Interleukin-6 and interleukin-11 act synergistically with thrombopoietin and stem cell factor to modulate ex vivo expansion of human CD41+ and CD61+ megakaryocytic cells

BACKGROUND AND OBJECTIVE

Thrombopoietin (TPO), the ligand for the c-mpl receptor, regulates in vivo platelet production and increases the number of colony-forming unit megakaryocytes (CFU-MK). Other cytokines including interleukin (IL) -3, IL-6, IL-11 and stem cell factor (SCF) can stimulate megakaryopoiesis. The aim of this study was to evaluate the effects of different combinations of cytokines involved in megakaryocytopoiesis on stroma-free liquid cultures of purified human CD34+ cells.

DESIGN AND METHODS

Peripheral blood cells were collected after mobilization with granulocyte colony-stimulating factor (G-CSF). Purified CD34+ cells were then cultured with different combinations of TPO, SCF, IL-3, IL-6 and IL-11.

RESULTS

The addition of TPO and SCF alone generated a population positive for the antigens CD41 (5.5+/-2.9%) and CD61 (6. 1+/-2.2%) but induced a low amplification of cell number (8.1+/-0.9 fold expansion). The presence of IL-6 or IL-11 was associated with MK progenitor cell expansion, and up to 7-10% of cultured cells were found to be CD41 and CD61 positive by flow cytometry. Conversely, the addition of IL-3 to this cytokine combination was associated with a prominent expansion of the myeloid lineage (70+/-10% of CD33+ cells) but only 0.9% and 2% of cultured cells were positive for CD61 and CD41 respectively.

INTERPRETATION AND CONCLUSIONS

Our study supports the idea that IL-6 and IL-11 play crucial roles in the proliferation of MK progenitors and the use of SCF, TPO, IL-6 and IL-11 for ex vivo expansion of this cell population.

Interleukin-11: its biology and prospects for clinical use

IL-11 is a multifunctional cytokine that has pleiotropic effects on a variety of tissue including the bone marrow and intestinal mucosa. IL-11 is useful in elevating the platelet count in cancer patients with chemotherapy-induced thrombocytopenia and has a cytoprotective effect on the bowel mucosa in a variety of causes of gut damage and a trophic effect on the villi after massive bowel resection.

IL-11 separates graft-versus-leukemia effects from graft-versus-host disease after bone marrow transplantation

We recently showed that IL-11 prevents lethal graft-versus-host disease (GVHD) in a murine bone marrow transplantation (BMT) model of GVHD directed against MHC and minor antigens. In this study, we have investigated whether IL-11 can maintain a graft-versus-leukemia (GVL) effect. Lethally irradiated B6D2F1 mice were transplanted with either T cell-depleted (TCD) bone marrow (BM) alone or with BM and splenic T cells from allogeneic B6 donors. Animals also received host-type P815 mastocytoma cells at the time of BMT. Recipients were injected subcutaneously with recombinant human IL-11 or control diluent twice daily, from 2 days before BMT to 7 days after BMT. TCD recipients all died from leukemia by day 23. All control- and IL-11-treated allogeneic animals effectively rejected their leukemia, but IL-11 also reduced GVHD-related mortality. Examination of the cellular mechanisms of GVL and GVHD in this system showed that IL-11 selectively inhibited CD4-mediated GVHD, while retaining both CD4- and CD8-mediated GVL. In addition, IL-11 treatment did not affect cytolytic effector functions of T cells after BMT either in vivo or in vitro. Studies with perforin-deficient donor T cells demonstrated that the GVL effect was perforin dependent. These data demonstrated that IL-11 can significantly reduce CD4-dependent GVHD without impairing cytolytic function or subsequent GVL activity of CD8(+) T cells. Brief treatment with IL-11 shortly after BMT may therefore represent a novel strategy for separating GVHD and GVL.

Leukemia inhibitory factor, Interleukin 6, and other cytokines using the GP130 transducing receptor: roles in inflammation and injury

Inflammation refers to a complex set of mechanisms by which tissues respond to injury and infection. Among the many soluble mediators associated with this process, cytokines are known to be crucial in regulating a variety of cellular and molecular events. Leukemia inhibitory factor (LIF), interleukin 6 (IL-6), IL-11, and possibly other members of this cytokine family are key mediators in various inflammatory processes such as the acute-phase reaction, tissue damage, and infection. These cytokines can act in both pro-inflammatory and anti-inflammatory ways, depending on a number of variables. We emphasize here recent work utilizing knockout mice, which has highlighted the roles of LIF and IL-6, particularly in interactions between the immune and nervous systems.

Interleukin-11. A gp130 cytokine

Interleukin (IL)-11 is a member of the gp130 family of cytokines. Comparison of IL-11 with another gp130 family member, IL-6, indicates that these two cytokines share many overlapping signal transduction mechanisms. However, unlike IL-6, treatment of patients with a recombinant human form of IL-11 (rhIL-11) does not increase body temperature, suggesting significant differences in the in vivo function of these two molecules. Recent studies demonstrate that IL-11 has potent anti-inflammatory activity in a variety of preclinical animal models of disease. rhIL-11 reduces production of proinflammatory mediators such as tumor necrosis factor-alpha and IL-12 from activated macrophages. This effect on proinflammatory cytokine production is mediated at the transcriptional level by inhibition of the transcription factor, NF- kappa B. To further understand the anti-inflammatory mechanisms of action of rhIL-11 and to elucidate differences between IL-11 and IL-6 signal transduction pathways, the effects of these two cytokines on in vitro macrophage function were compared.

