2-acetylaminofluorene up-regulates rat mdr1b expression through generating reactive oxygen species that activate NF-κB pathway

Overexpression of multidrug resistance genes and their encoded P-glycoproteins is a major mechanism for the development of multidrug resistance in cancer cells, The hepatocarcinogen 2-acetylaminofluorene (2-AAF) efficiently activates rat mdr1b expression. However, the underlying mechanisms are largely unknown. In this study, we demonstrated that a NF-kappaB site on the mdr1b promoter was required for this induction. Overexpression of antisense p65 and I kappaB alpha partially abolished the induction. We then delineated the pathway through which 2-AAF activates NF-kappaB. 2-AAF treatment led to the increase of intracellular reactive oxygen species (ROS) which causes activation of IKK kinases, degradation of I kappaB beta (but not I kappaB alpha), and increase in NF-kappaB DNA binding activity. Consistent with the idea that ROS may participate in mdr1b regulation, antioxidant N-acetylcysteine inhibited the induction of mdr1b by 2-AAF. Overproduction of a physiological antioxidant glutathione (GSH) blocked the activation of IKK kinase complex and NF-kappaB DNA binding. Based on these results, we conclude that 2-AAF up-regulates mdr1b through the generation of ROS, activation of IKK kinase, degradation of I kappaB beta, and subsequent activation of NF-kappaB. This is the first report that reveals the specific cis-elements and signaling pathway responsible for the induction of mdr1b by the chemical carcinogen 2-AAF.