Signal transduction through IL-6 receptor: involvement of multiple protein kinases, stat factors, and a novel H7-sensitive pathway

Proteomic identification of the oncoprotein STAT3 as a target of a novel Skp1 inhibitor

The S phase kinase-associated protein 1 (Skp1), an adaptor protein of the Skp1-Cul1-F-box protein complex, binds the ubiquitin E3 ligase Skp2 and is critical to its biological functions. Targeting of Skp1 by a small compound 6-O-angeloylplenolin (6-OAP) results in dissociation and degradation of Skp2 and mitotic arrest of lung cancer cells. Here, by using a proteome microarray containing 16,368 proteins and a biotinylated 6-OAP, we identified 99 proteins that could bind 6-OAP, with Skp1 and STAT3 sitting at the central position of the 6-OAP interactome. 6-OAP formed hydrogen bonds with Ser611/Ser613/Arg609 at the SH2 domain of STAT3 and inhibited the constitutive and interleukin-6-induced phosphorylated STAT3 (pSTAT3), leading to inhibitory effects on lung cancer cells and suppression of Skp2 transcription. STAT3 was overexpressed in tumor samples compared to counterpart normal lung tissues and was inversely associated with prognosis of the patients. 6-OAP inhibited tumor growth in SCID mice intravenously injected with lung cancer cells, and downregulated both STAT3 and Skp2 in tumor samples. Given that 6-OAP is a Skp1 inhibitor, our data suggest that this compound may target Skp1 and STAT3 to suppress Skp2, augmenting its anti-lung cancer activity.

The rat acute-phase protein α2-macroglobulin plays a central role in amifostine-mediated radioprotection

Previously we reported that elevated circulating concentrations of the acute-phase (AP) protein α(2)-macroglobulin (α(2)M), either as typically occurring in pregnant female rats or after administration to male rats, provides radioprotection, displayed as 100% survival of experimental animals exposed to total-body irradiation with 6.7 Gy (LD(50/30)) x-rays, that is as effective as that afforded by the synthetic radioprotector amifostine. The finding that amifostine administration induces a 45-fold increase in α(2)M in the circulation led us to hypothesise that α(2)M assumes an essential role in both natural and amifostine-mediated radioprotection in the rat. In the present work we examined the activation of cytoprotective mechanisms in rat hepatocytes after the exogenous administration of α(2)M and amifostine. Our results showed that the IL6/JAK/STAT3 hepatoprotective signal pathway, described in a variety of liver-injury models, upregulated the α(2)M gene in amifostine-pretreated animals. In both α(2)M- and amifostine-pretreated rats we observed the activation of the Akt signalling pathways that mediate cellular survival. At the cellular level this was reflected as a significant reduction of irradiation-induced DNA damage that allowed for the rapid and complete restoration of liver mass and ultimately at the level of the whole organism the complete restoration of body weight. We conclude that the selective upregulation of α(2)M plays a central role in amifostine-provided radioprotection.

Current developments in salivary diagnostics

Salivary diagnostics is an emerging field that has progressed through several important developments in the past decade, including the publication of the human salivary proteome and the infusion of federal funds to integrate nanotechnologies and microfluidic engineering concepts into developing compact point-of-care devices for rapid analysis of this secretion. In this article, we discuss some of these developments and their relevance to the prognosis, diagnosis and management of periodontitis, as an oral target, and cardiovascular disease, as a systemic example for the potential of these biodiagnostics. Our findings suggest that several biomarkers are associated with distinct biological stages of these diseases and demonstrate promise as practical biomarkers in identifying and managing periodontal disease, and acute myocardial infarction. The majority of these studies have progressed through biomarker discovery, with the identified molecules requiring more robust clinical studies to enable substantive validation for disease diagnosis. It is predicted that with continued advances in this field the use of a combination of biomarkers in multiplex panels is likely to yield accurate screening tools for these diagnoses in the near future.

Pathological role of IL-6 in the experimental allergic bronchial asthma in mice

Although allergic asthma was described to be associated with the presence of mucosal T helper (Th)2 cells, it is not entirely clear which factors are responsible for priming of T cells to differentiate into Th2 effector cells in this disease. Interleukin (IL)-6 has been recognized as important because it is secreted by cells of the innate immunity and induces the expansion of the Th2 effector cells, which are major players of the adaptive immune responses. Additionally, IL-6 released by dendritic cells (DCs) inhibits the suppressive function of CD4+CD25+ T regulatory cells, thus inhibiting the peripheral tolerance. The signal transduction of IL-6 has recently taught us how this cytokine influences different aspects of the immune response, especially under pathological conditions. IL-6 can bind to the soluble IL-6R, increased after allergen challenge in asthmatic patients, and, through a mechanism called trans-signaling, induces proliferation of cells expressing the cognate receptor gp130. This mechanism appears to be used for proliferation by developed Th2 cells in the airways. In contrast, through the membrane-bound IL-6R, IL-6 controls CD4+CD25+ survival, as well as the initial stages of the Th2 cells development in the lung. These findings impact the establishment of new therapies for allergic diseases; indeed, blockade of the soluble IL-6R through the fusion protein gp130Fc reduces Th2 cells in the lung, and by blocking the membrane-bound IL-6R, anti-IL-6R antibody treatment induces the number of T-regulatory cells in the lung, thereby reducing the local number of CD4+ T-effector cells in experimental asthma.

Differential expression of liver interleukin-6 receptor-alpha in female versus male ethanol-consuming rats

BACKGROUND

It is well known that women are more susceptible to alcoholic liver disease (ALD) than men, and inflammation is thought to play a major role in alcohol-induced liver injury. Increased circulating levels of the proinflammatory cytokine interleukin (IL)-6 are a marker for serious ALD in humans. However, IL-6 also has protective effects, such as induction of liver regeneration and inhibition of hepatocyte apoptosis. Although the roles of IL-6 in ALD have begun to be established, little is known about the expression of its receptor (IL-6Ralpha) during chronic alcohol administration.

METHODS

Male and female rats were intragastrically fed ethanol or control isocaloric liquid diet for 2 and 4 weeks. Liver samples were collected, and gene expression was assessed by reverse transcription-polymerase chain reaction and Western blot.

RESULTS

Herein, we show clear gender differences in alcohol-induced liver IL-6Ralpha expression. Analysis of rat liver samples showed that ethanol consumption significantly increased IL-6Ralpha messenger RNA and protein expression in females as compared with similarly treated males after 2 and 4 weeks. Increased STAT3 phosphorylation in the livers of ethanol-consuming females also indicated greater IL-6Ralpha activation in these animals. Conversely, ethanol-consuming males displayed increased IkappaB messenger RNA and protein expression, which may inhibit IL-6R expression, compared with females.

CONCLUSIONS

Given the association of inflammation with ethanol-induced liver damage, these data may offer insight into a possible mechanism by which females develop more severe ALD than males.

The two faces of IL-6 on Th1/Th2 differentiation

Interleukin (IL)-6 is a cytokine produced by several cell types including antigen presenting cells (APC) such as macrophages, dendritic cells, and B cells. IL-6 is involved in the acute phase response, B cell maturation, and macrophage differentiation. Here, we discuss a novel function of IL-6: the control of T helper (Th) 1/Th2 differentiation. IL-6 promotes Th2 differentiation and simultaneously inhibits Th1 polarization through two independent molecular mechanisms. IL-6 activates transcription mediated by nuclear factor of activated T cells (NFAT) leading to production of IL-4 by nai;ve CD4(+) T cells and their differentiation into effector Th2 cells. While the induction of Th2 differentiation by IL-6 is dependent upon endogenous IL-4, inhibition of Th1 differentiation by IL-6 is IL-4- and NFAT-independent. IL-6 inhibits Th1 differentiation by upregulating supressor of cytokine signaling (SOCS)-1 expression to interfere with IFNgamma signaling and the development of Th1 cells. Since IL-6 is abundantly produced by APC, it is a likely source of early Th1/Th2 control during CD4(+) T cell activation. Thus, by using two independent molecular mechanisms, IL-6 plays a dual role in Th1/Th2 differentiation.

Induction of NFATc2 expression by interleukin 6 promotes T helper type 2 differentiation

Interleukin (IL)-6 is produced by professional antigen-presenting cells (APCs) such as B cells, macrophages, and dendritic cells. It has been previously shown that APC-derived IL-6 promotes the differentiation of naive CD4+ T cells into effector T helper type 2 (Th2) cells. Here, we have studied the molecular mechanism for IL-6-mediated Th2 differentiation. During the activation of CD4+ T cells, IL-6 induces the production of IL-4, which promotes the differentiation of these cells into effector Th2 cells. Regulation of IL-4 gene expression by IL-6 is mediated by nuclear factor of activated T cells (NFAT), as inhibition of NFAT prevents IL-6-driven IL-4 production and Th2 differentiation. IL-6 upregulates NFAT transcriptional activity by increasing the levels of NFATc2. The ability of IL-6 to promote Th2 differentiation is impaired in CD4+ T cells that lack NFATc2, demonstrating that NFATc2 is required for regulation of IL-4 gene expression by IL-6. Regulation of NFATc2 expression and NFAT transcriptional activity represents a novel pathway by which IL-6 can modulate gene expression.

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.

STAT-signalling through the cytoplasmic compartment: consideration of a new paradigm

The binding of a large number of cytokines and growth factors to their cognate receptors on the surface of mammalian-cell plasma membrane activates a signalling cascade involving the cytoplasmic STAT-family proteins, which is characterized by the nuclear translocation of a cytokine- or growth factor-specific subset of the cytoplasmic pool of the respective tyrosine- and serine-phosphorylated STAT proteins and the consequent transcriptional activation of specific target genes. In the standard model of cytokine-induced STAT signalling such as that elicited by various interferons and interleukins, it is thought that STAT proteins are recruited to the cytoplasmic side of the cell-surface receptor complex from within a monomeric cytosolic pool, and upon tyrosine-phosphorylation by respective Janus kinase family members, dimerize and translocate to the nucleus. The mechanisms which determine and regulate the recruitment of cytosolic STAT proteins to the plasma membrane-receptor complex, the transit of "activated" STATs through the expanse of the cytoplasmic compartment from the plasma membrane to the nuclear pore region, and the transit of STATs through the nuclear pore complex into the nuclear compartment, remain largely unknown. New data from different laboratories suggests consideration of a model for STAT signalling in which STAT proteins function in the cytoplasm not only as free monomers and dimers but as part of heteromeric complexes ("statosomes"), with accessory proteins which may serve to present specific STATs to the plasma membrane-receptor complex, and to chaperone "activated" STATs through the cytoplasmic compartment toward the nucleus and then into the nuclear compartment.

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.

Both Stat3-Activation and Stat3-Independent BCL2 Downregulation Are Important for Interleukin-6–Induced Apoptosis of 1A9-M Cells

A unique subclone of a bone marrow-derived stromal cell line, BMS2.4, produces soluble factors that inhibit proliferation of several types of hematopoietic cell lines. An understanding of these molecules may be informative about negative regulatory circuits that can potentially limit blood cell formation. We used expression cloning to identify interleukin-6 (IL-6) as one factor that suppressed growth of a pre-B–cell variant line, 1A9-M. Moreover, IL-6 induced macrophage-differentiation and apoptosis of 1A9-M cells. During this process, IL-6 downregulated expression of BCL2 in 1A9-M cells and stimulated BCL-XL expression, but had no effect on p53, Bax, or Bak gene expression. Mechanisms for transduction of IL-6–induced signals were then evaluated in IL-6–stimulated 1A9-M cells. Whereas the signal transducer and activator of transcription 3 (Stat3) was phosphorylated and activated, there was no effect on either Stat1 or Stat5. The importance of BCL2 and Stat3 on IL-6–induced macrophage-differentiation and apoptosis was studied with 1A9-M cells expressing human BCL2 or a dominant-negative form of Stat3, respectively. IL-6–induced apoptosis, but not macrophage-differentiation, was blocked by continuously expressed BCL2. A dominant-negative form of Stat3 inhibited both macrophage-differentiation and apoptosis induced by IL-6. However, diminished Stat3 activity did not prevent IL-6–induced downregulation of the BCL2 gene. Therefore, activation of Stat3 is essential for IL-6–induced macrophage-differentiation and programmed cell death in this model. Whereas overexpression of BCL2 abrogates the apoptotic response, Stat3-independent signals appear to downregulate expression of the BCL2 gene.

