Cytokine signaling through nonreceptor protein tyrosine kinases

Identification of IFN regulatory factor-1 binding site in IL-12 p40 gene promoter

IL-12 is a heterodimer composed of p40 and p35 and is a key cytokine that functions to protect the host from viral and microbial infections. IL-12 links the innate immune system with the acquired immune system during infection, and induces differentiation of type 1 T cells that play an important role in the eradication of microbes. The induction of the IL-12 p40 gene is regulated by NF-kappaB in the presence of IFN-gamma. IFN-gamma induces IFN regulatory factor-1 (IRF-1), which in turn induces the transcription of the IL-12 p40 gene. However, the IRF-1 binding site in the promoter region of the IL-12 p40 gene has not yet been formally determined. In the present study, we demonstrated that IRF-1 directly binds to the IL-12 p40 gene promoter and identified its binding site. The IRF-1 binding site in the promoter region of the IL-12 p40 gene is shown to be in the -72 to -58 area of the 5'-upstream region. The -63 to -61 position is the critical site within this region for the binding of IRF-1 to the IL-12 p40 gene promoter. While IFN-gamma must be present for IL-12 p40 gene induction, the p35 gene is strongly induced by LPS, even in the absence of IFN-gamma, and therefore the induction of the p35 gene is IRF-1 independent.

Immunotherapy with a posttranscriptionally modified DNA vaccine induces complete protection against metastatic neuroblastoma

The successful induction of a T-cell-mediated tumor-protective immunity against poorly immunogenic malignancies remains a major challenge for cancer immunotherapy. We achieved this by immunization with a tyrosine hydroxylase (mTH)-based DNA vaccine, enhanced with the posttranscriptional regulatory acting RNA element (WPRE), derived from woodchuck hepatitis virus in combination with an antibody-cytokine fusion protein (ch14.18-IL-2) that targets interleukin-2 (IL-2) to the tumor microenvironment. This DNA vaccine mTH-WPRE was carried by attenuated Salmonella typhimurium and applied by oral gavage in a mouse model of neuroblastoma. Mice immunized with the mTH-WPRE vaccine, and which additionally received a boost with suboptimal doses of ch14.18-IL-2, were completely protected against hepatic neuroblastoma metastases. In contrast, all controls presented with disseminated metastases. Both T-cell and natural killer (NK) cell-dependent mechanisms were involved in the induction of a systemic tumor-protective immunity. Thus, up-regulation of interferon-gamma (IFN-gamma) expression in CD8(+) T cells occurred only in those animals that received the mTH-WPRE vaccine plus the ch14.18-IL-2 boost. Up-regulation of this proinflammatory cytokine was not observed in mice immunized with mTH-WPRE vaccine alone. A role for NK cells was indicated by the complete abrogation of systemic tumor-protective immunity in all animals that were depleted of NK cells in vivo. Taken together, these data demonstrate that immunization with a posttranscriptionally enhanced DNA vaccine encoding the WPRE sequence, combined with a boost of the ch14.18-IL-2 fusion protein, completely protects against hepatic metastases in a murine model of neuroblastoma and therefore may lead to a new strategy for immunotherapy and prevention of metastatic neuroblastoma.

Regulation of Akt-dependent cell survival by Syk and Rac

Interleukin-2 (IL-2) prevents cell apoptosis and promotes survival, but the involved mechanisms have not been completely defined. Although phosphatidylinositide 3-kinase (PI 3-kinase) has been implicated in IL-2-mediated survival mechanisms, none of the 3 chains of the IL-2 receptor (IL-2R) expresses a binding site for PI 3-kinase. However, IL-2Rbeta does express a Syk-binding motif. By using an IL-2-dependent natural killer (NK) cell line, followed by validation of the results in fresh human NK cells, we identified Syk as a critical effector essential for IL-2-mediated prosurvival signaling in NK cells. Down-regulation of Syk by piceatannol treatment impaired NK cellular viability and induced prominent apoptosis as effectively as suppression of PI 3-kinase function by LY294002. Expression of kinase-deficient Syk or pretreatment with piceatannol markedly suppressed IL-2-stimulated activation of PI 3-kinase and Akt, demonstrating that Syk is upstream of PI 3-kinase and Akt. However, constitutively active PI 3-kinase reversed this loss of Akt function caused by kinase-deficient Syk or piceatannol. Thus, Syk appears to regulate PI 3-kinase, which controls Akt activity during IL-2 stimulation. More important, we observed Rac1 activation by IL-2 and found that it mediated PI 3-kinase activation of Akt. This conclusion came from experiments in which dominant-negative Rac1 significantly decreased IL-2-induced Akt activation, whereas constitutively active Rac1 reelevated Akt activity not only in Syk-impaired but also in PI 3-kinase-impaired NK cells. These results constitute the first report of a Syk --> PI3K --> Rac1 --> Akt signal cascade controlled by IL-2 that mediates NK cell survival.

Transforming pathways activated by the v-Abl tyrosine kinase

The Abelson Murine Leukemia Virus (A-MuLV) is the acute transforming retrovirus encoding the v-abl oncogene. Two isolates of the virus encoding proteins of p120 Kd and 160 Kd have been extensively studied. These viral isolates have been found to transform both hematopoietic and fibroblastic cells in vitro, while inducing predominantly pre-B cell leukemias in vivo. Both p120(v-Abl) and p160(v-Abl) are plasma membrane-associated non-receptor tyrosine kinases and the transforming activity of these proteins requires their tyrosine kinase activity. A-MuLV infection of hematopoietic cells has often been found to result in the abrogation of their cytokine-dependence for growth. In addition, v-Abl expressing hematopoietic cells often lose their ability to differentiate in response to appropriate cytokines. This review discusses some of the early transformation studies of A-MuLV, as well as some of the findings concerning the structure and biochemical activity of the v-Abl protein. Finally, we discuss the mechanisms associated with v-Abl mediated transformation through examination of the various signal transduction pathways activated by this oncogene.

Inhibition of human T cell activation by novel Src kinase inhibitors is dependent upon the complexity of the signal delivered to the cell

The activity of a novel series of protein tyrosine kinase inhibitors that are selective for the Src family has been assessed. The activity of these compounds [named CT-SKI (Celltech Src kinase inhibitors)] was investigated by assessing their potential to modulate T cell receptor activation, an event thought to involve the Src kinases Lck and Fyn. This series of compounds contained low-nanomolar inhibitors of Src kinases with selectivity over Csk, epidermal growth factor receptor kinase, protein kinase C, and zeta-associated 70-kDa protein. These compounds were shown to attenuate anti-CD3-induced T cell proliferation and block interleukin (IL)-2, IL-4, and interferon-gamma production, and CD25 expression in anti-CD3-activated T cells. In addition, inhibition of anti-CD3-induced, but not phorbol ester and calcium ionophore-induced IL-2 production, correlated with inhibition of in vitro Lck kinase activity. When more complex stimuli were used to activate T cells, as in the mixed lymphocyte reaction (MLR), these inhibitors proved to be less effective and inhibition of the MLR did not correlate with inhibition of isolated Lck enzyme. Interestingly, inhibition of anti-CD3-induced proliferation could be reversed by the addition of exogenous IL-2, indicating that signaling through the IL-2 receptor may not be critically dependent on any functional Src enzymes.

Characterization of YM-90709 as a novel antagonist which inhibits the binding of interleukin-5 to interleukin-5 receptor

Interleukin-5 (IL-5) plays an important role in the activation of eosinophils in allergic inflammation including asthma and atopic dermatitis. A newly synthesized compound, YM-90709, 2,3-dimethoxy-6,6-dimethyl-5,6-dihydrobenzo[7,8]indolizino [2,3-b]quinoxaline, is reported here to inhibit the binding of IL-5 to its receptor on peripheral human eosinophils and butyric acid-treated eosinophilic HL-60 clone 15 cells, with IC50 values of 1.0 and 0.57 microM, respectively. In contrast, YM-90709 did not affect the binding of granulocyte-macrophage colony-stimulating factor (GM-CSF) to its receptor on eosinophils and eosinophilic HL-60 clone 15 cells. In functional assays, YM-90709 inhibited IL-5-prolonged eosinophil survival with an IC50 value of 0.45 microM and did not affect the GM-CSF-prolonged eosinophil survival. Furthermore, YM-90709 inhibited the IL-5-induced but not GM-CSF-induced tyrosine phosphorylation of Janus kinase 2 (JAK2) in eosinophilic HL-60 clone 15 cells. These results indicate that YM-90709 is a novel IL-5 inhibitor which selectively blocks the binding of IL-5 to the IL-5 receptor (IL-5R).

