Yin Yang 1 Promotes Antiprogrammed Cell Death‐1 Resistance in Hepatocellular Carcinoma through Polypeptide N‐Acetylgalactosaminyltransferase 16‐Mediated Glycosylation of Programmed Death Ligand‐1

Immune checkpoint inhibitors (ICIs) are widely used for treating hepatocellular carcinoma (HCC), yet their efficacy remains limited, with suboptimal response rates. The predictive power of the current biomarker, programmed death ligand-1 (PD-L1), is limited by detection variability and glycosylation, underscoring the need for complementary biomarkers to enhance predictive accuracy. In this study, mass spectrometry was employed to identify proteomic alterations in HCC tissues from responders and nonresponders to anti-programmed cell death-1 (PD-1) therapy. Survival analysis established the role of Yin Yang 1 (YY1) in determining ICI efficacy. Coculture models of hepatoma and CD8⁺ T cells revealed the immunosuppressive function of YY1. Transcriptome sequencing identified polypeptide N-acetylgalactosaminyltransferase 16 (GALNT16) as a transcriptional target of YY1, and subsequent Western blot and coimmunoprecipitation assays demonstrated that GALNT16 augments PD-L1 expression. Furthermore, in vivo mouse models demonstrated that YY1 knockdown potentiated the efficacy of anti-PD-1 therapy, an effect that was partially reversed by GALNT16 overexpression. Specifically, YY1 upregulates GALNT16, which in turn promotes PD-L1 glycosylation and stability, leading to diminished CD8⁺ T cell activity. Thus, GALNT16 knockdown rescued the compromised CD8⁺ T cell cytotoxicity induced by YY1. Collectively, these results elucidate the YY1/GALNT16/PD-L1 axis as a pivotal mechanism underlying HCC resistance to ICI therapy. This highlights the therapeutic potential of targeting PD-L1 glycosylation pathways.