An unusual cytokine:Ig-domain interaction revealed in the crystal structure of leukemia inhibitory factor (LIF) in complex with the LIF receptor

Leukemia inhibitory factor (LIF) receptor is a cell surface receptor that mediates the actions of LIF and other IL-6 type cytokines through the formation of high-affinity signaling complexes with gp130. Here we present the crystal structure of a complex of mouse LIF receptor with human LIF at 4.0 A resolution. The structure is, to date, the largest cytokine receptor fragment determined by x-ray crystallography. The binding of LIF to its receptor via the central Ig-like domain is unlike other cytokine receptor complexes that bind ligand predominantly through their cytokine-binding modules. This structure, in combination with previous crystallographic studies, also provides a structural template to understand the formation and orientation of the high-affinity signaling complex between LIF, LIF receptor, and gp130.     

Functional inhibition of hematopoietic and neurotrophic cytokines by blocking the interleukin 6 signal transducer gp130.

Functional pleiotropy and redundancy are characteristic features of cytokines. To understand the signaling mechanisms of such cytokines, we have proposed a two-chain interleukin (IL) 6 receptor model: IL-6 triggers the association of a ligand-binding chain (IL-6 receptor) and a nonbinding signal transducer (gp130) to form a high-affinity receptor complex, resulting in transmission of the signal by the cytoplasmic portion of gp130. This model would explain the functional redundancy of cytokines if we were to assume that gp130 interacts with several different receptor chains. Here we present data indicating that gp130 functions as a common signal transducer for IL-6, oncostatin M, leukemia inhibitory factor, and ciliary neurotrophic factor. We show that anti-gp130 monoclonal antibodies completely block the biological responses induced by all of these factors. Since leukemia inhibitory factor functions as a cholinergic differentiation factor in nerve cells, as does ciliary neurotrophic factor, these results suggest that gp130 may also play a role in the nervous system.     

Soluble interleukin-6 receptor triggers osteoclast formation by interleukin 6.

It has been reported that soluble interleukin (IL)-6 receptor (sIL-6R) is detected in the serum of healthy individuals and its level is increased in patients with multiple myeloma and human immunodeficiency virus infection. Although several reports have suggested that sIL-6R potentiates IL-6 action, its physiological role remains unclear. In this study, we examined the role of sIL-6R on osteoclast formation by IL-6, using a coculture of mouse osteoblasts and bone marrow cells. Neither recombinant mouse IL-6 (mIL-6) nor mouse sIL-6R (smIL-6R) induced osteoclast-like multinucleated cell (MNC) formation when they were added separately. In contrast, simultaneous treatment with mIL-6 and smIL-6R strikingly induced MNC formation. These MNCs satisfied major criteria of authentic osteoclasts, such as tartrate-resistant acid phosphatase (TRAP) activity, calcitonin receptors, and pit formation on dentine slices. The MNC formation induced by mIL-6 and smIL-6R was dose-dependently inhibited by adding monoclonal anti-mouse IL-6R antibody (MR16-1). It is likely that osteoblasts and osteoclast progenitors are capable of transducing a signal from a complex of IL-6 and sIL-6R through gp130, even though they may have no or a very small number of IL-6Rs. Factors such as IL-11, oncostatin M, and leukemia inhibitory factor, which are known to exert their functions through gp130 (the signal-transducing chain of IL-6R), also induced MNC formation in our coculture system. These results suggest that increased circulating or locally produced sIL-6R induces osteoclast formation in the presence of IL-6 mediated by a mechanism involving gp130. This may play an important physiological or pathological role in conditions associated with increased osteoclastic bone resorption.     

