ABIN-like facilitates the inflammatory response by promoting the nuclear translocation of p65 in Apostichopus japonicus.

The A20-Binding Inhibitors of NF-κB (ABINs) suppress p65 nuclear translocation to restrain inflammation, acting as a canonical anti-inflammatory regulator in mammals. However, the functions of ABIN proteins in invertebrates remain largely unknown. Here, an ABIN-like protein was identified from the Apostichopus japonicus, which contains an ORF (open reading frame) of 1917 bp and encodes a total of 638 amino acid polypeptides with a conserved UBAN ubiquitin-binding motif. Tissue expression profiling analysis demonstrated ubiquitous expression of AjABIN-like in all tested tissues, and its transcript level peaked in coelomocytes. After the Vibrio splendidus challenge in vivo, the mRNA levels of AjABIN-like and its cytoplasmic expression were significantly upregulated at 6 h. Functional analyses demonstrated that AjABIN-like knockdown markedly suppressed inflammation, as evidenced by reduced tissue damage, decreased iNOS and TNOS activities, and lower expression of the pro-inflammatory mediators VEGF, HMGB1, IL-17, and MMP1. Moreover, knockdown of AjABIN-like has significantly blocked the translocation to the nucleus of the p65, which transcriptionally controls the above inflammatory mediators. AjABIN-like also positively regulates cellular ubiquitination levels, in contrast to the regulatory pattern observed in mammals. However, AjABIN-like knockdown promoted coelomocyte apoptosis, which is consistent with the conserved anti-apoptotic of mammalian ABINs. Collectively, these findings identify AjABIN-like as an evolutionarily conserved regulator of apoptosis that has evolved a distinct role in controlling inflammatory signaling and pro-ubiquitination in echinoderms, providing new insights into the evolutionary development of ABIN-mediated immune regulation.