Fig. 1: USP18 is highly expressed in NPC and impairs radiosensitivity.

A Heatmap of differentially expressed proteins ( | fold change | > 1.5 and p < 0.05) identified by proteome sequencing in five paired NPC biopsy tissues from patients with (irradiation-resistant) or without (irradiation-sensitive) relapse after radiotherapy. B Venn diagram showing common proteins between differentially expressed proteins identified by proteome sequencing and DUBs from the iUUCD database. C Normalized protein expression level of USP18 in these five paired NPC tissues. D RT-qPCR analysis of relative USP18 mRNA expression in NP69 and various NPC cell lines (SUNE1, HONE1, HK-1, S18, 5-8 F, 6-10B and CNE1). E Western blot analysis of USP18 and α-Tubulin protein expression in NP69 and NPC cell lines, along with normal (N) and NPC (T) tissues. F GSEA of the GSE102349 dataset revealed enrichment of radiation response-related and DNA damage response pathways in the USP18 high-expression group. G Clonogenic assays and survival fraction curves of USP18-KO or NC HK1 cells after exposure to varying IR doses. H Flow cytometry analysis of apoptosis rates in USP18-KO or NC HK1 cells with or without 8 Gy IR exposure for 48 h. Representative images and quantitative analysis of γH2AX foci I, comet assay and tail moments J in USP18-KO or NC HK1 cells treated with 8 Gy IR for 0 h, 0.5 h and 4 h. Scale bars, 10 μm, n = 10 I. Scale bars, 100μm, n = 20 J. Macroscopic images K, average tumor volume L, and average weight M of excised tumors in each group (n = 6). Data are presented as mean ± SD in D, G to J, L and M; *p < 0.05, **p < 0.01, ***p < 0.001; p values were determined using two-way ANOVA; n = 3 independent experiments. The unprocessed images of the blots are shown in Fig. S11.