Table 1.
Different circRNAs: localization, mode of action, and biological functions
| circRNA | Mode of action | Biological functions | References |
|---|---|---|---|
| Cytoplasm | |||
| ciRS-7 (also called CDR1as) | miRNA sponge for miR-7 | positive regulator of insulin secretion, neuronal development, oncogenic functions | 1,2,76,131,170, 171, 172 |
| circHIPK3 | miRNA sponge for multiple miRNAs | tumor suppressor, positive regulator of insulin secretion | 132,172,173 |
| circZNF91 | miRNA sponge or decoy for miR-23b-3p | differentiation of epidermal stem cells | 51 |
| circBIRC6 | miRNA sponge or decoy for miR-34a and miR-145 | pluripotency maintenance | 174 |
| circMbl | protein sponge or decoy for Mbl and template for translation | regulator of neuronal functions | 26,27 |
| circCCDC66 | miRNA sponge or decoy for multiple tumor suppressor miRNAs | oncogenic functions | 175 |
| circPVT1 | miRNA sponge or decoy for miR-497-5p | positive regulator of cell cycle progression | 176 |
| circANRIL | protein sponge or decoy for PES1 | impairs pre-rRNA processing and ribosome biogenesis to induce nucleolar stress and activate p53 | 177 |
| circPABPN1 | protein sponge or decoy for HUR | suppresses PABPN1 translation and decreases cellular proliferation | 178 |
| circ- Amotl1 | protein scaffold (facilitates PDK1-dependent phosphorylation of AKT1) | cardioprotective role in doxorubicin-induced cardiomyopathy | 179 |
| circ-Foxo3 | protein scaffold (facilitates MDM2-dependent ubiquitylation of p53) and sponge for MDM2 (to prevent ubiquitylation of FOXO3) | induces the apoptosis of cancer cells | 103 |
| circ-ZNF609 | template for translation | regulates myoblast proliferation | 114 |
| circPINTexon2 | template for translation | tumor suppressor | 180 |
| circ-FBXW7 | template for translation | tumor suppressor | 181 |
| circ-SHPRH | template for translation | tumor suppressor | 182 |
| Nucleus | |||
| circPAIP2 | enhances protein function (positive regulator of RNA Pol II transcription) | positively regulates the expression of its parental gene | 21 |
| circEIF3J | enhances protein function (positive regulator of RNA Pol II transcription) | positively regulates the expression of its parental gene | 21 |
| ci- ankrd52 | enhances protein function (positive regulator of RNA Pol II transcription) | positively regulates the expression of its parental gene | 22 |
| FECR1 | protein recruitment (recruits TET1 to the promoter region of its own host gene) | oncogenic functions through upregulation of FLI1 | 55 |
| cia-cGAS | protein sponge or decoy for cGAS | protects long-term hematopoietic stem cells from exhaustion | 133 |
FECR1, FLI1 exonic circular RNA; MDM2, mouse double minute 2; PABPN1, poly(A) binding protein 1; PDK1, phosphoinositide-dependent protein kinase 1; PES1, pescadillo homolog 1; TET1, tet methylcytosine dioxygenase 1.