Circular RNA CDYL facilitates hepatocellular carcinoma stemness and PD-L1+ exosomes-mediated immunotherapy resistance via stabilizing hornerin protein by blocking synoviolin 1-mediated ubiquitination.

Despite the revolutionary progress in cancer immunotherapy, only a minority of hepatocellular carcinoma (HCC) patients respond to immune checkpoint inhibitors (ICIs). In this study, we found that the oncogenic circular RNA Circ-CDYL in HCC influences the efficacy of immunotherapy and the stemness characteristics of HCC cells by interacting with the hornerin (HRNR) protein. The degraded anti-PD-L1 immunotherapy responses induced by Circ-CDYL and HRNR were confirmed by peripheral blood mononuclear cells (PBMCs) killing assays in HCC cells, patient-derived organoids, and humanized immune system mouse models. Furthermore, Circ-CDYL interference reversed the cytotoxicity and proliferation of CD8+ T cells, resulting in ameliorated immune evasion in tumor spheroids upon anti-PD-L1 treatment. Mechanistically, Circ-CDYL upregulated HRNR expression by stabilizing the HRNR protein through the prevention of its degradation by the E3 ubiquitin ligase synoviolin 1 (SYVN1), which in sequence promoted the phosphorylation of the mTORC1 and p70S6K substrate. The abnormally activated mTORC1-p70S6K signaling increases the stemness of HCC cells and upregulates PD-L1 expression, which may attenuate anti-PD-L1 therapy efficacy via PD-L1+ exosomes. Our study revealed the mechanism by which Circ-CDYL and HRNR regulate the sensitivity of HCC to anti-PD-L1 therapy, and the findings have potential implications for patient stratification and clinical decision-making in HCC immunotherapy.