Recombinant human interleukin-11 synergizes with steel factor and interleukin-3 to promote directly the early stages of murine megakaryocyte development in vitro

The authors studied the role that interleukin (IL)-11 plays during the early stages of megakaryocyte (MK) development by investigating its in vitro effects on cell subpopulations enriched for bone marrow primitive progenitor cells and early and late committed progenitor cells. Progenitor subpopulations were isolated from bone marrow of normal or 5-fluorouracil (5FU)-treated mice and separated by sorting based on the surface antigens Sca-1, c-kit, and CD34. Functional analysis of the cell subpopulations, 5FU Lin(-)Sca-1(+)c-kit(+) or normal bone marrow (NBM) Lin(-)Sca-1(+)c-kit(+)CD34(-)cells, indicated that exposure of these cells to recombinant human (rh)IL-11 in combination with steel factor (SF) stimulates the formation of colonies in methylcellulose and their proliferation in single cell-containing liquid cultures. Kinetic studies of MK progenitor generation, in response to SF and rhIL-11, demonstrated that a significant number of the progenitors produced are committed to the MK lineage. RhIL-11 also synergized with both SF and IL-3 to stimulate MK colony growth from NBM Lin(-)Sca-1(+)c-kit(+) cells (early progenitors) and NBM Lin(-)Sca-1(-)c-kit(+) cells (committed late progenitors). In the presence of IL-3, NBM, Lin(-)Sca-1(-)c-kit(+) cells responded more strongly to rhIL-11 than SF. Consistent with these results is the observation that IL-11 receptor alpha chain mRNA is present in all the progenitor cells from which the MKs are derived. This cell culture and RNA analysis suggest that murine bone marrow primitive progenitor cells and early and late progenitor cells are direct targets of rhIL-11 and that rhIL-11 has the potential to promote megakaryocyte development at several very early stages. (Blood, 2000;95:503-509) (Blood. 2000;95:503-509)

Lack of expression of Gp-130 makes pancreatic beta cell lines unresponsive to the IL-6 family of cytokines

Cytokine receptors from the IL-6 receptor family are comprised of ligand specific alpha chains and a common signalling chain, gp-130, which is also required for high affinity binding. A cDNA library generated from the beta-TC3 SV40 T-antigen transformed insulinoma cell line was screened for members of this receptor family potentially relevant to both beta cell development and autoimmunity. Degenerate oligonucleotide primers to a consensus region of these receptors were used and the IL-11 receptor alpha chain was identified. Despite confirmation of IL-11 receptor mRNA expression, iodinated bioactive IL-11 did not bind specifically to beta-TC3 cells and gp-130-dependent cytokines did not elicit signalling events in beta cell lines. This was explained by absence of gp-130 protein or mRNA in the beta cell lines tested and in primary islets. We conclude from these results that the previously recognised effects of IL-6 family member cytokines on pancreatic islets must be indirect via other non-beta cells within the islet, rather than due to direct effects on beta cells themselves.

Emergence of excitotoxicity in cultured forebrain neurons coincides with larger glutamate-stimulated [Ca(2+)](i) increases and NMDA receptor mRNA levels

We examined several factors related to the increase in susceptibility to excitotoxicity that occurs in embryonic forebrain neurons over time in culture. Neuronal cultures were resistant to a 5-min exposure to 100 microM glutamate/10 microM glycine at 5 days in vitro (DIV), but became vulnerable to the same stimulus by 14 DIV. We used the fluorescent indicators, fura-2 and magfura-2, which have high and low affinity for Ca(2+), respectively, to measure changes in [Ca(2+)](i). Glutamate-stimulated increases in the fura-2 and magfura-2 ratio reached maximum values by 10 DIV. Fura-2 reported similar [Ca(2+)](i) changes with exposure to 3 or 100 microM glutamate for 5 min, whereas magfura-2 reported larger [Ca(2+)](i) increases with 5-min exposure to 100 microM glutamate than with exposure to 3 microM glutamate, 100 microM kainate or 50 mM K(+) from 10 DIV onward. This suggests that the magnitude of the [Ca(2+)](i) changes correlated with the excitotoxicity potential of a stimulus when magfura-2, but not fura-2, was used to measure Ca(2+). We also used RNase protection assays to measure NMDA receptor subunit mRNA levels. NR1 and NR2A mRNA increased continuously over time in culture, whereas NR2B mRNA increased dramatically during the first 10 days and subsequently remained stable. The time course of the increase in NR2B mRNA most closely followed the increase in glutamate-stimulated changes in the magfura-2 signal and neuronal injury. Therefore, the increases in the glutamate-stimulated [Ca(2+)](i) responses and NMDA receptor subunit mRNA levels (especially NR2B) are likely involved in the development of susceptibility to excitotoxicity in cultured rat forebrain neurons.

Molecular cloning of a novel CC chemokine, interleukin-11 receptor alpha-locus chemokine (ILC), which is located on chromosome 9p13 and a potential homologue of a CC chemokine encoded by molluscum contagiosum virus

Molluscum contagiosum virus (MCV) encodes a CC chemokine MC148R which is likely to have been acquired from the host. By a homology search employing MC148R as a probe, we have identified a novel CC chemokine whose gene exists next to the IL-11 receptor alpha (IL-11Ralpha) gene in both humans and mice. Thus, this chemokine maps to chromosome 9p13 in humans where IL-11Ralpha has been assigned. We term this novel chemokine IL-11Ralpha-locus chemokine (ILC). ILC has the highest homology to MC148R among the known human CC chemokines. Furthermore, ILC is strongly and selectively expressed in the skin where infection of MCV also takes place. Thus, ILC is likely to be the original chemokine of MC148R.

Unilateral GluR2(B) hippocampal knockdown: a novel partial seizure model in the developing rat

Kainic acid (KA) induces status epilepticus in both adult and young rats but with different consequences on pathology and gene expression. In adults, GluR2(B) AMPA subunit expression is markedly reduced in CA3 neurons before neurodegeneration. In pups, the GluR2(B) subunit is sustained, possibly contributing to neuronal survival. Mechanisms underlying the reduced vulnerability of developing neurons to seizures was investigated by examining the effects of unilateral microinfusions of GluR2(B) antisense oligodeoxynucleotides (AS-ODNs) into the hippocampus of young rats in the presence or absence of a subconvulsive dose of KA. GluR2(B) AS-ODN infusions resulted in spontaneous seizure-like behavior, high stimulus intensity population spikes in the absence of long-term potentiation, and neurodegeneration of CA3 neurons lateral to the infusion site. Electroencephalography revealed paroxysmal activity and high-frequency high-amplitude discharges associated with vigorous and continuous scratching, wild running, or bilateral jerking movements. Pups lacking phenotypic behavior exhibited high-rhythmic oscillations and status epilepticus by the dose of KA used. Radiolabeled AS-ODNs accumulated throughout the ipsilateral dorsal hippocampus. GluR2(B) but not GluR1(A) receptor protein was markedly reduced after GluR2(B) knockdown. In contrast, GluR1(A) knockdown reduced GluR1(A) but not GluR2(B) protein without change in behavior or morphology. Therefore, unilateral downregulation of hippocampal GluR2(B) but not GluR1(A) protein reduces the seizure threshold and survival of CA3 neurons in the immature hippocampus, possibly providing a novel partial seizure model in the developing rat.

