Klinge C M, Kaur K, Swanson H I
Department of Biochemistry, University of Louisville School of Medicine, Louisville, Kentucky, 40292, USA.
Arch Biochem Biophys. 2000 Jan 1;373(1):163-74. doi: 10.1006/abbi.1999.1552.
The molecular mechanisms underlying the apparent "cross-talk" between estrogen receptor (ER)- and arylhydrocarbon receptor (AHR)-mediated activities are unknown. To determine how AHR ligand 2, 3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) may inhibit ER action and, conversely, to examine how 17-beta-estradiol (E(2)) affects AHR activity, we examined discrete activities of each receptor, i.e., protein-protein interactions, DNA binding, and transcriptional activation. We report that AHR interacts directly with ERalpha, COUP-TF, and ERRalpha1, in a ligand-specific manner in vitro. Unoccupied or beta-napthoflavone (beta-NF)-occupied AHR showed stronger interaction with ERalpha, COUP-TF, and ERRalpha1 than when AHR was occupied by the partial antagonist alpha-naphthoflavone (alpha-NF), indicating a role for ligand in AHR interaction with these proteins. We also report that AHR interacts with COUP-TF in transfected CV-1 cells. In contrast, the AHR nuclear translocator protein (ARNT) did not interact with COUP-TF, ERRalpha1, or ERalpha. We next examined the interaction of either ERalpha or COUP-TF with a consensus xenobiotic response element (XRE). Purified ERalpha did not bind the consensus XRE, but COUP-TFI bound the consensus XRE, suggesting a role for COUP-TF as a AHR/ARNT competitor for XRE binding. In transiently transfected MCF-7 human breast cancer cells, overexpression of COUP-TFI inhibited TCDD-activated reporter gene activity from the CYP1A1 promoter. TCDD inhibited estradiol (E(2))-activated reporter gene activity from a consensus ERE and from the EREs in the pS2 and Fos genes, and COUP-TFI did not block the antiestrogenic activity of TCDD. The specific interaction of COUP-TF with XREs and AHR together with the inhibition of TCDD-induced gene expression by COUP-TF suggests that COUP-TF may regulate AHR action both by direct DNA binding competition and through protein-protein interactions.
雌激素受体（ER）介导的活性与芳烃受体（AHR）介导的活性之间明显的“串扰”背后的分子机制尚不清楚。为了确定AHR配体2,3,7,8-四氯二苯并 - 对二恶英（TCDD）如何抑制ER作用，相反，为了研究17-β-雌二醇（E₂）如何影响AHR活性，我们检测了每个受体的离散活性，即蛋白质 - 蛋白质相互作用、DNA结合和转录激活。我们报告，在体外，AHR以配体特异性方式直接与ERα、COUP-TF和ERRα1相互作用。未占据的或被β-萘黄酮（β-NF）占据的AHR与ERα、COUP-TF和ERRα1的相互作用比被部分拮抗剂α-萘黄酮（α-NF）占据的AHR更强，表明配体在AHR与这些蛋白质的相互作用中起作用。我们还报告AHR在转染的CV-1细胞中与COUP-TF相互作用。相反，AHR核转运蛋白（ARNT）不与COUP-TF、ERRα1或ERα相互作用。接下来，我们检测了ERα或COUP-TF与共有外源性反应元件（XRE）的相互作用。纯化的ERα不结合共有XRE，但COUP-TFI结合共有XRE，提示COUP-TF作为AHR/ARNT竞争XRE结合的作用。在瞬时转染的MCF-7人乳腺癌细胞中，COUP-TFI的过表达抑制了来自CYP1A1启动子的TCDD激活的报告基因活性。TCDD抑制了来自共有雌激素反应元件（ERE）以及pS2和Fos基因中ERE的雌二醇（E₂）激活的报告基因活性，并且COUP-TFI不阻断TCDD的抗雌激素活性。COUP-TF与XRE和AHR的特异性相互作用以及COUP-TF对TCDD诱导的基因表达的抑制表明，COUP-TF可能通过直接的DNA结合竞争和蛋白质 - 蛋白质相互作用来调节AHR作用。
