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Recombinant thrombopoietin induces rapid protein tyrosine phosphorylation of Janus kinase 2 and Shc in human blood platelets.

A cDNA for the thrombopoietin has been cloned by several groups. The recombinant thrombopoietin has been reported to stimulate the megakaryocytopoiesis and thrombopoiesis. Little is known regarding the molecular basis of its effects. To elucidate the molecular mechanism involved in signal transduction, we have investigated the effects of thrombopoietin on platelet tyrosine phosphorylation. We report here that thrombopoietin induced time- and dose-dependent tyrosine phosphorylation of several proteins including Janus kinase 2 (Jak2) and a 52-kD protein, Shc, in human blood platelets. Both Jak2 and Shc were tyrosine phosphorylated within 15 seconds after stimulation. The tyrosine phosphorylation of Jak2 was accompanied by increased kinase activity, whereas Shc tyrosine phosphorylation induced its association with a 25-kD protein, Grb2. Thus, our data suggest that Jak2, Shc, and Grb2 may be involved in signal transduction after ligand binding to c-mpl in human platelets.

Adaptor Proteins, Signal Transducing↗

Differential expression of Janus kinase 3 (JAK3), matrix metalloproteinase 13 (MMP13), heat shock protein 60 (HSP60), and mouse double minute 2 (MDM2) in human colorectal cancer progression using human cancer cDNA microarrays.

In this study, we applied commercially available cDNA microarray systems (1068 genes) to investigate the genetic changes in six colorectal cancers (CRC). Thirty-two genes fell into the group of commonly upregulated genes. In addition, we immunohistochemically investigated the expression of the four top ranked upregulated genes, Janus kinase 3 (JAK3), matrix metalloproteinase 13 (MMP13), heat shock protein 60 (HSP60), and mouse double minute 2 (MDM2), in 44 CRC. JAK3 staining was located in the cancer cells. A comparison of JAK3 immunostaining and clinicopathological parameters showed a significant association of tumor differentiation, pT, and TMN stage. Staining of MMP13 and HSP60 was noted mainly in the cytoplasm of cancer cells. A significant association of these expressions was observed with tumor differentiation and pT. MDM2 staining was noted in the nucleus of cancer and non-cancer cells. No significant association of clinicopathological parameters with MDM2 expression was observed. In multivariate analysis, JAK3 immunoreactivity showed independent prognostically unfavorable predictors. These data suggest that JAK3, in particular, is a highly significant, prognostic immunohistochemical marker in CRC. This study proves that cDNA microarrays, plotted by a small number of genes from a few samples, are both practical and useful.

Adenoma↗

Ras and signal transducer and activator of transcription (STAT) are essential and sufficient downstream components of Janus kinases in cell proliferation.

Cytokines exert their activities in cell growth and differentiation by binding specific cell membrane receptors. Janus kinases (JAKs) are cytoplasmic protein tyrosine kinases that physically interact with intracellular domains of the cytokine receptors and they play crucial roles in transducing signals triggered by the cytokine-receptor interaction. We have previously shown that conditional activation of JAK through membrane-proximal dimerization confers cytokine-independence on interleukin-3 (IL-3)-dependent Ba / F3 lymphoid cells and that the cytokine-independent proliferation is completely inhibited by dominant negative Ras. In this work, we demonstrate that ectopic expression of a dominant negative form of Stat5, a major signal transducer and activator of transcription (STAT) expressed in Ba / F3 cells, also inhibits JAK-triggered mitogenesis. In contrast, overexpression of constitutively active Ras or conditional activation of Stat5 by chemical dimerization fails to confer cytokine-independence. However, concomitant activation of ectopic Ras and Stat5 molecules in Ba / F3 cells suffices for cell proliferation in the absence of IL-3. Our results indicate that Ras and STAT are essential and sufficient components of JAK-triggered mitogenesis. Our findings further indicate that the cytokine signal bifurcates into Ras and STAT pathways following JAK activation.

Animals↗

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.

