Activation of AP-1 through the MAP kinase pathway: a potential mechanism of the carcinogenic effect of arenediazonium ions.
Arenediazonium ions such as those found in the common mushroom Agaricus bisporus have been convincingly demonstrated to be tumorigenic. The specific mechanism of their tumorigenicity remains unclear. It has been shown that arenediazonium ions can be metabolized to aryl radicals, and that reaction of these aryl radicals with DNA produces aryl adducts. These metabolic processes also produce the reactive oxygen species superoxide and hydroxyl radicals which have been implicated in AP-1 activation. To further investigate the mechanism of tumorigenesis by arenediazonium ions, we studied the effect of a representative arenediazonium ion on AP-1 activation and phosphorylation of the signal transduction proteins ERK1, ERK2, JNK, and p38 kinase, both in vitro and in vivo. We also identified the specific radicals produced by spin trapping and ESR analysis. Here, it was found that p-methylbenzenediazonium ion (2a) induced a 16-fold increase in the extent of AP-1 activation at micromolar concentrations, and that this increase coincided with phosphorylation of the signaling kinases ERK1 and -2 and p38 kinase, but not JNK, in JB6 mouse epithelial cells. In vivo studies using AP-1 luciferase reporter-bearing transgenic mice supported the increase in the extent of AP-1 activation in 2a-treated mice over controls, and showed that this effect was different in different tissue types. The antioxidant N-acetylcysteine (NAC), a general antioxidant, showed an inhibitory effect on 2a-mediated AP-1 induction, while aspirin, a hydroxyl radical scavenger, had no effect. Spin trapping studies showed that while NAC suppressed radical formation from 2a, aspirin did not alter radical production from 2a. It appears that 3a, a carbon-centered radical formed from 2a, is responsible for AP-1-induced activation, and therefore, radical species that are not oxygen-centered are also capable of inducing AP-1. These results represent a step toward understanding the mechanism of tumorigenicity of arenediazonium ions.
Gannett
P M
PM
Department of Basic Pharmaceutical Sciences, School of Pharmacy, West Virginia University, P.O. Box 9530, Morgantown, West Virginia 26506, USA. pgannett@hsc.wvu.edu
Ye
J
J
Ding
M
M
Powell
J
J
Zhang
Y
Y
Darian
E
E
Daft
J
J
Shi
X
X
D000111:Acetylcysteine / Q000737:chemistry; D000818:Animals; D002273:Carcinogens / Q000633:toxicity*; D002460:Cell Line; D003979:Diazonium Compounds / Q000633:toxicity*; D004578:Electron Spin Resonance Spectroscopy; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D020536:Enzyme Activators / Q000633:toxicity*; D016166:Free Radical Scavengers / Q000737:chemistry; D007202:Indicators and Reagents; D008156:Luciferases / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism / Q000502:physiology*; D010766:Phosphorylation; D010957:Plasmids; D011494:Protein Kinases / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000502:physiology*
D002273:Carcinogens; D003979:Diazonium Compounds; D020536:Enzyme Activators; D016166:Free Radical Scavengers; D007202:Indicators and Reagents; D018808:Transcription Factor AP-1; D008156:Luciferases; D011494:Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D000111:Acetylcysteine