CSTF2-mediated 3'UTR shortening drives oncogenic activation of GPC3 in hepatocellular carcinoma.

Alternative polyadenylation (APA) generates mRNA isoforms with distinct 3' untranslated regions (3'UTRs), thereby influencing transcript stability and translation. In cancer, 3'UTR shortening can activate oncogenes by escaping microRNA (miRNA)-mediated repression, but its role in hepatocellular carcinoma (HCC) remains poorly defined. Here, we profiled mRNA length alterations in multistage human HCC transcriptome datasets and investigated their functional consequences. Approximately 77% of mRNAs with altered length exhibited 3'UTR shortening. Glypican-3 (GPC3) was the most prominently upregulated shortened transcript, and high GPC3 expression was associated with poor prognosis in HCC. GPC3 knockdown reduced proliferation and induced apoptosis, whereas GPC3 overexpression promoted cell growth. Among APA regulators, Cleavage Stimulation Factor 2 (CSTF2) was upregulated in HCC, correlated positively with GPC3 expression, and predicted adverse clinical outcomes. Modulation of CSTF2 expression altered GPC3 3'UTR length, with CSTF2 overexpression promoting GPC3 3'UTR shortening, increasing GPC3 protein expression, enhancing proliferation, and suppressing apoptosis. Further analysis revealed that GPC3 3'UTR shortening removed binding sites for miR-96-5p and miR-140-5p, relieving miRNA-mediated translational repression. These findings identify CSTF2-driven APA as a mechanism of oncogenic GPC3 activation in HCC and suggest the CSTF2-GPC3 axis as a potential therapeutic target.