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.