Ligand-independent homomeric and heteromeric complexes between interleukin-2 or -9 receptor subunits and the gamma chain

Evolving cognition of the JAK-STAT signaling pathway: autoimmune disorders and cancer

The Janus kinase (JAK) signal transducer and activator of transcription (JAK-STAT) pathway is an evolutionarily conserved mechanism of transmembrane signal transduction that enables cells to communicate with the exterior environment. Various cytokines, interferons, growth factors, and other specific molecules activate JAK-STAT signaling to drive a series of physiological and pathological processes, including proliferation, metabolism, immune response, inflammation, and malignancy. Dysregulated JAK-STAT signaling and related genetic mutations are strongly associated with immune activation and cancer progression. Insights into the structures and functions of the JAK-STAT pathway have led to the development and approval of diverse drugs for the clinical treatment of diseases. Currently, drugs have been developed to mainly target the JAK-STAT pathway and are commonly divided into three subtypes: cytokine or receptor antibodies, JAK inhibitors, and STAT inhibitors. And novel agents also continue to be developed and tested in preclinical and clinical studies. The effectiveness and safety of each kind of drug also warrant further scientific trials before put into being clinical applications. Here, we review the current understanding of the fundamental composition and function of the JAK-STAT signaling pathway. We also discuss advancements in the understanding of JAK-STAT-related pathogenic mechanisms; targeted JAK-STAT therapies for various diseases, especially immune disorders, and cancers; newly developed JAK inhibitors; and current challenges and directions in the field.

Interleukin (IL)-9 Supports the Tumor-Promoting Environment of Chronic Lymphocytic Leukemia

Simple Summary

Interleukin 9 (IL-9), a soluble factor secreted by immune cells, has been found in several tumor niches where, depending on the specific tumor type, it either promotes or counteracts tumor development. Recently, IL-9 has been implicated in the development of chronic lymphocytic leukemia, although the underlying molecular mechanism remains unknown. Here, we summarize the current knowledge concerning the roles of IL-9 in disease, with a focus on its implication in the pathogenesis of chronic lymphocytic leukemia.

Abstract

Interleukin (IL)-9 is a soluble factor secreted by immune cells into the microenvironment. Originally identified as a mediator of allergic responses, IL-9 has been detected in recent years in several tumor niches. In solid tumors, it mainly promotes anti-tumor immune responses, while in hematologic malignancies, it sustains the growth and survival of neoplastic cells. IL-9 has been recently implicated in the pathogenesis of chronic lymphocytic leukemia; however, the molecular mechanisms underlying its contribution to this complex neoplasia are still unclear. Here, we summarize the current knowledge of IL-9 in the tumor microenvironment, with a focus on its role in the pathogenesis of chronic lymphocytic leukemia.

Pivotal factors associated with the immunosuppressive tumor microenvironment and melanoma metastasis

BACKGROUND

Considering melanoma is the deadliest malignancy among dermatoma and presently lacks effective therapies, there is an urgent need to investigate the potential mechanisms underlying melanoma metastasis and determine prospective therapeutic targets for precise treatment of melanoma.

METHOD

Hub genes in melanoma metastasis were identified by analyzing RNA-seq data (mRNA, miRNA, and lncRNA) obtained from TCGA database. Then the identified hub genes were validated in human tissues with qRT-PCR, followed by survival analysis. Competing endogenous RNAs of the hub genes were defined to clarify potential molecular mechanism of melanoma progression. Then central gene-related signaling pathways were analyzed, followed by immune cell abundance analysis in tumor microenvironment with CYTERSORTx.