Chimeric cytokine receptor can transduce expansion signals in interleukin 6 receptor alpha (IL-6Ralpha)-, IL-11Ralpha-, and gp130-low to -negative primitive hematopoietic progenitors

We generated transgenic mice expressing chimeric receptors, which comprise extracellular domains of the human granulocyte-macrophage colony-stimulating factor (hGM-CSF) receptor and transmembrane and cytoplasmic domains of the mouse leukemia inhibitory factor receptor. In suspension cultures of lineage-negative (Lin(-)), 5-fluorouracil-resistant bone marrow cells of the transgenic mice, a combination of hGM-CSF and stem cell factor (SCF) induced exponential expansions of mixed colony-forming unit. The combination of hGM-CSF and SCF was effective on enriched, Lin(-)Sca-1(+)c-kit(+) progenitors and increased either mixed colony-forming unit or cobblestone area-forming cells. In case of stimulation with hGM-CSF and SCF, interleukin-6 (IL-6) and SCF, or IL-11 and SCF, the most efficient expansion was achieved with hGM-CSF and SCF. When Lin(-)Sca-1(+)c-kit(+)CD34(-) further enriched progenitors were clone sorted and individually incubated in the presence of SCF, hGM-CSF stimulated a larger number of cells than did IL-6, IL-6 and soluble IL-6 receptor (IL-6R), or IL-11. These data suggest the presence of IL-6Ralpha-, IL-11Ralpha-, and gp130-low to -negative primitive hematopoietic progenitors. Such primitive progenitors are equipped with signal transduction molecules and can expand when these chimeric receptors are genetically introduced into the cells and stimulated with hGM-CSF in the presence of SCF.

Differential expression of glutamate receptors by the dopaminergic neurons of the primate striatum

Neostriatal neurons are targets of glutamatergic input from the cortex and thalamus. Glutamate receptors are abundantly, but differentially, expressed by the striatal neurons. We previously described the presence of dopaminergic cells intrinsic to the primate striatum that increase in number following MPTP treatment. In this study we have used double-label immunocytochemistry to analyze the expression of the glutamate receptor subunits GluR1, GluR2/3, NR1, mGluR1, and mGluR5 in the dopaminergic cells of the striatum. Our results show that 75% of these cells express GluR1 while 25% of them express NR1. They do not express GluR2/3 or the group 1 metabotropic receptors. Our results suggest that this potentially important population of cells expresses only calcium-permeable ionotropic glutamate receptors. We speculate that glutamate may play a role in regulating the number of these dopaminergic neurons after MPTP treatment and may also influence their ability to release dopamine.

Hematopoietic, immunomodulatory and epithelial effects of interleukin-11

Interleukin 11 (IL-11) is a pleiotropic cytokine with biological activities on many different cell types. Recombinant human IL-11 (rhIL-11) is produced by recombinant DNA technology in Escherichia coli. Both in vitro and in vivo, rhIL-11 has shown effects on multiple hematopoietic cell types. Its predominant in vivo hematopoietic activity is the stimulation of peripheral platelet counts in both normal and myelosuppressed animals. This activity is mediated through effects on both early and late progenitor cells to stimulate megakaryocyte differentiation and maturation. rhIL-11 has been approved for the treatment of chemotherapy-induced thrombocytopenia. The hematopoietic effects of rhIL-11 are most likely direct effects on progenitor cells and megakaryocytes in combination with other cytokines or growth factors. rhIL-11 also induces secretion of acute phase proteins (ferritin, haptoglobin, C-reactive protein, and fibrinogen) from the liver. The induction of heme oxidase and inhibition of several P450 oxidases have been reported from in vitro studies. In vivo, rhIL-11 treatment decreases sodium excretion by the kidney by an unknown mechanism and induces hemodilution. rhIL-11 also exhibits anti-inflammatory effects in a variety of animal models of acute and chronic inflammation, including inflammatory bowel disease, inflammatory skin disease, autoimmune joint disease, and various infection-endotoxemia syndromes. rhIL-11 has trophic effects on non-transformed intestinal epithelium under conditions of mucosal damage. The mechanism of the anti-inflammatory activity of rhIL-11 has been extensively studied. rhIL-11 directly affects macrophage and T cell effector function. rhIL-11 inhibits tumor necrosis factor-alpha (TNF alpha), interleukin 1beta (IL-1beta), interleukin 12 (IL-12), interleukin 6 (IL-6), and nitric oxide (NO) production from activated macrophages in vitro. The inhibition of cytokine production was associated with inhibition of nuclear translocation of the transcription factor, nuclear factor kappa B (NF-kappaB). The block to NF-kappaB nuclear translocation correlates with the ability of rhIL-11 to maintain or enhance production of the inhibitors of NF-kappaB, IkappaB-alpha and IkappaB-beta. In addition to effects on macrophages, rhIL-11 also reduces CD4+ T cell production of Th1 cytokines, such as IFN gamma induced by IL-12, while enhancing Th2 cytokine production. rhIL-11 also blocks IFN gamma production in vivo. The molecular effects of rhIL-11 have also been studied in a clinical trial. Molecular analysis of skin biopsies of patients with psoriasis before and during rhIL-11 treatment demonstrates a decrease in mRNA levels of TNF alpha, IFN gamma and iNOS. These activities suggest that in addition to its thrombopoietic clinical use, rhIL-11 may also be valuable in the treatment of inflammatory diseases. The clinical utility of the anti-inflammatory properties of rhIL-11 is being investigated in patients with Crohn's disease, psoriasis and rheumatoid arthritis. These diseases are believed to be initiated and maintained by activated CD4+ Th1 cells in conjunction with activated macrophages.

