Endocytic regulation of cytokine receptor signaling

TRAF2 Knockdown in Nasopharyngeal Carcinoma Induced Cell Cycle Arrest and Enhanced the Sensitivity to Radiotherapy

TRAF2 is a crucial adaptor protein involved in various signaling pathways. However, its biological functions in nasopharyngeal carcinoma (NPC) remain largely unknown. In the present study, we found that TRAF2 was overexpressed in nasopharyngeal carcinoma (NPC) cells. Knockdown of TRAF2 with shRNA significantly suppressed NPC cell proliferation and colony formation. The growth of xenograft tumor significantly reduced after TRAF2 was silenced. Conversely, the ectopic overexpression of TRAF2 significantly promoted cell proliferation and anchorage-independent growth. In TRAF2 knockdown cells, EGF-induced activation of transcriptional factors, including MSK1, CREB, and ATF2, markedly decreased. Accordingly, the transcriptional activity of AP-1 was substantially decreased in TRAF2-deficient cells. With the suppression of gene transcription, the expression of cyclin D1 was significantly impaired, which gave rise to the G0/G1 cell cycle arrest. Moreover, the overexpression of TRAF2 in NPC cells was associated with resistance to irradiation, and the potency of irradiation was substantially enhanced after TRAF2 was knocked down. Briefly, our studies demonstrated that TRAF2 had a crucial role in NPC development, and it might be of great potential to targeting TRAF2 for NPC prevention and treatment.

Brainstem inflammation modulates the ventilatory pattern and its variability after acute lung injury in rodents

KEY POINTS

Compared with sham rats, rats a week after acute lung injury (ALI) express more pro-inflammatory cytokines in their brainstem respiratory control nuclei, exhibit a higher respiratory frequency (fR) and breathe with a more predictable pattern. These characteristics of the respiratory pattern persist in in situ preparations even after minimizing pulmonary and chemo-afferent inputs. Interleukin (IL)-1β microinjected in the nucleus tractus solitarii increases fR and the predictability of the ventilatory pattern similar to rats with ALI. Intracerebroventricular infusion of indomethacin, an anti-inflammatory drug, mitigates the effect of ALI on fR and ventilatory pattern variability. We conclude that changes in the ventilatory pattern after ALI result not only from sensory input due to pulmonary damage and dysfunction but also from neuro-inflammation.

ABSTRACT

Acute lung injury (ALI) increases respiratory rate (fR) and ventilatory pattern variability (VPV), but also evokes peripheral and central inflammation. We hypothesized that central inflammation has a role in determining the ventilatory pattern after ALI. In rat pups, we intratracheally injected either bleomycin to induce ALI or saline as a sham control. One week later, we recorded the ventilatory pattern of the rat pups using flow-through plethysmography, then formed in situ preparations from these pups and recorded their 'fictive' patterns from respiratory motor nerves. Compared with the ventilatory pattern of the sham rat pups, injured rat pups had increased fR and predictability. Surprisingly, the fictive patterns of the in situ preparations from ALI pups retained these characteristics despite removing their lungs to eliminate pulmonary sensory inputs and perfusing them with hyperoxic artificial cerebral spinal fluid to minimize peripheral chemoreceptor input. Histological processing revealed increased immunoreactivity of the pro-inflammatory cytokine Interleukin-1β (IL-1β) in the nucleus tractus solitarii (nTS) from ALI but not sham rats. In subsequent experiments, we microinjected IL-1β in the nTS bilaterally in anaesthetized naïve adult rats, which increased fR and predictability of ventilatory pattern variability (VPV) after 2 h. Finally, we infused indomethacin intracerebroventricularly during the week of survival after ALI. This did not affect sham rats, but mitigated changes in fR and VPV in ALI rats. We conclude that neuro-inflammation has an essential role in determining the ventilatory pattern of ALI rats.

Lysosomotropic drugs enhance pro-inflammatory responses to IL-1β in macrophages by inhibiting internalization of the IL-1 receptor

Interleukin (IL)-1 signaling leads to production of pro-inflammatory mediators and is regulated by receptor endocytosis. Lysosomotropic drugs have been linked to increased pro-inflammatory responses under sterile inflammatory conditions but the underlying mechanisms have not been fully elucidated. Here, we report that lysosomotropic drugs potentiate pro-inflammatory effects in response to IL-1β via a mechanism involving reactive oxygen species, p38 mitogen-activated protein kinase and reduced IL-1 receptor internalization. Chloroquine and hydroxychloroquine increased IL-1β-induced CXCL8 secretion in macrophages which was critically dependent on the lysosomotropic character and inhibition of macroautophagy but independent from the NLRP3 inflammasome. Co-stimulation with the autophagy inducer interferon gamma attenuated CXCL8 release. Other lysosomotropic drugs like bafilomycin A₁, fluoxetine and chlorpromazine but also the endocytosis inhibitor dynasore showed similar pro-inflammatory responses. Increased cell surface expression of IL-1 receptor suggests reduced receptor degradation in the presence of lysosomotropic drugs. Our findings provide new insights into a potentially crucial immunoregulatory mechanism in macrophages that may explain how lysosomotropic drugs drive sterile inflammation.