Transformation of hematopoietic cells and activation of JAK2-V617F by IL-27R, a component of a heterodimeric type I cytokine receptor

From a patient with acute myeloid leukemia (AML), we have identified IL-27Ra (also known as TCCR and WSX1) as a gene whose expression can induce the transformation of hematopoietic cells. IL-27Ra (IL-27R) is a type I cytokine receptor that functions as the ligand binding component of the receptor for IL-27 and functions with the glycoprotein 130 (gp130) coreceptor to induce signal transduction in response to IL-27. We show that IL-27R is expressed on the cell surface of the leukemic cells of AML patients. 32D myeloid cells transformed by IL-27R contain elevated levels of activated forms of various signaling proteins, including JAK1, JAK2, STAT1, STAT3, STAT5, and ERK1/2. Inhibition of JAK family proteins induces cell cycle arrest and apoptosis in these cells, suggesting the transforming properties of IL-27R depend on the activity of JAK family members. IL-27R also transforms BaF3 cells to cytokine independence. Because BaF3 cells lack expression of gp130, this finding suggests that IL-27R-mediated transformation of hematopoietic cells is gp130-independent. Finally, we show that IL-27R can functionally replace a homodimeric type I cytokine receptor in the activation of JAK2-V617F, a critical JAK2 mutation in various myeloproliferative disorders (MPDs). Our data demonstrate that IL-27R possesses hematopoietic cell-transforming properties and suggest that, analogous to homodimeric type I cytokine receptors, single-chain components of heterodimeric receptors can also enhance the activation of JAK2-V617F. Therefore, such receptors may play unappreciated roles in MPDs.     

IL-6 trans-signaling via STAT3 directs T cell infiltration in acute inflammation

Interleukin (IL)-6 signaling through its soluble receptor (IL-6 transsignaling) directs transition between innate and acquired immune responses by orchestrating the chemokine-directed attraction and apoptotic clearance of leukocytes. Through analysis of mononuclear cell infiltration in WT and IL-6-deficient mice during peritoneal inflammation, we now report that IL-6 selectively governs T cell infiltration by regulating chemokine secretion (CXCL10, CCL4, CCL5, CCL11, and CCL17) and chemokine receptor (CCR3, CCR4, CCR5, and CXCR3) expression on the CD3+ infiltrate. Although blockade of IL-6 trans-signaling prevented chemokine release, chemokine receptor expression remained unaltered suggesting that this response is regulated by IL-6 itself. To dissect the signaling events promoting T cell migration, inflammation was established in knock-in mice expressing mutated forms of the universal signal-transducing element for IL-6-related cytokines gp130. In mice (gp130Y757F/Y757F) deficient in SHP2 and SOCS3 binding, but presenting hyperactivation of STAT1/3, T cell recruitment and CCL5 expression was enhanced. Conversely, both of these parameters were suppressed in mice with ablated gp130-mediated STAT1/3 activation (gp130DeltaSTAT/DeltaSTAT). T cell migration was related to STAT3 activity, because monoallelic deletion of Stat3 in gp130(Y757F/Y757F) mice (gp130Y757F/Y757F:Stat3+/-) corrected the exaggerated responses observed in gp130Y757F/Y757F mice. Consequently, STAT3 plays a defining role in IL-6-mediated T cell migration.     

gp130 and c-Kit signalings synergize for ex vivo expansion of human primitive hemopoietic progenitor cells.

gp130, a signal-transducing receptor component of interleukin 6 (IL-6), associates with an IL-6 and IL-6 receptor (IL-6) complex and transduces signals. To examine the role of gp130 signaling in the expansion of human hemopoietic progenitor cells, we tested the effects of a recombinant soluble human IL-6 receptor (sIL-6R) and/or IL-6 in combination with other cytokines on purified human umbilical cord blood CD34+ cells, using methylcellulose clonal assay and suspension culture in the presence or absence of serum. A combination of sIL-6R and IL-6 (sIL-6R/IL-6), but not sIL-6R or IL-6 alone, was found to dramatically stimulate expansion of hemopoietic progenitor cells as well as CD34+ cells in the presence of stem cell factor. Significant generation of multipotential hemopoietic progenitors over a period of 3 weeks in suspension culture and efficient formation of colonies, especially multilineage and blast cell colonies, in methylcellulose assay supplemented with a combination of sIL-6R/IL-6 together with stem cell factor were observed in serum-containing and serum-free culture. Addition of anti-gp130 monoclonal antibodies or anti-IL-6R monoclonal antibodies to the above cultures dose-dependently inhibited the expansion of progenitor cells in suspension culture and also completely blocked the formation of multilineage colonies in methylcellulose culture. These findings demonstrated that the significant expansion of human primitive hemopoietic progenitors could be achieved with the gp130 and c-Kit signalings initiated by the sIL-6R/IL-6 complex in the presence of stem cell factor and suggested the possible application of this method for ex vivo expansion of CD34+ cells for bone marrow transplantation.     

