Janus Family Of Tyrosine Kinases Research Articles

Gallein, G protein βγ subunits inhibitor, suppresses the TGF-α-induced migration of hepatocellular carcinoma cells via inhibition of the c-Jun N-terminal kinase.

G protein-coupled receptor (GPCR) signaling regulates a wide range of pathophysiological cell functions via G protein α and βγ subunits. Small molecules targeting the subunits of Gα and Gβγ have been developed as cancer therapeutics. We have previously reported that transforming growth factor-α (TGF-α) induces the migration of human hepatocellular carcinoma (HCC) HuH7 cells through the activation of AKT, p38 mitogen-activated protein kinase (MAPK), Rho-kinase and c-Jun N-terminal kinase (JNK). This study aims to determine whether Gβγ subunits regulate the TGF-α-induced migration of HCC HuH7 cells using gallein, a Gβγ subunits inhibitor. The Janus family of tyrosine kinase (JAK)/signal transducer and activator of transcription 3 (STAT3) signaling pathway was also involved in the regulation of the migration. Gallein significantly reduced the TGF-α-induced cell migration. In contrast, fluorescein, a gallein-related compound that has no effect on Gβγ subunits, failed to affect the cell migration. Gallein suppressed the TGF-α-stimulated phosphorylation of JNK without affecting the phosphorylation of epidermal growth factor receptor, AKT, p38 MAPK, target protein of Rho-kinase and STAT3. Conversely, fluorescein did not attenuate the phosphorylation of JNK. These results strongly suggest that Gβγ subunits act as positive regulators in TGF-α-induced migration of HCC cells via the JNK signalling pathway.

Investigation of Janus Kinase (JAK) Inhibitors for Lung Delivery and the Importance of Aldehyde Oxidase Metabolism

The Janus family of tyrosine kinases (JAK1, JAK2, JAK3, and TYK2) play an essential role in the receptor signaling of cytokines that have been implicated in the pathogenesis of severe asthma, and there is emerging interest in the development of small-molecule-inhaled JAK inhibitors as treatments. Here, we describe the optimization of a quinazoline series of JAK inhibitors and the results of mouse lung pharmacokinetic (PK) studies where only low concentrations of parent compound were observed. Subsequent investigations revealed that the low exposure was due to metabolism by aldehyde oxidase (AO), so we sought to identify quinazolines that were not metabolized by AO. We found that specific substituents at the quinazoline 2-position prevented AO metabolism and this was rationalized through computational docking studies in the AO binding site, but they compromised kinome selectivity. Results presented here highlight that AO metabolism is a potential issue in the lung.

Therapeutic targeting of JAKs: from hematology to rheumatology and from the first to the second generation of JAK inhibitors.

Several cytokines and growth factors, as well as their downstream signalling pathways, are implicated in the pathogenesis of haematological and immune-mediated diseases. These mediators act through binding to their cognate receptor and activation of one or more of the four Janus family tyrosine kinases (JAKs). Gene knock-out studies together with evidence from patients carrying activating mutant forms of JAKs (eg, JAK2 V617F in myeloproliferative disorders) provided strong rationale for the development of JAK inhibitors. Based on encouraging preclinical data showing the capacity of JAK inhibitors to suppress the signalling from multiple cytokines, an extensive drug development program was set out, with the initial successful introduction of tofacitinib, baricitinib and ruxolitinib in various chronic rheumatic and myeloproliferative diseases, respectively. Importantly, advancements with the design of next-generation, hyper-selective JAK inhibitors hold promise for the better control of inflammation, while reducing the risk for harms, in an expanding spectrum of medical disorders.