The anti-inflammatory potential of cefazolin as common gamma chain cytokine inhibitor

A continuing quest for specific inhibitors of proinflammatory cytokines brings promise for effective therapies designed for inflammatory and autoimmune disorders. Cefazolin, a safe, first-generation cephalosporin antibiotic, has been recently shown to specifically interact with interleukin 15 (IL-15) receptor subunit α (IL-15Rα) and to inhibit IL-15-dependent TNF-α and IL-17 synthesis. The aim of this study was to elucidate cefazolin activity against IL-2, IL-4, IL-15 and IL-21, i.e. four cytokines sharing the common cytokine receptor γ chain (γ_c). In silico, molecular docking unveiled two potential cefazolin binding sites within the IL-2/IL-15Rβ subunit and two within the γ_c subunit. In vitro, cefazolin decreased proliferation of PBMC (peripheral blood mononuclear cells) following IL-2, IL-4 and IL-15 stimulation, reduced production of IFN-γ, IL-17 and TNF-α in IL-2- and IL-15-treated PBMC and in IL-15 stimulated natural killer (NK) cells, attenuated IL-4-dependent expression of CD11c in monocyte-derived dendritic cells and suppressed phosphorylation of JAK3 in response to IL-2 and IL-15 in PBMC, to IL-4 in TF-1 (erythroleukemic cell line) and to IL-21 in NK-92 (NK cell line). The results of the study suggest that cefazolin may exert inhibitory activity against all of the γ_c receptor-dependent cytokines, i.e. IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21.

IL23 induces IL23R recycling and amplifies innate receptor-induced signalling and cytokines in human macrophages, and the IBD-protective IL23R R381Q variant modulates these outcomes

OBJECTIVE

The interleukin (IL)23 pathway contributes to IBD pathogenesis and is being actively studied as a therapeutic target in patients with IBD. Unexpected outcomes in these therapeutic trials have highlighted the importance of understanding the cell types and mechanisms through which IL23 regulates immune outcomes. How IL23 regulates macrophage outcomes and the consequences of the IL23R R381Q IBD-protective variant on macrophages are not well defined; macrophages are key players in IBD pathogenesis and inflammation.

DESIGN

We analysed protein and RNA expression, signalling and localisation in human monocyte-derived macrophages (MDMs) through western blot, ELISA, real-time PCR, flow cytometry, immunoprecipitation and microscopy.

RESULTS

IL23R was critical for optimal levels of pattern-recognition receptor (PRR)-induced signalling and cytokines in human MDMs. In contrast to the coreceptor IL12Rβ1, IL23 induced dynamic IL23R cell surface regulation and this required clathrin and dynamin-mediated endocytosis and endocytic recycling-dependent pathways; these pathways were essential for IL23R-mediated outcomes. The IBD-protective IL23R R381Q variant showed distinct outcomes. Relative to IL23R R381, HeLa cells expressing IL23R Q381 showed decreased IL23R recycling and reduced assembly of IL23R Q381 with Janus kinase/signal transducer and activator of transcription pathway members. In MDMs from IL23R Q381 carriers, IL23R accumulated in late endosomes and lysosomes on IL23 treatment and cells demonstrated decreased IL23R- and PRR-induced signalling and cytokines relative to IL23R R381 MDMs.

CONCLUSION

Macrophage-mediated inflammatory pathways are key contributors to IBD pathogenesis, and we identify an autocrine/paracrine IL23 requirement in PRR-initiated human macrophage outcomes and in human intestinal myeloid cells, establish that IL23R undergoes ligand-induced recycling, define mechanisms regulating IL23R-induced signalling and determine how the IBD-protective IL23R R381Q variant modulates these processes.

Siglecs as Immune Cell Checkpoints in Disease

Sialic acid-binding immunoglobulin-type lectins (Siglecs) are expressed on the majority of white blood cells of the immune system and play critical roles in immune cell signaling. Through recognition of sialic acid-containing glycans as ligands, they help the immune system distinguish between self and nonself. Because of their restricted cell type expression and roles as checkpoints in immune cell responses in human diseases such as cancer, asthma, allergy, neurodegeneration, and autoimmune diseases they have gained attention as targets for therapeutic interventions. In this review we describe the Siglec family, its roles in regulation of immune cell signaling, current efforts to define its roles in disease processes, and approaches to target Siglecs for treatment of human disease.

TYK2 in Tumor Immunosurveillance

We review the history of the tyrosine kinase 2 (TYK2) as the founding member of the Janus kinase (JAK) family and outline its structure-function relation. Gene-targeted mice and hereditary defects of TYK2 in men have established the biological and pathological functions of TYK2 in innate and adaptive immune responses to infection and cancer and in (auto-)inflammation. We describe the architecture of the main cytokine receptor families associated with TYK2, which activate signal transducers and activators of transcription (STATs). We summarize the cytokine receptor activities with well characterized dependency on TYK2, the types of cells that respond to cytokines and TYK2 signaling-induced cytokine production. TYK2 may drive beneficial or detrimental activities, which we explain based on the concepts of tumor immunoediting and the cancer-immunity cycle in the tumor microenvironment. Finally, we summarize current knowledge of TYK2 functions in mouse models of tumor surveillance. The biology and biochemistry of JAKs, TYK2-dependent cytokines and cytokine signaling in tumor surveillance are well covered in recent reviews and the oncogenic properties of TYK2 are reviewed in the recent Special Issue ‘Targeting STAT3 and STAT5 in Cancer’ of Cancers.