Important immunoregulatory role of interleukin-11 in the inflammatory process in rheumatoid arthritis

OBJECTIVE

To investigate the possible immunoregulatory role of interleukin-11 (IL-11) in rheumatoid arthritis (RA).

METHODS

IL-11 protein was assayed in RA tissue, and the effect of exogenous IL-11 on neutralization of endogenous IL-11 was investigated with respect to tumor necrosis factor alpha (TNFalpha), matrix metalloproteinase (MMP), and tissue inhibitor of metalloproteinases (TIMP) production.

RESULTS

IL-11 was found in RA synovial membranes, synovial fluids, and blood sera. Blockade of endogenous IL-11 resulted in a 2-fold increase in TNFalpha levels, which increased to 22-fold if endogenous IL-10 was also blocked. Addition of exogenous IL-11 inhibited spontaneous TNFalpha production in RA synovium only in the presence of soluble IL-11 receptor. However, exogenous IL-11 directly inhibited spontaneous MMP-1 and MMP-3 production, and up-regulated TIMP-1 in RA synovial tissue.

CONCLUSION

IL-11 has important endogenous immunoregulatory effects in RA synovium, which suggests that exogenous IL-11 may have therapeutic activity in RA.

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.

Production of interleukin-11 in bone-derived endothelial cells and its role in the formation of osteolytic bone metastasis

The interactions of the cells in the bone microenvironment play important roles in bone remodeling. Osteoblasts are involved in the bone remodeling through the production of soluble factors that regulate proliferation and differentiation of osteoclasts and through cell-cell interactions. Histological studies have suggested that endothelial cells are also associated with some osteolytic bone diseases. However, it is still unclear how endothelial cells contribute to bone resorption. We established bone-derived endothelial cells (BDECs) to study their roles in bone remodeling. The established BDECs promoted bone resorption in a murine neonatal calvaria organ culture system by secreting a soluble bone resorption-inducing factor(s) when stimulated by several inflammatory cytokines. This bone resorption-inducing factor was identified as interleukin-11 (IL-11). IL-11 is known to enhance bone resorption by promoting osteoclastogenesis and by suppressing the activity of osteoblasts. The production of IL-11 in BDECs was also promoted by conditioned medium of human melanoma A375M cells. Because A375M cells formed osteolytic bone metastasis in vivo, BDECs might be involved in pathological osteolysis by producing IL-11. These results suggest that endothelial cells in bone play important roles in the promotion of bone resorption by secreting IL-11 in physiological and pathological conditions.

Interleukin-11

Interleukin-11 (IL-11) is an IL-6-type cytokine that is produced by a variety of stromal cells including fibroblasts, epithelial cells and osteoblasts. It binds to a multimeric receptor complex which contains an IL-11-specific alpha subunit and a promiscuous 130 kDa beta subunit (gp130). IL-11 stimulates multiple aspects of hematopoiesis and hepatocyte production of acute phase response proteins. It also inhibits the genesis of adipocytes, activates osteoclasts, alters neural phenotype, stimulates tissue fibrosis and regulates chondrocyte, synoviocyte and B cell function. In other settings, IL-11 minimizes tissue injury. This may be the result of its ability to protect clonogenic stem cells, regulate epithelial cell proliferation, inhibit apoptosis and inhibit macrophage cytokine production. Thus, IL-11 appears to play an important role in hematopoiesis, bone metabolism and tissue remodeling and may be an important protector of mucosal surfaces.

Interleukin-10 is a growth factor for human myeloma cells by induction of an oncostatin M autocrine loop

We have a previously reported that interleukin-10 (IL-10) is a potent but IL-6-unrelated growth factor for freshly explanted myeloma cells (Lu et al, Blood 85:2521, 1995). We have also shown that exogenous IL-10 supported the growth of XG-1 and XG-2 human myeloma cell lines (HMCL) through an IL-6-independent mechanism. (Lu et al, Blood 85:2521, 1995). Because the IL-10 receptor does not involve the gp 130 IL-6 transducer, we have attempted to elucidate the mechanisms of IL-10 action on myeloma cells. Our results indicate that the myeloma cell growth factor activity of IL-10 was abrogated by an antibody to the gp 130 IL-6 transducer, indicating that it was mediated through one of the gp 130-activating cytokines. We found that myeloma cells from XG-1 and XG-2 HMCL and from 5 of 6 patients' tumoral samples produced oncostatin M (OM) constitutively but failed to produce IL-6, IL-11 and leukemia-inhibitory factor (LIF). The autocrine OM was inactive in the absence of IL-10 due to lack of a functional OM receptor on myeloma cells. IL-10, by inducing the receptor for LIF (LIFR), produced a functional autocrine OM loop in XG-1 and XG-2 cells and in primary myeloma cells from 2 patients. We also found that some myeloma cell lines (XG-4, XG-6, and XG-7) an fresh myeloma cells from 3 of 6 patients produced an autocrine IL-10 and that these cells constitutively expressed LIFR. One HMCL (XG-7) produced IL-10, OM, and IL-6 an expressed LIFR. The XG-7 cells used OM and IL-6 as autocrine growth factors. We have previously shown that IL-10 could induce IL-11 receptor in myeloma cells and confer on them sensitivity to IL-11 (Lu et al, FEBS Lett 377:515, 1995). Taken together, these results show that IL-10 is a key cytokine for inducing the expression of LIFR and IL-11R and possibly another uncharacterized OM coreceptor on myeloma cells and that OM and IL-10 might be produced by myeloma cells. They also emphasize that all myeloma cell growth factors reported to data involve an activation of the gp130 IL-6 transducer.

