SOX2/TSTA3 suppresses CD8+ T-cell-mediated immune response in breast cancer by regulating programmed death ligand-1 fucosylation

Abstract

Immune escape in breast cancer is a primary contributor to immunotherapy resistance and poor patient prognosis. Fucosylation is essential for tumor progression, but the regulatory mechanism of its key enzyme, guanosine diphosphate-L-fucose synthase (TSTA3), within the breast cancer immune microenvironment remains unexplored. This study combined bioinformatics and experimental approaches to investigate TSTA3 in breast cancer. TSTA3 expression was validated by quantitative real-time reverse transcription polymerase chain reaction and western blotting. Functional assays in a tumor–T-cell coculture system showed that TSTA3 knockdown enhanced CD8+ T-cell cytotoxicity and suppressed tumor malignancy. Mechanistically, TSTA3 fucosylated programmed death ligand-1, and this modification was confirmed by Ulex europaeus agglutinin-1 chromatography and co-immunoprecipitation. SOX2 was identified as an upstream transcription factor of TSTA3 via chromatin immunoprecipitation and dual-luciferase assays. The SOX2/TSTA3/programmed death ligand-1 axis was functionally validated in rescue experiments and in vivo tumor models. TSTA3 was highly expressed in breast cancer tumors. Its knockdown enhanced CD8+ T-cell cytotoxicity and suppressed tumor proliferation, migration, and invasion in vitro. Mechanistically, TSTA3 upregulated programmed death ligand-1 expression in a fucose-dependent manner and, partly through programmed death ligand-1, suppressed CD8+ T-cell-mediated antitumor immune responses. SOX2 directly activated TSTA3 transcription, leading to programmed death ligand-1 stabilization via fucosylation. In vivo, targeting the SOX2/TSTA3/programmed death ligand-1 axis inhibited tumor growth and boosted CD8+ T-cell activity. Collectively, this study uncovered a novel mechanism whereby SOX2 transcriptionally activated TSTA3, which fucosylated programmed death ligand-1 and, partly through programmed death ligand-1, suppressed CD8+ T-cell-mediated antitumor immune responses, providing a theoretical basis for targeting the SOX2/TSTA3/programmed death ligand-1 axis to enhance immunotherapy in breast cancer.