Brynes, A. | bioRxiv Science

bioRxiv2026

Productive Mayaro Virus Infection Requires Host Fatty Acid Synthase for nsP1 S-palmitoylation

To date, twenty-seven pathogenic human viruses require host-catalyzed de novo fatty acid biosynthesis for replication. This pathway is driven by fatty acid synthase (FASN), which produces palmitate. Palmitate is a precursor for various functions during viral infection, including lipid droplet formation for assembly, beta-oxidation for ATP generation, and post-translational modification of proteins. Whether Mayaro virus (MAYV), an emerging alphavirus that causes debilitating arthritogenic disease, required FASN for infection was unknown. Using genetic and pharmacological approaches in a human cell line and primary cell model, we found that MAYV requires FASN-dependent palmitate synthesis for virion production. To determine how palmitate contributes to infection, we pharmacologically inhibited pathways downstream of FASN and found that only 2-bromopalmitate (2-BP), a protein palmitoylation inhibitor, led to a 94% reduction in MAYV infection. S-palmitoylation is a post-translational modification in which palmitate is attached to sulfur atoms in cysteine residues. In chikungunya virus, a related alphavirus, FASN-dependent palmitoylation of nonstructural protein 1 (nsP1) is essential for membrane association and replication. Consequently, we hypothesized that MAYV nsP1 is palmitoylated in a FASN-dependent manner. Using an alkyne acetate analog, Alk-4, metabolized by FASN into alkyne palmitate, we observed specific labeling of wild-type nsP1 at conserved cysteine residues (C417-419), but not of a cysteine-to-alanine triple mutant. Treatment with TVB-2640 or 2-BP abrogated Alk-4 labeling of wild-type nsP1 during active infection, reinforcing that MAYV protein palmitoylation is a FASN-dependent process. Our findings reveal a conserved mechanism of FASN-dependent protein palmitoylation in alphaviruses and highlight FASN as a potential anti-viral target. ImportanceMayaro virus (MAYV) is a neglected, mosquito-borne tropical virus that causes debilitating pathologies, such as chronic joint pain that can last from months to years. Currently, MAYV transmissions are endemic in sylvatic and peri-urban regions in Central and South America and the Caribbean. However, MAYV has been detected in urban-adapted mosquitos like Aedes aegypti (Ae. aegypti) and is a concern for potential global spread. Consequently, investigating the mechanisms of MAYV infection is critical to uncover opportunities for antiviral drug development. In this study, we report that MAYV infection requires host fatty acid synthase (FASN) derived palmitate for palmitoylation of the viral non-structural protein 1 (nsP1). In addition, we report that inhibiting FASN with the clinically advanced small molecule TVB-2640 significantly reduced MAYV infection and nsP1 palmitoylation. This study highlights FASN as an essential host factor for MAYV replication and establishes it as a promising therapeutic target for MAYV and related alphaviruses.

microbiology↗

bioRxiv2024

Human metapneumovirus SH protein promotes JAK1 degradation to impair host IL-6 signaling

Human metapneumovirus (HMPV) is a leading cause of respiratory infections in children, older adults, and those with underlying conditions 1,2,3,4. HMPV must evade immune defenses to replicate successfully; however, the viral proteins used to accomplish this are poorly characterized. The HMPV small hydrophobic (SH) protein has been reported to inhibit signaling through type I and type II interferon (IFN) receptors in vitro, in part by preventing STAT1 phosphorylation5. HMPV infection also inhibits IL-6 signaling. However, the mechanisms by which SH inhibits signaling, and its involvement in IL-6 signaling inhibition are unknown. Here, we used transfection of SH expression plasmids and SH-deleted virus ({Delta}SH) to show that SH is the viral factor responsible for inhibition of IL-6 signaling during HMPV infection. Transfection of SH-expression vectors or infection with wildtype, but not {Delta}SH virus, blocked IL-6 mediated STAT3 activation. Further, JAK1 protein (but not RNA) was significantly reduced in cells infected with wildtype but not {Delta}SH virus. The SH-mediated reduction of JAK1 was partially restored by addition of proteasome inhibitors, suggesting proteasomal degradation of JAK1. Confocal microscopy indicated that infection relocalized JAK1 to viral replication factories. Co-immunoprecipitation showed that SH interacts with JAK1 and ubiquitin, further linking SH to proteasomal degradation machinery. These data indicate that SH inhibits IL-6 and IFN signaling in infected cells in part by promoting proteasomal degradation of JAK1 and that SH is necessary for IL-6 and IFN signaling inhibition in infection. These findings enhance our understanding of the immune evasion mechanisms of an important respiratory pathogen. ImportanceHuman metapneumovirus (HMPV) is a common cause of severe respiratory illness, especially in children and older adults, in whom it is a leading cause of hospitalization. Prior research suggests that severe HMPV infection is driven by a strong immune response to the virus, and especially by inflammatory immune signals like interferons (IFN). HMPV produces a small hydrophobic protein (SH) that is known to block IFN signaling, but the mechanism by which it functions, and its ability to inhibit other important immune signals remains unexplored. This paper demonstrates that SH can inhibit another related immune signal, IL-6, and demonstrates that SH depletes JAKs, critical proteins involved in both IL-6 and IFN signaling. A robust understanding of how HMPV and related viruses interfere with immune signals important for disease could pave the way for future treatments aimed at mitigating severe infections.

immunology↗