The Type VI secretion system of Burkholderia cenocepacia affects multiple Rho family GTPases disrupting the actin cytoskeleton and the assembly of NADPH oxidase complex in macrophages.
Burkholderia cenocepacia is a Gram-negative opportunistic pathogen of patients with cystic fibrosis and chronic granulomatous disease. The bacterium survives intracellularly in macrophages within a membrane-bound vacuole (BcCV) that precludes the fusion with lysosomes. The underlying cellular mechanisms and bacterial molecules mediating these phenotypes are unknown. Here, we show that intracellular B. cenocepacia expressing a type VI secretion system (T6SS) affects the activation of the Rac1 and Cdc42 RhoGTPase by reducing the cellular pool of GTP-bound Rac1 and Cdc42. The T6SS also increases the cellular pool of GTP-bound RhoA and decreases cofilin activity. These effects lead to abnormal actin polymerization causing collapse of lamellipodia and failure to retract the uropod. The T6SS also prevents the recruitment of soluble subunits of the NADPH oxidase complex including Rac1 to the BcCV membrane, but is not involved in the BcCV maturation arrest. Therefore, T6SS-mediated deregulation of Rho family GTPases is a common mechanism linking disruption of the actin cytoskeleton and delayed NADPH oxidase activation in macrophages infected with B. cenocepacia.
Centre for Human Immunology, Department of Microbiology and Immunology Department of Medicine, University of Western Ontario, London, ON N6A 5C1, Canada.
Roberto
R
Rosales-Reyes
Alexander M
AM
Skeldon
Daniel F
DF
Aubert
Miguel A
MA
Valvano
D008841:Actin Cytoskeleton / Q000378:metabolism*; D000818:Animals; D057508:Burkholderia cenocepacia / Q000472:pathogenicity*; D002460:Cell Line; D006160:Guanosine Triphosphate / Q000378:metabolism; D008264:Macrophages / Q000201:enzymology / Q000378:metabolism / Q000382:microbiology*; D051379:Mice; D008954:Models, Biological; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors*; D009479:Neuropeptides / Q000037:antagonists & inhibitors*; D020764:cdc42 GTP-Binding Protein / Q000037:antagonists & inhibitors*; D020744:rac GTP-Binding Proteins / Q000037:antagonists & inhibitors*; D020830:rac1 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
D009479:Neuropeptides; C484602:Rac1 protein, mouse; D006160:Guanosine Triphosphate; D019255:NADPH Oxidases; D020764:cdc42 GTP-Binding Protein; D020744:rac GTP-Binding Proteins; D020830:rac1 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein