Transcription factor NF-κB in a basal metazoan, the sponge, has conserved and unique sequences, activities, and regulation

Abstract

Biological and biochemical functions of immunity transcription factor NF-{kappa}B in basal metazoans are largely unknown. Herein, we characterize transcription factor NF-{kappa}B from the demosponge Amphimedon queenslandica (Aq), in the phylum Porifera. Structurally and phylogenetically, the Aq-NF-{kappa}B protein is most similar to NF-{kappa}B p100 and p105 among vertebrate proteins, with an N-terminal DNA-binding/dimerization domain, a C-terminal Ankyrin (ANK) repeat domain, and a DNA binding-site profile more similar to human NF-{kappa}B proteins than Rel proteins. Aq-NF-{kappa}B also resembles the mammalian NF-{kappa}B protein p100 in that C-terminal truncation results in translocation of Aq-NF-{kappa}B to the nucleus and increases its transcriptional activation activity. Overexpression of a human or sea anemone I{kappa}B kinase (IKK) can induce C-terminal processing of Aq-NF-{kappa}B in vivo, and this processing requires C-terminal serine residues in Aq-NF-{kappa}B. Unlike human NF-{kappa}B p100, however, the C-terminal sequences of Aq-NF-{kappa}B do not effectively inhibit its DNA-binding activity when expressed in human cells. Tissue of another demosponge, a black encrusting sponge, contains NF-{kappa}B site DNA-binding activity and an NF-{kappa}B protein that appears mostly processed and in the nucleus of cells. NF-{kappa}B DNA-binding activity and processing is increased by treatment of sponge tissue with LPS. By transcriptomic analysis of A. queenslandica we identified likely homologs to many upstream NF-{kappa}B pathway components. These results present a functional characterization of the most ancient metazoan NF-{kappa}B protein to date, and show that many characteristics of mammalian NF-{kappa}B are conserved in sponge NF-{kappa}B, but the mechanism by which NF-{kappa}B functions and is regulated in the sponge may be somewhat different.