Expression and regulation of gp130 messenger ribonucleic acid in cultured immature rat Sertoli cells

The expression of glycoprotein 130 (gp130) was studied in rat primary Sertoli cells by Northern blot analysis. Gp130 mRNA of 9.0 and 7.5 kb were detected in a variety of rat tissues including the testis. Gp130 mRNAs were detected in isolated, immature Sertoli cells. The levels of gp130 were significantly stimulated by the addition of interleukin-1-beta (IL-1-beta) or interleukin-6 (IL-6) but not by the addition of follicle-stimulating hormone (FSH). IL-6 activates intracellular signaling by binding with a receptor consisting of an 80-kDa ligand-binding protein, IL-6 receptor (IL-6R), and a second 130-kDa protein, gp130. As previously reported, expression of IL-6R mRNA in rat Sertoli cells was stimulated not only by IL-1-beta and IL-6 but also by FSH. In contrast, gp130 mRNA expression was not stimulated by FSH in our analysis. These data suggest that gp130 expression may be regulated by more than 1 mechanism and that production of gp130 and IL-6R, the 2 components of the IL-6 receptor system, may be regulated, at least in part, by a different pathway.     

Opposing roles of gp130-mediated STAT-3 and ERK-1/ 2 signaling in liver progenitor cell migration and proliferation

Gp130-mediated IL-6 signaling may play a role in oval cell proliferation in vivo. Levels of IL-6 are elevated in livers of mice treated with a choline-deficient ethionine-supplemented (CDE) diet that induces oval cells, and there is a reduction of oval cells in IL-6 knockout mice. The CDE diet recapitulates characteristics of chronic liver injury in humans. In this study, we determined the impact of IL-6 signaling on oval cell-mediated liver regeneration in vivo. Signaling pathways downstream of gp130 activation were also dissected. Numbers of A6(+ve) liver progenitor oval cells (LPCs) in CDE-treated murine liver were detected by immunohistochemistry and quantified. Levels of oval cell migration and proliferation were compared in CDE-treated mouse strains that depict models of gp130-mediated hyperactive ERK-1/2 signaling (gp130(deltaSTAT)), hyperactive STAT-3 signaling (gp130(Y757F) and Socs-3(-/deltaAlb)) or active ERK-1/2 as well as active STAT-3 signaling (wild-type). The A6(+ve) LPC numbers were increased with IL-6 treatment in vivo. The gp130(Y757F) mice displayed increased A6(+ve) LPCs numbers compared with wild-type and gp130(deltaSTAT) mice. Numbers of A6(+ve) LPCs were also increased in the livers of CDE treated Socs-3(-/deltaAlb) mice compared with their control counterparts. Lastly, inhibition of ERK-1/2 activation in cultured oval cells increased hyper IL-6-induced cell growth. For the first time, we have dissected the gp130-mediated signaling pathways, which influence liver progenitor oval cell proliferation. Conclusion: Hyperactive STAT-3 signaling results in enhanced oval cell numbers, whereas ERK-1/2 activation suppresses oval cell proliferation.     

Soluble interleukin-6 (IL-6) receptor with IL-6 stimulates megakaryopoiesis from human CD34(+) cells through glycoprotein (gp)130 signaling

