Background and Aims: Topoisomerase I (TOP1) participates the repair of DNA double-strand breaks (DSBs) upon radiation therapy (RT). RNF144A mediates ubiquitination of catalytic subunit of DNA protein kinase (DNA-PKcs), a critical factor in DSB repair. This study aimed to investigate the natural killer (NK) cell-mediated radiosensitization with TOP1 inhibition and the mechanism by DNA-PKcs/RNF144A.
Methods: In vitro synergism with TOP1i or cocultured NK cells and RT were evaluated in human hepatocellular carcinoma (HCC) cell lines (Huh7/PLC5) by clonogenic survivals. Orthotopic xenografts were treated with Lipotecan and/or RT. Protein expression was analyzed by western blotting, immunoprecipitation, subcellular fractionation, and confocal microscopy.
Results: Lipotecan/RT had a superior synergistic effect to RT on HCC cells. Combined RT/Lipotecan reduced the xenograft size by 7-fold than RT ( p <0.05). Lipotecan caused more radiation-induced DNA damage and DNA-PKcs signaling. The expression of major histocompatibility complex class I-related chain A and B (MICA/B) on tumor cells is associated with the sensitivity to NK cell-mediated lysis. Cocultured NK and HCC cells with Lipotecan radiosensitized HCC cells/tissues with the expression of MICA/B. RNF144A increased more in Huh7 cells with combined RT/TOP1i, and reduced the prosurvival function of DNA-PKcs. The effect was reversed by inhibiting the ubiquitin/proteasome system. In comparison, RNF144A decreased through nuclear translocation with the cumulated DNA-PKcs and radio-resistance of PLC5 cells.
Conclusions: TOP1i reinforces NK cell-activated anti-HCC effect of RT through RNF144A mediated DNA-PKcs ubiquitination. RNF144A provides a reason for differentiating radiosensitization effect between HCC cells.
Competing Interests: WNY is a full-time employee of Taiwan Liposome Company. JCHC has been an editorial board member of Journal of Clinical and Translational Hepatology since 2021. The other authors have no conflict of interests related to this publication.
(© 2023 Authors.)