Tyrphostin AG-490 inhibits cytokine-mediated JAK3/STAT5a/b signal transduction and cellular proliferation of antigen-activated human T cells

JAK/STAT signaling pathway affects CCR5 expression in human CD4+ T cells

CCR5 serves as R5-tropic HIV co-receptor. Knocking out CCR5 in HIV patients, which has occurred <10 times, is believed important for cure. JAK/STAT inhibitors tofacitinib and ruxolitinib inhibit CCR5 expression in HIV+ viremic patients. We investigated the association of JAK/STAT signaling pathway with CCR5/CCR2 expression in human primary CD4+ T cells and confirmed its importance. Six of nine JAK/STAT inhibitors that reduced CCR5/CCR2 expression were identified. Inhibitor-treated CD4+ T cells were relatively resistant, specifically to R5-tropic HIV infection. Furthermore, single JAK2, STAT3, STAT5A, and STAT5B knockout and different combinations of JAK/STAT knockout significantly reduced CCR2/CCR5 expression of both RNA and protein levels, indicating that CCR5/CCR2 expression was positively regulated by JAK-STAT pathway in CD4+ T cells. Serum and glucocorticoid-regulated kinase 1 (SGK1) knockout affected CCR2/CCR5 gene expression, suggesting that SGK1 is involved in CCR2/CCR5 regulation. If cell surface CCR5 levels can be specifically and markedly down-regulated without adverse effects, that may have a major impact on the HIV cure agenda.

Discovery of JAK2/3 Inhibitors from Quinoxalinone-Containing Compounds

Janus kinases (JAKs) are involved in a wide variety of cell signaling associated with T-cell and B-cell mediated diseases. The pathogenesis of common lymphoid-derived diseases and leukemia cancer has been implicated in JAK2 and JAK3. Therefore, to decrease the risk of these diseases, targeting this pathway using JAK2/3 inhibitors could serve as a valuable research tool. Herein, we used a combination of the computational and biological approaches to identify the quinoxalinone-based dual inhibitors of JAK2/3. First, an in-house library of 49 quinoxalinones was screened by molecular docking. Then, the inhibitory activities of 17 screened compounds against both JAKs as well as against two human erythroleukemia cell lines, TF1 and HEL were examined. The obtained results revealed that several quinoxalinones could potentially inhibit JAK2/3, and among them, ST4j showed strong inhibition against JAKs with the IC₅₀ values of 13.00 ± 1.31 nM for JAK2 and 14.86 ± 1.29 nM for JAK3, which are better than ruxolitinib and tofacitinib. In addition, ST4j potentially inhibited TF1 cells (IC₅₀ of 15.53 ± 0.82 μM) and HEL cells (IC₅₀ of 17.90 ± 1.36 μM), similar to both tofacitinib ruxolitinib. Mechanistically, ST4j inhibited JAK2 autophosphorylation and induced cell apoptosis in dose- and time-dependent manners. From molecular dynamics simulations, ST4j was mainly stabilized by van der Waals interactions, and its hydroxyl group could form hydrogen bonds in the hinge region at residues S936 and R938 of JAK2. This research highlights the potential of ST4j to be a novel therapeutic agent for the treatment of lymphoid-derived diseases and leukemia cancer.

Pharmacophore-Based Virtual Screening and Experimental Validation of Pyrazolone-Derived Inhibitors toward Janus Kinases

Janus kinases (JAKs) are nonreceptor protein tyrosine kinases that play a role in a broad range of cell signaling. JAK2 and JAK3 have been involved in the pathogenesis of common lymphoid-derived diseases and leukemia cancer. Thus, inhibition of both JAK2 and JAK3 can be a potent strategy to reduce the risk of these diseases. In the present study, the pharmacophore models built based on the commercial drug tofacitinib and the JAK2/3 proteins derived from molecular dynamics (MD) trajectories were employed to search for a dual potent JAK2/3 inhibitor by a pharmacophore-based virtual screening of 54 synthesized pyrazolone derivatives from an in-house data set. Twelve selected compounds from the virtual screening procedure were then tested for their inhibitory potency against both JAKs in the kinase assay. The in vitro kinase inhibition experiment indicated that compounds 3h, TK4g, and TK4b can inhibit both JAKs in the low nanomolar range. Among them, the compound TK4g showed the highest protein kinase inhibition with the half-maximal inhibitory concentration (IC₅₀) value of 12.61 nM for JAK2 and 15.80 nM for JAK3. From the MD simulations study, it could be found that the sulfonamide group of TK4g can form hydrogen bonds in the hinge region at residues E930 and L932 of JAK2 and E903 and L905 of JAK3, while van der Waals interaction also plays a dominant role in ligand binding. Altogether, TK4g, found by virtual screening and biological tests, could serve as a novel therapeutical lead candidate.

The prohibitin protein complex promotes mitochondrial stabilization and cell survival in hematologic malignancies

Prohibitins (PHB1 and PHB2) have been proposed to play important roles in cancer development and progression, however their oncogenic mechanism of action has not been fully elucidated. Previously, we showed that the PHB1 and PHB2 protein complex is required for mitochondrial homeostasis and survival of normal human lymphocytes. In this study, novel evidence is provided that indicates mitochondrial prohibitins are overexpressed in hematologic tumor cells and promote cell survival under conditions of oxidative stress. Immunofluorescent confocal microscopy revealed both proteins to be primarily confined to mitochondria in primary patient lymphoid and myeloid tumor cells and tumor cell lines, including Kit225 cells. Subsequently, siRNA-mediated knockdown of PHB1 and PHB2 in Kit225 cells significantly enhanced sensitivity to H₂O₂-induced cell death, suggesting a protective or anti-apoptotic function in hematologic malignancies. Indeed, PHB1 and PHB2 protein levels were significantly higher in tumor cells isolated from leukemia and lymphoma patients compared to PBMCs from healthy donors. These findings suggest that PHB1 and PHB2 are upregulated during tumorigenesis to maintain mitochondrial integrity and therefore may serve as novel biomarkers and molecular targets for therapeutic intervention in certain types of hematologic malignancies.

Janus kinase 2 activation participates in prostaglandin E2-induced hyperalgesia

Prostaglandin E2 (PGE2) is one of the major signaling molecules involved in hyperalgesia, acting directly on nociceptors and resulting in the activation of PKA and PKC. Once active, these kinases phosphorylate many cellular proteins, resulting in changes on nociceptors sensorial transduction properties. The Janus Kinases (JAKs) are a family of intracellular signaling molecules generally associated with cytokine signaling, and their activity can be increased in nociceptors after peripheral inflammation. However, there are no evidences of JAKs direct involvement in PGE2 mediated sensitization of nociceptors. Therefore, the aim of the present study was to explore a possible role for JAKs in PGE2 mediated sensitization. In cultured dorsal root ganglion (DRG) neurons, we observed that the administration of PGE2 increases capsaicin induced calcium transients, and a pre-incubation of DRG cells with the JAK inhibitor AG490 blocks this PGE2 in vitro effect. Intrathecal administration of AG490 to ten-weeks-old male Wistar rats reduces the hyperalgesia induced by the intraplantar administration of PGE2 or carrageenan in the right hind paw. We also observed that carrageenan administration in the right hind paw induced an increase in membrane associated PKCepsilon in the ipsilateral L5 DRG, and this increase was blocked by intrathecal AG490 administration. In conclusion the present study indicates that the JAKs expressed in the DRG and spinal cord may have a role in the sensitization of nociceptors by a peripheral inflammatory event. Moreover, the inhibition of JAKs may be a possible novel pharmacological target for the control of the inflammatory hyperalgesia.