RESULT

A tetrad of IL2RA, IL2RG, IFNG, and IL7R genes were determined as hub genes and verified by qRT-PCR, which were significantly associated with unfavorable prognosis in melanoma. LINC02446, LINC01857, and LINC02384 may act as competing endogenous lncRNAs of IL2RA and IL7R through absorbing their shared miR.891a.5p and miR.203b.3p. JAK-STAT signaling pathway identified as the most relevant pathway in melanoma metastasis, as well as a wealthy of genes including TNFRSF 13B, TNFRSF17, TNFRSF9, TNFRSF8, TNFRSF13C, TNFRSF11B, LAG3, NRP1, ENTPD1, NT5E, CCL21, and CCR7, may induce tumor autoimmune suppression through enhancing regulatory T-cell abundance and performance in the tumor microenvironment. And regulatory T-cell proportion was indeed critically elevated in metastatic melanoma relative to primary melanoma, as well as in highly expressed IL2RA, IL2RG, IL7R, and IFNG group than their respective counterparts.

CONCLUSION

Elevated IL2RA, IL2RG, IL7R, and IFNG expression may play a central role in promoting melanoma metastasis through up regulation of intratumoral regulatory T-cell proportion mainly by activation of JAK-STAT signaling pathway. LINC02446, LINC01857, and LINC02384 may stimulate melanoma progression by reducing tumor-protecting miR.891a.5p and miR.203b.3p. A number of identified molecules including TNFRSF13B, LAG3, NRP1, ENTPD1, NT5E, CCL21, and CCR7 can serve as future therapeutic targets in melanoma treatment.

Interleukin-9 Inhibits Lung Metastasis of Melanoma through Stimulating Anti-Tumor M1 Macrophages

Interleukin-9 (IL-9) is well known for its role in allergic inflammation. For cancer, both pro- and anti-tumor effects of IL-9 were controversially reported, but the impact of IL-9 on tumor metastasis has not yet been clarified. In this study, IL-9 was expressed as a secretory form (sIL-9) and a membrane-bound form (mbIL-9) on B16F10 melanoma cells. The mbIL-9 was engineered as a chimeric protein with the transmembrane and cytoplasmic region of TNF-α. The effect of either mbIL-9 or sIL-9 expressing cells were analyzed on the metastasis capability of the cancer cells. After three weeks of tumor implantation into C57BL/6 mice through the tail vein, the number of tumor modules in lungs injected with IL-9 expressing B16F10 was 5-fold less than that of control groups. The percentages of CD4+ T cells, CD8+ T cells, NK cells, and M1 macrophages considerably increased in the lungs of the mice injected with IL-9 expressing cells. Among them, the M1 macrophage subset was the most significantly enhanced. Furthermore, peritoneal macrophages, which were stimulated with either sIL-9 or mbIL-9 expressing transfectant, exerted higher anti-tumor cytotoxicity compared with that of the mock control. The IL-9-stimulated peritoneal macrophages were highly polarized to M1 phenotype. Stimulation of RAW264.7 macrophages with sIL-9 or mbIL-9 expressing cells also significantly increased the cytotoxicity of those macrophages against wild-type B16F10 cells. These results clearly demonstrate that IL-9 can induce an anti-metastasis effect by enhancing the polarization and proliferation of M1 macrophages.

IL-2 receptors preassemble and signal in the ER/Golgi causing resistance to antiproliferative anti-IL-2Rα therapies

Interleukin-2 (IL-2) and IL-15 play pivotal roles in T cell activation, apoptosis, and survival, and are implicated in leukemias and autoimmune diseases. Their heterotrimeric receptors share their β- and γ_c-chains, but have distinct α-chains. Anti-IL-2Rα (daclizumab) therapy targeting cell surface-expressed receptor subunits to inhibit T cell proliferation has only brought limited success in adult T cell leukemia/lymphoma (ATL) and in multiple sclerosis. We asked whether IL-2R subunits could already preassemble and signal efficiently in the endoplasmic reticulum (ER) and the Golgi. A combination of daclizumab and anti-IL-2 efficiently blocked IL-2-induced proliferation of IL-2-dependent wild-type (WT) ATL cells but not cells transfected with IL-2, suggesting that in IL-2-producing cells signaling may already take place before receptors reach the cell surface. In the Golgi fraction isolated from IL-2-producing ATL cells, we detected by Western blot phosphorylated Jak1, Jak3, and a phosphotyrosine signal attributed to the γ_c-chain, which occurred at much lower levels in the Golgi of WT ATL cells. We expressed EGFP- and mCherry-tagged receptor chains in HeLa cells to study their assembly along the secretory pathway. Confocal microscopy, Förster resonance energy transfer, and imaging fluorescence cross-correlation spectroscopy analysis revealed partial colocalization and molecular association of IL-2 (and IL-15) receptor chains in the ER/Golgi, which became more complete in the plasma membrane, further confirming our hypothesis. Our results define a paradigm of intracellular autocrine signaling and may explain resistance to antagonistic antibody therapies targeting receptors at the cell surface.

