Role of the ESCRT-III complex in controlling integrity of the Salmonella-containing vacuole.

Intracellular pathogens need to establish specialised niches for survival and proliferation in host cells. The enteropathogen Salmonella enterica accomplishes this by extensive reorganisation of the host endosomal system deploying the SPI2-encoded type III secretion system (SPI2-T3SS). Fusion events of endosomal compartments with the Salmonella-containing vacuole (SCV) form elaborate membrane networks within host cells enabling intracellular nutrition. However, which host compartments exactly are involved in this process and how the integrity of Salmonella-modified membranes is accomplished are not fully resolved. An RNA interference knockdown screen of host factors involved in cellular logistics identified the ESCRT (endosomal sorting complex required for transport) system as important for proper formation and integrity of the SCV in infected epithelial cells. We demonstrate that subunits of the ESCRT-III complex are specifically recruited to the SCV and membrane network. To investigate the role of ESCRT-III for the intracellular lifestyle of Salmonella, a CHMP3 knockout cell line was generated. Infected CHMP3 knockout cells formed amorphous, bulky SCV. Salmonella within these amorphous SCV were in contact with host cell cytosol, and the attenuation of an SPI2-T3SS-deficient mutant strain was partially abrogated. ESCRT-dependent endolysosomal repair mechanisms have recently been described for other intracellular pathogens, and we hypothesise that minor damages of the SCV during bacterial proliferation are repaired by the action of ESCRT-III recruitment in Salmonella-infected host cells.