Cell-based phenotypic screening of mast cell degranulation unveils kinetic perturbations of agents targeting phosphorylation

Mast cells play an essential role in initiating allergic diseases. The activation of mast cells are controlled by a complicated signal network of reversible phosphorylation, and finding the key regulators involved in this network has been the focus of the pharmaceutical industry. In this work, we used a method named Time-dependent cell responding profile (TCRP) to track the process of mast cell degranulation under various perturbations caused by agents targeting phosphorylation. To test the feasibility of this high-throughput cell-based phenotypic screening method, a variety of biological techniques were used. We further screened 145 inhibitors and clustered them based on the similarities of their TCRPs. Stat3 phosphorylation has been widely reported as a key step in mast cell degranulation. Interestingly, our TCRP results showed that a Stat3 inhibitor JSI124 did not inhibit degranulation like other Stat3 inhibitors, such as Stattic, clearly inhibited degranulation. Regular endpoint assays demonstrated that the distinctive TCRP of JSI124 potentially correlated with the ability to induce apoptosis. Consequently, different agents possibly have disparate functions, which can be conveniently detected by TCRP. From this perspective, our TCRP screening method is reliable and sensitive when it comes to discovering and selecting novel compounds for new drug developments.

Leptin inhibits amyloid β-protein fibrillogenesis by decreasing GM1 gangliosides on the neuronal cell surface through PI3K/Akt/mTOR pathway

Leptin is a centrally acting hormone that controls metabolic pathways. Recent epidemiological studies suggest that plasma leptin is protective against Alzheimer's disease. However, the mechanism that underlies this effect remains uncertain. To investigate whether leptin inhibits the assembly of amyloid β-protein (Aβ) on the cell surface of neurons, we treated primary neurons with leptin. Leptin treatment decreased the GM1 ganglioside (GM1) levels in the detergent-resistant membrane microdomains (DRMs) of neurons. The increase in GM1 expression induced by leptin was inhibited after pre-treatment with inhibitors of phosphatidylinositol 3-kinase (LY294002), Akt (triciribine) and the mammalian target of rapamycin (i.e. rapamycin), but not by an inhibitor of extracellular signal-regulated kinase (PD98059). In addition, pre-treatment with these reagents blocked the induction of GM1 in DRMs by leptin. Furthermore, Aβ assembly on the cell surface of neurons was inhibited greatly after treatment with leptin. This reduction was markedly inhibited after pre-treatment with LY294002, triciribine, and rapamycin. These results suggest that leptin significantly inhibits Aβ assembly by decreasing GM1 expression in DRMs of the neuronal surface through the phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin pathway. These findings highlight the importance of understanding the function of leptin in AD brains. In this study, our aim was to determine whether leptin regulates the expression and localization of GM1 on the neuronal membrane and if it induces the formation of Aβ assembly on the cell surface of neurons. Our results suggest that leptin regulates the expression of GM1 in DRMs of the neuronal membranes. Moreover, leptin does not seem to facilitate fibrillogenesis of exogenously added soluble Aβ from the cell surface of neurons.

Dual inhibitors of Janus kinase 2 and 3 (JAK2/3): designing by pharmacophore- and docking-based virtual screening approach

JAK2 and JAK3 are non-receptor protein tyrosine kinases implicated in B-cell- and T-cell-mediated diseases. Both enzymes work via different pathways but are involved in the pathogenesis of common lymphoid-derived diseases. Hence, targeting both Janus kinases together can be a potential strategy for the treatment of these diseases. In the present study, two separate pharmacophore-based 3D-QSAR models ADRR.92 (Q(2)(test)0.663, R(2)(train) 0.849, F value 219.3) for JAK2 and ADDRR.142 (Q(2)(test)0.655, R(2)(train) 0.869, F value 206.9) for JAK3 were developed. These models were employed for the screening of a PHASE database of approximately 1.5 million compounds; subsequently, the retrieved hits were screened employing docking simulations with JAK2 and JAK3 proteins. Finally, ADME properties of screened dual inhibitors displaying essential interactions with both proteins were calculated to filter candidates with poor pharmacokinetic profiles. These candidates could serve as novel therapeutic agents in the treatment of lymphoid-related diseases.

Pro-inflammatory cytokines negatively regulate PPARγ mediated gene expression in both human and murine macrophages via multiple mechanisms

PPARγ is a lipid activated transcription factor that connects lipid metabolism and immune function. It is known that anti-inflammatory cytokines, such as IL-4 that mediates the differentiation of alternatively activated macrophages, positively modulate PPARγ at three levels: by (1) increasing its expression (2), initiating a complex formation with STAT6 enhances its transcriptional activity and (3) increasing endogenous ligand production. On the other hand, PPARγ is known to inhibit inflammatory processes via transrepression. However, the impact of a pro-inflammatory cytokine milieu on PPARγ transcriptional activity in macrophages is less understood. We hypothesized that pro-inflammatory cytokines, such as IFNγ and TNFα negatively regulate PPARγ activity and sought to test this within human and murine macrophage models using both global and single target gene expression analysis. We found that IFNγ/TNFα inhibited PPARγ expression in human CD14+ monocytes derived macrophages and mouse bone marrow derived macrophages, but not in macrophages originating from CD34+ stem cells or Thp-1 monocytic cells. Irrespective of the model system, the ability of PPARγ to regulate gene expression was inhibited. Moreover, we demonstrated that in Thp-1 cells PPARγ in vitro DNA binding remained unchanged following IFNγ/TNFα pre-treatment. Taken together, our data suggest that pro-inflammatory conditions inhibit PPARγ activity at the gene expression level and propose two, mutually not exclusive models as mechanisms: (1) the level of PPARγ itself is down-regulated by the cytokines leading to loss of function, while (2) PPARγ itself remains associated with the DNA though unable to initiate gene expression. These findings support that inflammatory conditions skew the lipid sensing function of macrophages, further contributing to the vicious circle of metabolic disorders.