Thrombopoietic potential and serial repopulating ability of murine hematopoietic stem cells constitutively expressing interleukin 11

Based on transplantation studies with bone marrow cultured under various conditions, a role of interleukin 11 (IL-11) in the self-renewal and/or the differentiation commitment of hematopoietic stem cells has been indicated. To better evaluate the in vivo effects of IL-11 on stem/progenitor cell biology, lethally irradiated mice were serially transplanted with bone marrow cells transduced with a defective retrovirus, termed MSCV-mIL-11, carrying the murine IL-11 (mIL-11) cDNA and the bacterial neomycin phosphotransferase (neo) gene. High serum levels (i.e., > 1 ng/ml) of mIL-11 in all (20/20) primary and 86% (12/14) of secondary long-term reconstituted mice, as well as 86% (12/14) of tertiary recipients examined at 6 weeks posttransplant, demonstrated persistence of vector expression subsequent to transduction of bone marrow precursors functionally definable as totipotent hematopoietic stem cells. In agreement with results obtained with human IL-11 in other myeloablation models, ectopic mIL-11 expression accelerated recovery of platelets, neutrophils, and, to some extent, total leukocytes while preferentially increasing peripheral platelet counts in fully reconstituted mice. When analyzed 5 months posttransplant, tertiary MSCV-mIL-11 recipients had a significantly greater percentage of G418-resistant colony-forming cells in their bone marrow compared with control MSCV animals. Collectively, these data show that persistent stimulation of platelet production by IL-11 is not detrimental to stem cell repopulating ability; rather, they suggest that IL-11 expression in vivo may have resulted in enhanced maintenance of the most primitive hematopoietic stem cell compartment. The prolonged expression achieved by the MSCV retroviral vector, despite the presence of a selectable marker, contrasts with the frequent transcriptional extinction observed with other retroviral vectors carrying two genes. These findings have potentially important implications for clinical bone marrow transplantation and gene therapy of the hematopoietic system.

In vitro tracking of IL-7 responsiveness and gene expression during commitment of bipotent B-cell/macrophage progenitors

BACKGROUND

The development of B lymphocytes from multipotent hematopoietic stem cells occurs through a series of intermediate cell types with increasingly restricted developmental potential. Despite intensive investigation, the underlying basis for commitment to a given lineage or the restriction in developmental potential of multipotent cells is unknown. To gain insight into this process we have developed an in vitro system that tracks a bipotent progenitor, which has the capacity to give rise to both B lymphocytes and macrophages, as it makes the transition to a B-lineage-committed precursor. The development of mature B lymphocytes from bipotent progenitors is dependent on interleukin 7 (IL-7), a pre-B-cell growth factor, in addition to other stromal-cell-derived factors such as IL-11 and mast cell growth factor (MGF). IL-7 acts on pre-B lymphocytes, but the stage of differentiation at which B-lineage cells become responsive to this factor, and its potential role in lineage commitment have not been investigated thoroughly. Here, we examine the requirements for IL-7 during the development of B lymphocytes from bipotent progenitors. Furthermore, we define onset of B-lineage-associated gene expression during the development of committed B-lineage cells under defined culture conditions.

RESULTS

We demonstrate that, under our experimental conditions, bipotent progenitors commit to differentiation through either the B or macrophage lineages within the first 3 days of culture. Cells that require IL-7 for survival first develop on day 3 of culture; however, commitment to the B lineage occurs at the same frequency in the presence or absence of this factor. After day 3 of culture, IL-7 is required both for the proliferation and survival of committed B-lineage progenitors and for the expression of several B-cell-associated genes, such as lambda5, VpreB, mb-1 and Rag1.

CONCLUSIONS

Our results demonstrate that the growth factor combination of IL-11 and MGF provides sufficient support for bipotent progenitors to commit to either the B or the macrophage lineage. Single-cell cloning assays revealed that IL-7 does not influence the decision to commit to the B lineage, despite the observation that the bipotent cells potentially respond to IL-7, as indicated by an increase in cell number, prior to the commitment event. Furthermore, the addition of IL-7 to cells developing along the B-cell pathway promotes the expression of mRNA transcripts which encode several B-cell-specific genes.

Interleukin-11 induces intestinal epithelial cell growth arrest through effects on retinoblastoma protein phosphorylation

Recombinant human (rh) interleukin (IL)-11 has been shown to reduce gastrointestinal mucosal injury after chemotherapy or irradiation in several animal models. As reduction of cellular proliferation can be cytoprotective, we have examined the effect of rhIL-11 compared with transforming growth factor (TGF)-beta 1 on the proliferation and cell cycle progression of a rat intestinal cell line, IEC-6. IEC-6 cells treated with rhIL-11 or rhTGF-beta 1 exhibited a reduced proliferative rate as measured by cell counts and [3H]thymidine incorporation. The presence of neutralizing anti-TGF-beta 1 antibodies did not block the antiproliferative effect of rhIL-11 indicating that the rhIL-11 activity was not mediated through the induction of endogenous TGF-beta 1 production. Growth inhibition correlated with delayed entry into S phase of the cell cycle. Cell cycle arrest was associated with suppression of retinoblastoma protein phosphorylation. Transient cell cycle arrest is a possible mechanism by which rhIL-11 may protect intestinal epithelial cells from damage induced by chemotherapy or radiation therapy. This study provides a rationale for the clinical use of rhIL-11 to preserve the integrity of the gastrointestinal mucosa during cancer treatment regimens.

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.

Importance of the carboxy-terminus of human interleukin-11 in conserving its biological activity

Biological activities of the carboxy-terminal (C-terminal) deletion mutants of human interleukin-11 (IL-11) were analyzed. Removal of only 1 amino-acid residue (leucine) from the C-terminus caused nearly an 80% loss of its biological activity. This shows the importance of C-terminus of human IL-11 in terms of conserving the biological activity.