An Update on Interleukin-9: From Its Cellular Source and Signal Transduction to Its Role in Immunopathogenesis

Interleukin-9 (IL-9) is a pleiotropic cytokine and was primarily studied in the context of T helper 2 (TH2)-associated immuno-pathological conditions such as asthma and parasitic infections. There was a paradigm shift in the biology of IL-9 after the recent discovery of TH9 cells, a new subtype of TH cells which secrete IL-9 in copious amounts. This has resulted in renewed interest in this cytokine, which was neglected since discovery because it was considered it to be just another TH2 cytokine. Recent studies have shown that it has multiple cellular sources and is critically involved in the immune-pathogenesis of inflammatory diseases and in guarding immune tolerance. In this review, we will discuss its discovery, gene organization, cellular sources, and signaling pathways. Especially, we will give an update on the recent development regarding its relevance in the immune pathogenesis of human diseases.

Differential effect of inhibitory strategies of the V617 mutant of JAK2 on cytokine receptor signaling

BACKGROUND

Janus kinase (JAK) 2 plays pivotal roles in signaling by several cytokine receptors. The mutant JAK2 V617F is the most common molecular event associated with myeloproliferative neoplasms. Selective targeting of the mutant would be ideal for treating these pathologies by sparing essential JAK2 functions.

OBJECTIVE

We characterize inhibitory strategies for JAK2 V617F and assess their effect on physiologic signaling by distinct cytokine receptors.

METHODS

Through structure-guided mutagenesis, we assessed the role of key residues around F617 and used a combination of cellular and biochemical assays to measure the activity of JAKs in reconstituted cells. We also assessed the effect of several specific JAK2 V617F inhibitory mutations on receptor dimerization using the NanoBiT protein complementation approach.

RESULTS

We identified a novel Janus kinase homology 2 (JH2) αC mutation, A598F, which is suggested to inhibit the aromatic stacking between F617 with F594 and F595. Like other JAK2 V617F inhibitory mutations, A598F decreased oncogenic activation and spared cytokine activation while preventing JAK2 V617F-promoted erythropoietin receptor dimerization. Surprisingly, A598F and other V617F-inhibiting mutations (F595A, E596R, and F537A) significantly impaired IFN-γ signaling. This was specific for IFN-γ because the inhibitory mutations preserved responses to ligands of a series of receptor complexes. Similarly, homologous mutations in JAK1 prevented signaling by IFN-γ.

CONCLUSIONS

The JH2 αC region, which is required for JAK2 V617F hyperactivation, is crucial for relaying cytokine-induced signaling of the IFN-γ receptor. We discuss how strategies aiming to inhibit JAK2 V617F could be used for identifying inhibitors of IFN-γ signaling.

Minimum degree of overlap between IL-9R and IL-2R on human T lymphoma cells: A quantitative CLSM and FRET analysis

