Threonine 66 in the death domain of IRAK-1 is critical for interaction with signaling molecules but is not a target site for autophosphorylation.
TL;DR: Evidence is provided that T66 critically impacts the secondary structure of the IRAK‐1 DD, which ensures the transient manner of interactions between IRAk‐1 and the other signaling molecules.
Abstract: Ligand binding in the TLR/IL-1R family results in the transient formation of an intracellular signaling complex, which contains, amongst others, the serine/threonine-specific kinase IL-1R-associated kinase 1 (IRAK-1). Concomitantly, the kinase function of IRAK-1 becomes activated, resulting in massive autophosphorylation and finally in the dissociation of the initially constituted signaling complex. The death domain (DD) of IRAK-1 mediates the interaction with other molecules of the signaling complex, e.g., the adaptor MyD88, the silencer Tollip, and the activator kinase IRAK-4. The conserved threonine at position 66 (T66), located within the DD, is a putative autophosphorylation target site. Here, we provide evidence that T66 critically impacts the secondary structure of the IRAK-1 DD. Thereby, it ensures the transient manner of interactions between IRAK-1 and the other signaling molecules. This essential role, however, is not regulated by phosphorylation of T66 itself.
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TL;DR: The potential targeting of these essential protein kinases therapeutically is discussed, given their critical role in IL-1/TLR signalling, and the IRAK family members have been implicated in certain disease models including human immunodeficiencies.
263 citations
TL;DR: Regulation of the IL‐1/IL‐1R system in the brain will be described, as an example of the peculiarities of organ‐specific modulation of inflammation.
Abstract: The extracellular forms of the IL-1 cytokines are active through binding to specific receptors on the surface of target cells. IL-1 ligands bind to the extracellular portion of their ligand-binding receptor chain. For signaling to take place, a non-binding accessory chain is recruited into a heterotrimeric complex. The intracellular approximation of the Toll-IL-1-receptor (TIR) domains of the 2 receptor chains is the event that initiates signaling. The family of IL-1 receptors (IL-1R) includes 10 structurally related members, and the distantly related soluble protein IL-18BP that acts as inhibitor of the cytokine IL-18. Over the years the receptors of the IL-1 family have been known with many different names, with significant confusion. Thus, we will use here a recently proposed unifying nomenclature. The family includes several ligand-binding chains (IL-1R1, IL-1R2, IL-1R4, IL-1R5, and IL-1R6), 2 types of accessory chains (IL-1R3, IL-1R7), molecules that act as inhibitors of signaling (IL-1R2, IL-1R8, IL-18BP), and 2 orphan receptors (IL-1R9, IL-1R10). In this review, we will examine how the receptors of the IL-1 family regulate the inflammatory and anti-inflammatory functions of the IL-1 cytokines and are, more at large, involved in modulating defensive and pathological innate immunity and inflammation. Regulation of the IL-1/IL-1R system in the brain will be also described, as an example of the peculiarities of organ-specific modulation of inflammation.
203 citations
TL;DR: A brief overview of TLR signal transduction pathways is presented, the current understanding of the Myddosome and the proteins that comprise its structure are summarized, including MyD88 and members of the IL‐1 receptor‐associated kinase (IRAK) family are summarized.
Abstract: TLRs are expressed on the plasma and endosomal membranes of innate immune cells acting as sensors of foreign and inherent danger signals that threaten the host. Upon activation, TLRs facilitate the assembly of large intracellular oligomeric signaling complexes, termed Myddosomes, which initiate key signal transduction pathways to elicit critical inflammatory immune responses. The formation of the Myddosome is integral for TLR signaling; however, the molecular mechanisms controlling its formation, disassembly, and the subsequent proximal signaling events remain to be clearly defined. In this review, we present a brief overview of TLR signal transduction pathways, summarize the current understanding of the Myddosome and the proteins that comprise its structure, including MyD88 and members of the IL-1 receptor-associated kinase (IRAK) family. Finally, we will discuss recent advances and open questions regarding early TLR signaling in the context of the Myddosome complex.
106 citations
TL;DR: The multitasking role of Tollip associated with its modular architecture is discussed, which is a critical regulator of Toll-like receptor (TLR)-mediated innate immune responses.
92 citations
Cites background from "Threonine 66 in the death domain of..."
...Whereas the IRAK-1 DD has been shown to mediate homodimerization and to interact with Tollip [59] by its CUE domain [24], the ProST domain has been implicated in modulating Tollip-IRAK-1 association [60]....
