The Virulence Protein SopD2 Regulates Membrane Dynamics of Salmonella-Containing Vacuoles

Abstract

Salmonella enterica serovar Typhimurium is a Gram-negative bacterial pathogen causing gastroenteritis in humans and a systemic typhoid-like illness in mice. The capacity of Salmonella to cause diseases relies on the establishment of its intracellular replication niche, a membrane-bound compartment named the Salmonella-containing vacuole (SCV). This requires the translocation of bacterial effector proteins into the host cell by type three secretion systems. Among these effectors, SifA is required for the SCV stability, the formation of Salmonella-induced filaments (SIFs) and plays an important role in the virulence of Salmonella. Here we show that the effector SopD2 is responsible for the SCV instability that triggers the cytoplasmic release of a sifA − mutant. Deletion of sopD2 also rescued intra-macrophagic replication and increased virulence of sifA− mutants in mice. Membrane tubular structures that extend from the SCV are the hallmark of Salmonella-infected cells. Until now, these unique structures have not been observed in the absence of SifA. The deletion of sopD2 in a sifA− mutant strain re-established membrane trafficking from the SCV and led to the formation of new membrane tubular structures, the formation of which is dependent on other Salmonella effector(s). Taken together, our data demonstrate that SopD2 inhibits the vesicular transport and the formation of tubules that extend outward from the SCV and thereby contributes to the sifA− associated phenotypes. These results also highlight the antagonistic roles played by SopD2 and SifA in the membrane dynamics of the vacuole, and the complex actions of SopD2, SifA, PipB2 and other unidentified effector(s) in the biogenesis and maintenance of the Salmonella replicative niche.

Dual RNA-seq of pathogen and host

“…Nevertheless, the effect of STnc440 inhibition was comparable to that of several well-established SPI-2 effectors such as SopD2 (Brumell et al, 2003;Schroeder et al, 2010). As a negative control, disrupting the locus of the conjugal transfer regulator FinO -that has not been related to infection and virulence -had no effect on Salmonella pathogenicity.…”

Impact ofSalmonella entericaType III Secretion System Effectors on the Eukaryotic Host Cell

“…Both PipB2 and the complex SifA-SKIP bind to kinesin-1, link the SCV and nascent tubules to microtubules, and promote the elongation of tubules along microtubules. SopD2 associates to late endosome and can contribute to SIF formation by targeting endocytic vesicles to the SCV and nascent tubules [59]. Finally, SseF and SseG mediate bundling of microtubules near the SCV that can promote fusion of aggregated vesicles into tubules [60].…”

“…Similarly to SIFs and SISTs, they form along microtubules in a kinesin-1-dependent manner, but they lack all the markers of SIFs and SISTs except vATPase. A report suggests that SifA and SopD2 exert positive and negative roles, respectively, in the formation of LNTs and that PipB2 is involved in their centrifugal extension [59]. The role of the Salmonellainduced tubular networks is unclear, although it could be related to the interception of nutrients or membranes from host cell trafficking [58].…”

Maintenance of vacuole integrity by bacterial pathogens

“…SseF and SseG promote retention of the SCV at the MTOC by recruiting dynein [7]. PipB2 and SopD2 recruit kinesin-1 to the SCV [8,9]; the presence of high levels of kinesin-1 on the SCV causes vacuole instability [10] but another bacterial effector, SifA, recruits kinesin-1-interacting protein SKIP to promote the transport of membrane filaments and vesicles toward the cell periphery [10,11]. This delicate balance of interactions with cytoskeletal motors is critical for maintenance of SCV integrity.…”

“…Inhibition of myosin II, kinesin-1 or dynein leads to loss of SCV integrity as does the absence of sifA [5,6,12]. Schroeder et al recently demonstrated that the accumulation of kinesin-1 on the SCV resulting from the absence of sifA can be prevented by the further deletion of sopD2 and pipB2 [9]. The authors observed a novel type of tubule extending from the SCV that is absent in the presence of SopD2 suggesting that SopD2 suppresses the formation of a novel type of tubule extending from the SCV that can compensate for the lack of SifA-induced filaments.…”