title: Rac mediates TNF-induced cytokine production via modulation of NF-kappaB.
abstract: TNF is a key factor in a variety of inflammatory diseases. Here we report that TNF induced pro-inflammatory cytokine synthesis of IL-6 and IL-8 is mediated by the Rho GTPase Rac. TNF induces p42/p44, p54 and p38 MAPK kinase; these kinases have been implicated in control of cytokine synthesis. However, over-expression of a dominant negative form of Rac strongly inhibited TNF-induced p42/44 MAPK kinase activation, but had little effect upon JNK and no effect upon p38 MAPK activity. Another key signalling pathway controlling cytokine expression is NF-kappaB. When analyzing TNF-induced NF-kappaB activity via luciferase-reporter assays or via EMSA, we were able to show that the dominant negative version of Rac could completely abrogate TNF-induced NF-kappaB activity. In addition, we also observed that inhibition of the ERK pathway led to a reduction in TNF-induced NF-kappaB transcriptional activity; this was accompanied by an ablation of TNF-induced p65 phosphorylation at serine 276. This would suggest that TNF-induced activation of Rac, lies upstream of NF-kappaB activation, and that the inhibition of this pathway results in inhibition of cytokine production.
authors.affiliation: Kennedy Institute of Rheumatology Division, Imperial College London, Hammersmith, London W6 8LH, United Kingdom. lynn.williams@imperial.ac.uk
authors.forename: Lynn M
authors.initials: LM
authors.lastname: Williams
authors.forename: Ferdinand
authors.initials: F
authors.lastname: Lali
authors.forename: Kate
authors.initials: K
authors.lastname: Willetts
authors.forename: Cristina
authors.initials: C
authors.lastname: Balague
authors.forename: Nuria
authors.initials: N
authors.lastname: Godessart
authors.forename: Fionula
authors.initials: F
authors.lastname: Brennan
authors.forename: Marc
authors.initials: M
authors.lastname: Feldmann
authors.forename: Brian M J
authors.initials: BM
authors.lastname: Foxwell
mesh_terms: D002460:Cell Line; D002478:Cells, Cultured; D005347:Fibroblasts; D006801:Humans; D015850:Interleukin-6 / Q000096:biosynthesis* / Q000276:immunology; D016209:Interleukin-8 / Q000096:biosynthesis* / Q000276:immunology; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D016328:NF-kappa B / Q000276:immunology / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology / Q000378:metabolism*; D020744:rac GTP-Binding Proteins / Q000276:immunology / Q000378:metabolism*
chemical_list: D015850:Interleukin-6; D016209:Interleukin-8; D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D020929:Mitogen-Activated Protein Kinase Kinases; D020744:rac GTP-Binding Proteins