Cell-specific regulation of human aryl hydrocarbon receptor expression by transforming growth factor-beta(1).
Previous studies showed that TGF-beta down-regulates aryl hydrocarbon (AhR) expression in human lung carcinoma cells A549. Here we analyzed the molecular mechanisms by which TGF-beta modulates AhR expression. A 5799-nucleotide 5'-flanking region of human AhR gene was isolated. Transient transfection studies of full-length (hAhRP) and deletion promoter constructs indicate the requirement of a cis-regulatory element encompassing -1980 to -1892 for full constitutive activity. Basal hAhRP activity occurs in a cell-specific manner; human hepatoma HepG2 cells possess a 10-fold higher activity compared with A549 cells. TGF-beta exerts cell-specific effects on hAhRP activity. Treatment of cells with 100 pM TGF-beta leads to a 50% inhibition in A549 and a 3-fold induction in HepG2 cells. Deletion mutagenesis identified a TGF-beta-responsive sequence containing a functional conserved Smad-binding element. Transient overexpression of Smad 2, 3, and 4 indicates that these signal transducers modulate hAhRP activity. The down-regulation of AhR by TGF-beta is modulated by 5'-TG-3'-interacting factor (TGIF). Transient overexpression of TGIF in MDA-MB231 and HepG2 cells led to inhibition of hAhRP activity and a similar decrease of AhR mRNA expression. Our findings indicate that Smad proteins are involved in the cell-specific regulation of AhR expression by TGF-beta.
Department of Experimental Toxicology, Medical Institute of Environmental Hygiene at the Heinrich-Heine-University, Düsseldorf, Germany.
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S
Wolff
P A
PA
Harper
J M
JM
Wong
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V
Mostert
Y
Y
Wang
J
J
Abel
D020121:5' Untranslated Regions / Q000235:genetics; D030201:Activin Receptors, Type I; D001665:Binding Sites / Q000235:genetics; D002277:Carcinoma / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D018398:Homeodomain Proteins / Q000378:metabolism; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics / Q000378:metabolism*; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018336:Receptors, Aryl Hydrocarbon / Q000235:genetics / Q000378:metabolism*; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism*; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D012097:Repressor Proteins; D051899:Smad2 Protein; D051900:Smad3 Protein; D051901:Smad4 Protein; D015534:Trans-Activators / Q000378:metabolism; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D020121:5' Untranslated Regions; D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; D018125:Receptors, Transforming Growth Factor beta; D012097:Repressor Proteins; C497782:SMAD2 protein, human; C497790:SMAD3 protein, human; C497796:SMAD4 protein, human; D051899:Smad2 Protein; D051900:Smad3 Protein; D051901:Smad4 Protein; C097504:TGIF1 protein, human; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I