Diseases such as asthma, psoriasis (disease affecting the skin), inflammatory bowel disease or cancer are associated with a dysregulation of the inflammatory response. In our laboratory, we try to improve the understanding of the role of cytokines (small signaling proteins) in inflammation. More specifically, we focus our researches on two cytokines, IL-9 and IL-22, which are crucial players in the inflammatory process.
Cytokines are molecules produced by cells, such as lymphocytes, in response to a stimulus. These proteins act on various cells types that express their specific receptors. They play a major role in the host’s inflammatory response against infection. Excessive inflammation however may also be the origin of many diseases.
Our lab is particularly interested in diseases affecting the skin, such as psoriasis and the gastro- intestinal system such as colitis. We have special focus on two cytokines, IL-9 and IL-22, which were both discovered by our lab.
We have shown that IL-9 is a double-edged sword depending on the diseases. For instance, this cytokine is involved in the protection against worm infection whereas it plays detrimental role in asthma and in the development of T lymphoma.
In an experimental mouse model of worm infection that is very similar to the human form of trichuris trichiuria, which infect the large intestine, we have shown that in presence of IL-9 mice are completely protected. In contrast, if we blocked IL-9 activity, the worm survives and the intestinal infection persists.
The bad side of IL-9 is that its overexpression can cause bronchial hyperresponsiveness upon exposure to various allergens. Our observations showed that IL-9 promotes asthma through induction of another factor, namely IL-13. Asthma is a common chronic inflammatory disease, of the airways, characterized by reversible airflow obstruction and bronchospasm. Common symptoms include wheezing, coughing, chest tightness, and shortness of breath. The potential aggravating role of IL-9 in asthma was confirmed by genetic analyses performed by others and pointing to both IL-9 and the IL-9 receptor genes as major candidate genes for human asthma. In addition, we found that asthmatic patients produce increased amounts of IL-9. We collaborate with pharmaceutical companies to produce molecules that could block IL-9 activity, in order to improve the quality of life of asthmatic patients.
The role of IL-9 in tumor formation was first demonstrated, with the observation that in vivo overexpression of IL-9 does not modify T cell development or T cell numbers, but causes the spontaneous development of thymic lymphomas at a low frequency. We have evidence that indicate that IL-9 is not a conventional oncogene, but rather favors tumor development in response to exogenous stimuli. Dysregulation of IL-9 signaling is also implicated in tumoral transformation, and this process has been studied in an in vitro tumorigenesis model, leading to the identification of oncogenic mutations of the JAK1 gene. JAK1 is an intracellular protein that plays a critical role in initiating responses to different cytokines. Constitutive activation of the protein is frequently found in cancer and contributes to oncogenesis.
Recently, we investigated the role of IL-22 in Psoriasis lesions. Psoriasis is a chronic skin disorder that affects 2% of the world population and develops by variable course, periodically improving and worsening. This skin disease is believed to have a genetic component and is not contagious. Psoriasis is characterized by dry flakes of skin that result from the unusual rapid proliferation of keratinocytes triggered by immune cells and cytokines. By using experimental psoriasis models, we have shown for the first time that IL-22 is produced in skin lesions. In addition, we have shown that administration of an antibody blocking the IL-22 activity is able to decrease some features of the psoriasis such as scaly lesions and redness, demonstrating the deleterious role of this cytokine in psoriasis.
We have also started translational studies on contact dermatitis, which is an inflammatory skin disorder caused by external substances in contact with the skin. Currently our focus is on allergic contact dermatitis, caused by agents that are presents in perfume and cosmetics such as methylisothiasolinone, a preservative agent presents in shampoo. Our aim is to characterize the immunological process that accompanies the clinical response. We have also developed experimental models to understand the role of different factors in this disease. This study is performed in collaboration with the dermatology department of Saint Luc Hospital.
In contrast to the skin, we have shown that IL-22 plays a beneficial role in inflammatory bowel disease, by protecting the gut mucosa. Crohn’s disease and ulcerative colitis are the most common types of inflammatory bowel disease. They affect, any part of the digestive tract (Crohn’s) or only the colon and rectum (Colitis). Crohn’s disease is caused by chronic inflammation, in which the immune system of the body attacks the gastrointestinal tract. Currently, there is no cure for this disease and treatments are restricted to controlling symptoms.
In the future, we will investigate the role of other factors that are related to IL-22 and are also up-regulated in some of our experimental models of psoriasis or of colitis. These studies will help to improve the understanding of the inflammatory responses observed in these two diseases and treatments that are administrated to patient.
Our team is deciphering the biological activities of cytokines in inflammatory and tumoral processes using various preclinical models. In addition, we are investigating the signal transduction pathways underlying these activities at the molecular level.
