Fig. 1

CircRNAs regulate their host genes expression at the transcriptional level. A CircRNAs can be classified into three subtypes: exonic circRNAs (ecircRNAs), intronic circRNAs (ciRNAs), and exon-intron circRNAs (EIciRNAs). Some ciRNAs and EIciRNAs can promote the transcriptional activity of their host genes by binding to RNA polymerase II (Pol II). B CircRNAs can function as protein decoys, scaffolds or recruiters to promote or inhibit their host genes expression. C Some circRNAs, such as circSMARCA5, can increase the cleavage efficiency of homologous exon-defective mRNA by forming R-loops, which in turn terminated transcription, and affect their host genes expression