Department of Pediatrics (G.M., S.K.N.), Department of Biomedical Sciences (G.M.), Department of Medicine (S.K.N.), and Department of Cellular and Molecular Medicine (S.K.N.), University of California at San Diego, La Jolla, California; and Department of Pediatrics, Dalhousie University and IWK Health Centre, Halifax, Nova Scotia, Canada (J.B.T.).
Mol Pharmacol. 2013 Dec;84(6):808-23. doi: 10.1124/mol.113.088229. Epub 2013 Sep 13.
The transcriptional regulation of drug-metabolizing enzymes and transporters (here collectively referred to as DMEs) in the developing proximal tubule (PT) is not well understood. As in the liver, DME regulation in the PT may be mediated through nuclear receptors, which are thought to "sense" deviations from homeostasis by being activated by ligands, some of which are handled by DMEs, including drug transporters. Systems analysis of transcriptomic data during kidney development predicted a set of upstream transcription factors, including hepatocyte nuclear factor 4α (Hnf4a) and Hnf1a, as well as Nr3c1 (Gr), Nfe2l2 (Nrf2), peroxisome proliferator-activated receptor α (Pparα), and Tp53. Motif analysis of cis-regulatory enhancers further suggested that Hnf4a and Hnf1a are the main transcriptional regulators of DMEs in the PT. Available expression data from tissue-specific Hnf4a knockout tissues revealed that distinct subsets of DMEs were regulated by Hnf4a in a tissue-specific manner. Chromatin immunoprecipitation combined with massively parallel DNA sequencing was performed to characterize the PT-specific binding sites of Hnf4a in rat kidneys at three developmental stages (prenatal, immature, adult), which further supported a major role for Hnf4a in regulating PT gene expression, including DMEs. In ex vivo kidney organ culture, an antagonist of Hnf4a (but not a similar inactive compound) led to predicted changes in DME expression, including among others Fmo1, Cyp2d2, Cyp2d4, Nqo2, as well as organic cation transporters and organic anion transporters Slc22a1 (Oct1), Slc22a2 (Oct2), Slc22a6 (Oat1), Slc22a8 (Oat3), and Slc47a1 (Mate1). Conversely, overexpression of Hnf1a and Hnf4a in primary mouse embryonic fibroblasts, sometimes considered a surrogate for mesenchymal stem cells, induced expression of several of these proximal tubule DMEs, as well as epithelial markers and a PT-enriched brush border marker Ggt1. These cells had organic anion transporter function. Taken together, the data strongly supports a critical role for HNF4a and Hnf1a in the tissue-specific regulation of drug handling and differentiation toward a PT-like cellular identity. We discuss our data in the context of the "remote sensing and signaling hypothesis" (Ahn and Nigam, 2009; Wu et al., 2011).
药物代谢酶和转运体（以下统称 DMEs）在发育中的近端肾小管（PT）中的转录调控机制尚不清楚。与肝脏一样，PT 中的 DME 调控可能通过核受体介导，这些核受体被认为通过配体激活来“感知”体内平衡的偏差，其中一些配体由 DME 处理，包括药物转运体。对肾脏发育过程中转录组数据的系统分析预测了一组上游转录因子，包括肝细胞核因子 4α（Hnf4a）和 Hnf1a，以及 Nr3c1（Gr）、Nfe2l2（Nrf2）、过氧化物酶体增殖物激活受体α（Pparα）和 Tp53。顺式调控增强子的基序分析进一步表明，Hnf4a 和 Hnf1a 是 PT 中 DME 的主要转录调控因子。来自组织特异性 Hnf4a 敲除组织的可用表达数据表明，不同的 DME 亚群以组织特异性方式受 Hnf4a 调控。在三个发育阶段（产前、未成熟、成年），用染色质免疫沉淀结合大规模平行 DNA 测序对大鼠肾脏中 Hnf4a 的 PT 特异性结合位点进行了表征，这进一步支持了 Hnf4a 在调节 PT 基因表达（包括 DMEs）方面的主要作用。在离体肾脏器官培养中，Hnf4a 的拮抗剂（而不是类似的无活性化合物）导致 DME 表达的预测变化，包括 Fmo1、Cyp2d2、Cyp2d4、Nqo2 以及有机阳离子转运体和有机阴离子转运体 Slc22a1（Oct1）、Slc22a2（Oct2）、Slc22a6（Oat1）、Slc22a8（Oat3）和 Slc47a1（Mate1）。相反，Hnf1a 和 Hnf4a 在原代小鼠胚胎成纤维细胞中的过表达，有时被认为是间充质干细胞的替代物，诱导了这些近端肾小管 DMEs 以及上皮标志物和 PT 丰富的刷状缘标记物 Ggt1 的表达。这些细胞具有有机阴离子转运体功能。综上所述，数据强烈支持 HNF4a 和 Hnf1a 在药物处理的组织特异性调节以及向 PT 样细胞特征的分化中发挥关键作用。我们在“远程感应和信号假说”（Ahn 和 Nigam，2009；Wu 等人，2011）的背景下讨论我们的数据。
