Mitogen-activated protein kinases and ribosomal S6 protein kinases are involved in signaling pathways shared by interleukin-11, interleukin-6, leukemia inhibitory factor, and oncostatin M in mouse 3T3-L1 cells

The Emerging Role of Interleukin-(IL)-11/IL-11R in Bone Metabolism and Homeostasis: From Cytokine to Osteokine

Interleukin-(IL)-11 is a cytokine involved in hematopoiesis, cancer metastasis, and inflammation. IL-11 belongs to the IL-6 cytokine family, binding to the complex of receptors glycoprotein gp130 and the ligand-specific-receptor subunits (IL-11Rα or their soluble counterpart sIL-11R). IL-11/IL-11R signaling enhances osteoblast differentiation and bone formation and mitigates osteoclast-induced bone resorption and cancer bone metastasis. Recent studies have shown that systemic and osteoblast/osteocyte-specific IL-11 deficiency leads to reduced bone mass and formation, but also adiposity, glucose intolerance, and insulin resistance. In humans, mutations of IL-11 and the receptor IL-11RA genes are associated with height reduction, osteoarthritis, and craniosynostosis. In this review, we describe the emerging role of IL-11/IL-11R signaling in bone metabolism by targeting osteoblasts, osteoclasts, osteocytes, and bone mineralization. Furthermore, IL-11 promotes osteogenesis and suppresses adipogenesis, thereby influencing the fate of osteoblast/adipocyte differentiation derived from pluripotent mesenchymal stem cells. We have newly identified IL-11 as a bone-derived cytokine that regulates bone metabolism and the link between bone and other organs. Thus, IL-11 is vital in bone homeostasis and could be considered a potential therapeutic strategy.

Effects of IL-11/IL-11 Receptor Alpha on Proliferation and Steroidogenesis in Ovarian Granulosa Cells of Dairy Cows

Granulosa cells (GCs) are essential for follicular growth, oocyte maturation, and steroidogenesis in the ovaries. Interleukin (IL)-11 is known to play a crucial role in the decidualization of the uterus, however, the expression of the IL-11 system (IL-11, IL-11Rα, and gp130) in the bovine ovary and its exact role in GCs have not been extensively studied. In this study, we identified the IL-11 signaling receptor complex in the bovine ovary and investigated the regulatory effects and underlying mechanism of IL-11Rα on the proliferation and steroidogenesis of GCs. We observed that the IL-11 complex was highly expressed in the GCs of large follicles. IL-11Rα knockdown significantly inhibited GC proliferation by inducing cell cycle arrest at the G1 phase, along with a significant downregulation of proliferating cell nuclear antigen (PCNA) and Cyclin D1 (CCND1) protein, and induced GC apoptosis by significantly upregulating the ratio of BCL-2-associated X protein (BAX) and B-cell lymphoma-2 (BCL-2). In addition, IL-11Rα knockdown attenuated the Janus kinase (JAK) 1-signal transducer and activator of transcription 3 (STAT3) signaling, which is related to cell proliferation and apoptosis. Furthermore, the enzyme-linked immunosorbent assay (ELISA) indicated that IL-11Rα silencing decreased the basal and forskolin (FSK)-stimulated secretions of estradiol and progesterone in GC culture medium concomitantly with a remarkable decrease in cytochrome P450 family 19 subfamily A member 1 (CYP19A1) and steroidogenic acute regulatory protein (StAR). We subsequently determined that this reduction in steroidogenesis was in parallel with the decrease in phosphorylations of protein kinase A (PKA) substrates, cAMP-response element binding protein (CREB), extracellular regulated protein kinase (ERK) 1/2, and p38 mitogen-activated protein kinase (MAPK). Taken together, these data indicate that the effects of IL-11/IL-11Rα on the proliferation and steroidogenesis in bovine GCs is mediated by the JAK1-STAT3, PKA-CREB, p38MAPK, and ERK1/2 signaling pathways. Our findings provide important insights into the local action of the IL-11 system in regulating ovarian function.

Interleukin 11: similar or opposite roles in female reproduction and reproductive cancer?

During placental development and carcinogenesis, cell invasion and migration are critical events in establishing a self-supporting vascular supply. Interleukin (IL)-11 is a pleiotropic cytokine that affects the invasive and migratory capabilities of trophoblast cells that form the placenta during pregnancy, as well as various malignant cell types. The endometrium is the site of embryo implantation during pregnancy; conversely, endometrial carcinoma is the most common gynaecological malignancy. Here, we review what is known about the role of IL-11 in trophoblast function and in gynaecological malignancies, focusing primarily on the context of the uterine environment.

A panoramic review and in silico analysis of IL-11 structure and function

Human Interleukin (IL)-11 is a multifunctional cytokine, recognized for its thrombopoietic effects for more than two decades; clinically, IL-11 is used in the treatment of thrombocytopenia. IL-11 shares structural and functional similarities with IL-6, a related family member. In recent years, there has been a renewed interest in IL-11, because its distinct biological activities associated with cancers of epithelial origin and inflammatory disorders have been revealed. Although the crystal structure of IL-11 was resolved more than two years, a better understanding of the mechanisms of IL-11 action is required to further extend the clinical use of IL-11. This review will discuss the available structural, functional, and bioinformatics knowledge concerning IL-11 and will summarize its relationship with several diseases.

Interleukin-11 alters placentation and causes preeclampsia features in mice

Preeclampsia (PE) is a pregnancy-specific disorder characterized by hypertension and proteinuria after 20 wk gestation. Abnormal extravillous trophoblast (EVT) invasion and remodeling of uterine spiral arterioles is thought to contribute to PE development. Interleukin-11 (IL11) impedes human EVT invasion in vitro and is elevated in PE decidua in women. We demonstrate that IL11 administered to mice causes development of PE features. Immunohistochemistry shows IL11 compromises trophoblast invasion, spiral artery remodeling, and placentation, leading to increased systolic blood pressure (SBP), proteinuria, and intrauterine growth restriction, although nonpregnant mice were unaffected. Real-time PCR array analysis identified pregnancy-associated plasma protein A2 (PAPPA2), associated with PE in women, as an IL11 regulated target. IL11 increased PAPPA2 serum and placental tissue levels in mice. In vitro, IL11 compromised primary human EVT invasion, whereas siRNA knockdown of PAPPA2 alleviated the effect. Genes regulating uterine natural killer (uNK) recruitment and differentiation were down-regulated and uNK cells were reduced after IL11 treatment in mice. IL11 withdrawal in mice at onset of PE features reduced SBP and proteinuria to control levels and alleviated placental labyrinth defects. In women, placental IL11 immunostaining levels increased in PE pregnancies and in serum collected from women before development of early-onset PE, shown by ELISA. These results indicate that elevated IL11 levels result in physiological changes at the maternal-fetal interface, contribute to abnormal placentation, and lead to the development of PE. Targeting placental IL11 may provide a new treatment option for PE.

Information theoretic approach to complex biological network reconstruction: application to cytokine release in RAW 264.7 macrophages

BACKGROUND

High-throughput methods for biological measurements generate vast amounts of quantitative data, which necessitate the development of advanced approaches to data analysis to help understand the underlying mechanisms and networks. Reconstruction of biological networks from measured data of different components is a significant challenge in systems biology.

RESULTS

We use an information theoretic approach to reconstruct phosphoprotein-cytokine networks in RAW 264.7 macrophage cells. Cytokines are secreted upon activation of a wide range of regulatory signals transduced by the phosphoprotein network. Identifying these components can help identify regulatory modules responsible for the inflammatory phenotype. The information theoretic approach is based on estimation of mutual information of interactions by using kernel density estimators. Mutual information provides a measure of statistical dependencies between interacting components. Using the topology of the network derived, we develop a data-driven parsimonious input-output model of the phosphoprotein-cytokine network.

CONCLUSIONS

We demonstrate the applicability of our information theoretic approach to reconstruction of biological networks. For the phosphoprotein-cytokine network, this approach not only captures most of the known signaling components involved in cytokine release but also predicts new signaling components involved in the release of cytokines. The results of this study are important for gaining a clear understanding of macrophage activation during the inflammation process.