Redistribution of ERK/MAP kinase to uropod-like structures in interleukin-3-induced cell shape changes

Interleukin-3 (IL-3) is one of the cytokines of significance for the regulation of hematopoiesis and inflammation. Recently, we established IL-3-dependent Ba/F3 pro-B cells ectopically expressing RON tyrosine kinase, a receptor for macrophage-stimulating protein (MSP), and showed that MSP stimulation specifically promoted cell morphological changes through tyrosine phosphorylation of the IL-3 common beta-chain receptor subunit (betac) by activated RON kinase without activation of JAK2 tyrosine kinase. Here we investigate the IL-3 signaling pathway leading to morphological changes through tyrosine phosphorylation of betac. Treatment of RON-expressing cells with PD98059 or U0126, inhibitors of mitogen-activated protein kinase kinase activity, blocked both IL-3- and MSP-induced morphological changes. Upon stimulation with IL-3 or MSP, extracellular-regulated kinase (ERK) and F-actin were redistributed in uropod-like structures. ERK and F-actin were colocalized within uropod-like structures, and a majority of F-actin were localized around the peripheries of accumulated ERK. Tyrosine phosphorylation of ERK was detected after stimulation with IL-3 or MSP, whereas treatment with U0126 specifically inhibited IL-3- or MSP-induced ERK phosphorylation but not tyrosine phosphorylation of betac. These results suggest that the activation and localization of ERK to uropod-like structures play a role in IL-3-induced morphological changes.

Enforced expression of Bcl-2 restores the number of NK cells, but does not rescue the impaired development of NKT cells or intraepithelial lymphocytes, in IL-2/IL-15 receptor beta-chain-deficient mice

IL-2/IL-15Rbeta-deficient mice display impaired development of NK cells, NKT cells, and intraepithelial lymphocytes of the intestine and skin. To determine the role of survival signals mediated by IL-2/IL-15R in the development of these innate lymphocytes, we introduced a bcl-2 transgene into IL-2/IL-15Rbeta-deficient mice. Enforced expression of Bcl-2 restored the number of NK cells in IL-2/IL-15Rbeta-deficient mice, but the rescued NK cells showed no cytotoxic activity. The numbers of NKT cells and intestinal intraepithelial lymphocytes did not increase significantly, and skin intraepithelial lymphocytes remained undetectable in the bcl-2 transgenic IL-2/IL-15Rbeta-deficient mice. These results indicate an essential role of IL-2/IL-15R-mediated survival signals in the development of NK cells, but they also show that additional nonsurvival signals from IL-2/IL-15R are necessary for innate lymphocyte development.

IL-2 negatively regulates IL-7 receptor alpha chain expression in activated T lymphocytes

Interleukin (IL)-2 is a type I four-alpha-helical bundle cytokine that plays vital roles in antigen-mediated proliferation of peripheral blood T cells and also is critical for activation-induced cell death. We now demonstrate that IL-2 potently decreases expression of IL-7 receptor alpha chain (IL-7Ralpha) mRNA and protein. The fact that IL-7Ralpha is a component of the receptors for both IL-7 and thymic stromal lymphopoietin (TSLP) suggests that IL-2 can negatively regulate signals by each of these cytokines. Previously it was known that the IL-2 and IL-7 receptors shared the common cytokine receptor gamma chain, gamma(c), which suggested a possible competition between these cytokines for a receptor component. Our findings now suggest a previously unknown type of cross-talk between IL-2 and IL-7 signaling by showing that IL-2 signaling can diminish IL-7Ralpha expression via a phosphatidylinositol 3-kinase/Akt-dependent mechanism.

Prediction of the structure of human Janus kinase 2 (JAK2) comprising JAK homology domains 1 through 7

A theoretical model of human Janus kinase 2 (JAK2) comprising all seven Janus homology domains is presented. The model was generated by application of homology modelling approaches. The three-dimensional structure contains, starting from the N-terminus, FERM (4.1, ezrin, radixin, moesin), SH2 (Src homology region 2), tyrosine kinase-like, and tyrosine kinase domains. The predicted inter-domain orientation in JAK2 is discussed and the currently existing mutational data for Janus kinases are evaluated. Structural details of the SH2 and the FERM domains are presented. The predictions indicate that the SH2 domain is not fully functional. A number of hydrophobic amino acids of the FERM domain that are predicted to be involved in the constitutive association with the cytokine receptors are highlighted. The model gives new insights into the structure-function relationship of this important protein, and areas that could be investigated by mutation studies are highlighted.

IL-6 in autoimmune disease and chronic inflammatory proliferative disease

Interleukin 6 (IL-6), which was originally identified as a B-cell differentiation factor, is now known to be a multifunctional cytokine that regulates the immune response, hematopoiesis, the acute phase response, and inflammation. Deregulation of IL-6 production is implicated in the pathology of several disease processes. The expression of constitutively high levels of IL-6 in transgenic mice results in fatal plasmacytosis, which has been implicated in human multiple myeloma. Increased IL-6 levels are also observed in several diseases, including rheumatoid arthritis (RA), systemic-onset juvenile chronic arthritis (JCA), osteoporosis, and psoriasis. IL-6 is critically involved in experimentally induced autoimmune disease, such as antigen-induced arthritis (AIA), and experimental allergic encephalomyelitis. All these clinical data and animal models suggest that IL-6 plays critical roles in the pathogenesis of autoimmune diseases. Here we review the evidence for the involvement of IL-6 in the pathophysiology of autoimmune diseases and chronic inflammatory proliferative diseases (CIPD) and discuss the possible molecular mechanisms of its involvement.

Acute myeloid leukemia

Through the hard work of a large number of investigators, the biology of acute myeloid leukemia (AML) is becoming increasingly well understood, and as a consequence, new therapeutic targets have been identified and new model systems have been developed for testing novel therapies. How these new therapies can be most effectively studied in the clinic and whether they will ultimately improve cure rates are questions of enormous importance. In this article, Dr. Jacob Rowe presents a summary of the current state-of-the-art therapy for adult AML. His contribution emphasizes the fact that AML is not a single disease, but a number of related diseases each distinguished by unique cytogenetic markers which in turn help determine the most appropriate treatment. Dr. Jerald Radich continues on this theme, emphasizing how these cytogenetic abnormalities, as well as other mutations, give rise to abnormal signal transduction and how these abnormal pathways may represent ideal targets for the development of new therapeutics. A third contribution by Dr. Frederick Appelbaum describes how AML might be made the target of immunologic attack. Specifically, strategies using antibody-based or cell-based immunotherapies are described including the use of unmodified antibodies, drug conjugates, radioimmunoconjugates, non-ablative allogeneic transplantation, T cell adoptive immunotherapy and AML vaccines. Finally, Dr. John Dick provides a review of the development of the NOD/SCID mouse model of human AML emphasizing both what it has taught us about the biology of the disease as well as how it can be used to test new therapies. Taken together, these reviews are meant to help us understand more about where we are in the treatment of AML, where we can go and how we might get there.

Ephrins in reverse, park and drive

Eph receptors and their membrane-anchored ephrin ligands are thought to orchestrate cell movements by transducing bidirectional tyrosine-kinase-mediated signals into both cells expressing the receptors and cells expressing the ligands. Whether the resulting event is repulsion of an axonal growth cone, directing the orderly segmentation of hindbrain rhombomere cells or controlling angiogenic remodelling, such elaborate and diverse cell movements require intricate changes in the actin cytoskeleton, as well as precise regulation of cellular adhesion. Recent work by several groups has begun to link ephrin reverse signals to intracellular pathways that regulate actin dynamics and might help to explain how these ligands function as receptors to direct cell movement, adhesion and de-adhesion events.