Angiotensin II Causes Biphasic STAT3 Activation Through TLR4 to Initiate Cardiac Remodeling

Evidence indicates that Ang II (angiotensin II) activates STAT3 (signal transducer and activator of transcription 3) in cardiomyocytes. However, the mechanisms underlying STAT3 activation and downstream responses are not fully known. In this study, we show that Ang II caused biphasic STAT3 activation in cardiomyocytes. A rapid and early activation was mediated by direct association between TLR4 (toll-like receptor-4) and STAT3. This early activation increased IL-6 (interleukin-6) production, which in turn, induced the second STAT3 activation through the IL-6/gp130 (glycoprotein 130)/JAK2 (Janus-family tyrosine kinases 2) pathway, resulting in unregulated expression of genes for cardiac remodeling. Moreover, STAT3 inhibition or TLR4 knockout in mice protected against Ang II-induced hypertrophy, fibrosis, and cardiac functional deficits. Thus, Ang II-induced STAT3 activation in cardiomyocytes was biphasic, providing a sequential induction of IL-6 and myocardial remodeling genes, respectively. This work supports a novel mechanism on STAT3 activation in Ang II-induced cardiac dysfunction and remodeling.

Zeylenone inhibits proliferation and promotes apoptosis in ovarian carcinoma cells via Janus kinase 2 / signal transducers and activators of transcription 3 pathways.

Ovarian cancer is the fifth common cancer in females. The aim of our study was to determine function of Zeylenone on cell viability and apoptosis of ovarian carcinoma SKOV3 cells. Cell viability was measured by Cell counting kit-8 (CCK8) assay; Mitochondrial membrane potential (MMP) and apoptosis were detected by flow cytometry. The mRNA and protein levels of related factors were determined by Real-time quantitative polymerase chain reaction (RT-qPCR) and Western blot, respectively. Cell viability was decreased by Zeylenone in a dose-dependent manner. Zeylenone with concentrations of 2.5, 5 and 10 μmol/L was used to treat ovarian carcinoma SKOV3 cells for 24 h in the following study. The loss of MMP and apoptosis were both significantly increased by Zeylenone. The mRNA and protein levels of cytochrome c (cyto c) and apoptosis inducing factor (AIF) in cytosol were increased by Zeylenone. The mRNA and protein levels of Caspase-3, Fas, Fasl and Bax were increased; while the expression of Bcl-2 was decreased by Zeylenone. The expression of (Janus family of tyrosine kinase) p-JAK and signal transducer and activator of transcription (p-STAT) was decreased significantly by Zeylenone. Zeylenone inhibited cell proliferation and promoted apoptosis in ovarian carcinoma cells. The JAK-STAT pathway was involved in this progress.

TNF-α-sensitive brain pericytes activate microglia by releasing IL-6 through cooperation between IκB-NFκB and JAK-STAT3 pathways

Interleukin (IL)-6 is an important mediator of neurovascular dysfunction, neurodegeneration and/or neuroinflammation. We previously reported that brain pericytes released higher levels of IL-6 than did glial cells (astrocytes and microglia) in response to tumor necrosis factor (TNF)-α. Moreover, pericytes stimulated with TNF-α enhanced activation of BV-2 microglia. In this study, we investigated the mechanisms of TNF-α mediated induction of IL-6 release from brain pericytes and astrocytes and whether pericyte-derived IL-6 would facilitate activation of BV-2 microglia. Using rat brain pericyte and astrocyte primary cultures and pharmacological inhibitors, we found that, TNF-α induced the highest levels of IL-6 release from pericytes by activating the inhibitor kappa B (IκB)-nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) and Janus family of tyrosine kinase (JAK)-signal transducer and activator of transcription (STAT)3 pathways. STAT3 contributed to TNF-α induced nuclear translocation of phospho-NFκB in pericytes. TNF-α-induced IL-6 release in astrocytes was mediated by NFκB but not by STAT3. The presence of pericytes amplified TNF-α-induced iNOS mRNA expression in BV-2 microglia. This effect was blocked by a neutralizing antibody for IL-6. These findings indicated that crosstalk between the IκB-NFκB and JAK-STAT3 pathways is a pericyte specific mechanism, not occurring in astrocytes, for TNF-α-induced IL-6 release. IL-6 derived from pericytes enhanced microglial activation. Our findings increase understanding of the role of pericyte-microglia crosstalk in the brain under neuroinflammatory conditions and suggest a potentially attractive therapeutic target for brain inflammation.

