ISG15 and non-small cell lung carcinoma: To confirm whether TRIM21 is also ISGylated under physiological conditions, we treated human non-small-cell lung carcinoma A549 cells with IFN-β or IFNA2 and found that the expression of all the studied components of the ISG15-conjugating system were highly elevated, and the two ISGylated bands of TRIM21 were evident (Figs. 1C, D and S2).