ALKBH5 deficiency suppresses hepatocarcinogenesis in mice via mA-dependent STAT1 restoration.

RNA mA methylation, as the most prevalent modification in mRNA, is a dynamic and reversible process primarily regulated by mA methyltransferases ("writers"), mA demethylases ("erasers"), and mA recognition proteins ("readers"). It has been shown that N6-methyladenosine (mA) plays a pivotal role in hepatocellular carcinoma (HCC). In this study we investigated the contribution of the mA eraser AlkB homolog 5 (ALKBH5) to hepatocarcinogenesis, particularly during the early stages of liver cancer development. We found that liver-specific Alkbh5 conditional knockout (Alkbh5-cKO) profoundly suppressed DEN/CCl-induced HCC tumorigenesis and development in mice. We further showed that exogenous ALKBH5 expression drove the malignant transformation of immortal normal hepatocytes (HHL5, BNL), whereas ALKBH5 depletion in HCC cells restored hepatocyte-specific functions and suppressed malignancy. By conducting integrated MeRIP-seq/RNA-seq analyses, we identified STAT1 as a key target of ALKBH5-mediated mA demethylation. ALKBH5 directly bound to STAT1 mRNA and reduced its mA modification, thereby decreasing mRNA stability and suppressing STAT1 expression. Downregulated STAT1 inactivated the hepatocyte nuclear factor FOXA3, blocking hepatic differentiation and promoting malignancy. In 42 pairs of clinical HCC samples analyzed, STAT1 was negatively correlated with ALKBH5, and HCC patients with high ALKBH5 and low STAT1 expression exhibited worse clinical outcomes. We conclude that ALKBH5 is a critical oncogene in hepatocarcinogenesis. These results provide novel insights into the epigenetic regulation of hepatocarcinogenesis.