Inflammatory bowel disease-associated ubiquitin ligase RNF183 promotes lysosomal degradation of DR5 and TRAIL-induced caspase activation

RNF183 is a ubiquitin ligase containing RING-finger and transmembrane domains, and its expression levels are increased in patients with inflammatory bowel disease (IBD), including Crohn’s disease and ulcerative colitis, and in 2,4,6-trinitrobenzene sulfonic acid-induced colitis mice. Here, we further demonstrate that RNF183 was induced to a greater degree in the dextran sulfate sodium (DSS)-treated IBD model at a very early stage than were inflammatory cytokines. In addition, fluorescence-activated cell sorting and polymerase chain reaction analysis revealed that RNF183 was specifically expressed in epithelial cells of DSS-treated mice, which suggested that increased levels of RNF183 do not result from the accumulation of immune cells. Furthermore, we identified death receptor 5 (DR5), a member of tumour necrosis factor (TNF)-receptor superfamily, as a substrate of RNF183. RNF183 mediated K63-linked ubiquitination and lysosomal degradation of DR5. DR5 promotes TNF-related apoptosis inducing ligand (TRAIL)-induced apoptosis signal through interaction with caspase-8. Inhibition of RNF183 expression was found to suppress TRAIL-induced activation of caspase-8 and caspase-3. Thus, RNF183 promoted not only DR5 transport to lysosomes but also TRAIL-induced caspase activation and apoptosis. Together, our results provide new insights into potential roles of RNF183 in DR5-mediated caspase activation in IBD pathogenesis.

Rab4b Deficiency in T Cells Promotes Adipose Treg/Th17 Imbalance, Adipose Tissue Dysfunction, and Insulin Resistance

Obesity modifies T cell populations in adipose tissue, thereby contributing to adipose tissue inflammation and insulin resistance. Here, we show that Rab4b, a small GTPase governing endocytic trafficking, is pivotal in T cells for the development of these pathological events. Rab4b expression is decreased in adipose T cells from mice and patients with obesity. The specific depletion of Rab4b in T cells causes adipocyte hypertrophy and insulin resistance in chow-fed mice and worsens insulin resistance in obese mice. This phenotype is driven by an increase in adipose Th17 and a decrease in adipose Treg due to a cell-autonomous skew of differentiation toward Th17. The Th17/Treg imbalance initiates adipose tissue inflammation and reduces adipogenesis, leading to lipid deposition in liver and muscles. Therefore, we propose that the obesity-induced loss of Rab4b in adipose T cells may contribute to maladaptive white adipose tissue remodeling and insulin resistance by altering adipose T cell fate.

Kinetics of cytokine receptor trafficking determine signaling and functional selectivity

Cytokines activate signaling via assembly of cell surface receptors, but it is unclear whether modulation of cytokine-receptor binding parameters can modify biological outcomes. We have engineered IL-6 variants with different affinities to gp130 to investigate how cytokine receptor binding dwell-times influence functional selectivity. Engineered IL-6 variants showed a range of signaling amplitudes and induced biased signaling, with changes in receptor binding dwell-times affecting more profoundly STAT1 than STAT3 phosphorylation. We show that this differential signaling arises from defective translocation of ligand-gp130 complexes to the endosomal compartment and competitive STAT1/STAT3 binding to phospho-tyrosines in gp130, and results in unique patterns of STAT3 binding to chromatin. This leads to a graded gene expression response and differences in ex vivo differentiation of Th17, Th1 and Treg cells. These results provide a molecular understanding of signaling biased by cytokine receptors, and demonstrate that manipulation of signaling thresholds is a useful strategy to decouple cytokine functional pleiotropy.

Amyloid-beta impairs TOM1-mediated IL-1R1 signaling

Defects in interleukin-1β (IL-1β)-mediated cellular responses contribute to Alzheimer's disease (AD). To decipher the mechanism associated with its pathogenesis, we investigated the molecular events associated with the termination of IL-1β inflammatory responses by focusing on the role played by the target of Myb1 (TOM1), a negative regulator of the interleukin-1β receptor-1 (IL-1R1). We first show that TOM1 steady-state levels are reduced in human AD hippocampi and in the brain of an AD mouse model versus respective controls. Experimentally reducing TOM1 affected microglia activity, substantially increased amyloid-beta levels, and impaired cognition, whereas enhancing its levels was therapeutic. These data show that reparation of the TOM1-signaling pathway represents a therapeutic target for brain inflammatory disorders such as AD. A better understanding of the age-related changes in the immune system will allow us to craft therapies to limit detrimental aspects of inflammation, with the broader purpose of sharply reducing the number of people afflicted by AD.

Pharmacological correction of morphofunctional retinal injury using 11-amino acid fragment of darbepoetin in the experiment

Introduction: The retinoprotective effect of the 11-amino acid fragment of darbepoetin PRK-002 on the models of hypertensive retinal angiopathy and hypertensive neuroretinopathy in Wistar rats was investigated in comparison with carbamylated darbepoetin and sulodexide.

Materials and methods: The protective effects of the pharmacological agents were assessed using the following criteria: a semi-quantitative assessment of changes in the eye fundus when performing ophthalmoscopy, the retinal blood flow, the b/a coefficient, eNOs expression in retinal vessels, specific number of neuronal nuclei in the inner nuclear layer, and p53 expression in the retina.

Results and discussion: A pronounced protective effect, exceeding sulodexide at a dose of 150 LRU/kg and carbamylated darbepoetin at a dose of 300 μg/kg when correcting retinal angiopathy was observed in PRK-002 at a dose of 4 µg/kg, which expressed in adjustment of the retinal vessels’ calibers, removing retinal arterio-venous crossings, reaching the target levels of the retinal microcirculation, the b/a coefficient, and the restoration of eNOs expression in the endothelium of retinal vessels. PRK-002 at a dose of 4 µg/kg has a pronounced neuroprotective effect comparable to carbamylated darbepoetin at a dose of 300 µg/kg in correction of hypertensive neuroretinopathy, which expressed in the normalization of the fundus image, reaching the b/a target values, the specific number of neuronal nuclei in the inner nuclear layer, inhibition of p53 expression in the neurons of the inner nuclear and ganglionic layers.

Conclusion: The study revealed angio- and neuroprotective activity of the 11-amino acid fragment of darbepoetin PRK-002 in correction of retinal injury formed on the background of hypertension.

