Sorting nexin 3 (SNX3) is a component of a tubular endosomal network induced by Salmonella and involved in maturation of the Salmonella-containing vacuole

Abstract

SummarySalmonella enterica serovar Typhimurium is an intracellular pathogen that grows within a modified endomembrane compartment, the Salmonellacontaining vacuole (SCV). Maturation of nascent SCVs involves the recruitment of early endosome markers and the remodelling of phosphoinositides at the membrane of the vacuole, in particular the production of phosphatidylinositol 3-phosphate [PI(3)P]. Sorting nexins (SNXs) are a family of proteins characterized by the presence of a phox homology (PX) domain that binds to phosphoinositides and are involved in intracellular trafficking in eukaryotic cells. We therefore studied whether sorting nexins, particularly sorting nexin 3 (SNX3), play a role in Salmonella infection. We found that SNX3 transiently localized to SCVs at early times post invasion (10 min) and presented a striking tubulation phenotype in the vicinity of SCVs at later times (30-60 min). The bacterial effector SopB, which is known to promote PI(3)P production on SCVs, was required for the formation of SNX3 tubules. In addition, RAB5 was also required for the formation of SNX3 tubules. Depletion of SNX3 by siRNA impaired RAB7 and LAMP1 recruitment to the SCV. Moreover, the formation of Salmonella-induced filaments (Sifs) was altered by SNX3 knock-down. Therefore, SNX3 plays a significant role in regulating the maturation of SCVs.

Vaccinia Virus Infection Requires Maturation of Macropinosomes

“…Depletion of the same factors had no inhibitory effect on SFV (not shown). Another hit, SNX3, has been reported to promote recruitment of Rab7a to Salmonella ‐containing vacuoles (SCVs) 25. Microscopy‐based localization of EGFP‐SNX3 during VACV infection indicated that SNX3 was recruited to MV‐containing vacuoles with similar kinetics as Rab7a (Figure S4).…”

“…Some SNXs have also been reported to facilitate macropinosome maturation and function 23, 25, 59. Having identified SNX3 as a hit in the RNAi screen, we investigated its localization in cells that had internalized VACV MVs.…”

“…SNX3 was predominantly found in MV‐containing LMs (Figure S4). Interestingly, SNX3 has been shown to localize to SCVs where it facilitates SCV maturation to late compartments 25.…”

“…Macropinosomes may also acquire Rab34 and early endosome antigen 1 (EEA1) needed for pinosome formation and fusion 19, 20. Acquisition of sorting nexins (SNXs) promotes tubulation to facilitate cargo recycling and macropinosome maturation 21, 22, 23, 24, 25. As they move deeper into the cytoplasm, macropinosomes acidify and acquire Rab7, Rab21 and lysosome‐associated membrane protein 1 (LAMP1) 26, 27.…”

Salmonella Acquires Lysosome-associated Membrane Protein 1 (LAMP1) on Phagosomes from Golgi via SipC Protein-mediated Recruitment of Host Syntaxin6

“…Recent studies have shown (41) that in epithelial cells LAMP1 recruitment on SCV is dependent on SopB and SNX3 interaction. SNX3 regulates trafficking in both the endocytic and secretory pathways (42)(43)(44), and depletion of SNX3 by siRNA only partially inhibits the recruitment of LAMP1 on SCV (41) suggesting that other host proteins could be involved in this process. Our results have shown that SipC is specifically required for LAMP1 recruitment, and SopB has no role in this process in macrophages.…”