Interleukin-11: stimulation in vivo and in vitro by respiratory viruses and induction of airways hyperresponsiveness

To address the role of IL-11 in viral airways dysfunction, we determined whether infectious agents that exacerbate asthma stimulate stromal cell IL-11 production, determined whether IL-11 could be detected at sites of viral infection and evaluated the effects of IL-11 on airway physiology. Respiratory syncytial virus (RSV), parainfluenza virus type 3 (PIV3), and rhinovirus (RV) 14 were potent stimulators while cytomegalovirus and adenovirus only weakly stimulated and herpes simplex virus type 2 and bacteria did not stimulate IL-11 elaboration. IL-11 was not detected or barely detected in nasal aspirates from children without, but was detected in aspirates from children with viral upper respiratory tract infections. The levels of IL-11 were highest in patients with clinically detectable wheezing. IL-11 also caused nonspecific airways hyperresponsiveness in BALB/c mice. These studies demonstrate that three major causes of viral-induced asthma, RSV, RV, and PIV, in contrast to other viruses and bacteria, share the ability to induce stromal cell IL-11 production. They also demonstrate that IL-11 can be detected in vivo during viral respiratory infections, that the presence of IL-11 correlates with clinical bronchospasm and that IL-11 is a potent inducer of airways hyperresponsiveness. IL-11 may be an important mediator in viral airways disorders.

Thrombopoietic activity of recombinant human interleukin 11 in cancer patients receiving chemotherapy

Interleukin 11 (IL-11) is a newly identified hematopoietic growth factor that exerts its primary effect on megakaryocyte maturation and platelet production. It has a unique receptor, signaling by which is mediated by the glycoprotein (GP) 130 pathway. IL-11 is synergistic with stem-cell factor (c-kit ligand) in vitro, enhancing proliferation of primitive hematopoietic stem cells, and has been shown to be critical to the process of polyploidization and maturation. In preclinical models, IL-11 was shown to enhance platelet recovery following intensive chemotherapy, and in murine bone-marrow transplant models it accelerates the recovery of all hematopoietic lineages. Nonhuman primate studies have demonstrated a dose-related thrombopoietic effect; however, no myeloid effect has been observed. In clinical phase I trials, subcutaneous IL-11 was well tolerated and induced a dose-related thrombopoietic effect in women with breast cancer. IL-11 at doses of > 25 micrograms/kg per day appeared to reduce the severity of chemotherapy-induced thrombocytopenia. In a randomized phase II trial, IL-11 at 50 micrograms/kg reduced the requirement for platelet transfusions as compared with that in placebotreated controls. IL-11 is an interesting factor; however, further studies are needed to confirm its activity and are in progress.

Interleukin-11 (IL-11) acts as a synergistic factor for the proliferation of human myeloid leukaemic cells

Interleukin-11 is a stromal cells derived cytokine which stimulates the proliferation of primitive haemopoietic progenitor cells. For this paper we have studied the constitutive expression of IL-11 mRNA in a panel of wellknown leukaemic cell lines and samples from AML patients at diagnosis. Moreover, the same cellular populations were evaluated for their proliferative response to recombinant-human-(r-hu). IL-11 alone and combined with r-hu-IL-3, granulocyte-macrophage colony stimulating factor (GM-CSF) and stem cell factor (SCF, c-kit ligand). The colony-forming ability of HL60, K562, KG1 cells and eight fresh AML cell populations was assessed by a clonogenic assay in methylcellulose. In eight additional AML cases the number of S-phase leukaemic cells induced by IL-11 was determined by the bromodeoxyuridine (BRDU) incorporation assay after 3d of liquid culture. IL-11, as single cytokine, did not stimulate the colony formation of the three myeloid cell lines under serum-containing and serum-free conditions. In contrast, the proliferation of the leukaemic cells in response to IL-3, GM-CSF and SCF was enhanced by co-incubation with IL-11, and this effect was reversed in blocking experiments by the anti-IL-11 Moab. When tested on primary AML samples, IL-11 alone showed little, if any, proliferative activity. However, it increased the IL-3-dependent blast colony formation in eight out of eight cases and GM-CSF in seven cases. IL-11 also augmented synergistically the number of CFU-L stimulated by SCF in seven cases. A combination of three factors (IL-11, SCF and IL-3) yielded optimal colony formation. The BRDU studies showed the significant increase of AML cells in S-phase when IL-11 was combined with SCF, whereas the two CSF had no activity on their own. Positive interaction was also observed when IL-11 was added to IL-3 supplemented cultures in five out of eight cases tested. Reverse transcriptase-polymerase chain reaction amplification (RT-PCR) demonstrated the constitutive expression of IL-11 mRNA in all the cell lines and 11/12 AML samples studied at diagnosis. These results indicate that IL-11 is expressed in leukaemic myeloid cells and that their proliferation is regulated by the cytokine which acts as a synergistic factor.