Forskolin-inducible cAMP pathway negatively regulates T-cell proliferation by uncoupling the interleukin-2 receptor complex

Cytokine-mediated regulation of T-cell activity involves a complex interplay between key signal transduction pathways. Determining how these signaling pathways cross-talk is essential to understanding T-cell function and dysfunction. In this work, we provide evidence that cross-talk exists between at least two signaling pathways: the Jak3/Stat5 and cAMP-mediated cascades. The adenylate cyclase activator forskolin (Fsk) significantly increased intracellular cAMP levels and reduced proliferation of the human T-cells via inhibition of cell cycle regulatory genes but did not induce apoptosis. To determine this inhibitory mechanism, effects of Fsk on IL-2 signaling was investigated. Fsk treatment of MT-2 and Kit 225 T-cells inhibited IL-2-induced Stat5a/b tyrosine and serine phosphorylation, nuclear translocation, and DNA binding activity. Fsk treatment also uncoupled IL-2 induced association of the IL-2Rβ and γc chain, consequently blocking Jak3 activation. Interestingly, phosphoamino acid analysis revealed that Fsk-treated cells resulted in elevated serine phosphorylation of Jak3 but not Stat5, suggesting that Fsk can negatively regulate Jak3 activity possibly mediated through PKA. Indeed, in vitro kinase assays and small molecule inhibition studies indicated that PKA can directly serine phosphorylate and functionally inactivate Jak3. Taken together, these findings suggest that Fsk activation of adenylate cyclase and PKA can negatively regulate IL-2 signaling at multiple levels that include IL-2R complex formation and Jak3/Stat5 activation.

Interleukin-13-induced activation of signal transducer and activator of transcription 6 is mediated by an activation of Janus kinase 1 in cultured human bronchial smooth muscle cells

BACKGROUND

The current study was carried out to identify the JAK molecule(s) that is involved in the IL-13-induced activation of STAT6 in cultured human bronchial smooth muscle cells (hBSMCs).

METHODS

Cultured hBSMCs were stimulated with IL-13 in the absence and presence of JAK inhibitor-I (a nonspecific JAKs inhibitor), tyrphostin-AG490 (a specific JAK2 inhibitor), WHI-P131 (a specific JAK3 inhibitor), or tyrphostin-AG9 (a specific Tyk2 inhibitor), and levels of phosphorylated STAT6 were measured by immunoblot analyses.

RESULTS

The IL-13-induced phosphorylation of STAT6 was abolished by JAK inhibitor-I, whereas the other inhibitors had no significant effect.

CONCLUSION

These findings indicate that the STAT6 phosphorylation/activation induced by IL-13 is mediated by an activation of JAK1 in cultured hBSMCs.

Influence of Tyrphostin AG490 on the expression of diabetes-associated markers in human adipocytes

Tyrosine kinase inhibitors (TKi) hold promise as a treatment for a variety of disorders ranging from those in oncology to diseases thought as immune mediated. Tyrphostin AG490 is a potent Jak-Stat TKi shown effective in the prevention of allograft transplant rejection, experimental autoimmune disease, as well as the treatment of cancer. However, given its ability to modulate this important but pleiotropic intracellular pathway, we thought that it is important to examine its effects on glucose metabolism and expression of major transcription factors and adipokines associated with insulin insensitivity and diabetes. We investigated the metabolic effects of AG490 on glucose levels in vivo using an animal model of diabetes, nonobese diabetic (NOD) mice, and transcription factor expression through assessment of human adipocytes. AG490 treatment of young nondiabetic NOD mice significantly reduced blood glucose levels (p = 0.002). In vitro, treatment of adipocytes with rosiglitazone, an insulin sensitizer that binds to peroxisome proliferator-activated receptor (PPAR) receptors and increases the adipocyte response to insulin, significantly increased the expression of the antidiabetic adipokine adiponectin. Importantly, the combination of rosiglitazone plus Tyrphostin AG490 further increased this effect and was specifically associated with significant upregulation of C-enhanced binding protein (C/EBP) (p < 0.0001). In terms of the mechanism underlying this action, regulatory regions of the PPARγ, ADIPOQ, and C/EBP contain the Stat5 DNA-binding sequences and were demonstrated, by gel shift experiments in vitro. These data suggest that blocking Jak-Stat signaling with AG490 reduces blood glucose levels and modulates the expression of transcription factors previously associated with diabetes, thereby supporting its potential as a therapy for this disease.

The effect of erythropoietin on normal and neoplastic cells

Erythropoietin (Epo) is an essential hormone that binds and activates the Epo receptor (EpoR) resident on the surface of erythroid progenitor cells, thereby promoting erythropoiesis. Recombinant human erythropoietin has been used successfully for over 20 years to treat anemia in millions of patients. In addition to erythropoiesis, Epo has also been reported to have other effects, such as tissue protection and promotion of tumor cell growth or survival. This became of significant concern in 2003, when some clinical trials in cancer patients reported increased tumor progression and worse survival outcomes in patients treated with erythropoiesis-stimulating agents (ESAs). One of the potential mechanisms proffered to explain the observed safety issues was that functional EpoR was expressed in tumors and/or endothelial cells, and that ESAs directly stimulated tumor growth and/or antagonized tumor ablative therapies. Since then, numerous groups have performed further research evaluating this potential mechanism with conflicting data and conclusions. Here, we review the biology of endogenous Epo and EpoR expression and function in erythropoiesis, and evaluate the evidence pertaining to the expression of EpoR on normal nonhematopoietic and tumor cells.

Tyrphostin AG490 agent modestly but significantly prevents onset of type 1 in NOD mouse; implication of immunologic and metabolic effects of a Jak-Stat pathway inhibitor

Previously, we have reported that the Jak-Stat signaling pathway is defective in NOD mice. In this study, prediabetic female NOD mice (4 weeks) were treated by intraperitoneal injection either with AG490 or DMSO three times per week for 4 consecutive weeks, followed by once a week for an additional 6 weeks. The onset of diabetes was attenuated in NOD mice treated with AG490 relative to DMSO treated control mice (p < 0.02). From an immunological standpoint, AG490 induced the expression of Foxp3 in CD4(+)CD25(-) T-cells and down-regulated expression of co-stimulatory molecules in dendritic cells (DC) both in vitro and in vivo. AG490 treated CD4+CD25- T-cells and DC in vitro, acquired regulatory functions; namely, the ability to suppress proliferation of a responding cell population in vitro. AG490 treatment resulted in significant reduction of blood glucose values and increased expression of PPARγ in splenocytes and markedly increased expression PPARγ2 but not PPARγ1 in adipocyte in vitro. Presence of multiple Stat5 DNA binding consensus sequences within the promoter region of the PPARγ gene in human and in mouse suggests that PPARγ is downstream to the Jak-Stat signaling pathway. This study highlights a critical role of the Jak-Stat signaling pathway in the pathogenesis of T1D and suggests that blocking the Jak-Stat signaling pathway by AG490 as a tyrosine kinase inhibitor may provide an effective means for preventing autoimmune T1D via both immunological and metabolic effects.

The tyrphostin agent AG490 prevents and reverses type 1 diabetes in NOD mice

BACKGROUND

Recent studies in the NOD (non-obese diabetic) mouse model of type 1 diabetes (T1D) support the notion that tyrosine kinase inhibitors have the potential for modulating disease development. However, the therapeutic effects of AG490 on the development of T1D are unknown.

MATERIALS AND METHODS

Female NOD mice were treated with AG490 (i.p, 1 mg/mouse) or DMSO starting at either 4 or 8 week of age, for five consecutive week, then once per week for 5 additional week. Analyses for the development and/or reversal of diabetes, insulitis, adoptive transfer, and other mechanistic studies were performed.

