title: Expression of the Salmonella spp. virulence factor SifA in yeast alters Rho1 activity on peroxisomes.
abstract: The Salmonella typhimurium effector protein SifA regulates the assembly and tubulation of the Salmonella phagosome. SifA localizes to the phagosome and interacts with the membrane via its prenylated tail. SifA is a structural homologue of another bacterial effector that acts as a GTP-exchange factor for Rho family GTPases and can bind GDP-RhoA. When coexpressed with a bacterial lipase that is activated by RhoA, SifA can induce tubulation of mammalian endosomes. In an effort to develop a genetic system to study SifA function, we expressed SifA and characterized its activity in yeast. GFP-SifA predominantly localized to yeast peroxisomal membranes. Under peroxisome-inducing conditions, GFP-SifA reduced the number of free peroxisomes and promoted the formation of large peroxisomes with membrane invaginations. GFP-SifA activity depended on the recruitment to peroxisomes of wild-type Rho1p and Pex25p, a receptor for Rho1p. GFP-SifA could also rescue the actin organization defects in pex25Δ and rho1 mutants, suggesting that SifA may recruit and potentiate Rho1p activity. We reexamined the distribution of GFP-SifA in mammalian cells and found the majority colocalizing with LAMP1-positive compartment and not with the peroxisomal marker PMP70. Together, these data suggest that SifA may use a similar mode of action via Rho proteins to alter yeast peroxisomal and mammalian endosomal membranes. Further definition of SifA activity on yeast peroxisomes could provide more insight into its role in regulating host membrane dynamics and small GTPases.
authors.affiliation: Department of Medicine, Immunology, Microbiology, and Genome Sciences, University of Washington, Seattle, WA 98195, USA.
authors.forename: Dani B N
authors.initials: DB
authors.lastname: Vinh
authors.forename: Dennis C
authors.initials: DC
authors.lastname: Ko
authors.forename: Richard A
authors.initials: RA
authors.lastname: Rachubinski
authors.forename: John D
authors.initials: JD
authors.lastname: Aitchison
authors.forename: Samuel I
authors.initials: SI
authors.lastname: Miller
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D001426:Bacterial Proteins / Q000378:metabolism*; D016466:CHO Cells; D002451:Cell Compartmentation; D006224:Cricetinae; D003412:Cricetulus; D011992:Endosomes / Q000378:metabolism / Q000648:ultrastructure; D006023:Glycoproteins / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism / Q000648:ultrastructure; D008856:Microscopy, Fluorescence; D009154:Mutation / Q000235:genetics; D053140:Organelle Shape; D020675:Peroxisomes / Q000378:metabolism* / Q000648:ultrastructure; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology* / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D012486:Salmonella typhimurium / Q000472:pathogenicity*; D037521:Virulence Factors / Q000378:metabolism*; D020741:rho GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D000199:Actins; D001426:Bacterial Proteins; D006023:Glycoproteins; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; C421862:SifA protein, Salmonella; D037521:Virulence Factors; D049452:Green Fluorescent Proteins; C051302:RHO1 protein, S cerevisiae; D020741:rho GTP-Binding Proteins