Animals↗

Targeting Janus kinase 3 in the treatment of leukemia and inflammatory diseases.

Janus tyrosine kinases (JAKs) are cytoplasmic protein tyrosine kinases that play a crucial role in the initial steps of cytokine signaling. JAK3, a member of JAK kinase family of four (JAK1, JAK2, JAK3 and TYK2), is abundantly expressed in lymphoid cells. JAK3 has been found to initiate signaling of interleukin (IL)-2, IL-4, IL-7, IL-9, IL-13 and IL-15. Indispensable role of JAK3 in lymphocyte development and function has been revealed recently. Because of the involvement of JAK3 in T cell activation and proliferation, and the documented genetic evidence for the role of JAK3 in autoimmune or transplant -induced inflammatory disorders, the selective targeting of JAK3 in T cells may potentially be clinically beneficial in T cell-derived pathologic disorders. In this review we discuss inhibitors of JAK3 as a new class of immunomodulatory agents with immunosuppressive, anti-inflammatory, anti-allergic, and anti-leukemic properties. Preclinical data from multiple experimental model systems of autoimmune diabetes, allergy, solid organ transplantation, pancreatic islet transplantation and bone marrow transplantation are discussed in the context of the clinical need for new immunomodulatory agents with such properties.

Animals↗

A specific inhibitor of janus kinase-3 increases survival in a transgenic mouse model of amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a progressive, fatal neurodegenerative disorder involving the motor neurons of cortex, brain stem, and spinal cord. About 10% of all ALS patients are familial cases (FALS), of which 20% have mutations in the Cu, Zn-superoxide dismutase (SOD1) gene. The murine model for FALS, which overexpresses a FALS variant of the SOD1 gene, exhibits progressive limbic paralysis followed by death. Treatment of FALS mice with WHI-P131, a specific inhibitor of Janus kinase 3 (JAK3), increased survival by more than two months, suggesting that specific inhibitors of JAK3 may be useful in the treatment of human ALS. These results uniquely establish JAK3 as a novel molecular target for the treatment of FALS.

Animals↗

Leptin inhibits apoptosis in thymus through a janus kinase-2-independent, insulin receptor substrate-1/phosphatidylinositol-3 kinase-dependent pathway.

The cytokine-like hormone leptin is known to exert important functions on the modulation of immune responses. Some of these effects are dependent on the property of leptin to modulate the apoptosis of thymic cells. In the present study, we used Wistar rats to investigate the molecular mechanisms involved in leptin-dependent control of apoptosis in thymus. Apoptosis was evaluated by flow cytometry and ELISA for nucleosome determination, whereas signal transduction was evaluated by immunoprecipitation, immunoblot, and confocal microscopy. The Ob receptor (ObR) was expressed in most thymic cells and its relative amount reduced progressively during thymocyte maturation. ObR expression was colocalized with Janus kinase (JAK)-2 and signal transducer and activator of transcription-3, and an acute, in vivo, injection of leptin promoted the tyrosine phosphorylation of JAK-2 and the engagement of signal transducer and activator of transcription-3. The treatment with leptin also led to the tyrosine phosphorylation of insulin receptor substrate (IRS)-1 and serine phosphorylation of Akt. Chronic treatment with leptin reduced thymic apoptosis, an effect that was not inhibited by the JAK inhibitor AG(490) but was significantly inhibited by the phosphatidylinositol 3-kinase inhibitor LY(294002) and an antisense oligonucleotide to IRS-1. Thus, leptin inhibits the apoptosis of thymic cells through a mechanism that is independent of the activation of JAK-2 but depends on the engagement of the IRS-1/phosphatidylinositol 3-kinase pathway.

Animals↗

Ca2+-calmodulin and janus kinase 2 are required for activation of sodium-proton exchange by the Gi-coupled 5-hydroxytryptamine 1a receptor.

