Structural analysis of the gene encoding the murine interleukin-11 receptor alpha-chain and a related locus

Interleukin-11 (IL11) inhibits myogenic differentiation of C2C12 cells through activation of extracellular signal-regulated kinase (ERK)

Cancer-associated cachexia (CAC) is a multifactorial wasting syndrome characterized by loss of skeletal muscle. Interleukin-11 (IL11), one of the IL6 family cytokines, is highly expressed in various types of cancer including cancers frequently associated with cachexia. However, the impact of IL11 on muscle metabolism remains to be determined. Since one of the mechanisms of muscle wasting in cachexia is defective muscle regeneration due to impaired myogenic differentiation, we examined the effect of IL11 on the differentiation of C2C12 mouse myoblasts. Treatment of C2C12 cells with recombinant mouse IL11 resulted in decreased myotube formation. In addition, IL11 treatment reduced the protein and mRNA levels of myosin heavy chain (MHC), a marker of myogenic differentiation. Moreover, the levels of myogenic regulatory factors including myogenin and Mrf4 were significantly reduced by IL11 treatment. IL11 treatment increased the number of BrdU-positive cells and the level of phosphorylated retinoblastoma (Rb) protein, while the levels of p21^Waf1 and p27^Kip1 were reduced by IL11 treatment in differentiating C2C12 cells, suggesting that IL11 interferes with cell cycle exit during the early stages of myogenic differentiation. Consistent with this, IL11 treatment at the late stage of differentiation did not affect myotube formation and MHC expression. IL11 treatment resulted in an activation of ERK, STAT3, and AKT in differentiating C2C12 cells. However, only ERK inhibitors including PD98059 and U0126 were able to ameliorate the suppressive effect of IL11 on the expression of MHC and myogenin. Additionally, pretreatment with PD98059 and U0126 resulted in improved myotube formation and reduced BrdU staining in IL11-treated cells. Together, our results suggest that IL11 inhibits myogenic differentiation through delayed cell cycle exit in an ERK-dependent manner. To our knowledge, this study is the first to demonstrate an inhibitory role of IL11 in myogenic differentiation and identifies the previously unrecognized role of IL11 as a possible mediator of CAC.

Interleukin-11 receptor subunit α-1 is required for maximal airway responsiveness to methacholine after acute exposure to ozone

Interleukin (IL)-11, a multifunctional cytokine, contributes to numerous biological processes, including adipogenesis, hematopoiesis, and inflammation. Asthma, a respiratory disease, is notably characterized by reversible airway obstruction, persistent lung inflammation, and airway hyperresponsiveness (AHR). Nasal insufflation of IL-11 causes AHR in wild-type mice while lung inflammation induced by antigen sensitization and challenge, which mimics features of atopic asthma in humans, is attenuated in mice genetically deficient in IL-11 receptor subunit α-1 (IL-11Rα1-deficient mice), a transmembrane receptor that is required conjointly with glycoprotein 130 to transduce IL-11 signaling. Nevertheless, the contribution of IL-11Rα1 to characteristics of nonatopic asthma is unknown. Thus, based on the aforementioned observations, we hypothesized that genetic deficiency of IL-11Rα1 attenuates lung inflammation and increases airway responsiveness after acute inhalation exposure to ozone (O3), a criteria pollutant and nonatopic asthma stimulus. Accordingly, 4 and/or 24 h after cessation of exposure to filtered room air or O3, we assessed lung inflammation and airway responsiveness in wild-type and IL-11Rα1-deficient mice. With the exception of bronchoalveolar lavage macrophages and adiponectin, which were significantly increased and decreased, respectively, in O3-exposed IL-11Rα1-deficient as compared with O3-exposed wild-type mice, no other genotype-related differences in lung inflammation indices that we quantified were observed in O3-exposed mice. However, airway responsiveness to acetyl-β-methylcholine chloride (methacholine) was significantly diminished in IL-11Rα1-deficient as compared with wild-type mice after O3 exposure. In conclusion, these results demonstrate that IL-11Rα1 minimally contributes to lung inflammation but is required for maximal airway responsiveness to methacholine in a mouse model of nonatopic asthma.

Cergutuzumab amunaleukin (CEA-IL2v), a CEA-targeted IL-2 variant-based immunocytokine for combination cancer immunotherapy: Overcoming limitations of aldesleukin and conventional IL-2-based immunocytokines

We developed cergutuzumab amunaleukin (CEA-IL2v, RG7813), a novel monomeric CEA-targeted immunocytokine, that comprises a single IL-2 variant (IL2v) moiety with abolished CD25 binding, fused to the C-terminus of a high affinity, bivalent carcinoembryonic antigen (CEA)-specific antibody devoid of Fc-mediated effector functions. Its molecular design aims to (i) avoid preferential activation of regulatory T-cells vs. immune effector cells by removing CD25 binding; (ii) increase the therapeutic index of IL-2 therapy by (a) preferential retention at the tumor by having a lower dissociation rate from CEA-expressing cancer cells vs. IL-2R-expressing cells, (b) avoiding any FcγR-binding and Fc effector functions and (c) reduced binding to endothelial cells expressing CD25; and (iii) improve the pharmacokinetics, and thus convenience of administration, of IL-2. The crystal structure of the IL2v-IL-2Rβγ complex was determined and CEA-IL2v activity was assessed using human immune effector cells. Tumor targeting was investigated in tumor-bearing mice using 89Zr-labeled CEA-IL2v. Efficacy studies were performed in (a) syngeneic mouse models as monotherapy and combined with anti-PD-L1, and in (b) xenograft mouse models in combination with ADCC-mediating antibodies. CEA-IL2v binds to CEA with pM avidity but not to CD25, and consequently did not preferentially activate Tregs. In vivo, CEA-IL2v demonstrated superior pharmacokinetics and tumor targeting compared with a wild-type IL-2-based CEA immunocytokine (CEA-IL2wt). CEA-IL2v strongly expanded NK and CD8+ T cells, skewing the CD8+:CD4+ ratio toward CD8+ T cells both in the periphery and in the tumor, and mediated single agent efficacy in syngeneic MC38-CEA and PancO2-CEA models. Combination with trastuzumab, cetuximab and imgatuzumab, all of human IgG1 isotype, resulted in superior efficacy compared with the monotherapies alone. Combined with anti-PD-L1, CEA-IL2v mediated superior efficacy over the respective monotherapies, and over the combination with an untargeted control immunocytokine. These preclinical data support the ongoing clinical investigation of the cergutuzumab amunaleukin immunocytokine with abolished CD25 binding for the treatment of CEA-positive solid tumors in combination with PD-L1 checkpoint blockade and ADCC competent antibodies.