Mechanism of internalization of MDA-7/IL-24 protein and its cognate receptors following ligand-receptor docking

Melanoma differentiation associated gene-7 (mda-7/IL-24) is a member of the IL-10 family of cytokines, with ubiquitous direct and "bystander" tumor-selective killing properties. MDA-7/IL-24 protein binds distinct type II cytokine heterodimeric receptor complexes, IL-20R1/IL-20R2, IL-22R1/IL-20R1 and IL-22R1/IL-20R2. Recombinant MDA-7/IL-24 protein induces endogenous mda-7/IL-24 expression in a receptor-dependent manner; since A549 cells that lack a complete set of cognate receptors are not responsive to exogenous protein. The mechanism of MDA-7/IL-24 ligand-receptor biology is not well understood. We explored the interaction of MDA-7/IL-24 with its' receptors and the consequences of ligand-receptor docking. Using both pharmacological and genetic approaches we demonstrate that MDA-7/IL-24 internalization employs the clathrin-mediated endocytic pathway leading to degradation of receptors via the lysosomal/ubiquitin proteosomal pathway. This clathrin-mediated endocytosis is dynamin-dependent. This study resolves a novel mechanism of MDA-7/IL-24 protein "bystander" function, which involves receptor/protein-mediated internalization and receptor degradation.

High-resolution crystal structure of arthropod Eiger TNF suggests a mode of receptor engagement and altered surface charge within endosomes

The tumour necrosis factor alpha (TNFα) superfamily of proteins are critical in numerous biological processes, such as in development and immunity. Eiger is the sole TNFα member described in arthropods such as in the important model organism Drosophila. To date there are no structural data on any Eiger protein. Here we present the structure of the TNF domain of Eiger from the fall armyworm Spodoptera frugiperda (SfEiger) to 1.7 Å from a serendipitously obtained crystal without prior knowledge of the protein sequence. Our structure confirms that canonical trimerization is conserved from ancestral TNFs and points towards a mode of receptor engagement. Furthermore, we observe numerous surface histidines on SfEiger, potentially acting as pH switches following internalization into endosomes. Our data contributes to the genome annotation of S. frugiperda, a voracious agricultural pest, and can serve as a basis for future structure-function investigations of the TNF system in related arthropods such as Drosophila.

Palmitoylation is required for TNF-R1 signaling

BACKGROUND

Binding of tumor necrosis factor (TNF) to TNF-receptor 1 (TNF-R1) can induce either cell survival or cell death. The selection between these diametrically opposed effects depends on the subcellular location of TNF-R1: plasma membrane retention leads to survival, while endocytosis leads to cell death. How the respective TNF-R1 associated signaling complexes are recruited to the distinct subcellular location is not known. Here, we identify palmitoylation of TNF-R1 as a molecular mechanism to achieve signal diversification.

METHODS

Human monocytic U937 cells were analyzed. Palmitoylated proteins were enriched by acyl resin assisted capture (AcylRAC) and analyzed by western blot and mass spectrometry. Palmitoylation of TNF-R1 was validated by metabolic labeling. TNF induced depalmitoylation and involvement of APT2 was analyzed by enzyme activity assays, pharmacological inhibition and shRNA mediated knock-down. TNF-R1 palmitoylation site analysis was done by mutated TNF-R1 expression in TNF-R1 knock-out cells. Apoptosis (nuclear DNA fragmentation, caspase 3 assays), NF-κB activation and TNF-R1 internalization were used as biological readouts.

RESULTS

We identify dynamic S-palmitoylation as a new mechanism that controls selective TNF signaling. TNF-R1 itself is constitutively palmitoylated and depalmitoylated upon ligand binding. We identified the palmitoyl thioesterase APT2 to be involved in TNF-R1 depalmitoylation and TNF induced NF-κB activation. Mutation of the putative palmitoylation site C248 interferes with TNF-R1 localization to the plasma membrane and thus, proper signal transduction.

CONCLUSIONS

Our results introduce palmitoylation as a new layer of dynamic regulation of TNF-R1 induced signal transduction at a very early step of the TNF induced signaling cascade. Understanding the underlying mechanism may allow novel therapeutic options for disease treatment in future.

Alterations in IL-4, IL-10 and IFN-γ levels synergistically decrease lipid content and protein expression of FAS and mature SREBP-1 in human sebocytes

When anti-acne alternatives from dietary and plant sources are ingested, systemic alterations of interleukin (IL)-4, IL-10, IL-12 and interferon (IFN)-γ, individually or simultaneously, are induced at a 0.1-10.0-fold (×) range of normal physiological concentrations (1×). However, little is known about the effects of these cytokines on excess sebum, a pathophysiological factor of acne development. In this study, human sebocytes were treated with 0.1-10.0× of IL-4, IL-10, IL-12 and IFN-γ for 3 or 5 days to elucidate the effects on lipid content. Treatment with individual cytokines decreased the lipid content at specific concentrations rather than in a concentration-dependent manner. Specifically, 5.0× of IL-4, 5.0× of IFN-γ (5.0IFN), and 0.5×, 5.0× and 10.0× of IL-10 for 3 days, and 0.5× of IL-4 (0.5IL4) for 5 days decreased lipid content to 87.6-93.0% of the control. Treatment with other concentrations of IL-4, IL-10 and IFN-γ, and 0.1-10.0× of IL-12 did not alter lipid content. Combined treatment with 0.5IL4, 5.0IFN and 0.5× of IL-10 for 3 or 5 days decreased the lipid content more than each individual treatment. However, this effect was more evident after 3 days, in parallel with decreased levels of triglycerides, cholesterol esters and free fatty acids, the major lipid compositions of sebocytes, and decreased protein expression of fatty acid synthase (FAS) and mature sterol response element-binding protein-1 (SREBP-1), the lipogenesis-related factors, without altered cell proliferation. We demonstrated that suppressed IL-4 and IL-10 with enhanced IFN-γ synergistically decreased lipid content and protein expression of FAS and mature SREBP-1 in human sebocytes.

