Janus Tyrosine Kinase/signal Transducer And Activator Of Transcription Research Articles

JAK/STAT signaling regulated intestinal regeneration defends insect pests against pore-forming toxins produced by Bacillus thuringiensis.

A variety of coordinated host-cell responses are activated as defense mechanisms against pore-forming toxins (PFTs). Bacillus thuringiensis (Bt) is a worldwide used biopesticide whose efficacy and precise application methods limits its use to replace synthetic pesticides in agricultural settings. Here, we analyzed the intestinal defense mechanisms of two lepidopteran insect pests after intoxication with sublethal dose of Bt PFTs to find out potential functional genes. We show that larval intestinal epithelium was initially damaged by the PFTs and that larval survival was observed after intestinal epithelium regeneration. Further analyses showed that the intestinal regeneration caused by Cry9A protein is regulated through c-Jun NH (2) terminal kinase (JNK) and Janus tyrosine kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathways. JAK/STAT signaling regulates intestinal regeneration through proliferation and differentiation of intestinal stem cells to defend three different Bt proteins including Cry9A, Cry1F or Vip3A in both insect pests, Chilo suppressalis and Spodoptera frugiperda. Consequently, a nano-biopesticide was designed to improve pesticidal efficacy based on the combination of Stat double stranded RNA (dsRNA)-nanoparticles and Bt strain. This formulation controlled insect pests with better effect suggesting its potential use to reduce the use of synthetic pesticides in agricultural settings for pest control.

Suppression of NK Cell Activation by JAK3 Inhibition: Implication in the Treatment of Autoimmune Diseases.

Natural killer (NK) cell is an essential cytotoxic lymphocyte in our innate immunity. Activation of NK cells is of paramount importance in defending against pathogens, suppressing autoantibody production and regulating other immune cells. Common gamma chain (γc) cytokines, including IL-2, IL-15, and IL-21, are defined as essential regulators for NK cell homeostasis and development. However, it is inconclusive whether γc cytokine-driven NK cell activation plays a protective or pathogenic role in the development of autoimmunity. In this study, we investigate and correlate the differential effects of γc cytokines in NK cell expansion and activation. IL-2 and IL-15 are mainly responsible for NK cell activation, while IL-21 preferentially stimulates NK cell proliferation. Blockade of Janus tyrosine kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway by either JAK inhibitors or antibodies targeting γc receptor subunits reverses the γc cytokine-induced NK cell activation, leading to suppression of its autoimmunity-like phenotype in vitro. These results underline the mechanisms of how γc cytokines trigger autoimmune phenotype in NK cells as a potential target to autoimmune diseases.

Thymoquinone Inhibits JAK/STAT and PI3K/Akt/ mTOR Signaling Pathways in MV4-11 and K562 Myeloid Leukemia Cells.

Constitutive activation of Janus tyrosine kinase-signal transducer and activator of transcription (JAK/STAT) and Phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin (PI3K/Akt/mTOR) signaling pathways plays a crucial role in the development of acute myeloid leukemia (AML) and chronic myeloid leukemia (CML). Thymoquinone (TQ), one of the main constituents of Nigella sativa, has shown anti-cancer activities in several cancers. However, the inhibitory effect mechanism of TQ on leukemia has not been fully understood. Therefore, this study aimed to investigate the effect of TQ on JAK/STAT and PI3K/Akt/mTOR pathways in MV4-11 AML cells and K562 CML cells. FLT3-ITD positive MV4-11 cells and BCR-ABL positive K562 cells were treated with TQ. Cytotoxicity assay was assessed using WSTs-8 kit. The expression of the target genes was evaluated using RT-qPCR. The phosphorylation status and the levels of proteins involved in JAK/STAT and PI3K/Akt/mTOR pathways were investigated using Jess western analysis. TQ induced a dose and time dependent inhibition of K562 cells proliferation. TQ significantly downregulated PI3K, Akt, and mTOR and upregulated PTEN expression with a significant inhibition of JAK/STAT and PI3K/Akt/mTOR signaling. In conclusion, TQ reduces the expression of PI3K, Akt, and mTOR genes and enhances the expression of PTEN gene at the mRNA and protein levels. TQ also inhibits JAK/STAT and PI3K/Akt/mTOR pathways, and consequently inhibits proliferation of myeloid leukemia cells, suggesting that TQ has potential anti-leukemic effects on both AML and CML cells.

