RACK1 Associates with RNA-Binding Proteins Vigilin and SERBP1 to Facilitate Dengue Virus Replication.

Dengue virus (DENV) is a mosquito-borne flavivirus responsible for dengue disease, a major human health concern for which no effective treatment is available. DENV relies heavily on the host cellular machinery for productive infection. Here, we show that the scaffold protein RACK1, which is part of the DENV replication complex, mediates infection by binding to the 40S ribosomal subunit. Mass spectrometry analysis of RACK1 partners coupled to an RNA interference screen-identified Vigilin and SERBP1 as DENV host-dependency factors. Both are RNA-binding proteins that interact with the DENV genome. Genetic ablation of Vigilin or SERBP1 rendered cells poorly susceptible to DENV, as well as related flaviviruses, by hampering the translation and replication steps. Finally, we established that a Vigilin or SERBP1 mutant lacking RACK1 binding but still interacting with the viral RNA is unable to mediate DENV infection. We propose that RACK1 recruits Vigilin and SERBP1, linking the DENV genome to the translation machinery for efficient infection. IMPORTANCE We recently identified the scaffolding RACK1 protein as an important host-dependency factor for dengue virus (DENV), a positive-stranded RNA virus responsible for the most prevalent mosquito-borne viral disease worldwide. Here, we have performed the first RACK1 interactome in human cells and identified Vigilin and SERBP1 as DENV host-dependency factors. Both are RNA-binding proteins that interact with the DENV RNA to regulate viral replication. Importantly, Vigilin and SERBP1 interact with RACK1 and the DENV viral RNA (vRNA) to mediate viral replication. Overall, our results suggest that RACK1 acts as a binding platform at the surface of the 40S ribosomal subunit to recruit Vigilin and SERBP1, which may therefore function as linkers between the viral RNA and the translation machinery to facilitate infection.

FHL1 is a key player of chikungunya virus tropism and pathogenesis.

Chikungunya is an infectious disease caused by the chikungunya virus (CHIKV), an alphavirus transmitted to humans by Aedes mosquitoes, and for which there is no licensed vaccine nor antiviral treatments. By using a loss-of-function genetic screen, we have recently identified the FHL1 protein as an essential host factor for CHIKV tropism and pathogenesis. FHL1 is highly expressed in muscles cells and fibroblasts, the main CHIKV-target cells. FHL1 interacts with the viral protein nsP3 and plays a critical role in CHIKV genome amplification. Experiments in vivo performed in FHL1-deficient mice have shown that these animals are resistant to infection and do not develop muscular lesions. Altogether these observations, published in the journal Nature [1], show that FHL1 is a key host factor for CHIKV pathogenesis and identify the interaction between FHL1 and nsP3 as a promising target for the development of new antiviral strategies.

Le chikungunya est une maladie infectieuse causée par le virus chikungunya (CHIKV), un alphavirus transmis à l'Homme par les moustiques Aedes et contre lequel il n'existe ni vaccin, ni traitements antiviraux. En utilisant une approche de crible génétique par perte de fonction, nous avons récemment identifié la protéine FHL1 comme un facteur cellulaire essentiel pour le tropisme et la pathogénèse du CHIKV. FHL1 est une molécule présente majoritairement dans les cellules musculaires et les fibroblastes, les cibles privilégiées de CHIKV. FHL1 interagit avec la protéine virale nsP3 et joue un rôle décisif dans le mécanisme d'amplification du génome de CHIKV. Des expériences in vivo chez des souris déficientes pour FHL1 ont montré que ces animaux sont résistants à l'infection et ne développent pas de lésions musculaires. L'ensemble de ces observations publiées dans la revue Nature [1] montrent que FHL1 est un facteur cellulaire clé pour la pathogénèse de CHIKV et identifient l'interaction entre FHL1 et nsp3 comme une cible prometteuse pour le développement de nouvelles stratégies antivirales.

FHL1 is a major host factor for chikungunya virus infection.

Chikungunya virus (CHIKV) is a re-emerging alphavirus that is transmitted to humans by mosquito bites and causes musculoskeletal and joint pain1,2. Despite intensive investigations, the human cellular factors that are critical for CHIKV infection remain unknown, hampering the understanding of viral pathogenesis and the development of anti-CHIKV therapies. Here we identified the four-and-a-half LIM domain protein 1 (FHL1)3 as a host factor that is required for CHIKV permissiveness and pathogenesis in humans and mice. Ablation of FHL1 expression results in the inhibition of infection by several CHIKV strains and o'nyong-nyong virus, but not by other alphaviruses and flaviviruses. Conversely, expression of FHL1 promotes CHIKV infection in cells that do not normally express it. FHL1 interacts directly with the hypervariable domain of the nsP3 protein of CHIKV and is essential for the replication of viral RNA. FHL1 is highly expressed in CHIKV-target cells and is particularly abundant in muscles3,4. Dermal fibroblasts and muscle cells derived from patients with Emery-Dreifuss muscular dystrophy that lack functional FHL15 are resistant to CHIKV infection. Furthermore,  CHIKV infection  is undetectable in Fhl1-knockout mice. Overall, this study shows that FHL1 is a key factor expressed by the host that enables CHIKV infection and identifies the interaction between nsP3 and FHL1 as a promising target for the development of anti-CHIKV therapies.