ALYREF Promotes Progression of Intrahepatic Cholangiocarcinoma through Increasing the Level of Isocitrate Dehydrogenase 1 in an m5C-Dependent Manner.

RNA 5-methylcytosine (m5C) modification has emerged as an important regulatory mechanism in the progression of human cancers, including hepatobiliary tumors. The m5C "reader" Aly/REF export factor (ALYREF) was recently found to be identified as a prognostic biomarker in liver cancer. However, its exact role in intrahepatic cholangiocarcinoma (ICC) progression is unclear. In this study, ALYREF was found to be upregulated in ICC tissues and cells. The gain- and loss-of-function experiments indicated that ALYREF promoted cell proliferation and invasion and suppressed cell apoptosis. Moreover, we found that isocitrate dehydrogenase 1 (IDH1), a metastatic marker of liver cancer, was also upregulated in ICC tissues, displayed a relatively strong positive correlation with the level of ALYREF, and was positively regulated by ALYREF. As an m5C "reader", ALYREF interacted with m5C-IDH1 mRNA and increased its stability. ALYREF knockdown partially eliminated the promotion of IDH1 on ICC cell proliferation and invasion. ALYREF positively regulated NRF2-driven glutathione synthesis in ICC cells, which was reversed by IDH1 silencing. Finally, in a xenograft tumor mouse model, knockdown of ALYREF or treatment with ivosidenib (an IDH1 inhibitor) significantly suppressed tumor growth in vivo. In conclusion, ALYREF promotes ICC progression by increasing IDH1 levels in an m5C-dependent manner.