The cellular effects of Pulsed Electromagnetic Fields on osteoblasts: A review

Electromagnetic fields (EMFs) have long been known to interact with living organisms and their cells and to bear the potential for therapeutic use. Among the most extensively investigated applications, the use of Pulsed EMFs (PEMFs) has proven effective to ameliorate bone healing in several studies, although the evidence is still inconclusive. This is due in part to our still-poor understanding of the mechanisms by which PEMFs act on cells and affect their functions and to an ongoing lack of consensus on the most effective parameters for specific clinical applications. The present review has compared in vitro studies on PEMFs on different osteoblast models, which elucidate potential mechanisms of action for PEMFs, up to the most recent insights into the role of primary cilia, and highlight the critical issues underlying at least some of the inconsistent results in the available literature. Bioelectromagnetics. 2019;9999:XX-XX. © 2019 Bioelectromagnetics Society.

A toolbox for the immunomagnetic purification of signaling organelles

Homeostasis and the complex functions of organisms and cells rely on the sophisticated spatial and temporal regulation of signaling in different intra- and extracellular compartments and via different mediators. We here present a set of fast and easy to use protocols for the target-specific immunomagnetic enrichment of receptor containing endosomes (receptosomes), plasma membranes, lysosomes and exosomes. Isolation of subcellular organelles and exosomes is prerequisite for and will advance their detailed subsequent biochemical and functional analysis. Sequential application of the different subprotocols allows isolation of morphological and functional intact organelles from one pool of cells. The enrichment is based on a selective labelling using receptor ligands or antibodies together with superparamagnetic microbeads followed by separation in a patented matrix-free high-gradient magnetic purification device. This unique magnetic chamber is based on a focusing system outside of the empty separation column, generating an up to 3 T high-gradient magnetic field focused at the wall of the column.

Immune Complex Vaccination

Antibody/antigen binding results in immune complexes (IC) that have a variety of regulatory functions. One important feature is the enhanced host immune activation against antigen contained in the complex. ICs play important roles at several critical steps that lead to B and T cell activation, including antigen targeting/retention, facilitated antigen uptake, antigen presenting cell activation and proper balancing of positive and negative stimulatory signals. In both poultry industry and clinical health care, ICs have been used as preventive and therapeutic vaccines. With our deepening understanding of antibody biology, particularly in light of new revelations of regulatory functions of Fc receptors, mechanistically more precise engineering has spearheaded tailored use of this tool for infection control and cancer therapy. IC-based treatment and prophylaxis have been tested to different extents in HBV, HIV and influenza viral infection control and are actively examined as an alternative treatment for several forms of tumor. As a part of this book series, this chapter aims to discuss the mechanistic aspects of IC signaling and their impact on immune cells. We give samples how this old technology has been used by practitioners over the last several decades and suggest potential paths for future development of IC-based immune therapy.

[Traffic and signalisation of the leptin receptor]

Receptors are the master regulators conveying the information provided by the hormone from the extracellular environment to the intracellular milieu. As a result, the level of receptors at the cell surface can determine the signaling strength. Regulation of receptor trafficking to the cell surface or receptor retention processes in intracellular compartments are key mechanisms for leptin receptor (ObR) activity. An alteration of these mechanisms leads to the development of obesity. However, the canonical mechanism of plasma membrane receptors activation is challenged by the discovery that intracellular receptors also have their own signaling activity inside specific intracellular compartments. These intracellular receptors can trigger signaling that regulates a particular function, different from, or in continuity with, surface receptor signaling. We will address both these aspects by focusing particularly on the case of the leptin receptor (ObR), i.e., i) the regulation of its level of exposure to the cell surface and its impact on the development of obesity, and ii) the discovery of its location and signaling in some intracellular compartments.

PAR-1 is a novel mechano-sensor transducing laminar flow-mediated endothelial signaling

Recent studies have indicated that protease-activated receptor-1 (PAR-1) is involved in cytoprotective and anti-inflammatory responses in endothelial cells (ECs). However, the role of PAR-1 in laminar flow-mediated atheroprotective responses remains unknown. Herein, we investigated whether PAR-1 regulates laminar flow-mediated mechanotransduction in ECs. Confocal analysis showed that PAR-1 was internalized into early endosomes in response to laminar flow. In addition, flow cytometry analysis showed that cell surface expression of PAR-1 was reduced by laminar flow, suggesting that PAR-1 was activated in response to laminar flow. Depletion of PAR-1 using human PAR-1 siRNA inhibited unidirectional laminar flow-mediated actin stress fiber formation and cellular alignment as well as atheroprotective gene expressions in HUVECs. Moreover, PAR-1 knockdown inhibited laminar flow-stimulated eNOS phosphorylation, and inhibited the phosphorylations of Src, AMPK, ERK5 and HDAC5. Furthermore, PAR-1 depletion inhibited laminar flow-mediated anti-inflammatory responses as demonstrated by reduced TNFα-induced VCAM-1 expression and by monocyte adhesion to HUVECs, and prevented laminar flow-mediated anti-apoptotic response. An investigation of the role of PAR-1 in vasomotor modulation using mouse aortic rings revealed that acetylcholine-induced vasorelaxation was diminished in PAR-1 deficient mice compared to littermate controls. Taken together, these findings suggest that PAR-1 be viewed as a novel pharmacologic target for the treatment of vascular diseases, including atherosclerosis.

