When GREB1 protein expression was examined in cancer cell lines using an anti-GREB1 antibody (#1) that recognizes the N-terminal region of GREB1 (Supplementary Fig. S1B), full-length GREB1 (216 kDa) was detected only in HepG2 (hepatoblastoma) and MCF7 (breast cancer) but not in melanoma cell lines (Fig. 1C, left blot). Here, GREB1 is linked to breast cancer.