title: Fragile X-related protein FXR1 controls post-transcriptional suppression of lipopolysaccharide-induced tumour necrosis factor-alpha production by transforming growth factor-beta1.
abstract: Tumour necrosis factor-alpha (TNF-alpha) is a key mediator of inflammation in host defence against infection and in autoimmune disease. Its production is controlled post-transcriptionally by multiple RNA-binding proteins that interact with the TNF-alpha AU-rich element and regulate its expression; one of these is Fragile X mental retardation-related protein 1 (FXR1). The anti-inflammatory cytokine transforming growth factor-beta1 (TGF-beta1), which is involved in the homeostatic regulation of TNF-alpha, causes post-transcriptional suppression of lipopolysaccharide (LPS)-induced TNF-alpha production. We report here that this depends on FXR1. Using RAW 264.7 cells and bone marrow-derived macrophages (BMDMphi) stimulated with LPS and TGF-beta1, we show that TGF-beta1 inhibits TNF-alpha protein secretion, whereas TNF-alpha mRNA expression remains unchanged. This response is recapitulated by the 3'-UTR of TNF-alpha, which is known to bind FXR1. TGF-beta1 induces FXR1 with a pattern of expression distinct from that of tristetraprolin, T-cell intracellular antigen 1, or human antigen R. When FXR1 is knocked down, TGF-beta1 is no longer able to inhibit LPS-induced TNF-alpha protein production, and overexpression of FXR1 suppresses LPS-induced TNF-alpha protein production. Targeting the p38 mitogen-activated protein kinase pathway of LPS-treated cells with small molecule inhibitors can induce FXR1 protein and mRNA expression. In summary, TGF-beta1 opposes LPS-induced stabilization of TNF-alpha mRNA and reduces the amount of TNF-alpha protein, through induction of expression of the mRNA-binding protein FXR1.
authors.affiliation: Department of Cellular and Molecular Medicine, School of Medical Sciences, University of Bristol, Bristol, UK. t.khera@bristol.ac.uk
authors.forename: Tarnjit K
authors.initials: TK
authors.lastname: Khera
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Dick
authors.forename: Lindsay B
authors.initials: LB
authors.lastname: Nicholson
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D006801:Humans; D008070:Lipopolysaccharides / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D008264:Macrophages / Q000187:drug effects; D051379:Mice; D020297:Mice, Congenic; D008810:Mice, Inbred C57BL; D012333:RNA, Messenger / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D016601:RNA-Binding Proteins / Q000378:metabolism*; D014158:Transcription, Genetic; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology*; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism
chemical_list: C496283:Fxr1h protein, mouse; D008070:Lipopolysaccharides; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D053773:Transforming Growth Factor beta1; D014409:Tumor Necrosis Factor-alpha