Fragile X-related Protein FXR1P Regulates Proinflammatory Cytokine Tumor Necrosis Factor Expression at the Post-transcriptional Level

Abstract

Tumor necrosis factor (TNF) is regulated post-transcriptionally by the AU-rich element (ARE) within the 3-untranslated region of its mRNA. This regulation modulates translational efficacy and mRNA stability. By using a cRNA probe containing the TNF ARE sequence, we screened a macrophage protein expression library and identified FXR1P. Macrophages that we generated from FXR1 knock-out mice had enhanced TNF protein production compared with wild type macrophages following activation. Expression of several other proteins that are regulated by ARE sequences was also affected by FXR1P deficiency. A GFP-ARE reporter that has green fluorescent protein (GFP) expression under control of the 3-untranslated region of TNF mRNA had enhanced expression in transfected macrophages deficient in FXR1P. Finally, we found that the ablation of FXR1P led to a dramatically enhanced association of the TNF mRNA with polyribosomes demonstrating the important role of FXR1P in the post-transcriptional regulation of TNF expression. Our data suggest that release of this repression by FXR1P occurs during lipopolysaccharideinduced macrophage activation. Finally, complementation of the knock-out macrophages with recombinant FXR1P resulted in decreased TNF protein production, supporting our findings that FXR1P operates as a repressor of TNF translation.

Identifying candidate colon cancer tumor suppressor genes using inhibition of nonsense-mediated mRNA decay in colon cancer cells

“…FXR1, which is mutated in LS180 cells, has recently been shown to post-transcriptionally regulate the expression of genes containing AU-rich elements within the 3 0 -untranslated regions of their mRNA. This regulation modulates translational efficacy and mRNA stability (Garnon et al, 2005). The plant homeodomain finger protein (PHF14) gene that is mutated in HCT116 cells contains a plant homeodomain (PHD) finger domain known to be involved in chromatin-mediated transcriptional regulation (Aasland et al, 1995).…”

Regulation of monocyte induced cell migration by the RNA binding protein, FXR1

“…16 Moreover, FXR1 depletion resulted in altered expression of TNFa 23 and other cytokine and chemokine mRNAs 16 such as IL1b and CCL2 (Figs. [3][4] that are involved in monocyte functions such as neighboring cell migration.…”

“…FXR1 can regulate mRNA levels 16 apart from translation, 23 and could thereby, affect monocyte functions. We therefore, investigated the mRNAs that are affected by FXR1 depletion in serum grown and 24 h serum-starved cells.…”

“…6 FXR1 is similar to Fragile-X-Mental Retardation Protein 1 (FMR1), 4,[7][8][9][10][11][12][13][14] and is implicated at multiple levels of post-transcriptional control, including translation, mRNA stability and transport. 7-10, 12-13, 15-18 FXR1 is associated with negative regulation of specific growth factor and cytokine mRNAs in myocytes 5,[19][20][21][22] and macrophages, 16 which can control development, cell differentiation and cell state specific functions. However, our previous studies demonstrated that a spliced isoform of FXR1, FXR1a, promotes specific mRNA translation independent of RNA levels, in association with an altered microRNP (microRNA-protein complex), in distinct conditions, such as oocytes and quiescent (> 24 h, 30-48 h extended serum-starved) mammalian cells.…”

Suppression of Lipopolysaccharide-stimulated Tumor Necrosis Factor-α Production by Adiponectin Is Mediated by Transcriptional and Post-transcriptional Mechanisms

“…The stability of the TNF-␣ mRNA is regulated by the binding of several RNA-binding proteins, including tristetraprolin (TTP), HuR, and AUF-1 to the 3Ј-UTR (17). Recent data have also suggested an important role for microribonucleoprotein-related proteins, including fragile X mental retardation-related protein 1 and argonaute 2, in the post-transcriptional regulation of TNF-␣ mRNA (28,29). Micro-RNAs and microribonucleoprotein-related proteins appear to be involved in both translational repression and activation (29,30) as well as mRNA stability (31).…”