RESULTS

AG490 significantly inhibited the development of T1D (p = 0.02, p = 0.005; at two different time points). Monotherapy of newly diagnosed diabetic NOD mice with AG490 markedly resulted in disease remission in treated animals (n = 23) in comparision to the absolute inability (0%; 0/10, p = 0.003, Log-rank test) of DMSO and sustained eugluycemia was maintained for several months following drug withdrawal. Interestingly, adoptive transfer of splenocytes from AG490 treated NOD mice failed to transfer diabetes to recipient NOD.Scid mice. CD4 T-cells as well as bone marrow derived dendritic cells (BMDCs) from AG490 treated mice, showed higher expression of Foxp3 (p<0.004) and lower expression of co-stimulatory molecules, respectively. Screening of the mouse immune response gene arrary indicates that expression of costimulaotry molecule Ctla4 was upregulated in CD4+ T-cell in NOD mice treated with AG490, suggesting that AG490 is not a negative regulator of the immune system.

CONCLUSION

The use of such agents, given their extensive safety profiles, provides a strong foundation for their translation to humans with or at increased risk for the disease.

Uncoupling JAK3 activation induces apoptosis in human lymphoid cancer cells via regulating critical survival pathways

In the current work, we report that specific inhibition of Janus tyrosine kinase (JAK3) via NC1153 induces apoptosis of certain leukemia/lymphoma cell lines. Affymetrix microarray profiling following NC1153 treatment unveiled JAK3 dependent survival modulating pathways (p53, TGF-beta, TNFR and ER stress) in Kit225 cells. IL-2 responsive NC1153 target genes were regulated in human JAK3 positive, but not in JAK3 negative lymphoid tumor cells. Moreover, primary lymphoma samples revealed that a number of these genes were reciprocally regulated during disease progression and JAK3 inhibition suggesting that downstream targets of JAK3 could be exploited in the development of novel cancer treatment regimes.

Cellular cholesterol involvement in Src, PKC, and p38/JNK transduction pathways by porins

Biological membranes are described as a mosaic of different domains where interactions between membrane components induce the formation of subdomains with different characteristics and functions. Lipids play an important role in the formation of lipid-enriched microdomains where they dynamically associate to form platforms important for membrane protein sorting and construction of signaling complexes. Cholesterol confined in lipid domains is a crucial component required by microorganisms, directly or indirectly, to enter or exit the intracellular compartment. Cellular activation mediated by superficial bacterial component may be modified by local cholesterol depletion. Therefore, new perspectives for unconventional therapeutic intervention in Gram-negative infections may be envisaged. We tested this hypothesis by using methyl-beta-cyclodextrin (mbetaCD) as a cholesterol-complexing agent to alter the U937 plasma membrane cholesterol content. Our results demonstrate that cholesterol depletion of U937 cells inhibited Salmonella enterica serovar Typhimurium porins-mediated phosphorylation of Src kinase family, protein kinase C (PKC), JNK, and p38, while cholesterol repletion restored the phosphorylation. Lipopolysaccharide (LPS) extracted from the same bacterial strain has been used as a control. Our data demonstrate that the lack of activation of signal transduction pathway observed following cholesterol depletion differently modulates the release of interleukin-6 (IL-6) or tumor necrosis factor-alpha (TNF-alpha), suggesting that Src, associated to lipid domains, may represent an important pathway in Gram-negative-induced cellular signal.

STAT3 is a substrate of SYK tyrosine kinase in B-lineage leukemia/lymphoma cells exposed to oxidative stress

We provide unprecedented genetic and biochemical evidence that the antiapoptotic transcription factor STAT3 serves as a substrate for SYK tyrosine kinase both in vitro and in vivo. Induction of SYK in an ecdysone-inducible mammalian expression system results in STAT3 activation, as documented by tyrosine phosphorylation and nuclear translocation of STAT3, as well as amplified expression of several STAT3 target genes. STAT3 activation after oxidative stress (OS) is strongly diminished in DT40 chicken B-lineage lymphoma cells rendered SYK-deficient by targeted disruption of the syk gene. Introduction of a wild-type, C-terminal or N-terminal SH2 domain-mutated, but not a kinase domain-mutated, syk gene into SYK-deficient DT40 cells restores OS-induced enhancement of STAT-3 activity. Thus, SYK plays an important and indispensable role in OS-induced STAT3 activation and its catalytic SH1 domain is critical for this previously unknown regulatory function. These results provide evidence for the existence of a novel mode of cytokine-independent cross-talk that operates between SYK and STAT3 pathways and regulates apoptosis during OS. We further provide experimental evidence that SYK is capable of associating with and phosphorylating STAT3 in human B-lineage leukemia/lymphoma cells challenged with OS. In agreement with a prerequisite role of SYK in OS-induced STAT3 activation, OS does not induce tyrosine phosphorylation of STAT3 in SYK-deficient human proB leukemia cells. Notably, inhibition of SYK with a small molecule drug candidate prevents OS-induced activation of STAT3 and overcomes the resistance of human B-lineage leukemia/lymphoma cells to OS-induced apoptosis.

Patented small molecules against psoriasis

BACKGROUND

It is hypothesized that psoriasis is an autoimmune disease. The most recent therapeutic approach that proved to be more effective than earlier methods of treatment is the use of mAb/fusion proteins. Efforts nowadays are focused on investigating the antipsoriatic affect of small molecules that can be administered orally, some of which are capable of entering cells, and being selective in targeting intracellular pathways.

OBJECTIVE

Preclinical patented small molecules that are recommended for the treatment of psoriasis are reviewed. Emphasis is placed on their mechanism of action.

METHODS

http://ep.espacenet.com/ , Pubmed, Scopus and Google websites were the main sources used for the patented small molecule search. A number of patents were poorly described and difficulties were faced in trying to figure out the patentee(s) explanation. Moreover, most patents were recommended for the treatment of a number of autoimmune diseases and cancer, and not only for psoriasis.

RESULTS/CONCLUSIONS

Small molecules that inhibit the activation of T lymphocytes, leukocyte trafficking, leukotriene activity/production and angiogenesis, and promote apoptosis have been patented. Small molecules that have been patented for the treatment of other autoimmune diseases and could be used for treating psoriasis are described. Moreover, other possible mechanistic approaches using small molecules are discussed.

