TONSL promotes hepatocellular carcinoma progression and radioresistance by orchestrating DNA damage repair and cell cycle dynamics

Tonsoku-like, DNA repair protein (TONSL) plays a critical role in DNA replication in normal cells. However, its function in hepatocellular carcinoma (HCC) and its role in HCC radiotherapy-resistant remains largely unknown. The goal of the current study is to identify the function role of TONSL and its underlying mechanism in HCC. The mRNA expression level of TONSL and its correlation with clinical features was evaluated from the Cancer Genome Atlas (TCGA), the Gene expression Omnibus (GEO), and ICGC Data Portal (ICGC-LIRI-JP) databases. The protein expression level of TONSL in HCC was further verified by immunohistochemical staining from HCC tissue microarray. Kaplan–Meier analysis was conducted to explore the association between TONSL expression level and the prognosis of patients with HCC. The correlation between TONSL expression level and immune cell infiltration was explored using CIBERSORT TIMER algorithms and multiplex immunohistochemistry (mIHC) staining assay. The function role of TONSL in HCC was explored by CCK-8, Edu, and colony formation assays. The underlying mechanism of TONSL in HCC was investigated by western blotting and flow cytometry assays. Our study demonstrated that the expression level of TONSL was significantly higher in HCC tissues compared to that in non-tumor tissues using RNA expression profile from the TCGA, GEO, and ICGC-LIRI-JP datasets. The high expression level of TONSL was further confirmed at the protein level using the immunohistochemical staining from HCC tissue microarray. It was found that TONSL was mainly expressed in the nucleus of HCC cells, which was consistence with the subcellular localization of other cancer cells as detected by immunofluorescent staining from the Human Protein Atlas (HPA) databases. High expression of TONSL predicted poor overall survival (OS), disease-free survival (DFS), and recurrence-free survival (RFS) in patients with HCC. Bioinformatics analysis showed that TONSL was positively correlated with the infiltration of exhausted T cells and regulatory T cells in HCC, and negatively correlated with the infiltration of effector CD8 T cells. Consistently, mIHC further confirmed that high TONSL expression was associated with an immunosuppressive tumor microenvironment. Functionally, silencing TONSL inhibited HCC cell proliferation by reducing cells entering the proliferation phase, in the meantime enhancing cell apoptosis. TONSL expression was higher in radiotherapy-resistant HCC cells in comparison with its parental HCC cell line. Downregulation of TONSL re-sensitized the radioresistant HCC cells to radiotherapy through the homologous recombination (HR) repair pathway. Furthermore, high expression of TONSL was negatively associated with the response to sorafenib treatment. Knockdown of TONSL alleviated sorafenib resistance in HCC cells. Finally, pan-cancer analysis showed that TONSL was highly expressed in various cancer types and was associated with poor prognosis in various cancer types. Our finding highlights the critical role of TONSL in HCC progression and its contribution to radiotherapy and sorafenib resistance by orchestrating DNA damage repair and cell cycle dynamics, suggesting its potential as a therapeutic target and prognostic biomarker.