Interleukin-11 (IL-11) enhances clonal proliferation of acute myelogenous leukemia cells with strong expression of the IL-11 receptor alpha chain and signal transducing gp130

We examined the effect of recombinant human interleukin (IL)-11 alone or in combination with various colony-stimulating factors (CSFs), including IL-3, granulocyte/macrophage (GM)-CSF, granulocyte (G)-CSF, stem cell factor (SCF), flt3 ligand (FL), and thrombopoietin (TPO), on colony formation by leukemic progenitor cells (L-CFU) obtained from 33 patients with acute myelogenous leukemia (AML). Leukemic colony formation was found in approximately 70 to 80% of the patients in the presence of at least one of the above CSFs. Although IL-11 alone did not support L-CFU, the growth of these progenitors in the presence of other cytokines was enhanced by IL-11 in 16 out of 33 patients and it showed a synergistic action with G-CSF in 12 of them. This synergistic action occurred in seven out of nine M5 patients (French-American-British (FAB) classification). A single cell clone-sorting experiment clearly demonstrated that this synergistic effect was operative at the single progenitor cell level. The number of leukemic cells proliferating in the presence of G-CSF+IL-11 was significantly higher than in the presence of G-CSF alone, suggesting that IL-11 recruited dormant leukemic progenitors into the cell cycle. Flow cytometric analysis revealed that all types of AML blast cells (M0 approximately M6) ubiquitously expressed gp130, although the level of expression was significantly higher in M5 cells. In contrast, expression of the IL-11 receptor alpha chain (IL-11Ralpha) varied between FAB types. Blast cells obtained from M1, M3 and M5 patients showed higher levels of expression, with M5 cells showing the strongest expression. Interestingly, the leukemic progenitor cells for which proliferation was synergistically enhanced by IL-11 had significantly higher expression of both IL-11Ralpha and gp130. These results suggest that administration of IL-11 in vivo may stimulate the proliferation of leukemic progenitor cells, particularly M5 cells, in the presence of G-CSF, and that the responsiveness of L-CFU to IL-11 may be predicted by a simple receptor assay.

A fusion protein of interleukin-11 and soluble interleukin-11 receptor acts as a superagonist on cells expressing gp130

Interleukin-11 is a hematopoietic cytokine that signals via the signal transducer gp130. Although gp130 is ubiquitously expressed, interleukine-11 responsiveness is restricted to cells that express the interleukine-11 receptor alpha-subunit. The interleukine-11 receptor alpha-subunit can be functionally replaced by its soluble form indicating that the transmembrane and cytoplasmic parts are not required for signal transduction. Here, we show that a recombinant fusion protein of a fragment of the human interleukine-11 receptor alpha-subunit ectodomain linked to human interleukine-11 acts as a superagonist on cells expressing gp130 but lacking the membrane-bound interleukine-11 receptor alpha-subunit. It induces acute phase protein synthesis in hepatoma cells and efficiently promotes proliferation of Ba/F3 cells stably, transfected with gp130. In these bioassays, the fusion protein of a fragment of the human interleukine-11 receptor alpha-subunit ectodomain linked to human interleukine-11 is 50 times more potent than the combination of interleukine-11 and the soluble interleukine-11 receptor alpha-subunit. Thus, our findings support the concept that covalent fusion of two soluble proteins required for receptor activation dramatically increases their bioactivity.

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.

Identification of three distinct receptor binding sites of murine interleukin-11

Interleukin-11 (IL-11) is a member of the gp130 family of cytokines. These cytokines drive the assembly of multisubunit receptor complexes, all of which contain at least one molecule of the transmembrane signaling receptor gp130. A complex of IL-11 and the IL-11 receptor (IL-11R) has been shown to interact with gp130, with high affinity, and to induce gp130- dependent signaling. In this study, we have identified residues crucial for the binding of murine IL-11 (mIL-11) to both the IL-11R and gp130 by examining the activities of mIL-11 mutants in receptor binding and cell proliferation assays. The location of these residues, as predicted from structural studies and a model of IL-11, reveals that mIL-11 has three distinct receptor binding sites. These are structurally and functionally analogous to the previously defined receptor binding sites I, II, and III of interleukin-6 (IL-6). This supports the hypothesis that IL-11 signals via the formation of a hexameric receptor complex and indicates that site III is a generic feature of cytokines that signal via association with gp130.

Activation of the signal transducer glycoprotein 130 by both IL-6 and IL-11 requires two distinct binding epitopes

The coordination and regulation of immune responses are primarily mediated by cytokines that bind to specific cell surface receptors. Glycoprotein 130 (gp130) belongs to the family of class I cytokine receptors and is the common signal-transducing receptor subunit shared by the so-called IL-6 type cytokines (IL-6, IL-11, ciliary neurotrophic factor, leukemia inhibitory factor, oncostatin M, and cardiotrophin-1). The inflammatory cytokines IL-6 and IL-11 induce gp130 homodimerization after binding to their specific alpha receptors, which leads to the activation of the Janus kinase/STAT signal transduction pathway. A molecular model of IL-6/IL-6R/gp130, which is based on the structure of the growth hormone/growth hormone receptor complex, allowed the selection of several amino acids located in the cytokine-binding module of gp130 for mutagenesis. The mutants were analyzed with regard to IL-6- or IL-11-induced STAT activation and ligand binding. It was found that Y190 and F191 are essential for the interaction of gp130 with IL-6 as well as IL-11, suggesting a common mode of recognition of helical cytokines by class I cytokine receptors. Furthermore, the requirement of the gp130 N-terminal Ig-like domain for ligand binding and signal transduction was demonstrated by the use of deletion mutants. Thus, besides the observed analogy to the growth hormone/growth hormone receptor complex, there is a substantial difference in the mechanism of receptor engagement by cytokines that signal via gp130.

Trophic effects of cardiotrophin-1 and interleukin-11 on rat dorsal root ganglion neurons in vitro

Cardiotrophin-1 (CT-1) was originally isolated for its hypertrophy inducing effects on cardiac myocytes whereas interleukin-11 (IL-11) was identified due to its ability to stimulate an interleukin-6 (IL-6) dependent plasmocytoma cell line. Both cytokines are structurally and functionally related to a group of factors called neuropoietic cytokines, which also includes IL-6, ciliary neurotrophic factor (CNTF), leukemia inhibitory factor (LIF), and oncostatin M. These factors have trophic effects on subsets of neurons. In the present study we examined the influence of CT-1 and IL-11 on newborn rat dorsal root ganglion neuron survival in vitro. Mouse CT-1 showed prominent trophic effects that were comparable to those of CNTF and LIF. Mouse IL-11 alone did not enhance neuronal survival, but soluble mouse IL-11 receptor alpha rendered neurons sensitive to IL-11. Surprisingly, soluble IL-11 receptor alpha even had slight neurotrophic effects by itself. These results suggest that CT-1 and IL-11 might also be involved in the physiological regulation of sensory neuron survival. Thus, they might, like CNTF, become tools for the therapeutic intervention in neurodegeneration due to disease, toxicity, and trauma.

