SalmonellaImpairs RILP Recruitment to Rab7 during Maturation of Invasion Vacuoles

Abstract

After invasion of epithelial cells, Salmonella enterica Typhimurium resides within membrane-bound vacuoles where it survives and replicates. Like endocytic vesicles, the Salmonella-containing vacuoles (SCVs) undergo a maturation process that involves sequential acquisition of Rab5 and Rab7 and displacement toward the microtubule-organizing center. However, SCVs fail to merge with lysosomes and instead develop subsequently into a filamentous network that extends toward the cell periphery. We found that the initial centripetal displacement of the SCV is due to recruitment by Rab7 of Rab7-interacting lysosomal protein (RILP), an effector protein that can simultaneously associate with the dynein motor complex. Unlike the early SCVs, the Salmonella-induced filaments (Sifs) formed later are devoid of RILP and dynein, despite the presence of active Rab7 on their membranes. Kinesin seems to be involved in the elongation of Sifs. SifA, a secreted effector of Salmonella, was found to be at least partly responsible for uncoupling Rab7 from RILP in Sifs and in vitro experiments suggest that SifA may exert this effect by interacting with Rab7. We propose that, by disengaging RILP from Rab7, SifA enables the centrifugal extension of tubules from the Salmonella-containing vacuoles, thereby providing additional protected space for bacterial replication.

The Salmonella effector protein PipB2 is a linker for kinesin-1

“…Perhaps SifA regulates some low level of kinesin-1 recruited to the SCV independent of PipB2 or possesses another unidentified activity, the lack of which is responsible for SCV membrane instability and the atypical intracellular positioning. This activity could possibly be the regulation of another molecular motor such as dynein because inhibition of dynein activity has been shown to stabilize the sifA Ϫ SCV to the same extent as does inhibition of kinesin activity (18), and this retrograde molecular motor is recruited onto the SCV by binding to a rab7͞RILP complex under certain circumstances (24,25). SifA contains a pentapeptide motif that has the potential to mimic small GTPases in their active GTP-bound form (26) and thus could potentially modulate the rab7͞RILP͞dynein cascade (27).…”

The Salmonella-containing vacuole—Moving with the times

“…But other data suggests that SpiC is a component of the T3SS2 translocon rather than an effector [39] and this issue remains unresolved. Redistribution of SCVs from the cell periphery to the MTOC/juxtanuclear region is mediated at least in part by the small GTP-binding protein rab7 together with its effector RILP, which are required for recruitment of the microtubule-based motor dynein [40][41][42]. Once at the MTOC two T3SS2 effectors that have the ability to interact with one another, SseG and SseF, are required to maintain SCV positioning over longer periods of time [43][44][45].…”

The Oxysterol-binding Protein Homologue ORP1L Interacts with Rab7 and Alters Functional Properties of Late Endocytic Compartments

“…Rab7 also regulates the microtubule-dependent motility of late endocytic compartments (Cantalupo et al, 2001;Jordens et al, 2001;Lebrand et al, 2002;Harrison et al, 2003). In addition, Rab7 has been connected to a variety of LE functions, such as cellular vacuolization induced by Helicobacter pylori (Papini et al, 1997;Li et al, 2004), intracellular replication of Salmonella (Guignot et al, 2004;Harrison et al, 2004;Marsman et al, 2004), maturation of phagosomes Vieira et al, 2003;Ng Yan Hing et al, 2004), formation of autophagic vacuoles (Gutierrez et al, 2004;Jager et al, 2004), internalization/degradation of nutrient receptors (Edinger et al, 2003), and cholesterol and sphingolipid egress from LEs (Choudhury et al, 2002). Mutations of the Rab7 gene in humans have been identified as the cause of ulcero-mutilating neuropathy (Verhoeven et al, 2003;Houlden et al, 2004).…”