STATs as mediators of cytokine-induced responses

Docosahexaenoic acid and eicosapentaenoic acid reduce C-reactive protein expression and STAT3 activation in IL-6-treated HepG2 cells

C-reactive protein (CRP), an acute phase protein in humans, is predominantly produced by hepatocytes in response to interleukin-6 (IL-6). Several epidemiological studies have reported that dietary intake of n-3 polyunsaturated fatty acids (n-3 PUFAs) is inversely associated with serum CRP concentration. However, the molecular mechanism by which n-3 PUFAs reduce the serum CRP level in HepG2 cells remains unclear. The aims of this study were to examine the effect of the n-3 PUFAs, docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), on the modulation of IL-6-induced CRP expression and to explore its possible mechanisms. We demonstrated that DHA and EPA inhibited IL-6-induced CRP protein and mRNA expression, as well as reduced CRP promoter activity in HepG2 cells. Knockdown of Signal Transducer and Activator of Transcription 3 (STAT3) and CCAAT box/Enhancer-Binding Protein β (C/EBPβ) by small interfering RNAs (siRNAs) significantly decreased IL-6-induced CRP promoter activity. Gel electrophoresis mobility shift assays (EMSA) showed that pretreatment with DHA and EPA decreased IL-6-induced STAT3 DNA binding activity but not C/EBPβ. By western blot analysis, DHA and EPA inhibited IL-6-induced STAT3 phosphorylation but not ERK1/2 or C/EBPβ. The suppression of the phosphorylation of STAT3 by DHA and EPA was further verified by immunofluorescence staining. Taken together, our results demonstrate that DHA and EPA are able to reduce IL-6-induced CRP expression in HepG2 cells via an inhibition of STAT3 activation. This mechanism, which explains the inhibitory effect of n-3 PUFAs on the CRP expression, provides new insights into the beneficial anti-inflammatory effect of n-3 PUFAs.

Exogenous IL-10 down-regulates STAT3 expression in pancreatic and hepatic tissue of rats with acute necrotizing pancreatitis

AIM: To investigate the effect of treatment with exogenous interleukin-10 (IL-10) on the expression of signal transducer and activator of transcription3 (STAT3) in pancreatic and hepatic tissue of rats with acute necrotizing pancreatitis (ANP).

METHODS: Ninety-two male Sprague-Dawley rats were divided randomly into three groups: control group (n = 24), ANP group (n = 36), and IL-10 group (n = 32). ANP was induced in rats by intraperitoneal injection (ip) of L-arginine. The IL-10 group was treated with 10 000 units of recombinant human IL-10 (rhIL-10) by ip at 2, 5, and 8 h after the last L-arginine injection. Rats were killed at 4, 12, 24, and 36 h after the last L-arginine injection. Pancreatic and hepatic histopathological changes were scored, and the expression of STAT3 was detected by immunohistochemical (IHC) staining.

RESULTS: Pancreatic and hepatic histopathological scores at all time points were significantly higher in the ANP group and IL-10 group than in the control group (all P < 0.01 or 0.05). Compared to the ANP group, pancreatic histopathological scores at 12, 24, and 36 h and hepatic histopathological score at 24 h were significantly lower in the IL-10 group (all P < 0.05 or 0.01). The expression levels of STAT3 in pancreatic and hepatic tissue at all time points were significantly lower in the ANP group and IL-10 group than in the control group (all P < 0.01). The expression levels of STAT3 in pancreatic (12 h: 174.61 ± 6.25 vs 146.10 ± 10.51; 24 h: 178.55 ± 10.36 vs 150.63 ± 9.11; 36 h: 193.37 ± 21.54 vs 155.55 ± 11.70, all P < 0.01 or 0.05) and hepatic tissue (24 h: 89.88 ± 18.89 vs 38.85 ± 10.27; 36 h: 48.79 ± 15.38 vs 23.51 ± 5.67, all P < 0.01) were significantly higher in the IL-10 group than in the ANP group.

CONCLUSION: STAT3 may be involved in the early inflammatory response to ANP. Exogenous IL-10 could improve pancreatic and hepatic tissue injury in ANP rats possibly by down-regulating STAT3 expression.