Preclinical biology of interleukin 11: a multifunctional hematopoietic cytokine with potent thrombopoietic activity

Interleukin 11 (IL-11) is a multifunctional hematopoietic cytokine which was originally identified as a factor produced by an IL-1-stimulated primate stromal cell line. The in vitro biological activities of recombinant human (rHu)IL-11 result predominantly from synergistic interactions with other growth factors. In combination with other cytokines, rHuIL-11 has been shown to support the formation of primitive hematopoietic and lymphohematopoietic progenitor colonies from bone marrow, to promote erythroid burst formation and to stimulate both early and late stages of megakaryocyte proliferation and differentiation. rHuIL-11 is biologically active in mice, rats, dogs and primates when administered as a single agent in vivo. The predominant effect of rHuIL-11 in naive mice was on cells of the megakaryocytic lineage, increasing the number of bone marrow megakaryocyte progenitors, stimulating megakaryocyte endoreplication and increasing peripheral platelet counts in a dose-dependent fashion. Similar megakaryocytic stimulatory activity was seen in nonhuman primates treated with rHuIL-11 where platelet counts were increased by as much as 300%. In several models of severe myelosuppression induced by chemotherapy and/or irradiation and in bone marrow transplant models, there were multilineage hematopoietic stimulation following rHuIL-11 treatment. In these models, accelerated recovery of platelets was a consistent observation, while some models show enhanced neutrophil and red blood cell recovery as well. These results from preclinical studies confirm the broad spectrum of biological activities exhibited by rHuIL-11 in vitro, and suggest that this cytokine may be an effective agent in the treatment of myelosuppression and thrombocytopenia associated with cancer chemotherapy and bone marrow transplantation.

Role of cytokines in bone resorption

It has been established during the past few years that interleukin(s)-1, -6, -11 (IL-1, IL-6, IL-11), and tumor necrosis factor (TNF) can stimulate osteoclast development and thereby the process of bone resorption. Moreover, upregulation of the production and/or action of IL-6 has been implicated in the pathogenesis of disease states characterized by excessive osteoclastic bone resorption, including the osteopenias associated with loss of either ovarian or testicular function. This article highlights this evidence and attempts to clarify the role of cytokines in the bone loss associated with gonadal deficiency. Specifically, it reviews data demonstrating that the protective effects of estrogens and androgens on the skeleton are mediated through their ability to inhibit IL-6 production. Both of these steroids exert their effects by inhibiting the transcriptional activity of the IL-6 gene promoter via mechanisms involving their respective specific receptors. Upon loss of gonadal function in either sex, there occurs an upregulation of osteoclast formation which is mediated by IL-6. Consistent with this, IL-6-deficient mice do not exhibit an increase in the formation of osteoclasts after ovariectomy or orchidectomy, and are protected from the bone loss caused by the loss of gonadal function in either sex. Even though these observations establish that IL-6 is an essential pathogenetic factor in the bone loss caused by gonadal deficiency, it remains unclear whether IL-6 is the sole pathogenetic factor or whether IL-1, TNF, and IL-11 may also be involved. However, in contrast to IL-6, these cytokines do not seem to be directly regulated by sex steroids.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin (IL)-11--mediated signal transduction

IL-11 is a multifunctional cytokine biologically related to IL-6, leukemia inhibitory factor (LIF), oncostatin M (OSM) and ciliary neurotrophic factor (CNTF). It has been shown that these cytokines can utilize common signal transducer, gp130. We have demonstrated that Jak tyrosine kinases, MAP kinases and pp90rsk are highly activated by IL-11 and related cytokines. In addition, we have identified pp90rsk as one of the H7 sensitive protein kinases critical for primary response gene expression induced by IL-11. Furthermore, activation of 3CH134 (a MAP kinase phosphatase) gene by IL-11 suggested that a MAP kinase phosphatase may be involved in IL-11-mediated signal transduction. Our data also suggested that tyrosine phosphorylation of Stat91 and related transcriptional factors is involved in IL-11 signaling but is not sufficient for the activation of primary response genes such as JunB, tis11, tis8 and MAP kinase phosphatase in mouse preadipocytes. The understanding of signal transduction pathways mediated by IL-11 and related cytokines may help to define the common and unique biological properties of these growth factors.

A herpesvirus saimiri protein required for interleukin-2 independence is associated with membranes of transformed T cells

A region of the herpesvirus saimiri genome encoding an mRNA with two open reading frames (ORFs) has been identified to be essential for transformation of T cells. Deletion of either ORF resulted in the loss of transforming ability. ORF-1 has been shown to code for a collagen-like oncoprotein. This study shows for the first time that the bicistronic mRNA can translate a 32-kDa protein from ORF-2. Polyclonal serum to ORF-2 was generated by using a glutathione fusion protein. Using this antiserum, ORF-2 was localized in cell membranes and is expressed on the outer cell membrane. The half-life of this membrane protein was found to be about 5.5 h. Limited sequence similarity was found between ORF-2 and interleukin-11; however, no secretion of ORF-2 protein was detected in supernatants from transformed cells. Further studies are required to investigate the potential interaction with the interleukin-11 receptor.

Structure-function relationships in human interleukin-11. Identification of regions involved in activity by chemical modification and site-directed mutagenesis

Chemical modification approaches combined with site-directed and deletion mutagenesis have been used to identify functionally critical regions/residues of recombinant human IL-11 (rhIL-11). Incubation of rhIL-11 with iodoacetic acid results in specific alkylation of a single methionine residue, Met58, and a 25-fold reduction of in vitro biological activity on mouse plasmacytoma cells. A similar decrease in activity is observed when Met58 is substituted with Ala, Leu, Gln, Glu, or Lys by site-directed mutagenesis. Treatment of rhIL-11 with succinic anhydride leads to modification of the amino-terminal amino group and partial labeling of 2 lysines, Lys41 and Lys98, and to a 3-fold decrease in activity. The activity losses can be attributed to modification of the lysine residues, since the succinyl derivative of the amino terminus is fully active. In addition, carboxyl-terminal deletion mutagenesis studies have demonstrated that removal of the last 4 residues reduces rhIL-11 activity 25-fold, whereas removal of 8 or more amino acids results in an inactive molecule. Based on secondary structure predictions and the location of exon/intron boundaries in the IL-11 genomic structure, we propose a four-helix bundle topology as a structural model for rhIL-11. This model has been tested by limited proteolysis using three side chain-specific endoproteinases. A limited number of protease-sensitive cleavage sites are present in rhIL-11, and all but two are located in the postulated helix interconnecting loops or at helix termini. alpha-Helices, which in the proposed structure form a compact core of the molecule, are inaccessible to digestion under limiting conditions. According to the model, Met58, Lys41 and Lys98 are located on the surface of the molecule, in agreement with their preferential accessibility to chemical modifications. By analogy with human growth hormone, we postulate that Met58 and the carboxyl terminus of rhIL-11 are involved in the primary receptor binding site (site I), whereas Lys41 and Lys98 may be a part of binding site II.

