In this study, OGT siRNA and the O-GlcNAc inhibitor L01 decreased cellular O-GlcNAcylation without affecting other types of glycosylation and then significantly attenuated the Nic-induced invasive phenotype in breast cancer cells, indicating that O-GlcNAcylation, but not other types of glycosylation, plays a key role in nicotine- induced breast cancer cell invasion. Here, OGT is linked to breast cancer.