JAK-STAT3 and somatic cell reprogramming

Reprogramming somatic cells to pluripotency, especially by the induced pluripotent stem cell (iPSC) technology, has become widely used today to generate various types of stem cells for research and for regenerative medicine. However the mechanism(s) of reprogramming still need detailed elucidation, including the roles played by the leukemia inhibitory factor (LIF) signaling pathway. LIF is central in maintaining the ground state pluripotency of mouse embryonic stem cells (ESCs) and iPSCs by activating the Janus kinase-signal transducer and activator of transcription 3 (JAK-STAT3) pathway. Characterizing and understanding this pathway holds the key to generate naïve pluripotent human iPSCs which will facilitate the development of patient-specific stem cell therapy. Here we review the historical and recent developments on how LIF signaling pathway regulates ESC pluripotency maintenance and somatic cell reprogramming, with a focus on JAK-STAT3.

Autocrine production of IL-11 mediates tumorigenicity in hypoxic cancer cells

IL-11 and its receptor, IL-11Ra, are expressed in human cancers; however, the functional role of IL-11 in tumor progression is not known. We found that IL11 is a hypoxia-inducible, VHL-regulated gene in human cancer cells and that expression of IL11 mRNA was dependent, at least in part, on HIF-1. A cooperative interaction between HIF-1 and AP-1 mediated transcriptional activation of the IL11 promoter. Additionally, we found that human cancer cells expressed a functional IL-11Ra subunit, which triggered signal transduction either by exogenous recombinant human IL-11 or by autocrine production of IL-11 in cells cultured under hypoxic conditions. Silencing of IL11 dramatically abrogated the ability of hypoxia to increase anchorage-independent growth and significantly reduced tumor growth in xenograft models. Notably, these results were phenocopied by partial knockdown of STAT1 in a human prostate cancer cell line (PC3), suggesting that this pathway may play an important role in mediating the effects of IL-11 under hypoxic conditions. In conclusion, these results identify IL11 as an oxygen- and VHL-regulated gene and provide evidence of a pathway "hijacked" by hypoxic cancer cells that may contribute to tumor progression.

Identification of steroid-sensitive gene-1/Ccdc80 as a JAK2-binding protein

The tyrosine kinase Janus kinase 2 (JAK2) is activated by many cytokine receptors, including receptors for GH, leptin, and erythropoietin. However, very few proteins have been identified as binding partners for JAK2. Using a yeast 2-hybrid screen, we identified steroid-sensitive gene-1 (SSG1)/coiled-coil domain-containing protein 80 (Ccdc80) as a JAK2-binding partner. We demonstrate that Ccdc80 preferentially binds activated, tyrosyl-phosphorylated JAK2 but not kinase-inactive JAK2 (K882E) in both yeast and mammalian systems. Ccdc80 is tyrosyl phosphorylated in the presence of JAK2. The binding of Ccdc80 to JAK2 occurs via 1 or more of the 3 DUDES/SRPX (DRO1-URB-DRS-Equarin-SRPUL/sushi repeat containing protein, x-linked) domain 5 domains of Ccdc80. Mutagenesis of the second DUDES domain suggests that the N-terminal third of the DUDES domain is sufficient for JAK2 binding. Ccdc80 does not alter the kinase activity of JAK2. However, Ccdc80 increases GH-dependent phosphorylation of Stat (signal transducer and activator of transcription) 5b on Tyr699 and substantially enhances both basal and GH-dependent phosphorylation/activation of Stat3 on Tyr705. Furthermore, Ccdc80 belongs to the group of proteins that function both in the intracellular compartment and are secreted. Secreted Ccdc80 associates with the extracellular matrix and is also found in the medium. A substantial portion of the Ccdc80 detected in the medium is cleaved. Finally, consistent with the DUDES domain serving as a JAK2-binding domain, we also demonstrate that another protein that contains a DUDES domain, SRPX2, binds preferentially to the activated tyrosyl-phosphorylated form of JAK2.

Identification of functional TFAP2A and SP1 binding sites in new TFAP2A-modulated genes

Background

Different approaches have been developed to dissect the interplay between transcription factors (TFs) and their cis-acting sequences on DNA in order to identify TF target genes. Here we used a combination of computational and experimental approaches to identify novel direct targets of TFAP2A, a key TF for a variety of physiological and pathological cellular processes. Gene expression profiles of HeLa cells either silenced for TFAP2A by RNA interference or not were previously compared and a set of differentially expressed genes was revealed.

Results

The regulatory regions of 494 TFAP2A-modulated genes were analyzed for the presence of TFAP2A binding sites, employing the canonical TFAP2A Positional Weight Matrix (PWM) reported in Jaspar http://jaspar.genereg.net/. 264 genes containing at least 2 high score TFAP2A binding sites were identified, showing a central role in "Cellular Movement" and "Cellular Development". In an attempt to identify TFs that could cooperate with TFAP2A, a statistically significant enrichment for SP1 binding sites was found for TFAP2A-activated but not repressed genes. The direct binding of TFAP2A or SP1 to a random subset of TFAP2A-modulated genes was demonstrated by Chromatin ImmunoPrecipitation (ChIP) assay and the TFAP2A-driven regulation of DCBLD2/ESDN/CLCP1 gene studied in details.

Conclusions

We proved that our computational approaches applied to microarray selected genes are valid tools to identify functional TF binding sites in gene regulatory regions as confirmed by experimental validations. In addition, we demonstrated a fine-tuned regulation of DCBLD2/ESDN transcription by TFAP2A.

Prokineticin-1 (PROK1) modulates interleukin (IL)-11 expression via prokineticin receptor 1 (PROKR1) and the calcineurin/NFAT signalling pathway

Prokineticin-1 (PROK1) is a multifunctional secreted protein which signals via the G-protein coupled receptor, PROKR1. Previous data from our laboratory using a human genome survey microarray showed that PROK1-prokineticin receptor 1 (PROKR1) signalling regulates numerous genes important for establishment of early pregnancy, including the cytokine interleukin (IL)-11. Here, we have shown that PROK1-PROKR1 induces the expression of IL-11 in PROKR1 Ishikawa cells and first trimester decidua via the calcium-calcineurin signalling pathway in a guanine nucleotide-binding protein (G(q/11)), extracellular signal-regulated kinases, Ca(2+) and calcineurin-nuclear factor of activated T cells dependent manner. Conversely, treatment of human decidua with a lentiviral miRNA to abolish endogenous PROK1 expression results in a significant reduction in IL-11 expression and secretion. Importantly, we have also shown a regulatory role for the regulator of calcineurin 1 isoform 4 (RCAN1-4). Overexpression of RCAN1-4 in PROKR1 Ishikawa cells using an adenovirus leads to a reduction in PROK1 induced IL-11 indicating that RCAN1-4 is a negative regulator in the calcineurin-mediated signalling to IL-11. Finally, we have shown the potential for both autocrine and paracrine signalling in the human endometrium by co-localizing IL-11, IL-11Ralpha and PROKR1 within the stromal and glandular epithelial cells of non-pregnant endometrium and first trimester decidua. Overall we have identified and characterized the signalling components of a novel PROK1-PROKR1 signalling pathway regulating IL-11.

Expression and hormonal regulation of IL-11Ralpha in canine uterus during early pregnancy

Embryo implantation is critical for the successful establishment of pregnancy. Interleukin-11 (IL-11) is essential for adequate decidualization in the mouse and human via binding to the specific IL-11 receptor alpha (IL-11Ralpha). But the expression and regulation of IL-11 and IL-11Ralpha in the canine endometrium remain unknown. The aim of this study was to investigate the differential expression of IL-11Ralpha in canine uterus during early pregnancy and its regulation under different conditions by in situ hybridization. Interleukin-11Ralpha mRNA was mainly localized in glandular epithelium in canine uterus. There was a low level of IL-11Ralpha expression in the glandular epithelium on days 6, 12 and 17 of pregnancy. On day 20 of pregnancy when embryo implanted, IL-11Ralpha mRNA was highly expressed in the glandular epithelium surrounding the embryo, but not in the luminal epithelium and stroma. On day 23 of pregnancy, the expression of IL-11Ralpha mRNA maintained a constant level compared with the expression of day 20 and increased on day 28 of pregnancy. During the oestrous cycle, a high level of IL-11Ralpha mRNA expression was seen in the oestrous uterus. Progesterone slightly induced the expression of IL-11Ralpha mRNA in the ovariectomized canine uterus. These results suggest that IL-11Ralpha expression is closely related to canine implantation and up-regulated by progesterone.

