NFĸB is an Unexpected Major Mediator of Interleukin-15 Signaling in Cerebral Endothelia

Abstract

Interleukin (IL)-15 and its receptors are induced by tumor necrosis factor α (TNF) in the cerebral endothelial cells composing the blood-brain barrier, but it is not yet clear how IL-15 modulates endothelial function. Contrary to the known induction of JAK/STAT3 signaling, here we found that nuclear factor (NF)- ĸB is mainly responsible for IL-15 actions on primary brain microvessel endothelial cells and cerebral endothelial cell lines. IL-15-induced transactivation of an NFĸB luciferase reporter resulted in phosphorylation and degradation of the inhibitory subunit IĸB that was followed by phosphorylation and nuclear translocation of the p65 subunit of NFĸB. An IĸB kinase inhibitor Bay 11-7082 only partially inhibited IL-15-induced NFĸB luciferase activity. The effect of IL-15 was mediated by its specific receptor IL-15Rα, since endothelia from IL-15Rα knockout mice showed delayed nuclear translocation of p65, whereas those from knockout mice lacking a co-receptor IL-2Rγ did not show such changes. At the mRNA level, IL-15 and TNF showed similar effects in decreasing the tight junction protein claudin-2 and increasing the p65 subunit of NFĸB but exerted different regulation on caveolin-1 and vimentin. Taken together, NFĸB is a major signal transducer by which IL-15 affects cellular permeability, endocytosis, and intracellular trafficking at the level of the blood-brain barrier.