The type 1 sodium-proton exchanger (NHE-1) is expressed ubiquitously and regulates key cellular functions, including mitogenesis, cell volume, and intracellular pH. Despite its importance, the signaling pathways that regulate NHE-1 remain incompletely defined. In this work, we present evidence that stimulation of the 5-hydroxytryptamine 1A (5-HT1A) receptor results in the formation of a signaling complex that includes activated Janus kinase 2 (Jak2), Ca2+/calmodulin (CaM), and NHE-1, and which involves tyrosine phosphorylation of CaM. The signaling pathway also involves rapid agonist-induced association of CaM and NHE-1 as assessed by coimmunoprecipitation studies and by bioluminescence resonance energy transfer studies in living cells. We propose that NHE-1 is activated through this pathway: 5-HT1A receptor --> G(i2)alpha and/or G(i3)alpha --> Jak2 activation --> tyrosine phosphorylation of CaM --> increased binding of CaM to NHE-1 --> induction of a conformational change in NHE-1 that unmasks an obscured proton-sensing and/or proton-transporting region of NHE-1 --> activation of NHE-1. The G(i/o)-coupled 5-HT1A receptor now joins a handful of Gq-coupled receptors and hypertonic shock as upstream activators of this emerging pathway. In the course of this work, we have presented clear evidence that CaM can be activated through tyrosine phosphorylation in the absence of a significant role for elevated intracellular Ca2+. We have also shown for the first time that the association of CaM with NHE-1 in living cells is a dynamic process.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

Human malignant mesothelioma cell growth: activation of janus kinase 2 and signal transducer and activator of transcription 1alpha for inhibition by interferon-gamma.

Intrapleural injections of recombinant human IFN-gamma have shown some efficacy in reducing tumor growth in early stages of diffuse malignant mesothelioma (DMM). Here, we have addressed the potential therapeutic effect of IFN-gamma in DMM by investigating the activation of the JAK/STAT signaling pathway in seven human mesothelioma cell lines (HMCLs) that were differentially responsive to the antiproliferative activity of IFN-gamma. We showed that janus kinase 2 (JAK2) and signal transducer and activator of transcription 1 (STAT1) were phosphorylated on tyrosine residues within 15 min in all the HMCLs in which IFN-gamma (500 units/ml) inhibited proliferation. In addition, STAT1 binding activity to the gamma-activated sites DNA sequence was detected within 15 min in electrophoretic mobility-shift assay analysis, and IFN regulatory factor-1 RNA expression was observed within 6 h in the more responsive cells (72.7-95.2% inhibition of DNA synthesis after 72 h of treatment). Conversely, in several HMCLs, absent or limited growth suppressive effect (less than 22% inhibition of DNA synthesis) was associated with alterations in expression or activation of JAK2 or STAT1 or, downstream, with low induction of IFN regulatory factor-1 RNA expression and/or STAT1 protein expression following IFN-gamma treatment. These data suggest that at least part of the IFN-gamma effect on proliferation of HMCLs is mediated directly through activation of the JAK/STAT1 signaling pathway, and it could account for the antitumoral activity reported in DMM patients treated with IFN-gamma.

Cell Division↗

Janus kinase-3 (JAK3) inhibition: a novel immunosuppressive option for allogeneic transplantation.

Current immunosuppressive therapy in clinical organ transplantation is based on drugs that suppress various functions of immunocompetent cells but still affect cells and organ compartments other than the immune system. Hence, these drugs have considerable side effects which lead to increased morbidity and reduced life-quality of transplant recipients. A major step forward in the rationale design of clinical immunosuppression resides in the elucidation of molecular targets that play a critical role specifically within the immune system. Recently, Janus kinase 3 (JAK3) has been identified as such a molecule. Genetic absence or ablation of this tyrosine kinase is associated with defective T-cell immunity that results in severe combined immunodeficiency (SCID) without apparent changes in other organ systems. Furthermore, pharmacological inhibition has significantly prolonged allograft survival in several experimental models of organ transplantation. The present review provides an overview of the emerging role of JAK3 in the immune system and the development of JAK3-inhibiting drugs. The potential clinical application of JAK3 inhibitors in organ transplantations is discussed in the light of a recent series of successful kidney transplantations in non-human primates immunosuppressed solely with a novel JAK3 inhibitor.