The protective effect of interleukin-11 on the cell death induced by X-ray irradiation in cultured intestinal epithelial cell

Interleukin-11 (IL-11) is a well known anti-inflammatory cytokine that is associated with cell growth, and also participates in limiting X-ray irradiation induced intestinal mucosal injury. The aim of this study was to evaluate the protective effect of IL-11 on the cell injury induced by X-ray irradiation in rat intestinal epithelial IEC-18 cells. Recombinant human IL-11 (rhIL-11) treated cells were irradiated and then examined for cell viability. To evaluate irradiation injury, trypan blue staining was used to detect the dead cells. The viability of irradiated cells was up-regulated by rhIL-11 treatment and also resulted in the activation of p90 ribosomal S6 kinase (p90RSK) and S6 ribosomal protein (S6Rp). Wortmannin, a specific inhibitor of PI3K, suppressed the activation of S6Rp in rhIL-11 treated cells, and decreased the up-regulation of viability by rhIL-11 treatment in irradiated cells. The TUNEL assay was also perfomed to estimate the rate of apoptosis in X-ray induced cell death. There was no difference in the results between trypan blue staining and the TUNEL assay. Further, rhIL-11 down-regulated the expression of cleaved caspase-3 in irradiated cells. These results suggest that rhIL-11 may play an important role in protection from radiation injury.

Leukemia Inhibitory Factor Induces DNA Synthesis in Swiss Mouse 3T3 Cells Independently of Cyclin D1 Expression through a Mechanism Involving MEK/ERK1/2 Activation

Leukemia inhibitory factor (LIF) and oncostatin M (OSM) induce DNA synthesis in Swiss 3T3 cells through common signaling mechanism(s), whereas other related cytokines such as interleukin-6 and ciliary neurotrophic factor do not cause this response. Induction of DNA replication by LIF or prostaglandin F2alpha (PGF2alpha) occurs, in part, through different signaling events. LIF and OSM specifically trigger STAT1 cytoplasmic to nuclear translocation, whereas PGF2alpha fails to do so. However, LIF and PGF2alpha can trigger increases in ERK1/2 activity, which are required for their mitogenic responses because U0126, a MEK1/2 inhibitor, prevents both ERK1/2 activation and induction of DNA synthesis by LIF or PGF2alpha treatment. PGF2alpha induces cyclin D expression and full phosphorylation of retinoblastoma protein. In contrast, LIF fails to promote increases in cyclin D mRNA/protein levels; consequently, LIF induces DNA synthesis without promoting full phosphorylation of retinoblastoma protein (Rb). However, both LIF and PGF2alpha increase cyclin E expression. Furthermore, LIF mitogenic action does not involve protein kinase C (PKC) activation, because a PKC inhibitor does not block this effect. In contrast, PKC activity is required for PGF2alpha mitogenic action. More importantly, the synergistic effect between LIF and PGF2alpha to promote S phase entry is independent of PKC activation. These results show fundamental differences between LIF- and PGF2alpha-dependent mechanism(s) that induce cellular entry into S phase. These findings are critical in understanding how LIF and other related cytokine-regulated events participate in normal cell cycle control and may also provide clues to unravel crucial processes underlying cancerous cell division.

Effects of adrenomedullin on cell proliferation in rat adventitia induced by lysophosphatidic acid

Lysophosphatidic acid (LPA) is a bioactive phospholipid having growth factor-like activity on fibroblasts and is involved in cardiovascular diseases such as hypertension and heart failure by inducing vascular remodeling, characterized by fibroblast proliferation and migration in adventitia. Among various bioactive factors that LPA works with, adrenomedullin (ADM) is a multiple functional peptide with an important cytoprotective effect against cardiovascular damage. We studied rat aortic adventitia to explore the possible paracrine/autocrine interaction between endogenous ADM and LPA. LPA stimulation of the adventitia to secrete ADM and express its mRNA was concentration dependent. ADM inhibited LPA-induced proliferation in adventitial cells and attenuated the activity of mitogen-activated protein kinase (MAPK) stimulated by LPA. In contrast, treatment with specific antagonists of the ADM receptor potentiated the LPA-induced proliferation in adventitial cells. We concluded that LPA stimulates the adventitia to produce and secrete ADM, which in turn regulates the vascular biological effects of LPA.

Interleukin 11 signaling in 3T3-L1 adipocytes

Interleukin 11 (IL-11) is an anti-inflammatory cytokine with receptors located on most cell types and tissues throughout the body. Its anti-inflammatory properties are mediated through suppression of cytokine synthesis, in large part by prevention of NF-kappaB activation. As adipose tissue synthesizes and secretes cytokines involved in establishing insulin resistance and due to the ability of IL-11 to suppress cytokine synthesis, we initiated an investigation to determine the signal transduction pathways initiated by IL-11 in adipose tissue. Using the 3T3-L1 adipocyte cell culture model we demonstrate the rapid activation of the p44/42MAP kinase, PI3-kinase, and STATs 1 and 3. Activation of MAP kinase is demonstrated to lead to the downstream activation of p90 RSK (ribosomal S6 kinase) as well as ATF-1 and CREB. PI3-kinase appears to activate the downstream target of p70 S6 kinase resulting in phosphorylation of ribosomal protein S6. STAT phosphorylation appears to be initiated through PI3-kinase and to a lesser degree through p44/42 MAP kinase. These studies demonstrate the activation of three major signaling pathways and support a role for IL-11 in the regulation of both transcription and protein synthesis in fully differentiated adipocytes.

Effects of adrenomedullin on aldosterone-induced cell proliferation in rat cardiac fibroblasts

Aldosterone induces cardiac remodeling in cardiovascular diseases by stimulating the proliferation, production and secretion of collagen in fibroblasts. It also stimulates vascular smooth muscle cells to produce and secrete adrenomedullin (ADM), which has a cytoprotective effect against cardiovascular damage. We examined the effect of aldosterone on ADM production and secretion in rat cardiac fibroblasts, and the effect of ADM on aldosterone-stimulated fibroblast proliferation to observe the interaction between endogenous ADM and aldosterone. We detected ADM produced and secreted from cultured cardiac fibroblasts and the intracellular cAMP level by radioimmunoassay; evaluated cell proliferation by the level of [3H]-thymine incorporation; measured preproADM gene expression by reverse transcriptase polymerase chain reaction (RT-PCR); and monitored extracellular signal related kinase (ERK) activity by the phosphorylation of myelin basic protein in the presence of [gamma-32P] ATP. Our results showed that aldosterone-stimulated secretion of ADM and its mRNA expression were concentration-dependent, which could be inhibited by the specific antagonist of mineralocorticoid receptor, spironolactone. In contrast, ADM inhibited aldosterone-induced fibroblast proliferation and ERK activity. Treatment with ADM24-50 (a new antagonist of specific ADM receptors) and calcitonin gene-related peptide (CGRP)8-37 (the antagonist of CGRP receptor type 1), to attenuate the action of endogenous ADM, reinforced the aldosterone-induced proliferation and inhibited the intracellular cAMP production stimulated by aldosterone. Thiorphan, an inhibitor of ADM degradation, inhibited the [3H]-thymine incorporation and reinforced the intracellular cAMP level induced by aldosterone. We reach the conclusion that aldosterone stimulates rat cardiac fibroblasts to produce and secrete ADM, which in turn regulates the proliferation-induced effects of aldosterone in these cells.

Effects of adrenomedullin on cell proliferation in rat adventitia induced by aldosterone

OBJECTIVE

Aldosterone is involved in cardiovascular diseases such as hypertension and heart failure by inducing sodium retention and vascular remodeling, which is characterized by fibroblast proliferation and migration in adventitia. It is well known that aldosterone stimulates vascular smooth muscle cells and fibroblasts to produce and secrete adrenomedullin (ADM), a multiple functional peptide with an important cytoprotective effect against cardiovascular damage. We examined the effect of aldosterone on ADM production and secretion and its mRNA expression in rat aortic adventitia to study the paracrine/autocrine interaction between endogenous ADM and aldosterone.

METHODS

ADM produced and secreted from adventitia stimulated by aldosterone in the absence or presence of spironolactone, RU486 or spironolactone together with RU486 were detected by radioimmunoassay, proliferation in adventitia cells was evaluated by the level of [H]-thymine incorporation, and preproADM gene expression was measured by semi-quantitative reverse transcriptase polymerase chain reaction.

RESULTS

Adventitial ADM secretion and mRNA expression stimulated by aldosterone were concentration-dependent as was the inhibitive effect of ADM on aldosterone-induced proliferation. The induction of aldosterone in ADM secretion was mediated by mineralocorticoid receptor. Antagonists of specific receptors of calcitonin gene-related peptide (CGRP) receptor type 1 and ADM both potentiated the proliferation effect induced by aldosterone; and thiorphan, an inhibitor of the enzyme for ADM degradation, inhibited the adventitial [H]-thymine incorporation induced by aldosterone. ADM inhibited the activity of extracellular signal related kinase (ERK) stimulated by aldosterone.

CONCLUSION

Aldosterone stimulates adventitia to produce and secrete ADM, which in turn, antagonizes the aldosterone-induced proliferation in adventitia.

Interleukin 11 treatment alters the protein content of Galpha(i2) and adipogenic transcription factors in 3T3-L1 adipocytes

Exposure of fully differentiated 3T3-L1 adipocytes to 5 nM interleukin 11 (IL-11) resulted in an increase (1.9+/-0.5 fold) in the protein content for the heterotrimeric G protein Galpha(i2). This G protein has been suggested to be involved in the control of the insulin responsive glucose transporter (GLUT4) translocation to the plasma membrane. Conversely, IL-11 had no effect on the content of three other G proteins, involved in insulin action. The alteration in Galpha(i2) protein corresponds to and provides a molecular rationale for our previously described IL-11 induced increase in plasma membrane glucose transporter content and increased rate of glucose transport. In addition, treatment with the cytokine altered the protein content of several transcription factors, C/EBPalpha and CHOP-10 decreased while PPARgamma and C/EBPbeta increased. These changes in transcription factor content are consistent with an alteration of phenotype with the cells reverting to an earlier stage of the differentiation process in response to IL-11.

Functional characterization of W147A: a high-affinity interleukin-11 antagonist

IL-11 is a member of the gp130 family of cytokines, which signal via assembly of multisubunit receptor complexes containing at least one molecule of the transmembrane signaling receptor gp130. IL-11 forms a high-affinity complex, thereby inducing gp130-dependent signaling. Previous studies have identified three distinct receptor binding sites, I, II, and III, crucial for the binding of murine IL-11 (mIL-11) to both the IL-11R and gp130. In this study, we have further characterized the role of the mIL-11 site III mutant W147A. We show that W147A is a high-affinity specific antagonist of mIL-11-mediated signaling in gp130/IL-11R-transfected Ba/F3 cells. The antagonistic action of W147A is due to its ability to competitively disrupt multimeric gp130/IL-11R signaling complex formation. We also show that W147A inhibits IL-11-mediated signaling in primary human endometrial cells, thus demonstrating the potential utility of W147A in suppressing IL-11 responses in vivo.

Oncostatin M-induced growth inhibition and morphological changes of MDA-MB231 breast cancer cells are abolished by blocking the MEK/ERK signaling pathway

Cytokine oncostatin M (OM) has profound effects on proliferation and differentiation of breast cancer cells. OM treated cells show reduced growth rate and differentiated phenotypes. The mechanisms underlying the OM growth-inhibitory activity in breast cancer cells have not been fully elucidated. In this study, we investigated the OM-elicited signaling pathways in breast cancer cell lines MDA-MB231 and MCF-7. We show that OM rapidly activates the extracellular signal-regulated kinase (ERK) and the signal transducer and activator of transcription (STAT) 1 and 3 in both cell lines. Intriguingly, OM-induced growth inhibition and morphological changes in MDA-MB231 cells are completely abolished by inhibitors to ERK upstream kinase MEK (nitrogen/extracellular-regulated protein kinase kinase), but the MEK inhibitors have little effects on OM growth-inhibitory activity in MCF-7 cells. In addition, expressions of the cyclin kinase inhibitors p21 and p27 are strongly induced by OM in MCF-7 cells, but their expression is only slightly increased by OM in MDA-MB231 cells. These data together demonstrate that the growth-inhibitory activity of OM can be mediated by different signaling pathways in a cell line-specific manner. While the MEK/ERK pathway is the predominant signaling pathway that leads to the growth inhibition of MDA-MB231 cells, activation of additional signaling pathways are necessary for OM to exert its growth-inhibitory activity in MCF-7 cells.

Interleukin-11 receptor expression in primary ovarian carcinomas

OBJECTIVES

The objectives of this study were to determine (1) the frequency of expression of the interleukin-11 receptor alpha subunit (IL-11Ralpha) and its signal transducing subunit, gp130, among primary ovarian carcinomas; (2) the frequency of expression of IL-11 in ovarian carcinomas; and (3) the potential role IL-11 might have in ovarian cancer cell biology.

METHODS

An immunohistochemical assay was used to determine the expression of IL-11Ralpha and the gp130 cofactor among primary ovarian carcinomas; the expression of IL-11 in ovarian malignancies was determined using reverse transcription polymerase chain reaction (RT-PCR). The ability of IL-11 to stimulate [3H]thymidine incorporation in IL-11R-expressing ovarian carcinoma cell lines (OVCAR-3 and SKOV-3) and/or abrogate cell death mediated by apoptosis-inducing agents using an ELISA assay that quantitates DNA fragmentation was also studied.

RESULTS

IL-11Ralpha was expressed in the malignant epithelial cells of 45 of 48 (93.8%) primary ovarian carcinoma samples studied. In 45 primary ovarian carcinoma samples where both components of the IL-11 receptor (IL-11Ralpha and gp130) were examined, coexpression was observed in 42 (93.3%). Expression of the IL-11 receptor components was also found in the stromal layer. Coexpression of IL-11Ralpha and gp130 was commonly observed in both benign ovarian tumors and in the epithelial layer of normal ovaries. In contrast, IL-11 mRNA was expressed in only 3 of 21 malignant samples studied (14.3%). Recombinant human IL-11 was unable either to stimulate [3H]thymidine incorporation or to block cell death effected by paclitaxel or Fas-activating antibodies in in vitro assays using OVCAR -3 or SKOV-3 cells.

CONCLUSIONS

The IL-11 receptor system is commonly expressed in both malignant and nonmalignant ovarian tissues, although its function in ovarian epithelial cell biology remains unclear.

Increased expression of the interleukin-11 receptor and evidence of STAT3 activation in prostate carcinoma

Previous investigations have shown that interleukin-6, a member of the JAK-STAT activating family of cytokines, plays an important role in prostate carcinoma. Here we demonstrate the co-expression of another member of this cytokine family, interleukin-11 (IL-11), and components of its receptor (interleukin-11 receptor; IL-11R), ie, IL-11Ralpha (involved in ligand recognition), and gp130 (involved in signal transduction) in cultured normal and malignant prostate-derived epithelial cell lines. In the DU-145 prostate carcinoma cell line, rhIL-11 stimulates a transient and dose-dependent increase in the tyrosine 705-phosphorylated, active form of STAT3 (STAT3 P-Tyr705), involved in the downstream signaling of IL-11R and other members of the gp130-dependent receptors. The ability of IL-11 to activate STAT3 in prostate-derived cells may be mechanistically important, given recent data suggesting that constitutively activated STAT3 may be associated with the malignant phenotype. In 51 human primary tissues derived from normal prostate, benign prostatic hyperplasia, and prostate carcinomas, IL-11Ralpha and gp130 were commonly expressed, with a statistically significant elevation in the expression of IL-11Ralpha in prostate carcinoma. Also, the tyrosine-phosphorylated, activated form of STAT3 was observed more prominently in the nuclei of cells residing in malignant glands compared to those in nonmalignant samples. Thus, the IL-11 receptor system is up-regulated in prostate carcinoma, and may be one part of a cytokine network that maintains STAT3 in its activated form in these tissues.

Interleukin-11 signals through the formation of a hexameric receptor complex

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. IL-11 has been shown to induce gp130-dependent signaling through the formation of a high affinity complex with the IL-11 receptor (IL-11R) and gp130. Site-directed mutagenesis studies have identified three distinct receptor binding sites of IL-11, which enable it to form this high affinity receptor complex. Here we present data from immunoprecipitation experiments, using differentially tagged forms of ligand and soluble receptor components, which show that multiple copies of IL-11, IL-11R, and gp130 are present in the receptor complex. Furthermore, it is demonstrated that sites II and III of IL-11 are independent gp130 binding epitopes and that both are essential for gp130 dimerization. We also show that a stable high affinity complex of IL-11, IL-11R, and gp130 can be resolved by nondenaturing polyacrylamide gel electrophoresis, and its composition verified by second dimension denaturing polyacrylamide gel electrophoresis. Results indicate that the three receptor binding sites of IL-11 and the Ig-like domain of gp130 are all essential for this stable receptor complex to be formed. We therefore propose that IL-11 forms a hexameric receptor complex composed of two molecules each of IL-11, IL-11R, and gp130.

Regulation of interleukin 6 production in a human gastric epithelial cell line MKN-28

Interleukin (IL-) 6 is closely related to gastrointestinal diseases. The question of whether gastric epithelial cell contributes to IL-6 production remains undefined. We aim to evaluate the regulatory pathway of IL-6 expression in gastric epithelial cells, by using different inflammatory cytokines, endotoxin, or protein kinase modulators. IL-6 was measured by ELISA. Phorbol-12-myristate-13-acetate (PMA), calcium ionophore A23187, TNF-alpha, IL-1beta, oncostatin M (OSM) but not lipopolysaccharide stimulated IL-6 production from gastric epithelial cell line MKN-28. Blocking protein tyrosine kinase (PTK) activation by herbimycin A or genistein, or blocking NF-kappaB activation by pyrrolidinedithiocarbamate, reduced the IL-6 expression induced by TNF-alpha, IL-1beta and OSM. Dexamethasone mimicked this effect. Protein kinase (PK) C inhibitor only reduced the PMA and OSM induced IL-6 production. Both inhibitors and activators for PKA and G-protein as well as IL-10 had no effects on IL-6 expression. These results indicate that inflammatory cytokines are crucial for IL-6 regulation in gastric epithelial cells. The IL-6 signal pathway is mediated through PTK, NF-kappaB, and also involve PKC, intracellular calcium and sensitive to dexamethasone, but is not related to PKA, G-protein and IL-10.

IL-11 activates human endothelial cells to resist immune-mediated injury

IL-11, a gp130-signaling cytokine, is protective in several in vivo models of immune-mediated and inflammatory injury. HUVECs express IL-11 receptor alpha-chain and gp130. Human IL-11 causes rapid (2-10 min) tyrosine phosphorylation of gp130. IL-11 at 0.1 and 10 ng/ml induces tyrosine phosphorylation of STAT3 and STAT1, respectively, although maximal responses require 50 ng/ml. Phospho-STAT3 and phospho-STAT1 levels peak rapidly (2.5 min) and disappear by 60 min. The p42 and p44 mitogen-activated protein kinases (MAPKs) are phosphorylated in response to 0.3 ng/ml IL-11 with maximal activation at 30 ng/ml IL-11. Phosphorylation of p42 and p44 MAPKs, which can be prevented by a mitogen-activated protein/extracellular signal-related kinase kinase-1 inhibitor, peaks by 15-20 min and largely disappears by 40 min. IL-11 does not activate NF-kappaB nor does it inhibit NF-kappaB activation by TNF. Similarly, IL-11 neither induces E-selectin or ICAM-1 nor blocks induction by TNF. Although IL-11 does not alter class I MHC complex molecule expression, pretreatment with 0.5 ng/ml IL-11 partially protects HUVECs against lysis by allospecific class I MHC-restricted cytolytic T lymphocytes or by anti-class I MHC Ab plus heterologous C. IL-11-induced cytoprotection is protein synthesis dependent and may depend on mitogen-activated protein/extracellular signal-related kinase kinase-1. Our results indicate that low (i.e., STAT3- and MAPK-activating) concentrations of IL-11 confer resistance to immune-mediated injury in cultured HUVECs without inhibiting proinflammatory responses.

Synergistic epithelial responses to endotoxin and a naturally occurring muramyl peptide

We have investigated the synergistic interactions of a naturally occurring peptidoglycan fragment (muramyl peptide) and bacterial endotoxin in the induction of inflammatory processes within respiratory epithelial cells, at the levels of both signal transduction events and ultimate cellular metabolic effects. The source of the muramyl peptide is Bordetella pertussis, the causative agent of the respiratory disease pertussis. During log-phase growth, B. pertussis releases the muramyl peptide tracheal cytotoxin (TCT), which has the structure N - acetylglucosaminyl - 1,6 - anhydro - N - acetylmuramyl - (L) - alanyl - gamma - (D) - glutamyl - meso - diaminopimelyl - (D) - alanine, equivalent to a monomeric subunit of gram-negative bacterial peptidoglycan. When applied to hamster trachea epithelial (HTE) cells, TCT and endotoxin were found to be highly synergistic in the induction of interleukin-1alpha (IL-1alpha), type II (inducible) nitric oxide synthase (iNOS), nitric oxide production, and inhibition of DNA synthesis. Neither molecule alone significantly triggered these responses. The serine/threonine protein kinase inhibitor H7 blocked induction of both IL-1alpha and iNOS. More selective inhibitors of protein kinase C, cyclic AMP-dependent protein kinase, and cyclic GMP-dependent protein kinase were not capable of blocking the effects of TCT and endotoxin, suggesting that the H7-inhibited component in this pathway is not among the commonly described kinase targets of H7. Treatment of HTE cells with exogenous IL-1 reproduced the induction of iNOS and DNA synthesis inhibition caused by TCT and endotoxin. H7 was not capable of interfering with effects caused by exogenous IL-1, implying that the H7-sensitive step in the pathway is upstream of IL-1 protein production. Similar assays with the phorbol ester phorbol myristate acetate indicate that it could effectively synergize with endotoxin but not with TCT, suggesting that TCT and endotoxin induce different signal transduction events that combine synergistically. The synergy observed with TCT and endotoxin in epithelial cells is significantly different from their interaction with other cell types, revealing a unique inflammatory response by epithelial cells to these natural bacterial products.

Influence of aging and caloric restriction on activation of Ras/MAPK, calcineurin, and CaMK-IV activities in rat T cells

The signaling cascade mediated by Ras (p21ras) and MAPK (mitogen-activated protein kinase) and calcium/calmodulin regulating enzymes, calcineurin (CaN) and CaMK-IV, are considered to be essential for T-cell growth and function. In the present study, the effect of aging and caloric restriction (CR) on the induction of Ras and MAPK activation by concanavalin A (ConA) was studied. Splenic T cells were isolated from young (4-6 months) and old (22-24 months) rats that had free access to food (control group), and from caloric restricted old (22-24 months) rats that beginning at 6 weeks of age were fed 60%(40% caloric restriction) of the diet consumed by the control rats. We found that the induction of Ras activity in T cells isolated from control old rats was lower (P<0.001) than that in control young rats. However, the levels of Ras activity in T cells isolated from CR old rats were similar to the levels in the age-matched control rats. The induction of MAPK activity in T cells isolated from control old rats and CR old rats was significantly less than in T cells isolated from control young rats, and caloric restriction significantly (P<0.05) reduced the age-related decline in MAPK activation. We also measured the induction of CaN and CaMK-IV activities by ConA in T cells from control young and old and CR old rats. The induction of both CaN and CaMK-IV activity decreased with age. Caloric restriction significantly (P<0.05) reduced the age-related decline in CaN activity, but had no significant effect on CaMK-IV activity. The changes in Ras/MAPK activation and in CaN and CaMK-IV activity with age or with CR were not associated with alterations in their corresponding protein levels. Thus, caloric restriction has a differential effect on the activation of the upstream signaling molecules that are altered with age.

Involvement of both the tyrosine kinase and the phosphatidylinositol-3' kinase signal transduction pathways in the regulation of lipoprotein lipase expression in J774.2 macrophages by cytokines and lipopolysaccharide

The regulation of macrophage lipoprotein lipase (LPL) by cytokines and lipopolysaccharide (LPS) is of potentially crucial importance in the pathogenesis of atherosclerosis and in the responses to endotoxin challenge. We show here that the reduction of LPL activity in J774.2 macrophages observed in the presence of interleukin (IL-1) and IL-11 was sensitive to herbimycin A, with the effect of LPS, interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha) on LPL activity being sensitive to both herbimycin A and wortmannin. The action of the inhibitors on the IFN-gamma-dependent reduction of LPL activity was mediated at the level of LPL mRNA metabolism, with translational and/or post-translational levels of regulation being involved in the action of all the other mediators tested. These observations suggest that both the tyrosine kinase and the phosphatidylinositol-3'-kinase signalling pathways are involved in the suppression of macrophage LPL expression by LPS and cytokines.

Cooperation between phosphorylation and acetylation processes in transcriptional control

We previously reported that the activation of the M promoter of the human choline acetyltransferase (ChAT) gene by butyrate and trapoxin in transfected CHP126 cells is blocked by PD98059, a specific mitogen-activated protein kinase kinase (MEK) inhibitor (E. Espinos and M. J. Weber, Mol. Brain Res. 56:118-124, 1998). We now report that the transcriptional effects of histone deacetylase inhibitors are mediated by an H7-sensitive serine/threonine protein kinase. Activation of the ChAT promoter by butyrate and trapoxin was blocked by 50 microM H7 in both transient- and stable-transfection assays. Overexpression of p300, a coactivator protein endowed with histone acetyltransferase activity, stimulated the ChAT promoter and had a synergistic effect on butyrate treatment. These effects were blocked by H7 and by overexpressed adenovirus E1A 12S protein. Moreover, both H7 and PD98059 suppressed the activation of the Rous sarcoma virus (RSV) and simian virus 40 promoters by butyrate in transfection experiments. Similarly, the induction of the cellular histone H1(0) gene by butyrate in CHP126 cells was blocked by H7 and by PD98059. Previous data (L. Cuisset, L. Tichonicky, P. Jaffray, and M. Delpech, J. Biol. Chem. 272:24148-24153, 1997) showed that the induction of the H1(0) gene by butyrate is blocked by okadaic acid, an inhibitor of protein phosphatases. We now show that the activation of the ChAT and RSV promoters by butyrate in transfected CHP126 cells is also blocked by 200 nM okadaic acid. Western blotting and in vivo metabolic labeling experiments showed that butyrate has a biphasic effect on histone H3 phosphorylation, i.e., depression for up to 16 h followed by stimulation. The data thus strongly suggest that the transcriptional effects of histone deacetylase inhibitors are mediated through the activation of MEK1 and of an H7-sensitive protein kinase in addition to protein phosphatases.

Protein kinase inhibitor H7 blocks the induction of immediate-early genes zif268 and c-fos by a mechanism unrelated to inhibition of protein kinase C but possibly related to inhibition of phosphorylation of RNA polymerase II

1-(5-Isoquinolinesulfonyl)-2-methylpiperazine (H7) has often been used in combination with protein kinase inhibitor (N-(2-guanidinoethyl)-5-isoquinolinesulfonamide) (HA1004) to assess the contribution of protein kinase C (PKC) to cellular processes, including the induction of gene expression. This use of H7 and HA1004 is based upon the fact that H7 inhibits PKC more potently than HA1004 in in vitro assays. Thus, although both compounds are broad spectrum protein kinase inhibitors, inhibition by H7, but not by HA1004, has often been interpreted as evidence for the involvement of PKC in the cellular process under study. Here we describe experiments that show that this interpretation is not correct with regard to the induction of two immediate-early genes, zif268 and c-fos, in PC12D cells. In these studies we confirmed that H7, but not HA1004, potently blocks the induction of zif268 and c-fos mRNA by nerve growth factor, carbachol, phorbol ester, Ca2+ ionophore, or forskolin. Surprisingly, however, H7 has no effect on the ability of these agents to activate mitogen-activated protein kinase (MAPK), an upstream activator of zif268 and c-fos gene expression. H7 also does not inhibit preactivated MAPK in vitro. Taken together, these results suggest that H7 blocks gene expression by acting at a site downstream from MAPK. H7 has previously been shown to block transcription in vitro by blocking the phosphorylation of the carboxyl-terminal domain of RNA polymerase II (Yankulov, K., Yamashita, K., Roy, R., Egly, J.-M., and Bentley, D. L.(1995) J. Biol. Chem. 270, 23922-23925). In this study, we show that pretreating PC12D cells with H7, but not with HA1004, significantly reduces levels of phosphorylated RNA polymerase II in vivo. These results suggest that H7 blocks gene expression by inhibiting the phosphorylation of RNA polymerase II, a step required for progression from transcription initiation to mRNA chain elongation.

Cytoplasmic Domains of the Leukemia Inhibitory Factor Receptor Required for STAT3 Activation, Differentiation, and Growth Arrest of Myeloid Leukemic Cells

Leukemia inhibitory factor (LIF) induces growth arrest and macrophage differentiation of mouse myeloid leukemic cells through the functional LIF receptor (LIFR), which comprises a heterodimeric complex of the LIFR subunit and gp130. To identify the regions within the cytoplasmic domain of LIFR that generate the signals for growth arrest, macrophage differentiation, and STAT3 activation independently of gp130, we constructed chimeric receptors by linking the transmembrane and intracellular regions of mouse LIFR to the extracellular domains of the human granulocyte macrophage colony-stimulating factor receptor (hGM-CSFR)  and βc chains. Using the full-length cytoplasmic domain and mutants with progressive C-terminal truncations or point mutations, we show that the two membrane-distal tyrosines with the YXXQ motif of LIFR are critical not only for STAT3 activation, but also for growth arrest and differentiation of WEHI-3B D+ cells. A truncated STAT3, which acts in a dominant negative manner was introduced into WEHI-3B D+ cells expressing GM-CSFR-LIFR and GM-CSFRβc-LIFR. These cells were not induced to differentiate by hGM-CSF. The results indicate that STAT3 plays essential roles in the signals for growth arrest and differentiation mediated through LIFR.

Induction of low density lipoprotein receptor (LDLR) transcription by oncostatin M is mediated by the extracellular signal-regulated kinase signaling pathway and the repeat 3 element of the LDLR promoter

Oncostatin M (OM) activates the transcription of the human low density lipoprotein receptor (LDLR) in HepG2 cells through a sterol-independent mechanism. Our previous studies showed that mutations within the repeat 3 sequence of the LDLR promoter significantly decreased OM activity on LDLR promoter luciferase reporter constructs that contain the sterol responsive element-1 (repeat 2) and Sp1 binding sites (repeats 1 and 3). In this study, we investigated the signal transduction pathways that are involved in OM-induced LDLR transcription. In HepG2 cells, OM induced a rapid increase in LDLR mRNA expression, with increases detected at 30 min and maximal induction at 1 h. This OM effect was not blocked by protein synthesis inhibitors, inhibitors of p38 kinase, phosphatidylinositol 3-kinase, or c-Jun N-terminal kinase, but OM activity was completely abolished by pretreating cells with inhibitors of the extracellular signal-regulated kinase (ERK) kinase (mitogen/ERK kinase (MEK)). To investigate whether the repeat 3 sequence of the LDLR promoter is the OM-responsive element that converts ERK activation at the promoter level, three luciferase reporters, pLDLR-TATA containing only the TATA-like elements of the promoter, pLDLR-R3 containing repeat 3 and the TATA-like elements, and pLDLR-234 containing repeats 1, 2, 3 and the TATA-like elements were constructed and transiently transfected into HepG2 cells. OM had no effect on the basal promoter construct pLDLR-TATA; however, including a single copy of repeat 3 sequence in the TATA vector (pLDLR-R3) resulted in a full OM response. The activity of OM on pLDLR-R3 was identical to that of pLDLR-234. Importantly, the ability of OM to increase luciferase activities in both pLDLR-R3- and pLDLR-234-transfected cells was blocked in a dose-dependent manner by inhibition of MEK. These results demonstrate that the mitogen-activated protein kinase MEK/ERK cascade is the essential signaling pathway by which OM activates LDLR gene transcription and provide the first evidence that the repeat 3 element is a new downstream target of ERK activation.

