Activation of NF-kappa B by ER stress requires both Ca2+ and reactive oxygen intermediates as messengers

The eukaryotic transcription factor NF-kappa B is activated by a large variety of stimuli. We have recently shown that ER stress, caused by an aberrant accumulation of membrane proteins within this organelle, also activates NF-kappa B. Here, we show that activation of NF-kappa B by ER stress requires an increase in the intracellular levels of both reactive oxygen intermediates (ROIs) and Ca2+. Two distinct intracellular Ca2+ chelators and a panel of structurally unrelated antioxidants prevented NF-kappa B activation by various ER stress-eliciting agents, whereas only antioxidants but not the Ca2+ chelators prevented NP-kappa B activation by the inflammatory cytokine TNF-alpha. Consistent with an involvement of calcium, the ER-resident Ca2+-ATPase inhibitors thapsigargin and cyclopiazonic acid (CPA), which trigger a rapid efflux of Ca2+ from the ER, also potently activated NF-kappa B. Pretreatment with a Ca2+ chelator abrogated this induction, The Ca2+ chelator BAPTA-AM inhibited ROI thapsigargin and CPA treatment, increase preceded ROI formation during NF-kappa B activation. The selective inhibitory effect of the drug tepoxalin suggests that the peroxidase activity of cyclooxy-genases or lipoxygenases was responsible for the increased ROI production in response to Ca2+ release by thapsigargin.