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A more recent version of this article appeared on July 1, 2004
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Submitted on February 3, 2004
Revised on April 12, 2004
Accepted on April 14, 2004
1 Department of Life Sciences, University of Toronto at Scarborough, 1265 Military Trail, Toronto, Ontario, Canada M1C 1A4
2 Infection, Immunity and Repair, The Hospital for Sick Children, 555 University Ave., Toronto, Ontario, Canada M5G 1X8
3 Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Universita degli Studi di Lecce, Via Monteroni, Lecce, Italy 73100
4 Division of Cell Biology, The Hospital for Sick Children, 555 University Ave., Toronto, Ontario, Canada M5G 1X8
5 Biotechnology Laboratory and Departments of Biochemistry and Molecular Biology, Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia, Canada, V6T 1Z3
* Corresponding author. E-mail address: sga{at}sickkids.ca.
Following invasion of epithelial cells, Salmonella enterica Typhimurium resides within membrane-bound vacuoles where it survives and replicates. Like endocytic vesicles, the Salmonella-containing vacuoles (SCV) undergo a maturation process that involves sequential acquisition of Rab5 and Rab7, and displacement toward the microtubule-organizing center. However, SCV 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 RILP (Rab7-Interacting Lysosomal Protein), an effector protein that can simultaneously associate with the dynein motor complex. Unlike the early SCV, the Salmonella-induced filaments (Sifs) formed later are devoid of RILP and dynein, despite the presence of active Rab7 on their membranes. Kinesin appears 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.