Abstract

Inhibitors of nuclear factor kappa B (I kappa Bs) are major control components of the Rel/NF-kappa B signaling pathway, a key regulator in the modulation of the expression of immune-related genes in vertebrates and invertebrates. The activation of the Rel/NF-kappa B signaling pathway depends largely in the degradation of I kappa B proteins and thus, I kappa Bs are a main target for the identification of genes whose expression is controlled by Rel/NF-kappa B pathway. In order to identify such regulation in bivalve mollusks, the cDNA sequence encoding an I kappa B protein was characterized in the scallop Argopecten purpuratus, ApI kappa B. The cDNA sequence of ApI kappa B is comprised of 1480 nucleotides with a 1086 bp open reading frame encoding for 362 amino acids. Bioinformatics analysis showed that ApI kappa B displays the conserved features of I kappa B proteins. The deduced amino acid sequence consists of a 39.7 kDa protein, which has an N-terminal degradation motif, six ankyrin repeats and a C-terminal phosphorylation site motif. Phylogenetic analysis revealed a high degree of identity between ApI kappa B and other I kappa Bs from mollusks, but also to arthropod cactus proteins and vertebrate I kappa Bs. Tissue expression analysis indicated that ApI kappa B is expressed in all examined tissues and it is upregulated in circulating hemocytes from scallops challenged with the pathogenic Gram-negative bacterium Vibrio splendidus. After inhibiting ApI kappa B gene expression using the RNA interference technology, the gene expression of the antimicrobial peptide big defensin was upregulated in hemocytes from non-challenged scallops. Results suggest that ApI kappa B may control the expression of antimicrobial effectors such as big defensin via a putative Rel/NF-kappa B signaling pathway. This first evidence will help to deepen the knowledge of the Rel/NF-kappa B conserved pathway in scallops. (C) 2016 Elsevier Ltd. All rights reserved.