Biology subjects

Hackbart, M.

Publications and source records attributed to Hackbart, M..

5 recordsLinked to original sources

bioRxiv2026

Circadian Clock Gene Modulation and Selective Reprogramming in Response to Virus Infection

The circadian clock regulates fundamental cellular processes that include the host response to infection. However, the intersection of the circadian clock and the mechanisms that drive antiviral immunity remains poorly understood. Copy-back viral genomes (cbVGs) generated during virus replication strongly stimulate immunity during infection with negative-sense RNA viruses. Here, we demonstrate at the single cell level that A549 lung epithelial cells, commonly used to model lung infections, sustain circadian rhythms and upon infection with Sendai virus (SeV) progressively remodel the circadian clock through an innate immune response driven primarily by cbVGs. Furthermore, we show that cbVG-driven changes in circadian gene expression are mediated through two distinct innate immune sensing pathways: the RIG-I adaptor MAVS is required for preferential induction of the BMAL1 paralog ARNTL2, whereas the double-stranded RNA sensor PKR is required for the cbVG-specific induction of the negative-feedback regulators NR1D1, NR1D2, and PER1. A similar cbVG-specific signature was observed during respiratory syncytial virus infection, suggesting that cbVG-driven circadian gene regulation is not unique to SeV. In addition, we established through gain- and loss-of-function experiments that ARNTL2 is functionally required for amplifying the transcriptional response to infection, with selective effects on the expression of specific antiviral genes, including CCL5. Together, these findings establish innate immune signaling triggered by cbVGs as selective driver of circadian clock gene expression during viral infection through distinct sensing pathways and identify ARNTL2 as a previously unrecognized regulator of virus-induced host transcriptional responses.

microbiology↗

bioRxiv2025

Terminal Loop Sequences in Viral Double-Stranded RNAs Modulate RIG-I Signaling

Detection of foreign RNAs is a crucial activation step for innate immunity pathways in response to viral infections. Retinoic acid-inducible gene I (RIG-I) is a cytoplasmic RNA sensor that triggers type I and III interferon (IFN) expression and activates the antiviral response in response to RNA virus infection. The activating ligand for RIG-I has been shown to be 5-triphosphated, blunt-ended, double-stranded (ds)RNA, but questions remain on the impact of other RNA motifs on RIG-I activation. Here we show that immune-activating copy-back viral genomes (cbVGs) contain RNA stem loops away from the 5 end of the RNA that enhance RIG-I signaling and IFN expression. Importantly, the sequence of the terminal loops of the activating motifs impacts the strength of IFN expression. Additionally, we show that synthetic versions of these cbVG-derived stem loops trigger innate immune responses in mice demonstrating their potential as immunostimulants in vivo.

microbiology↗

bioRxiv2023

S RNA Intergenic Deletions Drive Viral Interference during Arenavirus Infections

Arenaviruses, a family of negative-sense RNA viruses spread by rodents, are a leading cause of severe hemorrhagic fever in humans. Due to a paucity of antivirals and vaccines for arenaviruses, there is a need to identify new mechanisms for interfering with arenavirus replication. In several negative-sense RNA viruses, natural viral interference results from the production of non-standard viral genomes (nsVGs) that activate the innate immune system and/or compete for essential viral products. Although it is well established that arenaviruses produce strong interfering activities, it is unknown if they produce interfering nsVGs. Here we show that arenaviruses produce deletions within the intergenic region of their Small (S) RNA genome, which prevents the production of viral mRNA and protein. These deletions are more abundant when arenaviruses are grown in high-interfering conditions and are associated with inhibited viral replication. Overall, we found that arenaviruses produce internal deletions within the S RNA intergenic region that are produced by arenaviruses and can block viral replication. These natural arenavirus interfering molecules provide a new target for the generation of antivirals as well as an alternative strategy for producing attenuated arenaviruses for vaccines. AUTHOR SUMMARYArenaviruses are hemorrhagic fever-causing pathogens that infect millions of people a year. There are currently no approved antivirals that target arenaviruses and understanding natural mechanisms that inhibit arenavirus replication is crucial for the development of effective therapeutics. Here, we identify multiple deletions within arenavirus genomes that are associated with the inhibition of viral replication. We show that these deletions prevent viral protein production through the removal of the intergenic region of the viral genome. These deletions were found in all arenaviruses tested in this study representing a novel mechanism for development of new antivirals and vaccines that broadly target the arenavirus family.

