Drug Metabolism and Toxicology, Faculty of Pharmaceutical Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan.
Drug Metabolism and Toxicology, Faculty of Pharmaceutical Sciences, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan.
Biochem Pharmacol. 2014 Jul 15;90(2):179-87. doi: 10.1016/j.bcp.2014.05.002. Epub 2014 May 14.
Retinoid X receptor α (RXRα) forms a heterodimer with numerous nuclear receptors to regulate drug- or lipid-metabolizing enzymes. In this study, we investigated whether human RXRα is regulated by microRNAs. Two potential recognition elements of miR-34a were identified in the RXRα mRNA: one in the coding region and the other in the 3'-untranslated region (3'-UTR). Luciferase assays revealed that miR-34a recognizes the element in the coding region. The overexpression of miR-34a in HepG2 cells significantly decreased the endogenous RXRα protein and mRNA levels. The stability of RXRα mRNA was decreased by the overexpression of miR-34a, indicating that miR-34a negatively regulates RXRα expression by facilitating mRNA degradation. We found that the miR-34a-dependent down-regulation of RXRα decreases the induction of CYP26 and the transactivity of CYP3A4. miR-34a has been reported to be up-regulated by p53, which has an ability to promote liver fibrosis. The p53 activation resulted in an increase of the miR-34a level and a decrease of the RXRα protein level. In addition, the miR-34a levels in eight fibrotic livers were higher than those in six normal livers, and the reverse trend was found for the RXRα protein levels. An inverse correlation was observed between the miR-34a and the RXRα protein levels in the 14 samples. Taken together, the data show that miR-34a negatively regulates RXRα expression in human liver, and affects the expression of its downstream genes. This miR-34a-dependent regulation might be the underlying mechanism responsible for the decreased expression of the RXRα protein in fibrotic livers.
视黄醇 X 受体α（RXRα）与许多核受体形成异二聚体，以调节药物或脂质代谢酶。在这项研究中，我们研究了人 RXRα 是否受 microRNAs 调节。在 RXRα mRNA 中鉴定出 miR-34a 的两个潜在识别元件：一个在编码区，另一个在 3'非翻译区（3'UTR）。荧光素酶报告基因检测显示 miR-34a 识别编码区的元件。在 HepG2 细胞中过表达 miR-34a 显著降低内源性 RXRα 蛋白和 mRNA 水平。miR-34a 的过表达降低了 RXRα mRNA 的稳定性，表明 miR-34a 通过促进 mRNA 降解负调控 RXRα 表达。我们发现 miR-34a 依赖性下调 RXRα 降低了 CYP26 的诱导和 CYP3A4 的转录活性。miR-34a 已被报道受 p53 上调，p53 具有促进肝纤维化的能力。p53 的激活导致 miR-34a 水平升高和 RXRα 蛋白水平降低。此外，在 8 例纤维化肝脏中 miR-34a 水平高于 6 例正常肝脏，而 RXRα 蛋白水平则呈相反趋势。在 14 个样本中观察到 miR-34a 和 RXRα 蛋白水平之间存在负相关。总之，数据表明 miR-34a 在人肝中负调控 RXRα 的表达，并影响其下游基因的表达。这种依赖 miR-34a 的调节可能是纤维化肝脏中 RXRα 蛋白表达降低的潜在机制。
