Cytokine Receptors (Hematopoetin Receptor Family)
A broad array of molecules can be functionally termed cytokines. These secreted or membrane-bound regulatory factors control myriad developmental, metabolic and host defense processes in cells that display the correct assortment of surface receptors. Cytokine ligands and cellular receptors then form specific binding complexes that trigger intracellular signaling cascades to recast the fate of the cell. The rules of engagement between cytokines and receptors are highly structural in nature; cytokine and receptor families have distinct domain architectures that are employed in specific and highly conserved three-dimensional interactions.
The largest and most divergent family of cytokines are the hematopoietic factors that comprise around 50 distinct lymphokines, growth hormones, hemopoietins, neuropoietins and interleukins. In spite of minimal sequence homology, these hematopoietic cytokines have a singular four-α-helix protein fold that has been evolutionarily honed to interact with approximately 45 receptors that sport a distinctive pair of fibronectin-type-3 (Fn3) modules. As a number of receptor crystal structures reveal, these Fn3 modules fold as β-sheet sandwiches (reminiscent of Ig domains) with a characteristic “bent” hinge that forms a loop-rich binding site for their helical cytokine ligands. This conserved protein-protein interaction mode is capable of granting both high specificity or perplexing promiscuity to ligand binding, since both dedicated (or ‘private’) and shared receptors are found in the hematopoietic family. The latter type includes critical molecules such as Rγc (a common chain in IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21 receptor complexes), Rβc (likewise for IL-3, IL5 and GMCSF), gp130 for the IL-6-like cytokine clan, and IL-10R2 for the IL-10-like factors.
Though hematopoietic cytokines all share a common fold topology, sequence divergence has given rise to differences in the length and packing of their core α-helices, variations in loop geometry and extracore adornments such as short β-strands or α-helices nestled against the α-helical bundle core. These divergent architectural themes underlie the current classification of hematopoietic cytokines into three types, Short-chain (like the aforementioned ligands of Rγc and Rβc), Long-chain (comprising the IL-6-like cytokines, growth hormones, EPO and TPO) and Interferon-like (IFNs-α/β/γ and the IL-10-like cytokines). This structural division of cytokine ligands mirrors an evolutionary split of their respective receptors into Class 1 (or classically hematopoietic) Receptors for either Short- or Long-chain cytokines, and Class 2 (or Interferon-like) Receptors for Interferon-like cytokines.
Structural investigations have uncovered a greater complexity of ligand/receptor interactions than was first revealed in the paradigmatic framework of the growth hormone (GH) receptor complex where the cytokine was cradled between two receptor subunits that formed a face-to-face dimer. The majority of Class 1 and 2 hematopoietic cytokines utilize this scheme, driving association of a receptor homodimer (like GH, PRL, EPO and TPO) or heterodimer (all of the Short-chain and Interferon-like factors) to create an active signaling complex. The IL-6-like cytokines of the Class 1, Long-chain group, including IL-6, IL-11, IL-12, IL-23, IL-27, IL-31, CLC, CNTF, CT-1, GCSF, Leptin, LIF and OSM, have evolved an additional (non-GH-like) receptor-binding epitope that captures an N-terminal Ig domain of their second critical hematopoietic receptor signaling chain. This more elaborate choreography of gp130-like receptors assembling around IL-6-like cytokines is reflected in the subunit composition of the particular receptor complexes (see Table). However, exceptions exist in the form of three membrane-tethered Short-chain cytokines, namely FLT3L, MCSF and SCF, that are obligate dimers that appear to have escaped the confines of the hematopoietic cytokine receptor family and bind to three tyrosine-kinase receptors of the PDGFR class, FLT-3, FMS and KIT, respectively.
The hematopoietic cytokine/receptor system, which funnels its signals through conserved JAK/STAT intracellular pathways, is arguably the key regulator of the developmental fates and functional roles of blood cell types. As such, this system is critical in helping marshall and shape effective immune responses to pathogen attack. Dysregulation of this molecular network by mutation or pathogen deception, can contribute to a variety of human immuno-deficiencies or cancers. Nevertheless, efforts are underway to develop small molecule drugs that either augment or suppress hematopoietic receptor signaling by targeting critical points of interaction between cytokines and their receptors, or receptors and intracellular effectors.
The Tables below contain accepted modulators and additional information.
