Biology subjects

Schiavolin, L.

Publications and source records attributed to Schiavolin, L..

3 recordsLinked to original sources

bioRxiv2025

A pre-loaded and assembled human Ago2-miRISC orchestrates Shigella-induced vacuolar rupture through the targeting of RhoGDIα

The enteroinvasive bacterium Shigella flexneri causes bacillary dysentery. It invades intestinal epithelial cells and forms a bacterium-containing vacuole, which it rapidly ruptures to reach the cytosol. Here, we found that human Argonaute 2 (Ago2), the central component of miRNA-induced silencing complex (miRISC), positively regulates early steps of Shigella infection, including vacuolar rupture. This is consistent with the rapid recruitment of Ago2 at Shigella entry foci. The ability of Ago2 to form an assembled miRISC was found required for vacuolar maturation, while its slicer activity is dispensable for this process. Furthermore, we found that the RhoGTPase inhibitor RhoGDI is targeted by specific miRNAs, pre-loaded in Ago2, which, collectively, accelerate vacuolar rupture. Therefore, a pre-loaded and assembled Ago2-miRISC orchestrates vacuolar maturation by targeting RhoGDI. These findings may have wider implications in the understanding of how stored Ago2-loaded miRNAs control immediate steps of infection, prior to the differential expression of microbe-responsive miRNAs.

molecular biology↗

bioRxiv2024

The Streptococcus pyogenes M protein is involved in phenotypic resistance to phage A25 infection in presence of human serum.

Streptococcus pyogenes is responsible for mild to life-threatening infections. Bacteriophages, or phages, and their virulence genes play a key role in the emergence and expansion of epidemics. However, relatively little is known about the biology of S. pyogenes phages, particularly in biologically relevant environments. During infection, S. pyogenes conceals from the host immune system through the binding of human serum proteins. This evasion is mediated by surface proteins, such as the M protein which is a major virulence determinant of S. pyogenes. Here, we demonstrate that human serum proteins also confer phenotypic resistance to phage A25 infection by impeding phage adsorption. We have found that, although not directly involved in phage A25 infection, the M protein is involved in this inhibition through the binding of both IgG and albumin, especially in absence of bound fatty acids. These findings highlight the importance of studying phages within a physiological context, specifically in the environmental conditions in which they will be used. Author summaryThe issues of antimicrobial resistance and resurgence of life-threatening infection, like the recent cases of invasive S. pyogenes infections, are prompting the scientific community to use phages as a complementary therapy. Phages are often characterized in laboratory conditions which are very different from the infection site. During human infection, Streptococcus pyogenes uses serum proteins to protect against the immune system. Our data illustrate how the human host environment also modulates phage susceptibility of S. pyogenes. We found that human serum transiently protects a M25 strain against infection by the lytic phage A25. This protective effect is mediated in part by the M protein, a major virulence determinant and the target of current vaccines. This new function for the M protein highlights the need to characterize bacteria-phage interactions in a more physiological context to increase the chances of success of phage therapy.

microbiology↗

bioRxiv2022

A Legionella pneumophila effector impedes host gene silencing to promote virulence

RNA silencing is a gene silencing mechanism directed by small RNAs. Human miRNAs act as central regulators of host-bacteria interactions. However, it is unknown whether human pathogenic bacteria could impede RNA silencing to promote virulence. Here, we show that the Legionella pneumophila type IV-secreted effector LegK1 efficiently suppresses siRNA and miRNA activities in human cells. This effect depends on its known kinase activity, but also on its novel capacity, found here, to bind Argonaute (Ago) proteins. We further demonstrate that the ability of LegK1 to activate NF-{kappa}B signaling is required for RNA silencing suppression, establishing a link between effector-mediated NF-{kappa}B signaling and RNA silencing suppression. LegK1 also promotes L. pneumophila growth in both amoeba and human macrophages, supporting a role for this effector in virulence. Finally, we show that, in infected-macrophages, the latter activity relies, in part, on the genetic targeting of human Ago4. These findings indicate that a L. pneumophila effector has evolved to suppress RNA silencing to promote virulence. Significance StatementIt is now well established that mammalian viruses suppress RNAi to promote their replication in host cells. However, whether mammalian pathogenic bacteria use a similar virulence strategy remains unknown. Here, we show that the LegK1 effector from Legionella pneumophia, the causal agent of Legionnaires disease, efficiently suppresses RNAi in human cells. This effect depends on its ability to interact with Argonaute (Ago) proteins and to activate NF-{kappa}B signaling. In addition, LegK1 promotes virulence in infected-macrophages through the genetic targeting of human Ago4. Based on the lack of NF-{kappa}B-related factors in amoebae, and on the presence of canonical Ago proteins in these natural L. pneumophila hosts, we propose that the RNAi suppression activity of LegK1 represents its primary virulence function.

molecular biology↗