IKKs Participate in Regulation of Cytokine-Like System and Antiviral Responses of Innate Immune System.

The IKK-NF-κB signaling cascade is one of the crucial responsive mechanisms in inflammatory and immune responses. The key kinase proteins called inhibitor of kappa B kinases (IKKs) serve as the core elements involved in cascade activation. Here, the complete ORFs of IKK homologs, , , and , from the black tiger shrimp were identified and characterized for their functions in shrimp antiviral responses. The transcripts were widely expressed in various examined tissues and the IKKε protein was detected in all three types of shrimp hemocytes. Only the and were responsive to white spot syndrome virus (WSSV), yellow head virus (YHV) and a bacterium infection, while the exhibited no significant response to pathogen infection. On the contrary, suppression of and by dsRNA-mediated RNA interference (RNAi) resulted in a rapid death of WSSV-infected shrimp and the significant reduction of an IFN-like transcript. Whereas, the mRNA levels of the antimicrobial peptides, and , and a transcription factor, were significantly increased, those of , and were unaffected. Overexpression of IKKβ and IKKε in HEK293T cells differentially activated the NF-κB and IFNβ promoter activities, respectively. These results suggest that the IKKβ and IKKε may act as common factors regulating the expression of immune-related genes from various signaling pathways. Interestingly, the IKKs may also contribute a possible role in shrimp cytokine-like system and cross-talking between signaling transductions in innate immune responses.