Loss of zinc-finger protein 143 contributes to tumour progression by interleukin-8-CXCR axis in colon cancer.

Several studies have shown that expression of zinc‐finger protein 143 (ZNF143) is closely related to tumour progression including colon cancer. However, it remains unclear how ZNF143 expression is related to tumour progression within the tumour microenvironment. Here, we investigated whether ZNF143 expression affects the tumour microenvironment and tumour progression by screening molecules secreted by colon cancer cells stably expressing short‐hairpin RNAs against ZNF143 or control RNAs. We observed that secretion of interleukin (IL)‐8 was increased when ZNF143 expression was reduced in two colon cancer cell lines. The mRNA and protein levels of IL‐8 were increased in cells following ZNF143 knockdown, and this effect was reversed when ZNF143 expression was restored. The Janus tyrosine kinase/signal transducer and activator of transcription (JAK/STAT) and extracellular signal‐regulated kinase pathways were also shown to contribute to IL‐8 expression in ZNF143‐knockdown cells. The expression levels of ZNF143 and IL‐8 were inversely correlated with three‐dimensionally grown spheroids and colon cancer tissues. THP‐1 cells were differentiated when cells were incubated with condition media from colon cancer cell with less ZNF143, drastically. Loss of ZNF143 may contribute to the development of colon cancer by regulating intracellular and intercellular signalling for cell plasticity and the tumour microenvironment respectively.

Analysis of long non-coding RNA expression profiles in neonatal rats with hypoxic-ischemic brain damage.

Hypoxic-ischemic brain damage (HIBD) which is a common cause of acute mortality and neurological dysfunction in neonates still lacks effective therapeutic methods. Long non-coding RNAs (lncRNAs) were demonstrated to play a crucial role in many diseases. To give a foundation for subsequent functional studies of lncRNAs in HIBD, we investigated the profiling of lncRNAs and messenger RNAs (mRNAs) using neonatal HIBD rat model. Six neonatal rats were divided into sham-operated group (n=3) and HIBD group (n=3) randomly. Deep RNA sequencing was implemented to find out the meaningful lncRNAs and mRNAs. Quantitative real-time PCR was used to validate expressions of lncRNAs and mRNAs. The Gene Ontology (GO) and kyoto encyclopedia of genes a genomes (KEGG) database were used to predict functions of lncRNAs. A total of 328 differentially expressed lncRNAs (177 down-regulated vs 151 up-regulated) and 7157 differentially expressed mRNAs (2552 down-regulated vs 4605 up-regulated) were identified. The Quantitative real-time PCR results showed significant differential expressions of five lncRNAs and five mRNAs which were consistent with the RNA-Seq data. Gene ontology and KEGG analysis showed these lncRNAs and their expression-correlated mRNAs were closely related to the Janus tyrosine kinase-signal transducer and activator of transcription (JAK-STAT) signaling pathway, NF-kappa B signaling pathway, Toll-like receptor signaling pathway, calcium signaling pathway, Notch signaling pathway, mitogen activated protein kinase signaling pathway, neuroactive ligand-receptor interaction pathway and more. The results of our study identified the characterization and expression profiles of lncRNAs in neonatal HIBD and may be a basis for further therapeutic research. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* and *Open Data* because it provided all relevant information to reproduce the study in the manuscript and because it made the data publicly available. The data can be accessed at https://osf.io/yf3da/. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