Network-based approach to prediction and population-based validation of in silico drug repurposing

Here we identify hundreds of new drug-disease associations for over 900 FDA-approved drugs by quantifying the network proximity of disease genes and drug targets in the human (protein–protein) interactome. We select four network-predicted associations to test their causal relationship using large healthcare databases with over 220 million patients and state-of-the-art pharmacoepidemiologic analyses. Using propensity score matching, two of four network-based predictions are validated in patient-level data: carbamazepine is associated with an increased risk of coronary artery disease (CAD) [hazard ratio (HR) 1.56, 95% confidence interval (CI) 1.12–2.18], and hydroxychloroquine is associated with a decreased risk of CAD (HR 0.76, 95% CI 0.59–0.97). In vitro experiments show that hydroxychloroquine attenuates pro-inflammatory cytokine-mediated activation in human aortic endothelial cells, supporting mechanistically its potential beneficial effect in CAD. In summary, we demonstrate that a unique integration of protein-protein interaction network proximity and large-scale patient-level longitudinal data complemented by mechanistic in vitro studies can facilitate drug repurposing.

Repurposing approved drugs could accelerate treatment options for various diseases. Here, the authors use network proximity of disease gene products and drug targets in the human protein interactome to identify drug-disease associations for cardiovascular disease, and validate these using longitudinal healthcare data.

A genome-wide RNAi screen identifies MASK as a positive regulator of cytokine receptor stability

Cytokine receptors often act via the Janus kinase and signal transducer and activator of transcription (JAK/STAT) pathway to form a signalling cascade that is essential for processes such as haematopoiesis, immune responses and tissue homeostasis. In order to transduce ligand activation, cytokine receptors must dimerise. However, mechanisms regulating their dimerisation are poorly understood. In order to better understand the processes regulating cytokine receptor levels, and their activity and dimerisation, we analysed the highly conserved JAK/STAT pathway in Drosophila, which acts via a single receptor, known as Domeless. We performed a genome-wide RNAi screen in Drosophila cells, identifying MASK as a positive regulator of Domeless dimerisation and protein levels. We show that MASK is able to regulate receptor levels and JAK/STAT signalling both in vitro and in vivo We also show that its human homologue, ANKHD1, is also able to regulate JAK/STAT signalling and the levels of a subset of pathway receptors in human cells. Taken together, our results identify MASK as a novel regulator of cytokine receptor levels, and suggest functional conservation, which may have implications for human health.This article has an associated First Person interview with the first author of the paper.

Alternative Erythropoietin Receptors in the Nervous System

In addition to its regulatory function in the formation of red blood cells (erythropoiesis) in vertebrates, Erythropoietin (Epo) contributes to beneficial functions in a variety of non-hematopoietic tissues including the nervous system. Epo protects cells from apoptosis, reduces inflammatory responses and supports re-establishment of compromised functions by stimulating proliferation, migration and differentiation to compensate for lost or injured cells. Similar neuroprotective and regenerative functions of Epo have been described in the nervous systems of both vertebrates and invertebrates, indicating that tissue-protective Epo-like signaling has evolved prior to its erythropoietic function in the vertebrate lineage. Epo mediates its erythropoietic function through a homodimeric Epo receptor (EpoR) that is also widely expressed in the nervous system. However, identification of neuroprotective but non-erythropoietic Epo splice variants and Epo derivatives indicated the existence of other types of Epo receptors. In this review, we summarize evidence for potential Epo receptors that might mediate Epo's tissue-protective function in non-hematopoietic tissue, with focus on the nervous system. In particular, besides EpoR, we discuss three other potential neuroprotective Epo receptors: (1) a heteroreceptor consisting of EpoR and common beta receptor (βcR), (2) the Ephrin (Eph) B4 receptor and (3) the human orphan cytokine receptor-like factor 3 (CRLF3).

Direct and indirect pro-inflammatory cytokine response resulting from TC-83 infection of glial cells

Venezuelan equine encephalitis virus (VEEV) is a neurotropic arbovirus that is highly infectious as an aerosol and can result in an encephalitic phenotype in infected individuals. VEEV infections are known to be associated with robust inflammation that eventually contributes to neurodegenerative phenotypes. In this study, we utilize the TC-83 strain of VEEV, which is known to induce the expression of IL-6, IL-8, and other pro-inflammatory cytokines. We had previously demonstrated that TC-83 infection resulted in changes in mitochondrial function, eventually resulting in mitophagy. In this manuscript, we provide data that links upstream mitochondrial dysfunction with downstream pro-inflammatory cytokine production in the context of microglia and astrocytoma cells. We also provide data on the role of bystander cells, which significantly contribute to the overall inflammatory load. Use of a mitochondrial-targeted antioxidant, mitoquinone mesylate, greatly reduced the inflammatory cytokine load and ameliorated bystander cell inflammatory responses more significantly than a broad-spectrum anti-inflammatory compound (BAY 11-7082). Our data suggest that the inflammatory mediators, especially IL-1β, may prime naïve cells to infection and lead to increased infection rates in microglial and astrocytoma cells. Cumulatively, our data suggest that the interplay between mitochondrial dysfunction and inflammatory events elicited in a neuronal microenvironment during a TC-83 infection may contribute to the spread of infection.