Mutual education between hematopoietic cells and bone marrow stromal cells through direct cell-to-cell contact: factors that determine the growth of bone marrow stroma-dependent leukemic (HB-1) cells

A stroma-dependent cell line (HB-1) was established from myelogenous leukemic cells of CBA/N mouse. Characterization of the cells showed that HB-1 proliferated on hematopoietic supportive stromal cells (MS-10), but did not survive or proliferate on hematopoietic nonsupportive cells (MS-K). Direct contact between HB-1 and MS-10 appears to be necessary for HB-1 to proliferate on MS-10. We found that interleukin-1alpha (IL-1alpha) produced by MS-10 plays a major role in the survival and proliferation of HB-1. IL-11 did not support the proliferation of HB-1 cells by itself, but enhanced the proliferation of HB-1 cells in the presence of IL-1alpha. The expression of IL-1alpha and IL-11 was induced in MS-10 by the direct contact with HB-1 cells, and the expression of IL-1 receptor type I (IL-1RI) and interleukin-11 receptor (IL-11R) was induced in HB-1 cells by the attachment of the cells to MS-10. These findings show the existence of two-way interactions between HB-1 and MS-10.

Maternal IL-11Ralpha function is required for normal decidua and fetoplacental development in mice

In eutherian mammals, implantation and establishment of the chorioallantoic placenta are essential for embryo development and survival. As a maternal response to implantation, uterine stromal cells proliferate, differentiate, and generate the decidua, which encapsulates the conceptus and forms the maternal part of the placenta. Little is known about decidual functions and the molecular interactions that regulate its development and maintenance. Here we show that the receptor for the cytokine interleukin-11 (IL-11Ralpha) is required specifically for normal establishment of the decidua. Females homozygous for a hypomorphic IL-11Ralpha allele are fertile and their blastocysts implant and elicit the decidual response. Because of reduced cell proliferation, however, only small deciduae form. Mutant deciduae degenerate progressively, and consequently embryo-derived trophoblast cells generate a network of trophoblast giant cells but fail to form a chorioallantoic placenta, indicating that the decidua is essential for normal fetoplacentation. IL-11Ralpha is expressed in the decidua as well as in numerous other tissues and cell types, including the ovary and lymphocytes. The differentiation state and proliferative responses of B and T-lymphocytes in mutant females were normal, and wild-type females carrying IL-11Ralpha mutant ovaries had normal deciduae, suggesting that the decidualization defects do not arise secondarily as a consequence of perturbed IL-11Ralpha signaling defects in lymphoid organs or in the ovary. Therefore, IL-11Ralpha signaling at the implantation site appears to be required for decidua development.

Cotranscription and intergenic splicing of human galactose-1-phosphate uridylyltransferase and interleukin-11 receptor alpha-chain genes generate a fusion mRNA in normal cells. Implication for the production of multidomain proteins during evolution

In the past 10 years, much attention has been focused on transcription preinitiation complex formation as a target for regulating gene expression, and other targets such as transcription termination complex assemblage have been less intensively investigated. We established the existence of poly(A) site choice and fusion splicing of two adjacent genes, galactose-1-phosphate uridylyltransferase (GALT) and interleukin-11 receptor alpha-chain (IL-11Ralpha), in normal human cells. This 16-kilobase (kb) transcription unit contains two promoters (the first one is constitutive, and the second one, 8 kb downstream, is highly regulated) and two cleavage/polyadenylation signals separated by 12 kb. The promoter from the GALT gene yields two mRNAs, a 1.4-kb mRNA encoding GALT and a 3-kb fusion mRNA when the first poly(A) site is spliced out and the second poly(A) is used. The 3-kb mRNA codes for a fusion protein of unknown function, containing part of the GALT protein and the entire IL-11Ralpha protein. The GALT promoter/IL-11Ralpha poly(A) transcript results from leaky termination and alternative splicing. This feature of RNA polymerase (pol) II transcription, which contrasts with efficient RNA pol I and pol III termination, may be involved, together with chromosome rearrangements, in the generation of fusion proteins with multiple domains and would have major evolutionary implications in terms of natural processes to generate novel proteins with common motifs. Our results, together with accumulation of genomic informations, will stimulate new considerations and experiments in gene expression studies.

Suppression of interleukin-11-mediated bone resorption by cyclooxygenases inhibitors

We previously found that human melanoma (A375M) and human breast cancer (MDA-MB-231) cells formed osteolytic bone metastasis in vivo. These cancer cells produced interleukin-11 (IL-11) by themselves and stimulated its production from osteoblasts. Interleukin-11 could increase the number of osteoclasts and raise the calcium concentration in the medium of neonatal murine calvaria organ culture, indicating bone resorption in vitro. Therefore, IL-11 could play an important role in the promotion of osteolysis at the site of bone metastasis. In the present study, we used the calvaria culture system to try to clarify the mechanisms of IL-11-mediated bone resorption. The murine calvaria expressed both the specificity-determining alpha subunit and the signal-transducing beta subunit (gp130) of the IL-11 receptor. When IL-11 was added to the calvaria culture, the concentrations of prostaglandin E2 (PGE2) was elevated. Pretreatment of calvaria with cyclooxygenases inhibitors (e.g., indomethacin, NS-398, and dexamethasone) suppressed the production of PGE2 and the bone resorption induced by IL-11. Addition of exogenous PGE2 overcame the inhibitory effect of cyclooxygenases inhibitors and promoted bone resorption. These results indicate that IL-11 promotes bone resorption through a PGE2 synthesis-dependent mechanism and that cyclooxygenases inhibitors could be interesting drugs to suppress IL-11-mediated osteolytic bone metastasis of cancer cells.

Activation of the signal transducer gp130 by interleukin-11 and interleukin-6 is mediated by similar molecular interactions

The transmembrane glycoprotein gp130 is involved in many cytokine-mediated cellular responses and acts therein as the signal transducing receptor subunit. Interleukin-6 (IL-6) and interleukin-11 (IL-11), in complex with their specific alpha-receptors, homodimerize gp130 and, as a consequence, activate the Janus kinase (Jak)/signal transducer and activator of transcription (STAT) signalling pathway in their target cells. So far, it is not clear whether gp130 is bound to these cytokines and their specific alpha-receptor subunits through identical or different epitopes. In order to study the interaction of IL-11 and IL-11R with human gp130 the soluble form of the recently cloned human IL-11R was expressed in baculovirus-infected insect cells. By a coprecipitation binding-assay it is demonstrated that IL-11 and IL-6 compete for binding to gp130. Using deletion and point mutants of gp130 it is shown that IL-11-IL-11R and IL-6-IL-6R recognize overlapping binding motifs on gp130. Moreover, using well-established Jak-deficient cell lines we demonstrate that STAT activation by IL-11 requires Jak1. Taken together, our data support the concept that IL-6 and IL-11 activate gp130 by very similar molecular mechanisms.

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.

