RNF115 upregulation by YBX1-dependent m5C modification promotes hepatocellular carcinoma progression.

5-methylcytosine (m5C) RNA modification plays critical roles in post-transcriptional regulation and cancer progression. However, the downstream effectors of the m5C reader protein YBX1 and their mechanistic contribution to hepatocellular carcinoma (HCC) remain largely undefined. In this study, we performed transcriptome-wide m5C profiling and observed significant heterogeneity in m5C modification patterns in HCC, with differentially methylated genes broadly distributed across the genome except for chromosome Y. We found that YBX1 is markedly upregulated in HCC and significantly correlated with poor patient prognosis. Functionally, YBX1 promoted tumor cell proliferation, migration, and invasion in vitro and in vivo. By integrating m5C MeRIP-seq and YBX1 RIP-seq data, we identified RNF115 as a direct YBX1 target regulated in an m5C-dependent manner. Mechanistic experiments demonstrated that YBX1 binds to m5C-modified motifs within the 3' untranslated region (3'UTR) of RNF115 mRNA, thereby enhancing its stability and translation and resulting in elevated RNF115 protein expression. Clinical cohort analyses revealed that RNF115 overexpression is associated with advanced tumor stage, increased recurrence and metastasis, and poor prognosis in HCC patients. Functional assays in vitro and in vivo confirmed that RNF115 is essential for HCC malignant phenotypes, and RNF115 overexpression rescues the inhibitory effects of YBX1 knockdown. Further mechanistic studies showed that the YBX1/m5C-RNF115 axis promotes HCC progression primarily through activation of the PI3K/AKT signaling pathway. Collectively, our findings uncover a novel epitranscriptomic mechanism by which YBX1 drives HCC malignancy via m5C-dependent stabilization of RNF115, highlighting the YBX1/m5C-RNF115 axis as a promising diagnostic biomarker and therapeutic target for HCC.