We have recently shown that stimulation of glycoprotein (gp) 130, the membrane-anchored signal transducing receptor component of IL-6, by a complex of human soluble interleukin-6 receptor (sIL-6R) and IL-6 (sIL-6R/IL-6), potently stimulates the ex vivo expansion as well as erythropoiesis of human stem/progenitor cells in the presence of stem cell factor (SCF). Here we show that sIL-6R dose-dependently enhanced the generation of megakaryocytes (Mks) (IIbIIIa-positive cells) from human CD34(+) cells in serum-free suspension culture supplemented with IL-6 and SCF. The sIL-6R/IL-6 complex also synergistically acted with IL-3 and thrombopoietin (TPO) on the generation of Mks from CD34(+) cells, whereas the synergy of IL-6 alone with TPO was barely detectable. Accordingly, the addition of sIL-6R to the combination of SCF + IL-6 also supported a substantial number of Mk colonies from CD34(+) cells in serum-free methylcellulose culture, whereas SCF + IL-6 in the absence of sIL-6R rarely induced Mk colonies. The addition of monoclonal antibodies against gp130 to the suspension and clonal cultures completely abrogated the megakaryopoiesis induced by sIL-6R/IL-6 in the presence of SCF, whereas an anti-TPO antibody did not, indicating that the observed megakaryopoiesis by sIL-6R/IL-6 is a response to gp130 signaling and independent of TPO. Furthermore, human CD34(+) cells were subfractionated into two populations of IL-6R-negative (CD34(+) IL-6R-) and IL-6R-positive (CD34(+) IL-6R+) cells by fluorescence-activated cell sorting. The CD34(+) IL-6R- cells produced a number of Mks as well as Mk colonies in cultures supplemented with sIL-6R/IL-6 or TPO in the presence of SCF. In contrast, CD34(+) IL-6R+ cells generated much less Mks and lacked Mk colony forming activity under the same conditions. Collectively, the present results indicate that most of the human Mk progenitors do not express IL-6R, and that sIL-6R confers the responsiveness of human Mk progenitors to IL-6. Together with the presence of functional sIL-6R in human serum and relative unresponsiveness of human Mk progenitors to IL-6 in vitro, current results suggest that the role of IL-6 may be mainly mediated by sIL-6R, and that the gp130 signaling initiated by the sIL-6R/ IL-6 complex is involved in human megakaryopoiesis in vivo.     

Receptor engagement by viral interleukin-6 encoded by Kaposi sarcoma-associated herpesvirus.

Receptor usage by viral interleukin-6 (vIL-6), a virokine encoded by Kaposi sarcoma- associated herpesvirus, is an issue of controversy. Recently, the crystal structure of vIL-6 identified vIL-6 sites II and III as directly binding to glycoprotein (gp)130, the common signal transducer for the IL-6 family of cytokines. Site I of vIL-6, however, comprising the outward helical face of vIL-6, where human IL-6 (hIL-6) would interact with the specific alpha-chain IL-6 receptor (IL-6R), is accessible and not occupied by gp130. This study examined whether this unused vIL-6 surface is available for IL-6R binding. By enzyme-linked immunosorbent assay, vIL-6 bound to soluble gp130 (sgp130) but not to soluble IL-6R (sIL-6R). Using plasmon surface resonance, vIL-6 bound to sgp130 with a dissociation constant of 2.5 microM, corresponding to 1000-fold lower affinity than that of hIL-6/sIL-6R complex for gp130. sIL-6R neither bound to vIL-6 nor affected vIL-6 binding to gp130. In bioassays, vIL-6 activity was neutralized by 4 monoclonal antibodies (mAbs) recognizing a domain within vIL-6 site I, mapped to the C-terminal part of the AB-loop and the beginning of helix B. The homologous region in hIL-6 participates in site I binding to IL-6R. In addition, binding of vIL-6 to sgp130 was interfered with specifically by the 4 neutralizing anti-vIL-6 mAbs. Based on the vIL-6 crystal structure, the vIL-6 neutralizing mAbs map outside the binding interface to gp130, suggesting that they either produce allosteric changes or block necessary conformational changes in vIL-6 preceding its binding to gp130. These results document that vIL-6 does not bind IL-6R and suggest that conformational change may be critical to vIL-6 function.     

gp130 signaling pathways: Recent advances and implications for cardiovascular disease

gp130 was initially identified as a signal-transducing receptor component that associates with the interleukin 6 receptor (IL-6R) when the receptor is occupied by interleukin 6 (IL-6). It has been revealed that the receptor complexes for IL-6, IL-11, leukemia inhibitory factor (LIF), oncostatin M (OM), and ciliary neurotrophic factor (CNTF) utilize this gp130 protein as a common signal-transducing component, explaining how these cytokines mediate overlapping biological function. Recent observations with mice lacking gp130 or having continuously activated gp130 protein have disclosed an important biological function of gp130 in cardiovascular system: the former mice show extremely hypoplastic development of the ventricular myocardium at 16.5 days postcoitum (dpc), and the latter exhibit hypertrophy of myocardium. These cardiovascular abnormalities are considered to be the results of the perturbation of gp130, which also transduces the signal of cardiotrophin-1 (CT-1), a recently isolated factor causing hypertrophy in cultured cardiomyocytes and having sequence similarity with IL-6, IL-11, LIF, CNTF, and OM. In fact, CT-1 shares gp130 with these cytokines as a critical signaling component. Besides various well-established mechanisms by which cardiac growth and development are regulated, a gp130 signaling may be a newly discovered mechanism that regulates these events.     

