Sonja M. Best

Infection with dengue virus (DENV) is a major global public health threat, driven by mosquito transmission of four closely related virus serotypes. For effective transmission between hosts, DENV rapidly remodels the host cell to overcome multiple innate immune barriers and produce progeny virions. Here we review how DENV evades cell-intrinsic sensing and interferon (IFN) responses in both human and mosquito hosts. We highlight the roles of replication organelles, nonstructural proteins NS2B/3 and NS5, and subgenomic flaviviral RNAs in escaping RIG-I-like receptor and cGAS-STING signaling, disrupting JAK-STAT pathways, and subverting autophagy and ER-phagy. We further discuss NS1-mediated vascular leak, exploitation of TAM receptors, serotype-specific differences in IFN antagonism, and how these mechanisms might shape pathogenesis, host range, and epidemiological fitness. Finally, we consider how defined immune evasion strategies inform rational design of antivirals and next-generation live-attenuated tetravalent dengue vaccines to mitigate the escalating global dengue burden.

Summary: Middle East respiratory syndrome coronavirus (MERS-CoV), first reported in 2012, belongs to the Betacoronavirus genus, including SARS-CoV and SARS-CoV-2. Human-to-human transmission of MERS-CoV appears inefficient, but repeated spillover events have been reported from at least 27 countries, raising concern for future emergent events. Coronaviruses (CoVs) rely extensively on host proteins to support their replication. Several studies have implicated the paraspeckle non-POU domain-containing octamer-binding protein (NONO) as an RNA-binding protein (RBP) that binds to CoV genomes, but the role of this protein in regulating replication is unknown. Here, we show that NONO is required for expression of dipeptidyl peptidase 4 (DPP4, also known as CD26), the major cellular receptor required for MERS-CoV attachment and entry. NONO did not impact DPP4 mRNA processing or stability but instead promoted DPP4 transcription through control of active H3K4me3 and repressive H3K27me3 histone modifications at the DPP4 locus. Together, these findings identify NONO as a key proviral host factor for MERS-CoV and reveal an epigenetic mechanism linking a host RBP to viral entry receptor expression that may represent a target for therapeutic strategies.

Summary: Type-I interferons (IFN-I) and IFN-stimulated genes (ISGs) are central to antiviral defense, while dysregulation can drive autoimmunity. IFNB1 expression is controlled by a highly ordered multiprotein complex composed of IRF3/7, NFκB, and ATF2/c-Jun (AP-1) that recruit coactivators and chromatin-remodeling proteins to expose the IFNB1 promoter for the RNA polymerase II (RNA Pol II) transcriptional machinery. Here, we identified the paraspeckle protein non-POU domain-containing octamer-binding protein (NONO) as a critical facilitator of innate immune activation. Loss of NONO enhanced replication of multiple orthoflaviviruses including West Nile virus due to impaired induction of IFN-I and ISGs. NONO did not affect upstream signaling but instead promoted chromatin accessibility and promoter access for RNA Pol II to drive expression of IFNB1 , ISGs, and proinflammatory cytokines. These findings position NONO as a key regulator of antiviral gene expression and reveal chromatin-levels of control that determine effective antiviral immunity.

TRIpartite Motif (TRIM) protein 5 alpha (TRIM5α) is a well-characterized cellular inhibitor of lentivirus replication that limits transmission of related viruses between primates. We previously reported that TRIM5α derived from humans and rhesus macaques inhibits replication of orthoflaviviruses belonging to the tick-borne encephalitis virus (TBEV) serocomplex, including TBEV, Kyasanur forest disease virus and Langat virus (LGTV), but interestingly not the tick-borne Powassan virus (POWV). To further characterize the primate TRIM5α and orthoflavivirus interface, we screened TRIM5α variants from representative old- and new-world primates for restriction capacity. TRIM5α from old-world African green monkey, De Brazza’s monkey and chimpanzee demonstrated virus-specific restriction of tick-borne orthoflaviviruses. Efforts to determine why TRIM5α fails to inhibit POWV revealed that our lab stock had acquired a non-synonymous mutation in NS3 that, when introduced into a POWV molecular clone, facilitated virus replication in the presence of all inhibitory primate TRIM5α proteins. Infection of human dendritic cells with TRIM5α-resistant POWV resulted in high early replication and strong induction of interferon responses that limited replication compared with the wild-type virus. Thus, primate TRIM5α functions as a potent cellular barrier to infection with tick-borne orthoflaviviruses that restrains replication to a level that may help avoid early innate immune recognition.

