Quinone reductase inhibitors block SAPK/JNK and NFκB pathways and potentiate apoptosis

A variety of environmental stresses stimulate the mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEKK) > stress-activated protein kinase (SAPK)-ERK kinase (SEK) > SAPK/c-Jun NH2-terminal kinase (JNK) stress-activated protein kinase cascade and coordinately activate the transcription factor NF kappa B, Mechanisms of stress activation upstream of MEKK1 have not been precisely determined, Redox mechanisms involving sulfhydryls are likely because N-acetyl-cysteine at millimolar concentrations blocks stress signals. Because intracellular sulfhydryl concentrations can be regulated through redox cycling involving reactive quinones (1), we tested the ability of quinone reductase inhibitors to alter stress signaling, Several quinone reductases are inhibited by dicoumarol, a coumarin derivative, Dicoumarol prevented SAPK activation in vivo by chemical cell stressors and also prevented SAPK activation induced by expression of the tumor necrosis factor alpha (TNF alpha) receptor-associated protein TRAF2 but not by expression of truncated active MEKK1, Other coumarin derivatives failed to block. SAPK activation, but other inhibitors of quinone reductases, particularly menadione, similarly blocked SAPK. activation. Cells deficient in a major quinone reductase, NQO1, displayed hypersensitivity to dicoumarol stress inhibition, whereas SAPK in cells reconstituted with the NQO1 gene displayed relative dicoumarol resistance. Consistent with the proposed role of overlapping upstream signaling cascades in activation of NF kappa B, dicoumarol also blocked NF kappa B activation in primary macrophages stimulated with either lipopolysaccharide or TNF alpha In addition, dicoumarol strongly potentiated TNF alpha-induced apoptosis in HeLa cells, probably by blocking the anti-apoptotic effect of NF kappa B, The ability of dicoumarol to simultaneously inhibit SAPK and NF kappa B activation and to potentiate apoptotic cell death suggests that SAPK is not an obligate participant in apoptosis, Dicoumarol, currently in clinical use as an oral anticoagulant, represents a potential therapeutic inhibitor of the SAPK and NF kappa B response.