In a hypoxic environment, CircDENND4C, which has been shown to be upregulated by HIF-1 in breast cancer cells, actively stimulates cell proliferation (Liang et al. 2017) to achieve the Warburg effect by providing sufficient energy for rapidly growing cancer cells.c-Myc, one of the most significant oncogenic TFs, can initiate the Warburg effect. Here, HIF1A is linked to breast cancer.