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.

Requirement for phosphatidylinositol-3'-kinase in cytokine-mediated germ cell survival during fetal oogenesis in the mouse

Apoptosis is responsible for primordial germ cell (PGC) attrition in the developing fetal ovary. In monolayer cultures of murine PGC, stem cell factor (SCF) and leukemia inhibitory factor (LIF) independently promote survival in vitro; however, the relevance of these data to fetal ovarian oogonium and oocyte survival, as well as the intracellular events involved in transducing the antiapoptotic actions of these cytokines in germ cells, remain to be elucidated. In this report, we investigated the effects of SCF and LIF, alone and in combination, on the survival of oogonia and oocytes, and elaborated on components of the signal transduction pathway used by these molecules, after validating a method of culturing fetal mouse ovaries. We further employed this system to also test the hypothesis that insulin-like growth factor-I (IGF-I), a classic antiapoptotic molecule, and transforming growth factor-beta (TGF-beta), a classic pro-apoptotic molecule, interact with the SCF/LIF pathway and function in a reciprocal fashion to precisely regulate germ cell numbers during fetal oogenesis. Freshly isolated embryonic day 13.5 ovaries contained nonapoptotic germ cells, as determined by histologic analysis of cellular morphology and in situ 3'-end-labeling of DNA integrity. In vitro culture of fetal ovaries without tropic support for 24, 48, and 72 h resulted in a time-dependent induction of germ cell apoptosis, such that most oogonia and oocytes present after 72 h were apoptotic. Morphometric analysis of serially sectioned ovaries indicated that the numbers of nonapoptotic germ cells remaining after 24, 48, and 72 h of culture were 78%, 38%, and 10%, respectively, of the number present before culture (P < 0.05 for all time points vs. 0 h). Inclusion of SCF (100 ng/ml) together with LIF (100 ng/ml) in the culture medium significantly attenuated germ cell apoptosis, with the SCF/LIF-treated ovaries retaining 5.5-fold more oogonia and oocytes after 72 h of culture as compared with control ovaries deprived of tropic support (P < 0.05). However, SCF or LIF, when added separately, had no (SCF) or little (LIF) inhibitory effect on germ cell apoptosis. Provision of 50 ng/ml IGF-I maintained survival of approximately two-thirds of the germ cells in cultured ovaries (P < 0.05), whereas a combination of all three growth factors (SCF, LIF, IGF-I) completely preserved the fetal ovary in culture to that resembling a freshly-isolated gonad. Cotreatment with 25 ng/ml TGF-beta partially reversed the survival actions of IGF-I or SCF/LIF, such that only one-third of the starting number of oogonia/oocytes remained after 72 h of culture (P < 0.05). Lastly, the antiapoptotic effects of SCF/LIF or IGF-I were almost entirely eliminated by cotreatment of fetal ovaries with either one of two inhibitors of phosphatidylinositol-3'-kinase (PI3K), LY294002 (5 microM) or wortmannin (50 nM), whereas cotreatment with an inhibitor of p70 S6 kinase (rapamycin, 25 ng/ml) was without effect. These data indicate that the combined actions of SCF, LIF, and IGF-I are required for maximal inhibition of apoptosis in germ cells of fetal mouse ovaries, and that the PI3K signaling pathway is an essential component of cytokine-mediated female germ cell survival. Moreover, TGF-beta can partially override the antiapoptotic actions of SCF/LIF or IGF-I in oogonia and oocytes, suggesting the existence of a complex signaling network that ultimately determines fetal ovarian germ cell fate.

IL-6-Deficient Mice Are Resistant to Experimental Autoimmune Encephalomyelitis: Roles of IL-6 in the Activation and Differentiation of Autoreactive T Cells

Although autoreactive T cells recognizing self myelin Ags are present in most individuals, autoimmune disease of the central nervous system is a relatively rare medical condition. Development of autoimmune disease may require not only the presence of autoreactive T cells but also that autoreactive T cells become activated. Activation of T cells may require a minimum of two signals: an Ag-specific signal delivered by MHC-peptide complex and a second signal delivered by costimulatory molecules or cytokines. Although in vitro studies have suggested that cytokines, especially proinflammatory cytokines such as IL-1, IL-6, and TNF are involved in T cell activation, their precise roles in vivo are not clear. To determine the roles of proinflammatory cytokines in T cell activation in vivo and in the development of autoimmune disease, we have studied experimental autoimmune encephalomyelitis (EAE) in mice deficient in IL-6. We found that IL-6-deficient mice were completely resistant to EAE induced by myelin oligodendrocyte glycoprotein (MOG), whereas IL-6-competent control mice developed EAE characterized by focal inflammation and demyelination in the central nervous system and deficiency in neurologic functions. Furthermore, we established that the resistance to EAE in IL-6-deficient mice was associated with a deficiency of MOG-specific T cells to differentiate into either Th1 or Th2 type effector cells in vivo. These results strongly suggest that IL-6 plays a crucial role in the activation and differentiation of autoreactive T cells in vivo and that blocking IL-6 function can be an effective means to prevent EAE.

Self-renewal of pluripotent embryonic stem cells is mediated via activation of STAT3

The propagation of embryonic stem (ES) cells in an undifferentiated pluripotent state is dependent on leukemia inhibitory factor (LIF) or related cytokines. These factors act through receptor complexes containing the signal transducer gp130. The downstream mechanisms that lead to ES cell self-renewal have not been delineated, however. In this study, chimeric receptors were introduced into ES cells. Biochemical and functional studies of transfected cells demonstrated a requirement for engagement and activation of the latent trancription factor STAT3. Detailed mutational analyses unexpectedly revealed that the four STAT3 docking sites in gp130 are not functionally equivalent. The role of STAT3 was then investigated using the dominant interfering mutant, STAT3F. ES cells that expressed this molecule constitutively could not be isolated. An episomal supertransfection strategy was therefore used to enable the consequences of STAT3F expression to be examined. In addition, an inducible STAT3F transgene was generated. In both cases, expression of STAT3F in ES cells growing in the presence of LIF specifically abrogated self-renewal and promoted differentiation. These complementary approaches establish that STAT3 plays a central role in the maintenance of the pluripotential stem cell phenotype. This contrasts with the involvement of STAT3 in the induction of differentiation in somatic cell types. Cell type-specific interpretation of STAT3 activation thus appears to be pivotal to the diverse developmental effects of the LIF family of cytokines. Identification of STAT3 as a key transcriptional determinant of ES cell self-renewal represents a first step in the molecular characterization of pluripotency.

Activation of phosphatidylinositol 3-kinase through glycoprotein 130 induces protein kinase B and p70 S6 kinase phosphorylation in cardiac myocytes

Phosphatidylinositol (PI) 3-kinase is known to be activated by cytokine stimulation through different types of receptors to transduce intracellular responses. We have previously reported that leukemia inhibitory factor (LIF) induces the activation of Janus kinase signal transducer and activator of transcription (JAK-STAT) and mitogen-activated protein (MAP) kinase pathways through glycoprotein (gp) 130 in cardiac myocytes. However, whether PI 3-kinase is involved in regulation of gp130 signaling and the activation mechanisms by which it associates with other tyrosine-phosphorylated proteins remain unknown. We found that LIF induced the activation of PI 3-kinase in cardiac myocytes. Moreover, JAK1 binds to PI 3-kinase, and LIF stimulation increases the PI 3-kinase activity in JAK1 immunoprecipitates. Activation of MAP kinase and protein kinase B by LIF was attenuated by wortmannin. LIF-induced p70 S6 kinase activation, protein synthesis, and c-fos mRNA expression were inhibited by wortmannin and rapamycin. Both inhibitors failed to appreciably affect the phosphorylation of STAT3. In conclusion, PI 3-kinase is activated with LIF in cardiac myocytes, and JAK1 is found to associate with this enzyme. PI 3-kinase provides a crucial link between gp130, MAP kinase, protein kinase B, and p70 S6 kinase in cardiac myocytes.

