To investigate the molecular mechanism of circPFKFB4 in promoting BC progression under hypoxia, we implemented biotin-labeled RNA pull-down assay combined with LC/MS analysis to explore the potential circPFKFB4-binding proteins and revealed that DDB1 and DDB2 were captured by the biotin-labeled probe against circPFKFB4 (Fig. 5A, Fig. 5B, Fig. S5 and Fig. S6). Here, DDB1 is linked to breast cancer.