IRAK4 kinase activity controls Toll-like receptor–induced inflammation through the transcription factor IRF5 in primary human monocytes

Abstract

Interleukin-1 receptor-associated kinase 4 (IRAK4) plays a critical role in innate immune signaling by Toll-like receptors (TLRs), and loss of IRAK4 activity in mice and humans increases susceptibility to bacterial infections and causes defects in TLR and IL1 ligand sensing. However, the mechanism by which IRAK4 activity regulates the production of downstream inflammatory cytokines is unclear. Using transcriptomic and biochemical analyses of human monocytes treated with a highly potent and selective inhibitor of IRAK4, we show that IRAK4 kinase activity controls the activation of interferon regulatory factor 5 (IRF5), a transcription factor implicated in the pathogenesis of multiple autoimmune diseases. Following TLR7/8 stimulation by its agonist R848, chemical inhibition of IRAK4 abolished IRF5 translocation to the nucleus and thus prevented IRF5 binding to and activation of the promoters of inflammatory cytokines in human monocytes. We also found that IKKβ, an upstream IRF5 activator, is phosphorylated in response to the agonist-induced TLR signaling. Of note, IRAK4 inhibition blocked IKKβ phosphorylation but did not block the nuclear translocation of NFκB, which was surprising, given the canonical role of IKKβ in phosphorylating IκB to allow NFκB activation. Moreover, pharmacological inhibition of either IKKβ or the serine/threonine protein kinase TAK1 in monocytes blocked TLR-induced cytokine production and IRF5 translocation to the nucleus, but not nuclear translocation of NFκB. Taken together, our data suggest a mechanism by which IRAK4 activity regulates TAK1 and IKKβ activation, leading to the nuclear translocation of IRF5 and induction of inflammatory cytokines in human monocytes.

Understanding early TLR signaling through the Myddosome

“…Second, the MAPK pathways are induced downstream of the TAK1 complex leading to activation of the transcription factors activator protein‐1 (AP‐1) and CREB. Third, TRAF6 facilitates activation of IFN regulatory factor 5 (IRF5) via a TAK1‐IKK‐β axis . The activation and cooperative binding of these transcription factors to specific gene promoters culminates in production of potent proinflammatory cytokines and chemokines that elicit an acute inflammatory response.…”

“…Reconstitution of IRAK4 ‐deficient human fibroblasts with IRAK4‐KI (K213A/K214A), also restores NF‐κB and AP‐1 luciferase activity similarly to WT IRAK4 . Additionally, whereas NF‐κB and MAPK activation is reported to be only moderately affected following TLR activation in the presence of IRAK4 kinase inhibition in human monocytes, IRF5 activation and subsequent nuclear translocation is inhibited . Because the expression of most cytokine genes requires cooperative binding of both IRF5 and NF‐κB within promoter regions, the loss of activated IRF5 significantly reduces cytokine expression .…”

“…Additionally, whereas NF‐κB and MAPK activation is reported to be only moderately affected following TLR activation in the presence of IRAK4 kinase inhibition in human monocytes, IRF5 activation and subsequent nuclear translocation is inhibited . Because the expression of most cytokine genes requires cooperative binding of both IRF5 and NF‐κB within promoter regions, the loss of activated IRF5 significantly reduces cytokine expression . Therefore, it appears the kinase activity of IRAK4 is essential for activation of IRF5, but potentially dispensable for NF‐κB and MAPK signaling.…”

Mechanism of dysfunction of human variants of the IRAK4 kinase and a role for its kinase activity in interleukin-1 receptor signaling

“…Additionally, we have shown that whereas complete inhibition of IRAK4 autophosphorylation has minimal effects on IL-1-induced cytokines and MAPK and NF-B signaling, it has profound effects on TLR-induced cytokines (7). Recently, we demonstrated that cytokines produced by TLR signaling in monocytes are controlled by the IRAK4 kinase-dependent activation of the transcription factor IRF5 (11). However, the precise role of IRAK4 in IL-1 signaling is still not completely understood.…”

CB2/miR-124 signaling down-regulate the expression of purinergic P2X4 and P2X7 receptor in dorsal spinal cord of CCI rats

“…Subsequently, we found that the inhibition of ROCK/P38MAPK and NF-κB and activation can obviously . Further more, IKKβ activation can lead to the nuclear translocation of IRF5 and induction of inflammatory cytokines in human monocytes [52]. IRF5 can directly bind to DNA in the 5' upstream region of the TNF, its recruitment to the 3' downstream region of the TNF gene depends on the protein-protein interactions with NF-κB RelA [53].…”