Recombinant soluble interleukin-11 (IL-11) receptor alpha-chain can act as an IL-11 antagonist

We have expressed a soluble N-glycosylated form of the murine interleukin-11 (IL-11) receptor alpha-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 human interleukin-11 directly promotes megakaryocytopoiesis in vitro

We have investigated the mechanism of action of the thrombopoietic cytokine, recombinant human interleukin-11 (rhIL-11), on megakaryocytopoiesis in vitro. We have shown that rhIL-11-induced murine and human megakaryocytopoiesis are not mediated by thrombopoietin (Tpo). Murine megakaryocytes (MKs) were produced from bone marrow (BM) mononuclear cells cultured with rhIL-11, IL-3, and a combination of the two cytokines. Conditioned media (CM) were collected and assayed for the presence of biologically active Tpo. Tpo activity was not detected in any of the CMs tested. Next, human BM CD34+ cells were cultured in serum-free fibrin clot medium with rhIL-11, IL-3, or rhIL-11 plus IL-3 and an antibody that neutralizes human Tpo activity. No inhibition of either burst-forming unit-MK- or colony-forming unit-MK-derived colony formation was observed. The antibody did partially inhibit steel factor-induced MK-colony formation, suggesting that the actions of this cytokine are mediated, in part, by Tpo. We determined that MKs can be direct targets of rhIL-11 by showing the expression of functional IL-11 receptor on these cells. Total RNA was prepared from cultured human BM CD41+CD14- cells (MKs) and IL-11 receptor alpha chain mRNA was detected in the MKs by reverse transcription-polymerase chain reaction. Analysis of single-sorted CD41+CD14- cells confirmed that the observed IL-11 receptor expression was not due to contaminating CD41- cells in the pool. The presence of rhIL-11 receptor alpha chain protein in the cells was established by Western blot analysis. After a short exposure of purified BM MKs to rhIL-11, enhanced phosphorylation of both its signal transduction subunit, gp130, and the transcription factor, STAT3 was detected, showing a direct activation of receptor signaling by the cytokine. Consistent with the lack of effect of rhIL-11 on platelets in vivo, IL-11 receptor alpha chain mRNA and protein were not detected in isolated human platelets. These data indicate that rhIL-11 acts directly on MKs and MK progenitors but not on platelets.

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 alpha-chain (IL-11R alpha). Two genes potentially encode the IL-11R alpha: 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-11R alpha, 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.

Reconstitution of two isoforms of the human interleukin-11 receptor and comparison of their functional properties

Long-term stable Ba/F3 transfectants (B13R alpha1 and B13R alpha2) expressing two isoforms of the human IL-IIR alpha receptor (alpha1 full length or alpha2 lacking the cytoplasmic domain) in combination with human gp130 were established. IL-11R alpha1 and IL-11R alpha2 were each expressed and detected as three bands upon Western blot analysis, with apparent molecular masses in agreement with those of the polypeptide backbone (47 and 44 kDa, respectively) with no, one or two N-linked sugars. B13R alpha1 and B13R alpha2 bound IL-11-thioredoxin with similar efficiencies and proliferated with superimposable dose-response curves to IL-11, demonstrating that the intracellular domain of IL-11R alpha has no significant contribution on ligand binding and signaling. Analysis of a set of anti-human gp130 mAbs confirmed the similar responsiveness of B13R alpha1 and B13R alpha2 transfectants.

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.

Expression of murine interleukin 11 and its receptor alpha-chain in adult and embryonic tissues

Interleukin 11 (IL-11) is a multifunctional cytokine that has diverse effects on blood cells and their precursors and on a number of cell types outside of the hematopoietic system. The cDNAs encoding murine IL-11 and its receptor alpha-chain (IL-11R alpha) have recently been isolated. We have used the RNase protection assay to examine the expression of murine IL-11 and IL-11R alpha in a range of adult mouse tissues, in embryos, and during development of embryonic stem (ES) cells into cystic embryoid bodies in vitro. The testis showed a high level of IL-11 gene expression while a much lower level of expression was detected in the lung, stomach, small intestine, and large intestine. Expression of IL-11 was not detected between day 10.5 and day 18.5 post coitum of embryonic development or in differentiating ES cells in vitro. In contrast, the IL-11R alpha was found to be expressed in all adult tissues examined, during embryonic development, and in totipotent and differentiating ES cells.

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.

Functional expression of soluble human interleukin-11 (IL-11) receptor alpha and stoichiometry of in vitro IL-11 receptor complexes with gp130

The interleukin-6 (IL-6) family of cytokines activates signaling through the formation of either gp130 homodimers, as for IL-6, or gp130-leukemia inhibitory factor receptor (LIFR) heterodimers as for ciliary neurotrophic factor (CNTF), leukemia inhibitory factor, oncostatinM, and cardiotrophin-1. Recent in vitro studies with IL-6 and CNTF have demonstrated that higher order hexameric receptor complexes are assembled in which signaling chain dimerization is accompanied by the dimerization of both the cytokine molecule and its specific receptor alpha subunits (IL-6Ralpha or CNTFRalpha, respectively). IL-11 is a member of the IL-6 family and known to require gp130 but not LIFR for signaling. In this study we investigate the functional and biochemical composition of the IL-11 receptor complex. The human IL-11 receptor alpha-chain was cloned from a human bone marrow cDNA library. IL-11Ralpha was shown to confer IL-11 responsiveness to human hepatoma cells either by cDNA transfection or by adding a soluble form of the receptor (sIL11Ralpha) expressed in the baculovirus system to the culture medium. In vitro immunoprecipitation experiments showed that sIL11Ralpha specifically binds IL-11 and that binding is enhanced by gp130. Similarly to IL-6 and CNTF, gp130 is able to induce dimerization of the IL-11.IL-11Ralpha subcomplex, the result of which is the formation of a pentameric receptor complex. However, in contrast to the other two cytokines, IL-11 was unable to induce either gp130 homodimerization or gp130/LIFR heterodimerization. These results strongly suggest that an as yet unidentified receptor beta-chain is involved in IL-11 signaling.

Mediation of interleukin-11-dependent biological responses by a soluble form of the interleukin-11 receptor

Interleukin-11 (IL-11) is a polyfunctional cytokine whose biological actions require a specific IL-11 receptor (IL-11R) and the transmembrane transducer gp130. Here we report the production of a soluble form of the murine IL-11R and demonstrate that it interacts with IL-11 ligand with high affinity. The affinity of IL-11 alone for gp130 is below the level of detection, but a complex of IL-11 and soluble IL-11R interacts with gp130 with high affinity. The addition of soluble IL-11R potentiates the effects of exogenous IL-11 in cells that are normally responsive to IL-11. A biological response to IL-11 can be reconstituted in BAF cells transfected with gp130 by addition of IL-11 and soluble IL-11R. These findings show that the cytoplasmic domain of the IL-11R is not required for the biological effects of IL-11 and that a complex of IL-11 and IL-11R mediates signalling by association with gp130.

