CDKN1A and cancer: In non-cancer mouse cells, circFoxo3 binds to the cell cycle-associated proteins CDK2 (cyclin dependent kinase 2) and p21 (CDKN1A, cyclin dependent kinase inhibitor 1A), reducing the formation of cyclin E/CDK2 complexes, thereby blocking the G1 to S phase transition in the cell cycle [148].