title: Effect of transforming growth factor-beta1 on expression of aryl hydrocarbon receptor and genes of Ah gene battery: clues for independent down-regulation in A549 cells.
abstract: An inhibitory effect on both constitutive and inducible expression of cytochrome P450 isoenzymes has been shown for different cytokines and growth factors. We previously described an inhibition of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced CYP1A1 mRNA and enzyme activity by transforming growth factor-beta1 (TGF-beta1) in human lung cancer A549 cells. In the present study, we report that not only TCDD-induced expression of CYP1A1 but also basal mRNA expression of CYP1A1, CYP1B1, and aryl hydrocarbon receptor (AHR) was down-regulated by TGF-beta1 in cells not treated with TCDD. In contrast, mRNA expression of the AHR partner protein Arnt (aryl hydrocarbon receptor nuclear translocator) was not influenced. Furthermore, TCDD-induced expression of CYP1B1 and NMO-1 was inhibited, and the IC50 values of 5-10 pM TGF-beta1 were in the same range as observed for inhibition of CYP1A1 and AHR mRNA expression. Transfection studies with a plasmid containing a luciferase reporter gene under control of two dioxin-responsive elements indicate an effect on AHR protein expression. Results of time-course studies revealed a parallel inhibition of AHR and CYP1 mRNA expression, indicating that TGF-beta1 is a direct negative regulator of transcription of these genes. The treatment of cells with cycloheximide led to a superinduction of TCDD-induced CYP1A1 and CYP1B1 mRNA expression and abolished the inhibitory effect of TGF-beta1 on basal as well as TCDD-induced CYP1 and AHR mRNA expression. TGF-beta1 seems not to influence the stability of AHR mRNA. The results suggest that TGF-beta1 induces rapid transcription and translation of an as-yet-unknown negative regulatory factor or factors that may directly regulate expression of AHR and genes of Ah gene battery.
authors.affiliation: Medical Institute of Environmental Hygiene, Heinrich-Heine-University of Düsseldorf, Department of Toxicology, Germany.
authors.forename: O
authors.initials: O
authors.lastname: Döhr
authors.forename: R
authors.initials: R
authors.lastname: Sinning
authors.forename: C
authors.initials: C
authors.lastname: Vogel
authors.forename: P
authors.initials: P
authors.lastname: Münzel
authors.forename: J
authors.initials: J
authors.lastname: Abel
mesh_terms: D002460:Cell Line; D003513:Cycloheximide / Q000494:pharmacology; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics; D015536:Down-Regulation; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D007700:Kinetics; D008156:Luciferases / Q000037:antagonists & inhibitors / Q000378:metabolism; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000235:genetics; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics; D018336:Receptors, Aryl Hydrocarbon / Q000235:genetics*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
chemical_list: D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; D016212:Transforming Growth Factor beta; D003513:Cycloheximide; D008156:Luciferases; D019363:Cytochrome P-450 CYP1A1; D016660:NAD(P)H Dehydrogenase (Quinone)