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

Abstract Semaphorins (SEMAs) comprise a diverse family of membrane-associated proteins whose dysregulation is implicated in various cancers, influencing tumor progression and immune responses. However, the role of SEMAs in colorectal cancer (CRC) remains underexplored. This study demonstrates that Semaphorin 6A (SEMA6A) is downregulated in CRC tissues, with low SEMA6A expression correlating with increased tumor aggressiveness and poor prognosis in CRC patients. Functional assays illustrate that SEMA6A overexpression exerts anti-tumor effects both in vitro and in vivo, while integrated RNA-seq and proteomic analyses identify ISG15 as a key downstream effector negatively regulated by SEMA6A. Mechanistically, SEMA6A inhibits the JAK-STAT3 pathway, leading to decreased ISG15 expression, which in turn abrogates the ISGylation-dependent stabilization of TGF-β1 and promotes its degradation, as confirmed by molecular docking, co-immunoprecipitation, and cycloheximide chase assays. Consequently, in vitro co-culture assays and in vivo experiments reveal that SEMA6A overexpression in tumor cells enhances CD8 + T cell cytotoxicity via blocking the ISG15/TGFβ axis. Bioinformatics analyses indicate that patients with CRC exhibiting high SEMA6A and low ISG15 expression show improved responses to immunotherapy. Importantly, SEMA6A overexpression reshapes the tumor microenvironment, boosts anti-tumor immunity of CD8 + T cells and inhibits immune evasion, thereby potentiating anti-PD-1 immunotherapy in vivo . Collectively, these findings highlight the potential of SEMA6A as a dual therapeutic strategy in CRC: inhibiting cancer progression while enhancing anti-tumor immunity by targeting the ISG15/TGF-β1 axis. Thus, SEMA6A represents both a prognostic indicator and a promising target to improve immunotherapy efficacy and enable personalized treatment strategies in CRC.