Inhibiting signal transduction: recent advances in the development of receptor tyrosine kinase and Ras inhibitors

Since aberrant cell signaling is implicated in the initiation, growth, and progression of cancer, proteins involved in signal transduction are rational therapeutic targets. Receptor tyrosine kinases (RTK) and Ras oncoprotein are examples of critical signaling proteins that mediate the processes of cellular growth and differentiation. Agents presently being evaluated as inhibitors of signal transduction include both natural and synthetic compounds, monoclonal antibodies, and antisense oligonucleotides. Preclinical studies of compounds which inhibit RTK and Ras have shown that these targets can be blocked, while side effects in animal models are minimal. Early clinical trials reveal that, in general, treatment with these compounds is both feasible and tolerable. However, many issues about STI remain unresolved including how to optimize schedule, how long to continue treatment, specific mechanisms of action, and how to optimize combinations of STI with standard therapeutic modalities. Addressing these issues may require a shift in the traditional paradigm of drug development, as conventional endpoints may not adequately capture the potential benefits from agents believed to act in a cytostatic vs. cytotoxic manner. This review will discuss the rationale and application of inhibiting signal transduction using inhibitors of RTK and Ras as prototypes of this class of agents.

Potential roles of extracellular signal-regulated kinase but not p38 during myeloid differentiation of U937 cells stimulated by cytokines: augmentation of differentiation via prolonged activation of extracellular signal-regulated kinase

OBJECTIVE

To clarify the signaling mechanism of human myeloid differentiation by hematopoietic growth factors and cytokines, we investigated the role of extracellular signal-regulated kinase (ERK) during the differentiation of human monoblastic U937 cells stimulated by granulocyte-macrophage colony-stimulating factor (GM-CSF) and tumor necrosis factor (TNF).

MATERIALS AND METHODS

Myeloid differentiation was evaluated by morphology, function (respiratory burst activity), and cell surface expression of adhesion molecule (CD11b), and activation of ERK and/or p38 was determined by Western blotting and/or in vitro kinase assay. Inhibition of the ERK pathway was performed using PD98059, a specific inhibitor of this pathway.

RESULTS

U937 cells were induced to be differentiated by the combination of GM-CSF and TNF, but only minimally by either cytokine alone. Transient phosphorylation and activation of ERK was induced by both GM-CSF alone and combination of the two cytokines, whereas sustained phosphorylation and activation was induced only by the combination. In addition, PD98059, a specific inhibitor of ERK pathway, almost completely abolished this prolonged phosphorylation of ERK and completely blocked differentiation. In contrast, both TNF alone and cytokine combination equivalently phosphorylated p38 in U937 cells, which was dissociated from differentiation, and a specific inhibitor of p38 (SB203580) did not inhibit differentiation.

CONCLUSIONS

The results indicate potential roles of sustained activation of ERK but not of p38 in the signaling pathways for human myeloid differentiation in U937 cells synergistically stimulated by the two physiologic cytokines GM-CSF and TNF.

Direct signal transduction via functional interferon-alphabeta receptors in CD34+ hematopoietic stem cells

Affinity purified, freshly isolated CD34+ progenitors were shown to express low levels of type I interferon (IFN) receptors (740 +/- 60 binding sites/cell, K(d) 0.7 +/- 0.04 nM) determined by Scatchard's analysis using a radiolabelled, neutralizing, monoclonal antibody directed against the IFNAR1 chain of the human type I IFN receptor. Treatment of freshly isolated (day 0), highly purified (>95% pure) CD34+ cells with recombinant IFN-alpha resulted in rapid tyrosine phosphorylation and activation of STAT1, Tyk2 and JAK1 as shown by Western immunoblotting. Similarly, IFN treatment was shown by confocal microscopy to result in rapid nuclear localization of the transcription factors IRF1 and STAT2, demonstrating the presence of functional IFN receptors on freshly isolated (day 0) CD34+ cells. The number of specific type I IFN receptor binding sites expressed on hematopoietic progenitor cells increased to some 1440 +/- 40 per cell after 11 days of cultivation of CD34+ cells in vitrosuggesting that receptor expression increases with cell differentiation. IFN-mediated signal transduction and the inhibitory effect of IFN-alpha on 7 or 14 days CFU-GM and BFU-E colony formation was abrogated in the presence of the anti-IFNAR1 mAb, indicating that IFN-alpha acts directly on the proliferation of human hematopoietic progenitor cells via receptor activated signal transduction without excluding the induction of other cytokines or growth factors by residual accessory cells.

JAKs, STATs and Src kinases in hematopoiesis

Hematopoiesis is the cumulative result of intricately regulated signal transduction cascades that are mediated by cytokines and their cognate receptors. Proper culmination of these diverse signaling pathways forms the basis for an orderly generation of different cell types and aberrations in these pathways is an underlying cause for diseases such as leukemias and other myeloproliferative and lymphoproliferative disorders. Over the past decade, downstream signal transduction events initiated upon cytokine/growth factor stimulation have been a major focus of basic and applied biomedical research. As a result, several key concepts have emerged allowing a better understanding of the complex signaling processes. A group of transcription factors, termed signal transducers and activators of transcription (STATs) appear to orchestrate the downstream events propagated by cytokine/growth factor interactions with their cognate receptors. Similarly, cytoplasmic Janus protein tyrosine kinases (JAKs) and Src family of kinases seem to play a critical role in diverse signal transduction pathways that govern cellular survival, proliferation, differentiation and apoptosis. Accumulating evidence suggests that STAT protein activation may be mediated by members of both JAK and Src family members following cytokine/growth factor stimulation. In addition, JAK kinases appear to be essential for the phosphorylation of the cytokine receptors which results in the creation of docking sites on the receptors for binding of SH2-containing proteins such as STATs, Src-kinases and other signaling intermediates. Cell and tissue-specificity of cytokine action appears to be determined by the nature of signal transduction pathways activated by cytokine/receptor interactions. The integration of these diverse signaling cues from active JAK kinases, members of the Src-family kinases and STAT proteins, leads to cell proliferation, cell survival and differentiation, the end-point of the cytokine/growth factor stimulus.

Cytokine control of developmental programs in normal hematopoiesis and leukemia

The establishment of a system for in vitro clonal development of hematopoietic cells made it possible to discover the cytokines that regulate hematopoiesis. These cytokines include colony stimulating factors and others, which interact in a network, and there is a cytokine cascade which couples growth and differentiation. A network allows considerable flexibility and a ready amplification of response to a particular stimulus. A network may also be necessary to stabilize the whole system. Cells called hematopoietic stem cells (HSC) can repopulate all hematopoietic lineages in lethally irradiated hosts, and under appropriate conditions give rise to neuronal, muscle, and epithelial cells. Granulocyte colony stimulating factor induces migration of both HSC and in vitro colony forming cells from the bone marrow to peripheral blood. Granulocyte colony stimulating factor is also used clinically to repair irradiation and chemotherapy associated suppression of normal hematopoiesis in cancer patients, and to stimulate normal granulocyte development in patients with infantile congenital agranulocytosis. It is suggested that there may also be appropriate conditions under which in vitro colony forming cells have a wider differentiation potential similar to that shown by HSC. An essential part of the developmental program is cytokine suppression of apoptosis by changing the balance in expression of apoptosis inducing and suppressing genes. Decreasing the level of cytokines that suppress therapeutic induction of apoptosis in malignant cells can improve cancer therapy. Cytokines and some other compounds can reprogram abnormal developmental programs in leukemia, so that the leukemic cells differentiate to mature non dividing cells, and this can also be used for therapy. There is considerable plasticity in the developmental programs of normal and malignant cells.

The paradigm of IL-6: from basic science to medicine

IL-6 is a pleiotropic cytokine with a wide range of biological activities in immune regulation, hematopoiesis, inflammation, and oncogenesis. Its activities are shared by IL-6-related cytokines such as leukemia inhibitory factor and oncostatin M. The pleiotropy and redundancy of IL-6 functions have been identified by using a unique receptor system comprising two functional proteins: an IL-6 receptor (IL-6R) and gp130, the common signal transducer of cytokines related to IL-6. Signal transduction through gp130 is mediated by two pathways: the JAK-STAT (Janus family tyrosine kinase-signal transducer and activator of transcription) pathway and the Ras mitogen-activated protein kinase pathway. The negative regulators of IL-6 signaling have also been identified, although the physiological roles of the molecules are not yet fully understood. The pathological roles of IL-6 have also been clarified in various disease conditions, such as inflammatory, autoimmune, and malignant diseases. On the basis of the findings, a new therapeutic approach to block the IL-6 signal using humanized anti-IL-6R antibody for rheumatoid arthritis, Castleman's disease, and multiple myeloma has been attempted.

