MicroRNAs (miRNAs) are an evolutionarily conserved class of small regulatory noncoding RNAs, binding to complementary target mRNAs and resulting in mRNA translational inhibition or degradation, and they play an important role in regulating many aspects of physiologic and pathologic processes in mammalian cells. Thus, efficient manipulations of miRNA functions may be exploited as promising therapeutics for human diseases. Two commonly used strategies to inhibit miRNA functions include direct transfection of chemically synthesized miRNA inhibitors and delivery of a gene vector that instructs intracellular transcription of miRNA inhibitors. While most miRNA inhibitors are based on antisense molecules to bind and sequester miRNAs from their natural targets, it is challenging to achieve effective and stable miRNA inhibition. Here we develop a user-friendly system to express circular inhibitors of miRNA (CimiRs) by exploiting the noncanonical head-to-tail backsplicing mechanism for generating endogenous circular RNA sponges. In our proof-of-principle experiments, we demonstrate that the circular forms of the hsa-miR223-binding site of human β-arrestin1 (ARRB1) 3′ UTR sponge RNA (BUTR), the bulged anti-miR223 (cirBulg223) and bulged anti-miR21 (cirBulg21), exhibit more potent suppression of miRNA functions than their linear counterparts. Therefore, the engineered CimiR expression system should be a valuable tool to target miRNAs for basic and translational research.

MicroRNA (miRNA) 是一类进化上保守的小调控非编码 RNA，与互补的靶 mRNA 结合并导致 mRNA 翻译抑制或降解，它们在调节哺乳动物细胞生理和病理过程的许多方面发挥着重要作用。因此，对 miRNA 功能的有效操作可以作为人类疾病的有希望的治疗方法。抑制 miRNA 功能的两种常用策略包括直接转染化学合成的 miRNA 抑制剂和传递指导 miRNA 抑制剂在细胞内转录的基因载体。虽然大多数 miRNA 抑制剂都是基于反义分子来结合和隔离 miRNA 与其天然靶标，但实现有效且稳定的 miRNA 抑制具有挑战性。在这里，我们开发了一种用户友好的系统，通过利用非规范的头尾反向剪接机制来生成内源性环状 RNA 海绵，来表达 miRNA 的环状抑制剂 (CimiRs)。在我们的原理验证实验中，我们证明了人 β-arrestin1 (ARRB1) 3'UTR 海绵 RNA (BUTR) 的 hsa-miR223 结合位点的圆形形式、凸出的抗 miR223 (cirBulg223) 和凸出的抗 miR223 (cirBulg223) anti-miR21 (cirBulg21) 比其线性对应物表现出更有效的 miRNA 功能抑制作用。因此，工程化的 CimiR 表达系统应该成为靶向 miRNA 的基础和转化研究的有价值的工具。