ASS1 Promotes Colorectal Cancer Immune Evasion Through CPT1A-Mediated S100A10 Succinylation.

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Background: Colorectal cancer (CRC) progression is frequently driven by metabolic reprogramming and immune evasion. A crucial metabolic enzyme, argininosuccinate synthetase 1 (ASS1), is dysregulated in a number of malignancies; however, its role in CRC and its effects on the tumor immune microenvironment remain poorly understood. Carnitine palmitoyltransferase 1A (CPT1A)-mediated fatty acid oxidation and post-translational modifications, including succinylation, are emerging as important regulators of tumor behavior.Methods: ASS1 expression was analyzed using The Cancer Genome Atlas (TCGA) database and further validated in 40 paired clinical CRC specimens and cell lines. Functional roles were assessed through knockdown and overexpression experiments in CRC cells, evaluating proliferation, colony formation, migration, and invasion. Mechanisms were explored via co-immunoprecipitation, succinylation assays, protein stability measurements, and co-culture systems with CD8⁺ T cells. Additionally, in vivo tumor growth and changes in the immune milieu were evaluated using a mouse CT26 transplantation model.Results: ASS1 was markedly upregulation in both cultured cell lines and CRC tissues. ASS1 knockdown decreased programmed cell death protein-1 (PD-1) expression and T cell fatigue while enhancing interferon-γ, tumor necrosis factor-α, perforin, and granzyme B secretion, which in turn increased CD8⁺ T cell cytotoxicity and inhibited malignant phenotypes in vitro. Mechanistically, ASS1 transcriptionally activated CPT1A, which promoted S100 calcium-binding protein A10 (S100A10) succinylation at lysine 47, thereby stabilizing S100A10 protein. Overexpression of either CPT1A or S100A10 reversed the tumor growth suppression and impaired immune activation resulting from ASS1 knockdown. In vivo, ASS1 knockdown inhibited tumor growth, downregulated CPT1A and S100A10 expression, and increased CD8⁺ T cell infiltration while reducing PD-1 levels.Conclusions: ASS1 promotes CRC progression and immune escape by regulating the CPT1A-mediated succinylation and stabilization of S100A10. These findings highlight the ASS1/CPT1A/S100A10 axis as a potential therapeutic target for CRC.