The sialyltransferase ST3GAL1 mediates MUCL1 sialylation to exacerbate breast cancer progression.

Breast cancer is highly heterogeneous and involves complex molecular mechanisms, posing significant therapeutic challenges. Glycosylation modifications, particularly sialylation, play a critical role in tumor progression. The sialyltransferase ST3GAL1 is highly expressed in breast cancer, yet its functional interaction with MUCL1 and underlying mechanisms remain elusive. Using in vitro and in vivo models, this study systematically investigated the ST3GAL1-mediated sialylation of MUCL1 and its functional impact on breast cancer progression. The results demonstrated that ST3GAL1 directly binds to MUCL1 and catalyzes its sialylation, thereby increasing MUCL1 protein stability and promoting malignant phenotypes. ST3GAL1 knockdown significantly inhibited cell proliferation, migration, and invasion while inducing apoptosis; its overexpression resulted in the opposite effects. These protumorigenic phenotypes were effectively reversed by treatment with the sialyltransferase inhibitor Lith-O-Asp or MUCL1 knockdown. Moreover, ST3GAL1 knockdown suppressed tumor growth and lung metastasis in vivo. These findings reveal a novel ST3GAL1-MUCL1 regulatory axis that drives breast cancer progression through sialylation, offering a promising target for glycotherapy.