Specificity of signaling by hematopoietic cytokine receptors: instructive versus permissive effects

The helical cytokines constitute a family of proteins with a common three-dimensional structure. They exert a wide variety of biological effects with a preference for the hematopoietic system. The effects of helical cytokines are mediated by cell surface receptors, which belong to the cytokine receptor superfamily and signal by activating cytoplasmic tyrosine kinases of the Janus kinase (Jak) family and other downstream signaling pathways. The relevance of each of these pathways for eliciting a specific cellular response remains to be determined. This review will focus on cytokine receptors which play a role in the regulation of hematopoiesis and summarize data the address the question how specificity of signaling is achieved.     

A knowledgebase resource for interleukin-17 family mediated signaling

Interleukin-17 (IL-17) belongs to a relatively new family of cytokines that has garnered attention as the signature cytokine of Th17 cells. This cytokine family consists of 6 ligands, which bind to 5 receptor subtypes and induce downstream signaling. Although the receptors are ubiquitously expressed, cellular responses to ligands vary across tissues. The cytokine family is associated with various autoimmune disorders including rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, asthma and psoriasis in addition to being implicated in the pathogenesis of cancer. In addition, this family plays a role in host defense against bacterial and fungal infections. The signaling mechanisms of the IL-17 family of proinflammatory cytokines are not well explored. In this study, we present a resource of literature-annotated reactions induced by IL-17. The reactions are catalogued under 5 categories, namely; molecular association, catalysis, transport, activation/inhibition and gene regulation. A total of 93 molecules and 122 reactions have been annotated. The IL-17 pathway is freely available through NetPath, a resource of signal transduction pathways previously developed by our group.     

The Induction of IL-33 in the Sinus Epithelium and Its Influence on T-Helper Cell Responses

BackgroundChronic rhinosinusitis (CRS) is characterized by epithelial activation and chronic T-cell infiltration in sinonasal mucosa and nasal polyps. IL-33 is a new cytokine of the IL-1 cytokine family that has a pro-inflammatory and Th2 type cytokine induction property. The role of IL-33 in the pathomechanisms of CRS and its interaction with other T cell subsets remain to be fully understood.MethodsThe main trigger for IL-33 mRNA expression in primary human sinonasal epithelial cells was determined in multiple cytokine and T-cell stimulated cultures. The effects of IL-33 on naïve, Th0 and memory T-cells was studied by PCR, ELISA and flow cytometry. Biopsies from sinus tissue were analyzed by PCR and immunofluorescence for the presence of different cytokines and receptors with a special focus on IL-33.ResultsIL-33 was mainly induced by IFN-γ in primary sinonasal epithelial cells, and induced a typical CRSwNP Th2 favoring cytokine profile upon co-culture with T-helper cell subsets. IL-33 and its receptor ST2 were highly expressed in the inflamed epithelial tissue of CRS patients. While IL-33 was significantly up-regulated in the epithelium for CRSsNP, its receptor was higher expressed in sinus tissue from CRSwNP.ConclusionsThe present study delineates the influence of IL-33 in upper airway epithelium and a potential role of IL-33 in chronic inflammation of CRSwNP by enhancing Th2 type cytokine production, which could both contribute to a further increase of an established Th2 profile in CRSwNP.     

Thematic review series: The immune system and atherogenesis. Cytokines affecting endothelial and smooth muscle cells in vascular disease

The cellular and extracellular matrix accumulations that comprise the lesions of atherosclerosis are driven by local release of cytokines at sites of predilection for lesion formation, and by the specific attraction and activation of cells expressing receptors for these cytokines. Although cytokines were originally characterized for their potent effects on immune and inflammatory cells, they also promote endothelial cell dysfunction and alter smooth muscle cell (SMC) phenotype and function, which can contribute to or retard vascular pathologies. This review summarizes in vivo studies that have characterized endothelial- and smooth muscle-specific effects of altering cytokine signaling in vascular disease. Although multiple reports have identified cytokines as pivotal players in endothelial and SMC responses in vascular disease, they also have highlighted the need to delineate the critical genes and specific cellular functions regulated by individual cytokine signaling pathways.     

Receptor fusion proteins for the inhibition of cytokines

Cells are exposed to a large variety of cytokines that signal through corresponding cytokine receptors. In healthy tissues or tissues that respond properly to disturbed homeostasis, the cross-talk of a few conserved core signaling pathways downstream of the cytokine receptors is translated into an adequate cellular response. In chronic inflammatory diseases but also in cancer associated inflammation cytokine expression and the downstream signaling networks are dysregulated. Targeted therapies are aimed at the specific interference with dysregulated cytokine signaling. In this article some concepts of pharmacological intervention with cytokine signaling will be reviewed including biologics that target cytokines and cytokine receptors. Receptor fusion proteins consisting of the ligand-binding domains of cytokine receptors are highly specific and potent cytokine inhibitors and will be discussed in more detail.     