Integration of the Endocytic System into the Network of Cellular Functions

Maintenance of physiologic cellular functions and homeostasis requires highly coordinated interactions between different cellular compartments. In this regard, the endocytic system, which plays a key role in cargo internalization and trafficking within the cell, participates in upkeep of intracellular dynamics, while communicating with multiple organelles. This chapter will discuss the function of endosomes from a standpoint of cellular integration. We will present examples of different types of interactions between endosomes and other cellular compartments, such as the endoplasmic reticulum (ER), mitochondria, the plasma membrane (PM), and the nuclear envelope. In addition, we will describe the incorporation of endocytic components, such as endosomal sorting complexes required for transport (ESCRT) proteins and Rab small GTPases, into cellular processes that operate outside of the endolysosomal pathway. The significance of endosomal interactions for processes such as signaling regulation, intracellular trafficking, organelle dynamics, metabolic control, and homeostatic responses will be reviewed. Accumulating data indicate that beyond its involvement in cargo transport, the endocytic pathway is comprehensively integrated into other systems of the cell and plays multiple roles in the complex net of cellular functions.

Dysfunction of autophagy and endosomal-lysosomal pathways: Roles in pathogenesis of Down syndrome and Alzheimer's Disease

Individuals with Down syndrome (DS) have an increased risk of early-onset Alzheimer's Disease (AD), largely owing to a triplication of the APP gene, located on chromosome 21. In DS and AD, defects in endocytosis and lysosomal function appear at the earliest stages of disease development and progress to widespread failure of intraneuronal waste clearance, neuritic dystrophy and neuronal cell death. The same genetic factors that cause or increase AD risk are also direct causes of endosomal-lysosomal dysfunction, underscoring the essential partnership between this dysfunction and APP metabolites in AD pathogenesis. The appearance of APP-dependent endosome anomalies in DS beginning in infancy and evolving into the full range of AD-related endosomal-lysosomal deficits provides a unique opportunity to characterize the earliest pathobiology of AD preceding the classical neuropathological hallmarks. Facilitating this characterization is the authentic recapitulation of this endosomal pathobiology in peripheral cells from people with DS and in trisomy mouse models. Here, we review current research on endocytic-lysosomal dysfunction in DS and AD, the emerging importance of APP/βCTF in initiating this dysfunction, and the potential roles of additional trisomy 21 genes in accelerating endosomal-lysosomal impairment in DS. Collectively, these studies underscore the growing value of investigating DS to probe the biological origins of AD as well as to understand and ameliorate the developmental disability of DS.

The topology of lymphotoxin β receptor accumulated upon endolysosomal dysfunction dictates the NF-κB signaling outcome

Cytokine receptors, such as tumor necrosis factor receptor I (TNFRI) and lymphotoxin β receptor (LTβR), activate inflammatory NF-κB signaling upon stimulation. We previously demonstrated that depletion of ESCRT components leads to endosomal accumulation of TNFRI and LTβR, and their ligand-independent signaling to NF-κB. Here, we studied if other perturbations of the endolysosomal system could trigger intracellular accumulation and signaling of ligand-free LTβR. While depletion of CORVET had no effect, knockdown of HOPS or Rab7, or pharmacological inhibition of lysosomal degradation, caused endosomal accumulation of LTβR and its increased interactions with TRAF2/TRAF3 signaling adaptors. However, the NF-κB pathway was not activated under these conditions. We found that knockdown of HOPS or Rab7 led to LTβR sequestration in intraluminal vesicles of endosomes, thus precluding NF-κB signaling. This was in contrast to LTβR localization on the outer endosomal membrane after ESCRT depletion that was permissive for signaling. We propose that the inflammatory response induced by intracellular accumulation of endocytosed cytokine receptors critically depends on the precise receptor topology within endosomal compartments.

Endosomal Redox Signaling in the Antiphospholipid Syndrome

PURPOSE OF REVIEW

It is well established that the antiphospholipid syndrome (APS) is caused by antiphospholipid antibodies (aPL). While several underlying mechanisms have been described in the past, many open questions remain. Here, we will review data on endosomal signaling and, in particular, redox signaling in APS.

RECENT FINDINGS

Endosomal redox signaling has been implicated in several cellular processes including signaling of proinflammatory cytokines. We have shown that certain aPL can activate endosomal NADPH-oxidase (NOX) in several cell types followed by induction of proinflammatory and procoagulant cellular responses in vitro. Involvement of endosomes in aPL signaling has also been reported by others. In wild-type mice but not in NOX-deficient mice, aPL accelerate venous thrombus formation underscoring the relevance of endosomal NOX. Furthermore, hydroxychloroquine (HCQ) inhibits activation of endosomal NOX and prevents thrombus formation in aPL-treated mice. Endosomal redox signaling is an important novel mechanism involved in APS pathogenesis. This makes endosomes a potential target for future treatment approaches of APS.

The ERM Protein Moesin Regulates CD8+ Regulatory T Cell Homeostasis and Self-Tolerance

The ezrin-radixin-moesin (ERM) proteins are a family of membrane-associated proteins that link membrane proteins with actin filaments in the cell cortex and regulate many cellular processes, including cell shape determination, membrane transport, and signal transduction. Lymphocytes predominantly express two ERM members, ezrin and moesin. Mutations in the moesin gene in humans are associated with primary immunodeficiency with profound lymphopenia, and moesin-deficient mice exhibit a similar lymphopenia phenotype. In this study, we show that aging moesin-deficient mice develop a systemic lupus erythematosus-like autoimmune phenotype, which is characterized by elevated serum autoantibody levels and glomerulonephritis. Younger moesin-deficient mice exhibited elevated basal levels of several Ig isotypes and enhanced Ab affinity maturation upon immunization. Germinal center B cells and follicular helper T cells spontaneously accumulated in unimmunized mice, and CD8⁺CD44⁺CD122⁺Ly49⁺ regulatory T (CD8⁺ Tregs) cells, which inhibit the expansion of follicular helper T cells, were severely reduced in these mice. Isolated CD8⁺ Treg cells from moesin-deficient mice showed impaired proliferation in response to IL-15, which was accompanied by defects in STAT5 activation and IL-15Rα internalization, suggesting that moesin plays a key role in IL-15-mediated signaling. These findings underscore the importance of moesin in IL-15-dependent CD8⁺ Treg cell homeostasis and, thus, the control of self-tolerance.

