Biology subjects

Streicher, F.

Publications and source records attributed to Streicher, F..

4 recordsLinked to original sources

bioRxiv2025

Compositional analysis of yellow fever virus induced stress granules reveals a functional connection to mitochondrial homeostasis

The phase separation of biomolecules into so-called stress granules (SGs) allows the cell to tightly regulate translation activity in response to different stimuli, such as oxidative stress, starvation, or the recognition of non-cellular RNA. Recent reports suggest SGs induced during viral infection, may act as a crossroad between the cellular stress response and the activation of the innate immune response. Here, we aimed to dissect the role of SGs in the context of yellow fever virus (YFV) infection. We found that YFV infection resulted in translational shut-off from 24 hpi on followed by the formation of SGs at 48 hpi, a delay potentially associated with the ability of the YFV capsid to inhibit SG formation, through an interaction with the major SG scaffolding protein G3BP1. To elucidate the role of YFV-induced SGs during infection, we inhibited SG assembly using a small-molecule inhibitor and find that SG formation does not influence viral replication. Uncovering the first proteome of virus-induced SGs, our compositional analysis revealed a specific enrichment of proteins associated with mitochondrial processes in YFV-induced SGs. Indeed, we show that YFV infection results in mitochondrial damage and dysfunction. Together, we propose that YFV-induced SGs may be involved not only in the modulation of cellular homeostasis but also in influencing mitochondrial functions. Author SummaryViruses impose a major burden on the infected host - from structural rearrangements needed to assemble replication complexes, to exploiting cellular energy resources and genetic rewiring associated with antiviral responses. The assembly of membrane-less organelles such as stress granules (SGs) enable cells to rapidly tune cellular processes upon sensing of stresses such as viruses. Moreover, the cells innate immune response is proposed to be regulated by SGs and in turn many viruses disrupt or highjack their components. Yet, the molecular basis for SG functions during infection remain ambiguous. Here we investigated the interplay between yellow fever virus (YFV) infection and SGs. We demonstrate that infection with attenuated or pathogenic viruses result in the formation of SGs. Their compositional analysis reveal that they sequester mitochondrial proteins, correlating with altered mitochondrial functions during infection. This highlights a novel complex interplay between membrane-bound and membrane-less organelles which could present novel opportunities for antiviral therapies.

microbiology↗

bioRxiv2025

The type I and III interferon responses restrict infection with tick-borne orthoflaviviruses through IFI6

Tick-borne orthoflaviviruses (TBOVs) are a growing global health concern. Several representatives of this viral family cause fatal disease in humans with increasing case numbers throughout the last decades. The innate immune response, especially interferon (IFN)-dependent signaling, is an essential part of the human defense system that counteracts infection with TBOVs and other viruses. Even though they activate the same signaling cascade, IFNs belonging to the type I and III families trigger differing gene expression patterns. Which genes the two IFN families induce to restrict infection with TBOVs remains poorly characterized. Here we show that type I and III IFNs are both capable of restricting TBOV infection of human cell lines in a cell type-specific manner. Infection of C57BL/6J mice with knockouts for either IFN type I or III receptors further underscored the critical role of IFN signaling in controlling TBOV replication in vivo. To assess the contribution of single genes to controlling TBOV infection in human cells, we used a CRISPR/Cas9-KO-based screening approach. This strategy identified IFI6 as a central player for IFN type I- and III-driven responses against TBOVs. We further defined IFI6 as an ER-resident protein that restricts TBOV replication at a post-entry step. Our work thus opens new perspectives for targeting weak points in the life cycle of TBOVs and other orthoflaviviruses, potentially paving the way for the development of new antiviral therapeutics. One Sentence SummaryType I and III interferons are crucial for protection against tick-borne orthoflavivirus infection in vitro and in vivo, both relying on IFI6 as a main antiviral effector.