Our work focuses on Interleukin-9 (IL-9) and IL-22, two cytokines discovered in our laboratory. IL-9 is produced by a particular T lymphocyte population, called TH9, and plays a role in immune responses against intestinal parasites and asthma. Dysregulation of IL-9 signaling is also implicated in tumoral transformation, and this process has been studied in an in vitro tumorigenesis model, leading to the identification of oncogenic mutations of the JAK1 gene. IL-22, originally identified as a gene induced by IL-9 in T lymphocytes, upregulates the production of acute phase reagents and antibacterial proteins in the liver, the lung and intestinal mucosae, and in the skin. IL-22 appears to play a key role in wound healing and skin inflammation processes such as psoriasis. The role of these cytokines in inflammation is being investigated using transgenic and gene-targeted mice for these cytokines and their receptors, and by using an original strategy of anti-cytokine vaccination.
Interleukin-9 (IL-9) was discovered in our group through its ability to sustain antigen-independent growth of certain murine T helper clones. Although IL-9 did not turn out to be a T cell growth factor for freshly isolated T cells, it was found particularly potent on T cell lymphomas as an anti-apoptotic agent. To determine the biological activities of this factor, we generated transgenic mice overexpressing this cytokine. Analysis of these animals disclosed two essential properties of IL-9: its activity on mast cells and eosinophils with consecutive implications in asthma, and its tumorigenic potential in T lymphocytes.
IL-9 tg mice : Parasite infections and asthma
Although IL-9 overproduction does not affect mouse viability and IL-9 transgenic mice did not show any major abnormality at first look, they were found to harbor increased numbers of mast cells in the intestinal and respiratory epithelia, and were characterized by a general hypereosinophilia. This phenotypic characteristic was found to increase the capacity of these animals to expel nematodes such as Trichinella spiralis or Trichuris muris, suggesting that IL-9 administration could protect susceptible hosts against these parasites. Conversely, blocking IL-9 activity resulted in a failure to expel T. muris parasites and a decreased eosinophilic response against the parasite. The other side of the coin was the discovery that IL-9 overexpression, such as that characterizing the IL-9 transgenic animals, resulted in bronchial hyperresponsiveness upon exposure to various allergens. Our observations showed that IL-9 promotes asthma through both IL-13-dependent and IL-13-independent pathways. The potential aggravating role of IL-9 in asthma was confirmed by genetic analyses, performed by others, and pointing to both IL-9 and the IL-9 receptor genes as major candidate genes for human asthma. In addition, we found that asthma patients produce increased amounts of IL-9.
IL-9 tg mice : T cell lymphomas
IL-9 transgenic animals showed normal T cell development and T cell numbers but spontaneously developed thymic lymphomas at low frequency. Two lines of evidence indicate that IL-9 is not a conventional oncogene, but rather favors tumor development in response to exogenous stimuli. Firstly, the tumor incidence was significantly lower when mice were maintained under pathogen-free conditions. Secondly, all IL-9 transgenic mice, when exposed to subliminal doses of a chemical carcinogen or to irradiation, developed T cell lymphomas that were innocuous in wild type mice. The anti-apoptotic activity of IL-9 provides an attractive explanation for these observations, namely that IL-9 could lead to increased survival of abnormal cells generated by exposure to minimal doses of oncogenic stimuli. The potential implication of IL-9 in oncology was also confirmed in human systems by its constitutive expression in Hodgkin lymphomas.
IL-9R and signal transduction
Analysis of the mode of action of IL-9 at the molecular level was initiated by cloning the murine and human IL-9 receptor (IL-9R) cDNAs. By further dissecting the signal transduction cascade triggered by IL-9, we showed that, upon IL-9 binding, the IL-9R associates with a co-receptor protein called γc. This induces the phosphorylation of the JAK1 and JAK3 tyrosine kinases, which are associated with IL-9R and γc, respectively. A single tyrosine residue of the IL-9R is then phosphorylated and acts as a docking site for 3 transcription factors of the STAT family, STAT-1, -3 and -5, which become phosphorylated and migrate to the nucleus, where they activate the transcription of a number of genes. This pathway is common to many cytokines but is often dispensable for their biological activities. For IL-9, our group demonstrated that activation of the STAT transcription factors is crucial for all the effects of IL-9 studied on various cell lines, including positive and negative regulation of cell proliferation, as well as inhibition of corticoid-induced apoptosis in T cell lymphomas. Further analysis demonstrated that STAT-1, -3 and -5 play specific, redundant and synergistic roles in the different activities of IL-9 in vitro. The pathways responsible for IL-9-induced proliferation were studied in detail, and this process was found to depend mainly on the activation of STAT-5, on the recruitment of the IRS-1 adaptor, and on the activation of the Erk MAP-Kinase pathway.
