Evidence that reactive oxygen species do not mediate NF- B activation

Abstract

It has been postulated that reactive oxygen species (ROS) may act as second messengers leading to nuclear factor (NF)-kB activation. This hypothesis is mainly based on the ®ndings that N-acetyl-L-cysteine (NAC) and pyrrolidine dithiocarbamate (PDTC), compounds recognized as potential antioxidants, can inhibit NF-kB activation in a wide variety of cell types. Here we reveal that both NAC and PDTC inhibit NF-kB activation independently of antioxidative function. NAC selectively blocks tumor necrosis factor (TNF)-induced signaling by lowering the af®nity of receptor to TNF. PDTC inhibits the IkB± ubiquitin ligase activity in the cell-free system where extracellular stimuli-regulated ROS production does not occur. Furthermore, we present evidence that endogenous ROS produced through Rac/NADPH oxidase do not mediate NF-kB signaling, but instead lower the magnitude of its activation.

Role of reactive oxygen species in brucein D-mediated p38-mitogen-activated protein kinase and nuclear factor-κB signalling pathways in human pancreatic adenocarcinoma cells

“…Surprisingly, pre-treatment of the most widely used antioxidant, NAC, did not show any regulatory effect on NF-kB in PANC-1 cells with or without BD treatment. Hayakawa et al (2003) showed that endogenous ROS produced through Rac/NADPH oxidase do not mediate NF-kB signalling. It is thus plausible that the inhibition of NF-kB activity was independent of the ROS induced by BD treatment.…”

“…Moreover, we have recently reported that BD induces apoptosis in pancreatic cancer cells by activating the phosphorylation of p38-mitogenactivated protein kinase (MAPK) (Lau et al, 2009). Although the function of ROS in the activation of p38-MAPK (Yi et al, 2004;Lee et al, 2008;Chen et al, 2009), and the regulation of NF-kB activity (Hayakawa et al, 2003;Fujioka et al, 2004), has been characterised in substances-induced apoptosis in various cancer cells, the involvement of ROS in BD-induced pancreatic cancer cell apoptosis is yet to be elucidated. Given that ROS have an important function in an array of biological responses and diverse signalling pathways, we hypothesised that BD activates pro-apoptotic pathways through the enhancement of ROS production and the inhibition of NF-kB activity in pancreatic cancer cells.…”

Inhibitors of NF-κB signaling: 785 and counting

“…Therefore, all antioxidants probably do not act at the same level to inhibit NF-kB. Moreover, at least one report has suggested that the NF-kB inhibitory activity of PDTC can be separated from its antioxidant activity (Hayakawa et al, 2003).…”

Signals from within: the DNA-damage-induced NF-κB response

“…7 Several authors argued that mainly cytoplasmic effects such as the production of oxygen radicals or sphingomyelin breakdown products like ceramide cause DNA damageinduced NF-kB activation, while the induction of DNA breaks would be an unrelated event. These studies are mainly based on the use of antioxidants such as PDTC or NAC as inhibitors of the DNA damage-induced NF-kB response (e.g., Simon et al, 8 Mohan and Meltz, 9 Kaltschmidt et al, 10 Boland et al, 11 Bian et al 12 and Wang et al 13 ) and on the argument that NF-kB has been described as an oxygen stress-responsive factor (although the latter has been questioned lately 14 ). However, there are at least as many reports showing the opposite result (e.g., Li et al 15 and Hellin et al 16 ), and it is becoming more and more apparent that the inhibitory effects of PDTC or NAC are not always related to their antioxidant properties.…”

“…However, there are at least as many reports showing the opposite result (e.g., Li et al 15 and Hellin et al 16 ), and it is becoming more and more apparent that the inhibitory effects of PDTC or NAC are not always related to their antioxidant properties. 14,17 Furthermore, camptothecin (CPT) induces NF-kB activation without being able to generate free radicals in a cell, 18 strongly suggesting that other mechanisms must be operational as well.…”