Transcription analysis of the interaction between chicken thymus and recombinant avian leukosis virus isolate FJ15HT0

Avian leukosis virus (ALV) induces multiple avian tumors, growth decrease and immune suppression. Previously, a novel natural recombinant ALV isolate FJ15HT0 was proven to be associated with significant body weight decrease, immune suppression and lymphocytoma in infected SPF chickens. In order to uncover the interaction between virus and host, we compared differences in the transcriptomes of the thymuses from the mock chickens and simulated congenitally infected chickens at 5days (d), 13d and 21d of age by RNA-seq analysis of the thymuses. Signaling pathways including cytokine–cytokine receptor interactions, peroxisome proliferator-activated receptor (PPAR) signaling pathway, Janus tyrosine kinase/signal transducers and activators of transcription (Jak-STAT) signaling pathway and fatty acid degradation were involved in the interaction between FJ15HT0 and SPF chickens. Interestingly, fold change of ciliary neurotrophic factor receptor α (CNTFRα) in infected donor collected from 2d to 21d showed a significant positive correlation with the corresponding expression of the viral gp85 gene in thymuses (r=0.656, P<0.01) and in livers (r=0.525, P<0.05). It will provide new insights for the molecular pathogenesis of ALV infection.

Human cytokines activate JAK–STAT signaling pathway in porcine ocular tissue

BackgroundThe JAK/STAT (Janus Tyrosine Kinase, Signal Transducers and Activators of Transcription) pathway is associated with cytokine or growth factor receptors and it is critical for growth control, developmental regulation and homeostasis. The use of porcine ocular cells as putative xenotransplants appears theoretically possible. The aim of this study was to investigate the response of various porcine ocular cells in vitro to human cytokines in regard to the activation of JAK-STAT signaling pathways.MethodsPorcine lens epithelial cells, pigmented iris epithelial cells and pigmented ciliary body cells were used in this study. These cells were isolated from freshly enucleated porcine eyes by enzymatic digestion. Cultured cells between passages 3–8 were used in all experiments. Electromobility shift assay (EMSA), proliferation assay, immunofluorescence staining and flow cytometry were used to evaluate the JAK-STAT signaling pathway in these cells.ResultsJAK/STAT signaling pathways could be activated in porcine pigmented epithelial ciliary body cells, in pigmented iris epithelial cells and in lens epithelial cells in response to porcine and human interferons and cytokines. All cells showed very strong STAT1 activation upon stimulation with porcine interferon-gamma. Porcine ocular cells also respond to human cytokines; IFN-alpha induced strong activation of STAT1 in EMSA, flow cytometry and immunofluorescence experiments whereas activation of STAT3 was less strong in EMSA, but strong in flow cytometry and immunofluorescence. Human recombinant IL-6 activated STAT3 and human IL-4 activated STAT6. With the help of immunofluorescence assay and flow cytometry we observed nuclear localization of STAT proteins after activation of porcine ocular cells with cytokines and interferons. Human IFN-α had an inhibitory effect on porcine ocular cells in proliferation assays.ConclusionOur study demonstrated that some types of human cytokines and interferon activate intracellular JAK-STAT signaling pathways in porcine ocular cells. We hypothesize that direct stimulation of the JAK-STAT pathway in porcine cells in response to human cytokines will lead to complications or failure, if pig-to-human ocular tissue xenotransplantation were to be carried out. For successful xenotransplantation among other obstacles there must be new approaches developed to regulate signaling pathways.

