Denis Gerlier

The Hendra and Nipah viruses (HeV and NiV) are zoonotic biosafety level‐4 pathogens belonging to the Paramyxoviridae family. We previously showed that their W protein, a key player in the evasion of the host antiviral response, forms highly flexible, curved fibrils in vitro. Here, we show that the cysteine oxidation state acts as a molecular switch controlling the formation of either amorphous aggregates or flexible fibrils, and that residues 2 to 29 are essential for fibrillation. We also uncover that the HeV W protein (W ^HeV ) can also self‐assemble in cellula. W ^HeV forms distinct types of nuclear condensates that exhibit different dependencies on the cysteine redox state. While deletion of residues 2–29 prevents formation of nuclear filaments, cysteine‐to‐serine substitution mainly impairs the formation of non‐filamentous condensates. Both infection and W ^HeV ectopic expression trigger oxidative stress, presumably favorable to W ^HeV condensation. Finally, we show that impaired ability to form redox‐sensitive, non‐filamentous condensates is associated with a reduced W ability to inhibit the NF‐κB pathway, while it conversely enhances W ability to repress the interferon response pathway by enhancing W binding to STAT1.

Airborne RNA viruses of the Paramyxoviridae family are major human pathogens. These include measles virus (MeV) and Nipah virus (NiV), the latter being on the World Health Organization's blueprint list due to its high case-fatality rate and critical risk of emergence. Although an effective vaccine is available for MeV, this is not the case for NiV. Moreover, there is no cure for MeV- or NiV-infected patients that prevents the acute respiratory syndrome or lethal encephalitis. To identify new host factors to target for inhibiting viral growth, a library of metabolic modulators was screened for activity against MeV using an in vitro infection model. Results showed that Molidustat, a pharmacological inhibitor of Prolyl-Hydroxylase Domain (PHD) enzymes, inhibits MeV infection in a Hypoxia-Inducible Factor (HIF)-dependent manner. We then tested the antiviral effect of Molidustat in organotypic cultures of hamster cerebellum. Molidustat induced the hypoxia-response pathway in this ex vivo model as assessed by transcriptomic analysis, and inhibited MeV infection. A similar antiviral effect was observed with Roxadustat and Daprodustat, two PHD enzyme inhibitors chemically unrelated to Molidustat. Finally, we showed that Molidustat inhibits NiV infection in organotypic cultures of hamster cerebellum and lung, thereby validating its effect in the two organs mainly targeted during infection. Taken together, our results provide evidence that pharmacological activation of the hypoxia-response pathway restricts MeV and NiV infections, highlighting HIF-inducing drugs as promising candidates to consider in the development of treatments.

The Hendra and Nipah viruses (HeV and NiV) are zoonotic biosafety level-4 pathogens belonging to the Paramyxoviridae family. We previously showed that their W protein, a key player in the evasion of the host antiviral response, forms highly flexible, curved fibrils in vitro . Here, we show that the cysteine oxidation state acts as a molecular switch controlling the formation of either amorphous aggregates or flexible fibrils, and that residues 2 to 29 are essential for fibrillation. We also uncover that the HeV W protein (W ^HeV ) can also self-assemble in cellula . W ^HeV forms distinct types of nuclear condensates that exhibit different dependencies on the cysteine redox-state. While deletion of residues 2-29 prevents formation of nuclear filaments, cysteine-to-serine substitution mainly impairs the formation of non-filamentous condensates. Both infection and W ^HeV ectopic expression trigger oxidative stress presumably favorable to W ^HeV condensation. Finally, we show that impaired ability to form redox-sensitive, non-filamentous condensates is associated with a reduced W ability to inhibit the NF-κB pathway, while it conversely enhances W ability to repress the interferon response pathway.

The cessation of measles virus (MeV) vaccination in more than 40 countries as a consequence of the COVID-19 pandemic is expected to significantly increase deaths due to measles. MeV can infect the central nervous system (CNS) and lead to lethal encephalitis. Substantial part of virus sequences recovered from patients’ brain were mutated in the matrix and/or the fusion protein (F). Mutations of the heptad repeat domain located in the C terminal (HRC) part of the F protein were often observed and were associated to hyperfusogenicity. These mutations promote brain invasion as a hallmark of neuroadaptation. Wild-type F allows entry into the brain, followed by limited spreading compared with the massive invasion observed for hyperfusogenic MeV. Taking advantage of our ex vivo models of hamster organotypic brain cultures, we investigated how the hyperfusogenic mutations in the F HRC domain modulate virus distribution in CNS cells. In this study, we also identified the dependence of neural cells susceptibility on both their activation state and destabilization of the virus F protein. Type I interferon (IFN-I) impaired mainly astrocytes and microglial cells permissiveness contrarily to neurons, opening a new way of consideration on the development of treatments against viral encephalitis.

