p38 mitogen-activated protein kinase negatively regulates the induction ofphase II drug-metabolizing enzymes that detoxify carcinogens

Phase II drug-metabolizing enzymes, such as glutathione S-transferase and q uinone reductase, play an important role in the detoxification of chemical carcinogens. The induction of these detoxifying enzymes by a variety of age nts occurs at the transcriptional level and is regulated bg a cis-acting el ement, called the antioxidant response element (ARE) or electrophile-respon se element. In this study, we identified a signaling kinase pathway that ne gatively regulates ARE-mediated gene expression. Treatment of human hepatom a HepG2 and murine hepatoma Hepalclc7 cells with tert-butylhydroquinone (tB HQ) stimulated the activity of p38, a member of mitogen-activated protein k inase family. Inhibition of p38 activation by its inhibitor, SB203580, enha nced the induction of quinone reductase activity and the activation of ARE reporter gene by tBHQ. In contrast, SB202474, a negative analog of SB203580 , had little effect. Consistent with this result, interfering with the p38 kinase pathway by overexpression of a dominant-negative mutant of p38 or MK K3, an immediate upstream regulator of p38, potentiated the activation of t he ARE reporter gene by tBHQ, whereas the wild types of p38 and MKK3 dimini shed such activation. In addition, inhibition of p38 activity augmented the induction of ARE reporter gene activity by tert-butylhydroxyanisole, sulfo raphane, and p-naphthoflavone. Thus, p38 kinase pathway functions as a nega tive regulator in the ARE-mediated induction of phase II detoxifying enzyme s.