Comparison of Activities of Transcription Factor NF-κB from Two Jellyfish Models

Herein, transcription factor Nuclear Factor-kappaB (NF-{kappa}B) is characterized as the downstream effector of putative innate immune signaling pathways from two model jellyfish, Aurelia aurita (Aa) and Clytia hemisphaerica (Ch). Both jellyfish NF-{kappa}B proteins consist primarily of the N-terminal DNA-binding/dimerization domain, and they lack the C-terminal ankyrin repeat inhibitory domain found in vertebrate NF-{kappa}B proteins. Both jellyfish NF-{kappa}B proteins bind to a consensus mammalian NF-{kappa}B binding site, and their AlphaFold3-predicted structures on DNA are similar to that of mouse NF-{kappa}B p50. Neither Aa- nor Ch-NF-{kappa}B activated transcription of an NF-{kappa}B-site reporter gene in human cells; however, Aa-NF-{kappa}B did activate transcription from a GAL4-site reporter gene in yeast, whereas Ch-NF-{kappa}B did not. Aa- and Ch-NF-{kappa}B were both constitutively located in the nucleus when expressed in vertebrate cells. Homologs of I{kappa}B-like proteins from both species interacted with their corresponding NF-{kappa}B proteins in co-immunoprecipitation assays in HEK 293T cells. These I{kappa}B-like proteins influenced the subcellular localization of their cognate NF-{kappa}B proteins in vertebrate cells, and their ankyrin repeat domains were predicted to interact with Ch-NF-{kappa}B in a manner similar to mammalian I{kappa}B and NF-{kappa}B. RNA-sequencing data from Ch animals indicate that Ch-NF-{kappa}B is expressed at high levels in early developmental stages, when Ch-I{kappa}B expression is low, suggesting that active Ch-NF-{kappa}B controls an early developmental process. In contrast, in adult animals the expression of Ch-I{kappa}B is high, suggesting that Ch-NF-{kappa}B requires a signal in order to become active. Overall, these results provide comparative information on the structure, activity, and mRNA expression of jellyfish NF-{kappa}B pathway proteins among jellyfish, and they suggest roles for NF-{kappa}B in developing and adult jellyfish.