Nile tilapia P38 MAPK interacts with Tak1 and is involved in the immune response to Streptococcus agalactiae, PolyI:C, and LPS stimulation.

The Nile tilapia (Oreochromis niloticus) is a globally recognised freshwater aquaculture species with high economic value. However, streptococcal disease, a bacterial infection, has the potential to inflict considerable economic losses on the aquaculture production of tilapia. Innate immune factors in fish play a pivotal role in disease resistance mechanisms. Consequently, a comprehensive study on the intrinsic immune response mechanisms of Nile tilapia against Streptococcus agalactiae is imperative. In this study, we conducted a comprehensive investigation of the Nile tilapia p38 MAPK gene, encompassing its molecular cloning, expression profile in both normal and post-stimulated fish, and the characteristics of its encoded polypeptide. The p38 gene is 1493 bp in length, with an open reading frame (ORF) of 1083 bp, which encodes a total of 360 amino acids. The deduced P38 protein contained an S_TKc structural domain, and the highest degree of homology was observed with the Neolamprologus brichardi at 98.16 %. The highest level of P38 expression was observed in the heart. LPS, Poly I:C, and S. agalactiae stimulation led to significant changes in the expression of P38 in the examined tissues. Subcellular localization studies revealed that P38 is distributed in the nucleus, cytoplasm and cell membrane. Furthermore, pull-down assays demonstrated an interaction between P38 and Tak1, but not between P38 and Tab1 proteins. These results provide a basis for further investigation of the mechanism of P38 involvement in this signalling pathway.