Role of JAK1 overexpression and mutation in tumor cell transformation
Constitutive activation of the JAK-STAT pathway is frequent in cancer and contributes to oncogenesis. Our observations indicate that JAK overexpression plays a role in such processes. Using a murine proB cell line that strictly depends on IL-3 for growth in vitro, cytokine-independent and tumorigenic clones were derived from a two-step selection process. Cells transfected with a defective IL-9 receptor acquired IL-9 responsiveness during a first step of selection, and progressed after a second selection step to autonomously growing tumorigenic cells. Microarray analysis pointed to JAK1 overexpression as a key genetic event in this transformation. Overexpression of JAK1 not only increased the sensitivity to IL-9 but, more importantly, allowed a second selection step that resulted in cytokine-independent growth with constitutive STAT activation. This progression was dependent on a functional FERM and kinase JAK1 domain. Similar results were observed after JAK2, JAK3 and TYK2 overexpression. All autonomous cell lines showed an activation of STAT5, ERK1-2 and AKT. Thus, JAK overexpression can be considered as one of the oncogenic events leading to the constitutive activation of the JAK-STAT pathway. Recently, we elucidated the mechanism responsible for the second step of this tumoral transformation process, as we found that the majority of the cytokine-independent tumorigenic clones acquired an activating mutation in the kinase or in the pseudokinase domain of JAK1.
In parallel to these observations, in collaboration with Professor Marco Tartaglia at the University of Rome, we identified activating mutations in JAK1 in 20% of T-cell acute lymphoblastic leukemia (T-ALL) and in 3% of B-ALL patients, confirming the relevance of our in vitro model-derived JAK1 mutations for human malignancies. Further analysis of human ALL samples showed that JAK1-mutated leukemias share a type I IFN transcriptional signature, suggesting that these mutants not only activate growth-promoting pathways, but also antiviral pathways. Expression of these activating JAK1 mutants in murine hematopoietic cell lines recapitulated this signature in the absence of IFN, but also strongly potentiated the in vitro response to IFN. Finally, we also showed in an in vivo leukemia model that cells expressing mutants such as JAK1(A634D) are hypersensitive to the anti-proliferative and anti-tumorigenic effect of type I IFN, suggesting that type I IFNs should be considered as a potential therapy for ALL with JAK1 activating mutations.
While most JAK1 mutants were sensitive to ATP-competitive JAK inhibitors, mutations targeting Phe958 and Pro960 in the hinge region of the kinase domain rendered JAK1 not only constitutively active, but also resistant to all tested JAK inhibitors. Furthermore, mutation of the homologous Tyr931 in JAK2 wild-type or JAK2 V617F mutant found in myeloproliferative neoplasms also conferred resistance to JAK inhibitors, including the clinically used INCB018424. These observations indicate that in JAK mutation positive patients, treatment with JAK inhibitors is likely to contribute to the selection of these mutations that combine increased oncogenicity and drug resistance.
Searching for genes specifically regulated by IL-9 in lymphomas, we identified a new gene that turned out to encode a 179 amino acid long protein, including a potential signal peptide and showing a weak but significant sequence homology with IL-10. This protein, originally designated IL-TIF for IL-10-related T-cell derived Inducible Factor, was later renamed IL-22. Despite its structural homology with IL-10, IL-22 fails to recapitulate any of IL-10 biological activities. Biological activities of IL- 22 include the induction of acute phase proteins in liver and protection against experimental hepatitis and colitis. Among the different T cell subsets, IL-22 was found to be preferentially produced by TH17 cells, which are associated with several autoimmune and inflammatory processes, and the aryl hydrocarbon receptor AhR turned out to be a major regulator of the expression of this cytokine.
IL-22 and psoriasis
We assessed the role of IL-22 in a mouse model of psoriasis, where skin inflammation is triggered by topical application of the TLR7/8 agonist, imiquimod. At the macroscopic level, scaly skin lesions induced by daily application of imiquimod in wild-type mice were almost completely absent in IL-22–deficient mice and in mice treated with a blocking anti–IL-22 Ab. At the microscopic level, IL-22–deficient mice showed a dramatic decrease in the development of pustules and neutrophil infiltration and a partial decrease in acanthosis. At the molecular level, the absence or inhibition of IL-22 strongly decreased the expression of chemotactic factors such as CCL3 and CXCL3 and of biomarkers such as S100A8, S100A7, and keratin 14, which reflect the antimicrobial and hyperproliferative responses of keratinocytes.
