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.