Synthetic Oleanane Triterpenoids: Multifunctional Drugs with a Broad Range of Applications for Prevention and Treatment of Chronic Disease

We review the rationale for the use of synthetic oleanane triterpenoids (SOs) for prevention and treatment of disease, as well as extensive biological data on this topic resulting from both cell culture and in vivo studies. Emphasis is placed on understanding mechanisms of action. SOs are noncytotoxic drugs with an excellent safety profile. Several hundred SOs have now been synthesized and in vitro have been shown to: 1) suppress inflammation and oxidative stress and therefore be cytoprotective, especially at low nanomolar doses, 2) induce differentiation, and 3) block cell proliferation and induce apoptosis at higher micromolar doses. Animal data on the use of SOs in neurodegenerative diseases and in diseases of the eye, lung, cardiovascular system, liver, gastrointestinal tract, and kidney, as well as in cancer and in metabolic and inflammatory/autoimmune disorders, are reviewed. The importance of the cytoprotective Kelch-like erythroid cell-derived protein with CNC homology-associated protein 1/nuclear factor (erythroid-derived 2)-like 2/antioxidant response element (Keap1/Nrf2/ARE) pathway as a mechanism of action is explained, but interactions with peroxisome proliferator-activated receptor γ (PARPγ), inhibitor of nuclear factor-κB kinase complex (IKK), janus tyrosine kinase/signal transducer and activator of transcription (JAK/STAT), human epidermal growth factor receptor 2 (HER2)/ErbB2/neu, phosphatase and tensin homolog (PTEN), the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathway, mammalian target of rapamycin (mTOR), and the thiol proteome are also described. In these interactions, Michael addition of SOs to reactive cysteine residues in specific molecular targets triggers biological activity. Ultimately, SOs are multifunctional drugs that regulate the activity of entire networks. Recent progress in the earliest clinical trials with 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO) methyl ester (bardoxolone methyl) is also summarized.

A Short Receptor Downregulates JAK/STAT Signalling to Control the Drosophila Cellular Immune Response

Author SummaryA specific microenvironment termed the “niche” supports long term maintenance of hematopoietic stem cells in vertebrates. A small group of specialised cells called the posterior signalling center (PSC) controls hemocyte (blood cell) homeostasis in the Drosophila larval hematopoietic tissue and thus fulfills a similar function to the vertebrate niche. The PSC acts at a distance to maintain JAK/STAT signalling in hematopoietic progenitors (prohemocytes), thereby ensuring their multipotent character. We report here that a short cytokine receptor encoded by CG14225/latran is required to extinguish JAK/STAT signalling in prohemocytes and thereby ensures their mass differentiation into lamellocytes, an immune cell type required to fight specific threats such as wasp parasitism. Domeless, a related receptor in Drosophila, was previously the only known cytokine receptor that signals through the JAK/STAT pathway. We show that Latran lacks the intracellular domains required for signal transduction and acts instead by antagonizing the function of Domeless in a dose-dependent manner. The role of Drosophila Latran in the repression of JAK/STAT signalling under specific immune conditions raises the question of whether short, nonsignalling receptors that antagonize full-length receptors could also control specific aspects of vertebrate immunity.

Abstract 4013: Functional analysis of Bcr-Abl-dependent phosphorylation of SOCSs

Abstract Previous studies have demonstrated that constitutive activation of JAK/STAT (Janus tyrosine kinase/signal transducers and activators of transcription) signaling is required for efficient transformation by the Abelson murine leukemia virus (A-MuLV), which results from the expression of the v-Abl oncogene. Although the activation of JAK/STAT signaling pathway in cells expressing BCR-ABL still remains controversial, there is increasing evidence that deregulation of the JAK or STAT activity plays an important role in BCR-ABL malignant transformation. The suppressors of cytokine signaling (SOCS) are inhibitors of Jak kinases and as such are critically involved in a negative feedback loop of Jak/STAT signal transduction pathway. The mechanism by which Abl oncogene bypasses SOCS negative regulation remains poorly defined. Here, we found that co-expression of BCR-ABL with some SOCS proteins resulted in phosphorylation of SOCSs. Moreover, we observed that BCR-ABL-dependent phosphorylation of SOCSs altered SOCS function at least at two levels. One involves alteration of direct interaction of SOCSs with JAKs, which maintains JAK kinase activity. The other level involves inhibition of interaction of SOCS box with the Elongin BC complex, which disrupted the formation of E3 ubiquitin ligase complex that mediates proteosomal degradation of JAK kinases. Together, these results suggest that the BCR-ABL may regulate the inhibitory function of SOCSs through mediating phosphorylation of SOCS proteins. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4013.

