Fig. 2.

Biological functions of circRNAs. circRNA (ciRS‐7, cir‐ITCH) acts as a (1) miRNA sponge that may compete with other classes of RNA for miRNA‐binding sites and perturb the complex network of interaction and gene regulation [16, 17, 18, 19, 20]; (2) RBP sponge [9, 21] and protein regulator [23, 24]. circRNAs (e.g., circFoxo3) are able to bind, store, sort, and sequester proteins to particular subcellular locations, and act as dynamic scaffolding molecules that modulate protein–protein interactions; (3) regulates transcription of parental gene in cis‐ or trans‐manners through interacting with U1 snRNP and promote transcription of their parental genes (e.g., circEIF3J and circPAIP2); recruiting TET1 demethylase to induce DNA demethylation of promoter or interacting with DNMT1 promoter that results in DNMT1 silencing (e.g., circFECR1) [12, 22]; (4) mRNA trap (e.g., circMbl) whereby the formation of circRNA competes with linear mRNA production [9]; and (5) template for circRNA translation (e.g., circβ‐catenin) as it contains an open reading frame (ORF) [25, 26, 27].