Overview of m6A and circRNAs in human cancers

N-6-methyladenosine (m(6)A), the richest post-transcriptional modification of RNA in eukaryotic cells, is dynamically installed/uninstalled by the RNA methylase complex ("writer") and demethylase ("eraser") and recognized by the m(6)A-binding protein ("reader"). M(6)A modification on RNA metabolism involves maturation, nuclear export, translation and splicing, thereby playing a critical role in cellular pathophysiology and disease processes. Circular RNAs (circRNAs) are a class of non-coding RNAs with a covalently closed loop structure. Due to its conserved and stable properties, circRNAs could participate in physiological and pathological processes through unique pathways. Despite the recent discovery of m(6)A and circRNAs remains in the initial stage, research has shown that m(6)A modifications are widespread in circRNAs and regulates circRNA metabolism, including biogenesis, cell localization, translation, and degradation. In this review, we describe the functional crosstalk between m(6)A and circRNAs, and illustrate their roles in cancer development. Moreover, we discuss the potential mechanisms and future research directions of m(6)A modification and circRNAs.