Stat3 beta inhibits gamma-globin gene expression in erythroid cells

We demonstrated previously gamma-globin gene inhibition in K562 cells and primary erythroid progenitors treated with interleukin-6. Although several cis-acting elements have been identified in the globin promoters, the precise mechanism for cytokine-mediated globin gene regulation remains to be elucidated. In this report we demonstrate inhibitors of Stat3 phosphorylation abrogate interleukin-6-mediated gamma gene silencing in erythroid cells. DNA-protein binding studies established Stat3 interaction in the 5'-untranslated gamma-globin promoter region. Furthermore, co-transfection experiments with Stat3 beta demonstrate gamma promoter inhibition in a concentration-dependent manner, which was significantly reversed when the cognate Stat3-binding site in the 5'-untranslated region was mutated. These studies establish a novel mechanism for gamma gene silencing through the STAT signal transduction pathway.

Functional dichotomy of a 20-mer and 16-mer peptide derived from Staphylococcus aureus protein A: importance of amino acid sequence

Protein A (PA) of Staphylococcus aureus possesses a wide variety of biological properties such as antitumor, antitoxic, anticarcinogenic, immunomodulatory, antifungal and antiparasitic. Since PA is a foreign protein, it is quite logical to assume that it may be cleaved into smaller peptide fragments in vivo, which may be responsible for the diverse biological activities of whole PA. We have shown that two proteolytic peptide fragments (20-mer and 16-mer) of PA mimics IgG binding and some of the immunomodulatory properties of PA. In the present study, we investigated upon the functional similarity and dissimilarity in these two peptides. The 16-mer peptide induces the production of IL6, IL10, TNFalpha and IL1alpha but it does not have any effect on secretion of IFNgamma and IL4. Whereas 20-mer peptide induces production of TNFalpha, IL1alpha along with induction of IFNgamma but it downregulates IL4, IL6 and IL10 production. IFNgamma to IL4 ratio clearly indicates that the 20-mer peptide induces Th1 type response, whereas 16-mer peptide induces Th0 type response. The 20-mer peptide retains the antitumor property of the native protein (PA) in Ehrlich ascitis tumor model, whereas 16-mer peptide does retain the same property only in vitro. The 16-mer peptide however can activate macrophages to kill Ehrlich ascitis tumor cells in vitro more efficiently than that of 20-mer peptide. Thus both the peptides although derived from same native protein and has had 13 aminoacid residues in common, appears to evoke different reactivites in the immune system. Thus it appears that the IgG binding ability which is seen with the native protein A molecule and also with both 16-mer and 20-mer peptides do not automatically confer upon them the antitumor property, and cytokine producing activities. Thus it appears that all different properties associated with Protein A may not be necessarily associated with its IgG binding abilities.

Cloning and characterization of a proliferation-associated cytokine-inducible protein, CIP29

We identified a novel erythropoietin (Epo)-induced protein (CIP29) in lysates of human UT-7/Epo leukemia cells using two-dimensional gel analysis and cloned its full-length cDNA. CIP29 contains 210 amino acids with a predicted MW of 24 kDa, and has a N-terminal SAP DNA-binding motif. CIP29 expression was higher in cancer and fetal tissues than in normal adult tissues. CIP29 mRNA expression is cytokine regulated in hematopoietic cells, being up-regulated by Epo in UT7/Epo cells, and by thrombopoietin (Tpo), FLT3 ligand (FL) and stem cell factor (SCF) in primary human CD34(+) cells. Up-regulation of CIP29 in UT7/Epo cells by Epo was associated with cell cycle progression but not with antiapoptosis. Epo withdrawal reduced CIP29 expression concomitant with cell cycle arrest. Overexpression of CIP29-GFP in HEK293 cells enhances cell cycle progression. CIP29 appears to be a new cytokine regulated protein involved in normal and cancer cell proliferation.

Characterization and location of Src-dependent tyrosine phosphorylation in rat brain mitochondria

Analysis of protein phosphorylation in highly purified rat brain mitochondria revealed the presence of several alkali-stable phosphoproteins whose phosphorylation markedly increases upon treatment with peroxovanadate and Mn(2+), a property indicating tyrosine phosphorylation. These include three prominent bands, with apparent sizes of 50, 60, and 75 kDa, which are detectable by anti-phosphotyrosine. Tyrosine phosphorylation disappears when mitochondria are treated with PP2, an inhibitor of the Src kinase family, suggesting the presence of members of this family in rat brain mitochondria. Immunoblotting and immunoprecipitation assays of mitochondrial lysates confirmed the presence of Fyn, Src and Lyn kinases, as well as Csk, a protein kinase which negatively controls the activity of the Src kinase family. Results show that tyrosine-phosphorylated proteins are membrane-bound and that they are located on the inner surface of the outer membrane and/or the external surface of the inner membrane. Instead, Src tyrosine kinases are mainly located in the intermembrane space - in particular, as revealed by immunogold experiments for Lyn kinase, in the cristal lumen. Rat brain mitochondria were also found to possess a marked level of tyrosine phosphatase activity, strongly inhibited by peroxovanadate.

Induction of the interleukin-2/15 receptor beta-chain by the EWS-WT1 translocation product

EWS-WT1 is a chimeric transcription factor resulting from fusion of the N-terminal domain of the Ewing sarcoma gene EWS to the three C-terminal zinc fingers of the Wilms tumor suppressor WT1. This translocation underlies desmoplastic small round cell tumor (DSRCT), which is noted for the abundance of reactive stroma surrounding islets of tumor cells, suggestive of paracrine signals contributing to tumor cell proliferation. Hybridization to high-density oligonucleotide microarrays can be used to identify targets of EWS-WT1. Expression of EWS-WT1 from a tetracycline-regulated promoter leads to the induction of growth-associated genes, of which the most remarkable is the beta-chain of the interleukin-2/15 receptor (IL-2/15Rbeta). Potent transcriptional activation by the chimeric protein maps to two bindings sites within the IL-2/15Rbeta promoter. Analysis of primary DSRCT tumor specimens demonstrates high levels of IL-2/15Rbeta within the tumor cells, along with expression of IL-2 and IL-15 by the abundant hyperplastic endothelial cells within the reactive stroma. Activation of this cytokine signaling pathway is consistent with the nuclear localization of its downstream effectors, phosphorylated STAT3 and STAT5. These observations suggest that the transcriptional induction of a cytokine receptor by a tumor-associated translocation product enables a proliferative response of epithelial cancer cells to ligands secreted by the surrounding stroma.

Distinct region of the granulocyte colony-stimulating factor receptor mediates proliferative signaling through activation of Janus kinase 2 and p44/42 mitogen-activated protein kinase

The granulocyte colony-stimulating factor receptor (G-CSFR) regulates the proliferation, differentiation and survival of neutrophilic progenitor cells. In these studies, we introduced mutant G-CSFRs with cytoplasmic domains truncated approximately every 30 amino acids from the C-terminus into interleukin-3 (IL-3)-dependent myeloid LGM-1 cells. The G-CSFR membrane proximal region containing the Box 2 homology sequence was determined to be critical for proliferative signaling, as well as for activation of Janus kinase (JAK2) and p44/42 mitogen-activated protein kinase (MAPK) following G-CSF stimulation. In the presence of increasing concentrations of JAK2 or p44/42 MAPK inhibitors, LGM-1 cells expressing the full-length G-CSFR exhibited a decreased capacity to proliferate in response to G-CSF. These results demonstrate that JAK2 and p44/42 MAPK activation is involved in proliferative signaling through the G-CSFR membrane proximal region containing the Box 2 homology sequence.

Cloning of rat thymic stromal lymphopoietin receptor (TSLPR) and characterization of genomic structure of murine Tslpr gene

Thymic stromal derived lymphopoietin receptor (TSLPR) is a novel receptor subunit that is related in sequence to the interleukin (IL)-2 receptor common gamma chain. TSLPR forms a heterodimeric complex with the IL-7 receptor alpha chain to form the receptor for thymic stromal derived lymphopoietin, a cytokine involved in B- and T-cell function. We have cloned the TSLP receptor from rat and find that the WSXWX motif commonly found in extracellular domains of cytokine receptors is conserved as a W(T/S)XV(T/A) motif among TSLP receptors from mouse, rat and human. As in the mouse, TSLP receptor is widely expressed in rats suggesting that TSLPR may have roles in signaling outside the hematopoietic system. A zooblot analysis revealed that TSLPR is expressed in all vertebrate species examined. The absence of TSLPR in Saccharomyces cerevisiae, Drosophila melanogaster and Caenorhabditis elegans genomes is similar to the expression of several other cytokine receptors that have been characterized thus far. We have also characterized the genomic structure of the murine Tslpr gene which shows that in addition to primary sequence homology, it shares a common genomic organization of coding exons with the murine IL-2 receptor common gamma chain (Il2rg). Use of an alternative splice acceptor site leads to two alternatively spliced transcript variants of murine TSLPR, both of which are functional receptors. Finally, using linkage analysis, we mapped the murine Tslpr gene to mouse chromosome 5 between the Ecm2 and Pxn genes.

