Interleukin-1 receptor family

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Interleukin-1 receptor
Identifiers
SymbolInterleukin-1 receptor
InterPro IPR015621
Membranome 13

Members of the very wide interleukin-1 receptor (IL-1R) family are characterized by extracellular immunoglobulin-like domains and intracellular Toll/Interleukin-1R (TIR) domain. It is a group of structurally homologous proteins, conserved throughout the species as it was identified from plants to mammals. Proteins of this family play important role in host defence, injury and stress. [1] There are four main groups of TIR domain-containing proteins in animals; Toll-like receptors, Interleukin-1 receptor (IL-1R), cytosolic adaptor proteins (such as MyD88 adaptor protein) and insect and nematode Toll. Each of these groups is involved mainly in host defence; Toll receptors are also involved in embryogenesis. [2]

Contents

TIR domain

The TIR domain is about 200 amino acids long and consists of 3 conserved boxes and between these boxes there are regions of variable length. If due to some mutation all of the three boxes are damaged, there is no surface expression of the protein. If only boxes one and two are mutated, there is loss of signalling activity. [2] There are also highly conserved regions between the three boxes as well. When the receptor is activated TIR domain recruits downstream cytoplasmic signalization adaptor proteins (such as Myd88 adaptor protein). [3]

In addition to its traditional role as a scaffolding protein, the TIR domain can also possess intrinsic enzymatic activity to cleave the metabolite NAD+, as first discovered in the protein SARM1. [4] The ability of TIR domains to consume NAD+ is a primordial function of this protein domain, as many TIR domain-containing proteins from bacteria and archaea can degrade NAD+ into the products nicotinamide and ADP-ribose (ADPR) (or cyclic-ADPR). [5]

Immunoglobulin-like domain

Ig-like domain is the part of receptor which is located extracellularly. There are minimal homologies in amino acid sequences of Ig-like domains between proteins of IL-1R family but they all show characteristic Ig-fold and two β-sheets joined together by disulfide bonds which form between cysteine residues. There are differences in number of Ig-like domains between members of IL-1R family. [2]

IL-1R signalization

After ligand binding, the first step of IL-1R family signalling is oligomerization of TIR domains present on receptors (IL-1R, TLR), coreceptors (IL-1R accessory protein, CD14) and adaptor molecules (MyD88). TIR domain present on receptor creates a heterodimer with TIR domain on accessory protein. This high affinity receptor complex recruits downstream signalling molecules. The signal is transduced by cytoplasmatic kinases (such as IRAKs) and by other adaptors, such as tumor necrosis factor 6 (TRAF6). The final step of signalization is phosphorilation of the inhibitory molecule IkB by IkB kinase complex leading to transcription factor NF-κB releasing. NF-κB is translocated into nucleus and by binding DNA intermediates inflammatory, alergic and non-alergic immune response. [6]

Interleukin-1 receptor

The term interleukin-1 includes IL-1α, IL-1β and Interleukin 1 receptor antagonist (IL-1Ra). IL-1Rs are involved in immune host defence and hematopoiesis. IL-1R signalization activates immune response by activation of transcription of IL-1 target genes such as IL-6, IL-8, MCP-1, COX-2, IκBα, IL-1α, IL-1β, MKP-1. Components of signalization pathway of IL-1R which are involved in cellular response to IL-1 also mediate responses to other cytokines (IL-18 and IL-33), Toll-like receptors (TLRs), and many forms of cytotoxic stress. IL-1R functions as a bridge between adaptive and innate immunity.

Interleukin 1 receptor, type I

Type I IL-1R (IL-1RI), also known as CD121a, is receptor for IL-1α, IL-1β and IL-1RA. IL-1RI signalling is involved in thymocyte proliferation, B cells development, IL-2 and IL-6 production, stress responses, inflammatory responses, sleep regulation and appetite. [2] IL-1RI signalling plays also important role in Th17 development. [7] [8] Studies of human autoimmune diseases such as sclerosis multiplex, Rheumatoid arthritis, psoriasis or autoimmune inflammatory bowel diseases show that defect in IL-1R1 signalling is responsible for Th17-mediated autoimmune diseases. [9] IL-1R signalling is regulated by negative regulators such as inhibitory IL-R1 type II (IL-1RII), soluble IL-1RI and sIL-RII and IL-1Ra. [10] It can be also regulated on the level of downstream signalling molecules by inhibiting recruitment of IRAKs, or by suppression of MyD88 secretion. IL-1R cooperates with receptor accessory protein and both are expressed on T cells, fibroblasts and endothelial cells. [10]

