ISG15 expression in response to double-stranded RNA or LPS in cultured Fetal Bovine Lung (FBL) cells

Fetal bovine lung (FBL) cells are used in the culture of viruses which infect cattle and ISG15 plays a role in innate immunity against viral infections. However, whether the expression of ISG15 gene can be induced in FBL cells is still unknown. In this work, the expression of ISG15 in cultured FBL cells was detected after stimulated with poly I:C or LPS. Real-time PCR analyses revealed that the transcript of ISG15 can be induced by poly I:C or LPS. The increased expression of free ISG15 was confirmed via Western blotting. Furthermore, immunofluorescence assays demonstrated that IRF-3 was translocated from the cytoplasm to the nucleus in the FBL cells treated with poly I:C. Chromatin immunoprecipitation assays showed that IRF-3 can bind to the promoter of the bISG15 gene. To demonstrate IRF-3 can promote the expression of bISG15, we establish a luciferase-reporter system of bovine ISG15 gene in 293 T cells. The luciferase assay showed that the over-expression of bovine IRF-3 could activate the promoter of bISG15 gene. Taken together, these results suggest that the expression of bISG15 can be induced in FBL cells stimulated with poly I:C or LPS, and IRF-3 may play a role in inducing the expression of ISG15 in FBL cells.