Oligonucleotide based-strategies for allergy with special reference to siRNA

BACKGROUND

Allergic diseases are a significant global health care problem. Current pharmacological approaches address symptoms but do not alter the underlying immune dysregulation. Current allergen-specific immunotherapy has several drawbacks. Therefore, approaches that attenuate allergic responses safely and effectively at the level of upstream causative events are desirable. Oligonuleotide-based therapies [CpG DNA, antisense oligonucleotides, and small interfering RNA (siRNA)] are promising approaches.

OBJECTIVE/METHODS

We review developments in oligonucleotide-based therapies and the potential of siRNA for treating allergy.

RESULTS/CONCLUSIONS

Strategies with oligonucleotides basically aim to reduce T helper type 2 (Th2) responses. It is controversial whether the reduction of Th2 responses does, in fact, attenuate allergic diseases. Increased understanding of allergic mechanisms will enhance the efficacy of oligonucleotide-based therapy.

Microarray analysis of IFN-gamma response genes in astrocytes

IFN-gamma (IFN-gamma) has been shown to activate astrocytes to acquire immune functions. In this study the effect of IFN-gamma on murine astrocytes was investigated via microarray analysis. The activating effect of IFN-gamma on the astrocyte transcriptome showed predominance toward pathways involved in adaptive immunity, initiation of the immune response and innate immunity. Previously unknown astrocytic genes expressed included members of the p47 GTPases and guanine nucleotide binding protein (GBP) families. Down-regulatory effects of IFN-gamma stimulation were confined to pathways involved in growth regulation, cell differentiation and cell adhesion. This data supports the notion that astrocytes are an important immunocompetant cell in the brain and indicate that astrocytes may have a significant role in various infectious diseases such as Toxoplasmic Encephalitis and neurological diseases with an immunological component such as Alzheimer's and autoimmune disorders.

Neurotrophins and neurotrophin receptors in allergic asthma

The neurotrophins nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3 (NT-3) and NT-4 play a pivotal role in the development of the nervous system. Despite their well-known effects on neurons, elevated neurotrophin concentrations have been observed under pathological conditions in sera of patients with inflammatory disorders. Patients with asthma feature both airway inflammation and an abnormal airway reactivity to many unspecific stimuli, referred to as airway hyperresponsiveness, which is, at least partly, neuronally controlled. Interestingly, these patients show increased levels of neurotrophins in the blood as well as locally in the lung. It has been demonstrated that neurotrophin release from immune cells is triggered by allergen contact. The presence of neurotrophins and the neurotrophin receptors p75 (p75NTR), tyrosine kinase A (TrkA), TrkB and TrkC have been described in several immune cells. There is strong evidence for an involvement of neurotrophins in regulation of hematopoiesis and, in addition, in modulation of immune cell function in mature cells circulating in blood or resting in lymphatic organs and peripheral tissues. The aim of this review is to demonstrate possible roles of neurotrophins during an allergic reaction in consideration of the temporospatial compartimentalization.

IL-4 synergistically enhances both IL-2- and IL-12-induced IFN-gamma expression in murine NK cells

Interleukin-4 (IL-4) is thought to influence T and natural killer (NK) cells by down-regulating T helper 1 (Th1)-type cytokines like interferon-gamma (IFN-gamma). While investigating IL-4 regulation of IFN-gamma expression, we found that IL-4 synergized with IL-2 or IL-12 to enhance IFN-gamma production and mRNA expression in spleen-derived, IL-2-cultured NK cells, as well as negatively sorted fresh DX5+/CD3- NK cells albeit at lower levels. The positive effect of IL-4 on IL-2-induced IFN-gamma production was dependent upon signal transducer and activator of transcription 6 (Stat6) because this response was virtually abrogated in Stat6-/- mice. Notably, though, IL-12 plus IL-4 synergy on IFN-gamma expression was intact in Stat6-/- mice. In exploring possible molecular mechanisms to account for the synergistic effects of IL-4 on murine NK cells, we found that IL-2 plus IL-4 stimulation resulted in a modest increase in tyrosine phosphorylation of Stat5, while IL-12 plus IL-4 treatment resulted in a more substantial increase in tyrosine-phosphorylated Stat4. Finally, to identify regions of the IFN-gamma promoter that may be involved, NK cells from human IFN-gamma promoter/luciferase transgenic mice were treated with cytokines. NK cells from proximal (-110 to +64) promoter region mice did not respond to cytokine stimulation; however, the intact -565 to +64 IFN-gamma promoter responded synergistically to IL-2 plus IL-4 and to IL-12 plus IL-4 in NK cells. These data demonstrate a role for IL-4 in enhancing IFN-gamma expression in murine NK cells that is partially dependent on Stat6 in IL-2 costimulation and completely independent of Stat6 in IL-12 costimulations.