Sevoflurane Postconditioning Reduces Apoptosis by Activating the JAK-STAT Pathway After Transient Global Cerebral Ischemia in Rats.

The antiapoptotic effects of sevoflurane postconditioning are responsible for neuroprotection against cerebral ischemia-reperfusion injury. Phosphorylation of the Janus family tyrosine kinases (JAK) 2-signal transducers and activators of transcription (STAT) 3 pathway is linked to antiapoptosis. Here, we determined whether the antiapoptotic effects of sevoflurane postconditioning are associated with activation of the JAK2-STAT3 pathway after global transient cerebral ischemia in rats. Forty-five rats were randomly assigned to 5 groups: sham (n=5), control (10 min of ischemia, n=10), sevoflurane postconditioning (2 periods of sevoflurane inhalation after ischemia for 10 min, n=10), AG490 (a JAK2 selective inhibitor, intraperitoneal administration of 40 mg/kg before ischemia, n=10), and sevoflurane postconditioning plus AG490 group (n=10). The number of apoptotic cells as well as the expression of JAK2, phosphorylated JAK2 (P-JAK2), STAT3, phosphorylated STAT3 (P-STAT3), Bcl-2 (antiapoptotic protein), and Bax (proapoptotic protein) were evaluated 3 days after ischemia. The apoptotic cell count was significantly lower in the sevoflurane postconditioning group than in the control, AG490, and sevoflurane postconditioning plus AG490 groups. JAK2 and STAT3 levels were comparable among all 5 groups. P-JAK2, P-STAT3, and Bcl-2 levels were higher and Bax levels were lower in the sevoflurane postconditioning group relative to the control, AG490, and sevoflurane postconditioning plus AG490 groups. Sevoflurane postconditioning reduced apoptosis by increasing P-JAK and P-STAT expression after transient global ischemia in rats, and AG490 reversed the beneficial antiapoptotic effects of sevoflurane postconditioning, suggesting that the JAK-STAT pathway may be involved in the antiapoptotic mechanism of sevoflurane postconditioning.

Electroacupuncture at GV20 and ST36 Exerts Neuroprotective Effects via the EPO-Mediated JAK2/STAT3 Pathway in Cerebral Ischemic Rats.

Background While electroacupuncture (EA) in cerebral ischemia has been used to promote functional recovery, the underlying mechanism of its protective effect remains poorly understood. Objective We investigated the effects of EA stimulation at GV20 and ST36 to observe the changes in erythropoietin- (EPO-) mediated Janus family tyrosine kinases 2 (JAK2) signal transducers and activators of the transcription 3 (STAT3) cell pathway. Methods Thirty-six specific pathogen-free Sprague-Dawley (SD) male rats were randomly assigned to three groups: the sham-operated group (S group), the middle cerebral artery occlusion (MCAO) group (M group), and the EA group. Neurological deficits were assessed through the Ludmila Belayev 12-score test and 2,3,5-triphenyltetrazolium chloride (TTC) staining was shown. The protein and mRNA expression levels of EPO, the EPO receptor (EpoR), p-JAK2, JAK2, p-STAT3, and STAT3 were examined to explore the EA effect on rats with cerebral ischemic reperfusion injury (CIRI). Results EA significantly decreased infarct size and improved neurological function. Furthermore, target EPO, EpoR, JAK2, and STAT3 mRNA and protein levels significantly increased in the EA group. Conclusions EA exerts a neuroprotective effect, possibly via the regulation of the EPO-mediated JAK2/STAT3 cell pathway and downstream apoptotic pathways in a rat CIRI model.

