BTV Remodels the oISG15-Association Proteome.

ISG15 is an interferon-induced ubiquitin-like protein that exerts diverse functions during viral infection. We previously reported that ovine ISG15 (oISG15) promoted bluetongue virus (BTV) replication by stabilizing viral NS1 and VP4 in an ISGylation-independent manner, although the mechanism remained unknown. Here, using the generated anti-oISG15 antibody, we performed immunoprecipitation (IP) coupled with label-free Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) to characterize the oISG15-associated proteome in BTV-infected and uninfected cells. The results showed that BTV infection markedly remodeled the oISG15 association landscape, with decreased enrichment of several autophagy- and trafficking-related proteins and increased enrichment of mitochondrial metabolic proteins in oISG15 immunoprecipitates. Functionally, oISG15 overexpression induced modest alterations in autophagy-related markers in uninfected cells yet attenuated these markers' abundance during BTV infection. Together, this study revealed BTV-induced changes in the oISG15-associated proteome that coincided with alterations in autophagy-related markers.