Transcription Factor Nf-Kappa B Is Modulated By Symbiotic Status In A Sea Anemone Model Of Cnidarian Bleaching

Transcription factor NF-kappa B plays a central role in immunity from fruit flies to humans, and NF-kappa B activity is altered in many human diseases. To investigate a role for NF-kappa B in immunity and disease on a broader evolutionary scale we have characterized NF-kappa B in a sea anemone ( Exaiptasia pallida; called Aiptasia herein) model for cnidarian symbiosis and dysbiosis ( i.e., "bleaching"). We show that the DNA-binding site specificity of Aiptasia NF-kappa B is similar to NF-kappa B proteins from a broad expanse of organisms. Analyses of NF-kappa B and I kappa B kinase proteins from Aiptasia suggest that non-canonical NF-kappa B processing is an evolutionarily ancient pathway, which can be reconstituted in human cells. In Aiptasia, NF-kappa B protein levels, DNA-binding activity, and tissue expression increase when loss of the algal symbiont Symbiodinium is induced by heat or chemical treatment. Kinetic analysis of NF-kappa B levels following loss of symbiosis show that NF-kappa B levels increase only after Symbiodinium is cleared. Moreover, introduction of Symbiodinium into naive Aiptasia larvae results in a decrease in NF-kappa B expression. Our results suggest that Symbiodinium suppresses NF-kappa B in order to enable establishment of symbiosis in Aiptasia. These results are the first to demonstrate a link between changes in the conserved immune regulatory protein NF-kappa B and cnidarian symbiotic status.