Class 1 (Short Chain) Hematopoietin Receptor Family
Receptor Fora | IL-2 | IL-3 | IL-4 | IL-5 | IL-7 |
Currently Accepted Name | IL-2 Receptor | IL-3 Receptor | IL-4 Receptor | IL-5 Receptor | IL-7 Receptor |
Alternative Name | TCGF | Multi-CSF MCGF | BCGF BSF-1 | EDF | PreBCGF |
Subunit Composition | IL2Rα (I0779)/ IL2Rβ (I0904)/ Rγc (I1029) | IL3Rα/ Rβc | IL4R/ Rγc | IL5Rα/ Rβc | IL7R2/ Rγc |
Selective Agonistsa,b | IL-2 (I2644, I7908 (h), I0523 (m)) IL-4 (I4269 (h), I1020 (m), I3650 (r)) IL-7 (I5896 (h), I4892 (m)) IL-15 (I8648) | IL-3 (I1646, I7389 (h), I4144 (m)) | IL-4 (I4269 (h), I1020 (m), I3650 (r)) | IL-5 (I5273 (h), I1145 (m)) | IL-7 (I5896 (h), I4892 (m)) |
Signal Transduction Mechanisms | JAK/STAT lyn lck | JAK/STAT | JAK/STAT IRS-1 | JAK/STAT 4PS lyn | JAK/STAT |
Radioligands of Choice | [125I]-IL-2 | [125I]-IL-3 | [125I]-IL-4 | [125I]-IL-5 | [125I]-IL-7 |
Tissue Expression | Thymus | Activated T-cells Mast cells Eosinophils | Th2-cells NK-T cells Mast cells | T-cells Mast cells | Bone marrow stromal cells T-cells |
Physiological Function | Hematopoiesis Proliferation of T- and B-cells | Growth/proliferation of immune cells | Proliferation/development of Th2 cells B-cell proliferation Activation of monocytes-macrophages | Growth/differentiation of B-cells and eosinophils | Early B- and T-cell development |
Disease Relevance | Therapeutic for many cancers | Myeloid leukemias | Allergy Asthma | Allergy Asthma | Psoriasis |
Receptor Fora | IL-9 | IL-13 | IL-15 | IL-21 |
Currently Accepted Name | IL-9 Receptor | IL-13 Receptor | IL-15 Receptor | IL-21 Receptor |
Alternative Name | ||||
Subunit Composition | IL9R/ Rγc | IL13Rα1/ IL4Rα IL13Rα2=decoy | IL15Rα/ IL2Rβ/ Rγc | IL21R/ Rγc |
Selective Agonistsa,b | IL-9 (I3394 (h), I3269 (m)) | IL-13 (I1771 (h), I1896 (m)) IL-7 (I5896 (h), I4892 (m)) IL-15 (I8648) | IL-15 (I8648) IL-2 (I2644, I7908) IL-4 (I4269) IL-7 (I5896) | IL-21 |
Signal Transduction Mechanisms | JAK/STAT | JAK/STAT lyn lck | JAK/STAT | JAK/STAT |
Radioligands of Choice | [125I]-IL-9 | [125I]-IL-13 | [125I]-IL-15 | [125I]-IL-21 |
Tissue Expression | Th2-cells | Activated Th2 cells | Placenta Skeletal muscle | Activated CD4+ T-cells |
Physiological Function | Eosinophil differentiation Mast cell proliferation | B-cell maturation/differentiation Downregulates macrophages | T cell stimulation | NK cell proliferation/maturation B- and T-cell function Inhibition of dendritic cells |
Disease Relevance | Asthma | Asthma | Arthritis | Psoriasis |
Receptor Fora | GMCSF | TSLP | FLT3L | MCSF | SCF |
Currently Accepted Name | GMCSF Receptor | TSLP Receptor | FLT3/FLK2 RTK | c-FMS RTK | c-KIT RTK |
Alternative Name | CSF2 | CSF-1 | MGF Steel | ||
Subunit Composition | GMCSFRα/ Rβc | TSLPR/ IL7Rα | (FLT3)2 | (FMS)2 | (KIT)2 |
Selective Agonistsa,b | GMCSF (G5035) | TSLP (IL-7) | Not Known | Not Known | Not Known |
Signal Transduction Mechanisms | JAK/STAT | JAK/STAT | Tyrosine Kinase | Tyrosine Kinase | Tyrosine Kinase |
Radioligands of Choice | [125I]-GMCSF | [125I]-TSLP | [125I]-FLT3L | [125I]-MCSF | [125I]-SCF |
Tissue Expression | Immune cells | Spleen Thymus Kidney Lung Bone marrow | Immune cells | Immune cells | Immune cells |