CAMP/PKA enhances interleukin-1β-induced interleukin-6 synthesis through STAT3 in glial cells

We previously reported that interleukin (IL)-1β induces IL-6 synthesis via activation of the IκB/NFκB pathway, p38 mitogen-activated protein (MAP) kinase, stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK), and signal transducer and activator of transcription (STAT)3, but not p44/p42 MAP kinase in rat glioma cell line, C6 cells and that cAMP enhances the IL-6 synthesis. However, the details behind enhancement of IL-1β-induced IL-6 synthesis by cAMP remain to be elucidated. In the present study, we investigated the exact mechanism of cAMP underlying the amplification of IL-1β-induced IL-6 synthesis in C6 cells. 8-Bromo cAMP significantly enhanced IL-1β-induced STAT3 phosphorylation without affecting phosphorylation of IκB, p38 MAP kinase or SAPK/JNK. In addition, we found that forskolin, a direct activator of adenylyl cyclase, significantly enhanced IL-1β-induced STAT3 phosphorylation. Janus family of tyrosine kinase (JAK) inhibitor I markedly suppressed the amplification by 8-bromo cAMP of IL-1β-induced IL-6 release. IL-1β induced JAK2 phosphorylation, and FLLL32, a specific JAK2 inhibitor, significantly reduced IL-1β-stimulated IL-6 release. 4-Cyano-3-methylisoquinoline, an inhibitor of protein kinase A (PKA), significantly attenuated the enhancing effect of 8-bromo cAMP on IL-1β-induced STAT3 phosphorylation. 8-Bromo cAMP markedly induced JAK2 phosphorylation. PKA siRNA transfection reduced enhancement of IL-1β-induced IL-6 release by 8-bromo cAMP. In conclusion, our results strongly suggest that the adenylyl cyclase/cAMP/PKA pathway upregulates IL-1β-induced IL-6 synthesis through enhancement of the JAK2/STAT3 pathway in C6 glioma cells.

The antihypertension drug doxazosin suppresses JAK/STATs phosphorylation and enhances the effects of IFN-α/γ-induced apoptosis.

Doxazosin, a commonly prescribed treatment for patients with benign prostatic hyperplasia, serves as an α1-blocker of the adrenergic receptors. In this study, we calculated its effect on the ovarian carcinoma cells. Doxazosin induces dose-dependent growth suppression and is additively activated through IFN-α or IFN-γ stimulation. They both enhanced G1 phase arrest, as well as the activity of caspase-3, and the reduction of cyclin D1 and CDK4 protein levels. Doxazosin growth suppression was abolished either by the Janus family of tyrosine kinase (JAK) or the signal transducer and activator of transcription (STAT) inhibitor treatment. The activity of JAK/STAT was dependent on the level of doxazosin, suggesting a requirement of doxazosin for the activation of JAK/STAT. Furthermore, doxazosin plus IFN-α or doxazosin plus IFN-γ additively suppressed the activation of the JAK/STAT signals through phosphorylation of JAK and STAT, thus affecting the activation of subsequent downstream signaling components PI3K, mTOR, 70S6K, and PKCδ. In vivo study demonstrated that doxazosin significantly suppressed tumor growth in an ovarian cancer cell xenograft mouse model, inducing apoptotic cell death by up-regulating the expression of p53, whereas c-Myc expression was markedly reduced. Our data indicate that doxazosin can modulate the apoptotic effects of IFN-α- and IFN-γ through the JAK/STAT signaling pathways. Collectively, we indicate that this action may be a potent chemotherapeutic property against ovarian carcinoma.

Serenoa Repens Induces Growth Arrest, Apoptosis and Inactivation of STAT3 Signaling in Human Glioma Cells.

Serenoa repens, the extract of berry in Southeastern United States, is one of several phytotherapeutic agents available for the treatment of Benign prostatic hyperplasia (BPH). In this study, we found for the first time that Serenoa repens effectively inhibited the growth of human U87 and U251 glioma cells. Flow cytometry assay showed that Serenoa repens induced apoptosis of U87 and U251 glioma cells in a dose-dependent manner. Also, Serenoa repens increased the expression of cleaved-PARP, Caspase-3 or p27 protein in these two cell lines, respectively. In addition, we found that Serenoa repens down-regulated basal level of phosphorylated form of signal transducer and activator of transcription 3 (STAT 3) in both U87 and U251 glioma cells. Furthermore, it was discovered that a Janus family of tyrosine kinase (JAK) inhibitor AG490 inhibit the growth of human U87 and U251 glioma cells and AG490 enhanced the ability of Serenoa repens to inhibit the growth of U87 and U251 glioma cells as measured by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. These results indicate that Serenoa repens reduces the growth, causes apoptosis of Glioma cells and inhibits STAT 3 signaling. In addition, it might also be useful for the treatment of individuals with glioma.

