Interaction of the Salmonella-containing Vacuole with the Endocytic Recycling System

Abstract

Upon entry of the pathogen Salmonella enterica serovar Typhimurium into host cells, the majority of bacteria reside in a membrane-bound compartment called the Salmonella-containing vacuole (SCV). Previous studies have established that the SCV transiently interacts with early endosomes but only acquires a subset of late endosomal/lysosomal proteins. However, the complete set of interactions between the SCV and the endocytic machinery has yet to be characterized. In this study, we have shown that four characterized regulators of endocytic recycling were present on the SCV after invasion. Interaction kinetics were different for each of the regulators; ARF6 and Rab4 associated immediately, but their presence was diminished 60 min post-infection, whereas syntaxin13 and Rab11 association peaked at 60 min. Using a dominant negative approach, we determined that Rab11 regulates the recycling of CD44 from the vacuole but had no effect on major histocompatibility complex (MHC) class I recycling. In contrast, syntaxin13 regulated the recycling of MHC class I but not of CD44. We also determined that maturation of the SCV, measured by the acquisition of lysosomal associated membrane protein-1, slowed when recycling was impaired. These findings suggest that protein movement through the endocytic recycling system is regulated through at least two concurrent pathways and that efficient interaction with these pathways is necessary for maturation of the Salmonella-containing vacuole. We also demonstrate the utility of using Salmonella invasion as a model of endosomal recycling events.

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

“…Previous studies have shown that intracellular pathogens either mimic or target these proteins to establish their niche in the host cells (20,21,24). Similarly, maturation of SCP also depends on the sequential removal and recruitment of different Rabs and syntaxins (2,3,15,19,28). In this study, we have determined the recruitment of different syntaxins on SCP at various stages of their maturation in macrophages and have shown that SCP specifically recruit higher amounts of Syntaxin6 after 90 min of internalization than at 5 min of internalization.…”

The Salmonella-containing vacuole—Moving with the times

“…By far the best-documented aspect of SCV biogenesis is the sequential delivery of endolysosomal membrane proteins that defines the conversion of early to intermediate SCVs. Thus the early SCV membrane is highly enriched in early endosome membrane markers, including EEA1, Rab5 and transferrin receptor, which are replaced within 20-40 min with late endosomal/lysosomal markers including Lamps and vATPase [7,8]. This change in membrane content is accompanied by a decrease in the luminal pH (pH scv ) to <4.5 [9,10] and redistribution of the SCV to a predominantly juxtanuclear position near the microtubule organizing center (MTOC) [11].…”

Manipulation of Rab GTPase Function by Intracellular Bacterial Pathogens

“…In the first step (0 to 15 min p.i. ), the SCV interacts with early endosomes and acquires the markers Rab4, Rab5, and EEA1 (175,181). The role of Rab5 in SCV biogenesis was explored by Baldeon and colleagues (12).…”

“…For example, SCVs recruit Rab11 and syntaxin 13, with a maximal association at 60 min p.i. (175). Using a dominant negative approach, we determined that Rab11 regulates the recycling of CD44 from SCVs but had no effect on major histocompatibility complex class I recycling.…”

“…These findings suggest that protein movement through the endocytic recycling system is regulated through at least two concurrent pathways and that efficient interaction with these pathways is necessary for the maturation of SCVs. Other factors involved in endosomal recycling (e.g., Arf6, Rab4, and Rab10) are also localized to SCVs and may promote the recycling of specific cargo from this compartment (175,176).…”