The immune system deploys a complex network of cells and signaling pathways to protect host integrity against exogenous threats, including measles virus (MeV). However, throughout its evolutionary path, MeV developed various mechanisms to disrupt and evade immune responses. Despite an available vaccine, MeV remains an important re-emerging pathogen with a continuous increase in prevalence worldwide during the last decade. Considerable knowledge has been accumulated regarding MeV interactions with the innate immune system through two antagonistic aspects: recognition of the virus by cellular sensors and viral ability to inhibit the induction of the interferon cascade. Indeed, while the host could use several innate adaptors to sense MeV infection, the virus is adapted to unsettle defenses by obstructing host cell signaling pathways. Recent works have highlighted a novel aspect of innate immune response directed against MeV unexpectedly involving DNA-related sensing through activation of the cGAS/STING axis, even in the absence of any viral DNA intermediate. In addition, while MeV infection most often causes a mild disease and triggers a lifelong immunity, its tropism for invariant T-cells and memory T and B-cells provokes the elimination of one primary shield and the pre-existing immunity against previously encountered pathogens, known as “immune amnesia”.

Nipah virus (NiV) is a highly pathogenic emerging bat-borne Henipavirus that has caused numerous outbreaks with public health concerns. It is able to inhibit the host innate immune response. Since the NF-κB pathway plays a crucial role in the innate antiviral response as a major transcriptional regulator of inflammation, we postulated its implication in the still poorly understood NiV immunopathogenesis. We report here that NiV inhibits the canonical NF-κB pathway via its nonstructural W protein. Translocation of the W protein into the nucleus causes nuclear accumulation of the cellular scaffold protein 14-3-3 in both African green monkey and human cells infected by NiV. Excess of 14-3-3 in the nucleus was associated with a reduction of NF-κB p65 subunit phosphorylation and of its nuclear accumulation. Importantly, W-S449A substitution impairs the binding of the W protein to 14-3-3 and the subsequent suppression of NF-κB signaling, thus restoring the production of proinflammatory cytokines. Our data suggest that the W protein increases the steady-state level of 14-3-3 in the nucleus and consequently enhances 14-3-3-mediated negative feedback on the NF-κB pathway. These findings provide a mechanistic model of W-mediated disruption of the host inflammatory response, which could contribute to the high severity of NiV infection.

Henipaviruses are BSL-4 zoonotic pathogens responsible in humans for severe encephalitis. Their V protein is a key player in the evasion of the host innate immune response. We previously showed that the Henipavirus V proteins consist of a long intrinsically disordered N-terminal domain (NTD) and a β-enriched C-terminal domain (CTD). The CTD is critical for V binding to DDB1, which is a cellular protein that is a component of the ubiquitin ligase E3 complex, as well as binding to MDA5 and LGP2, which are two host sensors of viral RNA. Here, we serendipitously discovered that the Hendra virus V protein undergoes a liquid-to-hydrogel phase transition and identified the V region responsible for this phenomenon. This region, referred to as PNT3 and encompassing residues 200–310, was further investigated using a combination of biophysical and structural approaches. Congo red binding assays, together with negative-staining transmisison electron microscopy (TEM) studies, show that PNT3 forms amyloid-like fibrils. Fibrillation abilities are dramatically reduced in a rationally designed PNT3 variant in which a stretch of three contiguous tyrosines, falling within an amyloidogenic motif, were replaced by three alanines. Worthy to note, Congo red staining experiments provided hints that these amyloid-like fibrils form not only in vitro but also in cellula after transfection or infection. The present results set the stage for further investigations aimed at assessing the functional role of phase separation and fibrillation by the Henipavirus V proteins.

Médecine/sciences (M/S), revue internationale dans le domaine de la recherche biologique, médicale et en santé

Replication of negative-strand RNA viruses relies on two components: a helical ribonucleocapsid and an RNA-dependent RNA polymerase composed of a catalytic subunit, the L protein, and a cofactor, the P protein. We show that the measles virus (MeV) C protein is an additional component of the replication complex. We provide evidence that the C protein is recruited to the ribonucleocapsid by the P protein and map the interacting segments of both C and P proteins. We conclude that the primary function of MeV C is to improve polymerase processivity and accuracy, rather than uniquely to antagonize the type I interferon response. Since most viruses of the Paramyxoviridae family express C proteins, their primary function may be conserved.