Syntaxin 3-SPI 2 dependent cross-talk facilitates the division of Salmonella containing vacuole (SCV)

Abstract

Intracellular membrane fusion is mediated by membrane-bridging complexes of soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs). SNARE proteins are one of the key players in the vesicular transport. Several reports shed light on intracellular bacteria modulating host SNARE machinery to establish infection successfully. The critical SNAREs in macrophages responsible for phagosome maturation are Syntaxin 3 (STX3) and Syntaxin 4 (STX4). Salmonella actively modulates its vacuole membrane composition to escape lysosomal fusion. A report showed that Salmonella containing vacuole (SCV) harbors recycling endosomal SNARE Syntaxin 12 (STX12). However, the role of host SNAREs in SCV biogenesis and pathogenesis is unclear. Upon knockdown of STX3, we have observed a reduction in bacterial proliferation and is restored upon the overexpression of STX3. Post infected live-cell imaging of cells showed STX3 localises to the SCV membranes and thus might help in fusion of SCV with intracellular vesicles to acquire membrane for its division. We also found this interaction abrogated when we infected with SPI-2 encoded T3SS apparatus mutant (STM {Delta}ssaV) but not with SPI-1 encoded T3SS (STM{Delta} invC). These observations were also consistent in mice model of Salmonella infection. Together, these results shed a light on the effector molecules secreted through SPI-2 encoded by T3SS possibly involved in interaction with host SNARE STX3, which is essential to maintain the division of Salmonella in SCV and maintenance the principle single bacterium per vacuole. SynopsisSalmonella Typhimurium infection in murine macrophage leads to upregulation of host Syntaxin 3 both at transcript and protein levels at late stage of infection. Syntaxin 3 cross-talk with Salmonella containing vacuoles (SCVs) is essential for establishment of replicative niche in host macrophages. The cross-talk between STX3 and SCVs is Salmonella pathogenicity island 2 (SPI-2) dependent and is consistent in mice model of Salmonella Typhimurium infection.