Fig. 5: Sorafenib promotes USP18 accumulation via the STING/IRF3/ISG15 axis in HCC cells.

A mRNA expression of USP18 in HepG2 cells treated with indicated concentrations of sorafenib for 24 h. B Expression of USP18 ubiquitination in anti-USP18 immunoprecipitation and whole-cell lysates (input) derived from HepG2 cells treated with indicated concentrations of sorafenib for 24 h and MG132 (10 μM) for 4 h. *, heavy chain. C mRNA expression of ISG15 in HepG2 cells treated with indicated concentrations of sorafenib for 24 h (means ± SEM, *p < 0.05, ****p < 0.0001, student’s t-test). D Protein expression of ISG15 in HCC-P and HCC-SR cells. The intensities of bands were analyzed by Image J and normalized to the corresponding HCC-P cells. E The ISG15 levels in HCC tissue samples of non-responders (NR) and responders (R) to sorafenib treatment were assessed using the GSE109211 dataset (means ± SEM, *p < 0.05, unpaired Student’s t-tests). F The Kaplan–Meier curves demonstrate the association between ISG15 expression and overall survival among HCC patients in the TCGA cohort. G Protein expression of USP18 in HCC cells transfected without or with HA-ISG15 plasmid for 48 h. H Protein expression of USP18 in HCC cells transfected without or with ISG15 siRNA for 48 h and treated with sorafenib for 24 h. I IRF3 binding sequence in the ISG15 promoter region was predicted with the JASPAR website. J Correlations between expression of IRF3 and ISG15 in HCC tissues. The r-value and p-value were calculated using Pearson correlation analysis. K The key protein expression of the STING signaling pathways in HCC cells treated with indicated concentrations of sorafenib for 24 h. L Protein expression of ISG15 and USP18 in HCC cells treated with 10 μM sorafenib and/or 2 μM H151 for 24 h. The intensities of bands were analyzed by Image J and normalized to the control cells treated with DMSO.