IKKβ mediates homeostatic function in inflammation via competitively phosphorylating AMPK and IκBα

Abstract

Inhibitor of nuclear factor kappa-B kinase subunit beta (IKK<i>β</i>) is one of important kinases in inflammation to phosphorylate inhibitor of nuclear factor kappa-B (I<i>κ</i>B<i>α</i>) and then activate nuclear factor kappa-B (NF-<i>κ</i>B). Inhibition of IKK<i>β</i> has been a therapeutic strategy for inflammatory and autoimmune diseases. Here we report that IKK<i>β</i> is constitutively activated in healthy donors and healthy <i>Ikkβ</i> ^<i>C46A</i> (cysteine 46 mutated to alanine) knock-in mice although they possess intensive IKK<i>β</i>-I<i>κ</i>B<i>α</i>-NF-<i>κ</i>B signaling activation. These indicate that IKK<i>β</i> activation probably plays homeostatic role instead of causing inflammation. Compared to <i>Ikkβ</i> ^<i>WT</i> littermates, lipopolysaccharides (LPS) could induce high mortality rate in <i>Ikkβ</i> ^<i>C46A</i> mice which is correlated to breaking the homeostasis by intensively activating p-I<i>κ</i>B<i>α</i>-NF-<i>κ</i>B signaling and inhibiting phosphorylation of 5' adenosine monophosphate-activated protein kinase (p-AMPK) expression. We then demonstrated that IKK<i>β</i> kinase domain (KD) phosphorylates AMPK<i>α</i>1 <i>via</i> interacting with residues Thr183, Ser184, and Thr388, while IKK<i>β</i> helix-loop-helix motifs is essential to phosphorylate I<i>κ</i>B<i>α</i> according to the previous reports. Kinase assay further demonstrated that IKK<i>β</i> simultaneously catalyzes phosphorylation of AMPK and I<i>κ</i>B<i>α</i> to mediate homeostasis. Accordingly, activation of AMPK rather than inhibition of IKK<i>β</i> could substantially rescue LPS-induced mortality in <i>Ikkβ</i> ^<i>C46A</i> mice by rebuilding the homeostasis. We conclude that IKK<i>β</i> activates AMPK to restrict inflammation and IKK<i>β</i> mediates homeostatic function in inflammation <i>via</i> competitively phosphorylating AMPK and I<i>κ</i>B<i>α</i>.