Yim Sujin, Oh Myoungsuk, Choi Su Mi, Park Hyunsung
Department of Life Science, University of Seoul, 90 Cheonnong-dong, Tongdaemun-gu, Seoul 130-743, Republic of Korea.
Biochem Biophys Res Commun. 2004 Sep 10;322(1):9-16. doi: 10.1016/j.bbrc.2004.07.072.
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) induces expression of the cytochrome P450 1A1 gene, cyp1a1, by binding to its receptor, aryl hydrocarbon receptor (AhR). TCDD-bound AhR translocates to the nucleus and forms a heterodimer with its partner protein, AhR nuclear translocator (Arnt). The AhR/Arnt heterodimer then binds to the dioxin-response elements (DREs) in the cyp1a1 enhancer and stimulates transcription of cyp1a1. We tested whether kinase pathways are involved in this process by treating Hepa1c1c7 cells with kinase inhibitors. The MEK-1 inhibitor PD98059 reduced TCDD-induced transcription of cyp1a1. TCDD treatment results in phosphorylation of p44/p42 mitogen-activated protein kinase (MAPK), a substrate of MEK-1. Overexpression of dominant negative form of p42 MAPK suppressed TCDD-dependent transcription of a reporter gene controlled by dioxin-response elements (DREs), and pretreatment with PD98059 also blocked this transcription. PD98059 pretreatment also inhibited TCDD-induced DRE binding of the AhR/Arnt heterodimer. Together these results indicate that TCDD activates the MEK-1/p44/p42 MAPK pathway, which in turn activates AhR and so facilitates binding of AhR to the cyp1a1 DRE.
2,3,7,8-四氯二苯并对二恶英（TCDD）通过与其受体芳烃受体（AhR）结合，诱导细胞色素P450 1A1基因（cyp1a1）的表达。与TCDD结合的AhR易位至细胞核，并与其伴侣蛋白芳烃受体核转运蛋白（Arnt）形成异二聚体。然后，AhR/Arnt异二聚体与cyp1a1增强子中的二恶英反应元件（DREs）结合，并刺激cyp1a1的转录。我们通过用激酶抑制剂处理Hepa1c1c7细胞来测试激酶途径是否参与此过程。MEK-1抑制剂PD98059降低了TCDD诱导的cyp1a1转录。TCDD处理导致p44/p42丝裂原活化蛋白激酶（MAPK）磷酸化，p44/p42丝裂原活化蛋白激酶是MEK-1的底物。p42 MAPK显性负性形式的过表达抑制了由二恶英反应元件（DREs）控制的报告基因的TCDD依赖性转录，并且用PD98059预处理也阻断了该转录。PD98059预处理还抑制了TCDD诱导的AhR/Arnt异二聚体与DRE的结合。这些结果共同表明，TCDD激活MEK-1/p44/p42 MAPK途径，进而激活AhR，从而促进AhR与cyp1a1 DRE的结合。