P-glycoprotein (MDR1/ABCB1) and breast cancer resistance protein (BCRP/ABCG2) restrict brain accumulation of the JAK1/2 inhibitor, CYT387

CYT387 is an orally bioavailable, small molecule inhibitor of Janus family of tyrosine kinases (JAK) 1 and 2. It is currently undergoing Phase I/II clinical trials for the treatment of myelofibrosis and myeloproliferative neoplasms. We aimed to establish whether the multidrug efflux transporters P-glycoprotein (P-gp; MDR1; ABCB1) and breast cancer resistance protein (BCRP;ABCG2) restrict oral availability and brain penetration of CYT387. In vitro, CYT387 was efficiently transported by both human MDR1 and BCRP, and very efficiently by mouse Bcrp1 and its transport could be inhibited by specific MDR1 inhibitor, zosuquidar and/or specific BCRP inhibitor, Ko143. CYT387 (10mg/kg) was orally administered to wild-type (WT), Bcrp1−/−, Mdr1a/1b−/− and Bcrp1;Mdr1a/1b−/− mice and plasma and brain concentrations were analyzed. Over 8h, systemic exposure of CYT387 was similar between all the strains, indicating that these transporters do not substantially limit oral availability of CYT387. Despite the similar systemic exposure, brain accumulation of CYT387 was increased 10.5- and 56-fold in the Bcrp1;Mdr1a/1b−/− mice compared to the WT strain at 2 and 8h after CYT387 administration, respectively. In single Bcrp1−/− mice, brain accumulation of CYT387 was more substantially increased than in Mdr1a/1b−/− mice, suggesting that CYT387 is a slightly better substrate of Bcrp1 than of Mdr1a at the blood–brain barrier. These results indicate a marked and additive role of Bcrp1 and Mdr1a/1b in restricting brain penetration of CYT387, potentially limiting efficacy of this compound against brain (micro) metastases positioned behind a functional blood–brain barrier.

P‐glycoprotein (ABCB1) and Breast Cancer Resistance Protein (ABCG2) restrict the brain penetration of the Janus family of tyrosine kinase (JAK) inhibitor CYT387

CYT387 is an oral Janus family of tyrosine kinase (JAK) 1/2 inhibitor and currently undergoes Phase I/II clinical trials for myelofibrosis and myeloproliferative neoplasm treatment. We aimed to establish whether the multidrug efflux transporters P‐glycoprotein (ABCB1) and Breast Cancer Resistance Protein (ABCG2) restrict oral availability and brain penetration of CYT387. To investigate this, plasma exposure and brain concentrations of CYT387 were analyzed after oral administration of CYT387 to wild type (WT), Abcb1a/1b−/−, Abcg2−/− and Abcb1a/1b−/−;Abcg2−/− mice. Over 8 hours, plasma exposure of CYT387 was similar between all the strains, indicating that these transporters do not limit oral availability of CYT387. Despite the similar systemic exposure, brain concentrations of CYT387 were increased ~10‐fold in the Abcb1a/1b−/−;Abcg2−/− mice, but not in the Abcb1a/1b−/− or Abcg2−/− mice, compared to the WT strain. However, in Abcg2−/− mice brain levels of CYT387 were slightly, albeit not significantly increased, suggesting that CYT387 might be a better substrate of Abcg2 rather than Abcb1a at the blood‐brain barrier. These results overall indicate a marked and additive role of Abcg2−/− and Abcb1a/1b−/− in restricting brain penetration of CYT387.