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.

Interleukin 11

IL-11 is a pleiotropic cytokine originally isolated from a bone marrow stromal cell line. It has been shown to share many activities with IL-6, namely to stimulate T cell-dependent B cell maturation, megakaryopoiesis and various stages of myeloid differentiation, but to inhibit adipogenesis. However, the activity of IL-11 on different stages of erythropoiesis in vitro clearly sets it apart form IL-6. IL-11 has little hematopoietic colony stimulatory activity of its own although it sustains terminal differentiation of the late erythroid progenitors CFU-E. In combination with IL-3, IL-11 has profound stimulatory effects on early multipotent hematopoietic progenitors (pre-CFCmulti), on multilineage colony-forming cells (CFCmulti), as well as on erythroid progenitors. The combination of IL-11 with the ligand for c-kit (KL) preferentially acts on early cells since it promotes the multiplication of pre-CFCmulti and stimulates highly proliferative erythroid progenitors that yields remarkable macroscopic erythroblast colonies in culture. The synergistic activity of IL-11 and KL, two stromal factors present in the bone marrow microenvironment, points to a pivotal role of IL-11 in early hematopoiesis. In vivo administration of recombinant human IL-11 elevates the number of circulating neutrophils and platelets and increased megakaryopoiesis in normal mice and primates.

Oncostatin M, leukemia inhibitory factor, and interleukin 6 induce the proliferation of human plasmacytoma cells via the common signal transducer, gp130

We analyzed the stimulatory effect of oncostatin M (OSM), leukemia inhibitory factor (LIF), interleukin 6 (IL-6), IL-11, and the inhibitory effect of anti-IL-6 antibody (Ab), anti-IL-6 receptor monoclonal antibody (mAb), and anti-gp130 mAb on the growth of human plasmacytoma cells freshly isolated from a patient with multiple myeloma. The purified cells showed a plasmacytoid morphology and expressed CD38, CD54, and CD56 antigens but no CD3, CD5, CD10, CD19, CD20, or very late antigen 5. IL-6 receptor (IL-6R) and its signal transducer, gp130, were expressed on their cell surface at a low level. Dose-dependent proliferation of the cells in response to OSM, LIF, and IL-6, but not to IL-11, was observed using [3H]TdR incorporation in vitro. Both anti-IL-6 Ab and anti-IL-6R mAb inhibited the growth of the cells in the presence or absence of exogenous IL-6. These cells release IL-6 but not OSM or LIF into the culture supernatant during short-term culture. Therefore, an autocrine growth mechanism mediated by IL-6, but not by OSM or LIF, was confirmed. Furthermore, anti-gp130 mAb completely inhibited the proliferation of the cells induced by OSM, LIF, as well as IL-6. These data indicate that OSM, LIF, and IL-6 can act as growth factors of human plasmacytoma cells through a common signal transducer, gp130, on their cell surface, and also suggest the potential therapeutic application of anti-gp130 mAb, as well as anti-IL-6R mAb against myeloma/plasmacytomas.

Interleukin-11: a new cytokine critical for osteoclast development

Stromal cells of the bone marrow control the development of osteoclasts through the production of cytokines capable of promoting the proliferation and differentiation of hematopoietic progenitors. Moreover, the deregulated production of the cytokine IL-6 in the bone marrow mediates an increase in osteoclastogenesis after estrogen loss. IL-6, however, does not influence osteoclastogenesis in the estrogen-replete state, suggesting that other cytokines might be responsible for osteoclast development under physiologic circumstances. We report here that IL-11, a newly discovered cytokine that is produced by marrow stromal cells, induced the formation of osteoclasts exhibiting an unusually high degree of ploidy in cocultures of murine bone marrow and calvarial cells. Osteoclasts formed in the presence of IL-11 were capable of bone resorption, as evidenced by the formation of resorption pits, as well as the release of 45Ca from prelabeled murine calvaria. Further, an antibody neutralizing IL-11 suppressed osteoclast development induced by either 1,25-dihydroxyvitamin D3, parathyroid hormone, interleukin-1, or tumor necrosis factor; whereas inhibitors of IL-1 or TNF had no effect on IL-11-stimulated osteoclast formation. The effects of IL-11 on osteoclast development were blocked by indomethacin; more important, however, they were independent of the estrogen status of the marrow donors.