A novel indole-3-propanamide exerts its immunosuppressive activity by inhibiting JAK3 in T cells

We previously identified an indole-3-propanamide derivative, 3-[1-(4-chlorobenzyl)indol-3-yl]-N-(pyridin-4-yl)propanamide (AD412), as a potential immunosuppressive agent. Here, we document that AD412 inhibited the proliferative response of CD3/CD28-stimulated human T cells without inhibiting their interleukin 2 (IL-2) production and also inhibited the proliferation of CTL-L2 cells in response to IL-2. These results prompted us to analyze the effect of our compound on the three main signaling pathways coupled to the IL-2 receptor. We provide evidence that AD412 inhibited the JAK1/3-dependent phosphorylations of Akt, STAT5a/b, and ERK1/2 in IL-2-stimulated CTL-L2 cells. In contrast, AD412 had little effect on the JAK1/2-dependent INF-gamma-induced phosphorylation of STAT1 in U266 cells. This suggested a preferential inhibition of JAK3 over JAK1 or JAK 2 activities by AD412 that was confirmed by in vitro kinase assays with purified JAK2 and JAK3 kinases. In addition, we provide evidence that the inhibition of IL-2 response by AD412 was not due to inhibition of IL-2Ralpha up-regulation because neither AD412 nor JAK3 inhibitors described previously [4-[(3-bromo-4-hydroxyphenyl)amino]-6,7-dimethoxyquinazoline (WHI-P154) and alpha-cyano-(3,4-dihydroxy)-N-benzylcinnamid (AG-490)] significantly inhibited IL-2-induced IL-2Ralpha overexpression. Finally, we further document the immunosuppressive activity of AD412 in vivo by showing that its administration per os significantly prolonged heart allograft graft survival. This molecule may thus represent an interesting lead compound to develop new immunosuppressive agents in the field of transplantation and autoimmune diseases.

STAT5 regulation of BCL10 parallels constitutive NFkappaB activation in lymphoid tumor cells

Background

Signal Transducer and Activator of Transcription 5 A and B (STAT5) are key survival factors in cells of the lymphoid lineage. Identification of novel, tissue-specific STAT5 regulated genes would advance the ability to combat diseases due to aberrant STAT5 signaling. In the present work a library of human STAT5 bound genomic elements was created and validated.

Results

Of several STAT5 responsive genomic regulatory elements identified, one was located within the first intron of the human BCL10 gene. Chromatin immuno-precipitation reactions confirmed constitutive in vivo STAT5 binding to this intronic fragment in various human lymphoid tumor cell lines. Interestingly, non-phosphorylated STAT5 was found in the nuclei of Kit225 and YT cells in the absence of cytokine stimulation that paralleled constitutive NFκB activation. Inhibition of the hyperactive JAK3/STAT5 pathway in MT-2 cells via the Mannich-base, NC1153, diminished the constitutive in vivo occupancy of BCL10-SBR by STAT5, reduced NFκB activity and BCL10 protein expression in a dose dependent manner. Moreover, depletion of STAT5 via selective antisense oligonucleotide treatment similarly resulted in decreased BCL10 mRNA and protein expression, cellular viability and impaired NFκB activity independent of IL-2.

Conclusion

These results suggest that the NFκB regulator BCL10 is an IL-2-independent STAT5 target gene. These findings proffer a model in which un-activated STAT5 can regulate pathways critical for lymphoid cell survival and inhibitors that disrupt STAT5 function independent of tyrosine phosphorylation may be therapeutically effective in treating certain leukemias/lymphomas.

Induction of granulysin in CD8+ T cells by IL-21 and IL-15 is suppressed by human immunodeficiency virus-1

Immunosuppression following infection with HIV-1 predisposes patients to a myriad of opportunistic pathogens, one of the most important of which is Mtb. Granulysin, expressed by NK cells and CTL, exhibits potent antimicrobial activity against Mtb and several other opportunistic pathogens associated with HIV-1 infection. The immune signals that promote granulysin expression in human CTL are not fully understood. Using primary human CD8+ T cells, in this study, we identify IL-21 as a strong inducer of granulysin, demonstrate that IL-21 and IL-15 activate granulysin expression within CD8+ CD45RO+ T cells, and establish a role for Jak/STAT signaling in the regulation of granulysin within CD8+ T cells. We show that infection of PBMC from healthy donors in vitro with HIV-1 suppresses granulysin expression by CD8+ T cells, concomitant with reduced p-STAT3 and p-STAT5, following activation with IL-15 and IL-21. Of note, simultaneous signaling through IL-15 and IL-21 could partially overcome the immunosuppressive effects of HIV-1 on granulysin expression by CD8+ T cells. These results suggest that HIV-1 infection of PBMC may reduce the antimicrobial profile of activated CD8+ T cells by disrupting signaling events that are critical for the induction of granulysin. Understanding the effects of HIV-1 on CD8+ T cell activation is essential to understanding the physiological basis for inadequate cytotoxic lymphocyte activity in HIV+ patients and for informed guidance of cytokine-based therapy to restore T cell function.

Antitumor effect of humanized anti–interleukin-6 receptor antibody (tocilizumab) on glioma cell proliferation

Object

Interleukin-6 (IL-6) is a pleiotropic cytokine that regulates diverse physiological functions, including cell proliferation and survival. Recent studies have shown that IL-6 expression is often elevated in response to several types of glioma. Although IL-6 is said to play an important role in glioma, the involvement of IL-6 signaling has been quite controversial. The aim of this study was to evaluate the involvement of IL-6 signaling in glioma and the inhibitory effect of IL-6 signaling on glioma tumor proliferation.

Methods

The expression of IL-6 receptors (IL-6Rs) was evaluated in glioma tissues by means of immunohistochemical analysis, and the involvement of IL-6 signaling in glioblastoma multiforme (GBM) U87MG cell proliferation was also determined. In addition, to examine the inhibitory effect of IL-6 signaling on glioma cell proliferation, the authors investigated the effects of tocilizumab, the humanized anti–human IL-6R antibody in U87MG cells.

Results

Increased immunoreactivity for IL-6R was predominantly found in the cytoplasm of endothelial cells in all GBM samples. Inhibition of IL-6 signaling by both IL-6– and IL-6R–specific small interfering RNA and AG490, a specific inhibitor of JAK2 phosphorylation, suppressed glioma cell proliferation. Furthermore, tocilizumab, a clinically developed humanized anti–human IL-6R antibody, exerted an antiproliferative effect on cells from the GBM cell line U87MG via the IL-6R–dependent JAK-STAT3 pathway.

Conclusions

The IL-6 signaling pathway plays an important role in glioma cell proliferation, and tocilizumab exerts an antitumor effect in U87MG glioma cells. These results may bring new insight into the molecular pathogenesis of glioma and may lead to a new therapeutic intervention.

Enhancement of TRAIL cytotoxicity by AG-490 in human ALL cells is characterized by downregulation of cIAP-1 and cIAP-2 through inhibition of Jak2/Stat3

The ability of death-inducing tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) to selectively kill a variety of cancer cells has been largely described, but one of the major concerns with the treatment is the occurrence of drug resistance and possible toxic side effects. Here, we report that TRAIL induces apoptosis in Jurkat and SUPT1 T cell lines and in human T-ALL blasts but not in healthy subject-derived peripheral blood mononuclear cells. In parallel, the treatment with TRAIL and Tyrphostin (AG-490), a selective Janus kinase 2 inhibitor, produces an evident enhancement of cytotoxicity, characterized by a significant inhibition of Stat3 phosphorylation compared to controls or to TRAIL alone-treated samples, and associated with a dramatic decrease of both cIAP-1 and cIAP-2 mRNA levels. Downregulation of cIAP-1 and cIAP-2 by specific small interference RNAs significantly amplifies TRAIL-reduced cytotoxicity. All together, these findings strongly indicate that cIAP-1 and cIAP-2 downregulation is a fundamental step in the signaling pathways mediating the combinatorial effect of TRAIL and AG-490 on T cell leukemia. These findings may help to open new routes for the development of less toxic pharmacological strategies in the treatment of patients affected by TRAIL-sensitive leukemias.

