Effect of Transforming Growth Factor-β1 on Expression of Aryl Hydrocarbon Receptor and Genes of AhGene Battery: Clues for Independent Down-Regulation in A549 Cells
- 1Medical Institute of Environmental Hygiene, Heinrich-Heine-University of Düsseldorf, Department of Toxicology, 40225 Düsseldorf, Germany (O.D., R.S., C.V., J.A.), and 2Institute of Toxicology, University of Tübingen, Wilhelmstraβe 56, 72074 Tübingen, Germany (P.M.)
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-β1 (TGF-β1) 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-β1 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 pmTGF-β1 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-β1 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-β1 on basal as well as TCDD-induced CYP1 and AHR mRNA expression. TGF-β1seems not to influence the stability of AHR mRNA. The results suggest that TGF-β1 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.
Footnotes
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Send reprint requests to: Dr. Josef Abel, Medical Institute of Environmental Hygiene at the Heinrich-Heine-University of Düsseldorf, Department of Toxicology, Auf’m Hennekamp 50, 40225 Düsseldorf, Germany. E-mail:josef.abel{at}uni-duesseldorf.de
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This work was supported by Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 503 (DFG-SFB 503/A5)
- Abbreviations:
- PAH
- polycyclic aromatic hydrocarbon
- ActD
- actinomycin D
- AHR
- aryl hydrocarbon receptor
- AP
- activator protein
- Arnt
- aryl hydrocarbon receptor nuclear translocator
- BMS
- basal medium supplement
- CHX
- cycloheximide
- DMEM
- Dulbecco’s modified Eagle’s medium
- DMSO
- dimethylsulfoxide
- DRE
- dioxin responsive element
- EROD
- 7-ethoxyresorufin-O-deethylase
- FCS
- fetal calf serum
- IL
- interleukin
- NMO
- NADPH:quinone oxidoreductase
- NRE
- negative regulatory element i
- RT
- reverse transcription or transcriptase
- PCR
- polymerase chain reaction
- TCDD
- 2,3,7,8-tetrachlorodibenzo-p-dioxin
- TGF
- transforming growth factor
- TNF
- tumor necrosis factor
- UGT
- UDP-glucuronosyltransferase
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- Received October 30, 1996.
- Accepted January 16, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