IL-22 and asthma
In contrast with this pro-inflammatory effect of IL-22 in skin inflammation, asthma models show that IL-22 can have a protective anti-inflammatory activity in lungs. This protective effect of IL-22 has been attributed to an inhibition of IL-13 activity on lung epithelial cells either for CCL17/TARC induction or for IL-25 production. Inhibiting IL-22 in vivo, through antibody treatment or by gene targeting, increased expression of these inflammatory mediators, infiltration by eosinophils and broncho-hyperrersponsiveness.
Both the psoriasis and asthma models have challenged the dogma that IL-22 is mainly produced by TH17 lymphocytes, and gamma-delta T cells as well as innate lymphoid cells turned out to be the major producers of this cytokine. We characterized the cells responsible for IL-22 production in response to TLR agonists such as LPS or flagelin. We identified a new innate lymphoid spleen cell population expressing CD25, CCR6 and IL-7R representing 1% of spleen cells from recombination activating gene (Rag2)-deficient mice. This population comprises 60% to 70% CD4+ cells, which produce IL-22, and are still present in common g chain-deficient mice; the CD4- subset coexpresses IL-22 and IL-17, and is common g chain-dependent. These cells share a transcriptional program with NKp46+ RORgt+ cells found in intestinal mucosae and involved in antibacterial responses. The importance of IL-22 production for the LPS-triggered response is highlighted by the fact that IL-22-deficient mice are more resistant to LPS-induced mortality, pointing to the pro-inflammatory activity of this cytokine.
IL-22 receptors and signal transduction
Although IL-22 does not share any biological activity with IL-10, these 2 cytokines share a common component of their respective receptor complex, IL-10Rß. Anti-IL-10Rß antibodies indeed block the IL-22-induced acute phase response in HepG2 cells. All receptor complexes for IL-10-related cytokines include a long chain and a short chain, based on the length of the cytoplasmic domain of these transmembrane proteins. IL-10Rß is a typical short chain component, with only 76 amino acids in the cytoplasmic domain, whose main function seems to consist of recruiting the Tyk2 tyrosine kinase. In addition to IL-10R ß, IL-22 signaling requires the expression of a long chain protein, called IL-22R, which comprises a 319 amino acid long cytoplasmic domain. This chain associates with JAK1 and is responsible for the activation of cytoplasmic signaling cascades such as the JAK/STAT, ERK, JNK and p38 MAP kinase pathways. An unexpected feature of the IL-22R chain is the fact that the C-terminal domain of this receptor is constitutively associated with STAT3, and that STAT3 activation by this receptor does not require the phosphorylation of the receptor, in contrast to the mechanism of STAT activation by most other cytokine receptors.
In addition to the membrane IL-22 receptor complex, we identified a protein of 231 amino acids, that presents 33% amino acid identity with the extracellular domains of IL-22R but is without any cytoplasmic or transmembrane domain. This soluble receptor has been named IL-22 binding protein (IL-22BP), because it binds IL-22 and blocks its activities in vitro, demonstrating that this protein can act as an IL-22 antagonist.
The crystal structure of IL-22, alone and bound to its cellular receptor IL-22R or to its soluble receptor IL-22BP, has been characterized in collaboration with Professor Igor Polikarpov of the University of Sao Paulo and is illustrated below.
We have showed that the IL-22R chain also forms a functional heterodimeric receptor complex by associating with IL-20Rß, the second short chain member of the IL-10R-related receptor family. This complex mediates STAT-1 and –3 activation by IL-20 and IL-24, but not by IL-22. Further more, IL-20 and IL-24 can also bind to other complexes consisting of IL-20Rα and IL-20Rß.
In addition to conventional gene targeting strategies that were used in our lab to generate mice deficient in the IL-9R, in IL-22 or in IL-22R, we developed a new strategy of anti-cytokine vaccination. Vaccinated mice produce anti-cytokine autoantibodies that block the biological activities of endogenous cytokines. Neutralizing auto-antibodies against cytokines such as IL-9, IL-12 and IL-17 have been induced upon vaccination with the autologous cytokines chemically coupled with OVA (IL-9, IL-17) or with the Pan DR T helper epitope PA-DRE (IL-12). This strategy contributed to the demonstration of IL-9’s role in an intestinal helminth infection, IL-12’s role in atherosclerosis and of IL-17’s role in experimental autoimmune encephalomyelitis. More recently, we developed another procedure for anti-cytokine vaccination, by taking advantage of tumor cells expressing peptides, fused with a human transmembrane proteins, as vaccines. These vaccination methods represent simple and convenient approaches to knock down the in vivo activity of soluble regulatory proteins, including cytokines and their receptors, and are validated with additional targets in inflammatory models.
Renauld JC, Druez C, Kermouni A, Houssiau F, Uyttenhove C, Van Roost E, Van Snick J.
Proc Natl Acad Sci U S A. 1992; 89(12):5690-4.
CYTOKINE ACTIVITIES AND SIGNALING