Generation of Soluble Interleukin-11 and Interleukin-6 Receptors: A Crucial Function for Proteases during Inflammation

The cytokines interleukin-11 (IL-11) and IL-6 are important proteins with well-defined pro- and anti-inflammatory functions. They activate intracellular signaling cascades through a homodimer of the ubiquitously expressed signal-transducing β-receptor glycoprotein 130 (gp130). Specificity is gained through the cell- and tissue-specific expression of the nonsignaling IL-11 and IL-6 α-receptors (IL-11R and IL-6R), which determine the responsiveness of the cell to these two cytokines. IL-6 is a rare example, where its soluble receptor (sIL-6R) has agonistic properties, so that the IL-6/sIL-6R complex is able to activate cells that are usually not responsive to IL-6 alone (trans-signaling). Recent evidence suggests that IL-11 can signal via a similar trans-signaling mechanism. In this review, we highlight similarities and differences in the functions of IL-11 and IL-6. We summarize current knowledge about the generation of the sIL-6R and sIL-11R by different proteases and discuss possible roles during inflammatory processes. Finally, we focus on the selective and/or combined inhibition of IL-6 and IL-11 signaling and how this might translate into the clinics.

IL-11 signaling as a therapeutic target for cancer

IL-11 is a member of the IL-6 family of cytokines. While it was discovered over 20 years ago, we have very little understanding of the role of IL-11 during normal homeostasis and disease. Recently, IL-11 has gained interest for its newly recognized role in the pathogenesis of diseases that are attributed to deregulated mucosal homeostasis, including gastrointestinal cancers. IL-11 can increase the tumorigenic capacity of cells, including survival of the cell or origin, proliferation of cancerous cells and survival of metastatic cells at distant organs. Here we outline our current understanding of IL-11 biology and recent advances in our understanding of its role in cancer. We advocate that inhibition of IL-11 signaling may represent an emerging therapeutic opportunity for numerous cancers.

Proteolytic Cleavage Governs Interleukin-11 Trans-signaling

Interleukin (IL)-11 has been shown to be a crucial factor for intestinal tumorigenesis, lung carcinomas, and asthma. IL-11 is thought to exclusively mediate its biological functions through cell-type-specific expression of the membrane-bound IL-11 receptor (IL-11R). Here, we show that the metalloprotease ADAM10, but not ADAM17, can release the IL-11R ectodomain. Chimeric proteins of the IL-11R and the IL-6 receptor (IL-6R) revealed that a small juxtamembrane portion is responsible for this substrate specificity of ADAM17. Furthermore, we show that the serine proteases neutrophil elastase and proteinase 3 can also cleave the IL-11R. The resulting soluble IL-11R (sIL-11R) is biologically active and binds IL-11 to activate cells. This IL-11 trans-signaling pathway can be inhibited specifically by the anti-inflammatory therapeutic compound sgp130Fc. In conclusion, proteolysis of the IL-11R represents a molecular switch that controls the IL-11 trans-signaling pathway and widens the number of cells that can be activated by IL-11.

Emerging roles for IL-11 signaling in cancer development and progression: Focus on breast cancer

Interleukin (IL)-11 is a member of the IL-6 family of cytokines that is defined by the shared use of the GP130 signal transducing receptor subunit. In addition of its long recognized activities as a hemopoietic growth factor, IL-11 has an emerging role in epithelial cancer biology. Through the activation of the GP130-Janus kinase signaling cascade and associated transcription factor STAT3, IL-11 can confer many of the tumor intrinsic 'hallmark' capabilities to neoplastic cells, if they express the ligand-specific IL-11Rα receptor subunit. Accordingly, IL-11 signaling has recently been identified as a rate-limiting step for the growth tumors arising from the mucosa of the gastrointestinal tract. However, there is less appreciation for a potential role of IL-11 to support breast cancer progression, apart from its well documented capacity to facilitate bone metastasis. Here we review evidence that IL-11 expression in breast cancer correlates with poor disease outcome and discuss some of the molecular mechanisms that are likely to underpin these observations. These include the capacity of IL-11 to stimulate survival and proliferation of cancer cells alongside angiogenesis of the primary tumor and of metastatic progenies at distant organs. We review current strategies to interfere with IL-11 signaling and advocate that inhibition of IL-11 signaling may represent an emerging therapeutic opportunity for numerous cancers.

Functional characterization of c-Mpl ectodomain mutations that underlie congenital amegakaryocytic thrombocytopenia

Activation of the cell surface receptor, c-Mpl, by the cytokine, thrombopoietin (TPO), underpins megakaryocyte and platelet production in mammals. In humans, mutations in c-Mpl have been identified as the molecular basis of Congenital Amegakaryocytic Thrombocytopenia (CAMT). Here, we show that CAMT-associated mutations in c-Mpl principally lead to defective receptor presentation on the cell surface. In contrast, one CAMT mutant c-Mpl, F104S, was expressed on the cell surface, but showed defective TPO binding and receptor activation. Using mutational analyses, we examined which residues adjacent to F104 within the membrane-distal cytokine receptor homology module (CRM) of c-Mpl comprise the TPO-binding epitope, revealing residues within the predicted Domain 1 E-F and A-B loops and Domain 2 F'-G' loop as key TPO-binding determinants. These studies underscore the importance of the c-Mpl membrane-distal CRM to TPO-binding and suggest that mutations within this CRM that perturb TPO binding could give rise to CAMT.

Loss-of-function mutations in the IL-21 receptor gene cause a primary immunodeficiency syndrome

A primary immunodeficiency syndrome caused by loss-of-function mutations in the IL-21 receptor exhibits impaired B, T, and NK cell function.

Primary immunodeficiencies (PIDs) represent exquisite models for studying mechanisms of human host defense. In this study, we report on two unrelated kindreds, with two patients each, who had cryptosporidial infections associated with chronic cholangitis and liver disease. Using exome and candidate gene sequencing, we identified two distinct homozygous loss-of-function mutations in the interleukin-21 receptor gene (IL21R; c.G602T, p.Arg201Leu and c.240_245delCTGCCA, p.C81_H82del). The IL-21R^Arg201Leu mutation causes aberrant trafficking of the IL-21R to the plasma membrane, abrogates IL-21 ligand binding, and leads to defective phosphorylation of signal transducer and activator of transcription 1 (STAT1), STAT3, and STAT5. We observed impaired IL-21–induced proliferation and immunoglobulin class-switching in B cells, cytokine production in T cells, and NK cell cytotoxicity. Our study indicates that human IL-21R deficiency causes an immunodeficiency and highlights the need for early diagnosis and allogeneic hematopoietic stem cell transplantation in affected children.

