Benzyl isothiocyanate (BIT), a microconstituent found in cruciferous vegetables, is known to be a potent inducer of the detoxification enzyme, NAD(P)H: quinone reductase (QR). QR catalyzes a two-electron transfer to a wide variety of redox-cycling species, including quinones, transforming them into dihydrodiols, thereby preventing the mutation of DNA and reducing cancer risk. The upstream signaling mechanisms that lead to the induction of QR remain unclear. The 5' promoter region of the human QR gene contains the cis-acting AP-1 and NFkappaB transcription factor binding sites. When HT29 human colon cells were exposed to 25microM benzyl isothiocyanate, AP-1 binding increased, beginning at 3 hours and increasing until 16 hours. NFkappaB binding also increased, reaching a maximum at around 6 hours. We also found that c-Jun N-terminal kinase (JNK), which phosphorylates c-Jun, a component of AP-1, was activated 9-fold over controls, beginning at 60 minutes. The temporal sequence of these events supports the idea that JNK is involved in the induction of QR and that this is an initial event preceding an increase in transcription factor binding and subsequent QR activity.
Copyright 1999 Academic Press.