SEMA6A inhibits tumor progression and boosts anti-tumor immunity via blocking the ISG15/TGFβ axis in colorectal cancer

Semaphorin is an axon-guiding factor regulating nervous system development. A growing body of evidence shows that semaphorin could regulate tumor progress and immune responses. The research found that Semaphorin 6A (SEMA6A) may play a dual role in the occurrence and development of tumors. Nevertheless, the regulatory role of SEMA6A in colorectal cancer (CRC) remains unclear. This study aimed to investigate the prognostic value, expression pattern, clinical significance, and immune effects of SEMA6A in CRC. Through multi-database analyses and validation with clinical specimens and tissue microarray, we identified reduced SEMA6A expression in CRC tissues, establishing it as an independent prognostic factor. Functional enrichment and immune infiltration analyses revealed SEMA6A's protective role through tumor immune microenvironment modulation, with elevated expression correlating with enhanced immune cell infiltration. Cellular experiments including CCK8, Transwell, and immunofluorescence assay demonstrated SEMA6A can suppress the proliferation, migration, and invasion ability of CRC. Integrated RNA-seq and proteomic analyses, we identified ISG15 as a downstream effector of SEMA6A. Functional validation confirmed that ISG15 promotes malignant progression and counteracts SEMA6A-mediated tumor suppression. Coculture experiments revealed that SEMA6A can activate the CD8+ T cells and inhibit the expression of TGF-β1 by reducing the expression level of ISG15. Moreover, SEMA6A could induce the response of CRC to PD-1 monoclonal antibody by up-regulating immunostimulatory factors, thus playing an anti-tumor role in a subcutaneous CRC model. Our findings indicate that SEMA6A can stratify the risk of CRC patients and serve as a novel biomarker to predict response to immunotherapy, providing novel insights into precision medicine and immunotherapeutic strategies for CRC.