Both Stat3-Activation and Stat3-Independent BCL2 Downregulation Are Important for Interleukin-6–Induced Apoptosis of 1A9-M Cells

A unique subclone of a bone marrow-derived stromal cell line, BMS2.4, produces soluble factors that inhibit proliferation of several types of hematopoietic cell lines. An understanding of these molecules may be informative about negative regulatory circuits that can potentially limit blood cell formation. We used expression cloning to identify interleukin-6 (IL-6) as one factor that suppressed growth of a pre-B–cell variant line, 1A9-M. Moreover, IL-6 induced macrophage-differentiation and apoptosis of 1A9-M cells. During this process, IL-6 downregulated expression of BCL2 in 1A9-M cells and stimulated BCL-XL expression, but had no effect on p53, Bax, or Bak gene expression. Mechanisms for transduction of IL-6–induced signals were then evaluated in IL-6–stimulated 1A9-M cells. Whereas the signal transducer and activator of transcription 3 (Stat3) was phosphorylated and activated, there was no effect on either Stat1 or Stat5. The importance of BCL2 and Stat3 on IL-6–induced macrophage-differentiation and apoptosis was studied with 1A9-M cells expressing human BCL2 or a dominant-negative form of Stat3, respectively. IL-6–induced apoptosis, but not macrophage-differentiation, was blocked by continuously expressed BCL2. A dominant-negative form of Stat3 inhibited both macrophage-differentiation and apoptosis induced by IL-6. However, diminished Stat3 activity did not prevent IL-6–induced downregulation of the BCL2 gene. Therefore, activation of Stat3 is essential for IL-6–induced macrophage-differentiation and programmed cell death in this model. Whereas overexpression of BCL2 abrogates the apoptotic response, Stat3-independent signals appear to downregulate expression of the BCL2 gene.

Signal transduction through cytokine receptors

Receptors for interleukins, colony stimulating factors, and hormones have a homology in their extracellular regions, characterized by the conserved cysteine residues and the tryptophan-serine-x-tryptophan-serine motif, thus, they are classified to the type 1 cytokine receptor superfamily. Janus tyrosine kinase (JAKs) have been found to be involved in the signal transduction through type I cytokine receptors. JAKs associate with the membrane proximal region in the cytoplasmic domain having box1 and box2, which are conserved among the family, and upon the stimulation JAKs can be aggregated following the receptor dimerization and activated probably by transphosphorylation. JAKs then phosphorylate the receptor and various signal transducing molecules, including STATs (signal transducer and activator of transcriptions) and other SH2-containing adapter molecules. STATs were initially identified as transcription factors containing a SH2 domain and regulating interferons-inducible genes. STATs can be tyrosine phosphorylated by JAKs and form dimer (either hetero- or homo-dimers) to enter the nucleus, resulting in the expression of a set of genes. On the other hand, adapter molecules such as Shc, GRB2, and SHP-2 have been shown to link the cytokine receptors to Ras, followed by the activation of the Raf-MEK-MAP kinase pathway, leading to the activation of various transcription factors in the nucleus. These two signals are generated by different ways upon the stimulation of the receptors and they elicit a variety of biological functions in various cell types. In this review, we will discuss the mechanism by which cytokines activate JAKs, STATs, and a variety of adapter molecules. We further discuss the roles of each signal transduction pathways in the expression of biological activities of cytokines.

Signaling through Gp130: toward a general scenario of cytokine action

Cytokines play roles in a wide range of responses such as immune response, hematopoiesis and inflammation. A large volume of studies revealed that cytokines show functional pleiotropy and redundancy. Gp130 is a receptor subunit shared by the interleukin-6 family of cytokines. We describe and discuss signaling through gp130 in relation to a general scenario for cytokine signaling regulating cell growth, differentiation and survival.

H-7-induced apoptosis in the cells of a Drosophila neuronal cell line through affecting unidentified H-7-sensitive substance(s)

The present study was undertaken to reveal underlying mechanisms of apoptosis in neurons using clonal neuronal cells, ML-DmBG2-c2, derived from Drosophila larval central nervous system 1-(5-Isoquinolinesulfonyl)-2-methylpiperazine (H-7), a protein kinase inhibitor, induced cell death with typical features of apoptosis such as internucleosomal DNA fragmentation, nuclear condensation and apoptotic bodies in the cells. Though H-7 is known to inhibit cAMP-dependent protein kinase (PKA), protein kinase C (PKC), cGMP-dependent protein kinase (PKG), myosin light chain kinase (MLCK), and casein kinase I (CKI), specific inhibitors for these kinases such as H-89, calphostin C, ML-9, or CKI-7 did not induce apoptosis in the cells. Other kinases such as tyrosine kinase. PI3-kinase and Ca2+/CaM kinase II so far examined in the present study were interpreted not to be involved in the apoptotic cascade. Therefore, it is concluded that an H-7-sensitive substance(s) other than these kinases is responsible for the apoptosis in the neuronal cells. Caspase inhibitors prevented apoptosis in the cells treated with H-7. These results suggest that caspase(s) is involved downstream of the H-7-sensitive point in the cascade of the apoptosis.