A designer hyper interleukin 11 (H11) is a biologically active cytokine

Background

Interleukin 11 (IL-11) is a pleiotropic cytokine with anti-apoptotic, anti-inflammatory and hematopoietic potential. The IL-11 activity is determined by the expression of the IL-11R receptor alpha (IL-11Rα) and the signal transducing subunit β (gp130) on the cell membrane. A recombinant soluble form of the IL-11Rα (sIL-11Rα) in combination with IL-11 acts as an agonist on cells expressing the gp130 molecule. We constructed a designer cytokine Hyper IL-11 (H11), which is exclusively composed of naturally existing components. It contains the full length sIL-11Rα connected with the mature IL-11 protein using their natural sequences only. Such a construct has two major advantages: (i) its components are as close as possible to the natural forms of both proteins and (ii) it lacks an artificial linker what should avoid induction of antibody production.

Results

The H11 construct was generated, the protein was produced in a baculovirus expression system and was then purified by using ion exchange chromatography. The H11 protein displayed activity in three independent bioassays, (i) it induced acute phase proteins production in HepG2 cells expressing IL-11, IL-11Rα and gp130, (ii) it stimulated the proliferation of B9 cells (cells expressing IL-11Rα and gp130) and (iii) proliferation of Baf/3-gp130 cells (cells not expressing IL-11 and IL-11Rα but gp130). Moreover, the preliminary data indicated that H11 was functionally distinct from Hyper-IL-6, a molecule which utilizes the same homodimer of signal transducing receptor (gp130).

Conclusions

The biologically active H11 may be potentially useful for treatment of thrombocytopenia, infertility, multiple sclerosis, cardiovascular diseases or inflammatory disorders.

A model of the ternary complex of interleukin-10 with its soluble receptors

BACKGROUND

Interleukin-10 (IL-10) is a cytokine whose main biological function is to suppress the immune response by induction of a signal(s) leading to inhibition of synthesis of a number of cytokines and their cellular receptors. Signal transduction is initiated upon formation of a ternary complex of IL-10 with two of its receptor chains, IL-10R1 and IL-10R2, expressed on the cell membrane. The affinity of IL-10R1 toward IL-10 is very high, which allowed determination of the crystal structure of IL-10 complexed with the extracellular/soluble domain of IL-10R1, while the affinity of IL-10R2 toward either IL-10 or IL-10/sIL-10R1 complex is quite low. This so far has prevented any attempts to obtain structural information about the ternary complex of IL-10 with its receptor chains.

RESULTS

Structures of the second soluble receptor chain of interleukin-10 (sIL-10R2) and the ternary complex of IL-10/sIL-10R1/sIL-10R2 have been generated by homology modeling, which allowed us to identify residues involved in ligand-receptor and receptor-receptor interactions.

CONCLUSION

The previously experimentally determined structure of the intermediate/binary complex IL-10/sIL-10R1 is the same in the ternary complex. There are two binding sites for the second receptor chain on the surface of the IL-10/sIL-10R1 complex, involving both IL-10 and sIL-10R1. Most of the interactions are hydrophilic in nature, although each interface includes two internal hydrophobic clusters. The distance between C-termini of the receptor chains is 25 A, which is common for known structures of ternary complexes of other cytokines. The structure is likely to represent the biologically active signaling complex of IL-10 with its receptor on the surface of the cell membrane.

Interleukin-7 receptor alpha (IL-7Ralpha) deficiency: cellular and molecular bases. Analysis of clinical, immunological, and molecular features in 16 novel patients

Analysis of gene-targeted mice and patients with severe combined immunodeficiency due to mutations of the alpha chain of the interleukin-7 receptor (IL-7Ralpha) has shown important differences between mice and humans in the role played by IL-7 in lymphoid development. More recently, it has been shown that IL-7Ralpha is also shared by the receptor for another cytokine, thymic stromal lymphopoietin (TSLP). In this review, we discuss recent advances in IL-7- and TSLP-mediated signaling. We also report on the clinical and immunological features of 16 novel patients with IL-7Ralpha deficiency and discuss the results of hematopoietic stem cell transplantation.

Characterization and expression analysis of the chicken interleukin-11 receptor alpha chain

Interleukin-11 (IL-11) is a multifunctional cytokine involved in various pathways in blood cells, their precursors and many other cell types in vitro and in vivo. The effects of IL-11 are largely mediated by the IL-11 receptor alpha-chain (IL-11Ralpha). In this study, a putative cDNA sequence encoding the 414 amino acid propeptide of chicken IL-11R (chIL-11R) was identified. The predicted 414 amino acid sequence showed 42-43% sequence identity with mammalian homologues. In a domain search of the molecule, two fibronectin (FN) type-III domains were identified in the C- terminal portion. On comparison with mammalian IL-11R, 4 conserved cysteine residues and a WSXWS motif were observed within the FN type-III domains. Expression analysis revealed that chIL-11Ralpha is strongly expressed in brain, heart, lung, liver, glandular stomach, kidney, the immature testis, ovary and chicken blastodermal cells (CBCs) after 1-day-cultivation. These findings strongly indicate that the identified chicken cDNA sequence encodes chIL-11R alpha-chain homologue.

The first homozygous mutation (S226I) in the highly-conserved WSXWS-like motif of the GH receptor causing Laron syndrome: supression of GH secretion by GnRH analogue therapy not restored by dihydrotestosterone administration

OBJECTIVE

The study describes for the first time, a homozygous mutation in the WSXWS-like motif of the human GH receptor (GHR) in a patient with Laron syndrome and describe laboratory data during treatment with GnRHa to suppress puberty and dihydrotestosterone (DHT).

PATIENTS

A 16-year-old boy at Tanner puberty stage 2 with Laron syndrome was born SGA to consanguineous parents, presented severe growth retardation, obesity and micropenis.

METHODS AND MEASUREMENTS

GHR coding region was sequenced. GH, GHBP, IGF-I and IGFBP-3 were determined before, during and after GnRHa and DHT treatment.

RESULTS

A homozygous mutation in exon 7, replacing serine by isoleucine in codon 226 was identified. S226 is the last serine belonging to the WSXWS-like motif in GHR. No specific effect of S226I mutation in heterozygous state was observed. Laboratory data at the prepubertal age showed markedly high GH, low GHBP, IGF-I and IGFBP-3 levels. Re-evaluation at pubertal age showed normal basal serum IGFBP-3 levels and low but near normal IGF-I levels. We also noticed a sustained decrease in GH, IGF-I and IGFBP-3 levels after blocking puberty, which was not affected by short- and long-term DHT treatment. Pubertal hormonal profile was re-established after the GnRHa therapy was discontinued to allow the reactivation of the gonadal axis.

