Under hypoxic conditions, circPFKFB4 augmented the interaction between DDB1 and DDB2 within BC cells, and circPFKFB4, DDB1, and DDB2 formed trimers circPFKFB4 binds tightly to the CRL4DDB2 ubiquitin ligase complex, and it further facilitates the assembly of the CRL4DDB2 ubiquitin ligase complex Under hypoxic conditions. The gene discussed is DDB1; the disease is breast cancer.