Interleukin 1 receptor, type II

IL-1RII is predominantly expressed on lymphoid and myeloid cells including monocytes, neutrophils, bone marrow cells, macrophages and B cells, [11] also on T cells and epithelial cells. There are three Ig-like domains located extracellulary and highly homological with IL-1RI. Intracellulary there are 24 amino acid long domains which lack the TIR domain thus it is unable to signal. [12] IL-1RII is a surface receptor able to bind IL-1α, IL-1β and IL-1RI. It also forms a soluble form sIL-1RII. It is a decoy receptor – it inhibits activity of its ligands. Expression of IL-1RII is regulated by two different distal 5'UTRs and their associated promoter regions. [13]

IL-1 receptor accessory protein

IL-1RAcP is a second receptor subunit of IL-1RI. By forming a receptor heterodimer with IL-1RI facilitates signalization due to oligomerization of TIR domains of these proteins. [14] IL-1RAcP does not bind IL-1 but it binds IL-1RI through its Ig-like domains 1 and 2 and is necessary for IL-1R1 signalling. In response to stress or acute phase induction, a soluble form of this protein is produced by alternative splicing. [15]

IL 1 receptor-related protein 2 (IL-1R-rp2) consists of three Ig-like extracellular domains, transmembrane domain and cytoplasmic TIR domain. It was detected in lung, epithelium, brain vascular cells and in monocytes, keratinocytes, fibroblasts and endothelial cells. It activates NF-κB by binding IL-1ϵ. [16]

Related Research Articles

<span class="mw-page-title-main">Toll-like receptor</span> Pain receptors and inflammation

Toll-like receptors (TLRs) are a class of proteins that play a key role in the innate immune system. They are single-pass membrane-spanning receptors usually expressed on sentinel cells such as macrophages and dendritic cells, that recognize structurally conserved molecules derived from microbes. Once these microbes have reached physical barriers such as the skin or intestinal tract mucosa, they are recognized by TLRs, which activate immune cell responses. The TLRs include TLR1, TLR2, TLR3, TLR4, TLR5, TLR6, TLR7, TLR8, TLR9, TLR10, TLR11, TLR12, and TLR13. Humans lack genes for TLR11, TLR12 and TLR13 and mice lack a functional gene for TLR10. TLR1, TLR2, TLR4, TLR5, TLR6, and TLR10 are located on the cell membrane, whereas TLR3, TLR7, TLR8, and TLR9 are located in intracellular vesicles.

<span class="mw-page-title-main">Fc receptor</span> Surface protein important to the immune system

In immunology, a Fc receptor is a protein found on the surface of certain cells – including, among others, B lymphocytes, follicular dendritic cells, natural killer cells, macrophages, neutrophils, eosinophils, basophils, human platelets, and mast cells – that contribute to the protective functions of the immune system. Its name is derived from its binding specificity for a part of an antibody known as the Fc region. Fc receptors bind to antibodies that are attached to infected cells or invading pathogens. Their activity stimulates phagocytic or cytotoxic cells to destroy microbes, or infected cells by antibody-mediated phagocytosis or antibody-dependent cell-mediated cytotoxicity. Some viruses such as flaviviruses use Fc receptors to help them infect cells, by a mechanism known as antibody-dependent enhancement of infection.

<span class="mw-page-title-main">IRAK4</span>

IRAK-4, in the IRAK family, is a protein kinase involved in signaling innate immune responses from Toll-like receptors. It also supports signaling from T-cell receptors. IRAK4 contains domain structures which are similar to those of IRAK1, IRAK2, IRAKM and Pelle. IRAK4 is unique compared to IRAK1, IRAK2 and IRAKM in that it functions upstream of the other IRAKs, but is more similar to Pelle in this trait. IRAK4 has important clinical applications.

<span class="mw-page-title-main">Caspase 1</span> Protein-coding gene in the species Homo sapiens

Caspase-1/Interleukin-1 converting enzyme (ICE) is an evolutionarily conserved enzyme that proteolytically cleaves other proteins, such as the precursors of the inflammatory cytokines interleukin 1β and interleukin 18 as well as the pyroptosis inducer Gasdermin D, into active mature peptides. It plays a central role in cell immunity as an inflammatory response initiator. Once activated through formation of an inflammasome complex, it initiates a proinflammatory response through the cleavage and thus activation of the two inflammatory cytokines, interleukin 1β (IL-1β) and interleukin 18 (IL-18) as well as pyroptosis, a programmed lytic cell death pathway, through cleavage of Gasdermin D. The two inflammatory cytokines activated by Caspase-1 are excreted from the cell to further induce the inflammatory response in neighboring cells.