Engagement of Gab1 and Gab2 in erythropoietin signaling.

Several signaling cascades are activated during engagement of the erythropoietin receptor to mediate the biological effects of erythropoietin. The members of the insulin receptor substrate (IRS) family of proteins play a central role in signaling for various growth factor receptors and cytokines by acting as docking proteins for the SH2 domains of signaling elements, linking cytokine receptors to diverse downstream pathways. In the present study we provide evidence that the recently cloned IRS-related proteins, Gab1 and Gab2, of the Gab family of proteins, are rapidly phosphorylated on tyrosine during erythropoietin treatment of erythropoietin-responsive cells and provide docking sites for the engagement of the SHP2 phosphatase and the p85 subunit of the phosphatidylinositol 3'-kinase. Furthermore, our data show that Gab1 is the primary IRS-related protein activated by erythropoietin in primary erythroid progenitor cells. In studies to identify the erythropoietin receptor domains required for activation of Gab proteins, we found that tyrosines 425 and 367 in the cytoplasmic domain of the erythropoietin receptor are required for the phosphorylation of Gab2. Taken together, our data demonstrate that Gab proteins are engaged in erythropoietin signaling to mediate downstream activation of the SHP2 and phosphatidylinositol 3'-kinase pathways and possibly participate in the generation of the erythropoietin-induced mitogenic responses.     

A Family of Heptahelical Receptors With Adhesion-Like Domains: A Marriage Between Two Super Families

Abstract

Some G protein-coupled receptors (GPCRs) are regulators of cell adhesion via inside-out effector signaling pathways. Such is the case with leukocyte chemokine receptors which stimulate intracellular second messenger pathways resulting in upregulation of integrin adhesion to ligands present in the extracellular matrix or on opposing cells resulting in chemotaxis and extravasation during immune surveillance. Remarkably, a family of GPCRs has recently been discovered that may themselves be triggered by cell-cell or cell-matrix interactions. Along with a canonical heptahelical membrane-spanning region, these intriguing proteins contain putative cell adhesionlike modules. The evidence to date suggests that they are involved in lymphocyte activation, macrophage biology, synaptic exocytosis and planar polarization during organogenesis.     

Signal transduction in monocytes: the role of zinc ions

The availability of zinc has a regulatory role in the immune system. It can have either pro- or anti-inflammatory effects, which both seem to be a consequence of a direct interaction of zinc with the cytokine secretion by monocytes. In this review, the molecular basis for this effect, the interaction of zinc with the signal transduction of monocytes, is discussed. In particular, zinc seems to activate or inhibit several signaling pathways that interact with the signal transduction of pathogen sensing receptors, the so-called Toll-like receptors (TLR), which sense pathogen-derived molecular structures and, upon activation, lead to secretion of pro-inflammatory cytokines. The interaction of zinc with protein tyrosine phosphatases and protein kinase C, and a direct modulation of lipopolysaccharide binding to its receptor (TLR-4) all result in enhanced cytokine production. On the other hand, a complex interaction between zinc, NO and cyclic nucleotide signaling, and inhibition of interleukin-1 receptor associated kinase-1, and inhibitor of kappa B kinase all counteract the production of pro-inflammatory cytokines. A role for the zinc binding protein metallothionein as a regulator for intracellular zinc signaling is discussed. By acting on all these signaling molecules, the zinc status of monocytes can have a direct effect on inflammation.     

Identification of signaling components required for the prediction of cytokine release in RAW 264.7 macrophages

Background  

Release of immuno-regulatory cytokines and chemokines during inflammatory response is mediated by a complex signaling network. Multiple stimuli produce different signals that generate different cytokine responses. Current knowledge does not provide a complete picture of these signaling pathways. However, using specific markers of signaling pathways, such as signaling proteins, it is possible to develop a 'coarse-grained network' map that can help understand common regulatory modules for various cytokine responses and help differentiate between the causes of their release.     

