title: Rac1 and Cdc42 are required for phagocytosis, but not NF-kappaB-dependent gene expression, in macrophages challenged with Pseudomonas aeruginosa.
abstract: Macrophages respond to Gram-negative bacterial pathogens by phagocytosis and pro-inflammatory gene expression. These responses may require GTPases that have been implicated in cytoskeletal alterations and activation of NF-kappaB. To determine the role of Rac1 and Cdc42 in signal transduction events triggered by Pseudomonas aeruginosa, we expressed GTP binding-deficient alleles of Rac1 or Cdc42, or Chim-GAP, a Rac1/Cdc42-specific GTPase-activating protein domain, in a subline of RAW 264.7 cells, and challenged the transfected cells with a laboratory strain of P. aeruginosa, PAO1. Expression of Rac1 N17, Cdc42 N17, or Chim-GAP led to a marked reduction of phagocytosis. In contrast, nuclear translocation of p65 NF-kappaB was unaffected by expression of the same constructs. Incubation of macrophages with PAO1 led to NF-kappaB-dependent expression of inducible nitric-oxide synthase, COX-2, and tumor necrosis factor-alpha, which was unaffected by inhibition of Rac1 or Cdc42 function. Isogenic strains of PAO1 that lacked surface adhesins were poorly ingested; however, they induced pro-inflammatory gene expression with an efficiency equal to that of PAO1. These results indicate that the signal transduction events leading to phagocytosis and pro-inflammatory protein expression are distinct. Rac1 and Cdc42 serve as effectors of phagocytosis, but not NF-kappaB-dependent gene expression, in the macrophage response to P. aeruginosa.
authors.affiliation: Department of Pediatrics, Columbia University, New York, New York 10032, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Lee
authors.forename: D
authors.initials: D
authors.lastname: Cox
authors.forename: J
authors.initials: J
authors.lastname: Li
authors.forename: S
authors.initials: S
authors.lastname: Greenberg
mesh_terms: D000818:Animals; D001692:Biological Transport; D002451:Cell Compartmentation; D002467:Cell Nucleus; D002478:Cells, Cultured; D020848:Chimerin 1 / Q000235:genetics / Q000378:metabolism; D051546:Cyclooxygenase 2; D036781:Fimbriae Proteins; D005408:Flagellin; D015870:Gene Expression; D006160:Guanosine Triphosphate / Q000378:metabolism; D018836:Inflammation Mediators / Q000378:metabolism; D007527:Isoenzymes / Q000096:biosynthesis; D008264:Macrophages / Q000382:microbiology*; D008565:Membrane Proteins; D051379:Mice; D009154:Mutation; D016328:NF-kappa B / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000096:biosynthesis; D052247:Nitric Oxide Synthase Type II; D010587:Phagocytosis; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis; D011550:Pseudomonas aeruginosa / Q000472:pathogenicity*; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis; D020764:cdc42 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D020848:Chimerin 1; D018836:Inflammation Mediators; D007527:Isoenzymes; D008565:Membrane Proteins; D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D005408:Flagellin; D036781:Fimbriae Proteins; D006160:Guanosine Triphosphate; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein