Les cavéoles sont des invaginations en forme de coupelle à la membrane plasmique. Ces organelles multifonctionnelles jouent entre autres, un rôle clé dans la mécano-protection et la signalisation cellulaire. En effet, les cavéoles ont la faculté de s’aplanir en réponse à l’augmentation de la tension membranaire, afin de protéger la cellule des contraintes mécaniques. Les cavéoles jouant un rôle clé dans la signalisation cellulaire, nous avions émis l’hypothèse que le cycle mécano-dépendent de désassemblage/réassemblage des cavéoles constitue un interrupteur mécanique de certaines voies de signalisation. Ce projet consiste à élucider le mécanisme moléculaire responsable du contrôle de la voie de signalisation JAK-STAT par la mécanique des cavéoles. Dans ces travaux, nous avons pu démontré que la cavéoline-1 (Cav1), un constitutant essentiel des cavéoles est libérée et devient hautement mobile au niveau de la membrane plasmique. Considérant les propriétés de signalisation de Cav1, Nous avons testé l’effet du désassemblage des cavéoles sur la signalisation cellulaire. Un criblage à haut débit, nous a permis identifié la voie de signalisation JAK- STAT stimulée par l’IFN-α comme voie modèle pour cette étude. En effet, la transduction du signal JAK-STAT induit par l’IFN-α est modulée par la mécanique des cavéoles. Afin de disséquer le mécanisme moléculaire responsable du contrôle de la signalisation JAK-STAT par la mécanique des cavéoles, nous avons déterminé le rôle de Cav1 dans ce contrôle. Nous avons observé que Cav1 est un régulateur négatif de la phosphorylation de STAT3 dépendante de la kinase JAK1. De plus, nous avons démontré que Cav1 interagit avec JAK1 en fonction de la tension membranaire. Nous avons également démontré que cette interaction Cav1-JAK1 fait intervenir le « scaffolding domain » de Cav1 (CSD), et que celui-ci est responsable de l’abolition de l’activité kinase de JAK1. Par conséquent, l’interaction de Cav1 avec JAK1 empêche l’activation de STAT3 par la kinase JAK1. Ces résultats démontrent que les cavéoles sont des organelles de mécano-signalisation, qui, lors d’un stress mécanique, libèrent de la Cav1 non cavéolaire capable d’inactiver la kinase JAK1, empêchant ainsi, la transduction du signal JAK-STAT. / Caveolae are small cup-shaped plasma membrane invaginations. These multifunctional organelles play a key role in cell mechanoprotection and cell signaling. Indeed our laboratory reported that caveolae have the ability to flatten out upon membrane tension increase, protecting cells from mechanical strains. Since caveolae play a key role in cell signaling we hypothesized that the mechano-dependent cycle of caveolae disassembly/reassembly may constitute a mechanical switch for signaling pathways. In this project, we elucidated the molecular mechanism underlying the control of JAK-STAT signaling by caveolae mechanics. We showed that caveolin-1 (Cav1), an essential caveolar component is released and become highly mobile at the plasma membrane under mechanical stress. Considering that caveolae are important signaling hubs at the plasma membrane, we addressed the effects of the mechanical release of Cav1 on cell signaling. Using high throughput screening, we identified the JAK-STAT signaling pathway as a candidate. To further dissect the molecular mechanism underlying the control of JAK-STAT signaling by caveolae mechanics, we addressed the role of Cav1 in the control of JAK-STAT signaling stimulated by IFN-α. We found that Cav1 was a specific negative regulator of the JAK1 dependent STAT3 phosphorylation. Furthermore, the level of Cav1 interaction with JAK1 depended on mechanical stress. We could show that Cav1-JAK1 interaction was mediated by the caveolin scaffolding domain (CSD), abolishing JAK1 kinase activity, hence, interfering with STAT3 activation upon IFN-α stimulation. Altogether our results show that caveolae are mechanosignaling organelles that disassemble under mechanical stress, releasing non-caveolar Cav1, which binds to the JAK1 kinase and inhibits its catalytic activity, preventing thereby JAK-STAT signal transduction.

No description available.

Submitted by Augusto Santana Nascimento (nascimento@aluno.ibb.unesp.br) on 2017-01-19T12:49:36Z No. of bitstreams: 1 Dissertacao Augusto.docx: 2881032 bytes, checksum: c87b3b303b6f8075ca2bde19b2863849 (MD5) / Rejected by LUIZA DE MENEZES ROMANETTO (luizamenezes@reitoria.unesp.br), reason: Solicitamos que realize uma nova submissão seguindo as orientações abaixo: A versão final da dissertação/tese deve ser submetida no formato PDF (Portable Document Format). O arquivo PDF não deve estar protegido e a dissertação/tese deve estar em um único arquivo, inclusive os apêndices e anexos, se houver. Por favor, corrija o formato do arquivo e realize uma nova submissão. Agradecemos a compreensão. on 2017-01-20T11:53:55Z (GMT) / Submitted by Augusto Santana Nascimento (nascimento@aluno.ibb.unesp.br) on 2017-01-23T17:19:59Z No. of bitstreams: 1 Dissertacao Augusto.pdf: 2309354 bytes, checksum: a8372ec1b075dc9d75fd293868f6988a (MD5) / Approved for entry into archive by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br) on 2017-01-25T11:40:26Z (GMT) No. of bitstreams: 1 nascimento_as_me_bot.pdf: 2309354 bytes, checksum: a8372ec1b075dc9d75fd293868f6988a (MD5) / Made available in DSpace on 2017-01-25T11:40:26Z (GMT). No. of bitstreams: 1 nascimento_as_me_bot.pdf: 2309354 bytes, checksum: a8372ec1b075dc9d75fd293868f6988a (MD5) Previous issue date: 2016-11-18 / Embora algum progresso tenha sido alcançado nos últimos anos, ainda são necessários estudos capazes de desvendar os mecanismos moleculares envolvidos com o fenótipo de resistência a múltiplas drogas (MDR) em células tumorais. Com esta finalidade, estabelecemos o perfil quinômico (através do microarranjo de peptídeos, PepChip) das linhagens MCF7 e MCF7Res, fenótipo parental e resistente respectivamente, de células de câncer de mama. Os resultados obtidos pelo microarranjo de peptídeos e posteriormente, validados por western blotting, apontaram o envolvimento da via de sinalização Jak-Stat e isoformas de PKC no processo de resistência das células de câncer de mama. Além disso, mostramos envolvimento de p42/44-mapk, Ras e um aumento na expressão de MMP-9. Estes resultados mostram o potencial agressivo destas células resistentes, visto que estas vias estão envolvidas em mecanismos responsáveis pela proliferação e invasão celular. Como as proteínas Jak1 e Jak2 mostraram-se envolvidas, decidimos avaliar níveis de fosforilação de Stats 1, 2, 3, 5 e 6 e mostramos que todas estavam up-fosforiladas nas células resistentes. Baseado nestes resultados, decidimos avaliar através de um ensaio funcional, o papel de Jak2 no fenótipo resistente e, desta forma, avaliamos a viabilidade das células MCF7Res em pré-tratamento com 2 concentrações subtóxicas do inibidor de Jak2 (5µM e 10µM) e nossos resultados claramente mostraram que, inibindo Jak2, as células MCF7Res ficam mais sensíveis a daunorrubicina, aumentando a taxa de morte celular frente à resposta ao quimioterápico. Baseado nos resultados obtidos pelo fosfoproteoma concluímos que o fenótipo MDR envolve metabolismo específico em células tumorais de mama, onde isoformas de PKCs e sinalização Jak-Stat exercem função de destaque. Assim, estes dados apontam o potencial uso de inibidores de Jak2 como estratégia para o tratamento de pacientes não responsivos a terapias convencionais.

Made available in DSpace on 2014-06-12T15:07:01Z (GMT). No. of bitstreams: 2 arquivo3001_1.pdf: 1265385 bytes, checksum: 195917f7eadaa711ca792e1630574a84 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2011 / Faculdade de Amparo à Ciência e Tecnologia do Estado de Pernambuco / Um dos determinantes envolvidos no complexo ciclo de transmissão da dengue é o nível de susceptibilidade do Aedes aegypti ao vírus dengue (DENV), ou seja, a competência vetorial, que varia entre populações de mosquitos. Identificar moléculas envolvidas na interação mosquito-vírus pode auxiliar no conhecimento dos mecanismos envolvidos na competência vetorial, até então pouco elucidados. Estudos recentes mostraram a participação de certos mecanismos na interação mosquito-DENV, porém, pouco se sabe do real papel destes na modulação da competência vetorial em mosquitos de campo ou até da relação entre eles. Mediante isso, objetivamos analisar a expressão de três moléculas representantes de diferentes mecanismos de defesa antiviral no Ae. aegypti, em resposta à infecção com vírus dengue sorotipo 2 (DENV-2), sendo elas REL1, HOP e Dicer-2, em populações de campo e de laboratório do mosquito. Para isso, as diferentes linhagens foram artificialmente infectadas com DENV-2, e tecidos variados foram coletados em diversos momentos após infecção. Tanto a quantificação viral quanto a expressão das moléculas selecionadas nas amostras foram realizadas por PCR em tempo real quantitativo (qRT-PCR). Os resultados mostraram que tanto o padrão de infecção viral quanto a expressão das moléculas variaram entre as populações de A. aegypti nos diferentes momentos após infecção com DENV-2. Os resultados aqui obtidos poderão ser bastante relevantes na pesquisa da interação vetor-vírus e poderão auxiliar no desenvolvimento de novas estratégias de controle da dengue, como na pesquisa com mosquitos transgênicos

Asthma is a significant lung disease involving chronic inflammation and remodeling of the airways, resulting in reduced quality of life for those who suffer from the condition. Current therapeutic guidelines suggest the use of inhaled corticosteroids for long-term anti-inflammatory relief to manage moderate to severe chronic asthma; however, inhaled corticosteroids fail to provide prophylactic or reversal treatment of damaged airways incurred by chronic asthma as well as exhibiting adverse side effects (skeletal complications, diabetes, and weight gain).Therefore, there is a need for a new type of drug therapy to address these gaps in the treatment of chronic asthma. There is growing interest aimed towards the inhibition of the Janus Kinase and Signal Transducer and Activator of Transcription (JAK-STAT) pathway for the treatment of asthma. Despite the promising opportunity to investigate this new pathway towards this clinical application, no published work is available using an established and characterized JAK 1/3 inhibitor for the treatment of chronic asthma delivered via inhalation. This work investigated tofacitinib citrate, a selective JAK 3 inhibitor, and its potential to be delivered locally to the lungs for the treatment of chronic asthma. Several preformulation studies were conducted to determine the basic physical and chemical properties of the compound and its free base, tofacitinib, for proper inhalational formulation development. The drug was delivered to BALB/c mice challenged with house dust mite (HDM) allergen via nebulization utilizing a nose-only chamber. After a three week dosing schedule, mice treated with tofacitinib citrate exhibited an increase in monocyte cell numbers with a simultaneous decrease in eosinophil cell count, gathered from BAL fluid. Further, the experimental groups treated with tofacitinib citrate had a decrease in total protein concentrations in comparison to the experimental groups that were only challenged with HDM or were both exposed to HDM and vehicle. These findings demonstrated that the proper formulation was developed for nebulized delivery of tofacitinib citrate, and that the compound was capable of reducing total protein concentrations and eosinophil cell recruitment, both recognized as biomarkers for an asthmatic response. Although significant work is still needed to be done, these data hold promise for the potential of a locally delivered JAK 3 inhibitor as a treatment for chronic asthma. Further, the solubility of tofacitinib citrate and five other pharmaceutical salts were determined in HFA 134a, HFA 227, and DFP with varying cosolvent content (0-20% v/v ethanol). The experimental solubilities of the free acid and base compounds were larger than the solubilities of their respective salts in all three systems for tofacitinib, albuterol, and salicylic acid. Warfarin, phenytoin, and ciprofloxacin had similar solubilities with their respective salt forms. Solubilities also increased with increasing cosolvent concentration for all compounds investigated. The model propellant, DFP, provided a slightly stronger correlation of solubility values with HFA 134a in comparison to HFA 227. The observed solubility values were also compared to calculated values obtained from the ideal solubility model, where it was determined that the observed solubility was indeed also dependent on its surrounding solvent interactions and not solely on its ideal solubility (melting point). While some physical changes were observed for the pharmaceutical salts in HFA 134a and 227, more quantitative studies are needed for a larger database of compounds to better understand the factors that contribute to the solubility of pharmaceutical salts (and their correlation to DFP), in HFA-based systems. This information could potentially contribute to a predictive model, saving time and money during the process of pMDI formulation development.

Epilepsy, a disease characterized by recurring spontaneous seizures, affects over 65 million people, 2% of the world’s population. Over 30% of patients are refractory to all current medical therapy, and for those that can be treated, many suffer from severe drug side-effects. Understanding the molecular basis of epilepsy is vital to the advancement of better therapeutic options and an eventual cure. Upregulation of brain-derived neurotrophic factor (BDNF) is highly associated with epileptogenesis in human patients, as well as animal models. Our laboratory discovered that BDNF induces the Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) pathway in neurons and that inhibition attenuates spontaneous seizures in a temporal lobe epilepsy model. The mechanism behind JAK/STAT signaling in neurons and its relationship to epilepsy still remains to be elucidated and is the subject of my thesis. Surprisingly, even though BDNF is such a major signaling molecule, its full genomic impact has never been assessed. We conducted a high-density RNA-sequencing analysis of the BDNF transcriptome in cortical neurons and probed such regulation with selective JAK inhibitors. Results suggest that 68% of BDNF-induced changes in gene expression implicated in epilepsy are regulated by JAK/STAT signaling. Eighty percent of BDNF-induced changes coding for proteins involved in synaptic neurotransmission (receptor subunits and ion channels) involve JAK/STATs. Additionally, these datasets include genes that have never been associated with BDNF regulation (such as Dopamine Receptor D5 and Galanin Receptor 1). Most interestingly, the datasets reveal that BDNF-induced JAK/STAT signaling in neurons is non-canonical, as STAT3 phosphorylation at tyrosine 705 is not required for action. To directly examine STAT3’s role in epileptogenesis, we studied the transcriptome of transgenic mice that express lower levels of STAT3 specifically in neurons. Using the intrahippocampal kainic-acid (KA) model of epilepsy, our datasets suggest that STAT3 knockdown in vivo, and selectively in neurons, protects mice from KA-induced dysregulation of the sphingolipid metabolism pathway that is associated with the trafficking, sorting, and stability of membrane-bound proteins, including neurotransmitter receptors and ion channels. Finally, we discuss a model for JAK/STAT signaling in neurons that includes structural aspects of an intracellular BDNF receptor (p75NTR) associated with JAK2. / 2021-06-14T00:00:00Z

Yes / The realisation that unregulated activation of the Janus kinase–signal transducer and activator of transcription (JAK–STAT) pathway is a key driver of a wide range of diseases has identified its components as targets for therapeutic intervention by small molecule inhibitors and biologicals. In this review, we discuss JAK-STAT signalling pathway inhibition by the inducible inhibitor “suppressor of cytokine signaling 3 (SOCS3), its role in diseases such as myeloproliferative disorders, and its function as part of a multi-subunit E3 ubiquitin ligase complex. In addition, we highlight potential applications of these insights into SOCS3-based therapeutic strategies for management of conditions such as vascular re-stenosis associated with acute vascular injury, where there is strong evidence that multiple processes involved in disease progression could be attenuated by localized potentiation of SOCS3 expression levels. / British Heart Foundation; Chief Scientist's Office; NHS Greater Glasgow and Clyde Research Endowment Fund; BBSRC

Hypothèse : Notre équipe étudie le rôle, mal connu, du trafic membranaire dans le contrôle de l’activation de la voie de signalisation JAK/STAT par les interférons (IFN), une voie clé du contrôle des processus cancéreux. La liaison de l’IFN-a à son récepteur IFNAR active les kinases JAK1 et TYK2 puis des transducteurs de signal comme STAT1, antiprolifératif, ou STAT3, qui a un pouvoir oncogénique. Le laboratoire a démontré récemment que le trafic membranaire d’IFNAR détermine la spécificité du signal des différents IFNs.L’objet de cette thèse est l’étude du rôle des cavéoles dans ce contrôle. Les cavéoles sont des invaginations membranaires enrichies en cholestérol et glycosphingolipides, formées par l’oligomérisation de la cavéoline1 (Cav1). Les cavéoles ou le gène CAV1 ont souvent été associés à la progression tumorale, notamment des cellules mammaires, mais ce rôle reste énigmatique et controversé. Le fait que IFNAR ait été détecté par biochimie dans des fractions de membrane enrichies en cholestérol et positives pour la cavéoline-1 chez la souris et le fait que l’expression du gène CAV1 ait été corrélée à l’action antitumorale de l’IFNa nous ont conduit à étudier le rôle des cavéoles dans l’action antitumorale des IFNs.Résultats: Le rôle putatif des cavéoles sur le contrôle de la voie JAK/STAT a été étudié dans des cellules murines MLEC n’exprimant pas Cav1 et dans des lignées humaines par interférence ARN contre Cav1. Nous avons pu démontrer que la présence de Cav1 régule de manière opposée deux étapes de la voie de signalisation de STAT3 activée par l’IFN-a. Par contre, ni l’activation de STAT1 par l’IFN-a ni celle de STAT3 par les autres IFNs ne nécessitent Cav1. Parallèlement, le laboratoire a montré que les cavéoles jouent un rôle capital dans la réponse cellulaire aux stress mécaniques en se dépliant lors d’un étirement membranaire, ce qui amortit la tension membranaire. Nous montrons qu’un tel stress mécanique par étirement module spécifiquement la signalisation de STAT3 par l’IFN-a d’une manière dépendante de Cav1 dans les cellules MLEC, suggérant pour la première fois un rôle de STAT3 et de l’IFN-a dans la mécanotransduction dépendante des cavéoles. Ce résultat permet aussi de relier les contraintes mécaniques présentes dans la masse tumorale et leur effet sur la progression tumorale. Perspectives : Les IFNs et la voie JAK/STAT sont bien caractérisés pour leur action antiproliférative, mais si l’IFN-a est utilisé en thérapeutique oncologique, les mécanismes de l’effet antitumoral sont mal connus. Nos résultats impliquent pour la première fois les cavéoles dans l’activation sélective du proto-oncogène STAT3 par l’IFN-a et proposent STAT3 comme un des nouveaux acteurs de la mécanotransduction par les cavéoles. Elucider les mécanismes moléculaires mis en jeu dans ces deux fonctions inédites des cavéoles devrait permettre d’identifier de nouvelles cibles thérapeutiques dans la progression tumorale. / Hypothesis: Our team studies the poorly investigated role of membrane trafficking in the control of the activation of the JAK / STAT signaling pathway by interferons (IFN), a key mechanism in the control of tumorigenesis. The binding of the IFN-a to its receptor IFNAR activates the kinases JAK1 and TYK2 and then, signal transducers and activators of transcription including the antiproliferative STAT1 or the oncogenic STAT3. The laboratory demonstrated recently that the trafficking of IFNAR at the plasma membrane determines the signal specificity of the various IFNs.The goal of this thesis was to study the role of caveolae in this control. Caveolae are specialized membrane invaginations enriched in cholesterol and glycosphingolipids, formed by the oligomerization of their main structural protein, caveolin-1 (Cav1). Caveolae or the CAV1 gene have often been associated with tumorigenesis, in particular in mammary cancer cells, but this role remains enigmatic and controversial. The fact that IFNAR was previously found in Cav1-positive lipid microdomains and the fact that the expression of the CAV1 gene had been functionally linked to the antitumoral function of IFN-a led us to investigate the role of caveolae in the antitumoral function of the IFNs.Results: The putative role of caveolae in the control of the JAK / STAT signaling pathway have been studied in murine lung endothelial MLEC cells that do not express Cav1 and in a human lineage by RNA interference against Cav1. We were able to demonstrate that the presence of Cav1 regulates in an opposite manner two stages of the signaling pathway of STAT3 activated by the IFN-a whereas the activation of STAT1 by IFN-a, or STAT3 by the other type I and II IFNs do not require Cav1.At the same time, the laboratory showed that caveolae play a major role in the cellular answer to mechanical stress by flattening during a membrane stretching, thus buffering the membrane tension. We show that mechanical stress by uniaxial cell stretching modulates specifically the signaling pathway of STAT3 activated by the IFN-a in a Cav1-dependant manner in MLEC cells. This result suggests for the first time a role of STAT3 and of IFN-a in caveolae-driven mechanotransduction. This result also allows us to link the mechanical constraints found in the tumoral mass to their effect on tumorigenesis.Prospects:The IFNs and the JAK / STAT signaling pathway protect the cells from tumorigenesis, but although IFN-a is used in oncology, the mechanisms of its antitumoral effect are poorly known. Our results involve for the first time caveolae in the selective activation of the proto-oncogenic STAT3 by the IFN-a and allow us to propose STAT3 and the IFN-a as new actors of the mechanotransduction by caveolae. Clarifying the molecular mechanisms involved in these two new functions of caveolae should allow us to identify new therapeutic targets in tumorigenesis.

Les néoplasmes myéloprolifératifs (NMP) sont hémopathies malignes aboutissant à la surproduction d'une ou plusieurs lignées myéloïdes. Elles sont dues à l'acquisition de mutations sur l'axe de signalisation MPL/JAK2 incluant des mutations de JAK2V617F, de MPL et plus récemment de la calréticuline (CALR), dont les deux principales sont CALRdel52 et CALRins5. Ces mutations de signalisations peuvent être accompagnées de mutations de l'épigénétique, les plus importantes étant des mutations dans TET2. Le but de cette thèse était d'étudier le rôle des mutations de TET2 et de la calrdel52 dans les NMP grâce à une technologie de cellules souches induites à la pluripotence (IPSC). Dans la première partie j'ai pu démontrer que TET2 joue un rôle dans le processus de reprogrammation, vraisemblablement de manière indépendante de son activité catalytique. Dans la seconde partie, j'ai démontré que CALRdel52 joue un rôle dans les MPN en provoquant une hypersensibilité et une pousse indépendante de la TPO des progéniteurs mégakaryocytaires ainsi qu'une hyperprolifération des mégacaryocytes, liées à l'activation constitutive de stat3 et de ERK. J'ai également démontré une pousse indépendante du GCSF des granulocytes. Ce travail a donc permis de mettre en lumière le rôle du facteur épigénétique TET2 dans le processus de reprogrammation ainsi que le rôle de CALRdel52 dans les MPN dans un contexte d'expression endogène. / Myeloproliferative neoplasms (NMP) are hematological malignancies that lead to an ovrproduction of one or more myeloid lineages. They are driving by mutations in MPLl/jak2 signaling pathway, mainly JAK2V617F, MPL, and more recently calreticulin (CARL), with two main mutations being calrdel52 and calrins5. These signaling mutations are sometimes associated with epigenetic mutations, the major one being in tet2. The objective of my thesis was to study the role of TET2 and CALRdel52 in MPN thanks to an induced pluripotent stem cells (IPSC) model. In the first part i demonstrated the role of TET2 in reprogramming process, probably independently of the catalytic domain. In the second part i demonstrated that CALRdel52 induced a TPO hypersensitivity and a TPO indenpendant growth of the megakaryocytic progenitors as well as a hyperproliferation of the megakaryocytes. This phenotype is associated with a constitutive activation of stat3 and ERK. A G-CSF independent growth of the granulocyte was also demonstrated. In conclusion this work underline the role of an epegenetic factor, TET2, in the reprogramming process and demonstrate the role of CALRdel52in MPN with an endogenous expression model.

