Multidrug resistance–associated protein 4 (MRP4), a member of the C subfamily of ATP-binding cassette transporters, is highly expressed in the kidneys of mammals and is responsible for renal elimination of numerous drugs. Adenosine deaminase acting on RNA 1 (ADAR1) has been reported to regulate gene expression by catalyzing adenosine-to-inosine RNA editing reactions; however, potential roles of ADAR1 in the regulation of MRP4 expression have not been investigated. In this study, we found that downregulation of ADAR1 increased the expression of MRP4 in human renal cells at the posttranscriptional level. Luciferase reporter assays and microarray analysis revealed that downregulation of ADAR1 reduced the levels of microRNA miR-381-3p, which led to the corresponding upregulation of MPR4 expression. Circular RNAs (circRNAs) are a type of closed-loop endogenous noncoding RNAs that play an essential role in gene expression by acting as miRNA sponges. We demonstrate that ADAR1 repressed the biogenesis of circRNA circHIPK3 through its adenosine-to-inosine RNA editing activity, which altered the secondary structure of the precursor of circHIPK3. Furthermore, in silico analysis suggested that circHIPK3 acts as a sponge of miR-381-3p. Indeed, we found overexpression of circHIPK3 induced the expression of MRP4 through its interference with miR-381-3p. Taken together, our study provides novel insights into regulation of the expression of xenobiotic transporters through circRNA expression by the RNA editing enzyme ADAR1.

多药耐药相关蛋白 4 (MRP4) 是 ATP 结合盒转运蛋白 C 亚家族的成员，在哺乳动物的肾脏中高度表达，负责多种药物的肾脏消除。据报道，作用于 RNA 1 (ADAR1) 的腺苷脱氨酶通过催化腺苷到肌苷 RNA 编辑反应来调节基因表达；然而，尚未研究 ADAR1 在调节 MRP4 表达中的潜在作用。在这项研究中，我们发现 ADAR1 的下调在转录后水平增加了人肾细胞中 MRP4 的表达。荧光素酶报告基因检测和微阵列分析显示，ADAR1 的下调降低了 microRNA miR-381-3p 的水平，从而导致 MPR4 表达的相应上调。环状 RNA (circRNA) 是一种闭环内源性非编码 RNA，通过充当 miRNA 海绵在基因表达中发挥重要作用。我们证明 ADAR1 通过其腺苷到肌苷 RNA 编辑活性抑制 circRNA circHIPK3 的生物发生，这改变了 circHIPK3 前体的二级结构。此外，计算机分析表明 circHIPK3 充当 miR-381-3p 的海绵。事实上，我们发现 circHIPK3 的过表达通过干扰 miR-381-3p 诱导了 MRP4 的表达。总之，我们的研究为通过 RNA 编辑酶 ADAR1 表达 circRNA 来调节外源性转运蛋白的表达提供了新的见解。