Activation of p21ras/MAPK signal transduction molecules decreases with age in mitogen-stimulated T cells from rats

Signal transduction is ubiquitously involved in the initiation of physiological signals that lead to growth and proliferation of cells. The signaling cascade mediated by the mitogen-activated protein kinase (MAPK) is considered essential for T cell growth and function. Therefore, it was of interest to determine the influence of age on the induction of MAPK in mitogen-activated T cells. T cells from young (4-6 months) and old (24-26 months) rats responded to concanavalin A (Con A) stimulation by increasing MAPK, c-jun amino terminal kinase (JNK), and p21ras activities. The time course of induction of MAPK/JNK and p21ras activities was similar in T cells isolated from young and old rats. The induction of JNK activity did not change significantly with age; however, the induction of MAPK and p21ras activities was significantly less (50 to 65%) in T cells from old rats than in T cells from young rats. Although the relative protein levels of p42 and p44 MAPK did not change with age, the proportion of the phosphorylated p44 MAPK decreased with age. In addition, it was found that the in vitro kinase activities of the T cell receptor-associated protein tyrosine kinase Lck (p56Lck) and ZAP-70 but not Fyn (p59Fyn) were lower in T cells from old rats than in T cells from young rats. The decline in activities of these signaling molecules with age was not associated with changes in their corresponding protein levels. Thus, our results demonstrate that aging alters the activation of the signal transduction cascade that leads to T cell activation.

Leukemia inhibitory factor: part of a large ingathering family

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

Coordinate regulation of STAT signaling and c-fos expression by the tyrosine phosphatase SHP-2

The src homology 2 (SH2) domain-containing protein-tyrosine phosphatase SHP-2 has been implicated as an important positive regulator of several mitogenic signaling pathways. SHP-2 has more recently been shown to be tyrosine phosphorylated and recruited to the gp130 component of the ciliary neurotrophic factor (CNTF) receptor complex upon stimulation with CNTF. CNTF does not, however, have a proliferative effect on responsive cells, but rather enhances the survival and differentiation of sympathetic, motor, and sensory neurons. In this study, expression of an interfering mutant of SHP-2 in the neuroblastoma cell line NBFL increased CNTF induction of a vasoactive intestinal peptide (VIP) reporter gene, and in cultures of sympathetic neurons, it resulted in an up-regulation of endogenous VIP and substance P (SP) gene expression. Members of the CNTF family of cytokines transmit their signal by activating signaling pathways involving both STAT and Fos-Jun transcription factors. In CNTF-stimulated NBFL cells that constitutively express the SHP-2 interfering mutant, there was increased and prolonged formation of STAT/DNA complexes, but decreased AP-1 binding activity, that mirrored a down-regulation of c-fos expression both at the mRNA and protein level. Taken together, these data indicate that SHP-2 has dual and opposing roles in a signaling cascade triggered by the same ligand, as illustrated by its ability to differentially regulate the levels of activity of both STAT and AP-1 transcription factors.

Expression of leukemia inhibitory factor and its receptor in breast cancer: a potential autocrine and paracrine growth regulatory mechanism

Leukemia inhibitory factor (LIF) is a pluripotent cytokine which has a diverse array of effects on hematopoietic and epithelial cells. Depending on the nature of the target cells, these effects can be growth-stimulatory or growth-inhibitory. Receptors for leukemia inhibitory factor (LIFR) have been identified on a variety of hematopoietic and epithelial cells. We have recently demonstrated in vitro growth stimulation of human breast cancer cells, both primary tumors and cultured cell lines, by LIF. To begin to understand the in vivo relevance of these observations, we investigated the expression of LIF and LIFR in human breast cancer specimens. Specimens from 50 cases were immunostained with mouse monoclonal antibodies D62.3 and M1 (to stain for LIF and LIFR, respectively). LIF expression was observed in 78% of the specimens and correlated with favorable biological features, i.e. low S-phase fraction (SPF) (P = 0.001) and diploidy (P = 0.08). LIFR expression was observed in 80% of the tumors and correlated with the presence of estrogen receptor (ER) (P = 0.04) and diploidy (P = 0.07). Coexpression of LIF and LIFR was associated with diploidy (P = 0.02) and low SPF (P = 0.05). LIF staining was primarily cytoplasmic whereas LIFR staining was cytoplasmic in the majority of cases and membranous in a minority of cases. The presence of LIFR in the primary tumor specimens correlated with the growth stimulation of tumor cells (derived from the same specimens) by exogenous LIF in methylcellulose colony assays. The findings support a widespread but probably complex role for LIF and LIFR in breast tumor growth regulation which should be investigated in greater detail in larger cohorts of tumors.

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

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

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

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

Signaling mechanisms through gp130: a model of the cytokine system

The interleukin-6 cytokine family plays roles in a wide variety of tissues and organs, including the immune hematopoietic and nervous systems. Gp130 is a signal-transducing subunit shared by the receptors for the IL-6 family of cytokines. The binding of a ligand to its receptor induces the dimerization of gp130, leading to the activation of JAK tyrosine kinase and tyrosine phosphorylation of gp130. These events lead to the activation of multiple signal-transduction pathways, such as the STAT, Ras-MAPK and PI-3 kinase pathways whose activation is controlled by distinct regions of gp130. We propose a model showing that the outcome of the signal transduction depends on the balance or interplay among the contradictory signal transduction pathways that are simultaneously generated through a cytokine receptor in a given target cell.

gp49B1, an inhibitory signaling receptor gene of hematopoietic cells, is induced by leukemia inhibitory factor in the uterine endometrium just before implantation

Leukemia inhibitory factor (LIF) is a cytokine involved in hematopoiesis, neuropoiesis, and embryogenesis. Transcriptional activation of various genes occurs subsequent to LIF signal transduction in its target cells. Using the mRNA differential display method, a LIF-inducible gene was isolated from LIF-stimulated M1 murine myeloid leukemia cells. By DNA sequencing, this gene turned out to be gp49B1, which has been reported as an inhibitory signaling receptor to attenuate mast cell activation. Because gp49B1 expression was limited to the uterus of a pregnant mouse, its uterine expression was examined especially in relation to LIF expression during pregnancy. gp49B1 was expressed specifically on day 4.0 of pregnancy, as was LIF, and the site of the most abundant expression of LIF and gp49B1 mRNA was the luminal epithelium of the uterine endometrium. These findings suggest that the gp49B1 expression in the uterine endometrium is induced just before implantation by paracrine and/or autocrine effects of LIF. Considering its function as an inhibitory signaling receptor on mast cells, a possible role for gp49B1 on the surface of the uterine endometrium as an immunoreceptor that allows blastocyst attachment is proposed.

Leukemia inhibitory factor-dependent transcriptional activation in embryonic stem cells

STAT transcription factors are induced by a number of growth factors and cytokines. Within minutes of induction, the STAT proteins are phosphorylated on tyrosine and serine residues and translocated to the nucleus, where they bind to their DNA targets. The leukemia inhibitory factor (LIF) mediates pleiotropic and sometimes opposite effects both in vivo and in cultured cells. It is known, for example, to prevent differentiation of embryonic stem (ES) cells in vitro. To get insights into LIF-regulated signaling in ES cells, we have analyzed protein-binding and transcriptional properties of STAT recognition sites in ES cells cultivated in the presence and in the absence of LIF. We have detected a specific LIF-regulated DNA-binding activity implicating the STAT3 protein. We show that STAT3 phosphorylation is essential for this LIF-dependent DNA-binding activity. The possibility that ERK2 or a closely related protein kinase, whose activity is modulated in a LIF-dependent manner, contributes to this phosphorylation is discussed. Finally, we show that the multimerized STAT3-binding DNA element confers LIF responsiveness to a minimal thymidine kinase promoter. This, together with our observation that overexpression of STAT3 dominant-negative mutants abrogates this LIF responsiveness, clearly indicates that STAT3 is involved in LIF-regulated transcriptional events in ES cells. Finally, stable expression of such a dominant negative mutant of STAT3 induces morphological differentiation of ES cells despite continuous LIF supply. Our results suggest that STAT3 is a critical target of the LIF signaling pathway, which maintains pluripotent cell proliferation.