CONCLUSION

The homozygous mutation S226I in WSXWS-like motif of GHR causes GH insensitivity. The decrease in IGF-I and IGFBP-3 levels after GnRHa therapy, which was not reversed with DHT administration, suggests that sex steroids have, through oestradiol, a GH-independent action on IGF-I and IGFBP-3 levels. A direct effect of GnRHa on GH secretion cannot be excluded.

Architectural defects in the spleens of Nkx2-3-deficient mice are intrinsic and associated with defects in both B cell maturation and T cell-dependent immune responses

Mice lacking the homeodomain transcription factor Nkx2-3 are either asplenic or develop a spleen of significantly reduced size with poorly organized white pulp. In this report, we analyze the effect of this mutation on B lymphocyte development and differentiation. Follicular dendritic cells in spleen, but not lymph node, of Nkx2-3(-/-) mice fail to express a developmental Ag (follicular dendritic cell-M2) and show an abnormal association with B cells, despite essentially normal expression of several chemokine genes. Bone marrow reconstitution studies show the splenic disorganization and absence of marginal zone B cells to be of stromal rather than hemopoietic origin. Furthermore, Nkx2-3(-/-) mice show an excess of conventional B cells in mesenteric lymph node and peritoneal cavity, whereas transitional B cells are rare in spleen but overrepresented in bone marrow. Finally, immunization of Nkx2-3(-/-) mice with a T cell-dependent Ag elicits clusters of germinal center B cells, although these fail to develop to the same extent as in controls and there is no evidence of affinity maturation in serum Ab. Similarly, Ab-forming cells fail to aggregate into foci early in the response. Collectively, these data indicate a substantial role for Nkx2-3 in the correct association of lymphocytes and splenic stromal elements that is independent of chemokine expression.

Expression and function of interleukin-11 and its receptor alpha in the human endometrium

The interleukin-11 (IL-11) receptor alpha has an important function in decidualization of mouse endometrial stroma but the function of IL-11 and its receptor in the human endometrium remains unknown. The mRNA for IL-11 and its receptor alpha in human endometrial tissue samples were analysed by semi-quantitative RT-PCR and RNase protection assays respectively. The proteins were detected in frozen endometrial tissue samples by immunofluorescence. The effect of heparin-binding epidermal growth factor (HB-EGF) on secretion of IL-11 by cultured endometrial stromal cells was assessed by enzyme-linked immunosorbent assay. The proliferative potential of IL-11 in endometrial stromal cells was assessed by [(3)H]thymidine uptake. IL-11 and its receptor alpha mRNAs and proteins were detected in the endometrium throughout the cycle. Distinct patterns of localization of the ligand and receptor were observed. HB-EGF induced IL-11 secretion by cultured stromal cells, and IL-11 induced [(3)H]thymidine uptake by these cells. Our data suggest that IL-11-receptor interactions may perform different functions in the human endometrium at different stages of the cycle, and that secretion of IL-11 is modulated by local growth factors.

The absence of Tssc6, a member of the tetraspanin superfamily, does not affect lymphoid development but enhances in vitro T-cell proliferative responses

The tetraspanins are a family of integral membrane proteins with four transmembrane domains. These molecules form multimolecular networks on the surfaces of many different cell types. Gene-targeting studies have revealed a role for tetraspanins in B- and T-lymphocyte function. We have isolated and deleted a novel tetraspanin, Tssc6, which is expressed exclusively in hematopoietic and lymphoid organs. Using a gene-trapping strategy, we generated an embryonic stem (ES) cell line with an insertion in the Tssc6 locus. Mice were derived from these ES cells and, using RNase protection and reverse transcription-PCR, we demonstrated that the insertion resulted in a null mutation of the Tssc6 allele. Mice homozygous for the gene trap insertion (Tssc6(gt/gt) mice) were viable and fertile, with normal steady-state hematopoiesis. Furthermore, responses to hemolysis and granulocyte colony-stimulating factor-induced granulopoiesis were equivalent to those of wild-type mice. Lymphoid development was normal in Tssc6(gt/gt) mice. Whereas Tssc6(gt/gt) B cells responded normally to lipopolysaccharide, anti-CD40, and anti-immunoglobulin M stimulation, Tssc6(gt/gt) T cells showed enhanced responses to concanavalin A, anti-CD3, and anti-CD28. This increased proliferation by Tssc6-deleted T lymphocytes was due to increased interleukin 2 production following T-cell receptor stimulation. These results demonstrate that Tssc6 is not required for normal development of the hematopoietic system but may play a role in the negative regulation of peripheral T-lymphocyte proliferation.

Failing to live up to the fanfare? A personal perspective on obstacles to the clinical development of thrombopoietic agents

A number of hematopoietic growth factors have been identified that are active on megakaryocytes and platelets, but only 2, interleukin-11 (IL-11) and thrombopoietin, are being actively pursued clinically, with IL-11 approved for treatment of thrombocytopenia. The development of these agents in general has been disappointing, and in part this reflects the inherent biology of these factors with a failure to match clinical need with physiological function. The delayed action of these factors is also a consequence of the intrinsic biology of megakaryocytes and platelets, and thus is likely to be limiting regardless of which factor is employed. In addition, the development of these agents has occurred at a time when there is something of a decreasing demand for platelets, at least in the context of chemotherapy-induced thrombocytopenia. This decrease is the result of increased use of blood stem cells to support intensive chemotherapy procedures, reduced thresholds for platelet transfusion, and a decreasing role for intensive chemotherapy. These issues are discussed.

Molecular characterisation of mouse and human TSSC6: evidence that TSSC6 is a genuine member of the tetraspanin superfamily and is expressed specifically in haematopoietic organs

Previous analyses of the murine and human TSSC6 (also known as Phemx) proteins were not carried out using the full length sequence. Using 5'-RACE and cDNA library screening, we identified an additional 5' sequence for both the murine Tssc6 cDNA and its human homologue TSSC6. This novel sequence encodes a 5' exon encoding an in frame, upstream start codon, an N-terminal cytoplasmic domain and a transmembrane domain. The deduced, and now full length, murine and human TSSC6 proteins contained four hydrophobic regions together with other features characteristic of the tetraspanin superfamily. Computational analyses of the full length sequences show that TSSC6 is a genuine, albeit relatively divergent member of this superfamily. Using RNA from a number of mouse tissues, we identified seven splice variants of Tssc6. Splice variants of the human gene were also detected. Tssc6 expression was detected early in embryogenesis in primitive blood cells and was confined to haematopoietic organs in the adult mouse. Tssc6 expression was detected in many haematopoietic cell lines and was highest in cell lines of the erythroid lineage.

