Salmonella Disrupts Host Endocytic Trafficking by SopD2-Mediated Inhibition of Rab7.

Intracellular bacterial pathogens of a diverse nature share the ability to evade host immunity by impairing trafficking of endocytic cargo to lysosomes for degradation, a process that is poorly understood. Here, we show that the Salmonella enterica type 3 secreted effector SopD2 mediates this process by binding the host regulatory GTPase Rab7 and inhibiting its nucleotide exchange. Consequently, this limits Rab7 interaction with its dynein- and kinesin-binding effectors RILP and FYCO1 and thereby disrupts host-driven regulation of microtubule motors.

Formin-mediated actin polymerization promotes Salmonella invasion.

Salmonella invade host cells using Type 3 secreted effectors, which modulate host cellular targets to promote actin rearrangements at the cell surface that drive bacterial uptake. The Arp2/3 complex contributes to Salmonella invasion but is not essential, indicating other actin regulatory factors are involved. Here, we show a novel role for FHOD1, a formin family member, in Salmonella invasion.

Salmonella exploits Arl8B-directed kinesin activity to promote endosome tubulation and cell-to-cell transfer.

The facultative intracellular pathogen Salmonella enterica serovar Typhimurium establishes a replicative niche, the Salmonella-containing vacuole (SCV), in host cells. Here we demonstrate that these bacteria exploit the function of Arl8B, an Arf family GTPase, during infection. Following infection, Arl8B localized to SCVs and to tubulated endosomes that extended along microtubules in the host cell cytoplasm.

Bacterial invasion: entry through the exocyst door.

Salmonella entry into host cells involves rearrangements of actin and mobilization of membranes. Here we discuss new findings showing that Salmonella recruits the exocyst complex, which plays a role in vesicle secretion, to the site of invasion to promote its entry.

The phosphoinositide phosphatase SopB manipulates membrane surface charge and trafficking of the Salmonella-containing vacuole.

Shifts in electrostatic surface charge of membranes have recently been highlighted as a significant factor contributing to protein targeting to the plasma membrane and nascent phagosomes. Intracellular, vacuole-adapted pathogens may also regulate surface charge of their vacuoles to establish a replicative niche. Since Salmonella enterica serovar Typhimurium controls trafficking of the Salmonella-containing vacuole (SCV) and inhibits its fusion with lysosomes, we investigated the contribution of surface charge to this process.

Salmonella-containing vacuoles: directing traffic and nesting to grow.

Salmonella enterica serovar Typhimurium (S. typhimurium) is a gram-negative facultative intracellular pathogen that can infect a broad range of mammalian hosts. Following invasion of host cells, the majority of S.

AP-1 and ARF1 control endosomal dynamics at sites of FcR mediated phagocytosis.

Phagocytosis, the mechanism of ingestion of large material and microorganisms, relies on actin polymerization and on the focal delivery of intracellular endocytic compartments. The molecular mechanisms involved in the formation and delivery of the endocytic vesicles that are recruited at sites of phagocytosis are not well characterized. Here we show that adaptor protein (AP)-1 but not AP-2 clathrin adaptor complexes are recruited early below the sites of particle attachment and are required for efficient receptor-mediated phagocytosis in murine macrophages.

A network of Rab GTPases controls phagosome maturation and is modulated by Salmonella enterica serovar Typhimurium.

Members of the Rab guanosine triphosphatase (GTPase) family are key regulators of membrane traffic. Here we examined the association of 48 Rabs with model phagosomes containing a non-invasive mutant of Salmonella enterica serovar Typhimurium (S. Typhimurium).

Linking exocytosis and endocytosis during phagocytosis.

Phagocytosis is used by macrophages, dendritic cells and neutrophils to capture and destroy pathogens and particulate antigens. Although localized assembly of actin filaments is the driving force for particle internalization, exocytosis of intracellular compartments, and in particular endocytic compartments, has been shown recently to be required for the early steps of phagosome formation. Here we report on the different compartments undergoing exocytosis during phagocytosis, with a special focus on late endosomes.

TI-VAMP/VAMP7 is required for optimal phagocytosis of opsonised particles in macrophages.

Phagocytosis relies on extension of plasmalemmal pseudopods generated by focal actin polymerisation and delivery of membranes from intracellular pools. Here we show that compartments of the late endocytic pathway, bearing the tetanus neurotoxin-insensitive vesicle-associated membrane protein (TI-VAMP/VAMP7), are recruited upon particle binding and undergo exocytosis before phagosome sealing in macrophages during Fc receptor (FcR)-mediated phagocytosis. Expression of the dominant-negative amino-terminal domain of TI-VAMP or depletion of TI-VAMP with small interfering RNAs inhibited phagocytosis mediated by Fc or complement receptors.

CLIPR-59 is a lipid raft-associated protein containing a cytoskeleton-associated protein glycine-rich domain (CAP-Gly) that perturbs microtubule dynamics.

We recently have identified a new cytoplasmic linker protein (CLIP), CLIPR-59, which is involved in the regulation of early endosome/trans-Golgi network dynamics. In contrast with CLIP-170, CLIPR-59 is not localized to microtubules at steady state but is associated with the trans-Golgi network and the plasma membrane. Here we show that the last 30 amino acids (C30) are sufficient for membrane targeting and that two cysteines in the C30 domain are palmitoylated.