The heterodimeric receptor complex of IL-9 consists of the cytokine-specific α-subunit and the common γc -chain shared with other cytokines, including IL-2, a central regulator of T cell function. We have shown previously the bipartite spatial relationship of IL-9 and IL-2 receptors at the surface of human T lymphoma cells: in addition to common clusters, expression of the two receptor kinds could also be observed in segregated membrane areas. Here we analyzed further the mutual cell surface organization of IL-9 and IL-2 receptors. Complementing Pearson correlation data with co-occurrence analysis of confocal microscopic images revealed that a minimum degree of IL-9R/IL-2R co-localization exists at the cell surface regardless of the overall spatial correlation of the two receptor kinds. Moreover, our FRET experiments demonstrated molecular scale assemblies of the elements of the IL-9/IL-2R system. Binding of IL-9 altered the structure and/or composition of these clusters. It is hypothesized, that by sequestering receptor subunits in common membrane areas, the overlapping domains of IL-9R and IL-2R provide a platform enabling both the formation of the appropriate receptor complex as well as subunit sharing between related cytokines. © 2018 International Society for Advancement of Cytometry.

Mapping Determinants of Cytokine Signaling via Protein Engineering

Cytokines comprise a large family of secreted ligands that are critical for the regulation of immune homeostasis. Cytokines initiate signaling via dimerization or oligomerization of the cognate receptor subunits, triggering the activation of the Janus Kinases (JAKs)/ signal transducer and activator of transcription (STATs) pathway and the induction of specific gene expression programs and bioactivities. Deregulation of cytokines or their downstream signaling pathways are at the root of many human disorders including autoimmunity and cancer. Identifying and understanding the mechanistic principles that govern cytokine signaling will, therefore, be highly important in order to harness the therapeutic potential of cytokines. In this review, we will analyze how biophysical (ligand-receptor binding geometry and affinity) and cellular (receptor trafficking and intracellular abundance of signaling molecules) parameters shape the cytokine signalosome and cytokine functional pleiotropy; from the initial cytokine binding to its receptor to the degradation of the cytokine receptor complex in the proteasome and/or lysosome. We will also discuss how combining advanced protein engineering with detailed signaling and functional studies has opened promising avenues to tackle complex questions in the cytokine signaling field.

IL-7 Induces an Epitope Masking of γc Protein in IL-7 Receptor Signaling Complex

IL-7 signaling via IL-7Rα and common γ-chain (γc) is necessary for the development and homeostasis of T cells. Although the delicate mechanism in which IL-7Rα downregulation allows the homeostasis of T cell with limited IL-7 has been well known, the exact mechanism behind the interaction between IL-7Rα and γc in the absence or presence of IL-7 remains unclear. Additionally, we are still uncertain as to how only IL-7Rα is separately downregulated by the binding of IL-7 from the IL-7Rα/γc complex. We demonstrate here that 4G3, TUGm2, and 3E12 epitope masking of γc protein are induced in the presence of IL-7, indicating that the epitope alteration is induced by IL-7 binding to the preassembled receptor core. Moreover, the epitope masking of γc protein is inversely correlated with the expression of IL-7Rα upon IL-7 binding, implying that the structural alteration of γc might be involved in the regulation of IL-7Rα expression. The conformational change in γc upon IL-7 binding may contribute not only to forming the functional IL-7 signaling complex but also to optimally regulating the expression of IL-7Rα.

Discovery and initial characterization of Th9 cells: the early years

The launch of the Th1/Th2 concept represented a decisive breakthrough concerning our understanding of how very diverse immune reactions can be regulated by functionally different T helper subpopulations via the secretion of different panels of cytokines. In this context, IL-9 was identified to be produced by T helper cell lines in addition to Th2 cytokines IL-4 and IL-5. Detailed analyses revealed that IL-9 production of mouse CD4⁺ T helper cells was dependent on a combination of IL-2, IL-4, and TGF-β. Roughly a decade later, it was found that TGF-β can also induce the development of CD4⁺ Treg cells. This finding engendered a series of studies on the central role of TGF-β for cytokine-mediated T helper cell differentiation which elucidated that IL-4 curbed the Treg cell-promoting effect of TGF-β while TGF-β impaired the Th2-promoting capacity of IL-4. Instead, TGF-β in combination with IL-4 induced the development of CD4⁺ T helper cells that preferentially produced IL-9 and that were different from Th2 cells which originally were thought to be the main source of IL-9. In addition, adoptive transfer of such IL-9-producing CD4⁺ T helper cells was shown to cause the development of colitis and peripheral neuritis. Hence, the unique cytokine expression pattern in combination with the inflammatory in vivo phenotype led to the designation of Th9 cells as a new CD4⁺ T helper subpopulation.