Alternate signalling pathways from the interleukin-2 receptor

Interleukin-2 (IL-2) plays a major role in the proliferation of cell populations during an immune reaction. The beta(c) and gamma(c) subunits of the IL-2 receptor (IL-2R) are sufficient and necessary for signal transduction. Despite lacking known catalytic domains, receptor engagement leads to the activation of a diverse array protein tyrosine kinases (PTKs). In resting or anergised T cells, Jak3 is not activated. Signals arising from the PROX domain of the gamma(c) subunit activate p56(lck) (lck) leading to the induction of anti-apoptotic mechanisms. When Jak3 is activated, in primed T cells, other PTKs predominantly mediate the induction of anti-apoptotic mechanisms and drive cellular proliferation. This review intends to suggest a role for these differences within the context of the immune system.

Role of pRB-family/E2F complex in the inhibition of IL-3-dependent lymphoid cell proliferation

Interleukin 3 (IL-3)-dependent proliferation of haematopoietic cells is specifically inhibited by p130, a member of the pRB-family proteins. p130 interacts with the cell-cycle regulatory E2F transcription factors, notably E2F-4 and E2F-5, and affects promoters containing E2F-binding sites through two distinct mechanisms. First, upon complex formation with E2F, it blocks transcriptional activation by E2F. Second, the formed p130-E2F complex binds to E2F sites and actively represses transcription by inhibiting the activity of surrounding enhancer elements on the promoter. To pursue the relative contributions of each mechanism in the p130-mediated inhibition of IL-3-dependent cell proliferation, we employed a dominant-negative DP-1, which suppresses both E2F-dependent transactivation and the formation of active transcriptional repressors. Ectopic expression of the dominant negative DP-1 in the IL-3-dependent BaF3 lymphoid cells gave rise to an inhibition of cell proliferation, which was concomitantly associated with a decrease in levels of cyclin E, an indispensable molecule for G1 to S-phase cell-cycle progression. Our results indicate that blocking E2F-dependent transactivation, but not the formation of p130-E2F transcriptional repressor complexes, is responsible for the inhibition of IL-3-dependent cell growth by p130.

Role for adapter proteins in costimulatory signals of CD2 and IL-2 on NK cell activation

Natural killer (NK) cells participate in both innate and adaptive immunity through the prompt secretion of cytokines and ability to lyse virally infected cells or tumor cells. Triggering of NK cells requires aggregation of surface receptors such as CD2 and CD16, and NK cell activity can be augmented in vitro by stimulation with IL-2. In this study, we examined the role of adapter proteins in the increased NK activation following CD2 crosslinking and IL-2 stimulation of NK3.3 cells. NK3.3 cells lysed NK-sensitive K562 cells in a CD2-dependent manner, and IL-2 markedly enhanced lytic activity in a 4h cytotoxic assay. IL-2 also enhanced spontaneous and CD2-mediated granule exocytosis from NK3.3 cells. CD2 crosslinking markedly induced tyrosine phosphorylation of Cbl associated with Grb2 or CrkL, Shc and LAT, compared with IL-2 stimulation. However, costimulation of IL-2 with CD2 crosslinking remarkably enhanced associations of Grb2-Shc and CrkL-Cbl, compared to IL-2 stimulation or CD2 crosslinking alone. In vitro binding studies using GST-fusion proteins revealed that interactions of Grb2-Shc and CrkL-Cbl were mediated through each SH2 domain in tyrosine phosphorylation-dependent manner. Furthermore, CD2 crosslinking, but not IL-2 stimulation, markedly induced tyrosine phosphorylation of LAT. Thus, tyrosine phosphorylation of different adapter proteins and consequent interactions between signaling molecules described here may explain the molecular mechanisms of the additive effects of IL-2 stimulation and CD2 crosslinking on NK cell activation.

Histidine protein kinases: key signal transducers outside the animal kingdom

Histidine protein kinases (HPKs) are a large family of signal-transduction enzymes that autophosphorylate on a conserved histidine residue. HPKs form two-component signaling systems together with their downstream target proteins, the response regulators, which have a conserved aspartate in a so-called 'receiver domain' that is phosphorylated by the HPK. Two-component signal transduction is prevalent in bacteria and is also widely used by eukaryotes outside the animal kingdom. The typical HPK is a transmembrane receptor with an amino-terminal extracellular sensing domain and a carboxy-terminal cytosolic signaling domain; most, if not all, HPKs function as dimers. They show little similarity to protein kinases that phosphorylate serine, threonine or tyrosine residues, but may share a distant evolutionary relationship with these enzymes. In excess of a thousand known genes encode HPKs, which are important for multiple functions in bacteria, including chemotaxis and quorum sensing, and in eukaryotes, including hormone-dependent developmental processes. The proteins divide into at least 11 subfamilies, only one of which is present in eukaryotes, suggesting that lateral gene transfer gave rise to two-component signaling in these organisms.

Interferon-alpha inhibits Stat5 DNA-binding in IL-2 stimulated primary T-lymphocytes

It has previously been shown that IFN-alpha is a potent inhibitor of IL-2 induced proliferation in primary T-lymphocytes, by selectively abrogating the downstream effects of IL-2 on the core cell cycle machinery regulating the G1/S transition. Theoretically this could be mediated through cross-talk between the signalling cascades activated by these cytokines, as several signalling components are known to be shared. IL-2 activates multiple signalling pathways that are important for T-cell proliferation and differentiation. In the present study, the effects of IFN-alpha on IL-2 signal transduction was investigated. The IFN-alpha induced inhibition of IL-2 induced proliferation in activated T-lymphocytes, was associated with a suppressed Jak3 protein expression as well as an inhibited prolonged Stat5 DNA binding, and a partially reduced expression of the Stat5 inducible gene IL-2R alpha. Our results provide a possible molecular link between the prominent antiproliferative effects of IFN-alpha on IL-2 induced T-cell proliferation and the signal transduction pathways emerging from the IL-2 receptor.

Constitutive activation of Stat1 and Stat3 in primary erythroleukemia cells

Signal transducers and activators of transcription (Stat) proteins play important roles in the regulation of hematopoiesis as downstream molecules of cytokine signal transduction. Previously, we demonstrated that Stat1 and Stat3 are activated by erythropoietin (EPO) in a human EPO-dependent erythroleukemia cell line UT-7/EPO. We report here that Stat1 and Stat3 are constitutively activated in freshly isolated erythroleukemia cells. In addition, EPO promoted cell growth of these cells, accompanied by enhanced activities of Stat1 and Stat3. Furthermore, mutation in the Statl/Stat3-binding sites of the c-myc gene promoter clearly blocked its promoter activity in EPO-stimulated primary erythroleukemia cells. Thus, Stat1 and Stat3 may support cell growth in part via c-myc gene activation in primary erythroleukemia cells.