Src family kinase-independent signal transduction and gene induction by leukemia inhibitory factor

Members of the interleukin-6 (IL-6) family of cytokines exert their biological effects via binding to their cognate ligand-binding receptor subunit on a target cell. The subsequent recruitment of the common signal transducer glycoprotein 130 and activation of the JAK/STAT and SHP-2/Ras/mitogen-activated protein kinase (MAPK) pathways are responsible for the majority of cellular responses elicited by IL-6 cytokines. Several types of experiments suggest that the Src family of kinases (SFK) also participates in IL-6 family cytokine-mediated signaling events. SYF cells, which lack expression of SFKs Src, Yes, and Fyn, were used to determine the role of SFKs in IL-6 family cytokine signaling and gene induction. SYF and wild type (WT) control fibroblasts displayed similar activation of signaling intermediates following stimulation with leukemia inhibitory factor (LIF). LIF-stimulated tyrosine phosphorylation of SHP-2 and subsequent activation of MAPK in SYF cells were identical to that seen in LIF-stimulated WT cells. Both LIF-stimulated tyrosine phosphorylation of STAT1 and STAT3, as well as LIF-stimulated DNA binding activity of STAT-containing nuclear complexes were indistinguishable when compared in SYF and WT cells. In addition, the phosphatidylinositol 3-kinase-sensitive Akt kinase and p38 MAPK were activated by LIF in both SYF and WT cells. Furthermore, LIF-stimulated expression of c-fos, egr-1, and suppressor of cytokine signaling-3 was retained in SYF cells. The IL-6 family cytokine oncostatin M was also capable of activating MAPK, STAT3, STAT1, Akt, and p38 in both WT and SYF cells. These results demonstrate that IL-6 family cytokines can activate a full repertoire of signaling pathways and induce gene expression independent of SFKs.     

Cross-talk at the crossroads of sphingosine-1-phosphate, growth factors, and cytokine signaling

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that mediates a wide array of biologic effects through its interaction with a family of five G protein-coupled receptors. Cytokines and growth factors interact with this signaling pathway in a variety of ways, including both activation and regulation of the expression of the enzymes that regulate synthesis and degradation of S1P. Not only do many growth factors and cytokines stimulate S1P production, leading to transactivation of S1P receptors, ligation of S1P receptors by S1P can also transactivate growth factor tyrosine kinase receptors and stimulate growth factor and cytokine signaling cascades. This review discusses the mechanisms involved in cross-talk between S1P, cytokines, and growth factors and the impact of that cross-talk on cell signaling and cell biology.     

Structural analysis of cytokines comprising the IL-10 family

Interleukin-10 (IL-10) family of cytokines includes a number of its viral homologs and eight cellular cytokines (IL-19, IL-20, IL-22, IL-24, IL-26, IL-28A, IL-28B, and IL-29). The latter three proteins are also known as IFN-λ2, IFN-λ3, and IFN-λ1, and are recognized as type III (or λ) interferons. Most of the cellular homologs of IL-10 are monomeric in solution, whereas IL-10 and its viral homologs are intercalated dimers consisting of two helical bundle domains topologically similar to the monomeric members of the family. A classical four-helix bundle, a signature element of all helical cytokines, is always found as part of the domain of each member of the IL-10 family. The only crystal structures of these cytokine receptors that have been determined to date are for their extracellular domains (ECDs). Each ECD consists of two β-sandwich domains connected in the middle by a linkage. Signal transduction occurs when a cytokine binds to its two appropriate receptor chains. IL-10 and its viral homologs use the same IL-10 receptor system, whereas the cellular homologs of IL-10 use their own receptors, which in some cases may overlap and be used in different pairwise combinations. The known structures of binary complexes allowed for marking of the receptor binding site, which always includes helix A, loop AB and helix F (IL-10 notations) on the side of a ligand, loops of the N-terminal and C-terminal domains directed toward the ligand, and the interdomain linkage of the ECD. An analysis of the published structures of both the binary and ternary complexes of all helical cytokines allowed for the generation of a model of the signaling complex of IL-10. The receptor binding site I of the high affinity receptor IL-10R1 is exactly the same as in the crystal structure of the binary IL-10/sIL-10R1 complex, whereas the receptor binding site II is located on the surface of the first and the third helices of the four-helix bundle. The receptor/receptor interface, or site III, is formed between the C-terminal domains of IL-10R1 and IL-10R2.     

Thrombopoietin: a pan-hematopoietic cytokine.

The recent discovery of thrombopoietin has enhanced our understanding of both hematopoiesis and platelet production. Thrombopoietin supports hematopoietic stem cell survival and expansion as well as promoting all aspects of megakaryocyte development. The hormone displays many structural similarities to other members of the hematopoietic cytokine family and some notable differences, and regulation of its expression requires both receptor-mediated removal and other mechanisms. Thrombopoietin induces receptor dimerization and tyrosine phosphorylation, and a series of signaling events including activation of JAK/STAT, Shc/Ras/MAPK and PI3K/Akt; these pathways overlap with those induced by other cytokines, but the differences that lead to the unique biological effects of the hormone are gradually being uncovered. Our growing appreciation of how cytokine signaling pathways are translated into megakaryocyte development is discussed.     