Conditionally immortalized cell line of inducible metanephric mesenchyme

BACKGROUND

The mesenchymal-epithelial conversion of metanephric mesenchyme (MM) in the formation of nephronic tubules has long served as a paradigm for inductive signaling in morphogenesis. However, the mechanisms underlying this differentiation have remained an enigma due to insufficient numbers of primary mesenchymal cells that must be isolated manually from animal embryos. To overcome this problem, we have established a conditionally immortalized cell line, the rat-inducible metanephric mesenchyme (RIMM-18) by transfection of primary mesenchymal cells with a vector, encoding an estradiol-dependent E1A-ER fusion protein.

METHODS

Reverse transcription-polymerase chain reaction (RT-PCR), luciferase reporter assay, electrophoretic mobility shift assay, immunocytochemical, and immunohistochemical stainings were used to characterize the established cell line.

RESULTS

We demonstrate that in the presence of estradiol, the RIMM-18 cell line proliferates continuously, maintaining mesenchymal characteristics for over 40 passages. These cells are vimentin-positive and cytokeratin-negative. Under inductive conditions in the absence of estradiol, they are responsive to a number of cytokines, which are established inducers of mesenchymal cells in vivo and in vitro [i.e., fibroblast growth factor 2 (FGF2), leukemia inhibitory factor (LIF), and transforming growth factor-beta 2 (TGF-beta 2)]. We show the presence in RIMM-18 cells of specific protein markers and functionally active signaling pathways required for induction of tubule formation in MM. Furthermore, induced RIMM-18 cells change morphology, acquiring epithelial-like features, and begin to express epithelial markers (e.g., E-cadherin, cytokeratin, gamma-glutamyl-transpeptidase, and secreted frizzled-related protein 2 (sFRP2).

CONCLUSION

This preliminary characterization of the RIMM-18 cell line suggests that it will be useful in the study of biochemical and molecular mechanisms of nephronic development and, possibly, of some types of renal cancer such as Wilms' tumor, which caricatures the normal process of kidney development.

Cytokine memory of T helper lymphocytes

Memory is one of the key features of the adaptive immune system. Specific T and B lymphocytes are primed for a particular antigen and upon challenge with it will react faster than naive lymphocytes. They also memorize the expression of key effector molecules, in particular cytokines, which determine the type and scale of an immune reaction. While in primary activations differential expression of cytokine genes is dependent on antigen-receptor signaling and differentiation signals, in later activations the expression is triggered by antigen-receptor signaling and dependent on the cytokine memory. The molecular basis of the cytokine memory implies differential expression of transcription factors and epigenetic modifications of cytokine genes and gene loci. GATA-3 for Th2 and T-bet for Th1 cells expressing interleukin-4 or interferon-gamma, respectively, are prime candidates for key transcription factors of cytokine memory. The essential role of epigenetic modifications is suggested by the requirement of DNA synthesis for the establishment of a cytokine memory in Th lymphocytes. At present the molecular link between transcription factors and epigenetic modifications of cytokine genes in the establishment and maintenance of cytokine memory is not clear. The initial cytokine memory is not stable against adverse differentiation signals, while in repeatedly stimulated lymphocytes it is stabilized by a variety of mechanisms.

