Elevated transcription and glycosylation of B3GNT5 promotes breast cancer aggressiveness

Abstract

Background: Basal-like breast cancer (BLBC) is the most aggressive subtype of breast cancer because of its aggressive biological characteristics and no effective targeted agents. However, the mechanism underlying its aggressive behavior remain poorly understood. β1,3-N-acetylglucosaminyltransferase V (B3GNT5) overexpression occurs specifically in BLBC. Here, we studied the possible molecular mechanisms of B3GBT5 promoting the aggressiveness of BLBC. Methods: The potential effects of B3GNT5 on breast cancer cells were tested by colony formation, mammosphere formation, cell proliferation assay, flow cytometry and Western blotting. The glycosylation patterns of B3GNT5 and associated functions were determined by Western blotting, quantitative real-time PCR and flow cytometry. The effect of B3GNT5 expression on BLBC was assessed by in vitro and in vivo tumorigenesis model. Results: In this study, we showed that B3GNT5 copy number amplification and hypomethylation of B3GNT5 promoter contributed to the overexpression of B3GNT5 in BLBC. Knockout of B3GNT5 strongly reduced surface expression of SSEA-1 and impeded cancer stem cell (CSC)-like properties of BLBC cells. Our results also showed that B3GNT5 protein was heavily N-glycosylated, which is critical for its protein stabilization. Clinically, elevated expression of B3GNT5 was correlated with high grade, large tumor size and poor survival, indicating poor prognosis of breast cancer patients. Conclusions: Our work uncovers the critical association of B3GNT5 overexpression and glycosylation with enhanced CSCs properties in BLBC. These findings suggest that B3GNT5 has the potential to become a prognostic marker and therapeutic target for BLBC.