The role of IL-II in hematopoiesis as revealed by a targeted mutation of its receptor

Interleukin 11 (IL-11) is a pleiotropic growth factor with several actions in common with members of the IL-6 family. IL-11 utilizes a specific receptor chain encoded by two genes, IL-11Ra, which is expressed in hematopoietic and other tissues and, IL-11Ra2, which has a restricted pattern of expression. The actions of IL-11 in the hematopoietic compartment include support of multilineage and committed progenitors contributing to myeloid, erythroid, megakaryocyte, and lymphoid lineages. IL-11 demonstrates a prominent thrombopoietic activity which is being evaluated in clinical trials. In contrast to the multiple in vitro and in vivo effects of IL-11, mice with a targeted mutation of the IL-11Ra gene (IL-11Ra-/-) did not exhibit an overt hematological phenotype. Generation of a null phenotype was confirmed by independent assays. The numbers of progenitor cells of various lineages as well as their terminally differentiated progeny were undisturbed in the IL-11Ra-/- mice. In addition, the mutant mice were able to respond appropriately to increased demand in situations of hematopoietic stress. This study has highlighted the growth factor redundancy operative in the hematopoietic compartment, and in addition, has served to identify a critical action of IL-11 in nonhematopoietic organs.

Gene duplications at the chemokine locus on mouse chromosome 4: multiple strain-specific haplotypes and the deletion of secondary lymphoid-organ chemokine and EBI-1 ligand chemokine genes in the plt mutation

The murine paucity of lymph node T cell (plt) mutation leads to abnormalities in leukocyte migration and immune response. The causative defect is thought to be a loss of secondary lymphoid-organ chemokine (SLC) expression in lymphoid tissues. We now find that the plt defect is due to the loss of both SLC and EBI-1 ligand chemokine (ELC) expression in secondary lymphoid organs. In an examination of the plt locus, we find that commonly used inbred mouse strains demonstrate at least three different haplotypes. Polymorphism at this locus is due to duplications of at least four genes, three of them encoding chemokines. At least two cutaneous T cell-attracting chemokine (CTACK), three SLC, and four ELC genes or pseudogenes are present in some haplotypes. All haplotypes share a duplication that includes two SLC genes, which demonstrate different expression patterns, a single functional ELC gene, and an ELC pseudogene. The plt mutation represents a deletion that includes the SLC gene expressed in secondary lymphoid organs and the single functional ELC gene, leaving only an SLC gene that is expressed in lymphatic endothelium and an ELC pseudogene. This lack of CCR7 ligands in the secondary lymphoid organs of plt mice provides a basis for their severe abnormalities in leukocyte migration and immune response.

Cloning, expression analysis, and chromosomal localization of murine and human homologues of a Xenopus mix gene

We report the cloning and chromosomal localization of murine and human Mix genes, members of a subclass of paired-like homeobox genes of which the Xenopus laevis Mix.1 gene is the founding member. The murine Mix gene was mapped to the distal region of chromosome 1 and the human region to the syntenic region 1q41-42. Northern analysis and RT-PCR of murine adult and embryonic tissues demonstrated that Mix expression was restricted to the early embryo. Whole-mount in situ hybridization revealed patchy but symmetrical Mix expression in visceral endoderm of embryonic day (E)5.5 embryos. In slightly older embryos, the expression was skewed to one side of the embryo and by E6.5, at the onset of gastrulation, expression was seen in the epiblast, visceral endoderm, nascent mesoderm, and the primitive streak. This expression pattern was maintained in mid- and late-streak embryos. In early bud-stage embryos, expression was strongest in the proximal two thirds of the streak, extending to the base of the allantois. By the headfold-stage, expression was confined to the remnant of the primitive streak in the caudal region of the embryo and, after E8.0, in the caudal notochord and tail bud mesoderm. Mix transcripts were no longer detectable after embryonic day 9.5.

ESkine, a novel beta-chemokine, is differentially spliced to produce secretable and nuclear targeted isoforms

Using the murine embryonal stem cell system, we have identified a novel gene encoding a highly divergent member of the beta-chemokine family of proinflammatory mediators and have called this protein ESkine. Much of the coding sequence for ESkine overlaps with the 3'-end of a novel interleukin 11 receptor alpha-like sequence on murine chromosome 4. ESkine is produced as two splice variants. One of these variants encodes a classical chemokine with an associated signal peptide, while the other variant (PESKY) possesses the main body of the chemokine but has replaced the signal peptide with an alternative stretch of amino acids that allows for nuclear targeting of this isoform. This differential splicing arises as a result of alternative 5' exon usage. These differentially spliced forms are expressed at discrete tissue loci. Thus, while ESkine is highly expressed in the placenta, PESKY is mainly expressed in the Testes and brain and weakly in the developing embryo. Studies on the proinflammatory properties of ESkine reveal it to be active in inducing polarization of CD4(+) T cells but to be inactive on other hemopoietic cellular populations.

Soluble cytokine receptors: basic immunology and clinical applications

Cytokine activity is tightly regulated at multiple levels. Soluble cytokine receptors (sCR) contribute to the regulation of cytokine activity by modulating the ability of cytokines to bind their membrane receptors and generating a response. Endogenous sCR are generated by proteolytic cleavage or "shedding" of the membrane receptor and/or by translation from alternatively spliced messages different from those encoding the membrane forms. The resulting soluble receptors retain their ligand-binding ability and with some exceptions act as competitive inhibitors of the binding and biologic activity of their ligand, both in vitro and in vivo. However, sCR can also have certain effects on cytokines, such as structural stabilization, protection from proteolysis, and prolonged in vivo half-life, which are consistent with an added role as carrier proteins, and which may under some conditions result in potentiation of cytokine activity in vivo. The exact contribution of endogenous sCR to the regulation of immune or inflammatory responses has not yet been established unequivocally. Nonetheless, evidence indicates that the levels of certain sCR in serum and biological fluids correlate with immunological activation and/or disease activity in a variety of clinical conditions. Hence, sCR levels may have significant value as markers in disease management and prognosis. Moreover, sCR have also shown promising potential as immunotherapeutic agents for a variety of clinical disorders, including sepsis, inflammation, and autoimmune and malignant diseases.

