FXR1 ‐Directed Alternative Splicing of MK5 Drives Hepatocellular Carcinoma Progression by Activating GSK3β Signaling

Alternative splicing plays a crucial role in the development and progression of hepatocellular carcinoma (HCC), yet the underlying regulatory mechanisms and therapeutic potential remain largely unexplored. Here, we identified the RNA-binding protein FMR1 autosomal homolog 1 (FXR1) as a key driver of HCC pathogenesis through the regulation of alternative splicing. FXR1 was highly expressed in HCC tissues, and its elevated expression was associated with a poor prognosis. Mechanistically, high FXR1 induced the retention of exon 6 in mitogen-activated protein kinase-activated protein kinase 5 (MK5), generating a long, kinase-competent isoform (termed MK5-L). This isoform acted as an important oncogenic factor for HCC progression by phosphorylating GSK3β and subsequently activating the Wnt/β-catenin pathway. Functional studies showed that the FXR1/MK5-L axis is critical for HCC cell proliferation and metastasis, both in vivo and in vitro. Importantly, therapeutic intervention using an FXR1-targeting antisense oligonucleotide (ASO) effectively suppresses tumor progression and metastasis in preclinical models by shifting splicing toward the inactive MK5-S isoform. Overall, our study unveils a novel splicing-mediated oncogenic pathway and establishes FXR1 and its downstream target MK5-L as promising prognostic biomarkers and therapeutic targets for HCC.