Interleukin-4-mediated protection of primary B cells from apoptosis through Stat6-dependent up-regulation of Bcl-xL

Apoptosis is an integral aspect of B lymphocyte development and homeostasis and is regulated by the engagement of antigen costimulatory and cytokine receptors. Although it is well established that interleukin 4 (IL-4) is a potent anti-apoptotic cytokine for B lymphocytes, little is known about the IL-4-induced molecular events regulating cell survival. Stat6 is rapidly activated after IL-4 stimulation, but its role in B lymphocyte apoptosis has not been explored. In this report we demonstrate that Stat6 is a critical signaling molecule for IL-4 in protecting primary B cells from passive and Fas-induced cell death. We show that expression of the Bcl-2 family member, Bcl-xL, is induced maximally by IL-4 and anti-IgM/IL-4 in a Stat6-dependent manner. Additionally, we demonstrate that bcl-xL transcription is likely to be directly activated through a Stat6 binding site in the bcl-xL-flanking region. Finally, reconstitution of Stat6-deficient splenic B cells with Bcl-xL was able to protect those cells from Fas-induced cell death. These results suggest that the anti-apoptotic activity of IL-4 in B cells is mediated through the activation of Stat6 and subsequent transcription of Bcl-xL.

The ribosomal S6 kinases, cAMP-responsive element-binding, and STAT3 proteins are regulated by different leukemia inhibitory factor signaling pathways in mouse embryonic stem cells

Mouse embryonic stem (ES) cells remain "pluripotent" in vitro in the continuous presence of leukemia inhibitory factor (LIF). In the absence of LIF, ES cells are irreversibly committed to differentiate into various lineages. In this study we have set up an in vitro assay based on the anti-apoptotic activity of LIF to distinguish pluripotent from "differentiation-committed" ES cells. We have examined the phosphorylation profiles of known (STAT3 and ERKs) and identified new (ribosomal S6 kinases (RSKs) and cAMP-responsive element-binding protein (CREB)) LIF-regulated targets in ES and in ES-derived neuronal cells. We have demonstrated that although STAT3, a crucial player in the maintenance of ES cell pluripotency, is induced by LIF in all cell types tested, the LIF-dependent activation of RSKs is restricted to ES cells. We have shown that LIF-induced phosphorylation of RSKs in ES cells is dependent on ERKs, whereas STAT3 phosphorylation is not mediated by any known MAPK activities. Our results also demonstrate that the LIF-dependent phosphorylation of CREB is partially under the control of the RSK2 kinase.

Simultaneous tyrosine and serine phosphorylation of STAT3 transcription factor is involved in Rho A GTPase oncogenic transformation

Stats (signal transducers and activators of transcription) are latent cytoplasmic transcription factors that on a specific stimulus migrate to the nucleus and exert their transcriptional activity. Here we report a novel signaling pathway whereby RhoA can efficiently modulate Stat3 transcriptional activity by inducing its simultaneous tyrosine and serine phosphorylation. Tyrosine phosphorylation is exerted via a member of the Src family of kinases (SrcFK) and JAK2, whereas the JNK pathway mediates serine phosphorylation. Furthermore, cooperation of both tyrosine as well as serine phosphorylation is necessary for full activation of Stat3. Induction of Stat3 activity depends on the effector domain of RhoA and correlates with induction of both Src Kinase-related and JNK activities. Activation of Stat3 has biological implications. Coexpression of an oncogenic version of RhoA along with the wild-type, nontransforming Stat3 gene, significantly enhances its oncogenic activity on human HEK cells, suggesting that Stat3 is an essential component of RhoA-mediated transformation. In keeping with this, dominant negative Stat3 mutants or inhibition of its tyrosine or serine phosphorylation completely abrogate RhoA oncogenic potential. Taken together, these results indicate that Stat3 is an important player in RhoA-mediated oncogenic transformation, which requires simultaneous phosphorylation at both tyrosine and serine residues by specific signaling events triggered by RhoA effectors.

Enhanced survival of lung granulocytes in an animal model of asthma: evidence for a role of GM-CSF activated STAT5 signalling pathway

BACKGROUND

As granulocyte/macrophage colony stimulating factor (GM-CSF) mediated delay of granulocyte apoptosis contributes to the accumulation of inflammatory cells at the site of inflammation in many diseases, we sought to determine whether asthma is also associated with a GM-CSF dependent increase in lung granulocyte survival. Moreover, because GM-CSF mediates its effects through activation of signal transducer and activator of transcription 5 (STAT5), we also investigated the potential role of STAT5 in allergic inflammation.

