Co-IP experiment between DDB2 and p27 demonstrated that the direct association between DDB2 and p27 was significantly elevated in hypoxic BC cells transfected with circPFKFB4 overexpression plasmid, while the interaction was remarkably impeded following circPFKFB4 knockdown, implying that circPFKFB4 increased the recognition and combination of p27 by the CRL4DDB2 ubiquitin ligase (Fig. S8A and B). Here, DDB2 is linked to breast cancer.