Hematopoietic abnormalities in mice deficient in gp130-mediated STAT signaling

OBJECTIVE: Studies on mice lacking the common receptor subunit gp130 reveal that activation of gp130-dependent signaling pathways is essential for normal fetal and adult hematopoiesis. However, the extent to which hematopoiesis is dependent upon activation of a particular gp130 signaling pathway, namely STAT1/3 or SHP2/MAPK, is unknown. This study examined the specific contribution of gp130-mediated STAT1/3 signaling to the regulation of hematopoiesis. MATERIALS AND METHODS: Hematopoiesis was examined at various developmental stages in mice homozygous for a targeted carboxy-terminal truncation mutation in gp130 (gp130(delta)/(delta)) that deletes all STAT1/3 binding sites, thereby abolishing gp130-mediated STAT1/3 activation. RESULTS: Adult gp130(delta)/(delta) mice have increased numbers of immature colony-forming unit spleen progenitor cells in the bone marrow and spleen, elevated numbers of committed myeloid progenitor cells in the spleen and peripheral blood, and leukocytosis. Increased progenitor cell production was observed in gp130(delta)/(delta) fetal livers from 14 days of gestation onward. In contrast, the circulating platelet count was reduced by 30% in gp130(delta)/(delta) mice, without any corresponding decrease in the number of bone marrow and splenic megakaryocytes. In liquid cultures, megakaryocytes from gp130(delta)/(delta) mice are smaller than those from wild-type mice and do not increase in size upon stimulation with interleukin-6 or interleukin-11. Administration of either interleukin-6 or interleukin-11 to gp130(delta)/(delta) mice failed to increase platelet numbers, despite an increase in the production of megakaryocytes. CONCLUSIONS: Collectively, these results reveal that gp130-mediated STAT1/3 activation is required to maintain the normal balance of hematopoietic progenitors during fetal and adult hematopoiesis. Furthermore, they suggest two distinct roles for gp130-mediated STAT1/3 activation in hematopoiesis, one restricting the production of immature hematopoietic progenitor cells and the other promoting the functional maturation of megakaryocytes to produce platelets.     

A receptor for interleukin 10 is related to interferon receptors.

We isolated cDNAs encoding a mouse interleukin 10 receptor (mIL-10R) from mouse mast cell and macrophage cell lines. The two cDNAs are substantially identical and express an approximately 110-kDa polypeptide in COS7 cells, which binds mIL-10 specifically. A mouse pro-B-cell line (Ba/F3) expressing transfected recombinant mIL-10R binds IL-10 with high affinity (approximately 70 pM) and proliferates in response to mIL-10. mIL-10R is structurally related to interferon receptors (IFNRs). Since IL-10 inhibits macrophage activation by IFN-gamma, a possible implication of this relationship interaction of IL-10R and IFN-gamma R or their signaling pathways.     

Influence of humanized anti-IL-6R antibody, tocilizumab on the activity of soluble gp130, natural inhibitor of IL-6 signaling

Tocilizumab, humanized anti-IL-6R antibody is a novel anti-rheumatic drug. In the present study, we examined the influence of tocilizumab on the inhibitory activity of soluble gp130 (sgp130) against IL-6 signaling. BAF-h130 cells, human gp130 transfected mouse pro-B cell line, were cultured with the mixture with IL-6, sIL-6R and sgp130 for 72 h. BAF-h130 cells proliferated by the addition of both IL-6 and sIL-6R, but not IL-6 or sIL-6R alone. The proliferation induced by IL-6/sIL-6R complex was inhibited by sgp130 concentration-dependently. Tocilizumab inhibited IL-6/sIL-6R-induced cell proliferation. On the other hand, it did not affect the suppressive property of sgp130. To examine if tocilizumab can dissociate IL-6/sIL-6R/sgp130 complex, we established an ELISA system to detect IL-6/sIL-6R/sgp130 complex using anti-IL-6R coated ELISA plate. The results clearly indicated that ELISA system established was detectable IL-6/sIL-6R/sgp130 complex in a concentration dependent manner. Tocilizumab was added to IL-6/sIL-6R/sgp130 complex-fixed plate and then remaining IL-6/sIL-6R/sgp130 complexes on the plate were measured. The amount of IL-6/sIL-6R/sgp130 complexes on the plate was not changed by the addition of tocilizumab. In conclusion, tocilizumab exerts its inhibitory effect through the inhibition of IL-6R directly without affecting natural inhibitor sgp130.     