microbiology↗

bioRxiv2021

Species-specific molecular barriers to SARS-CoV-2 replication in bat cells

Bats are natural reservoirs of numerous coronaviruses, including the potential ancestor of SARS-CoV-2. Knowledge concerning the interaction between coronaviruses and bat cells is sparse. We investigated the susceptibility of primary cells from Rhinolophus ferrumequinum and Myotis species, as well as of established and novel cell lines from Myotis myotis, Eptesicus serotinus, Tadarida brasiliensis and Nyctalus noctula, to SARS-CoV-2 infection. None of these cells were sensitive to infection, not even the ones expressing detectable levels of angiotensin-converting enzyme 2 (ACE2), which serves as the viral receptor in many mammalian species. The resistance to infection was overcome by expression of human ACE2 (hACE2) in three cell lines, suggesting that restriction to viral replication was due to a low expression of bat ACE2 (bACE2) or absence of bACE2 binding in these cells. Infectious virions were produced but not released from hACE2-transduced M. myotis brain cells. E. serotinus brain cells and M. myotis nasal epithelial cells expressing hACE2 efficiently controlled viral replication. This ability to control viral replication correlated with a potent interferon response. Our data highlight the existence of species-specific molecular barriers to viral replication in bat cells. These novel chiropteran cellular models are valuable tools to investigate the evolutionary relationships between bats and coronaviruses. Author summaryBats host ancestors of several viruses that cause serious disease in humans, as illustrated by the on-going SARS-CoV-2 pandemic. Progress in investigating bat-virus interactions have been hampered by a limited number of bat cell lines. We have generated primary cells and cell lines from several bat species that are relevant for coronavirus research. The varying susceptibilities of the cells to SARS-CoV-2 infection offered the opportunity to uncover some species-specific molecular restrictions to viral replication. All bat cells exhibited a potent entry-dependent restriction. Once this block was overcome by over-expression of human ACE2, which serves at the viral receptor, two bat cell lines controlled well viral replication, which correlated with the inability of the virus to counteract antiviral responses. Other cells potently inhibited viral release. Our novel bat cellular models contribute to a better understanding of the molecular interplays between bats and viruses.

microbiology↗

bioRxiv2020

RIG-I and PKR, but not stress granules, mediate the pro-inflammatory response to Yellow fever virus

Yellow fever virus (YFV) is an RNA virus primarily targeting the liver. Severe YF cases are responsible for hemorrhagic fever, plausibly precipitated by excessive pro-inflammatory cytokine response. Pathogen recognition receptors (PRRs), such as the cytoplasmic RIG-I-like receptors (RLRs), and the viral RNA sensor PKR are known to initiate a pro-inflammatory response upon recognition of viral genomes. Here, we sought to reveal the main determinants responsible for the acute cytokine expression occurring in human hepatocytes following YFV infection. Using a RIG-I-defective human hepatoma cell line, we found that RIG-I largely contributes to cytokine secretion upon YFV infection. In infected RIG-I-proficient hepatoma cells, RIG-I was localized in stress granules. These granules are large aggregates of stalled translation preinitiation complexes known to concentrate RLRs and PKR, and are so far recognized as hubs orchestrating RNA virus sensing. Using PKR-deficient hepatoma cells, we found that PKR contributes to both stress granule formation and cytokine induction upon YFV infection. However, stress granules disruption did not affect the cytokine response to YFV infection, as assessed by siRNA-knockdown-mediated inhibition of stress granule assembly. Finally, no viral RNA was detected in stress granules using a fluorescence in situ hybridization approach coupled with immunofluorescence. Our findings suggest that both RIG-I and PKR mediate pro-inflammatory cytokine induction in YFV-infected hepatocytes, in a stress granule-independent manner. Therefore, by showing the uncoupling of the early cytokine response from the stress granules formation, our model challenges the current view by which stress granules are required for the mounting of the acute antiviral response. ImportanceYellow fever is a mosquito-borne acute hemorrhagic disease caused by yellow fever virus (YFV). The mechanisms responsible for its pathogenesis remain largely unknown, although increased inflammation has been linked to worsened outcome. YFV targets the liver, where it primarily infects hepatocytes. We found that two RNA-sensing proteins, RIG-I and PKR, participate in the induction of pro-inflammatory mediators in human hepatocytes infected with YFV. We show that YFV infection promotes the formation of cytoplasmic structures, termed stress granules, in a PKR-, but not RIG-I-dependent manner. Whilst stress granules were previously postulated to be essential platforms for immune activation, we found that they are not required for pro-inflammatory mediators production upon YFV infection. Collectively, our work uncovered molecular events triggered by the replication of YFV, which could prove instrumental in clarifying the pathogenesis of the disease, with possible repercussions on disease management.

microbiology↗