microbiology↗

bioRxiv2023

VODKA2: An accurate method to detect copy-back and deletion viral genomes from next-generation sequencing data

During viral replication, viruses carrying an RNA genome produce non-standard viral genomes (nsVGs), including copy-back viral genomes (cbVGs) and deletion viral genomes (delVGs), that play a crucial role in regulating viral replication and pathogenesis. Because of their critical roles in determining the outcome of RNA virus infections, the study of nsVGs has flourished in recent years exposing a need for bioinformatic tools that can accurately identify them within Next-Generation Sequencing data obtained from infected samples. Here, we present our data analysis pipeline, Viral Opensource DVG Key Algorithm2 (VODKA2), that is optimized to run on a High Performance Computing (HPC) environment for fast and accurate detection of nsVGs from large data sets. Availability and implementationVODKA2 is freely available at GitHub (https://github.com/lopezlab-washu/VODKA2)

bioinformatics↗

bioRxiv2019

Coronavirus Interferon Antagonists Differentially Modulate the Host Response during Replication in Macrophages

Coronaviruses express a multifunctional papain-like protease, termed PLP2. PLP2 acts as a protease that cleaves the viral replicase polyprotein, and a deubiquitinating (DUB) enzyme which removes ubiquitin moieties from ubiquitin-conjugated proteins. Previous in vitro studies implicated PLP2 DUB activity as a negative regulator of the host interferon (IFN) response, but the role of DUB activity during virus infection was unknown. Here, we used X-ray structure-guided mutagenesis and functional studies to identify amino acid substitutions within the ubiquitin-binding surface of PLP2 that reduced DUB activity without affecting polyprotein processing activity. We engineered a DUB mutation (Asp1772 to Ala) into a murine coronavirus and evaluated the replication and pathogenesis of the DUB mutant virus (DUBmut) in cultured macrophages and in mice. We found that the DUBmut virus replicates similarly as the wild-type virus in cultured cells, but the DUBmut virus activates an IFN response at earlier times compared to the wild-type virus infection in macrophages, consistent with DUB activity negatively regulating the IFN response. We compared the pathogenesis of the DUBmut virus to the wild-type virus and found that the DUBmut-infected mice had a statistically significant reduction (p<0.05) in viral titer in livers and spleens at day 5 post-infection, albeit both wild-type and DUBmut virus infections resulted in similar liver pathology. Overall, this study demonstrates that structure-guided mutagenesis aids the identification of critical determinants of PLP2-ubiquitin complex, and that PLP2 DUB activity plays a role as an interferon antagonist in coronavirus pathogenesis. ImportanceCoronaviruses employ a genetic economy by encoding multifunctional proteins that function in viral replication and also modify the host environment to disarm the innate immune response. The coronavirus papain-like protease 2 (PLP2) domain possesses protease activity, which cleaves the viral replicase polyprotein, and also DUB activity (de-conjugating ubiquitin/ubiquitin-like molecules from modified substrates) using identical catalytic residues. To separate the DUB activity from the protease activity, we employed a structure-guided mutagenesis approach and identified residues that are important for ubiquitin-binding. We found that mutating the ubiquitin-binding residues results in a PLP2 that has reduced DUB activity but retains protease activity. We engineered a recombinant murine coronavirus to express the DUB mutant and showed that the DUB mutant virus activated an earlier type I interferon response in macrophages and exhibited reduced pathogenesis in mice. The results of this study demonstrate that PLP2/DUB is an interferon antagonist and a virulence trait of coronaviruses.

microbiology↗