Identification of a distinct low-affinity receptor for human interleukin-4 on pre-B cells

Biotinylated interleukin-4 (IL-4) was used to examine IL-4 receptor (IL- 4R) expression on a range of human B-cell lines by flow cytometry. Using high concentrations of biotinylated IL-4, we have identified a novel low-affinity IL-4 receptor expressed at high levels on pre-B lines. Expression of this low-affinity receptor did not correlate with detected mRNA levels for the previously cloned receptor or with reactivity of two anti-human IL-4R monoclonal antibodies (MoAb). Radiolabeled IL-4 cross-linking studies using pre-B lines showed a doublet of 65 to 75 Kd in contrast to the 110- to 130-Kd molecule detected on cells expressing the cloned IL-4R. A soluble IL-4 binding protein (IL-4bp) was purified from the supernatants of three pre-B lines expressing the low-affinity receptor on their surface. IL-4bp could block both IL-4-mediated CD23 induction on tonsil B cells and IL- 4-induced inhibition of proliferation of the pre-B line JM1. Partial N- terminal amino acid sequence was obtained from purified IL-4bp that confirmed this protein to be novel. A 12 amino acid peptide based on the IL-4bp sequence was used to produce a polyclonal antiserum that was reactive with purified IL-4bp, and also bound to the surface of pre-B cells but not to murine CTLL cells transfected with the human IL-4R. Blocking MoAb against the previously characterized high-affinity receptor inhibited IL-4-mediated proliferation of hIL-4R+ CTLL cells but had no effect on IL-4-induced inhibition of JM1 cell proliferation, and only partially inhibited IL-4-mediated CD23 and sIgM induction and proliferation of tonsil B cells. The data presented here provide evidence for a novel cell-surface expressed low-affinity IL-4R that also exists as a biologically active soluble IL-4 binding protein.     

Critical cytoplasmic region of the interleukin 6 signal transducer gp130 is conserved in the cytokine receptor family.

Interleukin 6 (IL-6) signal is transduced through gp130 that associates with a complex of IL-6 and IL-6 receptor. Truncations or amino acid substitutions offe introduced in the cytoplasmic region of human gp130, and the mutant cDNAs were transfected into murine interleukin 3-dependent cells to determine amino acid residues critical for generating the IL-6-mediated growth signal. In the 277-amino acid cytoplasmic region of gp130, a 61-amino acid region proximal to the transmembrane domain was sufficient for generating the growth signal. In this region, two short segments were significantly homologous with other cytokine-receptor family members. One segment is conserved in almost all members of the family, and the other is found especially in granulocyte colony-stimulating factor receptor, interleukin 2 receptor beta chain, erythropoietin receptor, KH97 (a granulocyte/macrophage colony-stimulating factor receptor-associated molecule), and interleukin 3 receptor. gp130 molecules with mutations in either of these two segments could not transduce growth signal. Loss of signal-transducing ability of gp130 with such a mutation coincided with disappearance of IL-6-induced tyrosine phosphorylation of gp130.     

