1 The first two authors contributed equally to this study.
SifA, a Type III Secreted Effector of Salmonella typhimurium, Directs Salmonella-Induced Filament (Sif) Formation Along Microtubules
Article first published online: 9 MAY 2002
Volume 3, Issue 6, pages 407–415, June 2002
How to Cite
Brumell, J. H., Goosney, D. L. and Finlay, B. B. (2002), SifA, a Type III Secreted Effector of Salmonella typhimurium, Directs Salmonella-Induced Filament (Sif) Formation Along Microtubules. Traffic, 3: 407–415. doi: 10.1034/j.1600-0854.2002.30604.x
- Issue published online: 9 MAY 2002
- Article first published online: 9 MAY 2002
- Received 26 November 2001,revised andaccepted for publication 4 March 2002
- microbial pathogenesis;
- type III secretion
A unique feature of Salmonella enterica serovar typhimurium (S. typhimurium) is its ability to enter into (invade) epithelial cells and elongate the vacuole it occupies into tubular structures called Salmonella-induced filaments (Sifs). This phenotype is dependent on SifA, a Salmonella virulence factor that requires the SPI-2-encoded type III secretion system for delivery into host cells. Previous attempts to study SifA and other type III secreted proteins have been limited by a lack of suitable reagents. We examined SifA function by expressing SifA with two internal hemagglutinin epitope tags. By employing subcellular fractionation techniques, we determined that translocated SifA was membrane associated in infected HeLa cells. Confocal microscopy revealed that SifA associated with the Salmonella vacuole and with Sifs. Our analysis also revealed that microtubules serve as a scaffold for Sifs, and that SifA colocalizes with microtubules at sites of interaction between lysosomal glycoprotein-containing vesicles and Sifs. Treatment with the microtubule inhibitor nocodazole blocked Sif formation but did not prevent SifA translocation into the Salmonella vacuole. While polymerized actin has been observed on Sifs, this phenotype was transient and did not play a role in promoting or maintaining Sif formation. Our findings demonstrate the essential role of microtubule dynamics in the formation of Sifs and the utility of this epitope tagging strategy for the study of bacterial type III secreted proteins.