Department of Pharmacology and Toxicology, Faculty of Pharmacy in Hradec Kralove, Charles University in Prague, Heyrovskeho 1203, Hradec Kralove, CZ-500 05, Czech Republic.
Pharmacol Rep. 2013;65(5):1322-35. doi: 10.1016/s1734-1140(13)71491-9.
Organic cation transporter 1 (OCT1, SLC22A1) is a membrane transporter that is important for therapeutic effect of the antidiabetic drug metformin. Its liver-specific expression in hepatocytes is strongly controlled by hepatocyte nuclear factor-4α (HNF4α). HNF4α expression and transcriptional activity have been demonstrated to be augmented by glucocorticoid receptor (GR) in human hepatocytes and rodent livers.
It was examined whether GR activation indirectly induces OCT1 gene expression via HNF4α up-regulation in primary human hepatocytes. We also examined which other transcription factors are involved in OCT1 gene expression and whether they are regulated by dexamethasone using qRT-PCR and gene reporter assays.
We found that dexamethasone significantly up-regulates OCT1 mRNA and protein in normal primary human hepatocytes, but not in hepatocyte-derived tumor cell lines HepG2 and MZ-Hep1. Consistently, we observed that HNF4α is induced by dexamethasone in primary human hepatocytes, but not in hepatocyte tumor-derived cell lines. Viral transduction of MZ-Hep1 cells with the expression constructs for HNF4α, CCAAT/enhancer binding proteins β (C/EBPβ) and peroxisome proliferator-activated receptor-γ coactivator 1α (PGC1α) demonstrated significant roles of the transcription factors in OCT1 gene regulation. We found that expression of OCT1 mRNA in human livers significantly correlates with C/EBPβ and HNF4α mRNAs expression and that C/EBPβ co-transfection stimulates OCT1 gene reporter construct in HepG2 cells. Nevertheless, neither C/EBPβ nor PGC1α were upregulated in human hepatocytes by dexamethasone.
We can conclude that GR-induced expression of HNF4α may contribute to indirect OCT1 gene up-regulation by dexamethasone in primary human hepatocytes, but not in hepatocyte-derived tumor cell lines.
有机阳离子转运体 1（OCT1，SLC22A1）是一种膜转运蛋白，对治疗药物二甲双胍的疗效至关重要。其在肝细胞中的肝脏特异性表达受肝核因子-4α（HNF4α）的强烈控制。已经证明糖皮质激素受体（GR）在人肝细胞和啮齿动物肝脏中增强了 HNF4α 的表达和转录活性。
我们研究了 GR 激活是否通过 HNF4α 的上调间接诱导原代人肝细胞中 OCT1 基因的表达。我们还研究了其他哪些转录因子参与 OCT1 基因的表达，以及它们是否通过地塞米松调节，使用 qRT-PCR 和基因报告基因测定。
我们发现地塞米松可显著上调正常原代人肝细胞中的 OCT1 mRNA 和蛋白，但在肝细胞源性肿瘤细胞系 HepG2 和 MZ-Hep1 中则不然。一致地，我们观察到地塞米松诱导原代人肝细胞中 HNF4α 的诱导，但在肝细胞源性肿瘤细胞系中则不然。MZ-Hep1 细胞的病毒转导与 HNF4α、CCAAT/增强子结合蛋白β（C/EBPβ）和过氧化物酶体增殖物激活受体-γ共激活因子 1α（PGC1α）的表达构建体表明，转录因子在 OCT1 基因调节中具有重要作用。我们发现，人肝脏中 OCT1 mRNA 的表达与 C/EBPβ 和 HNF4α mRNA 的表达显著相关，并且 C/EBPβ 共转染可刺激 HepG2 细胞中的 OCT1 基因报告基因构建体。然而，地塞米松并未使 C/EBPβ 或 PGC1α 在人肝细胞中上调。
我们可以得出结论，GR 诱导的 HNF4α 表达可能导致地塞米松在原代人肝细胞中间接上调 OCT1 基因，但在肝细胞源性肿瘤细胞系中则不然。
