To confirm whether HIF promotes the expression of lncRNA KB-1980E6.3 in breast cancer cells, we used lentivirus-mediated shRNAs against HIF-1α or HIF-2α to knockdown HIF expression in BT549 and Hs578T cells (Fig. S2a–d), which was further confirmed by expression of VEGFA, a known HIF target under hypoxia conditions (Fig. S2e, f). Here, EPAS1 is linked to breast cancer.