Interleukin-11 stimulates proopiomelanocortin gene expression and adrenocorticotropin secretion in corticotroph cells: evidence for a redundant cytokine network in the hypothalamo-pituitary-adrenal axis

We recently characterized leukemia inhibitory factor (LIF) as an important modulator of hypothalamo-pituitary-adrenal (HPA) axis activity. We now describe the role of interleukin (IL)-11, another member of the IL-6 cytokine family, in the neuro-immuno-endocrine modulation of the HPA axis. In murine hypothalamus, pituitary and corticotroph AtT-20 cells, IL-11 messenger RNA (mRNA) was detectable by RT-PCR only, whereas IL-11R mRNA transcripts were demonstrated by Northern blot. Using RT-PCR, IL-11 and IL-11R gene expression were also detected in normal human pituitaries, as well as in corticotropic and nonfunctioning pituitary adenomas. Incubation of AtT-20 cells for 24 h with 10(-9) M IL-11 stimulated ACTH secretion 1.4 +/- 0.1-fold (P < 0.01), whereas LIF at the same concentration caused a 1.5 +/- 0.1-fold increase (P < 0.001). POMC mRNA expression was induced by IL-11 (0.5 x 10(-9) M) and LIF (0.5 x 10(-9) M) 1.5 +/- 0.18-fold (P < 0.05) and 1.7 +/- 0.13-fold (P < 0.01), respectively. POMC promoter activity, assayed by a -706/+64 rat POMC promoter-luciferase construct, was stimulated by 0.5 x 10(-9) M IL-11 (1.9 +/- 0.06-fold; P < 0.001) and 5 mM Bu2cAMP (7.1 +/- 0.52-fold, P < 0.001), and combined treatment of IL-11 plus Bu2cAMP caused a synergistic 11.7+/-0.71-fold increase ofluciferase activity (P < 0.001 vs. Bu2cAMP alone). Gene expression of SOCS-3, an intracellular inhibitor of cytokine action, peaked as early as 60 min after incubation with IL-11 (0.5 x 10(-9) M) and was induced 3.5-fold. In comparison to mock-transfected AtT-20 cells (AtT-20M), stable overexpression of SOCS-3 (AtT-20S) resulted in significant inhibition of ACTH secretion induced by IL-11 alone (1.5 +/- 0.09 vs. 1.1 +/- 0.04-fold induction, P < 0.01) and IL-11 plus Bu2cAMP (2.1 +/- 0.21 vs. 1.5 +/- 0.06-fold, P < 0.05), but not by Bu2cAMP alone (1.5 +/- 0.12 vs. 1.4 +/- 0.06). In summary, human and murine pituitary express IL-11 and IL-11R transcripts. In murine corticotroph AtT-20 cells, IL- 11 induces POMC gene transcription and ACTH secretion. IL-11 induction of SOCS-3 indicates an intracellular negative feedback control of cytokine-induced POMC expression and ACTH secretion. Thus, IL-11 regulates the HPA axis similarly to LIF, providing further evidence for a redundant cytokine network in the neuro-immuno-endocrine regulation of the HPA axis.

Function of a C-rich sequence in the polypyrimidine/polypurine tract of the promoter of the chicken malic enzyme gene depends on promoter context

The promoters of many genes contain C-rich polypyrimidine/polypurine (PPY/PPU) sequences that are important for gene expression. The promoter of the chicken malic enzyme gene contains a long PPY/PPU tract that can act as an alternative promoter. This tract can be separated functionally into a C-rich and (CT)7 sequences. The (CT)7 region together with some 3' nucleotides is essential for function of the alternative transcription start site and the C-rich sequence as a regulatory element. In constructs that contained the PPY/PPU tract or the -147/+31-bp promoter of the malic enzyme gene connected to a reporter gene, deletion of the C-rich region increased gene expression. In constructs containing 5.8-kb 5'-flanking DNA of the gene, deletion of the same C-rich region decreased expression of the reporter gene. Positive function of the C-rich sequence required two upstream DNA regions, -237 to -147 bp and -3474 to -2715 bp. To understand the mechanism(s) by which the same sequence exerts different effects, we examined the transcription start sites in the construct where the C-rich region was deleted. We directly visualized transcription start sites by performing 5'-rapid amplification of cDNA ends and a subsequent primer extension on a single-stranded template. Deletion of the C-rich region from constructs containing 5.8 kb of 5'-flanking DNA almost completely abolished transcription initiation from the PPY/PPU promoter and reduced transcription from the major endogenous start site. DEAE fractionation of hepatic nuclear extract revealed more than 10 proteins that bound specifically to C-rich DNA. These results suggest that interactions between upstream DNA elements and the C-rich sequence and the selective use of DNA-binding activities may bestow different functions on the same nucleotide sequence.

epicardin: A novel basic helix-loop-helix transcription factor gene expressed in epicardium, branchial arch myoblasts, and mesenchyme of developing lung, gut, kidney, and gonads

We report the cloning, chromosomal localization, and analysis of the expression pattern of epicardin, a member of the basic helix-loop-helix (bHLH) family of transcription factors. Within its bHLH domain, the human and murine epicardin genes were most similar to paraxis, a bHLH gene important for segmentation of embryonic paraxial mesoderm. In situ hybridization studies revealed strong epicardin expression in murine embryos at 9.5 days postcoitum (dpc) in a region of the septum transversum at the base of the heart known as the proepicardial organ. This mesenchymal structure extends villous projections from which epicardial precursor cells emerge and migrate out over the surface of the myocardium. Strong expression was seen in individual migratory cells and clusters at 9.5 dpc and in a continuous epicardial cell layer in more mature hearts. Also from 9.5 dpc, epicardin transcripts were seen in endocardial cushions of the atrioventricular canal and outflow tract, in skeletal myoblasts within branchial arches and in condensing mesenchyme of gut, kidney, urinary tract, gonads, spleen, and lung. Northern analysis showed that expression persisted in mature visceral organs and heart, but was transient in skeletal muscle. The central role played by bHLH factors in pathways for tissue determination in the embryo suggests a function for epicardin in specification of select mesodermal cell populations associated with heart, cranial skeletal muscle, gut, and urogenital system.

musculin: a murine basic helix-loop-helix transcription factor gene expressed in embryonic skeletal muscle

We describe the embryonic expression of musculin, a new murine member of the bHLH family of transcription factors. Musculin protein is closely related to human ABF-1, which is expressed in activated B cells, and to epicardin/capsulin/Pod-1, which is expressed in branchial myoblasts, visceral and urogenital mesoderm and epicardium. In situ hybridisation revealed musculin expression in embryos was largely restricted to the embryonic skeletal muscle lineage. While all skeletal muscles expressed the gene, only a subset of myocytes within each muscle were positive, indicating molecular heterogeneity within fetal muscle.