Animals↗

Leptin interferes with adrenocorticotropin/3',5'-cyclic adenosine monophosphate (cAMP) signaling, possibly through a Janus kinase 2-phosphatidylinositol 3-kinase/Akt-phosphodiesterase 3-cAMP pathway, to down-regulate cholesterol side-chain cleavage cytochrome P450 enzyme in human adrenocortical NCI-H295 cell line.

CONTEXT: Obesity has adverse effects on adrenocortical functions. Adipocyte-derived leptin, a biomarker molecule of obesity, may directly control adrenal steroidogenesis via an unclear mechanism. OBJECTIVE: We studied the mechanism underlying leptin action on adrenal steroidogenesis in human adrenocortical NCI-H295 tumor cell line. METHODS: Levels of progesterone, cortisol, and cAMP were determined by ELISA. Western blotting was used to detect protein amounts of P450 side-chain cleavage (P450scc), Janus kinase 2 (JAK2), Akt, and their phosphorylated forms. The mRNA expressions of P450scc and leptin receptors were measured by RT-PCR and real-time PCR. P450scc promoter activity was analyzed with a luciferase reporter system. RESULTS: Cholera toxin mimicked ACTH action by increasing adrenal cAMP levels and steroid secretion. Leptin did not affect basal release but significantly inhibited ACTH/cholera toxin-induced steroid secretion. The concomitant inhibitions by leptin on cholera toxin-induced protein and ACTH/cholera toxin-induced mRNA expression of P450scc were confirmed. Leptin inhibited ACTH/cholera toxin-induced CYP11A1 promoter activity via a known cAMP-responsive region located between -1.7 and -1.5 kb. Leptin activated phosphorylations of JAK2 and Akt. Inhibitory effects of leptin on ACTH/cholera toxin-induced cAMP levels, CYP11A1 promoter activity, and steroid secretion were blunted by either inhibitor of JAK2 (AG490) or phosphatidylinositol 3-kinase/Akt (wortmannin) as well as inhibitors of cAMP-degrading phosphodiesterases (PDEs), including nonspecific 3-isobutyl-1-methylxanthine and PDE3-specific SKF94836. Leptin failed to affect the inductions of CYP11A1 promoter activity and steroid secretion by PDE-nonhydrolyzable N(6)-monobutyryl-cAMP. CONCLUSIONS: Leptin interferes with ACTH/cAMP signaling, possibly through a cAMP-degrading mechanism involving activation of JAK2, phosphatidylinositol 3-kinase, and PDE3, to down-regulate P450scc expression and consequent adrenal steroidogenesis.

Adrenal Cortex↗

Interplay between epidermal growth factor receptor and Janus kinase 3 regulates polychlorinated biphenyl-induced matrix metalloproteinase-3 expression and transendothelial migration of tumor cells.

We hypothesize that environmental toxicants, such as polychlorinated biphenyl congeners, can activate vascular endothelial cells and thus increase formation of blood-borne metastases. This study indicates that exposure of human microvascular endothelial cells to 2,2',4,6,6'-pentachlorobiphenyl can stimulate transendothelial migration of tumor cells through up-regulation of matrix metalloproteinase (MMP)-3. In a series of experiments with specific small interfering RNA and pharmacologic inhibitors, we provide evidence that 2,2',4,6,6'-pentachlorobiphenyl can activate epidermal growth factor receptor (EGFR) and Janus kinase 3 (JAK3) in a closely coordinated and cross-dependent fashion. Activated EGFR and JAK3 stimulate in concert c-Jun NH(2)-terminal kinase and extracellular signal-regulated kinase 1/2 as well as increase DNA-binding activity of transcription factors activator protein-1 and polyomavirus enhancer activator protein 3, leading to transcriptional up-regulation of MMP-3 expression. These results indicate that the interplay among EGFR, JAK3, and mitogen-activated protein kinases, such as c-Jun NH(2)-terminal kinase and extracellular signal-regulated kinase 1/2, is critical for polychlorinated biphenyl-induced MMP-3 expression and accelerated transendothelial migration of tumor cells.