The common γ-chain cytokine receptor: tricks-and-treats for T cells

Originally identified as the third subunit of the high-affinity IL-2 receptor complex, the common γ-chain (γc) also acts as a non-redundant receptor subunit for a series of other cytokines, collectively known as γc family cytokines. γc plays essential roles in T cell development and differentiation, so that understanding the molecular basis of its signaling and regulation is a critical issue in T cell immunology. Unlike most other cytokine receptors, γc is thought to be constitutively expressed and limited in its function to the assembly of high-affinity cytokine receptors. Surprisingly, recent studies reported a series of findings that unseat γc as a simple housekeeping gene, and unveiled γc as a new regulatory molecule in T cell activation and differentiation. Cytokine-independent binding of γc to other cytokine receptor subunits suggested a pre-association model of γc with proprietary cytokine receptors. Also, identification of a γc splice isoform revealed expression of soluble γc proteins (sγc). sγc directly interacted with surface IL-2Rβ to suppress IL-2 signaling and to promote pro-inflammatory Th17 cell differentiation. As a result, endogenously produced sγc exacerbated autoimmune inflammatory disease, while the removal of endogenous sγc significantly ameliorated disease outcome. These data provide new insights into the role of both membrane and soluble γc in cytokine signaling, and open new venues to interfere and modulate γc signaling during immune activation. These unexpected discoveries further underscore the perspective that γc biology remains largely uncharted territory that invites further exploration.

Distinct Acute Lymphoblastic Leukemia (ALL)-associated Janus Kinase 3 (JAK3) Mutants Exhibit Different Cytokine-Receptor Requirements and JAK Inhibitor Specificities

JAK1 and JAK3 are recurrently mutated in acute lymphoblastic leukemia. These tyrosine kinases associate with heterodimeric cytokine receptors such as IL-7 receptor or IL-9 receptor, in which JAK1 is appended to the specific chain, and JAK3 is appended to the common gamma chain. Here, we studied the role of these receptor complexes in mediating the oncogenic activity of JAK3 mutants. Although JAK3(V674A) and the majority of other JAK3 mutants needed to bind to a functional cytokine receptor complex to constitutively activate STAT5, JAK3(L857P) was unexpectedly found to not depend on such receptor complexes for its activity, which was induced without receptor or JAK1 co-expression. Introducing a mutation in the FERM domain that abolished JAK-receptor interaction did not affect JAK3(L857P) activity, whereas it inhibited the other receptor-dependent mutants. The same cytokine receptor independence as for JAK3(L857P) was observed for homologous Leu(857) mutations of JAK1 and JAK2 and for JAK3(L875H). This different cytokine receptor requirement correlated with different functional properties in vivo and with distinct sensitivity to JAK inhibitors. Transduction of murine hematopoietic cells with JAK3(V674A) led homogenously to lymphoblastic leukemias in BALB/c mice. In contrast, transduction with JAK3(L857P) induced various types of lymphoid and myeloid leukemias. Moreover, ruxolitinib, which preferentially blocks JAK1 and JAK2, abolished the proliferation of cells transformed by the receptor-dependent JAK3(V674A), yet proved much less potent on cells expressing JAK3(L857P). These particular cells were, in contrast, more sensitive to JAK3-specific inhibitors. Altogether, our results showed that different JAK3 mutations induce constitutive activation through distinct mechanisms, pointing to specific therapeutic perspectives.