Growth Hormone-induced JAK2 Signaling and GH Receptor Down-regulation: Role of GH Receptor Intracellular Domain Tyrosine Residues

GH receptor (GHR) mediates important somatogenic and metabolic effects of GH. A thorough understanding of GH action requires intimate knowledge of GHR activation mechanisms, as well as determinants of GH-induced receptor down-regulation. We previously demonstrated that a GHR mutant in which all intracellular tyrosine residues were changed to phenylalanine was defective in its ability to activate signal transducer and activator of transcription (STAT)5 and deficient in GH-induced down-regulation, but able to allow GH-induced Janus family of tyrosine kinase 2 (JAK2) activation. We now further characterize the signaling and trafficking characteristics of this receptor mutant. We find that the mutant receptor's extracellular domain conformation and its interaction with GH are indistinguishable from the wild-type receptor. Yet the mutant differs greatly from the wild-type in that GH-induced JAK2 activation is augmented and far more persistent in cells bearing the mutant receptor. Notably, unlike STAT5 tyrosine phosphorylation, GH-induced STAT1 tyrosine phosphorylation is retained and augmented in mutant GHR-expressing cells. The defective receptor down-regulation and persistent JAK2 activation of the mutant receptor do not depend on the sustained presence of GH or on the cell's ability to carry out new protein synthesis. Mutant receptors that exhibit resistance to GH-induced down-regulation are enriched in the disulfide-linked form of the receptor, which reflects the receptor's activated conformation. Furthermore, acute GH-induced internalization, a proximal step in down-regulation, is markedly impaired in the mutant receptor compared to the wild-type receptor. These findings are discussed in the context of determinants and mechanisms of regulation of GHR down-regulation.

Janus kinase inhibitors

The discovery of the JAK2 V617F mutation in the classical myeloproliferative neoplasms (MPNs) essential thrombocytosis, polycythemia vera, and primary myelofibrosis has ushered in a new era of scientific discovery in these diseases, resulting in a molecular classification and an improved understanding of disease pathogenesis. Alongside this period of discovery has been the rapid development of targeted therapy and, here, we summarize results from clinical trials involving these small molecule Janus family of tyrosine kinase (JAK) inhibitors. The JAK inhibitors consistently alleviate constitutional symptoms and reduce spleen size. Early phase testing indicates that some of these inhibitors have additional unique effects: INCB018424 results in a significant reduction in the level of pro-inflammatory cytokines; TG101348 may modify disease burden as assessed by JAK2 allele measurements; and CYT387 ameliorates anemia. The initial enthusiasm for these agents has been tempered by recognition that JAK2 V617F may represent only one component of lesions driving the heterogeneity of the MPN. Clinical trial design cannot address important disease endpoints such as thrombosis or leukemia transformation, but it appears that JAK inhibitors will offer an important palliative option and because of the molecular complexity in these diseases, it might be rational to give these inhibitors along with other agents that target alternate mechanisms of the disease pathogenesis.

The role of the JAK2-STAT3 pathway in pro-inflammatory responses of EMF-stimulated N9 microglial cells