Effect of recombinant human interleukin-11 on expressions of interleukin-11 receptor α-chain and glycoprotein 130 in intestinal epithelium cell line-6 after neutron irradiation

AIM: To explore the effect of recombinant human interleukin-11 (rhIL-11) on the expressions of interleukin-11 receptor α-chain (IL-11Rα) and an additional signal transducer glycoprotein 130 (gp130) in intestinal epithelium cell line-6 (IEC-6) after neutron irradiation.METHODS: Cultured IEC-6 cells were exposed to 4.0Gy neutron and treated with 100 ng/mL rhIL-11 12 h prior to or immediately after irradiation. The apoptosis and necrosis rates and expressions of IL-11Rα and gp130 were observed by flow cytometry, immunohistochemistry, Western blot and image analysis.RESULTS: The apoptosis rate of IEC-6 cells was increased by irradiation at 6 h (P ＜ 0.01), IL-11 stimulation resulted in a decreased apoptosis rate in irradiated IEC-6 cells (P ＜ 0.05). In normal control IEC-6 cells, intense immunoreactivity of IL-11Rα was located within the cell membrane and cytoplasm. The level of IL-11Rα expression significantly decreased at 6 h after irradiation (P ＜ 0.01) and restored at 24 h after irradiation. In IEC-6 cells treated with both radiation and rhIL-11, the level of IL-11Rα expression was higher than that of irradiated cells (P ＜ 0.05). When it came to gp130 protein, it was located in the cytoplasm of IEC-6 cells. After irradiation, we found a progressive decrease in the expression of gp130 protein (P ＜ 0.05) in 48 hours post-radiation, while in rhIL-11-stimulated cells, it came back to normal level at 24 h after irradiation and decreased at 48 h, but was still higher than that of only irradiated cells (P ＜ 0.05).CONCLUSION: rhIL-11 can protect IEC-6 cells from neutron irradiation. The protective effect of rhIL-11 might be connected with its ability to up-regulate the expressions of specific ligand-binding subunit IL-11Rα and signal-transducing subunit gp130.     

The interleukin 2 receptor (IL-2R): the IL-2R alpha subunit alters the function of the IL-2R beta subunit to enhance IL-2 binding and signaling by mechanisms that do not require binding of IL-2 to IL-2R alpha subunit.

Interleukin 2 (IL-2)-mediated signaling through its high-affinity receptor involves a complex interrelationship between IL-2 and two IL-2-binding chains, IL-2R alpha and beta chains. Previously with the reagents available it was difficult to define functional interactions between these two IL-2R subunits involved in IL-2 binding and signal transduction. To extend our understanding of the interplay between the two binding subunits we have done studies with the monoclonal antibody HIEI, which interferes with interaction of IL-2R alpha and beta chains (IL-2R alpha and IL-2R beta, respectively). Furthermore, we used two forms of IL-2, recombinant native IL-2 and F42A, an IL-2 analog (Phe-42----Ala substitution) that binds only to IL-2R beta. Analog F42A manifested 75-100% of the bioactivity of wild-type IL-2. This observation is inconsistent with the strict hierarchical IL-2-binding affinity conversion model previously proposed by Saito and coworkers [Saito Y., Sabe, H., Suzuki, N., Kondo, S., Ogura, T., Shimizu, A. & Honjo, T. (1988) J. Exp. Med. 168, 1563-1572] that predicted an ordered sequence of events in which IL-2 must first bind to IL-2R alpha before its interaction with IL-2R beta. Previous investigations using IL-2 variants were interpreted to show that IL-2R alpha merely acts to concentrate IL-2 to the cell surface and that no other meaningful interaction occurred between IL-2R alpha and IL-2R beta. However, our data are inconsistent with this view. We draw this conclusion on the basis of our observation that antibody HIEI, which reacts with an epitope of IL-2R alpha and interferes with interaction of this chain and IL-2R beta, inhibits the IL-2-dependent proliferative effects mediated by analog F42A. Furthermore, by blocking interaction of IL-2R alpha and IL-2R beta with the antibody HIEI, a decrease in the affinity of radiolabeled analog F42A for IL-2R beta was seen. In our proposed model IL-2R alpha contributes several functions to IL-2-mediated signaling through the high-affinity IL-2R. These functions include concentration of IL-2 within the two-dimensional surface of the plasma membrane as well as alteration of the functional capacity of IL-2R beta, an effect that does not require prior binding of IL-2R to IL-2R alpha. The IL-2R alpha-mediated augmentation of IL-2R beta functions involves affinity conversion of IL-2R beta, increasing its affinity for IL-2, and may involve facilitation of Il-2-mediated signaling after binding of IL-2 to this IL-2R beta.