Orange-spotted grouper Epinephelus coioides Tak1: molecular identification, expression analysis and functional study.

In this study, the complementary (c)DNA sequence encoding orange-spotted grouper Epinephelus coioides Tak1 (ectak1) was cloned, which has an open reading frame of 1728 bp that encodes 575 amino acids (aa). Sequence analysis indicated that Ectak1 contains two characteristic conserved domains, i.e. an N-terminal serine-threonine protein kinase catalytic domain (27-275 aa) and a C-terminal coiled-coil region (499-562 aa). Ectak1 shares high sequence identity with Tak1 from other fish species, especially those of Nile tilapia Oreochromis niloticus (96%) and zebra mbuna Maylandia zebra (96%). ectak1 transcripts were expressed broadly in all of the tissues tested, but ectak1 expression was reduced mainly in the local infection sites (skin and gill) after infection with Cryptocaryon irritans. Intracellular localization analysis showed that Ectak1 was distributed mainly in the cytoplasm. A luciferase reporter assay showed that Ectak1 significantly impaired the NF-κB activity induced by E. coioides Myd88 and Traf6. Overall, these results suggest that Ectak1 functions to reduce the activity of NF-κB induced by toll-like receptor (TLR) signal molecules in HEK-293T cells, and it might have an important role in host defences against parasitic infections.