A novel diagnostic and prognostic biomarker FSD1L facilitates EMT and Lenvatinib resistance via the WNT/β-catenin pathway in hepatocellular carcinoma.

BACKGROUND: FSD1L, a gene involved in cytoskeletal organization and cell adhesion, is highly expressed in hepatocellular carcinoma (HCC) tissues with invasion/metastasis and lenvatinib-resistant cells, but its role in HCC remains unclear. Therefore, this study aimed to investigate the function of FSD1L in HCC progression as well as the underlying molecular mechanisms.

METHODS: Database mining identified upregulated genes in invasive/metastatic HCC lesions and lenvatinib-resistant HCC cells. FSD1L expression was analyzed across 9 HCC cohorts (8 with normal tissues). Kaplan-Meier survival, ROC (diagnostic efficacy), and Cox regression (prognostic value) analyses were performed. Correlations between FSD1L and proliferation (MKI67/PCNA)/metastasis (MMP2/9) markers were examined. FSD1L was silenced via siRNA/shRNA in MHCC-97H, Huh7, and lenvatinib-resistant Huh7 cells, whereas Hep3B cells were subjected to overexpression plasmid transfection. Cell proliferation (CCK-8), apoptosis (flow cytometry), migration (wound-healing), and lenvatinib sensitivity (IC₅₀/CCK-8) were assessed in vitro, complemented by in vivo xenograft studies in nude mice to evaluate tumorigenicity. GSEA explored dysregulated oncogenic pathways. WNT agonist LiCl was used in rescue experiments to verify the role of WNT/β-catenin pathway in FSD1L-mediated EMT, proliferation, migration, and lenvatinib resistance.

RESULTS: FSD1L was consistently upregulated in lenvatinib-resistant cells and HCC lesions with invasion/metastasis. FSD1L/Fsd1l overexpression was observed in all 8 human HCC cohorts and a transgenic mouse HCC model (all p < 0.05). High FSD1L correlated with poor overall survival (OS) in TCGA-LIHC (HR = 1.77, p < 0.001), positively correlated with PCNA, KI67, MMP2, and MMP9. It showed favorable diagnostic efficacy (AUC: 0.645-0.97, all p < 0.05) and was an independent prognostic factor (multivariate Cox: HR = 3.207, p = 0.002). Loss- and gain-of-function studies established FSD1L as a promoter of malignancy and lenvatinib resistance, validated by xenograft tumor suppression upon sh-FSD1L-1 treatment. GSEA indicated enrichment of WNT/β-catenin pathway in FSD1L-high HCC. Mechanistically, FSD1L knockdown reduced β-catenin, c-Myc, p-GSK3β (Ser9), and modulated EMT markers; these effects were reversed by LiCl.

CONCLUSION: FSD1L is a novel oncogenic driver in HCC that is selectively enriched in metastatic and lenvatinib-resistant contexts. It activates the WNT/β-catenin pathway to regulate HCC proliferation, EMT and lenvatinib resistance. FSD1L holds promise as a dual biomarker for diagnosis/prognosis and a potential therapeutic target for lenvatinib resistance in HCC.