JAK2/Y343/STAT5 signaling axis is required for erythropoietin-mediated protection against ischemic injury in primary renal tubular epithelial cells

Erythropoietin has emerged as a potential therapy for the treatment of ischemic tissue injury. In erythroid cells, the JAK2/Y343/STAT5 signaling axis has been shown to be necessary for stress but not steady-state erythropoiesis. The requirement for STAT5 activation in erythropoietin-mediated protection from ischemic injury has not been well-studied. To answer this question, we induced reproducible necrotic ischemic injury in primary mouse renal tubular epithelial cells (RTEC) in vitro. Using RTEC from erythropoietin receptor mutant mice with differential STAT5 signaling capabilities, we demonstrated first, that EPO administration either before or during injury significantly protects against mild-moderate but not severe necrotic cell death; and second, the JAK2/Y343/STAT5 signaling axis is required for protection against ischemic injury in primary mouse RTEC. In addition, we identified Pim-3, a prosurvival STAT5 target gene, as responsive to EPO in the noninjured kidney both in vitro and in vivo.

Phosphorylation of human Jak3 at tyrosines 904 and 939 positively regulates its activity

Janus tyrosine kinase 3 (Jak3) is essential for signaling by interleukin-2 (IL-2) family cytokines and proper immune function. Dysfunctional regulation of Jak3 may result in certain disease states. However, the molecular mechanisms governing Jak3 activation are not fully understood. In this study, we used a functional-proteomics approach to identify two novel tyrosine phosphorylation sites within Jak3, Y904 and Y939, which are conserved among Jak family proteins. By using phosphospecific antibodies, both residues were observed to be rapidly induced by stimulation of cells with IL-2 or other gammac cytokines. Mechanistic studies indicated that Y904 and Y939 regulate Jak3 activities. A phenylalanine substitution at either site greatly reduced Jak3 kinase activity in vitro and its ability to phosphorylate signal transducer and activator of transcription 5 (Stat5) in vivo, suggesting that phosphorylation of these previously unrecognized residues positively regulates Jak3 activity. Y904 and Y939 were required for optimal ATP usage by Jak3, while phosphorylation of Y939 preferentially promoted Stat5 activity in intact cells. Together, these findings demonstrate positive functional roles for two novel Jak3 phosphoregulatory sites which may be similarly important for other Jak family members. Identification of these sites also provides new therapeutic opportunities to modulate Jak3 function.

STAT1 and STAT3 phosphorylation by porins are independent of JAKs but are dependent on MAPK pathway and plays a role in U937 cells production of interleukin-6

A group of transcription factors, termed signal transducers and activators of transcription (STATs), appears to orchestrate the downstream events propagated by cytokine/growth factor interactions with their cognate receptors. Similarly, cytoplasmic Janus kinases (JAKs) seem to play a critical role in diverse signal transduction pathways that govern cellular survival, proliferation, differentiation and apoptosis. In this work, we analysed the effects of the Salmonella enterica serovar Typhimurium porins on signaling by the JAK/STAT pathway and IL-6 release in U937 cells. Porins and LPS of membrane from Gram-negative bacteria are factors implicated in septic shock. In our assays porins induce interleukin-6 (IL-6) release (110+/-2.6pg/ml) 24h after stimulation and STAT1/STAT3 tyrosine (Tyr701/Tyr705) and serine (Ser727) phosphorylation after 15min. By using several selective inhibitors we demonstrate that porins modulate the activation of STAT1/STAT3 through mitogen activated protein kinases (MAPKs) and not JAKs. Furthermore, we demonstrated that STAT1 and STAT3 are not involved in the modulation of IL-6 release in U937 cells stimulated with porins. Inhibition of tyrosine/serine phosphorylation mediated by MAPKs of STAT1 and STAT3 decrease the IL-6 secretion following porin stimulation. Therefore, suggesting a key role of this pathway in phosphorylation of Ser 727 in STAT1 and STAT3. These results are confirmed by porin or LPS-induced nuclear translocation of STAT1 and STAT3 in U937 cells.

Histamine affects STAT6 phosphorylation via its effects on IL-4 secretion: role of H1 receptors in the regulation of IL-4 production

Signal Transducer and Activator of Transcription (STAT)-6 is a transcriptional factor activated mainly through the cytokines IL-4 and IL-13 leading to the Th2 cell differentiation. Th2 cells play a role in the etiology and pathogenesis of allergic disease. Histamine alters the Th1/Th2 cytokine balance towards the Th2 cytokine profile and consequently plays a role in allergic diseases and asthma. This study was designed to investigate the effects of histamine on the STAT6 phosphorylation. C57/BL6 splenocytes were pretreated with different concentrations of histamine (10(-)(4) M to 10(-)(13) M) followed by stimulation with PMA+ionomycin or IL-4. The phosphorylated and total basal STAT6 levels were assessed by employing the immunoblotting technique. Histamine caused the hyper-phosphorylation of STAT6. H1 receptor antagonist pyrilamine reversed the effect of histamine on STAT6 phosphorylation. However, H2 receptor antagonist ranitidine and H3/H4 receptor antagonist thioperamide did not affect the histamine mediated hyper-phosphorylation of STAT6. Furthermore, H1 receptor agonist betahistine enhanced the phosphorylation of STAT6 whereas H2 receptor agonist amthamine did not affect the phosphorylation STAT6. Furthermore, tyrosine kinase inhibitor, tyrphostin, inhibited the histamine mediated phosphorylation of STAT6 when stimulated with PMA+ionomycin. The effects of histamine on the STAT6 phosphorylation were indirect since they were blocked either by the antibodies to IL-4 and IL-13 or in IL-4 knock out mice in the presence of IL-13 antibody. These observations suggest that histamine indirectly affected the STAT6 phosphorylation via its effects on the secretion of cytokines (IL-4) and H1 receptor played a role in this process.

Drug insight: novel small molecules and drugs for immunosuppression

Gastrointestinal diseases can result from the inadequate or excessive response of the immune system to self or innocuous antigens. Moreover, the physiologic activation of the immune system against non-self antigens is a major clinical problem in liver organ transplantation. At present, many drugs are available that suppress the activation of the immune system, although most of the currently used immunosuppressive drugs lack specificity in terms of their molecular targets and, therefore, have the potential to generate numerous side effects. The advances that have been made in understanding the molecular events that underlie the activation of the immune system have led to the development of a new generation of 'small molecules' that are endowed with immunosuppressive properties and can serve as immunomodulatory agents. Among these new small molecules, inhibitors of Janus kinase 3, p21-Rac1 and p38 mitogen-activated protein kinase represent the most innovative approach to immunosuppression, and could be a promising alternative to current immunosuppressive therapies. Here, we report on the progress that has been made in the development of small molecules in the field of gastroenterology.

