Salmonella Inhibits Retrograde Trafficking of Mannose-6-Phosphate Receptors and Lysosome Function

Abstract

Salmonella enterica is an intracellular bacterial pathogen that replicates within membrane-bound vacuoles through the action of effector proteins translocated into host cells. Salmonella vacuoles have characteristics of lysosomes but are reduced in hydrolytic enzymes transported by mannose-6-phosphate receptors (MPRs). We found that the effector SifA subverted Rab9-dependent retrograde trafficking of MPRs, thereby attenuating lysosome function. This required binding of SifA to its host cell target SKIP/PLEKHM2. Furthermore, SKIP regulated retrograde trafficking of MPRs in noninfected cells. Translocated SifA formed a stable complex with SKIP and Rab9 in infected cells. Sequestration of Rab9 by SifA-SKIP accounted for the effect of SifA on MPR transport and lysosome function. Growth of Salmonella increased in cells with reduced lysosomal activity and decreased in cells with higher lysosomal activity. These results suggest that Salmonella vacuoles undergo fusion with lysosomes whose potency has been reduced by SifA.

Direct measurement of oxidative and nitrosative stress dynamics in Salmonella inside macrophages

“…4C). Both the sifA single mutant and the sifAsseJ double mutant are deficient in the inhibition of lysosome fusion, but only the sifA single mutant "escapes" the SCV and resides in the cytosol (24). Therefore, these results clearly suggest that cytosolic bacteria experience more redox stress than bacteria that reside inside the SVC.…”

“…It is known that from inside the SCV, S. Typhimurium regulates fusion with vesicles through the actions of SPI-2 effectors. For example, SPI-2 effector SifA directs trafficking of mannose-6-phospate receptors and thereby inhibits lysosome function (24). Additionally, SifA is implicated in maintaining the integrity of the SCV, and it is well documented that infection with the sifA mutant leads to loss of SCV integrity (25).…”

“…To determine whether this redox stress was caused by vacuole disruption or inhibition of lysosome fusion, a sifAsseJ double mutant was constructed. This mutant maintains SCV integrity but is unable to inhibit lysosome fusion (24,25). To determine the contribution of SPI-2 effector SseJ to redox stress in sifAsseJ, the double mutant was complemented by integration of sifA2HA in the chromosome, effectively creating a sseJ single-deletion mutant.…”

Rab Proteins and the Compartmentalization of the Endosomal System

“…Rab11 isoforms and their downstream effectors have critical roles in cell polarity, and defects underlie cancer, gastrointestinal, and degenerative disease (for reviews, see Jing and Prekeris 2009;Kelly et al 2012;Mitra et al 2012). Rab9 regulates the recycling of cargo (mannose-6-phosphate receptor) from late endosomes to the Golgi complex (Lombardi et al 1993;McGourty et al 2012;Dong et al 2013). The described GTPases contribute to the functional endosomal compartmentalization and cargo transport to early endosomes, plasma membrane, and Golgi recycling, and transport to degradation.…”

Burkholderia pseudomallei survival in lung epithelial cells benefits from miRNA-mediated suppression of ATG10

“…Preliminary evidence has indicated that several pathogens, such as Shigella, Salmonella, Mycobacteria, and influenza A virus, have evolved mechanisms that evade the autophagic response. [8][9][10][11] B. pseudomallei has the capacity to invade a number of cultured mammalian cell lines. 4 After entry, B. pseudomallei utilizes numerous strategies that enable it to survive in such a specialized niche as the intracellular environment.…”