Identification of the human erythropoietin receptor region required for Stat1 and Stat3 activation

Signal transducers and activators of transcription (Stat) proteins play important roles in the regulation of hematopoiesis as downstream molecules of cytokine signal transduction. It was previously demonstrated that erythropoietin (EPO), a major regulator of erythropoiesis, activates 3 different Stat members, Stat1, Stat3, and Stat5, in a human EPO-dependent cell line, UT-7/EPO. To clarify the mechanism by which EPO activates Stat1 and Stat3 via the EPO receptor (EPOR), a series of chimeric receptors was constructed bearing the extracellular domain of the granulocyte colony-stimulating factor receptor linked to the transmembrane domain of EPOR and the full length or several mutants of the cytoplasmic domain of EPOR, and these chimeric receptor complementary DNAs were introduced into UT-7/EPO cells. Tyr432 on human EPOR was important for activation of Stat1 and Stat3 and c-myc gene induction. In addition, Jak2 and Fes tyrosine kinases were involved in EPO-induced activation of Stat1 and Stat3. These results indicate that Stat1 and Stat3 are activated by EPO via distinct mechanisms from Stat5.

hTid-1, a human DnaJ protein, modulates the interferon signaling pathway

The Jak family of protein-tyrosine kinases are crucial for the signaling of a large number of different polypeptide ligands, including the interferons, many cytokines, erythropoietin, and growth factors. Through their interaction with receptors, the Jaks initiate a signaling cascade resulting in the activation of gene transcription and ultimately a cellular response to various ligands. In addition to their role in cellular signaling, alteration of Jak activity has been implicated in several disease states. In identifying Jak2-interacting proteins with the yeast two-hybrid system, we cloned the human homologue of the Drosophila melanogaster tumor suppressor gene lethal () tumorous imaginal discs, which encodes the protein Tid56. Drosophila Tid56 and its human homologue hTid-1 represent members of the DnaJ family of molecular chaperones. The TID1 gene encodes two splice variants hTid-1(S) and hTid-1(L). We confirmed the interaction between Jak2 and hTid-1(S) or hTid-1(L) by immunoprecipitation from COS-1 cells expressing these proteins. The interaction between endogenous hTid-1 and Jak2 was shown in HEp2 cells. We further showed that hTid-1 interacts with the human interferon-gamma (Hu-IFN-gamma) receptor subunit IFN-gamma R2. In addition, using a chimeric construct where the extracellular domain of IFN-gamma R2 was fused to the kinase domain of Jak2, we showed that hTid-1 binds more efficiently to the chimera with an active kinase domain than to a similar construct with an inactive kinase domain. Additionally, the data demonstrate that hTid-1 isoforms as well as Jak2 interact with Hsp70/Hsc70 in vivo, and the interaction between Hsp70/Hsc70 and hTid-1 is reduced after IFN-gamma treatment. Furthermore, both hTid-1(S) and hTid-1(L) can modulate IFN-gamma-mediated transcriptional activity.

The IL-15R alpha chain signals through association with Syk in human B cells

The alpha-chain of the IL-15R (IL-15Ralpha) serves as the specific, high-affinity receptor for IL-15. It is expressed by lymphoid and nonlymphoid cells, including B cell lymphoma lines. In this study, we have further explored IL-15Ralpha-mediated signaling in activated primary B cells and in Raji cells, a human B-lymphoblastoid cell line which expresses the IL-15Ralpha and IL-2Rgamma chains, but lacks the IL-2Rbeta chain. Stimulation of Raji cells with IL-15 induces their proliferation and rescues them from C2-ceramide-induced apoptosis. By immunoprecipitation and Western blotting, we show that treatment of Raji cells and activated primary B cells with IL-15 induces coprecipitation of Syk kinase with the IL-15Ralpha chain. Upon association, the activated Syk kinase phosphorylates the IL-15Ralpha chain as well as phospholipase Cgamma, which coprecipitates with Syk. Furthermore, transfection of Raji cells with stem-loop Syk antisense oligonucleotides prevents IL-15Ralpha and phospholipase Cgamma phosphorylation as well as the inhibition of apoptosis by IL-15. Mutation of a defined region of the intracellular signaling portion of IL-15Ralpha (Tyr227) abrogates both the IL-15Ralpha/Syk association and IL-15Ralpha phosphorylation. Taken together, this suggests that Syk kinase physically and functionally associates with the IL-15Ralpha chain in B cells and that Syk plays a key role in mediating IL-15-induced signal transduction, thus accounting for the distinct functional consequences of IL-15 vs IL-2 binding to B cells.

12-lipoxygenase metabolite 12(S)-HETE stimulates human pancreatic cancer cell proliferation via protein tyrosine phosphorylation and ERK activation

We previously reported that inhibition of the 12-lipoxygenase pathway abolished proliferation and induced apoptosis in several pancreatic cancer cell lines. Furthermore, the 12-lipoxygenase product 12(S)-HETE stimulated pancreatic cancer cell proliferation and reversed 12-lipoxygenase inhibitor-induced growth inhibition. We investigated the underlying mechanism for 12(S)-HETE-induced pancreatic cancer cell proliferation, using 2 human pancreatic cancer cell lines, PANC-1 and HPAF. Cell proliferation was monitored by both thymidine incorporation and cell number. Western blotting was used to investigate the effect of 12(S)-HETE on cellular protein tyrosine phosphorylation as well as ERK, P38 MAPK and JNK/SAPK phosphorylation. 12(S)-HETE markedly stimulated proliferation of pancreatic cancer cells in a time- and concentration-dependent manner. In parallel, 12(S)-HETE induced tyrosine phosphorylation of multiple cellular proteins, while inhibition of tyrosine kinase by genestein abolished 12(S)-HETE-induced proliferation, indicating that intracellular protein tyrosine kinase activation is involved in the mitogenic effects of 12(S)-HETE. Following treatment with 12(S)-HETE, both ERK and P38 MAPK, but not JNK/SAPK, were phosphorylated. The specific MEK inhibitors PD098059 and U0126, which in turn suppress ERK, abolished 12(S)-HETE-stimulated proliferation. In contrast, inhibition of P38 MAPK with SB203580 did not affect 12(S)-HETE-stimulated pancreatic cancer cell proliferation. Furthermore, 12(S)-HETE-stimulated ERK phosphorylation was inhibited by genestein, indicating that tyrosine phosphorylation is essential for ERK activation. These findings suggest that both ERK and cellular protein tyrosine kinase activation are involved in 12(S)-HETE-induced pancreatic cancer cell proliferation but P38 and JNK/SAPK are not involved in this mitogenic effect.

Signaling through a novel domain of gp130 mediates cell proliferation and activation of Hck and Erk kinases

Interleukin-6 (IL-6) induces the activation of the Src family kinase Hck, which is associated with the IL-6 receptor beta-chain, gp130. Here we describe the identification of an "acidic" domain comprising amino acids 771 to 811 of gp130 as a binding region for Hck, which mediates proliferative signaling. The deletion of this region of gp130 (i.e., in deletion mutant d771-811) resulted in a significant reduction of Hck kinase activity and cell proliferation upon stimulation of gp130 compared to wild-type gp130. In addition, d771-811 disrupted the growth factor-stimulated activation of Erk and the dephosphorylation of Pyk2. Based on these findings, we propose a novel, acidic domain of gp130, which is responsible for the activation of Hck, Erk, and Pyk2 and signals cell proliferation upon growth factor stimulation.

Specific DNA binding and transactivation potential of recombinant, purified Stat5

The signal transducers and activators of transcriptions (Stats) are central mediators of cytokine responses especially in hematopoietic cells. The detailed molecular mechanisms of Stat activation, particularly the role of post-translational modifications and co-operation with cellular transcription factors are subject to intense investigation. The phosphorylation of a tyrosine residue in the carboxyl terminal domain is a common characteristic for the biologically active state of all known Stats. We studied the biological potential of purified recombinant murine Stat5a and Stat5b. These proteins were expressed in Sf9 insect cells upon infection with Stat5 encoding baculoviruses. We also obtained the tyrosine phosphorylated, activated forms of the Stat5 proteins by expressing the tyrosine kinase Janus kinase2 (Jak) in the same cells through co-infection with a kinase encoding virus. After purification, only the tyrosine phosphorylated form was able to bind specifically in vitro to the Stat5 DNA response element. This activated form of Stat5 is also able to support specific cell free in vitro transcription of a gene with a Stat5 response element in its promoter region. The recombinant purified Stat5 proteins were treated with the tyrosine specific protein phosphatase or with potato acidic phosphatase, which removes phosphate groups from serine and tyrosine residues. Phosphatase treatment resulted in the loss of specific DNA binding ability. This property could be restored by an in vitro reaction with recombinant, purified EGF or PDGF receptor kinases. Tyrosine rephosphorylation in vitro also restored the transactivation potential of Stat5. This modification is, therefore, a sufficient prerequisite for transcriptional induction by Stat5.

