Characterization of two regulators of the TNF-α signaling pathway in Apostichopus japonicus: LPS-induced TNF-α factor and baculoviral inhibitor of apoptosis repeat-containing 2

The TNF-α signaling cascade is involved in the regulation of a variety of biological processes, including cell proliferation, differentiation, apoptosis and the immune response in vertebrates. Here, two regulatory genes, lipopolysaccharide-induced tumor necrosis factor α factor (LITAF) and baculoviral inhibitor of apoptosis repeat-containing 2 (BIRC2), were identified in coelomocytes from the sea cucumber Apostichopus japonicus by RNA-seq and RACE (denoted as AjLITAF and AjBIRC2, respectively). The full-length cDNA of AjLITAF was 1417 bp, with a 5′ untranslated region (UTR) of 189 bp, a 3′ UTR of 637 bp with one cytokine RNA instability motif (ATTTA) and an open reading frame (ORF) of 591 bp encoding a polypeptide of 196 amino acid residues and a predicted molecular weight of 22.1 kDa. The partial AjBIRC2 cDNA was 2324 bp with a 5′ UTR of 145 bp, a 3′ UTR of 469 bp and a complete ORF of 1710 bp encoding a polypeptide of 569 amino acid residues. Analysis of the deduced amino acid sequences revealed that both genes shared a remarkably high degree of structural conservation with their mammalian orthologs, including a highly conserved LITAF domain in AjLITAF and three types of BIR domains in AjBIRC2. Spatial expression analysis revealed that AjLITAF and AjBIRC2 were expressed at a slightly lower level in the intestine and tentacle tissues compared with the other four tissues examined. After challenging the sea cucumbers with Vibrio splendidus, the expression levels of AjLITAF and AjBIRC2 in coelomocytes were increased by 2.65-fold at 6 h and 1.76-fold at 24 h compared with the control group. In primary cultured coelomocytes, a significant increase in the expression of AjLITAF and AjBIRC2 was detected after 6 h of exposure to 1 µg mL−1 LPS. Together, these results suggest that AjLITAF and AjBIRC2 might be involved in the sea cucumber immune response during the course of a pathogenic infection or exposure to pathogen-associated molecular pattern (PAMP) molecules.