METHODS

Blood granulocytes were recovered from six healthy and six heaves affected horses, a model of asthma. Lung granulocytes were obtained by bronchoalveolar lavage (BAL) from the same horses. Granulocytes were cultured in the presence or absence of anti-GM-CSF receptor antibodies for different times and apoptosis was determined using the Annexin-V/propidium iodide detection method. Nuclear protein extracts from cultured granulocytes were analysed for STAT5 binding activity by electrophoretic mobility shift assay.

RESULTS

BAL fluid granulocytes from heaves affected horses demonstrated a significant delay in apoptosis compared with blood granulocytes from the same horses and blood and BAL fluid granulocytes from healthy horses. Conversely, the rate of apoptosis in blood granulocytes from healthy and heaves affected horses was comparable. The enhanced survival of BAL fluid granulocytes from affected horses was suppressed in the presence of antibodies directed against GM-CSF receptors. Increased levels of active STAT5 were found in BAL fluid granulocytes from heaves affected horses and were markedly reduced after treatment with anti-GM-CSF receptor antibodies.

CONCLUSIONS

These data indicate that granulocyte survival is enhanced in the lung of heaves affected horses and suggest a role for a GM-CSF activated STAT5 pathway in delaying apoptosis of lung granulocytes in this model of asthma.

Enhanced survival of lung granulocytes in an animal model of asthma: evidence for a role of GM-CSF activated STAT5 signalling pathway

BACKGROUND

As granulocyte/macrophage colony stimulating factor (GM-CSF) mediated delay of granulocyte apoptosis contributes to the accumulation of inflammatory cells at the site of inflammation in many diseases, we sought to determine whether asthma is also associated with a GM-CSF dependent increase in lung granulocyte survival. Moreover, because GM-CSF mediates its effects through activation of signal transducer and activator of transcription 5 (STAT5), we also investigated the potential role of STAT5 in allergic inflammation.

METHODS

Blood granulocytes were recovered from six healthy and six heaves affected horses, a model of asthma. Lung granulocytes were obtained by bronchoalveolar lavage (BAL) from the same horses. Granulocytes were cultured in the presence or absence of anti-GM-CSF receptor antibodies for different times and apoptosis was determined using the Annexin-V/propidium iodide detection method. Nuclear protein extracts from cultured granulocytes were analysed for STAT5 binding activity by electrophoretic mobility shift assay.

RESULTS

BAL fluid granulocytes from heaves affected horses demonstrated a significant delay in apoptosis compared with blood granulocytes from the same horses and blood and BAL fluid granulocytes from healthy horses. Conversely, the rate of apoptosis in blood granulocytes from healthy and heaves affected horses was comparable. The enhanced survival of BAL fluid granulocytes from affected horses was suppressed in the presence of antibodies directed against GM-CSF receptors. Increased levels of active STAT5 were found in BAL fluid granulocytes from heaves affected horses and were markedly reduced after treatment with anti-GM-CSF receptor antibodies.

CONCLUSIONS

These data indicate that granulocyte survival is enhanced in the lung of heaves affected horses and suggest a role for a GM-CSF activated STAT5 pathway in delaying apoptosis of lung granulocytes in this model of asthma.

Stat5a regulates T helper cell differentiation by several distinct mechanisms

We have previously shown that CD4(+) T cell-mediated allergic inflammation is diminished in signal transducer and activator of transcription (Stat)5a-deficient (Stat5a(-/-)) mice. To determine whether Stat5a regulates T helper cell differentiation, we studied T helper (Th)1 and Th2 cell differentiation of Stat5a(-/-)CD4(+) T cells at single-cell levels. First, Th2 cell differentiation from antigen-stimulated splenocytes was significantly decreased in Stat5a(-/-) mice as compared with that in wild-type mice. Further, Th2 cell differentiation was also impaired in Stat5a(-/-) mice even when purified CD4(+) T cells were stimulated with anti-CD3 plus anti-CD28 antibodies in the presence of interleukin-4. Moreover, the retrovirus-mediated gene expression of Stat5a in Stat5a(-/-)CD4(+) T cells restored the Th2 cell differentiation at the similar levels to that in wild-type CD4(+) T cells. In addition, interleukin-4 normally phosphorylated Stat6 in CD4(+) T cells from Stat5a(-/-) mice. Second, the development of CD4(+)CD25(+) immunoregulatory T cells was impaired in Stat5a(-/-) mice, as indicated by a significant decrease in the number of CD4(+)CD25(+) T cells in Stat5a(-/-) mice. Furthermore, the depletion of CD4(+)CD25(+) T cells from wild-type splenocytes significantly decreased Th2 cell differentiation but increased Th1 cell differentiation, whereas the depletion of CD4(+)CD25(+) T cells from Stat5a(-/-) splenocytes had no significant effect on the Th1 and Th2 cell differentiation. Together, these results indicate that the intrinsic expression of Stat5a in CD4(+) T cells is required for Th2 cell differentiation and that Stat5a is involved in the development of CD4(+)CD25(+) immunoregulatory T cells that modulate T helper cell differentiation toward Th2 cells.