Adhesion via CD43 induces Syk activation and cell proliferation in TF-1 cells

The effect of adhesion via CD43 (leukosialin, sialophorin) on cell proliferation and phosphorylation signaling were examined in a growth factor-dependent hematopoietic progenitor cell line, TF-1. TF-1 cells promptly resulted in death after withdrawal of growth factors. However, the viable cell number increased when TF-1 cells were cultured on anti-CD43 monoclonal antibody-coated plates. In this case, sustained activation of protein tyrosine kinase Syk and extracellular signal-regulated kinase (Erk) 1/2 were detected. Overexpression of exogenous Syk on TF-1 cells by the adenovirus vector system induced enhancement of the cell proliferation accompanied with enhancement of the Erk activation by a dominant-positive effect. The signal transducer and activator of transcription (STAT) 5 seemed not to be associated with the CD43-mediated cell proliferation. These results indicated that adhesion via CD43 induces the proliferation of TF-1 cells in the absence of growth factors in part by Syk-dependent Erk 1/2 signaling.

Involvement of Hgs/Hrs in signaling for cytokine-mediated c-fos induction through interaction with TAK1 and Pak1

Hgs/Hrs is a tyrosine-phosphorylated FYVE finger protein that is induced by stimulation with various cytokines and growth factors. Here we show that Hgs plays critical roles in the signaling pathway for the interleukin-2-induced activation of the serum-response element and cyclic AMP-response element of the c-fos promoter. We found that Hgs associated physically with transforming growth factor-beta-activated kinase 1 (TAK1) and p21-activated kinase 1 (Pak1), which mediate the activation of c-Jun N-terminal kinase and serum response factor, respectively, leading to transactivation via the serum-response element and cyclic AMP-response element. These results suggest that Hgs is involved in the TAK1-JNK and Pak1-serum response factor pathways for the c-fos induction that is initiated by cytokines.

IRF family of transcription factors as regulators of host defense

Interferon regulatory factors (IRFs) constitute a family of transcription factors that commonly possess a novel helix-turn-helix DNA-binding motif. Following the initial identification of two structurally related members, IRF-1 and IRF-2, seven additional members have now been reported. In addition, virally encoded IRFs, which may interfere with cellular IRFs, have also been identified. Thus far, intensive functional analyses have been done on IRF-1, revealing a remarkable functional diversity of this transcription factor in the regulation of cellular response in host defense. Indeed, IRF-1 selectively modulates different sets of genes, depending on the cell type and/or the nature of cellular stimuli, in order to evoke appropriate responses in each. More recently, much attention has also been focused on other IRF family members. Their functional roles, through interactions with their own or other members of the family of transcription factors, are becoming clearer in the regulation of host defense, such as innate and adaptive immune responses and oncogenesis.

Cross talk of the interferon-alpha/beta signalling complex with gp130 for effective interleukin-6 signalling

BACKGROUND

Signalling cross talk provides a molecular basis for modulating a given signalling pathway by another, and it is often critical for regulating cellular responses elicited by cytokines. Previously, we reported on the critical role of the IFN-alpha/beta signalling complex, generated by spontaneously produced IFN-alpha/beta, in efficient IFN-gamma signalling.

RESULTS

In the present study, we have demonstrated that the IFN-alpha/beta signalling complex also contributes to efficient IL-6 signalling. In fact, IL-6-induced activation of the Stat1 and Stat3 transcription factors is markedly diminished in the absence of the IFN-alpha/beta signalling complex. The induction of several target genes for these factors is also diminished, both in vitro and in vivo. We provide evidence that the cytoplasmic tyrosine residues of IFNAR-1, which remains phosphorylated by a weak IFN-alpha/beta stimulation, provide docking sites for Stat1 and Stat3 to form homo- or heterodimers following IL-6 stimulation. Furthermore, a chemical cross-linking experiment revealed that IFNAR-1 and gp130, a common signal transducer for the IL-6 family of cytokines, exist in close proximity.

CONCLUSIONS

The constitutive weak IFN-alpha/beta signal provides a foundation for strong cellular responses to IL-6, IFN-gamma, and possibly other cytokines. Our results also suggest the assembly of cytokine receptor subunits, which may represent a 'receptosome'-like structure, allowing the unique signalling cross talks to occur.

Src family kinases are required for prolactin induction of cell proliferation

Prolactin (PRL) is a pleiotropic cytokine promoting cellular proliferation and differentiation. Because PRL activates the Src family of tyrosine kinases (SFK), we have studied the role of these kinases in PRL cell proliferation signaling. PRL induced [(3)H]thymidine incorporation upon transient transfection of BaF-3 cells with the PRL receptor. This effect was inhibited by cotransfection with the dominant negative mutant of c-Src (K>A295/Y>F527, SrcDM). The role of SFK in PRL-induced proliferation was confirmed in the BaF-3 PRL receptor-stable transfectant, W53 cells, where PRL induced Fyn and Lyn activation. The SFK-selective inhibitors PP1/PP2 and herbimycin A blocked PRL-dependent cell proliferation by arresting the W53 cells in G1, with no evident apoptosis. In parallel, PP1/PP2 inhibited PRL induction of cell growth-related genes c-fos, c-jun, c-myc, and odc. These inhibitors have no effect on PRL-mediated activation of Ras/Mapk and Jak/Start pathways. In contrast, they inhibited the PRL-dependent stimulation of the SFKs substrate Sam68, the phosphorylation of the tyrosine phosphatase Shp2, and the PI3K-dependent Akt and p70S6k serine kinases. Consistently, transient expression of SrcDM in W53 cells also blocked PRL activation of Akt. These results demonstrate that activation of SFKs is required for cell proliferation induced by PRL.

Deletion of the acidic-rich domain of the IL-2Rbeta chain increases receptor-associated PI3K activity

Interleukin-2 (IL-2) regulates the proliferation and homeostasis of lymphocytes through the coordinated activation of distinct signaling pathways. Deletion of the acidic-rich domain of the IL-2 receptor beta chain (IL-2Rbeta) prevents association of Src tyrosine kinases to the receptor, as well as IL-2-induced Akt activation. Cells bearing this deletion (BafbetaDeltaA) maintain full proliferation in response to IL-2 both in vivo and in vitro, suggesting that those pathways are dispensable for this important function of IL-2. In this study, we re-examined phosphatidylinositol-3 kinase (PI3K) activation in BafbetaDeltaA cells and found that, in BaF/3 IL-2RbetaDeltaA cells, deletion of the acidic domain induced constitutive activation of the receptor-associated PI3K activity. This, in turn, was responsible for the higher basal Akt activity observed in cells expressing this deletion. Based on these data, and since pharmacological abrogation of PI3K activity prevented IL-2-driven cell proliferation of BafbetaDeltaA cells, we conclude that the PI3K/Akt pathway is still functionally relevant in cells bearing this mutation. Moreover, we show that the PI3K-induced signals are, at least in part, responsible for c-myc expression. In conclusion, we have used this model to better identify those signals that are integral components of the molecular mechanisms responsible for IL-2-regulated cell proliferation.

The YXXQ motif in gp 130 is crucial for STAT3 phosphorylation at Ser727 through an H7-sensitive kinase pathway

The signal transducer and activator of transcription (STAT) 3 is essential for mediating signals from the receptors for a variety of cytokines and growth factors, including IL-6 and EGF, and from cytoplasmic tyrosine kinases. Upon stimulation, STAT3 is phosphorylated at Ser727 and Tyr705. However, the role of phosphorylation at Ser727, and the kinase pathways responsible for this phosphorylation in IL-6 signaling remain obscure. Here we show that IL-6 activates at least two distinct STAT3 serine kinase pathways and that an H7-sensitive pathway is dominant over a PD98059-sensitive one in HepG2 cells stimulated with a low concentration of IL-6. The analysis, using a series of chimeric receptors containing the extracellular domain of the G-CSF receptor, the truncated form of gp 130, and additional short peptides at the gp 130 carboxy-terminus, showed that the YXXQ motif of gp 130 was sufficient for the H7-sensitive STAT3 Ser727 phosphorylation. This YXXQ-mediated pathway does not involve Erk, p38, JNK, or PKCdelta, and requires a site in the region from 533 to 711 of STAT3 for phosphorylation in vivo. Moreover, we show that Ser727 is required for full transcriptional activity of STAT3 for two different response elements. Thus, the YXXQ motif regulates STAT3 activities in two ways in response to even a low concentration of IL-6: it recruits STAT3 to the receptor for tyrosine phosphorylation, and activates an unidentified H7-sensitive pathway leading to the serine phosphorylation of STAT3.

