Riboflavin kinase couples TNF receptor 1 to NADPH oxidase

Abstract

Reactive oxygen species (ROS) produced by NADPH oxidase function as defence and signalling molecules related to innate immunity and various cellular responses. The activation of NADPH oxidase in response to plasma membrane receptor activation depends on the phosphorylation of cytoplasmic oxidase subunits, their translocation to membranes and the assembly of all NADPH oxidase components. Tumour necrosis factor (TNF) is a prominent stimulus of ROS production, but the molecular mechanisms by which TNF activates NADPH oxidase are poorly understood. Here we identify riboflavin kinase (RFK, formerly known as flavokinase) as a previously unrecognized TNF-receptor-1 (TNFR1)-binding protein that physically and functionally couples TNFR1 to NADPH oxidase. In mouse and human cells, RFK binds to both the TNFR1-death domain and to p22(phox), the common subunit of NADPH oxidase isoforms. RFK-mediated bridging of TNFR1 and p22(phox) is a prerequisite for TNF-induced but not for Toll-like-receptor-induced ROS production. Exogenous flavin mononucleotide or FAD was able to substitute fully for TNF stimulation of NADPH oxidase in RFK-deficient cells. RFK is rate-limiting in the synthesis of FAD, an essential prosthetic group of NADPH oxidase. The results suggest that TNF, through the activation of RFK, enhances the incorporation of FAD in NADPH oxidase enzymes, a critical step for the assembly and activation of NADPH oxidase.

cIAP1 and TAK1 protect cells from TNF-induced necrosis by preventing RIP1/RIP3-dependent reactive oxygen species production

“…A recent study reported that ROS generation requires recruitment of riboflavin kinase (RFK) and the NADPH oxidases Nox1 and Nox2 to TNFR1. 26,28 We found that specific repression of components of the NADPH oxidase complex (RFK, Nox1, and p22phox) by RNAi did not affect death induced by TNF or TNF þ BV6, but repression of NADH dehydrogenase (ubiquinone) 1 beta subcomplex 8 (NDUFB8) (subunit of mitochondrial complex I) strongly attenuated it (Figure 5f and data not shown). Our results therefore indicate that, in the absence of cIAP1, TNF-induced necrosis in L929 cells requires RIP1/3-mediated mitochondrial ROS production.…”

Glucocorticoids and Tumor Necrosis Factor α Increase Oxidative Stress and Suppress Wnt Protein Signaling in Osteoblasts

“…Although the mitochondrial electron transport chain is the main mechanism of ROS generation, oxygen radicals can also be produced by other enzymatic sources like NADPH oxidase, xanthine oxidase, and NOS. It has been shown previously that TNF␣ stimulates ROS generation by the NADP oxidase 1 (Nox1) system at the cell membrane (52,53) and that GCs increase oxidative stress by activating xanthine oxidase (54,55). Whether p66…”

Cross talk between stimulated NF-κB and the tumor suppressor p53

“…Similar as in replicational stress, linking p53 to NF-kB signaling allows antiapoptotic gene expression in cells where the tumor suppressor can execute apoptosis if necessary. Such situations arise, for example, when TNF promotes inflammation-related tumorigenesis by NF-kB activation (Pikarsky et al, 2004;Hayashi et al, 2007) or by TNF-mediated induction of reactive oxygen species bearing mutagenic potential (Yan et al, 2006;Li et al, 2007;Yazdanpanah et al, 2009). Of note, p53-positive cells can protect themselves from such cyto-and genotoxic molecules by inducing MnSOD, an antioxidizing enzyme known to balance TNF signaling (Gilmore and Herscovitch, 2006).…”