TRIpartite Motif (TRIM) protein 5 alpha (TRIM5α) is a well characterized cellular inhibitor of lentivirus replication that limits transmission of related viruses between primates. We previously reported that TRIM5α derived from humans and rhesus macaques inhibits replication of orthoflaviviruses belonging to the tick-borne encephalitis virus (TBEV) serocomplex, including TBEV, Kyasanur forest disease virus and Langat virus (LGTV), but interestingly not the tick-borne Powassan virus (POWV). To further characterize the primate TRIM5α and orthoflavivirus interface, we screened TRIM5α variants from representative old- and new-world primates for restriction capacity. TRIM5α from old-world African green monkey, De Brazza’s monkey and chimpanzee demonstrated virus-specific restriction of tick-borne orthoflaviviruses. Efforts to determine why TRIM5α fails to inhibit POWV revealed that our lab stock had acquired a non-synonymous mutation in NS3 that, when introduced into a POWV molecular clone, facilitated virus replication in the presence of all inhibitory primate TRIM5α proteins. Infection of human dendritic cells with TRIM5α-resistant POWV resulted in high early replication and strong induction of interferon responses that limited replication compared with the wild-type virus. Thus, primate TRIM5α functions as a potent cellular barrier to infection with tick-borne orthoflaviviruses that restrains replication to a level that may help avoid early innate immune recognition.

Uncontrolled systemic inflammatory responses are a critical pathological feature of fatal Ebola virus (EBOV) infection. While some inflammatory responses may originate from mononuclear phagocytes (MNPs), nonimmune cells vastly outnumber MNPs and may be an important source of inflammation. Here, we demonstrated that highly virulent EBOV induced a high and sustained pro-inflammatory response compared to less virulent ebolaviruses in non-MNPs through TLR4-independent NF-κB activation. We identified the EBOV matrix protein VP40 as a potent activator of NF-κB in non-MNPs, whose intrinsic inflammatory activation ability is higher than VP40 proteins from less virulent ebolaviruses. This suggests that VP40 is a virulence determinant inducing distinct degrees of pro-inflammatory responses among ebolaviruses. Mechanistically, VP40 activated the NF-κB signaling pathway, primarily via TNFR1 using a ligand-independent mechanism. These findings reveal mechanisms that may drive systemic inflammation and promote EBOV pathogenesis, suggesting potential therapeutic strategies to mitigate immune dysregulation in severe EBOV infections.

An Oropouche virus (OROV) outbreak occurred in South America in 2024. The pathogenic potential and host immunological response of this emerging virus are largely unknown, as animal models have been poorly explored. We infected nonhuman primate (NHP) species with OROV and followed viral replication dynamics and subsequent innate and adaptive immunological responses. OROV efficiently replicated in pigtail macaques, rhesus macaques, and vervet African green monkeys. OROV also replicated in sabeus African green monkey, albeit at lower levels than other hosts. OROV RNA was detected in plasma and nasal swabs and infection-induced high levels of innate inflammation, type I interferon gene signatures, immunoglobulin M–positive B cell expansion, high titers of neutralizing antibodies, and detectable frequencies of OROV-specific T cells. Prior infection was protective against reinfection up to 524 days post–initial infection, demonstrating possible protective immunity induction against OROV infection. These data suggest that multiple NHP species are appropriate models for OROV infection and the development of therapeutics and vaccinations.

The yellow fever virus 17D (YFV-17D) live attenuated vaccine is considered one of the most successful vaccines ever generated associated with high antiviral immunity, yet the signaling mechanisms that drive the response in infected cells are not understood. Here, we provide a molecular understanding of how metabolic stress and innate immune responses are linked to drive type I IFN expression in response to YFV-17D infection. Comparison of YFV-17D replication with its parental virus, YFV-Asibi, and a related dengue virus revealed that IFN expression requires RIG-I-Like Receptor signaling through MAVS, as expected. However, YFV-17D uniquely induces mitochondrial respiration and major metabolic perturbations, including hyperactivation of electron transport to fuel ATP synthase. Mitochondrial hyperactivity generates reactive oxygen species (ROS) including peroxynitrite, blocking of which abrogated MAVS oligomerization and IFN expression in non-immune cells without reducing YFV-17D replication. Scavenging ROS in YFV-17D-infected human dendritic cells increased cell viability yet globally prevented expression of IFN signaling pathways. Thus, adaptation of YFV-17D for high growth imparts mitochondrial hyperactivity to meet energy demands, resulting in generation of ROS as the critical messengers that convert a blunted IFN response into maximal activation of innate immunity essential for vaccine effectiveness.

Tripartite motif (TRIM) proteins comprise an important class of E3 ubiquitin ligases that regulate numerous biological processes including protein expression, cellular signaling pathways, and innate immunity. This ubiquitous participation in fundamental aspects of biology has made TRIM proteins a focus of study in many fields and has illuminated the negative impact they exert when functioning improperly. Disruption of TRIM function has been linked to the success of various pathogens and separately to the occurrence and development of several neurodegenerative diseases, making TRIM proteins an appealing candidate to study for novel therapeutic approaches. Here, we review the current findings on TRIM proteins that demonstrate their analogous properties in the distinct fields of viral infection and central nervous system (CNS) disorders. We also examine recent advancements in drug development and targeted protein degradation as potential strategies for TRIM-mediated therapeutic treatments and discuss the implications these technologies have on future research directions.