Physiological Function | Hemopoietic progenitor growth/differentiation | Myeloid stimulation Dendritic cell and B-cell development | Stem cell growth factor | Stem cell growth factor Macrophage development Immune defense Bone metabolism | Stem cell growth factor Mast cell development |
Disease Relevance | Therapeutic myeloid reconstitution | Not Known | Leukemia | Leukemia | Mast cell leukemia Piebaldism Gastrointestinal stromal tumor |
Class 1 (Long Chain) Hematopoietin Receptor Family
Receptor For | EPO | TPO | GH* | PRL | CLC | CNTF |
Currently Accepted Name | EPO Receptor (E0643) | TPO Receptor | GH Receptor | PRL Receptor | CLF and CNTF Receptor | CNTF Receptor |
Alternative Name | MegCSF MGDF MPL ligand | Somatotropin | Placental lactogen | BSF3 NNT1 | ||
Subunit Composition | (EPOR)2 | (TPOR)2 | (GHR)2 | (PRLR)2 | CLF/NR6 for secretion CNTFRα/gp130/LIFR | CNTFRα/gp130/LIFR |
Selective Agonistsa,b | EPO (E5627) | TPO (T1568) | GH/CS PRL (L4021) | PRL (L4021) GH/CS | CLC CNTF (C3710) | LIF (L5283) OSM (O9635) CT-1 IL-6 (I1395, I3268) IL-11 (I2406) CNTF (C3710) |
Signal Transduction Mechanisms | JAK/STAT | JAK/STAT | JAK/STAT | JAK/STAT | JAK/STAT | JAK/STAT |
Radioligands of Choice | [125I]-EPO | [125I]-TPO | [125I]-GH | [125I]-PRL | [125I]-CLC [125I]-CNTF [125I]-LIF [125I]-LIF [125I]-OSM | [125I]-CNTF [125I]-LIF [125I]-OSM |
Tissue Expression | Kidney Liver | Liver | Pituitary gland | Placenta | Lymph nodes Spleen PBLs Bone marrow Fetal liver | Central nervous sytem |
Physiological Function | Regulator of erythropoiesis | Regulator of thrombopoiesis Megakaryocyte development Platelets | Growth control Differentiation/proliferation of myoblasts | Promotes lactation by mammary gland | B-cell stimulation Neuronal regeneration | Neuronal regeneration |
Disease Relevance | Therapeutic for treatment of anemia | Therapeutic for platelet reconstitution Thrombocythemia | Dwarfism | Not Known | Not Known | Treatment for obesity Amyotrophic lateral sclerosis |
Receptor For | CT-1 | GCSF | Leptin | LIF | OSM | IL-6 |
Currently Accepted Name | CNTF Receptor | GCSF Receptor | Leptin Receptor | LIF Receptor | LIF Receptor and OSM Receptor | IL-6 Receptor (I5771) |
Alternative Name | CSF3 pluripoietin | Obese OB | HILDA | IFN-β2 BSF2 | ||
Subunit Composition | CNTFRα/gp130/LIFR | (GCSFR)2 | (LepR)2 | gp130/LIFR | gp130/LIFR gp130/OSMR | IL6Rα/(gp130)2 |
Selective Agonistsa,b | CT-1 LIF (L5283) OSM (O9635) CNTF (C3710) IL-6 (I1395, I3268) IL-11 (I2406) | GCSF (G0407) | Leptin (L4146) | LIF (L5283) OSM (O9635) IL-6 (I1395) CT IL-11 (I2406) CNTF (C3710) | LIF (L5283) OSM (O9635) CT IL-6 (I1395) IL-11 (I2406) CNTF (C3710) | IL-6 (I1395) (OSM (O9635) LIF (L5283) IL-11 (I2406) CNTF (C3710) CT) |
Signal Transduction Mechanisms | JAK/STAT | JAK/STAT SH-PTPase | JAK/STAT | JAK/STAT | JAK/STAT | JAK/STAT |
Radioligands of Choice | [125]-CT-1 [125I]-LIF [125I]-OSM | [125I]-GCSF | [125I]-Leptin | [125I]-LIF | [125I]-LIF [125I]-OSM | [125I]-IL-6 [125I]-OSM |
Tissue Expression | Heart Skeletal muscle Prostate Liver | Immune cells | Adipocytes Stem cells | Immune cells | Activated leukocytes | Immune cells |
