Sialylated IgG expressed in triple-negative breast cancer cells promotes cancer progression by promoting glycolysis

BACKGROUND: Triple-negative breast cancer (TNBC) is among the most aggressive and lethal subtypes of breast cancer. To date, there are no effective targeted treatment targets. Sialylated IgG (SIA-IgG), with unique sialylated modifications for N-glycosylation at site 162 of the heavy chain of IgG, which was found to be expressed in a variety of cancer cells as a novel procancer factor. Here, we aimed to investigate the expression frequency and procancer mechanisms of SIA-IgG in TNBC, and determine whether the SIA-IgG is a key factor that promotes TNBC and a novel target for TNBC therapy. METHODS: Immunohistochemical staining, immunofluorescence, and TCGA database analysis were performed to analyze the frequency of SIA-IgG expression in TNBC and the correlation between SIA-IgG expression and patient prognosis. Colony formation, transwell, and Matrigel-transwell assays were used to assess the proliferative and invasive abilities of SIA-IgG. Proteomic mass spectrometry and immunoprecipitation were utilized to identify the key procancer mechanisms of SIA-IgG. Oxygen consumption and extracellular acidification assays were used to elucidate the promotion of glucose metabolism and its mechanism in TNBC. Subcutaneous xenograft models were established to examine the antitumour effects of targeting SIA-IgG. RESULTS: SIA-IgG was frequently detected in TNBC cells and was negatively associated with prognosis. Moreover, exogenously added SIA-IgG significantly enhanced the proliferation, migration and invasion of TNBC cells. Importantly, SIA-IgG significantly promoted TNBC progression by accelerating glycolysis and lactate reuse, which was dependent on its unique N-glycosylation at the Asn162 site. Conversely, the inhibition of SIA-IgG inhibited cancer cell proliferation and invasion by decreasing ATP and lactate production. Knockdown of SIA-IgG, as well as treatment with the anti-SIA-IgG antibody, significantly inhibited TNBC growth in vivo. Mechanistically, SIA-IgG promoted glycolysis and the lactate cycle mainly through the activation of two pathways: the integrin α6β4-FAK-AKT-HIF-1α-MCT4 axis, and the integrin α6β4-CD44-MCT1 axis. CONCLUSIONS: These findings suggest that SIA-IgG, by enhancing glycolysis and the lactate cycle, induces metabolic reprogramming and thereby promotes the development of TNBC, making it a promising target for targeted therapy in TNBC.