<span class="mw-page-title-main">MYD88</span>

Myeloid differentiation primary response 88 (MYD88) is a protein that, in humans, is encoded by the MYD88 gene.

<span class="mw-page-title-main">Interleukin 18</span>

Interleukin-18 (IL-18), also known as interferon-gamma inducing factor is a protein which in humans is encoded by the IL18 gene. The protein encoded by this gene is a proinflammatory cytokine. Many cell types, both hematopoietic cells and non-hematopoietic cells, have the potential to produce IL-18. It was first described in 1989 as a factor that induced interferon-γ (IFN-γ) production in mouse spleen cells. Originally, IL-18 production was recognized in Kupffer cells, liver-resident macrophages. However, IL-18 is constitutively expressed in non-hematopoietic cells, such as intestinal epithelial cells, keratinocytes, and endothelial cells. IL-18 can modulate both innate and adaptive immunity and its dysregulation can cause autoimmune or inflammatory diseases.

TIR-domain-containing adapter-inducing interferon-β (TRIF) is an adapter in responding to activation of toll-like receptors (TLRs). It mediates the rather delayed cascade of two TLR-associated signaling cascades, where the other one is dependent upon a MyD88 adapter.

<span class="mw-page-title-main">Toll-like receptor 4</span> Protein-coding gene in the species Homo sapiens

Toll-like receptor 4 is a protein that in humans is encoded by the TLR4 gene. TLR4 is a transmembrane protein, member of the toll-like receptor family, which belongs to the pattern recognition receptor (PRR) family. Its activation leads to an intracellular signaling pathway NF-κB and inflammatory cytokine production which is responsible for activating the innate immune system.

<span class="mw-page-title-main">IRAK1</span> Protein-coding gene in the species Homo sapiens

Interleukin-1 receptor-associated kinase 1 (IRAK-1) is an enzyme in humans encoded by the IRAK1 gene. IRAK-1 plays an important role in the regulation of the expression of inflammatory genes by immune cells, such as monocytes and macrophages, which in turn help the immune system in eliminating bacteria, viruses, and other pathogens. IRAK-1 is part of the IRAK family consisting of IRAK-1, IRAK-2, IRAK-3, and IRAK-4, and is activated by inflammatory molecules released by signaling pathways during pathogenic attack. IRAK-1 is classified as a kinase enzyme, which regulates pathways in both innate and adaptive immune systems.

<span class="mw-page-title-main">TOLLIP</span>

Toll interacting protein, also known as TOLLIP, is an inhibitory adaptor protein that in humans is encoded by the TOLLIP gene.

<span class="mw-page-title-main">SIGIRR</span> Protein-coding gene in the species Homo sapiens

Single Ig IL-1-related receptor (SIGIRR), also called Toll/Interleukin-1 receptor 8 (TIR8) or Interleukin-1 receptor 8 (IL-1R8), is transmembrane protein encoded by gene SIGIRR, which modulate inflammation, immune response, and tumorigenesis of colonic epithelial cells.

<span class="mw-page-title-main">FCAR</span> Mammalian protein found in Homo sapiens

Fc fragment of IgA receptor (FCAR) is a human gene that codes for the transmembrane receptor FcαRI, also known as CD89. FcαRI binds the heavy-chain constant region of Immunoglobulin A (IgA) antibodies. FcαRI is present on the cell surface of myeloid lineage cells, including neutrophils, monocytes, macrophages, and eosinophils, though it is notably absent from intestinal macrophages and does not appear on mast cells. FcαRI plays a role in both pro- and anti-inflammatory responses depending on the state of IgA bound. Inside-out signaling primes FcαRI in order for it to bind its ligand, while outside-in signaling caused by ligand binding depends on FcαRI association with the Fc receptor gamma chain.

The interleukin-13 receptor is a type I cytokine receptor, binding Interleukin-13. It consists of two subunits, encoded by IL13RA1 and IL4R, respectively. These two genes encode the proteins IL-13Rα1 and IL-4Rα. These form a dimer with IL-13 binding to the IL-13Rα1 chain and IL-4Rα stabilises this interaction. This IL-13 receptor can also instigate IL-4 signalling. In both cases this occurs via activation of the Janus kinase (JAK)/Signal Transducer and Activator of Transcription (STAT) pathway, resulting in phosphorylation of STAT6. Phosphorylated STAT6 dimerises and acts as a transcription factor activating many genes, such as eotaxin.

