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

• Published in: The Journal of biological chemistry Vol. 293; no. 39; pp. 15208 - 15220
• Main Authors: De, Saurav, Karim, Fawziya, Kiessu, Ezechielle, Cushing, Leah, Lin, Lih-Ling, Ghandil, Pegah, Hoarau, Cyrille, Casanova, Jean-Laurent, Puel, Anne, Rao, Vikram R.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 28.09.2018; American Society for Biochemistry and Molecular Biology
• Subjects: Cell Line; cell signaling; Crystallography, X-Ray; cytokine; Humans; Immunity, Innate - genetics; Immunologic Deficiency Syndromes - genetics; Immunologic Deficiency Syndromes - immunology; Immunologic Deficiency Syndromes - pathology; inflammation; innate immunity; interleukin 1 (IL-1); Interleukin-1 - chemistry; Interleukin-1 - genetics; interleukin-1 receptor-associated kinase 4 (IRAK4); Interleukin-1 Receptor-Associated Kinases - chemistry; Interleukin-1 Receptor-Associated Kinases - deficiency; Interleukin-1 Receptor-Associated Kinases - genetics; Mutation; Myeloid Differentiation Factor 88 - chemistry; Myeloid Differentiation Factor 88 - genetics; myeloid differentiation primary response gene 88 (MyD88); NF-kappa B - genetics; Polymorphism, Single Nucleotide - genetics; protein kinase; Receptors, Interleukin-1 - chemistry; Receptors, Interleukin-1 - genetics; Signal Transduction; Toll/interleukin-1 receptor (TIR); cytokine; interleukin-1 receptor-associated kinase 4 (IRAK4); innate immunity; inflammation; cell signaling; interleukin 1 (IL-1); myeloid differentiation primary response gene 88 (MyD88); protein kinase; Toll/interleukin-1 receptor (TIR)
• DOI: 10.1074/jbc.RA118.003831
• ISSN: 0021-9258

Interleukin-1 receptor (IL1R)-associated kinase 4 (IRAK4) is a central regulator of innate immune signaling, controlling IL1R and Toll-like receptor (TLR)-mediated responses and containing both scaffolding and kinase activities. Humans deficient in IRAK4 activity have autosomal recessive primary immune deficiency (PID). Here, we characterized the molecular mechanism of dysfunction of two IRAK4 PID variants, G298D and the compound variant R12C (R12C/R391H/T458I). Using these variants and the kinase-inactive D329A variant to delineate the contributions of IRAK4's scaffolding and kinase activities to IL1R signaling, we found that the G298D variant is kinase-inactive and expressed at extremely low levels, acting functionally as a null mutation. The R12C compound variant possessed WT kinase activity, but could not interact with myeloid differentiation primary response 88 (MyD88) and IRAK1, causing impairment of IL-1–induced signaling and cytokine production. Quantitation of IL-1 signaling in IRAK4-deficient cells complemented with either WT or the R12C or D329A variant indicated that the loss of MyD88 interaction had a greater impact on IL-1–induced signaling and cytokine expression than the loss of IRAK4 kinase activity. Importantly, kinase-inactive IRAK4 exhibited a greater association with MyD88 and a weaker association with IRAK1 in IRAK4-deficient cells expressing kinase-inactive IRAK4 and in primary cells treated with a selective IRAK4 inhibitor. Loss of IRAK4 kinase activity only partially inhibited IL-1–induced cytokine and NF-κB signaling. Therefore, the IRAK4–MyD88 scaffolding function is essential for IL-1 signaling, but IRAK4 kinase activity can control IL-1 signal strength by modulating the association of IRAK4, MyD88, and IRAK1.