Transforming growth factor-β-activating kinase 1 and its binding protein 1 participate in the innate immune responses via modulating the IMD[sbnd]NF[sbnd]κB signaling in mud crab (Scylla paramamosain)

Transforming growth factor-β-activating kinase 1 (TAK1)is essential for diverse important biological functions, such as innate immunity, development and cell survival. In the present study, the homologs of TAK1 and TAK1-binding protein 1 (TAB1)were identified and characterized from mud crab Scylla paramamosain for the first time. The full-length cDNAs of SpTAK1 and SpTAB1 were 2, 226 bp and 2, 433 bp with 1, 782 bp and 1, 533 bp open reading frame (ORF), respectively. The deduced SpTAK1 protein contained a conserved S_TKc (Serine/threonine protein kinases, catalytic)domain, and the putative SpTAB1 protein possessed a typical PP2Cc (Serine/threonine phosphatases, family 2C, catalytic)domain and a potential TAK1 docking motif. Real-time PCR analysis showed that SpTAK1 and SpTAB1 were highly expressed at early development stages, suggesting their participation in crab's development process. Moreover, the expression levels of SpTAK1 and SpTAB1 in hepatopancreas were positively stimulated after challenge with Vibro alginolyticus and Poly (I:C), implying the involvement of SpTAK1 and SpTAB1 in innate immune responses against both bacterial and viral infections. When SpTAK1 or SpTAB1 were silenced in vivo, the expression levels of two IMD[sbnd]NF[sbnd]κB signaling components (SpIKKβ and SpRelish)and six antimicrobial peptide (AMP)genes (SpALF1-5 and SpCrustin)were significantly reduced, and the bacteria clearance capacity of crabs was also markedly impaired in SpTAK1 or SpTAB1 silenced crabs. Additionally, overexpression of SpTAK1 and SpTAB1 in HEK293T cells could markedly activate the mammalian NF-κB signaling. Collectively, our results suggested that TAK1 and TAB1 regulated crab's innate immunity via modulating the IMD[sbnd]NF[sbnd]κB signaling. These findings may provide new insights into the TAK1/TAB1-mediated signaling cascades in crustaceans and pave the way for a better understanding of crustacean innate immune system.