Cho Young C, Zheng Wenchao, Yamamoto Megumi, Liu Xiequing, Hanlon Paul R, Jefcoate Colin R
Department of Pharmacology and Molecular and Environmental Toxicology Center, University of Wisconsin-Madison, 53706, USA.
Arch Biochem Biophys. 2005 Jul 15;439(2):139-53. doi: 10.1016/j.abb.2005.04.025.
Stimulation of C3H10T1/2 cells by an adipogenic hormonal mixture (IDM) consisting of insulin (I), dexamethasone (D), and methylisobutylxanthine (M) substantially induces cytochrome P450 (CYP) 1B1 expression. This stimulation represents up to 40% of the level produced by maximum activation of the arylhydrocarbon receptor (AhR) with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Dexamethasone and methylisobutylxanthine in combination produced near maximum elevation of CYP1B1 along with a subsequent decline in AhR that paralleled the rise in peroxisome proliferator-activated receptorgamma1 (PPARgamma1). Inhibitors of AhR activity, which block TCDD induction, did not affect this increase of CYP1B1 expression, which was, therefore, independent of AhR activity. These responses were unaffected by inhibition of DNA synthesis, which was required for PPARgamma1 induction and terminal differentiation. Induction of CYP1B1 mRNA was paralleled by increased CYP1B1 promoter-luciferase reporter activity. The initial 0.8kb of promoter region, which was sufficient for 24h near maximum stimulation, did not contain either the key AhR-responsive elements that mediate the TCDD response or CREB and SF1 elements that mediate cAMP stimulation of rat CYP1B1 in steroidogenic cells. This reporter response to IDM stimulation, but not to TCDD, was maintained in AhR-null fibroblasts. CYP1B1 expression, unlike TCDD induction, was stimulated by IDM in only about half the cells. CYP1B1 expression partially overlapped with PPARgamma expression, which was also inversely related in clonal sub-lines. CYP1B1 expression may, therefore, represent an early stage of differentiation that requires factors associated with DNA synthesis to subsequently generate PPARgamma1.
由胰岛素（I）、地塞米松（D）和甲基异丁基黄嘌呤（M）组成的成脂激素混合物（IDM）刺激C3H10T1/2细胞可显著诱导细胞色素P450（CYP）1B1的表达。这种刺激所产生的水平高达用2,3,7,8 - 四氯二苯并 - p - 二恶英（TCDD）最大程度激活芳烃受体（AhR）所产生水平的40%。地塞米松和甲基异丁基黄嘌呤联合使用可使CYP1B1接近最大程度升高，随后AhR下降，这与过氧化物酶体增殖物激活受体γ1（PPARγ1）的升高平行。阻断TCDD诱导的AhR活性抑制剂并不影响CYP1B1表达的这种增加，因此，该增加与AhR活性无关。这些反应不受DNA合成抑制的影响，而DNA合成是PPARγ1诱导和终末分化所必需的。CYP1B1 mRNA的诱导与CYP1B1启动子 - 荧光素酶报告基因活性的增加平行。启动子区域最初的0.8kb足以在24小时内实现接近最大程度的刺激，该区域既不包含介导TCDD反应的关键AhR反应元件，也不包含介导类固醇生成细胞中cAMP刺激大鼠CYP1B1的CREB和SF1元件。这种报告基因对IDM刺激而非TCDD的反应在AhR基因敲除的成纤维细胞中得以维持。与TCDD诱导不同，IDM仅在约一半的细胞中刺激CYP1B1表达。CYP1B1表达与PPARγ表达部分重叠，在克隆亚系中也呈负相关。因此，CYP1B1表达可能代表分化的早期阶段，该阶段需要与DNA合成相关的因子来随后产生PPARγ1。
