SYT8 Drives Colorectal Cancer Progression and Immune Evasion via the SETD1A-H3K4me3 Axis

By integrating transcriptomic data from The Cancer Genome Atlas, Gene Expression Omnibus, and a self-established colorectal cancer (CRC) cohort, it was identified that synaptotagmin 8 (SYT8) is significantly up-regulated in tumors and is predictive of poor prognosis. Single-cell RNA sequencing, immunohistochemistry, and immunofluorescence experiments demonstrate that SYT8 expression is largely confined to tumor cells, predominantly in the nucleus. Functional assays reveal that depletion of SYT8 impairs, whereas its overexpression enhances, CRC cell proliferation and invasion. Transcriptomic profiling indicates an enrichment of cell cycle and epithelial-mesenchymal transition signatures. Mechanistically, co-immunoprecipitation/mass spectrometry identifies SET domain containing 1A (SETD1A) as a direct SYT8-interacting partner. The SYT8-SETD1A axis forms a positive-feedback loop that increases histone H3 lysine 4 trimethylation (H3K4me3) levels and drives the transcription of protumorigenic genes. Immune profiling further indicates that high SYT8 expression correlates with increased regulatory T-cell infiltration, suggesting an immunosuppressive microenvironment and potential resistance to immunotherapy. Collectively, SYT8 promotes CRC progression through the SETD1A/H3K4me3-mediated activation of the cell cycle, induction of epithelial-mesenchymal transition, and remodeling of the immune microenvironment. Therefore, SYT8 is established as a prognostic biomarker and serves as a therapeutic target in colorectal cancer.