Identification of JAK/STAT signalling components by genome-wide RNA interference

Signalling pathways mediating the transduction of information between cells are essential for development, cellular differentiation and homeostasis. Their dysregulation is also frequently associated with human malignancies. The Janus tyrosine kinase/signal transducer and activator of transcription (JAK/STAT) pathway represents one such signalling cascade whose evolutionarily conserved roles include cell proliferation and haematopoiesis. Here we describe a systematic genome-wide survey for genes required for JAK/STAT pathway activity. Analysis of 20,026 RNA interference (RNAi)-induced phenotypes in cultured Drosophila melanogaster haemocyte-like cells identified interacting genes encoding 4 known and 86 previously uncharacterized proteins. Subsequently, cell-based epistasis experiments were used to classify these proteins on the basis of their interaction with known components of the signalling cascade. In addition to multiple human disease gene homologues, we have found the tyrosine phosphatase Ptp61F and the Drosophila homologue of BRWD3, a bromo-domain-containing protein disrupted in leukaemia. Moreover, in vivo analysis demonstrates that disrupted dBRWD3 and overexpressed Ptp61F function as suppressors of leukaemia-like blood cell tumours. This screen represents a comprehensive identification of novel loci required for JAK/STAT signalling and provides molecular insights into an important pathway relevant for human cancer. Human homologues of identified pathway modifiers may constitute targets for therapeutic interventions.

Activated STAT3 in Choroidal Neovascular Membranes of Patients with Age-Related Macular Degeneration

Purpose: The Jak/STAT (Janus tyrosine kinase/signal transducers and activators of transcription) pathway is critical for growth control, developmental regulation and homeostasis. Here we studied the expression of STAT proteins in the proliferative disease of age-related macular degeneration (AMD) with choroidal neovascular membranes (CNVM). The STATs are cytoplasmic proteins with roles as signal messengers and transcription factors that participate in normal cellular responses to cytokines and growth factors. Abnormal activity of certain STAT family members, particularly STAT3 and STAT5, is associated with a wide variety of human malignancies and other diseases. Here were studied STAT activation in CNVM of patients with AMD. Methods: Sections of formalin-fixed, paraffin-embedded samples from 8 eyes with AMD and 5 controls were included in this study. Immunohistochemical staining was performed using antibodies against activated STAT1, STAT3 and STAT5 proteins, and tenascin. Results: In CNVM, we observed a strong positive staining for tenascin and STAT3 in retinal pigmented epithelial (RPE) cells restricted to areas of developing scars. In contrast, STAT3 immunoreactivity failed in areas completely composed of fibrovascular disciform scar material. In addition, no immunoreactivity for both STAT1 and STAT5 was detected in all CNVM and in all control samples. Conclusion: In CNVM, activation of STAT3 appears in RPE cells simultaneously with the formation of scars.

The complex of ciliary neurotrophic factor-ciliary neurotrophic factor receptor alpha up-regulates connexin43 and intercellular coupling in astrocytes via the Janus tyrosine kinase/signal transducer and activator of transcription pathway.

