Shrimp NF-κB binds to the immediate-early gene ie1 promoter of white spot syndrome virus and upregulates its activity

The immediate-early gene ie1 carried by white spot syndrome virus (WSSV) exhibits very strong promoter activity and expresses highly throughout the infection cycle. Here we identified a NF-κB binding motif in the ie1 promoter region. Electrophoretic mobility shift assays indicated that the recombinant Rel homology domain (RHD) of shrimp NF-κB homolog LvRelish bound to the putative NF-κB site in the ie1 promoter. A transactivity assay of the WSSV ie1 promoter in Drosophila Schneider 2 cells demonstrated that LvRelish could increase ie1 promoter activity. These results show that shrimp NF-κB homolog LvRelish transactivates WSSV ie1 gene expression and contributes to its high promoter activity. Further transactivation assays showed that WSSV IE1 protein expression upregulated the promoter activities of WSSV ie1 gene and antimicrobial peptide genes regulated by the NF-κB system. We suggested that WSSV may annex the shrimp NF-κB system, which it uses to enhance the expression of viral immediate-early genes.