Breast Neoplasms↗

Production of growth related oncogene protein-alpha in human umbilical vein endothelial cells stimulated with soluble interleukin-6 receptor-alpha: role of signal transducers, janus kinase 2 and mitogen-activated kinase kinase.

Growth-related oncogene protein-alpha (GRO-alpha) is a member of the C-X-C chemokine family with a wide variety of biological activities. We studied the production of GRO-alpha by human umbilical vein endothelial cells (HUVEC) in response to the stimulation with soluble form of interleukin-6 receptor alpha (sIL-6R). sIL-6R stimulated HUVEC to express GRO-alpha mRNA and secrete GRO-alpha protein in concentration-and time-dependent manners. The sIL-6R-induced GRO-alpha expression was inhibited by the pretreatment of the cells with AG490, a janus kinase 2 (JAK2) inhibitor, or with U0126, a MAP kinase-ERK kinase (MEK) inhibitor. sIL-6R also induced the phosphorylation of both Src homology 2-protein tyrosine phosphatase-2 (SHP-2), signal transducer and activator of transcription 3 (STAT3) and MEK. AG490 pretreatment inhibited the MEK phosphorylation but did not affect the STAT3 phosphorylation. We conclude that sIL-6R induces GRO-alpha expression in HUVEC through the activation of JAK2 and MEK.

Cells, Cultured↗

Bradykinin B2 receptors activate Na+/H+ exchange in mIMCD-3 cells via Janus kinase 2 and Ca2+/calmodulin.

We used a cultured murine cell model of the inner medullary collecting duct (mIMCD-3 cells) to examine the regulation of the ubiquitous sodium-proton exchanger, Na+/H+ exchanger isoform 1 (NHE-1), by a prototypical G protein-coupled receptor, the bradykinin B2 receptor. Bradykinin rapidly activates NHE-1 in a concentration-dependent manner as assessed by proton microphysiometry of quiescent cells and by 2'-7'-bis[2-carboxymethyl]-5(6)-carboxyfluorescein fluorescence measuring the accelerated rate of pH(i) recovery from an imposed acid load. The activation of NHE-1 is blocked by inhibitors of the bradykinin B2 receptor, phospholipase C, Ca2+/calmodulin (CaM), and Janus kinase 2 (Jak2), but not by pertussis toxin or by inhibitors of protein kinase C and phosphatidylinositol 3'-kinase. Immunoprecipitation studies showed that bradykinin stimulates the assembly of a signal transduction complex that includes CaM, Jak2, and NHE-1. CaM appears to be a direct substrate for phosphorylation by Jak2 as measured by an in vitro kinase assay. We propose that Jak2 is a new indirect regulator of NHE-1 activity, which modulates the activity of NHE-1 by increasing the tyrosine phosphorylation of CaM and most likely by increasing the binding of CaM to NHE-1.

Animals↗

Constitutive phosphorylation of Janus kinase 2 in the GL15 glioblastoma derived human cell line.

The notion that gliomas could originate from mutated glial precursor cells highlights the possibility of modulating the proliferative and migratory behaviour of glioma cells by acting on the molecular mechanisms operative during the development of the Central Nervous System (CNS), but absent in the normal adult brain. We show that the GL15 glioblastoma derived human cell line displays a high expression of nestin which, combined with the previously demonstrated high expression of vimentin, constitutes a characteristic of astrocyte restricted precursors. We also show that, in analogy with some leukaemia cells, GL15 cells display the constitutively phosphorylated form of Janus kinase 2 (JAK2), a tyrosine kinase expressed during CNS development but undetectable in the normal adult brain. The constitutive activation of JAK2 does not result from chromosomal aberrations involving the JAK2 gene, but most probably from abnormally activated transduction systems operative in glioblastoma cells. We then investigated the effects of tyrphostin AG490, an inhibitor of JAK2 autophosphorylation, on GL15 cell growth. In the absence of exogenous growth factors and cytokines, 10 microM tyrphostin AG490 induces an S phase arrest, combined with a partial impairment of the G2 phase of the cell cycle. The abnormally activated JAK2 could then potentially represent a target for a selective pharmacological approach in glioblastoma cells in which a combination of glial precursor characteristics and genetic alterations occurs.