BackgroundIn several neuropathological conditions, microglia can become overactivated and cause neurotoxicity by initiating neuronal damage in response to pro-inflammatory stimuli. Our previous studies have shown that exposure to electromagnetic fields (EMF) activates cultured microglia to produce tumor necrosis factor (TNF)-α and nitric oxide (NO) through signal transduction involving the activator of transcription STAT3. Here, we investigated the role of STAT3 signaling in EMF-induced microglial activation and pro-inflammatory responses in more detail than the previous study.MethodsN9 microglial cells were treated with EMF exposure or a sham treatment, with or without pretreatment with an inhibitor (Pyridone 6, P6) of the Janus family of tyrosine kinases (JAK). The activation state of microglia was assessed via immunoreaction using the microglial marker CD11b. Levels of inducible nitric oxide synthase (iNOS), TNF-α and NO were measured using real-time reverse transcription-polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA) and the nitrate reductase method. Activation of JAKs and STAT3 proteins was evaluated by western blotting for specific tyrosine phosphorylation. The ability of STAT3 to bind to DNA was detected with an electrophoresis mobility shift assay (EMSA).ResultsEMF was found to significantly induce phosphorylation of JAK2 and STAT3, and DNA-binding ability of STAT3 in N9 microglia. In addition, EMF dramatically increased the expression of CD11b, TNF-α and iNOS, and the production of NO. P6 strongly suppressed the phosphorylation of JAK2 and STAT3 and diminished STAT3 activity in EMF-stimulated microglia. Interestingly, expression of CD11b as well as gene expression and production of TNF-α and iNOS were suppressed by P6 at 12 h, but not at 3 h, after EMF exposure.ConclusionsEMF exposure directly triggers initial activation of microglia and produces a significant pro-inflammatory response. Our findings confirm that the JAK2-STAT3 pathway may not mediate this initial microglial activation but does promote pro-inflammatory responses in EMF-stimulated microglial cells. Thus, the JAK2-STAT3 pathway might be a therapeutic target for reducing pro-inflammatory responses in EMF-activated microglia.

Mechanisms of tumor necrosis factor-α-induced interleukin-6 synthesis in glioma cells

BackgroundInterleukin (IL)-6 plays a pivotal role in a variety of CNS functions such as the induction and modulation of reactive astrogliosis, pathological inflammatory responses and neuroprotection. Tumor necrosis factor (TNF)-α induces IL-6 release from rat C6 glioma cells through the inhibitory kappa B (IκB)-nuclear factor kappa B (NFκB) pathway, p38 mitogen-activated protein (MAP) kinase and stress-activated protein kinase (SAPK)/c-Jun N-terminal kinase (JNK). The present study investigated the mechanism of TNF-α-induced IL-6 release in more detail than has previously been reported.MethodsCultured C6 cells were stimulated by TNF-α. IL-6 release from the cells was measured by an enzyme-linked immunosorbent assay, and the phosphorylation of IκB, NFκB, the MAP kinase superfamily, and signal transducer and activator of transcription (STAT)3 was analyzed by Western blotting. Levels of IL-6 mRNA in cells were evaluated by real-time reverse transcription-polymerase chain reaction.ResultsTNF-α significantly induced phosphorylation of NFκB at Ser 536 and Ser 468, but not at Ser 529 or Ser 276. Wedelolactone, an inhibitor of IκB kinase, suppressed both TNF-α-induced IκB phosphorylation and NFκB phosphorylation at Ser 536 and Ser 468. TNF-α-stimulated increases in IL-6 levels were suppressed by wedelolactone. TNF-α induced phosphorylation of STAT3. The Janus family of tyrosine kinase (JAK) inhibitor I, an inhibitor of JAK 1, 2 and 3, attenuated TNF-α-induced phosphorylation of STAT3 and significantly reduced TNF-α-stimulated IL-6 release. Apocynin, an inhibitor of NADPH oxidase that suppresses intracellular reactive oxygen species, significantly suppressed TNF-α-induced IL-6 release and mRNA expression. However, apocynin failed to affect the phosphorylation of IκB, NFκB, p38 MAP kinase, SAPK/JNK or STAT3.ConclusionThese results strongly suggest that TNF-α induces IL-6 synthesis through the JAK/STAT3 pathway in addition to p38 MAP kinase and SAPK/JNK in C6 glioma cells, and that phosphorylation of NFκB at Ser 536 and Ser 468, and NADPH oxidase are involved in TNF-α-stimulated IL-6 synthesis.