Cytokines regulate numerous cell processes, including connexin expression and gap junctional coupling. In this study, we examined the effect of ciliary neurotrophic factor (CNTF) on connexin43 (Cx43) expression and intercellular coupling in astrocytes. Murine cortical astrocytes matured in vitro were treated with CNTF (20 ng/ml), soluble ciliary neurotrophic factor receptor alpha (CNTFRalpha) (200 ng/ml), or CNTF-CNTFRalpha. Although CNTF and CNTFRalpha alone had no effect on Cx43 expression, the heterodimer CNTF-CNTFRalpha significantly increased both Cx43 mRNA and protein levels. Cx43 immunostaining correlated with increased intercellular coupling as determined by dye transfer analysis. By using the pharmacological inhibitor alpha-cyano-(3,4-dihydroxy)-N-benzylcinnamide (AG490), the increase in Cx43 was found to be dependent on the Janus tyrosine kinase/signal transducer and activator of transcription (JAK/STAT) pathway. Immunocytochemical analysis revealed that CNTF-CNTFRalpha treatment produced nuclear localization of phosphorylated STAT3, whereas CNTF treatment alone did not. Transient transfection of constructs containing various sequences of the Cx43 promoter tagged to a LacZ reporter into ROS 17/2.8 cells confirmed that the promoter region between -838 to -1693 was deemed necessary for CNTF-CNTFRalpha to induce heightened expression. CNTF-CNTFRalpha did not alter Cx30 mRNA levels, suggesting selectivity of CNTF-CNTFRalpha for connexin signaling. Together in the presence of soluble receptor, CNTF activates the JAK/STAT pathway leading to enhanced Cx43 expression and intercellular coupling.

Down-regulation of STAT5b transcriptional activity by ligand-activated peroxisome proliferator-activated receptor (PPAR) alpha and PPARgamma.

The nuclear receptor peroxisome proliferator-activated receptor (PPAR) is activated by a diverse group of acidic ligands, including many peroxisome proliferator chemicals present in the environment. Janus tyrosine kinase-signal transducer and activator of transcription (JAK-STAT) signaling is activated by multiple cytokines and hormones and leads to the translocation of dimerized STAT proteins to the nucleus where they activate transcription of target genes. Previous studies have shown that growth hormone (GH)-activated STAT5b can inhibit PPAR-regulated transcription. Here, we show that this inhibitory cross-talk is mutual, and that GH-induced, STAT5b-dependent beta-casein promoter-luciferase reporter gene transcription can be inhibited up to approximately 80% by ligand-activated PPARalpha or PPARgamma. Dose-response experiments showed a direct relationship between the extent of PPAR activation and the degree of inhibition of STAT5-regulated transcription. PPAR did not block STAT5b tyrosine phosphorylation or inhibit DNA-binding activity. Both PPARs inhibited the transcriptional activity of a constitutively active STAT5b mutant, indicating that inhibition occurs downstream of the GH-stimulated STAT5 activation step. Transcriptionally inactive, dominant-negative PPAR mutants did not block STAT5b inhibition by wild-type PPAR, indicating that PPAR target gene transcription is not required. PPARalpha retained its STAT5b inhibitory activity in the presence of the histone deacetylase inhibitor trichostatin, indicating that enhanced histone deacetylase recruitment does not contribute to STAT5b inhibition. PPARalpha lacking the ligand-independent AF-1 trans-activation domain failed to inhibit STAT5b, highlighting the importance of the AF-1 region in STAT5-PPAR inhibitory cross-talk. These findings demonstrate the bidirectionality of cross-talk between the PPAR and STAT pathways and provide a mechanism whereby exposure to environmental chemical activators of PPAR can suppress expression of GH target genes.

Pim serine/threonine kinases regulate the stability of Socs-1 protein.

Studies of SOCS-1-deficient mice have implicated Socs-1 in the suppression of JAK-STAT (Janus tyrosine kinase-signal transducers and activators of transcription) signaling and T cell development. It has been suggested that the levels of Socs-1 protein may be regulated through the proteasome pathway. Here we show that Socs-1 interacts with members of the Pim family of serine/threonine kinases in thymocytes. Coexpression of the Pim kinases with Socs-1 results in phosphorylation and stabilization of the Socs-1 protein. The protein levels of Socs-1 are significantly reduced in the Pim-1(-/-), Pim-2(-/-) mice as compared with wild-type mice. Similar to Socs-1(-/-) mice, thymocytes from Pim-1(-/-), Pim-2(-/-) mice showed prolonged Stat6 phosphorylation upon IL-4 stimulation. These data suggest that the Pim kinases may regulate cytokine-induced JAK-STAT signaling through modulation of Socs-1 protein levels.

