Background: Radiotherapy is the main treatment for nasopharyngeal carcinoma (NPC); however radioresistance restricts its efficacy. Therefore, new molecular regulators are required to improve the radiosensitivity of NPC. Chromatin assembly factor 1 subunit B (CHAF1B) plays a role in DNA synthesis and repair, and participates in the progression of various malignancies. However, the expression and function of CHAF1B in NPC is unclear.

Methods: The expression of CHAF1B was determined using real-time PCR and western blotting. CHAF1B expression in 160 human NPC tissue samples was evaluated using immunochemistry (IHC). The correlations between CHAF1B expression and NPC clinicopathological features were determined. The effect of CHAF1B on the radiosensitivity of NPC cells was detected using 3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay and colony formation assays. Apoptosis rates were analyzed using flow cytometry. A nude mouse subcutaneous xenograft model and living fluorescence imaging were applied to evaluate tumor regression in vivo. The molecular mechanisms of radioresistance were confirmed by bioinformatics analysis and detection of phosphorylated H2A histone family member X (γH2AX) foci.

Results: Significantly increased CHAF1B levels were observed in NPC tissues, which correlated positively with radioresistance and poor prognosis. In addition, CHAF1B was upregulated in radioresistant NPC cell lines. Overexpression of CHAF1B reduced, while silencing of CHAF1B enhanced, the radiosensitivity of NPC cells in vitro and in vivo. Mechanistically, CHAF1B inhibited NPC cell apoptosis by promoting DNA damage repair. Finally, the DNA-dependent protein kinase (DNA-PK) pathway was observed to be essential for CHAF1B promotion of DNA damage repair-mediated radioresistance.

Conclusion: The results suggested CHAF1B enhances radioresistance by promoting DNA damage repair and inhibiting cell apoptosis, in a DNA-PK pathway-dependent manner. CHAF1B may serve as a novel factor for predicting radiorsensitivity. Besides, DNA-dependent protein kinase inhibitor could serve as a radiosensitizer for patients with NPC and high CHAF1B expression.