Regulation of CYP1A1 by indolo[3,2-b]carbazole in murine hepatoma cells.
To determine the basis for unexpected differences in CYP1A1 inducing potencies and efficacies for the diet-derived indole derivative, indolo[3,2-b]carbazole (ICZ) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), we conducted a systematic analysis of events involved in the induced expression of CYP1A1 in murine hepatoma-derived cell lines (Hepa-1). In contrast to the effects of TCDD, induction kinetics and CYP1A1 mRNA half-life were dependent on ICZ concentration, and the response from low doses of inducer was transient due to rapid clearance of ICZ. TCDD and ICZ produced the same maximum response (i.e. equal efficacies) from a TCDD-responsive CAT reporter construct in Hepa-1 cells. When measured by the immediate responses associated with CYP1A1 expression, including cellular uptake of inducer, receptor transformation and binding to DRE (gel mobility shift assay), initiation of transcription (nuclear run-on assay), and short-term accumulation of mRNA (Northern blot assay), ICZ also exhibited an efficacy equal to that of TCDD and a potency that corresponds to its receptor affinity. ICZ is a potent and selective noncompetitive inhibitor of ethoxyresorufin O-deethylase activity (Ki = 1.5 nM). Taken together these results indicate that ICZ is a bifunctional modulator of CYP1A1 expression with intrinsic efficacy equal to that of TCDD.
Chen
Y H
YH
Department of Nutritional Sciences, University of California, Berkeley 94720, USA.
Riby
J
J
Srivastava
P
P
Bartholomew
J
J
Denison
M
M
Bjeldanes
L
L
D000818:Animals; D001483:Base Sequence; D002227:Carbazoles / Q000008:administration & dosage* / Q000378:metabolism; D019363:Cytochrome P-450 CYP1A1; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D004357:Drug Synergism; D015870:Gene Expression / Q000187:drug effects; D066298:In Vitro Techniques; D007211:Indoles / Q000008:administration & dosage* / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008114:Liver Neoplasms, Experimental; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D010088:Oxidoreductases / Q000037:antagonists & inhibitors / Q000378:metabolism; D000072317:Polychlorinated Dibenzodioxins / Q000008:administration & dosage*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D014407:Tumor Cells, Cultured
D002227:Carbazoles; D065607:Cytochrome P-450 Enzyme Inhibitors; D004268:DNA-Binding Proteins; D007211:Indoles; D009838:Oligodeoxyribonucleotides; D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; C075954:indolo(3,2-b)carbazole; D003577:Cytochrome P-450 Enzyme System; D010088:Oxidoreductases; D019363:Cytochrome P-450 CYP1A1