Physiological Function | Cardiac myocte development | Regulates granulocyte proliferation/maturation | Early hematopoiesis Regulation of obesity and metabolism Bone development | Hematopoietic, neuronal and endothelial cell development | Liver development Hematopoiesis regulation | Proinflammatory Bone resorption control Hematopoiesis regulation Plasma cell development |
Disease Relevance | Not Known | Therapeutic against neutropenia | Obesity | Arthritis | Not Known | Therapeutic for cancers |
Receptor For | IL-11 | IL-12p35 | IL-23p19 | IL-27p28 | IL-31 |
Currently Accepted Name | IL-11 Receptor | IL-12 Receptor | IL-23 Receptor | IL-27 Receptor | IL-31 Receptor |
Alternative Name | AGIF | NKSF1 IL-12A | IL-23A | TCCR WSX-1 | GLMRL |
Subunit Composition | IL11R/gp130 | p40/IL12Rβ1/IL12Rβ2 | p40/IL12Rβ1/IL23R | EBI3/TCCR/gp130 | IL-31R/OSMR |
Selective Agonistsa,b | IL-11 (I2406) (OSM (O9635) CT IL-6 (I1395) LIF (L5283) CNTF (C3710) | IL-12p35/p40 (I2276) | IL-23p19/p40 | IL-27p28/EBI3 | IL-31 |
Signal Transduction Mechanisms | JAK/STAT | JAK/STAT | JAK/STAT | JAK/STAT | JAK/STAT |
Radioligands of Choice | [125I]-IL-11 | [125I]-IL-12p35/p40 | [125I]-IL-23p19/p40 | [125I]-IL-27p29/EBI3 | [125I]-IL-31 |
Tissue Expression | Stromal cells | Monocytes T-cells B-cells | Monocytes Dendritic cells T-cells NK-cells | Monocytes Dendritic cells | Activated Th2 cells |
Physiological Function | T-cell proliferation and regulation, stimulates platelet production | Promotes Th1 immune response NK cell cytotoxicity Pro-inflammatory | Promotes Th1 immune response IFN-γ inducer Proliferation of memory and naïve T-cells | Promotes Th1 immune response Proliferation of naïve CD4+ T-cells | Immune response |
Disease Relevance | Therapeutic for psoriasis | Chronic inflammatory diseases | Chronic inflammation | Chronic inflammation | Epithelial skin disorders Asthma Allergy |
Cytokine Receptors - Class 2 Hematopoietin Receptor Family
Receptor For | IFN-α/β** | IFN-γ | IL-10 | IL-19 | IL-20 |
Currently Accepted Name | IFN-α Receptor-2 | IFN-γ Receptor-1 | IL-10 Receptor-1 | IL-20 Receptor | IL-20 Receptor |
Alternative Name | CSIF | ||||
Subunit Composition | IFNαR2/IFNαR1 | IFNγR1/IFNsγR2 | (IL10R1)2/( IL10R2)2 | IL20R1/IL20R2 | IL20R1/IL20R2 IL22R1/IL20R2 |
Selective Agonists a,b | IFN-α** (I4401, I4276) IFN-β (I4151) | IFN-γ (I1520, I3265) | IL-10 (I9276) | IL-20 IL-24 IL-26 | IL-20 IL-19 IL-22 IL-24 IL-26 |
Signal Transduction Mechanisms | JAK/STAT PI3K NFkB MAPK PRMT1 | JAK/STAT PI3K MAPK NFkB | JAK/STAT | JAK/STAT | JAK/STAT |
Radioligands of Choice | [125I]-IFN-α/β | [125I]-IFN-γ | [125I]-IL-10 | [125I]-IL-19 | [125I]-IL-20 |
Tissue Expression | Dendritic cells | Th1 cells | Th2 cells, B cells | Monocytes, B cells | Immune cells |
Physiological Function | Immune response against viral infection, antiviral, antiproliferative | Immune response, triggers cytokine release | Immunosuppressive functions, blocking cytokine production | Immune response | Immune response |
Disease Relevance | Lupus, rheumatoid arthritis; treatment of Hepatitis-B and -C, multiple sclerosis | Chronic inflammatory disease | Asthma, allergy | Chronic inflammatory skin disease (e.g. psoriasis) | Psoriasis |
Receptor For | IL-22 | IL-24 | IL-26 | IL-28α/β*** | IL-29 |
Currently Accepted Name | IL-22 Receptor | IL-22 Receptor | IL-20 Receptor | IL-28 Receptor | IL-28 Receptor |
