Pregnane X receptor protects HepG2 cells from BaP-induced DNA damage
Pregnane X receptor protects HepG2 cells from BaP-induced DNA damage
复制标题
DOI：
10.1093/toxsci/kfn058
复制
发表时间：
2008-07-01
影响因子：
3.8
通讯作者：
Tian, Yanan
中科院分区：
文献类型：
--
作者：
Naspinski, Christine;Gu, Xinsheng;Tian, Yanan
妊娠素X受体（Pregnane X receptor， PXR）是一种协调调节I期和II期代谢酶转录表达的核受体。PXR在广泛的内源性和外源性化合物的药代动力学中起着重要作用，并且似乎在一定程度上进化为保护生物体免受有毒外源性药物的侵害。苯并[a]芘（BaP）是一种公认的致癌物和普遍存在的环境污染物，其代谢可导致其基因毒性形式的解毒或生物活化。因此，PXR可能通过改变代谢途径的平衡来调节BaP的遗传毒性，有利于BaP的解毒。为了研究PXR在BaP遗传毒性中的作用，我们在BaP处理的亲代HepG2细胞和人PXR转染的HepG2细胞中，用p -32后标记法测量了BaP- dna加合物的形成。与亲本细胞相比，转染PXR显著降低了加合物的水平50-65% (p < 0.001)，表明PXR可以保护肝细胞免受暴露于BaP引起的遗传毒性。为了分析肝细胞中pxr调控的潜在解毒途径，我们使用实时定量反转录PCR对一组参与I期和II期代谢和排泄的基因进行了研究。在过表达PXR的细胞中，CYP1A2、GSTA1、GSTA2、GSTM1、UGT1A6和BCRP （ABCG2）的信使RNA水平显著升高，与BaP暴露无关。此外，PXR的存在显著提高了GST酶的总活性（有利于BaP的代谢解毒）（p < 0.001），与BaP暴露无关。综上所述，这些结果表明PXR在保护DNA免受多环芳烃（PAHs）如BaP的损伤中起重要作用，这些保护作用可能是通过协调调节参与外源代谢的基因来实现的。
Pregnane X receptor (PXR) is a nuclear receptor that coordinately regulates transcriptional expression of both phase I and phase II metabolizing enzymes. PXR plays an important role in the pharmacokinetics of a broad spectrum of endogenous and xenobiotic compounds and appears to have evolved in part to protect organisms from toxic xenobiotics. Metabolism of benzo[a]pyrene (BaP), a well-established carcinogen and ubiquitous environmental contaminant, can result in either detoxification or bioactivation to its genotoxic forms. Therefore, PXR could modulate the genotoxicity of BaP by changing the balance of the metabolic pathways in favor of BaP detoxification. To examine the role of PXR in BaP genotoxicity, BaP-DNA adduct formation was measured by P-32-postlabeling in BaP-treated parental HepG2 cells and human PXR-transfected HepG2 cells. The presence of transfected PXR significantly reduced the level of adducts relative to parental cells by 50-65% (p < 0.001), demonstrating that PXR protects liver cells from genotoxicity induced by exposure to BaP. To analyze potential PXR-regulated detoxification pathways in liver cells, a panel of genes involved in phase I and phase II metabolism and excretion was surveyed with real-time quantitative reverse transcription PCR. The messenger RNA levels of CYP1A2, GSTA1, GSTA2, GSTM1, UGT1A6, and BCRP (ABCG2) were significantly higher in cells overexpressing PXR, independent of exposure to BaP. In addition, the total GST enzymatic activity, which favors the metabolic detoxification of BaP, was significantly increased by the presence of PXR (p < 0.001), independent of BaP exposure. Taken together, these results suggest that PXR plays an important role in protection against DNA damage by polycyclic aromatic hydrocarbons (PAHs) such as BaP, and that these protective effects may be through a coordinated regulation of genes involved in xenobiotic metabolism.