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IRAK4 kinase activity mediates IRF5 activation via IKKβ and TAK1

ABSTRACT: IRAK4 kinase plays a critical role in innate immune responses and inflammation by modulating the TLR/IL-1R signaling pathway, yet the mechanism by which it regulates downstream pathways and transcription factors to induce inflammatory cytokines is unclear. IRAK4 can mediate signaling events by mechanisms both dependent and independent of its kinase activity. Understanding this regulation is important for deciphering the role of IRAK4 and for the development of treatments for inflammatory diseases and cancer. Through transcriptomic and biochemical analyses of primary human monocytes treated with a highly potent and selective inhibitor of IRAK4, we show that IRAK4 kinase activity controls the transcription factor IRF5 which in turn induces inflammatory cytokine and type I interferon transcription in myeloid cells. We also show that IRAK4 kinase activity does not control activation of NF-κB. Following TLR stimulation, translocation of IRF5, but not NF-κB, to the nucleus in human monocytes is abolished by IRAK4 kinase inhibition. In addition, binding of IRF5, but not NF-κB p65, to promoters of inflammatory target genes (TNF-α and IP10) is blocked with an IRAK4 kinase inhibitor. IKKβ, a known activator of IRF5, is phosphorylated in response to TLR mediated signaling, and inhibition of IRAK4 kinase blocks IKKβ phosphorylation. Pharmacological inhibition of IKKβ and TAK1, the upstream kinase of IKKβ, in human monocytes blocks IL-1, IL-6 and TNF-α cytokine production, as well as IRF5 translocation to the nucleus. Taken together, our data suggest a novel mechanism by which IRAK4 kinase activity regulates TAK1 and IKKβ activation, leading to the translocation of IRF5 and induction of inflammatory cytokines in human monocytes.

ORGANISM(S): Homo sapiens

PROVIDER: GSE86234 | GEO | 2017/10/12

SECONDARY ACCESSION(S): PRJNA340985

REPOSITORIES: GEO

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Project description:Pathologic activation of the Toll-like receptor (TLR) pathway underlies various human disorders such as autoimmune diseases, chronic inflammatory diseases and lymphoid malignancies. Current therapy of these diseases relies on immunosuppressive or chemotherapeutic agents, but more effective therapeutics tailored to disease-causing mechanisms are needed. Pivotal to TLR signaling is the IL-1 receptor-associated kinase 4 (IRAK4), which is recruited to TLRs by the adaptor protein MyD88. Recruitment of IRAK kinases to MyD88, triggers the formation of a signaling competent myddosome complex, which underlies the pathogenesis of many immuno-inflammatory disorders, suggesting that IRAK4 inhibitors might be useful in the treatment of these diseases. Gain-of-function MYD88 mutations activate IRAK4 in several mature B cell malignancies, including activated B-cell-like diffuse large B cell lymphoma (ABC DLBCL). Development of selective IRAK4 inhibitors has been confounded by the challenging structure of the IRAK4 catalytic domain. Using structure-based drug design methodologies, we identified potent and selective IRAK4 inhibitors. These small molecules suppress LPS-induced TNFalpha production in vitro and in vivo, and are efficacious in mouse models of collagen-induced arthritis and MyD88-dependent inflammatory gout. Human ABC DLBCL cell lines that harbor the activating, oncogenic MyD88 L265P mutation are killed by IRAK4 inhibitors, both in vitro and in mouse xenograft models. IRAK4 inhibitors synergize with the BTK inhibitor ibrutinib, with the Syk inhibitor PRT062607, and with the Bcl-2 inhibitor ABT-199 in killing ABC DLBCL cells, suggesting new therapeutic strategies for this refractory cancer. Four ABC DLBCL cell lines (OCI-Ly10, TMD8, HBL1 and OCI-Ly3), were treated with either ND-2158 or the structurally related negative control compound ND-1659 for 6, 12, 24 or 36 h in culture. Gene expression profiling was performed using two-color human Agilent 4x44K gene expression arrays comparing signal from control compound-treated (ND-1659) control cells (Cy3), toÂ cells treated with ND-2158 for the indicated times (Cy5).

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IRAK4 kinase activity mediates IRF5 activation via IKKβ and TAK1

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