Alternative Name | IL-TIF | MDA7 FISP | AK155 | IFN-l2/l3 | IFN-l1 |
Subunit Composition | IL22R1/IL10R2 IL22bp=Decoy | IL22R1/IL20R2 IL20R1/IL20R2 | IL20R1/IL10R2 | IL28R1/IL10R2 | IL28R1/IL10R2 |
Selective Agonists a,b | IL-22 IL-20 | IL-24 IL-19 IL-20 IL-26 | IL-26 IL19 IL-20 IL-24 | IL-28α/β IL-29 | IL-29 IL-28α/β |
Signal Transduction Mechanisms | JAK/STAT | JAK/STAT | JAK/STAT | JAK/STAT | JAK/STAT |
Radioligands of Choice | [125I]-IL-22 | [125I]-IL-24 | [125I]-IL-26 | [125I]-IL-28α/β | [125I]-IL-29 |
Tissue Expression | T cells, mast cells, thymus, brain | Immune cells, PBLs, melanocytes | T-cells, monocytes, NK-cells, B-cells | T-cells | T-cells |
Physiological Function | Immune response | Immune response, apoptosis-inducing in tumor cells | Immune response | Immune response, antiviral, antiprolliferative | Immune response, antiviral, antiproliferative |
Disease Relevance | Allergy | Melanoma | Upregulated in T-cells by Herpesvirus infection, stimulation of cytotoxic activity of immune cells | Not Known | Not Known |
Footnotes
a) Product numbers refer to the human cytokine. For other species, please visit our website at www.sigmaaldrich.com and use our Product Search.
b) Agonists not in parentheses are primary agonists for the receptor.
* = GH and four closely related chorionic somatotropin homologs
** = IFNα,β,δ,ε,κ,τ,ω and limitin
*** = IL28α and IL28β are two closely related cytokines
Abbreviations
4PS: IL-4-induced phosphotyrosine substrate
AGIF: Adipogenesis inhibitory factor
BCGF: B cell growth factor
BSF: B cell stimulatory factor
CLC: Cardiotrophin like cytokine
CLF: Cytokine-like factor
CNTF: Ciliary neurotrophic factor
CS: Chorionic somatotropin
CSF: Colony stimulating factor
CSIF: Cytokine synthesis inhibitory factor) (CSIF).
CT: Cardiotrophin
EDF: Eosinophil differentiation factor
EPO: Erythropoietin
FISP: IL4 induced secreted protein
FLT-3: Fms-like tyrosine kinase 3
FLT3L: Fms-related tyrosine kinase 3 ligand)
FMS: formerly McDonough feline sarcoma viral (v-fms) oncogene homolog
GH: Growth Hormone
GHR: Growth hormone receptor
GMCSF: Granulocyte macrophage colony stimulating factor
GSCF: Granulocyte colony stimulating factor
IFN: Interferon
IL: Interleukin
IL-TIF: IL-10-related T-cell-derived inducible factor
IRS-1: Insulin receptor substrate-1
Jak: Janus kinase
KIT: V-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog
LIF: Leukemia inhibitory factor
Lck: Lymphocyte-specific protein tyrosine kinase
Lyn: V-yes-1 Yamaguchi sarcoma viral related oncogene homolog
MCSF: Macrophage colony stimulating factor
MDA7: Melanoma differentiation-associated protein 7
MGDF: megakaryocyte growth and development factor
MGF: Mast cell growth factor
NKSF1: NK cell stimulatory factor chain 1
NNT1: Novel neurotrophin 1
OSM: Oncostatin M
PBLs: Peripheral blood leukocytes
PDGF: Platelet-derived growth factor
PRL: Prolactin
RTK: Protein tyrosine kinase
SCF: Stem cell growth factor
SH-PTPase: Src homology domain 2-containing protein tyrosine phosphatase
STAT: Signal transducer and activator of transcription
TCCR: Type I T-cell cytokine receptor
TPO: Thrombopoietin
TSLP: Thymic stromal lymphopoietin
References
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