The identification of SiTRAF suggests the presence of a functional MyD88-TRAF signaling axis in the sea urchin Strongylocentrotus intermedius.

Abstract

Tumor necrosis factor receptor-associated factors (TRAFs) are key signaling proteins involved in cellular innate immune pathways. However, knowledge of TRAF genes in echinoderms remains limited. We cloned a novel TRAF gene (SiTRAF) from the sea urchin Strongylocentrotus intermedius. The full-length open reading frame of SiTRAF was 1,731 bp, encoding 576 amino acids. Domain prediction analysis showed that SiTRAF possessed domains conserved in the TRAF protein family. Phylogenetic analysis revealed that SiTRAF clustered with TRAF proteins from S. purpuratus, forming a relatively independent evolutionary branch within the echinoderm TRAF homologs. SiTRAF mRNA was detected in all tested sea urchin tissues, with the highest expression level in the intestine. Transcriptional expression of SiTRAF was significantly induced following stimulation with lipopolysaccharide and polyinosinic-polycytidylic acid. Additionally, RNA interference targeting SiTRAF suppressed the expression of IRFs, Rel, IL-17, and several strongylocin genes following lipopolysaccharide stimulation. Co-immunoprecipitation assays indicated a physical protein association between SiTRAF and SiMyD88, a key adaptor of the Toll-like receptor signaling pathway. Dual-luciferase reporter gene assays indicated that SiTRAF overexpression significantly inhibited the activity of a series of immune-related reporter genes and dose-dependently suppressed the SiMyD88-mediated activation of IL-6, AP-1, and NF-κB. Additionally, SiTRAF regulated the phosphorylation levels of MAPKs, such as P38, JNK, and Erk1/2. These findings suggest that SiTRAF participates in the innate immune regulatory processes of sea urchins. This study provides new insights into TRAF-mediated immune signaling in invertebrates and lays a theoretical foundation for the future selective breeding of disease-resistant sea urchin strains.