YBX1 is required for maintaining PD-L1 expression in intrahepatic cholangiocarcinoma by regulating STAT1 stability in an m5C-dependent manner.

[BACKGROUND] Intrahepatic cholangiocarcinoma (ICC) is the second most frequent primary liver cancer. The involvement of Y-box binding protein 1 (YBX1) in tumor advancement is well-documented. However, its function in ICC is not fully understood. This study aimed to explore the function and regulatory mechanism of YBX1 in ICC and provide evidence for YBX1 as a potential new approach for immunotherapy in ICC.

[METHODS] Tissue immunohistochemistry, TCGA, and GEO databases were used to analyze the expression of YBX1 in ICC. The expression of YBX1 was silenced and overexpressed in cell lines. Both in vitro and in vivo assays were conducted to examine the antitumor T-cell responses. Actinomycin D, RNA immunoprecipitation, and methylated RNA immunoprecipitation assays were used to identify mechanism of YBX1 on downstream genes. Immunofluorescence assay was used to validate the association between YBX1 and relevant genes in clinical specimens of ICC.

[RESULTS] The research findings indicated that ICC exhibited high levels of YBX1 expression, which was strongly associated with unfavorable outcomes. YBX1 promoted tumor progression by suppressing antitumor T-cell responses. YBX1 enhanced signal transducer and activator of transcription 1 (STAT1) translation by serving as a 5-methylated cytosine (m5C) reader and activating the STAT1/PD-L1 pathway. Mouse experiments and clinical samples of ICC confirmed the strong correlation between the levels of YBX1, STAT1, and PD-L1 expression.

[CONCLUSIONS] YBX1 regulates STAT1 stability in an m5C dependent manner and maintains PD-L1 expression in ICC.