Circular RNAs: A novel target among non-coding RNAs with potential roles in malignant tumors (Review)

Abstract

Circular RNA s (circRNA s) are a class of non-coding RNA s that are generated via alternative back-splicing, which connects the terminal 5' and 3'ends. Due to their unique loop structure, circRNA s are resistant to ribonucleases and more stable than linear RNA s. In vivo, they are usually highly conserved and stably expressed in tissue/developmental-stage-specific manners. Generally, circRNAs function as microRNA sponges and splicing regulators, as well as in protein binding and transcription. Some circRNA s contain open reading frames with internal ribosomal entry site elements and can thus encode specific proteins. Previously, circRNA s were thought to be erroneous splicing products or by-products of mRNA splicing. With the development of the next-generation sequencing techniques, it has become increasingly clear that circRNA s are abundantly widespread in eukaryotes and that they play significant roles in malignant tumor progression. The present review briefly introduces the biogenesis and functions of circRNA s, as well as summarizes recent research in several common malignancies. The present review also addresses the prospects of circRNA s in clinical applications.