All-trans retinoic acid stimulates IL-2-mediated proliferation of human T lymphocytes: early induction of cyclin D3

Vitamin A is established as an important immune regulator, but the mechanisms whereby vitamin A regulates T cell biology are poorly defined. In this study, we show that an active metabolite of vitamin A, all-trans retinoic acid (RA), potently stimulates T cell proliferation by modulating IL-2-mediated signaling downstream of IL-2R and independent of the induction of IL-2. Thus, at concentrations as low as 0.1 nM, RA enhanced the division of normal human T lymphocytes that were simultaneously stimulated with anti-CD3 mAbs and saturating concentrations of IL-2. At the optimal concentration of RA (50 nM), a 3-fold increase in T cell proliferation was observed. The induced proliferation was preceded by increased phosphorylation of the retinoblastoma protein and enhanced G1- to S-phase progression. Interestingly, the promitogenic effect of RA was found to be particularly directed toward increased expression of cyclin D3 at both the mRNA and protein level. Furthermore, the stimulatory effect of RA on cyclin D3 expression as well as on cell proliferation was completely abolished in the presence of the JAK inhibitor AG-490 or blocking IL-2R alpha mAbs, and RA also enhanced cyclin D3 expression and T cell proliferation in the presence of IL-2 alone. Finally, we showed that the proliferative effect of RA was mimicked by agonists of the retinoic acid receptor (RAR) and completely inhibited by a RAR-selective antagonist. In conclusion, our results indicate that RA, via RAR, stimulates IL-2-induced signaling in a JAK-dependent manner to enhance cyclin D3 expression and thereby promote T cell proliferation.

A Preferential Role for STAT5, not Constitutively Active STAT3, in Promoting Survival of a Human Lymphoid Tumor

STATs are believed to play key roles in normal and abnormal cell function. In the present work, we investigated the role of STATs in an IL-2-responsive human lymphoblastic lymphoma-derived cell line, YT. Only STAT3 was found constitutively tyrosine phosphorylated, but not other STATs. Hyperactive STAT3 was not attributable to a pre-existing intermediate affinity IL-2R complex and/or hyperactive Jak activity. Depletion of STAT3 protein expression reduced tumor cell viability with protracted kinetics (72-96 h), while TUNEL assays demonstrated cell death occurred via apoptosis. Interestingly, depletion of STAT5 in this same tumor induced more pronounced cell death compared with STAT3 depletion (24 h). Although IL-2 was able to rescue STAT3-depleted cells from death, it could not compensate for the loss of STAT5. To determine the prosurvival function of STAT3 vs STAT5 within the same tumor model, genes were profiled in STAT3- or STAT5-depleted YT cells by apoptosis-specific microarrays. Several differentially expressed genes were identified. Interestingly, those genes involved in NF-kappaB regulation, such as TNFR-associated factors 2 and 5 and B cell leukemia/lymphoma 10, were readily decreased upon STAT5, but not STAT3, depletion as validated by quantitative RT-PCR. These results suggest that STAT5 and, to a lesser extent, hyperactive STAT3 provide preferential and critical cell survival signals for certain human lymphoid tumors, indicating that nonhyperactive STATs should be considered as therapeutic targets for abrogating tumorigenesis.

Prevention of acute lung allograft rejection in rat by the janus kinase 3 inhibitor, tyrphostin AG490

BACKGROUND

Tyrphostin AG490 (AG490) potently and selectively inhibits gammac/Janus kinase 3-dependent signaling pathways, including downstream Stat5a/b activation and subsequent T cell proliferation by alloantigen stimulation. We evaluated the effects of AG490 on acute rat lung allograft rejection.

METHODS

A 7-day course of an intraperitoneal (IP) injection with 10 mg/kg, 15 mg/kg, or 20 mg/kg AG490 was administered to inhibit the rejection of orthotopically transplanted Brown Norway (RT1n) rat lung allografts in Fischer 344 (RT1(1vl)) rat recipients. The progression of allograft rejection was evaluated by X-ray with a semi-quantitative scoring system and was evaluated histologically with a semi-quantitative rejection scoring system for acute lung allograft rejection. Moreover, to determine whether AG490 regulates CD4+ T cell differentiation during acute rejection, flow cytometry was used to investigate Th1 (interferon-gamma) and Th2 (interleukin [IL]-4, IL-10) intracellular cytokine profiles and the CD4+CD25+ T cell population in recipient splenocytes.

RESULTS

Results of radiology and histology confirmed that treatment with AG490 significantly suppressed acute lung allograft rejection. Furthermore, the splenocytes of the AG490-treated recipients had significantly lower production of interferon-gamma and relatively higher production of IL-10, implying that a Th2 shift was induced by AG490. In addition, AG490-treated recipients had a significantly increased population of CD4+CD25+ T cells in their splenocytes on Day 6 after transplantation.

CONCLUSION

These findings suggest that treatment with AG490 prevents acute lung allograft rejection in rats. The effects of AG490 may contribute to development of CD4+CD25+ T cells and a Th2 shift of CD4+ T cells.

Role of H1 receptors in histamine-mediated up-regulation of STAT4 phosphorylation

Histamine shifts TH1/TH2 cytokine balance from TH1 to TH2 cytokines and regulates the function of lymphocytes after binding to histamine receptors. The phosphorylation of STAT factors and the translocation to the nucleus are important steps in the regulation of TH1/TH2 cytokine balance. This study was designed to investigate the effects of histamine on the phosphorylation of STAT4. C57BL/6 splenocytes were isolated and treated with histamine (10(-4) to 10(-9) M) after activation with either PMA (phorbol 12 myristate 13-acetate) plus ionomycin or IL-12. The phosphorylated STAT4 levels were analyzed by Western Blot Analysis. Unstimulated splenocytes expressed both STAT4 and phosphorylated STAT4. However, phosphorylated STAT4 gradually declined within 24 h. Histamine increased the phosphorylation of STAT4 at lower concentrations (10(-6) to 10(-9) M), and had no effect at higher concentrations (10(-4) and 10(-5) M) after the cells were stimulated with PMA + ionomycin. Histamine did not affect IL-12-induced phosphorylation of STAT4. To characterize the histamine receptor subtypes involved in the up-regulation of STAT4 phosphorylation, various H1, H2 and H3/H4 receptor antagonists and/or agonists were employed. H1 receptor agonist (betahistine), but not H2 receptor agonist (amthamine), induced phosphorylation of STAT4. H1 receptor antagonist (pyrilamine) inhibited histamine-mediated phosphorylation of STAT4. However, H2 receptor antagonist (ranitidine) and H3/H4 receptor antagonist (thioperamide) did not alter this effect. Tyrosine kinase inhibitor (tyrphostin) failed to block histamine-mediated phosphorylation of STAT4. These observations suggest that histamine up-regulated the phosphorylation of STAT4 via H1 receptors, and that the Ca2+-PKC pathway, but not the tyrosine kinase pathway, was involved in this effect.