Characteristic localization of gp130 (the signal-transducing receptor component used in common for IL-6/IL-11/CNTF/LIF/OSM) in the rat brain

The localization of gp130, the signal transducing receptor component used in common for interleukin (IL)-6, IL-11, ciliary neurotrophic factor (CNTF), LIF and OSM, in the rat brain was demonstrated by immunohistochemistry using an antibody specific to gp130. The gp130 immunoreactivity was observed in both glial and neuronal cells. Two distinct neuronal staining patterns were observed. The first showed neuropil staining, observed mainly in telencephalic structures including the hippocampus, cerebral cortex and caudate-putamen. The second pattern was observed on the cytoplasmic membrane of neuronal somata and was found primarily in the lower brainstem, in the large neurons of the reticular formation, and in spinal and cranial motor neurons. Electron-microscopic analysis revealed that both types of gp130 immunoreactivity were primarily associated with the cytoplasmic membrane and were not localized exactly at synaptic sites. Further, gp130 immunoreactivity was also observed in the oligodendrocytes and subependymal zone. These widespread but characteristic patterns of gp130 immunoreactivity overlap well with those of IL-6 receptor and CNTF alpha chains, suggesting a role of cytokines and growth factors such as IL-6 and CNTF via gp130 in certain specific regions of the brain.

Complex of the soluble IL-11 receptor and IL-11 acts as IL-6-type cytokine in hepatic and nonhepatic cells

The signaling functions of the membrane and soluble form of the mouse IL-11 receptor (mIL-11R) were compared in rat and human hepatoma cells, which have a low endogenous IL-11 response. The expression vectors encoding either the full length or a secretory form of the ligand binding subunit of mIL-11R together with IL-6-responsive reporter gene constructs were transiently transfected into the H-35 and HepG2 cells. An IL-11-specific stimulation of transcription was detected that was qualitatively similar to that mediated by the endogenous IL-6R. HepG2 cells were noted to synthesize constitutively IL-11, resulting in an autocrine stimulation of gene expression. Addition of COS cell-derived soluble mIL-11R to the hepatoma cell cultures prominently enhanced IL-11 regulation of transfected reporter gene constructs and expression of endogenous acute phase plasma protein genes. Similarly, the complex of soluble mIL-11R and IL-11 was capable of mediating an IL-6-type signaling in cells that are naturally deficient in IL-11 response as shown by the activation of STAT1 and STAT3 in mouse embryonal carcinoma cells and human T cells. The results indicate that the IL-11R can serve as a substitute to IL-6R in activating gene expression in target cells that are devoid of the appropriate ligand-binding receptor subunits.

Interleukin-6 family of cytokines induced activation of different functional sites expressed by gp130 transducing protein

Gp130 transducing protein was shown to be involved in the formation of the high affinity receptors for interleukin 6 (IL-6), interleukin-11 (IL-11), leukemia inhibitory factor, oncostatin M (OSM), ciliary neurotrophic factor (CNTF), and cardiotrophin-1. In the present study we have characterized the functional properties of antibodies directed against this protein and identified a group of monoclonal antibodies able to antagonize the biological activities of all the cytokines belonging to the IL-6 cytokine family. The B-R3 pan-blocking antibody weakly interfered with the binding of the radiolabeled ligands (with the exception of OSM, whose binding was abrogated in the presence of B-R3 monoclonal antibody) but inhibited the gp130 homodimerization or its association with gp190/leukemia inhibitory factor receptor, as well as the subsequent tyrosine phosphorylation events. In addition we identified antibodies that were able to neutralize only one single cytokine of the IL-6 family. This was the case for the B-K5 antibody, which antagonized the binding of OSM to gp130 but did not interfere with the signals provided by the related cytokines triggering the proliferation of the TF1 erythroleukemia cell line or the induction of haptoglobin synthesis in the HepG2 hepatoma cell line. Similarly, we also characterized two additional antibodies B-P8 and B-P4, which inhibited the TF1 cell proliferation observed in the presence of CNTF and IL-11, respectively. B-P8 antibody only faintly interfered with the binding of the gp130-ligands and might modulate the signal transduction pathways. This study indicates that in addition to functional site(s) required by the whole family of IL-6 type cytokines to transduce the signal insight the cell, specific cognate functional sites were recruited by OSM, CNTF, or IL-11.

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

In this study the gene for the murine interleukin-11 receptor alpha chain (IL-11Ralpha) has been characterized. The gene spans 9 kilobase pairs of DNA, and the organization of its 14 exons conforms to the pattern observed for other members of the hematopoietin receptor family. Analysis of the 5' end of the cDNA using 5' RACE showed that the first two exons, designated exons 1a and 1b, are spliced to form alternate transcripts. Transcripts initiating from exon 1b were not found in adult tissues but were present in embryonic stem cells. S1 nuclease and 5' rapid amplification of cDNA ends assays demonstrated multiple major and minor sites of transcription initiation for each exon. The putative promoter regions of both exons lacked TATA boxes, although potential recognition sites for several transcription factors including Sp1, AP1, and AP2 were present. A comparison of the murine and human IL-11Ralpha revealed that the 5' sequence upstream of the major site of transcription initiation site for exon 1b is highly conserved. Northern analysis showed that IL-11Ralpha is expressed in many adult murine tissues. A second IL-11Ralpha-like locus containing a sequence homologous to exons 2-13 was also identified.

The role of gp130-mediated signals in osteoclast development: regulation of interleukin 11 production by osteoblasts and distribution of its receptor in bone marrow cultures

Interleukin (IL)-11 is a multifunctional cytokine whose role in osteoclast development has not been fully elucidated. We examined IL-11 production by primary osteoblasts and the effects of rat monoclonal anti-mouse glycoprotein 130 (gp130) antibody on osteoclast formation, using a coculture of mouse osteoblasts and bone marrow cells. IL-1, TNF alpha, PGE2, parathyroid hormone (PTH) and 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25(OH)2D3) similarly induced production of IL-11 by osteoblasts, but IL-6, IL-4, and TGF beta did not. Primary osteoblasts constitutively expressed mRNAs for both IL-11 receptor (IL-11R alpha) and gp130. Osteotropic factors did not modulate IL-11R alpha mRNA at 24 h, but steady-state gp130 mRNA expression in osteoblasts was upregulated by 1 alpha,25(OH)2D3, PTH, or IL-1. In cocultures, the formation of multinucleated osteoclast-like cells (OCLs) in response to IL-11, or IL-6 together with its soluble IL-6 receptor was dose-dependently inhibited by rat monoclonal anti-mouse gp130 antibody. Furthermore, adding anti-gp130 antibody abolished OCL formation induced by IL-1, and partially inhibited OCL formation induced by PGE2, PTH, or 1 alpha,25(OH)2D3. During osteoclast formation in marrow cultures, a sequential relationship existed between the expression of calcitonin receptor mRNA and IL-11R alpha mRNA. Osteoblasts as well as OCLs expressed transcripts for IL-11R alpha, as indicated by RT-PCR analysis and in situ hybridization. These results suggest a central role of gp130-coupled cytokines, especially IL-11, in osteoclast development. Since osteoblasts and mature osteoclasts expressed IL-11R alpha mRNA, both bone-forming and bone-resorbing cells are potential targets of IL-11.

