriptional Responses.

Human noroviruses (HuNoV) are a leading cause of viral gastroenteritis worldwide and a significant cause of morbidity and mortality in all age groups. The recent finding that HuNoV can be propagated in B cells and mucosa-derived intestinal epithelial organoids (IEOs) has transformed our ability to dissect the life cycle of noroviruses. Using transcriptome sequencing (RNA-Seq) of HuNoV-infected intestinal epithelial cells (IECs), we have found that replication of HuNoV in IECs results in interferon (IFN)-induced transcriptional responses and that HuNoV replication in IECs is sensitive to IFN.

Epigenetic Suppression of Interferon Lambda Receptor Expression Leads to Enhanced Human Norovirus Replication .

Human norovirus (HuNoV) is the main cause of gastroenteritis worldwide, yet no therapeutics are currently available. Here, we utilize a human norovirus replicon in human gastric tumor (HGT) cells to identify host factors involved in promoting or inhibiting HuNoV replication. We observed that an interferon (IFN)-cured population of replicon-harboring HGT cells (HGT-Cured) was enhanced in their ability to replicate transfected HuNoV RNA compared to parental HGT cells, suggesting that differential gene expression in HGT-Cured cells created an environment favoring norovirus replication.

The Leader Protein of Theiler's Virus Prevents the Activation of PKR.

Leader (L) proteins encoded by cardioviruses are multifunctional proteins that contribute to innate immunity evasion. L proteins of Theiler's murine encephalomyelitis virus (TMEV), Saffold virus (SAFV), and encephalomyocarditis virus (EMCV) were reported to inhibit stress granule assembly in infected cells. Here, we show that TMEV L can act at two levels in the stress granule formation pathway: on the one hand, it can inhibit sodium arsenite-induced stress granule assembly without preventing eIF2α phosphorylation and, thus, acts downstream of eIF2α; on the other hand, it can inhibit eucaryotic translation initiation factor 2 alpha kinase 2 (PKR) activation and the consequent PKR-mediated eIF2α phosphorylation.

Nlrp3 inflammasome activation and Gasdermin D-driven pyroptosis are immunopathogenic upon gastrointestinal norovirus infection.

Norovirus infection is the leading cause of food-borne gastroenteritis worldwide, being responsible for over 200,000 deaths annually. Studies with murine norovirus (MNV) showed that protective STAT1 signaling controls viral replication and pathogenesis, but the immune mechanisms that noroviruses exploit to induce pathology are elusive. Here, we show that gastrointestinal MNV infection leads to widespread IL-1β maturation in MNV-susceptible STAT1-deficient mice.

Norovirus-Mediated Modification of the Translational Landscape via Virus and Host-Induced Cleavage of Translation Initiation Factors.

Noroviruses produce viral RNAs lacking a 5' cap structure and instead use a virus-encoded viral protein genome-linked (VPg) protein covalently linked to viral RNA to interact with translation initiation factors and drive viral protein synthesis. Norovirus infection results in the induction of the innate response leading to interferon stimulated gene (ISG) transcription. However, the translation of the induced ISG mRNAs is suppressed.

Feline Calicivirus Infection Disrupts Assembly of Cytoplasmic Stress Granules and Induces G3BP1 Cleavage.

Unlabelled: In response to stress such as virus infection, cells can stall translation by storing mRNAs away in cellular compartments called stress granules (SGs). This defense mechanism favors cell survival by limiting the use of energy and nutrients until the stress is resolved. In some cases it may also block viral propagation as viruses are dependent on the host cell resources to produce viral proteins.

Neurotropism of Saffold virus in a mouse model.

Saffold virus (SAFV) is a highly seroprevalent human Cardiovirus discovered recently. No clear association between SAFV infection and human disease has been established. Rare infection cases, however, correlated with neurological symptoms.

A Conserved Interaction between a C-Terminal Motif in Norovirus VPg and the HEAT-1 Domain of eIF4G Is Essential for Translation Initiation.

Translation initiation is a critical early step in the replication cycle of the positive-sense, single-stranded RNA genome of noroviruses, a major cause of gastroenteritis in humans. Norovirus RNA, which has neither a 5´ m7G cap nor an internal ribosome entry site (IRES), adopts an unusual mechanism to initiate protein synthesis that relies on interactions between the VPg protein covalently attached to the 5´-end of the viral RNA and eukaryotic initiation factors (eIFs) in the host cell. For murine norovirus (MNV) we previously showed that VPg binds to the middle fragment of eIF4G (4GM; residues 652-1132).

