ASalmonellainositol polyphosphatase acts in conjunction with other bacterial effectors to promote host cell actin cytoskeleton rearrangements and bacterial internalization

Abstract

A central feature of Salmonella pathogenicity is the bacterium's ability to enter into non‐phagocytic cells. Bacterial internalization is the consequence of cellular responses characterized by Cdc42‐ and Rac‐dependent actin cytoskeleton rearrangements. These responses are triggered by the co‐ordinated function of bacterial proteins delivered into the host cell by a specialized protein secretion system termed type III. We report here that SopB, a Salmonella inositol polyphosphatase delivered to the host cell by this secretion system, mediates actin cytoskeleton rearrangements and bacterial entry in a Cdc42‐dependent manner. SopB exhibits overlapping functions with two other effectors of bacterial entry, the Rho family GTPase exchange factors SopE and SopE2. Thus, Salmonella strains deficient in any one of these proteins can enter into cells at high efficiency, whereas a strain lacking all three effectors is completely defective for entry. Consistent with an important role for inositol phosphate metabolism in Salmonella‐induced cellular responses, a catalytically defective mutant of SopB failed to stimulate actin cytoskeleton rearrangements and bacterial entry. Furthermore, bacterial infection of intestinal cells resulted in a marked increase in Ins(1,4,5,6)P4, a consumption of InsP5 and the activation of phospholipase C. In agreement with the in vivo findings, purified SopB specifically dephosphorylated InsP5 to Ins(1,4,5,6)P4in vitro. Surprisingly, the inositol phosphate fluxes induced by Salmonella were not caused exclusively by SopB. We show that the SopB‐independent inositol phosphate fluxes are the consequence of the SopE‐dependent activation of an endogenous inositol phosphatase. The ability of Salmonella to stimulate Rho GTPases signalling and inositol phosphate metabolism through alternative mechanisms is an example of the remarkable ability of this bacterial pathogen to manipulate host cellular functions.

Vesicle-Associated Membrane Protein-8/Endobrevin Negatively Regulates Phagocytosis of Bacteria in Dendritic Cells

“…Salmonella had been reported to invade nonphagocytic cells by macropinocytosis and SopB is involved in regulating actin dynamics to promote Salmonella-induced invasion (33). Because HeLa cells are nonphagocytic cells, the route of bacteria uptake by HeLa cells in their study could most likely be via macropinocytosis instead of the phagocytic pathway.…”

Inhibition of Cdc42-dependent signalling in Saccharomyces cerevisiae by phosphatase-dead SigD/SopB from Salmonella typhimurium

“…SopB/ SigD, another Salmonella virulence factor translocated by the TTSS (Patel & Galán, 2005), has also been proposed to mediate actin cytoskeleton rearrangements and bacterial Abbreviations: DAPI, 4,6-diamidino-2-phenylindole; GAP, GTPaseactivating protein; GEF, GDP-GTP exchange factor; GST, glutathione S-transferase; MAPK, mitogen-activated protein kinase; PtdIns 4,5-P 2 , phosphatidylinositol 4,5-bisphosphate; PtdIns 3,4,5-P 3 , phosphatidylinositol-3,4,5-trisphosphate; TTSS, type III secretion system. entry in a Cdc42-dependent manner (Murli et al, 2001;Zhou et al, 2001). Recently, we have also reported that SigD produces a strong inhibitory effect in yeast (Alemán et al, 2005).…”

“…SigD, a Salmonella homologue of IpgD from Shigella (Niebuhr et al, 2000), is an inositol polyphosphate phosphatase, bearing characteristic motifs 1 and 2 of mammalian inositol 4-phosphatases, as well as a putative synaptojanin (inositol 5-phosphatase)-like domain (Hong & Miller, 1998;Norris et al, 1998;Marcus et al, 2001). Although Salmonella cells lacking sigD are still able to invade host cells (Zhou et al, 2001), elimination of phosphatidylinositol 4,5-bisphosphate (PtdIns 4,5-P 2 ) from invaginating regions during phagocytosis induced by the bacteria depends on SigD (Terebiznik et al, 2002). SigD also seems to be important for the generation of the characteristic pools of phosphatidylinositol 3-phosphate in the membrane of the Salmonella-containing vacuole (Hernández et al, 2004).…”

SopB activates the Akt-YAP pathway to promote Salmonella survival within B cells

“…SPI-1 is required for invasion during oral infection, and the effectors encoded in this pathogenicity island are involved in cytoskeleton rearrangements of epithelial cells to promote the entry of Salmonella via macropinocytosis [16,17]. SopE/SopE2 and the inositide phosphate phosphatase SopB are some of the effector proteins responsible for the induction of macropinocytosis.…”