The human interleukin-11 receptor alpha gene (IL11RA): genomic organization and chromosome mapping

The high-affinity receptor for interleukin-11 (IL-11) is composed of two subunits, IL-11 receptor alpha chain (IL-11R alpha) and gp130, the common subunit of the interleukin-6 (IL-6), ciliary neurotrophic factor (CNTF), leukemia inhibitory factor, and oncostatin M receptors. The IL-11 receptor-specific alpha chain shares homologies with the alpha chain of the CNTF and IL-6 receptors. We isolated and characterized genomic DNA clones encompassing the entire coding sequence of the IL-11R alpha cDNA. The exon-intron organization of the IL-11R gene (HGMW-approved symbol IL11RA) is consistent with the predicted structure of the different domains of the IL-11R alpha protein, confirming evolutionary conservation at the level of gene organization among the hematopoietic cytokine receptor family. The IL-11R gene has been assigned to chromosome 9 band p13 by in situ hybridization using human IL-11R alpha cDNA as a probe. The fact that the ciliary neurotrophic factor (CNTFR) gene has recently been localized on this same band and the conserved genomic structure between IL-11R and CNTFR suggest that they may have evolved from a common ancestor.

The human IL-11 receptor requires gp130 for signalling: demonstration by molecular cloning of the receptor

We describe the molecular cloning of a cDNA for the alpha chain of the human IL-11 receptor (IL-11R alpha) and demonstrate the requirement of either the human or mouse gp130 molecule for signalling. cDNA clones encoding IL-11R alpha were isolated from a bone marrow cDNA library using a fragment from the murine IL-11R alpha as a probe. The human receptor was predicted to consist of 422 amino acids and was found to share 84% identity with the murine protein. In the extra-cellular region it exhibited a single hemopoietin domain with conserved cysteine residues and WSTWS motif. The transmembrane region was followed by a short cytoplasmic tail which did not contain a tyrosine kinase domain. Interaction of the human IL-11R alpha with murine gp130 was demonstrated: expression of the human IL-11R alpha in murine M1 cells which constitutively express murine gp130 (and murine LIF receptor), resulted in the generation of specific high-affinity binding sites for IL-11 (Kd = 250 pM). In addition, expression of the human IL-11R alpha in these cells permitted the induction of macrophage differentiation in response to IL-11. These results suggested that the human IL-11R alpha chain was able to form a functional receptor complex in association with murine gp130. The requirement of gp130 for signalling was confirmed by expression of the human IL-11R alpha in Ba/F3 cells. BaF3 cells that expressed the human IL-11R alpha alone showed binding of radiolabelled IL-11 but no proliferative response. Introduction of human gp130 into these cells resulted in high-affinity IL-11 binding sites and IL-11 dependent cellular proliferation. Thus these results demonstrated the absolute requirement of gp130 for signalling.

Detection of receptors for interleukin-6, interleukin-11, leukemia inhibitory factor, oncostatin M, and ciliary neurotrophic factor in bone marrow stromal/osteoblastic cells

The functional receptor complexes assembled in response to interleukin-6 and -11 (IL-6 and IL-11), leukemia inhibitory factor (LIF), oncostatin M (OSM), and ciliary neurotrophic factor (CNTF), all involve the signal transducer gp130: IL-6 and IL-11 induce homodimerization of gp130, while the rest heterodimerize gp130 with other gp130-related beta subunits. Some of these cytokines (IL-6, IL-11, and CNTF) also require a specificity-determining alpha subunit not directly involved in signaling. We have searched for functional receptor complexes for these cytokines in cells of the bone marrow stromal/osteoblastic lineage, using tyrosine phosphorylation of the beta subunits as a detection assay. Collectively, murine calvaria cells, bone marrow-derived murine cell lines (+/+LDA11 and MBA13.2), as well as murine (MC3T3-E1) and human (MG-63) osteoblast-like cell lines displayed all the previously recognized alpha and beta subunits of this family of receptors. However, individual cell types had different constellations of alpha and beta subunits. In addition and in difference to the other cell types examined, MC3T3-E1 cells expressed a heretofore unrecognized form of gp130; and MG-63 displayed an alternative form (type II) of the OSM receptor. These findings establish that stromal/osteoblastic cells are targets for the actions of all the members of the cytokine subfamily that shares the gp130 signal transducer; and suggest that different receptor repertoires may be expressed at different stages of differentiation of this lineage.

Molecular cloning and characterization of the human interleukin-11 receptor alpha-chain gene, IL11RA, located on chromosome 9p13

The human gene coding for the interleukin-11 receptor (IL11RA) was cloned and its structure analyzed. The gene is composed of 13 exons comprising nearly 10 kb of DNA that was completely sequenced. The intron-exon boundaries were determined based on the mouse Etl2 and interleukin-11 receptor cDNAs that were recently cloned. The protein sequence predicted by the human gene was over 83% identical with its murine counterpart, with very strict conservation of functionally important domains and signatures. Fluorescence in situ hybridization showed the gene to be located on human chromosome 9p13, syntenic with the mouse etl2 gene on chromosome 4. The coding exons of the Interleukin-11 gene were sequenced in a patient with the cartilage-hair hypoplasia syndrome, which has been linked to a gene on chromosome 9, but no functional mutations were detected.

Interleukin-10 induces interleukin-11 responsiveness in human myeloma cell lines

Interleukin (IL)-6-dependent human myeloma cell lines (HMCL) can be reproducibly obtained from patients with multiple myeloma and terminal disease. The growth of some of these HMCL can also be supported by IL-11. We show that IL-11-responsive, but not -unresponsive, HMCL expressed the gene of human IL-11 receptor (IL-11R) and produced an autocrine IL-10. All HMCL expressed the IL-10 receptor. In addition, IL-10 induced IL-11R gene expression and conferred IL-11 responsiveness on unresponsive HMCL. The ability of HMCL to produce IL-10 was strictly correlated with the capacity of the original patient's myeloma cells to produce IL-10 or not, and with the presence or absence of IL-10 in the patient's plasma.

