METTL3-mediated m6A methylation on lncRNA H19 inhibits intrahepatic cholangiocarcinoma progression through PPARγ downregulation

Intrahepatic cholangiocarcinoma (ICCA), the second most prevalent primary liver malignancy, remains poorly understood at the molecular level. Research into the function of N6-methyladenosine (m6A) modification in the formation of ICCA and its potential as a therapeutic approach is being spurred by mounting evidence that it plays a crucial role in tumor biology. Immunohistochemical examination of patient samples in this investigation revealed a significant decrease in m6A methyltransferase METTL3 expression, accompanied by lower levels, which were associated with a lower overall survival rate. Functional assays demonstrated that the enforced expression of METTL3 inhibited ICCA cell proliferation and migration, while concurrently increasing the levels of the long non-coding RNA H19. Mechanistic experiments using RNA-binding protein immunoprecipitation and methylated RNA immunoprecipitation confirmed that METTL3 directly interacted with H19 and enhanced its m6A modification. Importantly, silencing of H19 reversed the growth- and migration-suppressive effects of METTL3, whereas H19 overexpression counteracted the phenotype induced by METTL3 downregulation. Further analysis revealed that the METTL3-H19 regulatory axis suppressed the expression of peroxisome proliferator-activated receptor gamma (PPARγ). Moreover, an oncolytic adenovirus engineered to overexpress H19, in combination with the PPARγ inhibitor BAY-4931, elicited potent antitumor effects both <i>in vitro</i> and <i>in vivo</i>. Collectively, these findings identify METTL3-mediated m6A modification of H19 as a critical suppressor of ICCA progression through modulation of PPARγ signaling. One interesting treatment option for ICCA may be the use of H19-armed oncolytic adenoviruses, especially when combined with PPARγ suppression.