Endosomal "sort" of signaling control: The role of ESCRT machinery in regulation of receptor-mediated signaling pathways

The endosomal sorting complexes required for transport (ESCRTs) machinery consists of four protein assemblies (ESCRT-0 to -III subcomplexes) which mediate various processes of membrane remodeling in the cell. In the endocytic pathway, ESCRTs sort cargo destined for degradation into intraluminal vesicles (ILVs) of endosomes. Cargos targeted by ESCRTs include various signaling molecules, mainly internalized cell-surface receptors but also some cytosolic proteins. It is therefore expected that aberrant trafficking caused by ESCRT dysfunction affects different signaling pathways. Here we review how perturbation of ESCRT activity alters intracellular transport of membrane receptors, causing their accumulation on endocytic compartments, decreased degradation and/or altered recycling to the plasma membrane. We further describe how perturbed trafficking of receptors impacts the activity of their downstream signaling pathways, with or without changes in transcriptional responses. Finally, we present evidence that ESCRT components can also control activity and intracellular distribution of cytosolic signaling proteins (kinases, other effectors and soluble receptors). The underlying mechanisms involve sequestration of such proteins in ILVs, their sorting for degradation or towards non-lysosomal destinations, and regulating their availability in various cellular compartments. All these ESCRT-mediated processes can modulate final outputs of multiple signaling pathways.

Role of ubiquitination and proteolysis in the regulation of pro- and anti-apoptotic TNF-R1 signaling

Tumor Necrosis Factor Receptor 1 (TNF-R1) transmits various intracellular signaling cascades leading to diverse biological outcomes, ranging from proliferation, differentiation, survival to the induction of various forms of cell death (i.e. apoptosis, necrosis, necroptosis). These signaling pathways have to be tightly regulated. Proteolysis is an important regulatory mechanism in TNF-R1 pro-apoptotic as well as anti-apoptotic/pro-inflammatory signaling. Some key players in these signaling cascades are known (mainly the caspase-family of proteases and a previously unrecognized "lysosomal death pathway" involving cathepsins), however the interaction of proteases in the regulation of TNF signaling is still enigmatic. Ubiquitination of proteins, both non-degradative degradative, which either results in proteolytic degradation of target substrates or regulates their biological function, represents another layer of regulation in this signaling cascade. We and others found out that the differences in signal quality depend on the localization of the receptors. Plasma membrane resident receptors activate survival signals, while endocytosed receptors can induce cell death. In this article we will review the role of ubiquitination and proteolysis in these diverse events focusing on our own contributions to the lysosomal apoptotic pathway linked to the subcellular compartmentalization of TNF-R1. This article is part of a Special Issue entitled: Proteolysis as a Regulatory Event in Pathophysiology edited by Stefan Rose-John.

C. elegans SMA-10 regulates BMP receptor trafficking

Signal transduction of the conserved transforming growth factor-β (TGFβ) family signaling pathway functions through two distinct serine/threonine transmembrane receptors, the type I and type II receptors. Endocytosis orchestrates the assembly of signaling complexes by coordinating the entry of receptors with their downstream signaling mediators. Recently, we showed that the C. elegans type I bone morphogenetic protein (BMP) receptor SMA-6, part of the TGFβ family, is recycled through the retromer complex while the type II receptor, DAF-4 is recycled in a retromer-independent, ARF-6 dependent manner. From genetic screens in C. elegans aimed at identifying new modifiers of BMP signaling, we reported on SMA-10, a conserved LRIG (leucine-rich and immunoglobulin-like domains) transmembrane protein. It is a positive regulator of BMP signaling that binds to the SMA-6 receptor. Here we show that the loss of sma-10 leads to aberrant endocytic trafficking of SMA-6, resulting in its accumulation in distinct intracellular endosomes including the early endosome, multivesicular bodies (MVB), and the late endosome with a reduction in signaling strength. Our studies show that trafficking defects caused by the loss of sma-10 are not universal, but affect only a limited set of receptors. Likewise, in Drosophila, we find that the fly homolog of sma-10, lambik (lbk), reduces signaling strength of the BMP pathway, consistent with its function in C. elegans and suggesting evolutionary conservation of function. Loss of sma-10 results in reduced ubiquitination of the type I receptor SMA-6, suggesting a possible mechanism for its regulation of BMP signaling.

Cytokine Receptor Endocytosis: New Kinase Activity-Dependent and -Independent Roles of PI3K

Type I and II cytokine receptors are cell surface sensors that bind cytokines in the extracellular environment and initiate intracellular signaling to control processes such as hematopoiesis, immune function, and cellular growth and development. One key mechanism that regulates signaling from cytokine receptors is through receptor endocytosis. In this mini-review, we describe recent advances in endocytic regulations of cytokine receptors, focusing on new paradigms by which PI3K controls receptor endocytosis through both kinase activity-dependent and -independent mechanisms. These advances underscore the notion that the p85 regulatory subunit of PI3K has functions beyond regulating PI3K kinase activity, and that PI3K plays both positive and negative roles in receptor signaling. On the one hand, the PI3K/Akt pathway controls various aspects downstream of cytokine receptors. On the other hand, it stimulates receptor endocytosis and downregulation, thus contributing to signaling attenuation.