Immune response-related gene expression profile of a novel molluscan I kappa B protein member from Manila clam (Ruditapes philippinarum)

Abstract

Mollusks lack an adaptive immune system and rely solely on the innate immune response. The nuclear factor-kappa B (NF-kappa B) signaling pathway is one of the most important components of the innate immune system and its activity is regulated by physical interaction with the inhibitor of NF-kappa B (I kappa B) protein. The manila clam, Ruditapes philippinarum (Rp), is a key species of the world's aquaculture industry, and recent pathogenic threats, such as the Gram-negative lipopolysaccharide (LPS)-expressing Vibrio tapetis bacteria, have produced severe adverse economic impacts. Here, we describe identification, characterization and immune responses of novel I kappa B (Rp-I kappa B) in the manila clam. The Rp-I kappa B cDNA is comprised of a 1,032 bp open reading frame, which encodes 343 amino acid residues and has a predicted molecular mass of 38 kDa. The Rp-I kappa B protein exhibits typical structural features of I kappa B family members, including the I kappa B degradation motif, PEST sequence, and six ankyrin repeats. Phylogenetic analysis showed that manila clam and other known molluscan I kappa B proteins grouped together in the invertebrate cluster. Analysis of the tissue expression distribution revealed that Rp-I kappa B was ubiquitously expressed. However, immune challenge with V. tapetis and purified LPS endotoxin induced significant up-regulation of Rp-I kappa B expression in gill and hemocytes. These results indicated that Rp-I kappa B may play an important role in manila clam defense against bacterial infection.