Deregulation of SYCP2 predicts early stage human papillomavirus-positive oropharyngeal carcinoma: A prospective whole transcriptome analysis.

This study was designed to identify significant differences in gene expression profiles of human papillomavirus (HPV)-positive and HPV-negative oropharyngeal squamous cell carcinomas (OPSCC) and to better understand the functional and biological effects of HPV infection in the premalignant pathway. Twenty-four consecutive patients with locally advanced primary OPSCC were included in a prospective clinical trial. Fresh tissue samples (tumor vs.

Porcine sapovirus replication is restricted by the type I interferon response in cell culture.

Porcine sapovirus (PSaV) of the family Caliciviridae, is the only member of the genus Sapovirus with cell culture and reverse genetics systems. When combined with the piglet model, these approaches provide a system to understand the molecular basis of sapovirus pathogenesis. The replication of PSaV in cell culture is, however, restricted, displaying an absolute requirement for bile acids and producing lower levels of infectious virus than other caliciviruses.

The OAS/RNaseL pathway and its inhibition by viruses.

RNase L is a well-known effector of the type I interferon pathway. This review focuses on the recent developments of RNase L activation and on the antagonism of the OAS-RNase L pathway by viral proteins. Recent structural data show that two 2'-5' oligoadenylate molecules can bridge ankyrin domains of two RNase L subunits bound in opposite orientations.

Both α2,3- and α2,6-linked sialic acids on O-linked glycoproteins act as functional receptors for porcine Sapovirus.

Sapovirus, a member of the Caliciviridae family, is an important cause of acute gastroenteritis in humans and pigs. Currently, the porcine sapovirus (PSaV) Cowden strain remains the only cultivable member of the Sapovirus genus. While some caliciviruses are known to utilize carbohydrate receptors for entry and infection, a functional receptor for sapovirus is unknown.

Murine norovirus: propagation, quantification, and genetic manipulation.

Murine norovirus (MNV) is a positive-sense, plus-stranded RNA virus in the Caliciviridae family. It is the most common pathogen in biomedical research colonies. MNV is also related to the human noroviruses, which cause the majority of nonbacterial gastroenteritis worldwide.

Inefficient type I interferon-mediated antiviral protection of primary mouse neurons is associated with the lack of apolipoprotein l9 expression.

Unlabelled: We examined the antiviral response promoted by type I interferons (IFN) in primary mouse neurons. IFN treatment of neuron cultures strongly upregulated the transcription of IFN-stimulated genes but conferred a surprisingly low resistance to infection by neurotropic viruses such as Theiler's murine encephalomyelitis virus (TMEV) or vesicular stomatitis virus (VSV). Response of primary mouse neurons to IFN treatment was heterogeneous, as many neurons failed to express the typical IFN response marker Mx1 after IFN treatment.

Evasion of antiviral innate immunity by Theiler's virus L* protein through direct inhibition of RNase L.

Theiler's virus is a neurotropic picornavirus responsible for chronic infections of the central nervous system. The establishment of a persistent infection and the subsequent demyelinating disease triggered by the virus depend on the expression of L*, a viral accessory protein encoded by an alternative open reading frame of the virus. We discovered that L* potently inhibits the interferon-inducible OAS/RNase L pathway.

Antiviral type I and type III interferon responses in the central nervous system.

The central nervous system (CNS) harbors highly differentiated cells, such as neurons that are essential to coordinate the functions of complex organisms. This organ is partly protected by the blood-brain barrier (BBB) from toxic substances and pathogens carried in the bloodstream. Yet, neurotropic viruses can reach the CNS either by crossing the BBB after viremia, or by exploiting motile infected cells as Trojan horses, or by using axonal transport.

Theiler's virus L* protein is targeted to the mitochondrial outer membrane.

The L* protein encoded by Theiler's murine encephalomyelitis virus (TMEV) is a unique example of a picornaviral protein encoded by an alternative open reading frame. This protein is an important determinant of TMEV persistence in the mouse central nervous system. We showed that in infected cells, L* is partitioned between the cytosol and the mitochondria.