Role of a Mitogen-activated Protein Kinase Pathway in the Induction of Phase II Detoxifying Enzymes by Chemicals

• Published in: The Journal of biological chemistry Vol. 274; no. 39; pp. 27545 - 27552
• Main Authors: Yu, Rong, Lei, Wei, Mandlekar, Sandhya, Weber, Michael J., Der, Channing J., Wu, Jie, Kong, A.-N. Tony
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 24.09.1999; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; Antineoplastic Agents - pharmacology; Carcinoma, Hepatocellular; Enzyme Induction; Enzyme Inhibitors - pharmacology; Flavonoids - pharmacology; Genes, Reporter; Humans; Hydroquinones - pharmacology; Isothiocyanates; JNK Mitogen-Activated Protein Kinases; Liver Neoplasms; Liver Neoplasms, Experimental; Mice; Mitogen-Activated Protein Kinase 1 - metabolism; Mitogen-Activated Protein Kinases - metabolism; NAD(P)H Dehydrogenase (Quinone) - biosynthesis; NAD(P)H Dehydrogenase (Quinone) - genetics; Recombinant Proteins - biosynthesis; Signal Transduction; Thiocyanates - pharmacology; Tumor Cells, Cultured
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.274.39.27545

Mitogen-activated protein kinase (MAPK) cascades are activated by diverse extracellular signals and participate in the regulation of an array of cellular programs. In this study, we investigated the roles of MAPKs in the induction of phase II detoxifying enzymes by chemicals. Treatment of human hepatoma (HepG2) and murine hepatoma (Hepa1c1c7) cells withtert-butylhydroquinone (tBHQ) or sulforaphane (SUL), two potent phase II enzyme inducers, stimulated the activity of extracellular signal-regulated protein kinase 2 (ERK2) but not c-Jun N-terminal kinase 1. tBHQ and SUL also activated MAPK kinase. Inhibition of MAPK kinase with its inhibitor, PD98059, abolished ERK2 activation and impaired the induction of quinone reductase, a phase II detoxifying enzyme, and antioxidant response element (ARE)-linked reporter gene by tBHQ and SUL. Overexpression of a dominant-negative mutant of ERK2 also attenuated tBHQ and SUL induction of ARE reporter gene activity. Interestingly, although expression of Ras and its mutant forms showed distinct effects on basal ARE reporter gene activity, they did not affect the activation of reporter gene by the inducers. Furthermore, a dominant-negative mutant of Ras had little effect on ERK2 activation by tBHQ and SUL, implicating a Ras-independent mechanism. Indeed, both tBHQ and SUL were able to stimulate Raf-1 kinase activity in vivo as well as in vitro. Thus, our results indicate that the induction of ARE-dependent phase II detoxifying enzymes is mediated by a MAPK pathway, which may involve direct activation of Raf-1 by the inducers.