Cell Cycle↗

Hypertonicity activates Na+/H+ exchange through Janus kinase 2 and calmodulin.

The type 1 sodium-hydrogen exchanger (NHE-1) is a ubiquitous electroneutral membrane transporter that is activated by hypertonicity in many cells. NHE-1 may be an important pathway for Na(+) entry during volume restoration, yet the molecular mechanisms underlying the osmotic regulation of NHE-1 are poorly understood. In the present study we conducted a screen for important signaling molecules that could be involved in hypertonicity-induced activation of NHE-1 in CHO-K1 cells. Hypertonicity rapidly activated NHE-1 in a concentration-dependent manner as assessed by proton microphysiometry and by measurements of intracellular pH on a FLIPR (fluorometric imaging plate reader). Inhibitors of Ca(2+)/calmodulin (CaM) and Janus kinase 2 (Jak2) attenuated this activation, whereas neither calcium chelation nor inhibitors of protein kinase C, the Ras-ERK1/2 pathway, Src kinase, and Ca(2+)/calmodulin-dependent enzymes had significant effects. Hypertonicity also resulted in the rapid tyrosine phosphorylation of Jak2 and STAT3 (the major substrate of Jak2) and CaM. Phosphorylation of Jak2 and CaM were blocked by AG490, an inhibitor of Jak2. Immunoprecipitation studies showed that hypertonicity stimulates the assembly of a signaling complex that includes CaM, Jak2, and NHE-1. Formation of the complex could be blocked by AG490. Thus, we propose that hypertonicity induces activation of NHE-1 in CHO-K1 cells in large part through the following pathway: hypertonicity --> Jak2 phosphorylation and activation --> tyrosine phosphorylation of CaM --> association of CaM with NHE-1 --> NHE-1 activation.

Animals↗

JSI-124 (cucurbitacin I) inhibits Janus kinase-3/signal transducer and activator of transcription-3 signalling, downregulates nucleophosmin-anaplastic lymphoma kinase (ALK), and induces apoptosis in ALK-positive anaplastic large cell lymphoma cells.

JSI-124 (cucurbitacin I) has been recently described as a specific inhibitor of signal transducer and activator of transcription-3 (STAT3). As STAT3 activation is pathogenetically important in anaplastic lymphoma kinase-positive anaplastic large cell lymphoma (ALK+ ALCL), we investigated whether JSI-124 can mediate significant inhibitory effects in this cell type. In two ALK+ ALCL cell lines (Karpas 299 and SU-DHL-1), JSI-124 significantly reduced the number of viable cells to 50% of that of negative controls at a dose of 5-10 micromol/l at 24 h and 1-1.25 micromol/l at 48 h. This decrease in viability was associated with apoptosis, as confirmed by the increase in the subG(0/1) fraction, poly(ADP-ribose)polymerase cleavage and expression of active caspase 3. JSI-124 decreased the phosphorylated-STAT3 and -Janus kinase-3 (JAK3) levels in a dose-dependent fashion, and these changes were coupled with significant decreases in several STAT3 downstream targets, including mcl-1, bcl-2, bcl-xL and cyclin D3. Interestingly, JSI-124 also dramatically decreased the protein levels of JAK3 and nucleophosmin (NPM)-ALK, and these effects were reversible by MG132. Our data support that JSI-124 is a potentially useful therapeutic agent for ALK+ ALCL. In addition to its role as a tyrosine kinase inhibitor, JSI-124 appears to be involved in regulating proteosome degradation for proteins such as JAK3 and NPM-ALK.

Antineoplastic Agents↗