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TL;DR: The discovery of complete human interleukin-1 receptor (IL-1R)-associated kinase 1 (IRAK-1) deficiency resulting from a de novo Xq28 microdeletion encompassing MECP2 and IRAK1 in a boy died very early, suggesting that human IRAK- 1 is essential downstream from TLRs but not IL-1Rs in fibroblasts, whereas it plays a redundant role downstream from both TLRs and IL-
Abstract: Most members of the Toll-like receptor (TLR) and interleukin-1 receptor (IL-1R) families transduce signals via a canonical pathway involving the MyD88 adapter and the interleukin-1 receptor-associated kinase (IRAK) complex. This complex contains four molecules, including at least two (IRAK-1 and IRAK-4) active kinases. In mice and humans, deficiencies of IRAK-4 or MyD88 abolish most TLR (except for TLR3 and some TLR4) and IL-1R signaling in both leukocytes and fibroblasts. TLR and IL-1R responses are weak but not abolished in mice lacking IRAK-1, whereas the role of IRAK-1 in humans remains unclear. We describe here a boy with X-linked MECP2 deficiency-related syndrome due to a large de novo Xq28 chromosomal deletion encompassing both MECP2 and IRAK1. Like many boys with MECP2 null mutations, this child died very early, at the age of 7 mo. Unlike most IRAK-4– or MyD88-deficient patients, he did not suffer from invasive bacterial diseases during his short life. The IRAK-1 protein was completely absent from the patient’s fibroblasts, which responded very poorly to all TLR2/6 (PAM2CSK4, LTA, FSL-1), TLR1/2 (PAM3CSK4), and TLR4 (LPS, MPLA) agonists tested but had almost unimpaired responses to IL-1β. By contrast, the patient’s peripheral blood mononuclear cells responded normally to all TLR1/2, TLR2/6, TLR4, TLR7, and TLR8 (R848) agonists tested, and to IL-1β. The death of this child precluded long-term evaluations of the clinical consequences of inherited IRAK-1 deficiency. However, these findings suggest that human IRAK-1 is essential downstream from TLRs but not IL-1Rs in fibroblasts, whereas it plays a redundant role downstream from both TLRs and IL-1Rs in leukocytes.
42 citations
References
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TL;DR: The intent in this review is to point out the similarities and differences in these two types of host response to infection, and to indicate the present level of understanding of how these can be integrated into a more complete description of the immune response.
1,586 citations
"Threonine 66 in the death domain of..." refers background in this paper
...Recognition of molecular patterns of microbial or viral origin by TLR on sentinel cells is an essential step in the activation of the innate as well as the adaptive immunity of the host [1, 2]....
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TL;DR: MyD88 plays the same role in IL-1 signaling as TRADD and Tube do in TNF and Toll pathways, respectively: it couples a serine/threonine protein kinase to the receptor complex.
1,141 citations
"Threonine 66 in the death domain of..." refers background or methods in this paper
...IRAK-1 can be activated by TIR ligand-induced signaling or by ectopic expression of exogenous IRAK-1, resulting in massive autophosphorylation and subsequently, in a reduced electrophoretic mobility in SDS-PAGE [14, 11 ]....
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...The expression vectors encoding human wild-type (w.t.) IRAK-1 (pRK5-IRAK) or kinase-inactive IRAK-1 (IRAK K239S) were kind gifts of Z. Cao (Amgen) and have been described elsewhere [ 11 ]....
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TL;DR: It is shown that, before IL-1β treatment, Tollip is present in a complex with IRAK, and that recruitment of Tollip–IRAK complexes to the activated receptor complex occurs through association of tollip with IL- 1RAcP, and it is concluded that tollip is an important constituent of theIL-1R signalling pathway.
Abstract: Interleukin-1 (IL-1) is a proinflammatory cytokine that elicits its pleiotropic effects through activation of the transcription factors NF-kappaB and AP-1. Binding of IL-1 to its receptor results in rapid assembly of a membrane-proximal signalling complex that consists of two different receptor chains (IL-1Rs), IL-1RI and IL-1RAcP, the adaptor protein MyD88, the serine/threonine kinase IRAK and a new protein, which we have named Tollip. Here we show that, before IL-1beta treatment, Tollip is present in a complex with IRAK, and that recruitment of Tollip-IRAK complexes to the activated receptor complex occurs through association of Tollip with IL-1RAcP. Co-recruited MyD88 then triggers IRAK autophosphorylation, which in turn leads to rapid dissociation of IRAK from Tollip (and IL-1Rs). As overexpression of Tollip results in impaired NF-kappaB activation, we conclude that Tollip is an important constituent of the IL-1R signalling pathway.
539 citations
"Threonine 66 in the death domain of..." refers background in this paper
...It was speculated that T66 of IRAK-1 is a target for phosphorylation, regulating the interaction with signaling molecules [6, 10], probably via alteration of the conformation of the DD [16]....
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...Although T66 is a putative (auto-) phosphorylation site, and its phosphorylation was suggested to be the mechanism regulating the above-mentioned characteristics [6, 9], T66 is not phosphorylated by IRAK-1 itself in vitro....
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...These interactions are mediated by the DD of IRAK-1 [6, 8], including the amino acid residue T66, which is highly conserved among DD-containing proteins....
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...In unstimulated cells, IRAK-1 is associated with the silencer Tollip [6, 7]....
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...This was regarded a regulatory mechanism, driven by the phosphorylation of T66, which is denied in IRAK-1 T66-A [6, 10]....
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TL;DR: The identification and characterization of a novel IRAK-like molecule is reported, and it is shown for the first time that members of the IRAK family are indispensable elements of lipopolysaccharide signal transduction.
446 citations
"Threonine 66 in the death domain of..." refers methods in this paper
...Lysis, immunoprecipitation, and immunoblotting were performed as described elsewhere [14, 15]....
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TL;DR: Recent developments indicate that in addition to the common signaling module MyD88/IRAK/Tollip, other molecules can modulate signaling by TLRs, especially of TLR4, resulting in differential biological answers to distinct pathogenic structures.
415 citations
"Threonine 66 in the death domain of..." refers background in this paper
...Finally, phosphorylated IRAK-1 is ubiquitinated and degraded at the proteasome [3]....
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...Upon activation of a TIR family member (with the exception of TLR3), the cytosolic serine/threonine kinases IL-1R-associated kinase 1 (IRAK-1) and IRAK-4, members of a small family of specialized adaptor molecules [3, 4], are recruited to the receptor intracellular TIR domains via the adaptor MyD88 [5]....
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