Immunotherapies such as
immune checkpoint blockade have achieved remarkable success in treating
cancer. Unfortunately, response rates have been limited in multiple
cancers including
hepatocellular carcinoma (HCC). The critical function of epigenetics in tumor immune evasion and anti-
tumor immunity supports harnessing epigenetic regulators as a potential strategy to enhance the efficacy of
immunotherapy. Here, we discovered a
tumor-promoting function of FTSJ3, an
RNA 2'-O-methyltransferase, in HCC by suppressing anti-
tumor immune responses. FTSJ3 was upregulated in
hepatocellular carcinoma, and high FTSJ3 expression correlated with reduced patient survival. Deletion of FTSJ3 blocked HCC growth and induced robust anti-
tumor immune responses. Mechanistically, FTSJ3 suppressed
double-stranded RNA (dsRNA)-induced IFNβ signaling in a 2'-O-methyltransferase manner. Deletion of
RNA sensors in HCC cells or systemic knockout of type I IFN receptor IFNAR in mice rescued the in vivo
tumor growth defect caused by FTSJ3 deficiency, indicating that FTSJ3 deletion suppresses
tumor growth by activating the
RNA sensor-mediated type I IFN pathway. Furthermore, FTSJ3 deletion significantly enhanced the efficacy of PD-1
immune checkpoint blockade. The combination of FTSJ3 deficiency and anti-PD-1 antibody treatment effectively eradicated
tumors and increased the survival time. In conclusion, this study reveals an epigenetic mechanism of tumor immune evasion and, importantly, suggests FTSJ3-targeting
therapies as potential approach to overcome
immunotherapy resistance in HCC patients.