Cooperating JAK1 and JAK3 mutants increase resistance to JAK inhibitors

The acquisition of growth signal self-sufficiency is 1 of the hallmarks of cancer. We previously reported that the murine interleukin-9-dependent TS1 cell line gives rise to growth factor-independent clones with constitutive activation of the Janus kinase (JAK)- signal transducer and activator of transcription (STAT) pathway. Here, we show that this transforming event results from activating mutations either in JAK1, JAK3, or in both kinases. Transient and stable expression of JAK1 and/or JAK3 mutants showed that each mutant induces STAT activation and that their coexpression further increases this activation. The proliferation of growth factor-independent TS1 clones can be efficiently blocked by JAK inhibitors such as ruxolitinib or CMP6 in short-term assays. However, resistant clones occur upon long-term culture in the presence of inhibitors. Surprisingly, resistance to CMP6 was not caused by the acquisition of secondary mutations in the adenosine triphosphate-binding pocket of the JAK mutant. Indeed, cells that originally showed a JAK1-activating mutation became resistant to inhibitors by acquiring another activating mutation in JAK3, whereas cells that originally showed a JAK3-activating mutation became resistant to inhibitors by acquiring another activating mutation in JAK1. These observations underline the cooperation between JAK1 and JAK3 mutants in T-cell transformation and represent a new mechanism of acquisition of resistance against JAK inhibitors.

Eliminative signaling by Janus kinases: role in the downregulation of associated receptors

Activation of cytokine receptor-associated Janus kinases (JAKs) mediates most, if not all, of the cellular responses to peptide hormones and cytokines. Consequently, JAKs play a paramount role in homeostasis and immunity. Members of this family of tyrosine kinases control the cytokine/hormone-induced alterations in cell gene expression program. This function is largely mediated through an ability to signal toward activation of the signal transducer and activator of transcription proteins (STAT), as well as toward some other pathways. Importantly, JAKs are also instrumental in tightly controlling the expression of associated cytokine and hormone receptors, and, accordingly, in regulating the cell sensitivity to these cytokines and hormones. This review highlights the enzymatic and non-enzymatic mechanisms of this regulation and discusses the importance of the ambidextrous nature of JAK as a key signaling node that integrates the combining functions of forward signaling and eliminative signaling. Attention to the latter aspect of JAK function may contribute to emancipating our approaches to the pharmacological modulation of JAKs.

A molecular perspective on TH2-promoting cytokine receptors in patients with allergic disease

The cytokines IL-4, IL-13, and thymic stromal lymphopoietin play a key role in allergic disease by virtue of their ability to initiate, maintain, and augment TH2 responses. These molecules mediate their effects through type 1 cytokine receptors, which bind cytokines with a characteristic structure. Receptors are expressed on a broad array of immune cell types and are integral to complex cytokine networks operating in health and disease. TH2-promoting cytokines bind different configurations of receptors. Receptor subunits can exist in surface-bound or soluble forms, as well as in isolation or in partnership with other subunits. Sharing of receptor subunits among different cytokine receptor complexes adds to the intricate landscape. This article describes the characteristics of receptors for IL-4, IL-13, and thymic stromal lymphopoietin and their respective ligands from a structure-function perspective. We detail the mechanisms of receptor complex assembly, the interrelated nature of these receptors, and the effect on allergic inflammation. The ability for novel and atypical types of receptors to modulate inflammatory processes is also discussed. We highlight current and emerging treatments that target TH2-promoting receptor complexes. Understanding the molecular features of these receptors provides insight into different disease phenotypes and the variable clinical outcomes arising from targeted therapies. These considerations can be used to inform future directions for research and creative strategies for treating individual patients.

Activating Janus kinase pseudokinase domain mutations in myeloproliferative and other blood cancers

The discovery of the highly prevalent activating JAK (Janus kinase) 2 V617F mutation in myeloproliferative neoplasms, and of other pseudokinase domain-activating mutations in JAK2, JAK1 and JAK3 in blood cancers, prompted great interest in understanding how pseudokinase domains regulate kinase domains in JAKs. Recent functional and mutagenesis studies identified residues required for the V617F mutation to induce activation. Several X-ray crystal structures of either kinase or pseudokinase domains including the V617F mutant of JAK2 pseudokinase domains are now available, and a picture has emerged whereby the V617F mutation induces a defined conformational change around helix C of JH (JAK homology) 2. Effects of mutations on JAK2 can be extrapolated to JAK1 and TYK2 (tyrosine kinase 2), whereas JAK3 appears to be different. More structural information of the full-length JAK coupled to cytokine receptors might be required in order to define the structural basis of JH1 activation by JH2 mutants and eventually obtain mutant-specific inhibitors.

