Discerning the role of a lysosomal tethering factor in promoting intravacuolar replication of Salmonella

Abstract

Salmonella (Salmonella enterica serovar typhimurium) is a successful intracellular pathogen that newlineextensively manipulates the host membrane trafficking machinery as it strives to establish its newlinereplication-competent vacuolar microenvironment within host cells; also known as Salmonella newlineContaining Vacuole (SCV). To maintain the integrity of its phagosome, Salmonella translocates newlineseveral virulence determinants into the host cytoplasm that intercept and instigate dynamic newlinemembrane exchanges with the endo-lysosomal compartments including late endosomes and newlinelysosomes, ultimately leading to metamorphosis of these endocytic membranes into an extensive newlinetubular network emanating from and interconnecting the SCVs (Salmonella Induced Filaments, newlineSIFs). This fusogenic activity is essential for the procurement of nutrients to mediate intracellular newlinesurvival and proliferation of this pathogen inside the vacuole. However, the mechanism by which newlineSalmonella constantly acquires these host membranes and endocytosed nutrients has been poorly newlinecharacterized. newlineHere in this study, we have uncovered an important aspect of Salmonella s intracellular survival newlinestrategy that involves recruitment of a multi-subunit lysosomal tether, HOPS (HOmotypic fusion newlineand Protein Sorting) complex to Salmonella-modified membranes in a temporal manner. Once newlinerecruited, HOPS functions as a molecular bridge linking the phagosomal membranes to the late newlineendo-lysosomal compartments, thereby promoting SCV maturation, SIF biogenesis and nutrient newlineacquisition for intravacuolar replication of this pathogen. Notably, in the absence of HOPS newlinecomplex subunits we observed a significantly reduced bacterial load in cultured cell lines as well newlineas in a mouse model of Salmonella infection. We also found that HOPS complex was required for newlinenutrient access to the SCV membranes. Finally, we identified that bacterial effector SifA in newlinecomplex with host protein SKIP recruits HOPS complex to SCV membranes.