Fig. 2

Functions and degradation of circRNAs. A Functions of circRNAs (a). CircRNAs play a regulatory role by binding to miRNAs (b). CircRNAs bind to proteins to act as a protein sponge or a protein scaffold (c). CircRNAs can be translated into proteins or peptides in cap-independent way, during which IRES or other initial elements are necessary (d). CircRNAs can be regulators of mRNA, including regulating translation of mRNA (up) and stability of mRNA (down). B Degradation of circRNAs (a). miR-671 is located in nucleus and directs the Ago2-slicer-dependent cleavage of circCDR1 (b). A middle region (Mid) in GW182 functions as a molecular scaffold to recruit decay factors, resulting in degradation of circRNAs (c). Highly structured circRNAs can be degraded by UPF1 and G3BP1. Both proteins are indispensable in this progress (d). RNase L can be activated once cells are invaded by virus. Subsequently, activated RNase L mediates the global degradation of circRNAs, which is essential to activate PKR in the early stage of the innate immune response (e). Cell excretion of circRNAs into the extracellular space through extracellular vesicles (EVs) may be a mechanism for cell clearance of circRNAs