The Mitogen-activated Protein (MAP) Kinase p38 and Its Upstream Activator MAP Kinase Kinase 6 Are Involved in the Activation of Signal Transducer and Activator of Transcription by Hyperosmolarity

Environmental stress (e.g. aniso-osmolarity and UV light), hypoxia/reoxygenation, and reactive oxygen species activate intracellular signaling cascades such as the "stress-responsive" mitogen-activated protein kinases and nuclear factor kappaB. We have recently shown that the Janus tyrosine kinase/signal transducer and activator of transcription (Jak/STAT) pathway is ligand-independently activated by hyperosmotic shock. In the present study, we show that besides STAT1 also the tyrosine phosphatase SHP2 became tyrosine-phosphorylated upon hyperosmolarity. SB 202190 and SB 203580 (specific inhibitors of p38) inhibited both STAT activation and tyrosine phosphorylation of SHP2 induced by hyperosmotic stress. Overexpression of wild-type p38 mitogen-activated protein kinase and its upstream activator mitogen-activated protein kinase kinase 6 (MKK6) resulted in an enhanced STAT1 tyrosine phosphorylation upon osmotic shock. Accordingly, overexpression of dominant negative mutants of p38 and MKK6 largely decreased hyperosmotic STAT1 activation and tyrosine phosphorylation of SHP2. Furthermore, we provide evidence that a genistein-sensitive tyrosine kinase different from Jak1 is involved in stress-activation of STAT1 and tyrosine phosphorylation of SHP2. These results strongly suggest that hyperosmotic shock activates STAT1 and SHP2 via p38 and its upstream activator MKK6.

The Membrane-Distal Cytoplasmic Region of Human Granulocyte Colony-Stimulating Factor Receptor Is Required for STAT3 But Not STAT1 Homodimer Formation

Signal transduction from the granulocyte colony-stimulating factor receptor (G-CSF-R) involves the activation of the Janus tyrosine kinase/signal transducer and activator of transcription (Jak/STAT) pathway. G-CSF induces tyrosine phosphorylation of Jak1, Jak2, STAT1, and STAT3. The membrane-proximal region of G-CSF-R is sufficient for activation of Jaks. It is still unclear how STAT proteins are activated by G-CSF-R. We investigated the possible involvement of the C-terminal region of G-CSF-R in the recruitment of STAT proteins using BAF3 cell transfectants expressing wild type (WT) G-CSF-R, C-terminal deletion mutants and tyrosine-to-phenylalanine substitution mutants. Electrophoretic mobility shift assays with STAT-binding oligonucleotides (m67) showed that activation of WT G-CSF-R induces three distinct STAT complexes, namely STAT3 homodimers, STAT1-STAT3 heterodimers, and STAT1 homodimers. However, STAT1 homodimers and STAT1-STAT3 heterodimers were predominantly formed after activation of a C-terminal deletion mutant d685, which lacks all four conserved cytoplasmic tyrosine residues, located at positions 704, 729, 744, and 764. Antiphosphotyrosine immunoblots of STAT3 immunoprecipitates showed that activation of WT G-CSF-R induced phosphorylation of STAT3. In contrast, no phosphorylation of STAT3 was observed after activation of deletion mutant d685. These findings establish that the C-terminal region of G-CSF-R plays a major role in the activation of STAT3. By using tyrosine-to-phenylalanine substitution mutants of G-CSF-R, we further show that tyrosine 704, present in a YXXQ consensus sequence shown to be essential for STAT3 binding to gp130, is not exclusively involved in the activation of STAT3 by G-CSF-R.