Next, we confirmed the nuclear localization of GREB1 in MNA+ NB cells (Fig. 1C), although some cytoplasmic staining was also observed (Fig. 1C), in support of its recently uncovered cytoplasmic function in ER+ breast cancer as an O-GlcNAc glycosyltransferase (14). Here, GREB1 is linked to breast carcinoma.