<span class="mw-page-title-main">Interleukin-17 receptor</span> Type of protein receptor

Interleukin-17 receptor (IL-17R) is a cytokine receptor which belongs to new subfamily of receptors binding proinflammatory cytokine interleukin 17A, a member of IL-17 family ligands produced by T helper 17 cells (Th17). IL-17R family consists of 5 members: IL-17RA, IL-17RB, IL-17RC, IL-17RD and IL-17RE. Functional IL-17R is a transmembrane receptor complex usually consisting of one IL-17RA, which is a founding member of the family, and second other family subunit, thus forming heteromeric receptor binding different ligands. IL-17A, a founding member of IL-17 ligand family binds to heteromeric IL-17RA/RC receptor complex. IL-17RB binds preferentially IL-17B and IL-17E and heteromeric IL-17RA/RE complex binds IL-17C. However, there is still unknown ligand for IL-17RD. The first identified member IL-17RA is located on human chromosome 22, whereas other subunits IL-17RB to IL-17RD are encoded within human chromosome 3.

The following outline is provided as an overview of and topical guide to immunology:

<span class="mw-page-title-main">Toll-like receptor 11</span>

Toll-like receptor 11 (TLR11) is a protein that in mice and rats is encoded by the gene TLR11, whereas in humans it is represented by a pseudogene. TLR11 belongs to the toll-like receptor (TLR) family and the interleukin-1 receptor/toll-like receptor superfamily. In mice, TLR11 has been shown to recognise (bacterial) flagellin and (eukaryotic) profilin present on certain microbes, it helps propagate a host immune response. TLR11 plays a fundamental role in both the innate and adaptive immune responses, through the activation of Tumor necrosis factor-alpha, the Interleukin 12 (IL-12) response, and Interferon-gamma (IFN-gamma) secretion. TLR11 mounts an immune response to multiple microbes, including Toxoplasma gondii, Salmonella species, and uropathogenic E. coli, and likely many other species due to the highly conserved nature of flagellin and profilin.

<span class="mw-page-title-main">Toll-interleukin receptor</span>

The toll-interleukin-1 receptor (TIR) homology domain is an intracellular signaling domain found in MyD88, SARM1, interleukin-1 receptors, toll receptors and many plant R proteins. It contains three highly conserved regions, and mediates protein-protein interactions between the toll-like receptors (TLRs) and signal-transduction components. TIR-like motifs are also found in plant proteins where they are involved in resistance to disease and in bacteria where they are associated with virulence. When activated, TIR domains recruit cytoplasmic adaptor proteins MyD88 (UniProt Q99836) and TOLLIP (toll-interacting protein, UniProt Q9H0E2). In turn, these associate with various kinases to set off signaling cascades. Some TIR domains have also been found to have intrinsic NAD+ cleavage activity, such as in SARM1. In the case of SARM1, the TIR NADase activity leads to the production of Nam, ADPR and cADPR and the activation of downstream pathways involved in Wallerian degeneration and neuron death.

<span class="mw-page-title-main">Interleukin-1 family</span> Group of cytokines playing a key role in the regulation of immune and inflammatory responses

The Interleukin-1 family is a group of 11 cytokines that plays a central role in the regulation of immune and inflammatory responses to infections or sterile insults.

<span class="mw-page-title-main">IL1RL1</span>

Interleukin 1 receptor-like 1, also known as IL1RL1 and ST2, is a protein that in humans is encoded by the IL1RL1 gene.

The interleukin-1 receptor (IL-1R) associated kinase (IRAK) family plays a crucial role in the protective response to pathogens introduced into the human body by inducing acute inflammation followed by additional adaptive immune responses. IRAKs are essential components of the Interleukin-1 receptor signaling pathway and some Toll-like receptor signaling pathways. Toll-like receptors (TLRs) detect microorganisms by recognizing specific pathogen-associated molecular patterns (PAMPs) and IL-1R family members respond the interleukin-1 (IL-1) family cytokines. These receptors initiate an intracellular signaling cascade through adaptor proteins, primarily, MyD88. This is followed by the activation of IRAKs. TLRs and IL-1R members have a highly conserved amino acid sequence in their cytoplasmic domain called the Toll/Interleukin-1 (TIR) domain. The elicitation of different TLRs/IL-1Rs results in similar signaling cascades due to their homologous TIR motif leading to the activation of mitogen-activated protein kinases (MAPKs) and the IκB kinase (IKK) complex, which initiates a nuclear factor-κB (NF-κB) and AP-1-dependent transcriptional response of pro-inflammatory genes. Understanding the key players and their roles in the TLR/IL-1R pathway is important because the presence of mutations causing the abnormal regulation of Toll/IL-1R signaling leading to a variety of acute inflammatory and autoimmune diseases.

References

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