Interleukin 6 and its receptor: ten years later

Ten years have passed since the molecular cloning of interleukin 6 (IL-6) in 1986. IL-6 is a typical cytokine, exhibiting functional pleiotropy and redundancy. IL-6 is involved in the immune response, inflammation, and hematopoiesis. The IL-6 receptor consists of an IL-6 binding alpha chain and a signal transducer, gp130, which is shared among the receptors for the IL-6 related cytokine subfamily. The sharing of a receptor subunit is a general feature of cytokine receptors and provides the molecular basis for the functional redundancy of cytokines. JAK tyrosine kinase is a key molecule that can initiate multiple signal-transduction pathways by inducing the tyrosine-phosphorylation of the cytokine receptor, gp130 in the case of IL-6, on which several signaling molecules are recruited, including STAT, a signal transducer and activator of transcription, and SHP-2, which links to the Ras-MAP kinase pathway. JAK can also directly activate signaling molecules such as STAT and Tec. These multiple signal-transduction pathways intimately regulate the expression of several genes including c-myc, c-myb, junB, IRF1, egr-1, and bcl-2, leading to the induction of cell growth, differentiation, and survival. The deregulated expression of IL-6 and its receptor is involved in a variety of diseases.

Extracellular signal-dependent nuclear import of Stat1 is mediated by nuclear pore-targeting complex formation with NPI-1, but not Rch1

In response to interferon-gamma (IFN-gamma), Stat1 is tyrosine phosphorylated and translocates to the nucleus where it activates transcription. In this study, we identified factors which mediate the nuclear import of Stat1. Tyrosine-phosphorylated Stat1 associated with the beta subunit (a 97 kDa component) of the nuclear pore-targeting complex via the NPI-1 family, but not the Rch1 family, of alpha subunit (a 58 kDa component) as a result of IFN-gamma stimulation. Antibodies against NPI-1 or beta subunit consistently inhibited the IFN-gamma-dependent nuclear import of Stat1 in living cells, although antibodies reactive to Rch1 had no effect. Solution binding assays with deletion mutants of NPI-1 showed that the Stat1-binding domain of NPI-1 was located in the carboxy-terminal region, which is clearly distinct from the SV40 large T antigen nuclear localization signal (NLS)-binding region. These results indicate that the extracellular signal-dependent nuclear transport of Stat1 is mediated by NPI-1, but not Rch1, in conjunction with beta subunit, and that these factors participate in, not only constitutive, but also the conditional nuclear import of proteins.

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.

Dual control of neurite outgrowth by STAT3 and MAP kinase in PC12 cells stimulated with interleukin-6

IL-6 induces differentiation of PC12 cells pretreated with nerve growth factor (NGF). We explored the signals required for neurite outgrowth of PC12 cells by using a series of mutants of a chimeric receptor consisting of the extracellular domain of the granulocyte-colony stimulating factor (G-CSF) receptor and the cytoplasmic domain of gp130, a signal-transducing subunit of the IL-6 receptor. The mutants incapable of activating the MAP kinase cascade failed to induce neurite outgrowth. Consistently, a MEK inhibitor, PD98059, inhibited neurite outgrowth, showing that activation of the MAP kinase cascade is essential for the differentiation of PC12 cells. In contrast, a mutation that abolished the ability to activate STAT3 did not inhibit, but rather stimulated neurite outgrowth. This mutant did not require NGF pretreatment for neurite outgrowth. Dominant-negative STAT3s mimicked NGF pretreatment, and NGF suppressed the IL-6-induced activation of STAT3, supporting the idea that STAT3 might regulate the differentiation of PC12 cells negatively. These results suggest that neurite outgrowth of PC12 cells is regulated by the balance of MAP kinase and STAT3 signal transduction pathways, and that STAT3 activity can be regulated negatively by NGF.

Soluble IL-6R in plasma cell dyscrasias

The understanding of the biology of multiple myeloma has advanced significantly in the past few years. The identification of the pivotal role of Interleukin-6 (IL-6), the soluble IL-6 receptor (sIL-6R), and how the ligand receptor complex interacts with the signal transducer gp130 has provided new biological insights into plasma cell disorders. Some studies have suggested that sIL-6R levels may have prognostic significance in MM, however this is not a consistent finding. Here the biology and function of IL-6 and sIL-6R are reviewed and the clinical significance of sIL-6R discussed.