Hematopoietic stem cells in the blood after stem cell factor and interleukin-11 administration: evidence for different mechanisms of mobilization

Peripheral blood stem cells and progenitor cells, collected during recovery from exposure to cytotoxic agents or after cytokine administration, are being increasingly used in clinical bone marrow transplantation. To determine factors important for mobilization of both primitive stem cells and progenitor cells to the blood, we studied the blood and splenic and marrow compartments of intact and splenectomized mice after administration of recombinant human interleukin-11 (rhlL-11), recombinant rat stem cell factor (rrSCF), and IL-11 + SCF. IL-11 administration increased the number of spleen colony-forming units (CFU-S) in both the spleen and blood, but did not increase blood long-term marrow-repopulating ability (LTRA) in intact or splenectomized mice. SCF administration increased the number of CFU-S in both the spleen and blood and did not increase the blood or splenic LTRA of intact mice, but did increase blood LTRA to normal marrow levels in splenectomized mice. The combination of lL-11 + SCF syngeristically enhanced mobilization of long-term marrow-repopulating cells from the marrow to the spleen of intact mice and from the marrow to the blood of splenectomized mice. These data, combined with those of prior studies showing granulocyte colony-stimulating factor mobilization of long-term marrow repopulating cells from the marrow to the blood of mice with intact spleens, suggest different cytokine-induced pathways for mobilization of primitive stem cells.

Molecular cloning of two isoforms of a receptor for the human hematopoietic cytokine interleukin-11

Interleukin-11 (IL-11) is a stromal cell-derived cytokine with multiple biologic activities on lymphohematopoietic cells. It belongs to a family of pleiotropic and redundant cytokines that use the gp 130 transducing subunit in their high affinity receptors. By amplifying human cDNA libraries with oligonucleotide primers corresponding to the conserved WSXWS motif found in the hematopoietic cytokine receptor family, a novel cytokine receptor cDNA was identified that, based on high (82%) sequence homology with the recently cloned murine IL-11 receptor, appears to encode the human IL-11 receptor. This receptor is a 422-amino acid protein containing a signal peptide followed by extracellular, transmembrane, and cytoplasmic domains. The extracellular region has a two-domain structure homologous to those of the IL-6 and ciliary neurotrophic factor (CNTF) receptors: an immunoglobulin-like domain and a cytokine receptor-like domain. In addition, an isoform of the human IL-11 receptor that lacks the cytoplasmic domain was also identified. In agreement with the pleiotropic effects of IL-11 on different hematopoietic lineages and bone cells, IL-11 receptor transcripts were found to be expressed by the myelogenous leukemia cell line K562, the megakaryocytic leukemia cell line Mo7E, the erythroleukemia cell line TF1, and the osteosarcoma cell lines MG-63 and Saos-2.

Update on development of interleukin-11

This paper reviews the recent studies of interleukin-11 gene expression and regulation, receptor and signal transduction, pharmacologic effects, and preclinical and clinical studies. Interleukin-11 is expressed in cells of mesenchymal origin and gene expression can be modulated by several inflammatory cytokines and agonists. The signaling pathways involved in cytokine induction of interleukin-11 gene expression vary between cell types. In vitro and in vivo studies reveal that interleukin-11 displays a wide spectrum of bioactivities including responses in hematopoietic and nonhematopoietic cells. Preclinical studies in animal models suggest that interleukin-11 may be useful in acceleration of the recoveries of both hematopoietic cells and gastrointestinal mucosal cells after cytoablative therapies. Several clinical studies have demonstrated interleukin-11 to be well tolerated and suggest interleukin-11 is a promising cytokine to prevent both neutropenia and thrombocytopenia in patients with cancer who are receiving chemotherapy.

Etl2, a novel putative type-I cytokine receptor expressed during mouse embryogenesis at high levels in skin and cells with skeletogenic potential

The regulatory effects of signaling proteins like hormones, growth factors, and cytokines are mediated by specific cell surface receptors which are grouped into distinct families on the basis of structural criteria. Here we report on the isolation and embryonic expression of a novel mouse gene, Etl2 (enhancer trap locus 2) which, based on its deduced amino acid sequence, constitutes a new member of the cytokine type-I receptor family. Among type-I receptors Etl2 is most similar to the alpha subunits of the human ciliary neurotrophic factor (CNTF) receptor and the mouse interleukin-6 (IL6) receptor with 32 and 30% identical amino acids, respectively. From Day 9 p.c. (postcoitum) onward low levels of Etl2 mRNA were detected in mesenchymal cells throughout the embryo and in parts of the nervous system, in particular in the ependymal linings of the spinal cord and the developing brain vesicles and in the neuronal layer of the retina. Highest levels of Etl2 expression were found on Day 12.5 p.c. in the craniofacial mesenchyme and during subsequent development in mesenchymal cells around all developing cartilages. At later stages, Etl2 transcripts were abundant in the dental papilla, the dermis, and hair follicles, as well as in the perichondrium and periost, i.e., in regions containing chondro and osteo progenitor cells. Etl2 mRNA was not detected, however, in mature odontoblasts, chondroblasts, osteoblasts, chondrocytes, and osteocytes. Our results suggest that Etl2 is a new orphan receptor belonging to the type-I cytokine receptor family and that Etl2 might have regulatory functions, particularly in the control of proliferation and/or differentiation of skeletogenic progenitor and other mesenchymal cells.

Cloning of a murine IL-11 receptor alpha-chain; requirement for gp130 for high affinity binding and signal transduction

An adult mouse liver cDNA library was screened with oligonucleotides corresponding to the conserved WSXWS motif of the haemopoietin receptor family. Using this method, cDNA clones encoding a novel receptor were isolated. The new receptor, named NR1, was most similar in sequence and predicted structure to the alpha-chain of the IL-6 receptor and mRNA was expressed in the 3T3-L1 pre-adipocytic cell line and in a range of primary tissues. Expression of NR1 in the factor-dependent haemopoietic cell line Ba/F3 resulted in the generation of low affinity receptors for IL-11 (Kd approximately 10 nM). The capacity to bind IL-11 with high affinity (Kd = 300-800 pM) appeared to require coexpression of both NR1 and gp130, the common subunit of the IL-6, leukaemia inhibitory factor (LIF), oncostatin M (OSM) and ciliary neurotrophic factor (CNTF) receptors. The expression of both NR1 and gp130 was also necessary for Ba/F3 cells to proliferate and M1 cells to undergo macrophage differentiation in response to IL-11.

Interleukin-11

Interleukin-11 (IL-11), a stromal cell-derived cytokine, has been known to act widely in hematopoietic and non-hematopoietic systems. IL-11 supports the growth of certain types of plasmacytoma and hybridoma cells, acts with interleukin-3 (IL-3) in shortening the Go period of early progenitors. IL-11 supports megakaryocyte colony formation and maturation, and acts as an autocrine growth factor in megakaryoblastic cell lines. In addition, IL-11 stimulates erythrocytopoiesis, enhances antigen-specific antibody responses, induces the synthesis of acute phase proteins, inhibits lipoprotein lipase activity and adipocyte differentiation, and promotes neuronal development. Administration of rhIL-11 to mice resulted in an increase of neutrophils and platelets. The human IL-11 gene is localized at 19q13.3-13.4, and codes 199 amino acids and 23 kDa with no N glycosylation. Its receptor and signal transduction share partially those of interleukin-6 (IL-6). Further analysis of its role in normal and pathological state is necessary to determine the exact function and its application for clinical uses.