Effect of Transforming Growth Factor-β₁on Expression of Aryl Hydrocarbon Receptor and Genes ofAhGene 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.

Activation of the Aryl Hydrocarbon Receptor by the Calcium/Calmodulin-Dependent Protein Kinase Kinase Inhibitor 7-Oxo-7H-benzimidazo[2,1-a]benz[de]isoquinoline-3-carboxylic Acid (STO-609)

“…This cell line, reported to be convenient for investigating AhR-driven gene regulation (Döhr et al, 1997), was retained because it has been described previously to lack LKB1 (also known as STK11), the other kinase known to activate AMPK␣ on Thr172 (Hurley et al, 2005), thus supporting the idea that phosphorylation of AMPK␣ is most likely driven only by CaMKK␤ in such cells. In contrast, LKB1-mediated activation of AMPK␣ has to be considered in MCF-7 cells (Wagner et al, 2006).…”

Dioxin Receptor Expression Inhibits Basal and Transforming Growth Factor β-induced Epithelial-to-mesenchymal Transition

“…The latter hypothesis is based on previous studies revealing a cross-regulation between AhR and TGF␤ in epithelial cells (10,32) and mesenchymal fibroblasts (28,30,31).…”

“…In addition, TGF␤ secreted by the stroma was able to increase the migration efficiency of primary AhR Ϫ/Ϫ keratinocytes in vitro and in vivo (10). Interestingly, TGF␤ exerts cell type-specific effects on AhR by inhibiting receptor expression and activation in A549 lung cancer cells while enhancing receptor function in HepG2 hepatoma cells (32,33). Thus, it is likely that AhR and TGF␤ could cross-talk during EMT.…”

Integrative analysis of gene expression patterns predicts specific modulations of defined cell functions by estrogen and tamoxifen in MCF7 breast cancer cells

“…Indeed, CYP1B1 (cytochrome P450) hydroxylates E 2 to the promutagenic metabolite 4-OH catechol estrogen (4-OH-E 2 ) (Hayes et al 1996). E 2 -induced underexpression of TGF , described here, could increase CYP1B1 expression (Dohr et al 1997) and thus enhance E 2 catabolism. On the other hand, our data show that E 2 induces underexpression of UDP glucuronosyltransferase, which is involved in the catechol-quinone detoxification system (Raftogianis et al 2000), thus contributing to increased production of semiquinone (E 2 -3,4-semiquinone) and quinone (E 2 -3,4-quinone) from 4-OH-E 2 (Fig.…”