Alternative signaling mechanism of leukemia inhibitory factor responsiveness in a differentiating embryonal carcinoma cell

Leukemia inhibitory factor (LIF) is a cytokine that plays an important role during mouse embryogenesis. We showed that adenovirus E1A represses the interleukin-6 signal transduction pathway that uses the same JAK tyrosine kinase and STAT (signal transducer and activator of transcription) transcription factor as LIF. Here, we report that the LIF-JAK-STAT signal transduction pathway is blocked in cellular E1A-expressing undifferentiated F9 cells, and that the block is overcome by retinoic acid-induced differentiation. LIF failed to stimulate the expression of the acute phase response element (APRE)-driven luciferase gene in undifferentiated F9 cells, whereas the luciferase activity was remarkably increased by LIF treatment in differentiated F9 (dF9) cells. We analyzed the mechanism of the APRE regulation and found that the LIF-induced APRE-binding activity was regulated in a differentiation-dependent manner. The protein levels and the tyrosine phosphorylation of JAK1, JAK2, and STAT3 in F9 cells were not different from those in dF9 cells. The exogenous expression of activated c-Ha-ras partially recovered the LIF responsiveness of the APRE-luciferase gene in F9 cells, but the dominant negative ras N-17 did not repress the LIF-induced activation of APRE-luciferase in dF9 cells. These results suggested that an unknown coactivation process that is partially compensated by Ras is required for STAT3-APRE binding in F9 cells.

Interferon-gamma-dependent nuclear import of Stat1 is mediated by the GTPase activity of Ran/TC4

In response to interferon-gamma (IFN-gamma), Stat1 enters the nucleus, where it activates transcription. In order to better understand the mechanism of the extracellular signal-induced protein import into the nucleus, we have established an in vivo assay system that uses recombinant Stat1 protein as a model transport substrate. Using this system, we found that Stat1 is actively transported through the nuclear pores in an IFN-gamma-dependent manner and tyrosine (Tyr701) phosphorylation of Stat1 is actually required for its nuclear import. When the antibody against Ran, which was identified as an essential factor for active nuclear protein transport, was injected, the IFN-gamma-dependent nuclear transport of Stat1 was completely inhibited. Furthermore, nuclear import of Stat1 was suppressed by microinjection of two mutant Ran proteins, one defective in GTP hydrolysis (G19V) and the other with little or no binding to GTP (T24N), both of which are known to act as dominant negative inhibitors of nuclear import. These results indicate that the conditional nuclear import of Stat1 requires GTP hydrolysis by Ran.

Two signals are necessary for cell proliferation induced by a cytokine receptor gp130: involvement of STAT3 in anti-apoptosis

gp130 is a common signal transducer for the interleukin-6-related cytokines. To delineate the gp130-mediated growth signal, we established a series of pro-B cell lines expressing chimeric receptors composed of the extracellular domain of the granulocyte colony-stimulating factor receptor and the transmembrane and cytoplasmic domains of gp130. The second tyrosine (from the membrane) of gp130, which was required for the tyrosine phosphorylation of SHP-2, its association with GRB2, and activation of a MAP kinase, was essential for mitogenesis, but not for anti-apoptosis. On the other hand, the tyrosine in the YXXQ motifs essential for STAT3 activation was required for bcl-2 induction and anti-apoptosis. Furthermore, dominant-negative STAT3 inhibited anti-apoptosis. These data demonstrate that two distinct signals, mitogenesis and anti-apoptosis, are required for gp130-induced cell growth and that STAT3 is involved in anti-apoptosis.

Distinct tumorigenic potential of abl and raf in B cell neoplasia: abl activates the IL-6 signaling pathway

The development of murine plasma cell tumors induced by raf/myc containing retroviruses is facilitated by T cells and completely dependent on IL-6. To determine whether kinases with differing specificities reflect alternative biochemical pathways in B cell tumorigenesis, we have employed an abl/myc containing retrovirus to assess neoplastic development. In contrast with raf/myc, abl/myc disease is T cell and IL-6 independent. An examination of the IL-6 signal transduction pathway reveals that this pathway, as defined by activation of Stat3, is inducible by IL-6 in raf/myc tumors but constitutively activated in abl/myc tumors. These findings provide a mechanism for the derivation of cytokine-independent plasma cell tumors and suggest that both IL-6-dependent and independent tumors may arise in vivo depending on the particular mutational events incurred during tumorigenesis.