Leukemia inhibitory factor: part of a large ingathering family

Leukemia Inhibitory Factor (LIF) has a wide variety of biological activities. It regulates the differentiation of embryonic stem cells, neural cells, osteoblasts, adipocytes, hepatocytes and kidney epithelial cells. It also triggers the proliferation of myoblasts, primordial germ cells and some endothelial cells. Many of these biological functions parallel those of interleukin-6, Oncostatin M, ciliary neurotrophic factor, interleukin-11 and cardiotrophin-1. These structurally related cytokines also share subunits of their receptors which could partially explain the redundancy in this system of soluble mediators. In vivo LIF proves important in regulating the inflammatory response by fine tuning of the delicate balance of at least four systems in the body, namely the immune, the hematopoietic, the nervous and the endocrine systems. Although we are far from its therapeutic applications, the fast increasing knowledge in this field may bring new insights for the understanding of the cytokine biology in general.

Infertility in female mice lacking the receptor for interleukin 11 is due to a defective uterine response to implantation

During early pregnancy, in response to the implanting embryo, the surrounding uterine stroma undergoes a dramatic transformation into a specialized tissue known as the decidua. The decidua encapsulates the developing embryo, facilitating nutrient transfer and limiting trophoblast invasion. Here we show that female mice with a null mutation of the interleukin-11 receptor alpha chain are infertile because of defective decidualization. A temporal analysis revealed IL-11 expression is maximal in the normal pregnant uterus at the time of decidualization, and in situ hybridization studies showed expression of the IL-11 and the IL-11 receptor alpha chain in the developing decidual cells. These observations reveal a previously unrecognized critical role for IL-11 signaling in female reproduction.

Approaches to DNA mutagenesis: an overview

In the last several years, the use of double-stranded DNA templates together with thermostable-polymerase PCR has essentially replaced the use single-stranded DNA templates using the thermolabile polymerase for in vitro mutagenesis. Numerous PCR methods are now available, such as overlap-extension PCR, megaprimer PCR, and inverse PCR. All these PCR methods are reliable, effective, and convenient, although they are more prone to high rates of spontaneous error in mutant DNAs than are methods using thermolabile polymerases. Some improvements, such as the introduction of methylated templates, have been employed to minimize PCR errors. On the other hand, because of the introduction of many selection measures (e.g., restoration of antibiotic resistance, restoration of replication origin and unique site elimination), both double-stranded and single-stranded DNAs can now be used as templates for mutagenesis using thermolabile polymerase methods. For PCR methods, selection measures such as nested PCR has developed. All these selection measures have greatly improved the efficiency of mutagenesis by removing wild-type templates prior to transformation. Many efficient methods are available for both SDM and REM. Mutations can be introduce in vitro or in vivo, either by mutagenic primers or by erroneous DNA synthesis. Thus, choices largely depend on the experimental needs and resources of the investigator.

Recombinant Soluble Interleukin-11 (IL-11) Receptor α-Chain Can Act as an IL-11 Antagonist

We have expressed a soluble N-glycosylated form of the murine interleukin-11 (IL-11) receptor α-chain (sIL-11R) and examined signaling in cells expressing the gp130 molecule. In the presence of gp130 but not the transmembrane IL-11R, the sIL-11R mediated IL-11–dependent differentiation of M1 leukemic cells and proliferation in Ba/F3 cells. Early intracellular events stimulated by the sIL-11R including phosphorylation of gp130, STAT 3, and SHP-2 were similar to signaling through the transmembrane IL-11R. IL-11 bound to sIL-11R with low affinity (kd 10 to 50 nmol/L). Binding of sIL-11R to gp130 was IL-11 dependent with intermediate affinity (kd 1.5 to 3.0 nmol/L). However, the concentration of IL-11 required for signaling through the sIL-11R was 10- to 20-fold greater than that required for cells expressing the transmembrane IL-11R and gp130 in the absence of sIL-11R. Furthermore, the sIL-11R was capable of antagonizing the activity of IL-11 when tested on cells expressing the transmembrane IL-11R and gp130. We propose that the observed IL-11 antagonism by the sIL-11R may depend on limiting numbers of gp130 molecules on cells already expressing the transmembrane IL-11R.

Recombinant Soluble Interleukin-11 (IL-11) Receptor α-Chain Can Act as an IL-11 Antagonist

We have expressed a soluble N-glycosylated form of the murine interleukin-11 (IL-11) receptor α-chain (sIL-11R) and examined signaling in cells expressing the gp130 molecule. In the presence of gp130 but not the transmembrane IL-11R, the sIL-11R mediated IL-11–dependent differentiation of M1 leukemic cells and proliferation in Ba/F3 cells. Early intracellular events stimulated by the sIL-11R including phosphorylation of gp130, STAT 3, and SHP-2 were similar to signaling through the transmembrane IL-11R. IL-11 bound to sIL-11R with low affinity (kd 10 to 50 nmol/L). Binding of sIL-11R to gp130 was IL-11 dependent with intermediate affinity (kd 1.5 to 3.0 nmol/L). However, the concentration of IL-11 required for signaling through the sIL-11R was 10- to 20-fold greater than that required for cells expressing the transmembrane IL-11R and gp130 in the absence of sIL-11R. Furthermore, the sIL-11R was capable of antagonizing the activity of IL-11 when tested on cells expressing the transmembrane IL-11R and gp130. We propose that the observed IL-11 antagonism by the sIL-11R may depend on limiting numbers of gp130 molecules on cells already expressing the transmembrane IL-11R.

Adult Mice With Targeted Mutation of the Interleukin-11 Receptor (IL11Ra) Display Normal Hematopoiesis

Interleukin-11 (IL-11) is a pleiotropic growth factor with a prominent effect on megakaryopoiesis and thrombopoiesis. The receptor for IL-11 is a heterodimer of the signal transduction unit gp130 and a specific receptor component, the α-chain (IL-11Rα). Two genes potentially encode the IL-11Rα: the IL11Ra and IL11Ra2 genes. The IL11Ra gene is widely expressed in hematopoietic and other organs, whereas the IL11Ra2 gene is restricted to only some strains of mice and its expression is confined to testis, lymph node, and thymus. To investigate the essential actions mediated by the IL-11Rα, we have generated mice with a null mutation of IL11Ra (IL11Ra−/−) by gene targeting. Analysis of IL11Ra expression by Northern blot and reverse transcriptase-polymerase chain reaction, as well as the absence of response of IL11Ra−/− bone marrow cells to IL-11 in hematopoietic assays, further confirmed the null mutation. Compensatory expression of the IL11Ra2 in bone marrow cells was not detected. IL11Ra−/− mice were healthy with normal numbers of peripheral blood white blood cells, hematocrit, and platelets. Bone marrow and spleen contained normal numbers of cells of all hematopoietic lineages, including megakaryocytes. Clonal cultures did not identify any perturbation of granulocyte-macrophage (GM), erythroid, or megakaryocyte progenitors. The number of day-12 colony-forming unit-spleen progenitors were similar in wild-type and IL11Ra−/− mice. The kinetics of recovery of peripheral blood white blood cells, platelets, and bone marrow GM progenitors after treatment with 5-flurouracil were the same in IL11Ra−/− and wild-type mice. Acute hemolytic stress was induced by phenylhydrazine and resulted in a 50% decrease in hematocrit. The recovery of hematocrit was comparable in IL11Ra−/− and wild-type mice. These observations indicate that IL-11 receptor signalling is dispensable for adult hematopoiesis.