STAT expression and localization in the central nervous system during autoimmune encephalomyelitis in Lewis rats

Autoimmune inflammation in the central nervous system (CNS) is maintained by secretion of a large number of cytokines. To elucidate its molecular mechanisms, we examined the expression and localization of STAT1, STAT3, STAT4 and STAT6 molecules, which are the downstream molecules of the cytokine signal transduction pathway, in the CNS during acute experimental autoimmune encephalomyelitis (EAE) induced in Lewis rats. Western blot analysis demonstrated that STAT1 protein increased gradually till the recovery stage, whereas STAT4 protein showed abrupt increase at the early stage followed by gradual decrease. STAT3 and STAT6 showed stable expression throughout the course of the disease. The kinetics of the phosphorylated form of STAT1 and STAT4 roughly paralleled that of the total protein although the peak of STAT3 phosphorylation was recognized at the preclinical stage. Immunohistochemical examinations revealed that STAT3 and STAT4, but not STAT1 and STAT6, immunoreactivities were mainly expressed in astrocytes and microglia, respectively, and were closely associated with inflammatory lesions. Taken together, these findings suggest that STAT3 and STAT4 play an important role in the formation of, and recovery from, autoimmune inflammation in the CNS.

The direct effect of IL-12 on tumor cells: IL-12 acts directly on tumor cells to activate NF-kappaB and enhance IFN-gamma-mediated STAT1 phosphorylation

IL-12 directly acts on T cells and NK cells to induce IFN-gamma production. IFN-gamma plays an important role in anti-tumor effect of IL-12. In spite of various functions of IL-12 on immunocytes, the direct effect of IL-12 on tumor cells has not been fully clarified. The present study investigated the direct effect of IL-12 on eight murine tumor cell lines in vitro. IL-12 did not directly up-regulate expression of MHC class I on tumor cells, but enhanced IFN-gamma-induced up-regulation of MHC class I expression in MC-38, MCA102, MCA205 and MCA207 cells. IL-12 alone did not activate STAT1, but IL-12 enhanced IFN-gamma-mediated STAT1 phosphorylation in MC-38, MCA102, MCA205, MCA207 and Colon-26-NL-17 cells, which expressed IL-12 receptor beta1 mRNA. In the other side, Panc-02, B16-BL6 and 266-6 cells were not affected by IL-12, in which expression of IL-12 receptor beta1 mRNA was not detected. Anti-IL-12 mAb inhibited the direct effect of IL-12 on MC-38 cells. Moreover, nuclear localization of NF-kappaB was observed after stimulation of IL-12 or IL-12 p40 in MC-38 and Colon-26-NL-17 cells, but not in Panc-02 cells. These findings suggest that IL-12 directly acts on tumor cells through IL-12 receptor beta1 to activate NF-kappaB and enhance IFN-gamma-mediated STAT1 phosphorylation.

Leukemia inhibitory factor enhances mast cell growth in a mast cell/fibroblast co-culture system through stat3 signaling pathway of fibroblasts

Leukemia inhibitory factor (LIF) enhanced mast cell growth in a mast cell/3T3 fibroblast co-culture system, however the precise mechanisms have not been defined. Western blot analysis showed that bone marrow-derived mast cells failed to express both LIF receptor (LIFR) and gp130, whereas 3T3 fibroblasts expressed both LIFR and gp130. This result indicates that the activity of LIF for mast cell growth is mediated by 3T3 fibroblasts. Signal transducer and activator of transcription (Stat) 3-transfected 3T3 fibroblasts enhanced mast cell growth. In addition, dominant-negative Stat3-transfected fibroblasts blocked LIF-mediated mast cell growth in the co-culture system. In conclusion, LIF-induced mast cell growth in the co-culture system is mediated by an indirect pathway via 3T3 fibroblasts through activating Stat3 signaling pathway in 3T3 fibroblasts.