The interferon system and interferon regulatory factor transcription factors -- studies from gene knockout mice

Interferon regulatory factors (IRFs) were initially identified as regulators of IFN-alpha/beta genes and to date nine members have been determined in human and mouse. They share a conserved DNA-binding domain in the N-terminal portion that recognizes similar DNA sequences. Despite their similar DNA binding specificity, the IRFs show diverse functions in response to extra cellular stimuli. Although the study of IRFs was started with respect to regulation of the IFN-alpha/beta gene expression, recent studies have revealed other aspects of IRF functions. In this review, we summarize our current knowledge of the functions of IRF family members revealed by our gene targeting study in mice, focusing on the regulation of the IFN system.

Cloning the full-length IL-2/15 receptor-beta cDNA sequence from mouse brain: evidence of enrichment in hippocampal formation neurons

Numerous studies have implicated interleukin-2 (IL-2) in various brain processes, and more recently, several studies have also attributed neurobiological actions to interleukin-15 (IL-15). On lymphocytes, receptors for IL-2 and IL-15 share a common subunit, the IL-2/15 receptor-beta (IL-2/15Rbeta) that is essential for intracellular signaling. Although a short segment of IL-2/15Rbeta has been cloned (0.35 kb) from normal brain cells, attempts to isolate the full-length cDNA have been unsuccessful, suggesting the possibility that the genes expressed by brain cells and lymphocytes may differ. Using conventional and anchored PCR cloning strategies, we isolated the full-length cDNA of IL-2/15Rbeta (2038 bp) from well-perfused, normal mouse forebrain. The coding sequence and the adjacent 5' and 3' UTR sequences from brain and lymphocyte were found to be fully homologous. Although evidence of expression of IL-2/15Rbeta can be found in many brain regions using PCR, clear evidence of gene expression by in situ hybridization was detectable only in the hippocampal formation, habenula and piriform cortex. This same pattern of mRNA expression in situ was also observed for the common gamma subunit shared by IL-2 and IL-15. In the hippocampus, IL-2/15Rbeta expression was localized to neurons by high resolution in situ hybridization and evidence of IL-2 receptor protein expression was also detected by radioligand receptor binding using hippocampal homogenates. Comparison of undifferentiated and differentiated, immortalized H19-7 hippocampal neurons showed that IL-2/15Rbeta was constitutively expressed across disparate stages of hippocampal neuronal differentiation. These data indicate that IL-2/15Rbeta may serve to modulate neuronal processes in the hippocampus and associated limbic brain regions.

Functional dissection of the cytoplasmic subregions of the interleukin-5 receptor alpha chain in growth and immunoglobulin G1 switch recombination of B cells

The interleukin-5 receptor alpha chain (IL-5Ralpha) is known to regulate the development and function of B cells and eosinophils. Although the functions of IL-5Ralpha cytoplasmic domain subregions have been studied extensively using cultured cell lines, this approach has limitations when studying the functions of distinct primary B-cell subpopulations and their responsiveness to IL-5. In the present study, we generated mice on an IL-5Ralpha null background, each expressing a mutant form of an IL-5Ralpha transgene ligated to a mu enhancer and VH promoter, either lacking the cytoplasmic DC3 region or substituting two proline residues for alanine (ApvA) in the membrane-proximal ppvp motif of the cytoplasmic domain. The ppvp motif, which mediates activation of JAK2/STAT5 and Btk, also contributes to c-fos, c-jun and c-myc expression. IL-5Ralpha null mutant mice showed impaired B-1-cell development, reduced serum immunoglobulin G3 (IgG3) and IgM, no IL-5-induced enhancement of B-cell proliferation and IL-5-induced switch recombination from the mu gene to gamma1 gene; these were not recovered following the expression of the ApvA mutant. In contrast, absence of the DC3 region affected the IL-5-induced switch recombination from the mu to the gamma1 gene and B-1-cell development, while IL-5-induced proliferation and IgM production were at levels similar to those of B cells expressing wild-type IL-5Ralpha transgene. The results clearly indicated that the ppvp motif and the DC3 region of IL-5Ralpha played distinct roles in B-cell proliferation and differentiation. Thus, this present approach offers new insights into the functions of the cytoplasmic subregions of IL-5Ralpha, in particular its carboxy-terminal region.

Lymph draining from foot joints in rheumatoid arthritis provides insight into local cytokine and chemokine production and transport to lymph nodes

OBJECTIVE

Rheumatoid arthritis (RA) is characterized by inflammatory reactions in joints and adjacent tissues unaccompanied by clinically evident changes in lymphatics and lymph nodes draining the inflamed areas. The explanation for this phenomenon, which contrasts with infectious processes in joints and soft tissues that evoke major changes in the lymphatic system, is unclear. To determine which inflammatory factors produced in the joints of RA patients are transported in lymph to lymph nodes, we measured levels of immunoglobulins, cytokines, and chemokines in prenodal lymph from the foot joints of RA patients and quantified their rate of transport to regional lymph nodes.

METHODS

Lymph was collected from the cannulated lymphatics draining the foot joints, tendons, fascia, and skin of 20 RA patients. Lymph flow rate and concentrations of proteins and immunoglobulins were measured. Cytokine and chemokine levels were quantified by enzyme-linked immunosorbent assays. Results were compared with those obtained in 20 control subjects.

RESULTS

In the cannulated vessel, the mean +/- SEM lymph flow rate in RA patients was almost 2-fold that in control subjects (22.6 +/- 3.2 ml/24 hours versus 13.2 +/- 1.1 ml/24 hours; P < 0.01). Lymph concentrations of total protein, IgG, and IgM were 1.80 +/- 0.14 gm/dl, 384 +/- 45 mg/dl, and 32.0 +/- 1.5 mg/dl, respectively, in RA patients and 1.66 +/- 0.14 gm/dl, 238 +/- 32 mg/dl, and 15.0 +/- 1.3 mg/dl, respectively, in control subjects. The corresponding lymph:serum (L:S) ratios were 0.21 +/- 0.02, 0.22 +/- 0.02, and 0.15 +/- 0.02, respectively, in RA patients and 0.22 +/- 0.02, 0.19 +/- 0.02, and 0.11 +/- 0.02, respectively, in control subjects. The L:S ratios of <1 and the absence of significant differences between groups suggested a lack of local production of immunoglobulins. In RA patients, lymph concentrations (in pg/ml) were as follows: interleukin-1beta (IL-1beta) 14.8 +/- 3.9, IL-6 511 +/- 143, tumor necrosis factor alpha (TNFalpha) 9.9 +/- 1.1, IL-1 receptor antagonist (IL-1Ra) 4,274 +/- 737, IL-10 13.3 +/- 4.4, IL-8 846 +/- 174, IL-15 6.2 +/- 0.9, granulocyte-macrophage colony-stimulating factor (GM-CSF) 2.30 +/- 0.15, vascular endothelial growth factor (VEGF) 80.4 +/- 8.6, and macrophage inflammatory protein 1alpha (MIP-1alpha) 171 +/- 34. In control subjects, these values were as follows: IL-1beta 1.50 +/- 0.25, IL-6 79.0 +/- 14.6, TNFalpha 4.4 +/- 1.1, IL-1Ra 208 +/- 52, IL-10 0.0, IL-8 216 +/- 83, IL-15 5.00 +/- 0.45, GM-CSF 0.40 +/- 0.05, VEGF 42.0 +/- 2.4, and MIP-1alpha 3.4 +/- 1.7 (P < 0.05 versus RA patients for all except IL-15). The L:S ratio was >1 in all RA patient samples for IL-1beta, IL-6, IL-1Ra, IL-8, GM-CSF, IL-10, IL-15, TNFalpha, and MIP-1alpha, indicating local production of cytokines. Great variability in lymph cytokine concentrations, presumably reflecting differences in the intensity of local inflammation, was not reflected in serum cytokine concentrations. Intravenously infused methylprednisolone decreased lymph cytokine levels to normal within 12 hours. In contrast, their concentrations in serum showed little or no change.

CONCLUSION

High lymph concentrations of cyto kines and chemokines, exceeding those in serum, were found in RA patients. The L:S concentration ratios of > 1 indicate the local production of these cytokines and chemokines in the inflamed tissues. High flow rates of lymph containing high cytokine concentrations through the regional lymph nodes are likely to affect node lymphocytes and dendritic cells. Analysis of cytokines in lymph should provide insight into events in inflamed tissues in RA and in regional lymph nodes.