Toll-like receptors: a family of pattern-recognition receptors in mammals

The innate immune system uses a variety of germline-encoded pattern-recognition receptors that recognize conserved microbial structures or pathogen-associated molecular patterns, such as those that occur in the bacterial cell-wall components peptidoglycan and lipopolysaccharide. Recent studies have highlighted the importance of Toll-like receptors (TLRs) as a family of pattern-recognition receptors in mammals that can discriminate between chemically diverse classes of microbial products. First identified on the basis of sequence similarity with the Drosophila protein Toll, TLRs are members of an ancient superfamily of proteins, which includes related proteins in invertebrates and plants. TLRs activate innate immune defense reactions, such as the release of inflammatory cytokines, but increasing evidence supports an additional critical role for TLRs in orchestrating the development of adaptive immune responses. The sequence similarity between the intracellular domains of the TLRs and the mammalian interleukin-1 and interleukin-18 cytokine receptors reflects the use of a common intracellular signal-transduction cascade triggered by these receptor classes. But more recent findings have demonstrated that there are in fact TLR-specific signaling pathways and cellular responses. Thus, TLRs function as sentinels of the mammalian immune system that can discriminate between diverse pathogen-associated molecular patterns and then elicit pathogen-specific cellular immune responses.     

H4R activation utilizes distinct signaling pathways for the production of RANTES and IL-13 in human mast cells

Context: The histamine H4 receptor functionally expressed on human mast cells and their signaling pathways for the production of IL-13 and RANTES have never been analyzed side by side in a directly comparable manner.

Objective: Therefore, the aim of the study was to investigate signaling transduction pathways of H4R via ERK1/2, Akt and NFκB leading to the induction of inflammatory cytokine expression.

Materials and methods: In the present study, HMC-1 cells and CBMCs were pretreated individually with H4R antagonist JNJ7777120, H1R antagonist mepyramine and signaling molecule inhibitors PD 98059, LY294002, Bay 117082 followed by stimulation was done with or without histamine or 4-MH. Furthermore, the siRNA mediated H4R gene silencing effects are studied at the H4R protein expression level and also signal transduction level.

Results: We found that the pretreatment with JNJ7777120 and H4R gene silencing decreased histamine, 4-MH induced phosphorylation of ERK1/2, Akt and NFκB-p65. Moreover, PD 98059, LY294002 and Bay 117082, which respectively inhibited the histamine and 4-methylhistamine induced phosphorylation of ERK1/2, Akt and NFκB-p65 respectively. We also found that the activation of H4R caused the release of IL-13 and RANTES on human mast cells. The MEK inhibitor PD98059 blocked H4R mediated RANTES/CCL5 production by 20.33?pg/ml and inhibited IL-13 generation by 95.71?pg/ml. In contrast, PI3 kinase inhibitor LY294002 had no effect on 4-MH induced RANTES/CCL5 production but blocked IL-13 generation by 117.58?pg/ml.

Discussion and conclusion: These data demonstrate that the H4R activates divergent signaling pathways to induce cytokine and chemokine production in human mast cells.     

Polymorphisms in the TOLLIP Gene Influence Susceptibility to Cutaneous Leishmaniasis Caused by Leishmania guyanensis in the Amazonas State of Brazil

IntroductionThe clinical outcome to Leishmania-infection is determined by the individual adaptive immune T helper cell responses and their interactions with parasitized host cells. An early development of a proinflammatory immune response (Th1 response) is necessary for Leishmania-infection resolution. The Toll-interacting protein (TOLLIP) regulates human Toll-like receptors signaling pathways by down regulating the proinflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) and inducing the ant-inflammatory cytokine interleukin-10 (IL-10). Polymorphisms in the TOLLIP gene are associated with infectious diseases.ResultsThe G and T alleles of the rs5743899 and rs3750920 were more common in patients with CL than in healthy individuals (P = 2.6 x10^-8 ; odds ratio [OR], 1.7 [ 95% confidence interval (CI) 1.4–2.0] and P = 1.9 x10^-8 ; OR, 1.6 [95% CI 1.4–1.9] respectively). The r² and D’ linkage disequilibrium between the two polymorphisms are 0.05 and 0.473 with a confidence bounds of 0.37 to 0.57 respectively.ConclusionThe two polymorphisms are independently associated with an increased risk of developing CL.