bcIRF5 activates bcTBK1 phosphorylation to enhance PANoptosis during GCRV infection

TBK1 is an important IFN antiviral signalling factor, and in previous work black carp TBK1 (bcTBK1) and black carp IRF5 (bcIRF5) together promoted cell death in GCRV-infected cells. In this research, bcTBK1 and bcIRF5 were investigated both in vivo and in vitro to delineate their individual and combined functions. This study demonstrated that both bcTBK1 and bcIRF5 expressions were modulated in response to GCRV infection across the intestine, gill, kidney and spleen. In bcgill cells, overexpression of bcTBK1 and bcIRF5 initially suppressed the expression of cell death-related genes, including RIPK1, caspase1, caspase3 and bax, but this suppression was negated upon GCRV infection. In vivo, mRNA expression levels of RIPK1 and related genes varied by tissue following bcTBK1 or bcIRF5 overexpression and GCRV infection. Notably, intracellular co-overexpression of bcTBK1 and bcIRF5 led to significant upregulation of caspase3, caspase1, bax, and IL1β, along with enhanced caspase3 activity post-GCRV infection. This co-expression correlated with higher survival rates in black carp during GCRV infection and increased caspase3 mRNA in the spleen and gills. Hematoxylin-eosin (HE) staining indicated disorganized spleen tissue and edematous, hyperplastic gill changes in co-transfected groups after infection. TUNEL staining of tissue sections showed that DNA breakage was significantly stronger in the co-transfected group than in the other groups during GCRV infection. Further phosphorylation experiments showed that bcIRF5 promoted phosphorylation modification of bcTBK1. Thus, these data suggest that bcIRF5 activates bcTBK1 by enhancing its phosphorylation and promotes PANoptosis in GCRV-infected cells.