Jaks and stats as therapeutic targets

Cytokines have critical functions in regulating immune responses. A large number of these factors bind related receptors termed the Type I and Type II families of cytokine receptors. These receptors activate Janus kinases (Jaks) and Stat family of transcription factors. The essential and specific function of Jaks and Stats is particularly well illustrated by human and mouse mutations. The possibility that these molecules could be targeted to produce novel immunosuppressive compounds is considered in this review.

T cell receptor-induced calcineurin activation regulates T helper type 2 cell development by modifying the interleukin 4 receptor signaling complex

The activation of downstream signaling pathways of both T cell receptor (TCR) and interleukin 4 receptor (IL-4R) is essential for T helper type 2 (Th2) cell development, which is central to understanding immune responses against helminthic parasites and in allergic and autoimmune diseases. However, little is known about how these two distinct signaling pathways cooperate with each other to induce Th2 cells. Here, we show that successful Th2 cell development depends on the effectiveness of TCR-induced activation of calcineurin. An inhibitor of calcineurin activation, FK506, inhibited the in vitro anti-TCR-induced Th2 cell generation in a dose-dependent manner. Furthermore, the development of Th2 cells was significantly impaired in naive T cells from dominant-negative calcineurin Aalpha transgenic mice, whereas that of Th1 cells was less affected. Efficient calcineurin activation in naive T cells upregulated Janus kinase (Jak)3 transcription and the amount of protein. The generation of Th2 cells induced in vitro by anti-TCR stimulation was inhibited significantly by the presence of Jak3 antisense oligonucleotides, suggesting that the Jak3 upregulation is an important event for the Th2 cell development. Interestingly, signal transducer and activator of transcription (STAT)5 became physically and functionally associated with the IL-4R in the anti-TCR-activated developing Th2 cells that received efficient calcineurin activation, and also in established cloned Th2 cells. In either cell population, the inhibition of STAT5 activation resulted in a diminished IL-4-induced proliferation. Moreover, our results suggest that IL-4-induced STAT5 activation is required for the expansion process of developing Th2 cells. Thus, Th2 cell development is controlled by TCR-mediated activation of the Ca(2+)/calcineurin pathway, at least in part, by modifying the functional structure of the IL-4R signaling complex.

The biology of Stat4 and Stat6

IL-4 and IL-12 are cytokines that are important regulators of the proliferation, differentiation and functional capacity of lymphocytes. STATs (signal transducers and activators of transcription) are transcription factors that provide a direct link between the cytokine receptors and cytokine induced gene transcription. Stat6 and Stat4 are two STAT family members that specifically mediate signals that emanate from the IL-4 and IL-12 receptors, respectively. Recently a great deal of progress has been made in understanding the specific roles that Stat6 and Stat4 play in lymphocyte function through in vitro as well as in vivo studies using Stat6 and Stat4-deficient mice. This report will summarize and describe the recent advances made in understanding the activation and regulation of Stat6 and Stat4 as well as their roles in the development of an immune response. Oncogene (2000).

Janus kinases and signal transducers and activators of transcription: their roles in cytokine signaling, development and immunoregulation

Cytokines play a critical role in the normal development and function of the immune system. On the other hand, many rheumatologic diseases are characterized by poorly controlled responses to or dysregulated production of these mediators. Over the past decade tremendous strides have been made in clarifying how cytokines transmit signals via pathways using the Janus kinase (Jak) protein tyrosine kinases and the Signal transducer and activator of transcription (Stat) proteins. More recently, research has focused on several distinct proteins responsible for inhibiting these pathways. It is hoped that further elucidation of cytokine signaling through these pathways will not only allow for a better comprehension of the etiopathogenesis of rheumatologic illnesses, but may also direct future treatment options.