Structural insights into the common γ-chain family of cytokines and receptors from the interleukin-7 pathway

Over the past 13 years, numerous crystal structures of complexes of the common γ-chain (γ(c)) cytokine receptors and their cytokines have been solved. Even with the remarkable progress in the structural biology of γ(c) receptors and their cytokines or interleukins, there are valuable lessons to be learned from the structural and biophysical studies of interleukin-7 (IL-7) and its α-receptor (IL-7Rα) and comparisons with other γ(c) family members. The structure of the IL-7/IL-7Rα complex teaches that interfaces between the γ(c) interleukins and their receptors can vary in size, polarity, and specificity, and that significant conformational changes might be necessary for complexes of interleukins and their receptors to bind the shared, activating γ(c) receptor. Binding, kinetic, and thermodynamic studies of IL-7 and IL-7Rα show that glycosylation and electrostatics can be important to interactions between interleukins and their receptor, even where the glycans and charged residues are distant from the interface. The structure of the IL-7Rα homodimer is a reminder that often-ignored non-activating complexes likely perform roles just as important to signaling as activating complexes. And last but not least, the structural and biophysical studies help explain and potentially treat the diseases caused by aberrant IL-7 signaling.

Structural reorganization of the interleukin-7 signaling complex

We report here an unliganded receptor structure in the common gamma-chain (γ(c)) family of receptors and cytokines. The crystal structure of the unliganded form of the interleukin-7 alpha receptor (IL-7Rα) extracellular domain (ECD) at 2.15 Å resolution reveals a homodimer forming an "X" geometry looking down onto the cell surface with the C termini of the two chains separated by 110 Å and the dimer interface comprising residues critical for IL-7 binding. Further biophysical studies indicate a weak association of the IL-7Rα ECDs but a stronger association between the γ(c)/IL-7Rα ECDs, similar to previous studies of the full-length receptors on CD4(+) T cells. Based on these and previous results, we propose a molecular mechanism detailing the progression from the inactive IL-7Rα homodimer and IL-7Rα-γ(c) heterodimer to the active IL-7-IL-7Rα-γ(c) ternary complex whereby the two receptors undergo at least a 90° rotation away from the cell surface, moving the C termini of IL-7Rα and γ(c) from a distance of 110 Å to less than 30 Å at the cell surface. This molecular mechanism can be used to explain recently discovered IL-7- and γ(c)-independent gain-of-function mutations in IL-7Rα from B- and T-cell acute lymphoblastic leukemia patients. The mechanism may also be applicable to other γ(c) receptors that form inactive homodimers and heterodimers independent of their cytokines.

FERM domain mutations induce gain of function in JAK3 in adult T-cell leukemia/lymphoma

Adult T-cell leukemia/lymphoma (ATLL) is an incurable disease where most patients succumb within the first year of diagnosis. Both standard chemotherapy regimens and mAbs directed against ATLL tumor markers do not alter this aggressive clinical course. Therapeutic development would be facilitated by the discovery of genes and pathways that drive or initiate ATLL, but so far amenable drug targets have not been forthcoming. Because the IL-2 signaling pathway plays a prominent role in ATLL pathogenesis, mutational analysis of pathway components should yield interesting results. In this study, we focused on JAK3, the nonreceptor tyrosine kinase that signals from the IL-2R, where activating mutations have been found in diverse neoplasms. We screened 36 ATLL patients and 24 ethnically matched controls and found 4 patients with mutations in JAK3. These somatic, missense mutations occurred in the N-terminal FERM (founding members: band 4.1, ezrin, radixin, and moesin) domain and induced gain of function in JAK3. Importantly, we show that these mutant JAK3s are inhibited with a specific kinase inhibitor already in human clinical testing. Our findings underscore the importance of this pathway in ATLL development and offer a therapeutic handle for this incurable cancer.

