G2E3 Suppresses the Tumor-Killing Function of CD8+ T Cells in Hepatocellular Carcinoma by Boosting CLCN2 Ubiquitination

In the pathogenesis of hepatocellular carcinoma (HCC), impaired CD8⁺ T cell function is a critical factor in immune evasion. Although CLCN2 has been implicated in immunomodulation, its role in regulating CD8⁺ T cell-mediated antitumor immunity in HCC remains unclear. The expression of G2E3 in HCC was analyzed using the TCGA database, qPCR, and western blot. The UbiBrowser database was employed to predict CLCN2 as a downstream substrate of G2E3. Protein interactions were validated via Co-IP and in vivo ubiquitination assays. IFN-γ, TNF-α, and Granzyme B levels were measured using ELISA kits, while CD44 and CD134 levels in CD8⁺ T cells were examined via flow cytometry. The cytotoxic activity of CD8⁺ T cells against HCC cells was evaluated using an LDH assay. An allograft mouse tumor model was utilized to determine whether the G2E3-CLCN2 axis drove HCC progression by suppressing T cell immunity. We herein discovered that G2E3 was highly expressed in HCC and positively linked with poor prognosis. Mechanistically, G2E3 functioned as an E3 ubiquitin Ligase, mediating the ubiquitination and subsequent degradation of CLCN2. Rescue experiments revealed that CLCN2 enhanced the antitumor activity of CD8⁺ T cells, whereas G2E3 overexpression attenuated this effect. Furthermore, in an allograft mouse tumor model, activation of the G2E3-CLCN2 axis reduced CD8⁺ T cell infiltration and activity in tumors, thereby driving tumor growth. This investigation elucidates the molecular mechanism by which HCC suppresses CD8⁺ T cell function to facilitate immune escape, suggesting that targeting the G2E3-CLCN2 axis may represent a potential therapeutic strategy to enhance antitumor immunity.