Poxvirus A51R proteins regulate microtubule stability and antagonize a cell-intrinsic antiviral response

TRIM Proteins and Antiviral Microtubule Reorganization: A Novel Component in Innate Immune Responses?

TRIM proteins are a family of innate immune factors that play diverse roles in innate immunity and protect the cell against viral and bacterial aggression. As part of this special issue on TRIM proteins, we will take advantage of our findings on TRIM69, which acts by reorganizing the microtubules (MTs) in a manner that is fundamentally antiviral, to more generally discuss how host-pathogen interactions that take place for the control of the MT network represent a crucial facet of the struggle that opposes viruses to their cell environment. In this context, we will present several other TRIM proteins that are known to interact with microtubules in situations other than viral infection, and we will discuss evidence that may suggest a possible contribution to viral control. Overall, the present review will highlight the importance that the control of the microtubule network bears in host-pathogen interactions.

Poxvirus A51R Proteins Negatively Regulate Microtubule-Dependent Transport by Kinesin-1

Microtubule (MT)-dependent transport is a critical means of intracellular movement of cellular cargo by kinesin and dynein motors. MT-dependent transport is tightly regulated by cellular MT-associated proteins (MAPs) that directly bind to MTs and either promote or impede motor protein function. Viruses have been widely shown to usurp MT-dependent transport to facilitate their virion movement to sites of replication and/or for exit from the cell. However, it is unclear if viruses also negatively regulate MT-dependent transport. Using single-molecule motility and cellular transport assays, we show that the vaccinia virus (VV)-encoded MAP, A51R, inhibits kinesin-1-dependent transport along MTs in vitro and in cells. This inhibition is selective as the function of kinesin-3 is largely unaffected by VV A51R. Interestingly, we show that A51R promotes the perinuclear accumulation of cellular cargo transported by kinesin-1 such as lysosomes and mitochondria during infection. Moreover, A51R also regulates the release of specialized VV virions that exit the cell using kinesin-1-dependent movement. Using a fluorescently tagged rigor mutant of kinesin-1, we show that these motors accumulate on A51R-stabilized MTs, suggesting these stabilized MTs may form a "kinesin-1 sink" to regulate MT-dependent transport in the cell. Collectively, our findings uncover a new mechanism by which viruses regulate host cytoskeletal processes.

Monkeypox: A Viral Zoonotic Disease of Rising Global Concern

Monkeypox (mpox) is a rare viral zoonotic disease, endemic to Central and West Africa, caused by the monkeypox virus, an orthopoxvirus similar to the variola virus (smallpox). Although sporadic travel-associated cases have historically occurred outside Africa, in May 2022, mpox began spreading globally in multiple nonendemic countries across several continents. In 2024, there has been an increase in globally reported confirmed cases of mpox and deaths from mpox, making it a public health emergency of international concern. The reasons for the unusual global spread are under investigation but likely relate to increased travel and waning population immunity to orthopoxviruses. Transmission now appears to be mainly through close, intimate contact, especially among men who have sex with men. Mpox is usually a self-limited disease. Although limited approved antiviral treatments are available, such as tecovirimat, which the European Medicines Agency approved in January 2022 for the treatment of mpox, their widespread availability and effectiveness in the current outbreak remain to be investigated. Public health control measures include surveillance, case identification/isolation, contact tracing, and targeted vaccination of contacts at high risk of exposure. However, challenges remain in curtailing the current unprecedented outbreak. Critical knowledge gaps include animal reservoir(s) responsible for initial spillover events, viral mutations that may enhance transmissibility, optimal diagnostics for noninvasive specimens, effective antiviral therapies, next-generation vaccines providing longer-term immunity, and building global capacity for outbreak response. This review summarizes the current literature on mpox virology, epidemiology, pathogenesis, clinical manifestations, diagnostics, treatment, prevention, and public health control measures. Ongoing investigation and research are needed to better understand mpox’s evolving epidemiology, pathogenicity, transmissibility, and ecology to guide strategies for containing the outbreak and preventing future global emergence.

Poxvirus A51R: A microtubule maestro and virulence virtuoso

Seo et al.1 shed light on virus-host interactions as they reveal how poxvirus A51R stabilizes microtubules in infected cells, which impacts vaccinia virus virulence in mice by potentially inhibiting reactive-oxygen-species-dependent antiviral responses in macrophages.

FEAR antiviral response pathway is independent of interferons and countered by poxvirus proteins

The human facilitates chromatin transcription (FACT) complex is a chromatin remodeller composed of human suppressor of Ty 16 homologue (hSpt16) and structure-specific recognition protein-1 subunits that regulates cellular gene expression. Whether FACT regulates host responses to infection remained unclear. We identify a FACT-mediated, interferon-independent, antiviral pathway that restricts poxvirus replication. Cell culture and bioinformatics approaches suggest that early viral gene expression triggers nuclear accumulation of SUMOylated hSpt16 subunits required for the expression of E26 transformation-specific sequence-1 (ETS-1)-a transcription factor that activates virus restriction programs. However, biochemical studies show that poxvirus-encoded A51R proteins block ETS-1 expression by outcompeting structure-specific recognition protein-1 binding to SUMOylated hSpt16 and by tethering SUMOylated hSpt16 to microtubules. Furthermore, A51R antagonism of FACT enhances poxvirus replication in human cells and virulence in mice. Finally, we show that FACT also restricts rhabdoviruses, flaviviruses and orthomyxoviruses, suggesting broad roles for FACT in antiviral immunity. Our study reveals the FACT-ETS-1 antiviral response (FEAR) pathway to be critical for eukaryotic antiviral immunity and describes a unique mechanism of viral immune evasion.