Lactate-associated H3K18la Upregulates RNF166 to Promote Immune Evasion in Hepatocellular Carcinoma by Remodeling C-Jun Ubiquitination

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related mortality, and PD-L1-mediated immune evasion is a major mechanism of tumor immune suppression and an important target of immune checkpoint blockade. Here, we identified RNF166 as an E3 ubiquitin ligase that promotes immune evasion in HCC. RNF166 expression was upregulated in HCC tissues and correlated with PD-L1 levels, whereas RNF166 did not directly affect the proliferation or apoptosis of HCC cells. In immunocompetent mouse models, RNF166 overexpression accelerated tumor growth and suppressed CD8 + T-cell infiltration and cytotoxic function, while these effects were dependent on PD-L1 signaling and were attenuated in immunodeficient settings. Mechanistically, RNF166 physically interacted with c-Jun and promoted K63-linked ubiquitination of c-Jun at K50/K56, which was associated with reduced K48-linked ubiquitination and enhanced c-Jun stability. Stabilized c-Jun bound to the PD-L1 promoter and promoted PD-L1 transcription, thereby linking RNF166-mediated c-Jun stabilization to tumor immune suppression. Upstream, lactate accumulation increased H3K18la enrichment at the RNF166 promoter and contributed to RNF166 transcriptional upregulation. Therapeutically, pharmacological inhibition of c-Jun with T-5224 enhanced the antitumor effect of anti-PD-L1 blockade. Collectively, our findings delineate a lactate-H3K18la-RNF166-c-Jun-PD-L1 axis that promotes immune evasion in HCC and suggest that targeting RNF166 or the RNF166-c-Jun axis may improve PD-1/PD-L1-based immunotherapy.