Ligand-activated signal transduction is a process critical to cell survival and function as it serves as a means of communication between the cells and their environment. Endocytosis is generally thought to down-regulate incoming signals by reducing the surface availability of receptors. However, increasing evidence in many systems suggests a notion which is referred to as the „signalling endosome" hypothesis - that endocytosis can also actively contribute to signalling apart from clearance of activated receptors and thereby attenuation of signalling. The functional aspect of signalling endosomes has been well-characterized in several pathways including RTK and TGF-β signalling. There are, however, various other signalling pathways where the active mechanism of endocytotic regulation is yet to be understood. In this study, we probe this aspect in the cytokine signalling system, where the receptors are known to internalize but the significance of such internalization and precise mechanism is unclear. My thesis aims to elucidate the function and molecular details of internalization of cytokine receptor using interleukin-4 receptor (IL-4R) signalling as a model. IL-4 and IL-13 ligands can induce assembly of three distinct complexes: IL4 induced IL-4Rα – IL-2Rγ (type I), IL-4 induced IL-4Rα – IL-13Rα1 (type II) or the IL-13 induced IL-13Rα1-IL-4Rα (type II). The formation of any of these complexes triggers signalling through the JAK/STAT pathway. However, models of how the oligomerization of the transmembrane receptors and activation takes place are very diverse and lack a clear molecular and biophysical understanding of the underlying receptor dynamics. Previous results of the lab had shown that the affinities between subunits are low, precluding complex formation at the plasma membrane at physiological concentrations. In addition, IL-4R subunits localize in to endosomal structures adjacent to the plasma membrane. It had already been shown that the shared IL-4R subunit IL-2Rγ is internalized by a specific, actin dependent, Rac1/Pak1 regulated endocytosis route in the IL-2 context. We could show that pharmacological suppression of this endocytosis pathway also prevented IL-4 induced JAK/STAT signalling, placing endocytosis upstream of signalling. Here I show using immuno-EM techniques that these endosomal structures are multivesicular bodies. Importantly, I could show that receptor subunits are highly enriched in the limiting membrane of these endosomes relative to the adjacent plasma membrane. Using quantitative loading assays I could furthermore demonstrate that this enrichment is achieved by constitutive internalization of receptors from the cell surface into cortical endosomes. The trafficking kinetics of the receptor subunits is independent of ligand occupancy. Pharmacological inhibition shows that receptors and ligand traffic via the previously identified Rac1/Pak1 pathway. Finally, Vav2 was identified as a candidate Guanine Exchange Factor (GEF) that may regulate Rac1 activity and thereby control the actin polymerization cascade driving IL-4R endocytosis. Immunoprecipitations showed that Vav2 interacts both with the cytoplasmic tail region of the receptors and the receptor associated 2 kinase JAK3. Vav2 may thus couple the receptor/JAK complexes to the Rac1/Pak1 mediated endocytosis route. Taken together, our results suggests that stable „signalling endosomes‟ adjacent to the plasma membrane act as enrichment centres, where ligand and receptor concentrations are locally increased by constitutive trafficking. The confined environment of the endosome then compensates for the weak affinities between the ligand and receptor and facilitates ligand-mediated receptor dimerization. Importantly, overexpression of both type II IL-4R subunits renders signal transduction resistant to endocytosis inhibition, strongly suggesting that the critical factor effecting signalling is sufficient concentration, which the endosomes facilitate achieving. The endosomes are thus dispensable as signalling scaffolds when the receptors are in sufficient concentration, where activated receptors could interact with downstream pathway components. Endocytosis thus provides a crucial means for the signalling process to overcome the thermodynamic hurdles for receptor oligomerization. In conclusion, our data propose a novel, purely thermodynamic role of endosomes in regulating cytokine receptor signalling not seen in any other signalling pathway.