Anti-gamma chain and anti-IL-2Rbeta mAbs in combination with donor splenocyte transfusion induce H-Y skin graft acceptance in murine model

BACKGROUND

The common cytokine receptor gamma chain signals regulate proliferation, differentiation, and apoptosis of peripheral T cells.

OBJECTIVE

To investigate whether simultaneous blockade of IL-2Rbeta and gamma chain signaling in combination with donor splenocyte transfusion (DST) induces transplant tolerance.

MATERIALS AND METHODS

C57BL/6 (H-2b) mice were randomly divided into 5 groups. In group 1, female mice received only H-Y skin grafts. In group 2, female mice received transfused splenocytes (5 x 10(6) cells) from syngeneic male mice on day 7 before H-Y skin grafting. In group 3, on days 2 and 4 after DST, female mice received intraperitoneal injections of a mixture of anti-IL-2Rbeta monoclonal antibody (mAb) and anti-gamma chain mAbs (4G3, 3E12, and TUGm2; 0.5 mg). After DST, group 4 received an intraperitoneal injection of the mixture of anti-gamma chain mAbs, and group 5 received intraperitoneal injection of anti-IL-2Rbeta mAb (TM-beta1). On day 7, H-Y skin grafting was performed.

RESULTS

Group 3 recipients accepted H-Y skin grafts for more than 100 days compared with group 1 (mean survival time [MST], 33.42 days), group 2 (MST, 14.71 days), group 4 (MST, 58.71 days), and group 5 (MST, 17.29 days). Statistical differences (P < .05) were observed between any 2 groups except groups 2 and 5.

CONCLUSION

Blockade of gamma chain signaling rather than IL-2Rbeta signaling combined with DST prolongs H-Y skin graft survival. Simultaneous blockade of IL-2Rbeta and gamma chain signaling may strengthen this effect.

Acute lymphoblastic leukemia-associated JAK1 mutants activate the Janus kinase/STAT pathway via interleukin-9 receptor alpha homodimers

Activating mutations in JAK1 have been reported in acute lymphoblastic leukemias, but little is known about the mechanisms involved in their constitutive activation. Here, we studied the ability of JAK1 V658F and A634D to activate the Janus kinase (JAK)/STAT pathway upon ectopic expression in HEK293 cells alone or together with the other components of the interleukin-9 receptor complex (IL-9Ralpha, gammac, and JAK3). Expression of JAK1 mutants alone failed to trigger STAT activation, but co-expression of the IL-9Ralpha chain promoted JAK1 mutant phosphorylation and STAT activation. Mutation of the FERM domain of JAK1, which is critical for cytokine receptor association, or of the single tyrosine of IL-9Ralpha involved in STAT recruitment abolished this activity, indicating that JAK1 mutants need to associate with a functional IL-9Ralpha to activate STAT factors. Several lines of evidence indicated that IL-9Ralpha homodimerization was involved in this process. IL-9Ralpha variants with mutations of the JAK-interacting BOX1 region not only failed to promote JAK1 activation but also acted as dominant negative forms reverting the effect of wild-type IL-9Ralpha. Coimmunoprecipitation experiments also showed the formation of IL-9Ralpha homodimers. Interestingly, STAT activation was partially inhibited by expression of gammac, suggesting that overlapping residues are involved in IL-9Ralpha homodimerization and IL-9Ralpha/gammac heterodimerization. Co-expression of wild-type JAK3 partially reverted the inhibition by gammac, indicating that JAK3 cooperates with JAK1 mutants within the IL-9 receptor complex. Similar results were observed with IL-2Rbeta. Taken together, our results show that IL-9Ralpha and IL-2Rbeta homodimers efficiently mediate constitutive activation of ALL-associated JAK1 mutants.