Ciliary neurotropic factor, interleukin 11, leukemia inhibitory factor, and oncostatin M are growth factors for human myeloma cell lines using the interleukin 6 signal transducer gp130

Interleukin 6 (IL-6) is a major growth factor for tumor plasma cells involved in human multiple myeloma (MM). In particular, human myeloma cell lines (HMCL), whose growth is completely dependent on addition of exogenous IL-6, can be obtained reproducibly from every patient with terminal disease. Four cytokines, ciliary neurotropic factor (CNTF), IL-11, leukemia inhibitory factor (LIF), and oncostatin M (OM), use the same transducer chain (signal transducer gp130) as IL-6 and share numerous biological activities with this IL. We found that these four cytokines stimulated proliferation and supported the long-term growth of two out of four IL-6-dependent HMCL obtained in our laboratory. Half-maximal proliferation was obtained with cytokine concentrations ranging from 0.4 to 1.2 ng/ml for IL-11, LIF, and OM. CNTF worked at high concentrations only (90 ng/ml), but addition of soluble CNTF receptor increased sensitivity to CNTF 30-fold. The growth-promoting effect of these four cytokines was abrogated by anti-gp130 antibodies, contrary to results for anti-IL-6 receptor or anti-IL-6 antibodies. No detectable changes in the morphology and phenotype were found when myeloma cells were cultured with one of these four cytokines instead of IL-6. Concordant with their IL-6-dependent growth, the four HMCL expressed membrane IL-6R and gp130 detected by FACS analysis. LIF-binding chain gene (LIFR) was expressed only in the two HMCL responsive to LIF and OM.

Interleukin-11 expression in donor bone marrow cells improves hematological reconstitution in lethally irradiated recipient mice

Lethally irradiated mice were transplanted with syngeneic bone marrow cells infected with a recombinant retrovirus vector containing the human interleukin-11 (hIL-11) cDNA under the control of the human cytomegalovirus (CMV) immediate early promoter. The hIL-11 RNA transcript from the vector was detected in the spleen and bone marrow of the recipient mice, and hIL-11 protein accumulated in their serum. The hematological reconstitution of these mice was compared with recipient mice rescued with bone marrow infected with the parental retrovirus vector not containing the hIL-11 cDNA. The hIL-11-expressing mice had an accelerated recovery of circulating platelets and red and white blood cells. Three months after the transplantation, bone marrow was harvested from the mice and used to rescue other lethally irradiated recipients. The hIL-11 mRNA and protein were also detected in these secondary recipients, and the mice showed improved hematological reconstitution relative to a control group. No abnormal cell proliferation or other histopathology was observed in the hIL-11-expressing mice.

Involvement of gp130/interleukin-6 receptor transducing component in interleukin-11 receptor

The recently cloned interleukin (IL)-11 displays many biological properties in common with those reported for IL-6. In order to analyze the nature and the functionality of the IL-11 receptor we developed a proliferative assay using the human multifactor-dependent cell line TF1. We showed that a blocking monoclonal antibody GPX7 raised against the gp130/IL-6 receptor transducing subunit was also able to inhibit the IL-11-triggered TF1 line proliferation. In addition, involvement of gp130 in IL-11 signaling was demonstrated by an induction of the transducing protein phosphorylation in response to IL-11, as observed for IL-6. In contrast, the blocking monoclonal antibody B-R6, which recognized the gp80/IL-6 binding subunit failed to interfere with the IL-11 proliferative signal in the TF1 cell line. Similarly, we did not observe any competition between IL-6 and IL-11 for a putative common binding site on the cell surface. These results suggest that the IL-11 binding component is different from the gp80/IL-6 receptor. In conclusion, IL-11, along with IL-6, leukemia inhibitory factor, oncostatin M and ciliary neurotrophic factor, belongs to the same family of cytokines, using gp130 as a transducing protein.

Interleukin 11: an overview

Interleukin (IL)-11 is a bone marrow fibroblast derived cytokine with a wide spectrum of in vitro biological activities in the hematopoietic, lymphopoietic, hepatic, adipose, neuronal and osteoclast systems, either alone or in synergy with other hematopoietic growth factors. In vivo administration of IL-11 in mice, rats and nonhuman primates has demonstrated the thrombopoietic effects of this cytokine. The expression of the human IL-11 gene, which is localized at 19q13.3-13.4, can be controlled at both the transcriptional and post-transcriptional levels. Initial biochemical characterization has identified a 151 kD protein as the potential IL-11 binding subunit of the receptor complex. Like other cytokines such as IL-6, leukemia inhibitory factor (LIF), oncostatin M (ONC) and ciliary neurotrophic factor (CNTF), IL-11 has been shown to utilize IL-6 signal transducer, gp130. Because of the overlapping biological activities, the similarities in the predicted tertiary structures, and the sharing of common signal transducer protein, we have compared the signal transduction pathways mediated by these cytokines in various cell types. Studies of protein tyrosine phosphorylation, primary response gene expression and signaling molecules known to be important in transducing mitogenic signals have suggested that there are convergent and divergent points along the signal transduction pathways utilized by IL-11, IL-6, LIF and ONC. These observations may explain the biological pleiotropy and redundancy of this group of cytokines.

Progenitor cell hyperplasia with rare development of myeloid leukemia in interleukin 11 bone marrow chimeras

Post 5-fluorouracil-treated murine bone marrow cells infected with a recombinant retrovirus (murine stem cell virus-interleukin 11 [MSCV-IL-11]) bearing a human IL-11 gene were transplanted into lethally irradiated syngeneic mice. Analysis of proviral integration sites in DNA prepared from hematopoietic tissues and purified cell populations of long-term reconstituted primary and secondary recipients demonstrated polyclonal engraftment by multipotential stem cells. High levels (100-1,500 U/ml) of IL-11 were detected in the plasma of the MSCV-IL-11 mice. Systemic effects of chronic IL-11 exposure included loss of body fat, thymus atrophy, some alterations in plasma protein levels, frequent inflammation of the eyelids, and often a hyperactive state. A sustained rise in peripheral platelet levels (approximately 1.5-fold) was seen throughout the observation period (4-17 wk). No changes were observed in the total number of circulating leukocytes in the majority of the transplanted animals (including 10 primary and 18 secondary recipients) despite a > 20-fold elevation in myeloid progenitor cell content in the spleen. The exceptions were members of one transplant pedigree which presented with myeloid leukemia during the secondary transplant phase. A clonal origin of the disease was determined, with significant expansion of the MSCV-IL-11-marked clone having occurred in the spleen of the primary host. Culturing of leukemic spleen cells from a quaternary recipient led to the establishment of a permanent cell line (denoted PGMD1). IL-11-producing PGMD1 myeloid leukemic cells are dependent on IL-3 for continuous growth in vitro and they differentiate into granulocytes and macrophages in response to granulocyte/macrophage colony-stimulating factor. The inability of autogenously produced IL-11 to support autonomous growth of PGMD1 cells argues against a mechanism of transformation involving a classical autocrine loop.

The biology of interleukin 11

Interleukin 11 (IL-11) is a multifunctional cytokine which may play a role in regulating the growth and development of cells in both the hematopoietic and lymphoid systems. IL-11 activity was originally detected in the conditioned medium of a primate bone marrow stromal cell line, and the human cDNA was cloned from a human fetal lung fibroblast cell line. The purified protein shows multifunctional activity, influencing lymphohematopoietic stem cell proliferation and differentiation, megakaryocyte progenitor cell proliferation and differentiation, erythroid progenitor cell proliferation, B lymphocyte maturation, activation of hepatocyte acute phase protein synthesis, and adipogenesis. At the molecular level, IL-11 is unique, containing no asparagine-linked glycosylation sites and no cysteine residues. The IL-11 receptor belongs to a family of cytokine receptors which includes the receptors for IL-6, leukemia inhibitory factor (LIF), oncostatin M (OSM), and ciliary neurotrophic factor (CNTF), which are all capable of interacting with the signal transducing receptor gp130 after ligand binding. IL-11 has demonstrated activity in preclinical models for the treatment of thrombocytopenia and, in some cases, neutropenia; studies are underway to confirm its usefulness in the clinic for treatment of myelosuppression associated with cancer chemotherapy and bone marrow transplantation.

Interleukin-11 and its receptor

Interleukin (IL)-11 is a bone marrow fibroblast derived cytokine with a wide spectrum of activities in different biological systems. It has been shown that IL-11 supports the growth of certain types of plasmacytoma and hybridoma cells, enhances antigen-specific antibody responses, synergizes with IL-3 in supporting megakaryocyte colony formation, acts synergistically with IL-3 in shortening the G0 period of early progenitors, induces the synthesis of acute phase proteins, and inhibits lipoprotein lipase activity and adipocyte differentiation. The human IL-11 gene, which is localized at 19q13.3-13.4, consists of five exons and four introns. Initial biochemical characterization has identified a 151 kDa protein as the potential IL-11 binding subunit of the receptor complex. Because of the overlapping biological activities between IL-6 and IL-11, we compared the signal transduction pathways mediated by IL-6 or IL-11 in cell lines responsive to both cytokines. Results from protein tyrosine phosphorylation and immediate response gene expression suggest that there are convergent and divergent points along the signal transduction pathways utilized by IL-6 or IL-11. The IL-6 signal transducer, gp130, appears to be involved in the IL-11 mediated signaling. Other cytokines such as leukemia inhibitory factor, oncostatin M and ciliary neurotrophic factor have also been shown to utilize gp130 as a signal transducer. The significance of growth factor sharing common biological activities and signaling pathways will be discussed.

[Function, molecular structure and gene expression of interleukin-11 (IL-11/AGIF)]

Interleukin-11 (IL-11) is a novel cytokine that was identified in a medium conditioned by the primate bone marrow-derived stromal cell line PU-34. It was originally identified as a growth factor for the IL-6-dependent plasmacytoma cell line T1165. Adipogenesis inhibitory factor (AGIF) was cloned from the human bone marrow-derived cell line KM-102. The AGIF cDNA sequence was revealed to be identical to that of the IL-11 cDNA. AGIF inhibits the process of adipogenesis of the bone marrow-derived preadipocyte cell line H-1/A. Other biological activities of IL-11/AGIF, megakaryocytopoiesis, stem-cell proliferation, hepatic acute phase responses and antigen-specific antibody responses are also summarized.

Interleukin-11: a novel stroma-derived cytokine

Interleukin-11 (IL-11) is a novel stroma-derived cytokine that acts on both hematopoietic progenitors and stromal cells. IL-11 was originally identified in a medium conditioned by the macaque bone marrow-derived stromal cell line PU-34 and cloned as a growth factor for the IL-6-dependent plasmacytoma cell line T1165. IL-11 stimulates T-cell dependent development of antibody-producing B cells and is synergistic with IL-3 to stimulate megakaryocyte colony formation. Adipogenesis inhibitory factor (AGIF) was cloned from the human bone marrow-derived stromal cell line KM-102. The AGIF cDNA sequence was revealed to be identical to that of the IL-11 cDNA. AGIF inhibits the process of adipogenesis of the bone marrow-derived preadipocyte cell line H-1/A. Other biological activities such as stimulation of stem-cell proliferation, erythropoiesis, lymphohematopoiesis and hepatic acute-phase response are also summarized. The human IL-11 gene consists of five exons and four introns, and was mapped on chromosome 19 at band 19q13.3-q13.4. A single class of high-affinity IL-11 receptor (IL-11R) of 151 kDa is present on 3T3-L1 preadipocytes. A protein-tyrosine kinase pathway may be involved in the initiation of the IL-11R-mediated signal transduction.