The Mannich base NC1153 promotes long-term allograft survival and spares the recipient from multiple toxicities

JAK3 is a cytoplasmic tyrosine kinase with limited tissue expression but is readily found in activated T cells. Patients lacking JAK3 are immune compromised, suggesting that JAK3 represents a therapeutic target for immunosuppression. Herein, we show that a Mannich base, NC1153, blocked IL-2-induced activation of JAK3 and its downstream substrates STAT5a/b more effectively than activation of the closely related prolactin-induced JAK2 or TNF-alpha-driven NF-kappaB. In addition, NC1153 failed to inhibit several other enzymes, including growth factor receptor tyrosine kinases, Src family members, and serine/threonine protein kinases. Although NC1153 inhibited proliferation of normal human T cells challenged with IL-2, IL-4, or IL-7, it did not block T cells void of JAK3. In vivo, a 14-day oral therapy with NC1153 significantly extended survival of MHC/non-MHC mismatched rat kidney allografts, whereas a 90-day therapy induced transplantation tolerance (>200 days). Although NC1153 acted synergistically with cyclosporin A (CsA) to prolong allograft survival, it was not nephrotoxic, myelotoxic, or lipotoxic and did not increase CsA-induced nephrotoxicity. In contrast to CsA, NC1153 was not metabolized by cytochrome P450 3A4. Thus, NC1153 prolongs allograft survival without several toxic effects associated with current immunosuppressive drugs.

Suppressor of cytokine signaling-1 selectively inhibits LPS-induced IL-6 production by regulating JAK-STAT

Suppressor of cytokine signaling-1 (SOCS-1) is one of the negative-feedback regulators of Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling. We previously showed that SOCS-1 participates in LPS signaling, but it is not entirely clear yet how SOCS-1 suppresses LPS signaling. In this study, we demonstrate that SOCS-1 selectively inhibits LPS-induced IL-6 production through regulation of JAK-STAT but not production of TNF-alpha, granulocyte colony-stimulating factor, IFN-beta, and other cytokines. We found that LPS directly activated Jak2 and Stat5, whereas SOCS-1 inhibited LPS-induced Jak2 and Stat5 activation. Furthermore, AG490, a Jak-specific inhibitor, and dominant negative Stat5 only reduced LPS-induced IL-6 production. Additionally, Stat5 interacted with p50, resulting in recruitment of Stat5 to the IL-6 promoter together with p50 in response to LPS stimulation. These findings suggest that the JAK-STAT pathway participates in LPS-induced IL-6 production and that SOCS-1 suppresses LPS signaling by regulating JAK-STAT.

Janus kinase 3: a novel target for selective transplant immunosupression

Existing immunosuppressants inhibit lymphocyte activation and T cell cytokine signal transduction pathways, reducing the rate of acute rejection episodes to < 10%. However, the widespread tissue distribution of their molecular targets engenders pleiotropic toxicities. One strategy to address this problem seeks to identify compounds that selectively inhibit a target restricted in distribution to the lymphoid system. Janus kinase (Jak) 3 is such a molecule; it mediates signal transduction via the gamma common chain of lymphokine surface receptors. Disruption of this lymphoid-restricted enzyme would not be predicted to produce collateral damage in other organ systems. Development of selective Jak3 inhibitors has been difficult due to crossreactivity with its homologue, Jak2. In contrast to all other putative antagonists, which are discussed in detail herein, one Jak3 inhibitor, NC1153, shows at least 40-fold greater selective inhibition for Jak3 than for Jak2, is robustly synergistic with calcineurin antagonists, and, either alone or in combination with cyclosporin, produces no adverse effects in rodents preconditioned to be at heightened risk for nephrotoxicity, bone marrow suppression, or altered lipid metabolism.

Combinatorial approach to identification of tyrphostin inhibitors of cytokine signaling

Aberrant or deregulated activity of certain cellular kinases has been shown to cause certain malignancies and other disorders. The tyrphostin molecule AG490 inhibits the action of the janus kinases JAK2 and JAK3. JAK2 is an indispensable molecule for transducing the signals conveyed by a large number of cytokines including IL-3 while JAK3 is essential for signaling by a smaller number of cytokines including IL-7. A synthetic combinatorial chemical library containing 599 compounds was created and screened for the ability to inhibit proliferation of IL3- and IL7-dependent cell lines to focus on molecules that interrupt those signaling pathways. This screen identified a meta-trifluoromethyl derivative of AG490, 5H4, that is approximately twice as potent as AG490 in cell-based assays. 5H4 blocked the factor-dependent proliferation of both of these cell lines, actively promoted cell death, and diminished the JAK kinase activity. Administration of 5H4 to lymphoma-prone IL-7 transgenic mice reduced their spontaneous lymphadenopathy. The improved characteristics of this novel compound bring this class of molecules closer to therapeutic utility.

Inhibitors of tyrosine kinase inhibit the production of urokinase plasminogen activator in human prostatic cancer cells

Urokinase-type plasminogen activator (uPA) seems to be an important protease in prostate cancer invasion, and tyrosine phosphorylation is thought to play a role in the regulation of its production. The amount of uPA was measured with a synthetic peptide substrate after treatment with various concentrations of tyrosine kinase inhibitors (TKI). The effect on proliferation and apoptosis was also assayed. Non-toxic levels of genistein or the tyrphostin AG 490 produced up to 50% reduction of the uPA production in PC-3 and DU-145. The tyrphostins AG 1296 and AG 1478 inhibited uPA production in PC-3 cells, whereas DU-145 showed a slight increase of uPA production. TKI neither induced any detectable apoptosis, nor was there any reduction in proliferation rate. TKI can profoundly modify the production of uPA in prostatic cancer cells, thus indicating their possible use as suppressors of the invasive phenotype. The therapeutic potential of TKI warrants further investigation.

Ligation of RARgamma inhibits proliferation of phytohaemagglutinin-stimulated T-cells via down-regulating JAK3 protein levels

The mechanisms whereby Vitamin A regulates the immune system are poorly understood. We have shown previously that retinoic acids, the Vitamin A derivatives, promote both apoptosis of neglected thymocytes and the activation-induced cell death of peripheral T-cells via ligating the nuclear retinoid receptor (RAR) gamma. In the present study, we found that human peripheral T-cells express RARalpha and gamma, but not RARbeta. Increasing concentrations of 9-cis RA inhibited phytohaemagglutinin (PHA)-induced proliferation of T-cells, an effect that could be mimicked only by addition of RARgamma agonists and could be inhibited by an RARgamma antagonist. Interleukin-2 (IL-2) produced is known to mediate PHA-induced proliferation of T lymphocytes. Ligation of RARgamma did not affect the PHA-induced high affinity IL-2 receptor expression, slightly reduced the PHA-induced IL-2 production, but interfered with the IL-2-mediated signal transduction resulting in inhibition of PHA-induced phosphorylation of retinoblastoma protein and of up-regulation of Bcl-2. Janus kinases JAK1 and JAK3 play a determinant role in IL-2-dependent signal transduction. Ligation of RARgamma did not affect the levels of JAK1, but prevented IL-2-induced expression of JAK3 resulting in inhibition of PHA-induced phosphorylation of Stat5 molecules. Our data suggest that the previously observed toxic effect of high concentrations of retinoids on the immune system might be mediated via formation of 9-cis RA, which via ligation of RARgamma not only induces cell death in immature thymocytes, but inhibits proliferation of T-cells as well.