Adult Mice With Targeted Mutation of the Interleukin-11 Receptor (IL11Ra) Display Normal Hematopoiesis

Interleukin-11 (IL-11) is a pleiotropic growth factor with a prominent effect on megakaryopoiesis and thrombopoiesis. The receptor for IL-11 is a heterodimer of the signal transduction unit gp130 and a specific receptor component, the α-chain (IL-11Rα). Two genes potentially encode the IL-11Rα: the IL11Ra and IL11Ra2 genes. The IL11Ra gene is widely expressed in hematopoietic and other organs, whereas the IL11Ra2 gene is restricted to only some strains of mice and its expression is confined to testis, lymph node, and thymus. To investigate the essential actions mediated by the IL-11Rα, we have generated mice with a null mutation of IL11Ra (IL11Ra−/−) by gene targeting. Analysis of IL11Ra expression by Northern blot and reverse transcriptase-polymerase chain reaction, as well as the absence of response of IL11Ra−/− bone marrow cells to IL-11 in hematopoietic assays, further confirmed the null mutation. Compensatory expression of the IL11Ra2 in bone marrow cells was not detected. IL11Ra−/− mice were healthy with normal numbers of peripheral blood white blood cells, hematocrit, and platelets. Bone marrow and spleen contained normal numbers of cells of all hematopoietic lineages, including megakaryocytes. Clonal cultures did not identify any perturbation of granulocyte-macrophage (GM), erythroid, or megakaryocyte progenitors. The number of day-12 colony-forming unit-spleen progenitors were similar in wild-type and IL11Ra−/− mice. The kinetics of recovery of peripheral blood white blood cells, platelets, and bone marrow GM progenitors after treatment with 5-flurouracil were the same in IL11Ra−/− and wild-type mice. Acute hemolytic stress was induced by phenylhydrazine and resulted in a 50% decrease in hematocrit. The recovery of hematocrit was comparable in IL11Ra−/− and wild-type mice. These observations indicate that IL-11 receptor signalling is dispensable for adult hematopoiesis.

The gene for the human interleukin-11 receptor alpha chain locus is highly homologous to the murine gene and contains alternatively spliced first exons

The gene for the murine interleukin-11 receptor alpha chain (mIL-11R alpha) contains two loci (1 and 2), of which locus 2 is restricted to only some mouse strains. Two alternatively spliced exons (1a and 1b) encode the 5' untranslated region (5'UTR) of the murine locus 1. We have characterized the gene for the human interleukin-11 receptor alpha chain locus (hIL-11R alpha), examined its expression by Northern analysis and determined its chromosomal location by fluorescence in situ hybridization. The presence of exon(s) encoding the 5'UTR and mapping of transcription initiation sites was determined by reverse-transcriptase polymerase chain reaction and 5' rapid amplification of cDNA ends (5'RACE) techniques. The human locus spanned 10 kilobasepairs (kb) and consisted of 14 exons. Two alternatively spliced first exons (1a and 1b) encoding the 5'UTR were identified and shared 76 and 73% nucleotide identity with murine exons 1a and 1b. Multiple transcription start sites were demonstrated for human exon 1a. The promoter regions of both human exons 1a and 1b did not display a canonical TATA box. A predominant 1.8 kb transcript for the hIL-11R alpha was present in heart, brain, skeletal muscle, lymph nodes, thymus, appendix, pancreas and foetal liver. The hIL-11R alpha gene was localized to chromosome 9p13. In summary, the hIL-11R alpha gene was highly related to locus 1 of the murine gene and there was no evidence of a second hIL-11R alpha locus.

Identification of a second murine interleukin-11 receptor alpha-chain gene (IL11Ra2) with a restricted pattern of expression

The interleukin-11 receptor alpha-chain, a member of the hematopoietin receptor superfamily, forms, together with gp130, a functional high-affinity receptor complex for interleukin 11. We, and others, reported the cloning of the murine interleukin 11 receptor alpha-chain cDNA (IL11Ra) and recently described the structure of the IL11Ra locus. We also described the presence of a second IL11Ra-like locus in some mouse strains. In this study we report that the second locus, designated IL11Ra2, encodes an mRNA species. The transcript was 99% identical to the IL11Ra transcript in the coding and 3'-untranslated region, but had a different 5'-untranslated region. The complete genomic organization of the IL11Ra2 locus is presented, and the two loci are shown to be located on a 200-kb NaeI genomic fragment. Comparison of the expression pattern of the IL11Ra and IL11Ra2 genes using an RT-PCR restriction fragment length polymorphism strategy revealed that while the expression of IL11Ra was widespread, expression of IL11Ra2 was restricted to testis, lymph node, and thymus.

Two differentially expressed interleukin-11 receptor genes in the mouse genome

Interleukin-11 (IL-11) is a multifunctional cytokine involved in the regulation of cell proliferation and differentiation in a variety of cell types and tissues in vitro and in vivo. The effects of IL-11 were shown to be mediated by the IL-11 receptor (hereafter referred to as IL-11 R alpha), which is a ligand-binding subunit and provides ligand specificity in a functional multimeric signal-transduction complex with gp130. Here we show that the mouse genome contains a second gene encoding an IL-11-binding protein, referred to as IL-11R beta. The structure of the IL-11R beta gene is highly similar to that of IL-11R alpha, and IL-11R beta exhibits 99% sequence identity with IL-11R alpha at the amino acid level. IL-11R beta is co-expressed with IL-11R alpha, albeit at lower levels, in embryos and in various adult tissues. IL-11R beta transcripts are abundant in testis, and, in contrast with IL-11R alpha, absent from skeletal muscle. IL-11R beta expressed in vitro binds IL-11 with high affinity, suggesting that the mouse genome contains a second functional IL-11R.

Cytokine receptor signal transduction and the control of hematopoietic cell development

The cytokine receptor superfamily is characterized by structural motifs in the exoplasmic domain and by the absence of catalytic activity in the cytosolic segment. Activated by ligand-triggered multimerization, these receptors in turn activate a number of cytosolic signal transduction proteins, including protein tyrosine kinases and phosphatases, and affect an array of cellular functions that include proliferation and differentiation. Molecular study of these receptors is revealing the roles they play in the control of normal hematopoiesis and in the development of disease.