A JAK2 Interdomain Linker Relays Epo Receptor Engagement Signals to Kinase Activation

JAK2 (Janus kinase 2) is essential for cytokine receptor signaling, and several lines of evidence support a causal role of an activating JAK2 mutation in myeloproliferative disorders. JAK2 activity is autoinhibited by its pseudokinase domain in the basal state, and the inhibition is released by cytokine stimulation; how engagement of the cognate receptor triggers this release is unknown. From a functional screen for gain-of-function JAK2 mutations, we discovered 13 missense mutations, nine in the pseudokinase domain and four in the Src homology 2 (SH2)-pseudokinase domain linker. These mutations identified determinants for autoinhibition and inducible activation in JAK2. Two of the mutants, K539I and N622I, resulted in erythrocytosis in mice. Scanning mutagenesis of the SH2-pseudokinase domain linker indicated that its N-terminal part was essential for interaction of JAK2 with the Epo receptor, whereas certain mutations in the C-terminal region conferred constitutive activation. We further showed that substitutions for Glu(543)-Asp(544) in this linker or Leu(611), Arg(683), or Phe(694) in the hinge proximal region of the pseudokinase domain resulted in activated JAK2 mutants that could not be further stimulated by Epo. These results suggest that the SH2-pseudokinase domain linker acts as a switch that relays cytokine engagement to JAK2 activation by flexing the pseudokinase domain hinge.

Serenoa repens induces growth arrest and apoptosis of human multiple myeloma cells via inactivation of STAT 3 signaling

Serenoa repens, a palm species native to the Southeastern United States, is one of the widely used phytotherapeutic agents in benign prostatic hyperplasia. In this study, we found for the first time that Serenoa repens induced growth arrest of a variety of human leukemia cells including U266 and RPMI 8226 multiple myeloma cells as measured by mitochondrial-dependent conversion of the 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay. TUNEL assays showed that Serenoa repens induced apoptosis of U266 cells in a time- and dose-dependent manner. Serenoa repens also increased the expression of cleaved-PARP or p27 protein in different human leukemia cell lines. In addition, we found that Serenoa repens down-regulated basal level of phosphorylated form of signal transducer and activator of transcription 3 (STAT 3) and Interleukin-6 induced level of phosphorylated form of STAT 3 and extracellular signal-related kinase (ERK) were also reduced after Serenoa repens treatment in U266 cells. Furthermore, we found that inhibition of STAT 3 signaling by Serenoa repens or Janus family of tyrosine kinase (JAK) inhibitor of AG490 enhanced the ability of docetaxel to inhibit the growth of U266 and RPMI 8226 cells, as measured by trypan blue exclusion test. These results indicate that Serenoa repens might be useful for the treatment of individuals with multiple myeloma.

Mechanisms of interleukin-1β-induced GDNF release from rat glioma cells

Glial cell line-derived neurotrophic factor (GDNF) is highly expressed both in neurons and astrocytes in injured tissues. Astrocytes support neurons by releasing neurotrophic factors including GDNF. It has been reported that various agents including cytokines such as interleukin (IL)-1β induce GDNF mRNA expression and the release in astrocytes. However, the mechanism behind the GDNF synthesis and release remains unclear. Herein, we investigated the mechanisms of the IL-1β-induced GDNF release from rat C6 glioma cells. IL-1β time dependently stimulated GDNF release from C6 cells. IL-1β induced the phosphorylation of inhibitor kappa B (IκB), p38 mitogen-activated protein (MAP) kinase, p44/p42 MAP kinase, stress-activated protein kinase/c- Jun N-terminal kinase (SAPK/JNK) and signal transducer and activator of transcription (STAT) 3. The IL-1β-stimulated levels of GDNF were suppressed by wedelolactone, an inhibitor of IκB kinase, SB203580, an inhibitor of p38 MAP kinase, PD98059, an inhibitor of MAP kinase kinase 1/2 or Janus family of tyrosine kinase (JAK) inhibitor I, an inhibitor of upstream kinase of STAT3. On the contrary, SP600125, an inhibitor of SAPK/JNK, failed to reduce the IL-1β-effect. These results strongly suggest that IL-1β stimulates GDNF release through the pathways of IκB-nuclear factor kappa B, p38 MAP kinase, p44/p42 MAP kinase and JAK-STAT3, but not through the SAPK/JNK pathway in glioma cells.