Up-regulation of interferon-stimulated gene 15 and its conjugation machinery, UbE1L and UbcH8 expression by tumor necrosis factor-α through p38 MAPK and JNK signaling pathways in human lung carcinoma

Interferon-stimulated gene 15 (ISG15) is a member of the family of ubiquitin-like proteins. Similar to ubiquitin, conjugation of ISG15 to cellular proteins requires cascade reactions catalyzed by at least 2 enzymes, UbE1L and UbcH8. Expression of ISG15 and its conjugates is up-regulated in many cancer cells, yet the underlying mechanism of up-regulation is still unclear. In this study, we showed that TNF-alpha, similar to the response by IFN-beta, could directly induce expression of ISG15 and its conjugation machinery, UbE1L and UbcH8, in human lung carcinoma, A549. The early response of their expression was effectively blocked by specific inhibitors of p38 MAPK (SB202190) and JNK (SP600125), but not by B18R, a soluble type-I IFN receptor. In addition, luciferase reporter assay together with serial deletions and site-directed mutagenesis identified a putative C/EBP beta binding element in the ISG15 promoter, which is necessary to the response by TNF-alpha. Taken together, expression of ISG15 and ISG15 conjugation machinery in cancer cells is directly up-regulated by TNF-alpha via p38 MAPK and JNK pathways through the activation of C/EBP beta binding element in the ISG15 promoter. This study provides a new insight toward understanding the molecular mechanism of ISG15 system and inflammatory response in cancer progression.