Small HBV surface antigen drives regorafenib resistance in HCC via KIAA1429‐dependent m6A modification of CCR9

Abstract A substantial body of literature, including our own, points to a connection between hepatitis B virus (HBV) infection and the development of drug resistance in hepatocellular carcinoma (HCC), particularly against sorafenib. However, the influence of HBV on resistance to regorafenib, another therapeutic agent, has been less studied. In this study, we used the GEO database (GSE87630) and clinical samples to demonstrate that C‐C motif chemokine receptor 9 (CCR9) was highly expressed in HBV‐related HCC and predicted poor overall survival. Its overexpression correlated with HBsAg‐positive HCC patients. Both univariate and multivariable Cox regression analysis elucidated CCR9 was an independent risk factor for poor overall survival in HCC patients. Our in vitro findings further revealed that HBV structural proteins, small HBV surface antigen (SHBs), triggered an upregulation of CCR9. Functional assays showed that SHBs enhanced HCC cell proliferation, migration, and invasion, increased ABCB1 and ABCC1 expression, and promoted regorafenib resistance via CCR9. Intriguingly, overexpression of HBV plasmid and an AAV‐HBV mouse model both exhibited a significant elevation in global N6‐methyladenosine (m6A) levels. Further investigations revealed that SHBs elevated these m6A levels, upregulated CCR9 and stabilized CCR9 mRNA through KIAA1429‐mediated m6A modification, with sites 1373 and 1496 on CCR9 mRNA being critical for modification. In conclusion, SHBs promoted HCC progression and regorafenib resistance via KIAA1429‐mediated m6A modification of CCR9. Our findings suggested that CCR9 could be a potential prognostic biomarker and a valuable molecular therapeutic target of regorafenib resistance in HBV‐related HCC.