Regulation of Stat3 transcriptional activity by the conserved LPMSP motif for OSM and IL-6 signaling

Ezh2Y641F mutations co-operate with Stat3 to regulate MHC class I antigen processing and alter the tumor immune response in melanoma

Enhancer of Zeste Homolog 2 (EZH2) is the catalytic component of the Polycomb Repressive Complex 2, a chromatin modifying complex, which mediates methylation of lysine 27 on histone 3 (H3K27me3), a repressive chromatin mark. Genetic alterations in EZH2 in melanoma include amplifications and activating point mutations at tyrosine 641 (Y641) whose underlying oncogenic mechanisms remain largely unknown. Here, we found that expression of Ezh2Y641F causes upregulation of a subset of interferon-regulated genes in melanoma cells. Upregulation of these genes was not a direct effect of changes in H3K27me3, but via a non-canonical interaction between Ezh2 and Signal Transducer and Activator of Transcription 3 (Stat3). Ezh2 and Stat3 together function as transcriptional activators to mediate gene activation of numerous genes, including MHC Class 1b antigen processing genes. Furthermore, expression of Stat3 is required to maintain an anti-tumor immune response in Ezh2Y641F melanomas and to prevent melanoma progression and recurrence.

Propofol mediates signal transducer and activator of transcription 3 activation and crosstalk with phosphoinositide 3-kinase/AKT

We previously demonstrated that propofol, an intravenous anesthetic with anti-oxidative properties, activated the phosphoinositide 3-kinase (PI3K)/AKT pathway to increase the expression of B cell lymphoma (Bcl)-2 and, therefore the anti-apoptotic potential on cardiomyocytes. Here, we wanted to determine if propofol can also activate the Janus kinase (JAK) 2/signal transducer and activator of transcription (STAT) 3 pathway, another branch of cardioprotective signaling. The cellular response of nuclear factor kappa B (NFκB) and STAT3 was also evaluated. Cardiac H9c2 cells were treated by propofol alone or in combination with pretreatment by inhibitors for JAK2/STAT3 or PI3K/AKT pathway. STAT3 and AKT phosphorylation, and STAT3 translocation were measured by western blotting and immunofluorescence staining, respectively. Propofol treatment significantly increased STAT3 phosphorylation at both tyrosine 705 and serine 727 residues. Sustained early phosphorylation of STAT3 was observed with 25~75 μM propofol at 10 and 30 min. Nuclear translocation of STAT3 was seen at 4 h after treatment with 50 μM propofol. In cultured H9c2 cells, we further demonstrated that propofol-induced STAT3 phosphorylation was reduced by pretreatment with PI3K/AKT pathway inhibitors wortmannin or API-2. Conversely, pretreatment with JAK2/STAT3 pathway inhibitor AG490 or stattic inhibited propofol-induced AKT phosphorylation. In addition, propofol induced NFκB p65 subunit perinuclear translocation. Inhibition or knockdown of STAT3 was associated with increased levels of the NFκB p65 subunit. Our results suggest that propofol induces an adaptive response by dual activation and crosstalk of cytoprotective PI3K/AKT and JAK2/STAT3 pathways. Rationale to apply propofol clinically as a preemptive cardioprotectant during cardiac surgery is supported by our findings.

Deletion of intestinal epithelial cell STAT3 promotes T-lymphocyte STAT3 activation and chronic colitis following acute dextran sodium sulfate injury in mice

BACKGROUND

Intestinal epithelial cell (IEC) STAT3 is required for wound healing following acute dextran sodium sulfate (DSS) injury. We hypothesized that loss of IEC STAT3 would promote the development of chronic colitis following acute DSS injury.

METHODS

Colitis was induced in IEC-specific STAT3-deficient mice (STAT3)[INCREMENT]IEC and littermate controls (STAT3 Flx/Flx) with 4% DSS for 7 days, followed by water consumption for 21 days. Epithelial and immune mediators and severity of colitis were determined.

RESULTS

Survival, colon length, and histologic injury were significantly worse at day 28 in STAT3[INCREMENT]IEC mice. IEC proliferation and apoptosis did not vary by genotype at day 14 or day 28. The colonic lamina propria frequency of pSTAT3* cells was increased at day 28 and correlated with histologic injury in STAT3 [INCREMENT]IEC mice. The frequency of colonic F480* pSTAT3* macrophages and CD3* pSTAT3* T lymphocytes were increased in STAT3[INCREMENT]IEC mice as compared with STAT3 Flx/Flx controls. In STAT3[INCREMENT]IEC mice, colonic expression of STAT3 target genes Reg3β and Reg3γ, which mediate epithelial restitution, were significantly decreased, whereas expression of interleukin (IL)-17a, IFNγ, CXCL2, CXCL10, and CCL2 were significantly increased and correlated with the increase in histologic severity at day 28(P < 0.05). IL-17a expression also correlated with the increased lamina propria frequency of CD3* pSTAT3* T lymphocytes.

CONCLUSIONS

Loss of intestinal epithelial STAT3 leads to more severe chronic inflammation following acute injury, which is not accounted for by a sustained defect in epithelial proliferation or apoptosis 7 or 21 days after 1 cycle of DSS but rather defective REG3 expression and expansion of pSTAT3* lymphocytes and IL-17A expression.

Targeting the interleukin-6/Jak/stat pathway in human malignancies

The Janus kinase/signal transducer and activator of transcription (Jak/Stat) pathway was discovered 20 years ago as a mediator of cytokine signaling. Since this time, more than 2,500 articles have been published demonstrating the importance of this pathway in virtually all malignancies. Although there are dozens of cytokines and cytokine receptors, four Jaks, and seven Stats, it seems that interleukin-6-mediated activation of Stat3 is a principal pathway implicated in promoting tumorigenesis. This transcription factor regulates the expression of numerous critical mediators of tumor formation and metastatic progression. This review will examine the relative importance and function of this pathway in nonmalignant conditions as well as malignancies (including tumor intrinsic and extrinsic), the influence of other Stats, the development of inhibitors to this pathway, and the potential role of inhibitors in controlling or eradicating cancers.

Crucial role of nuclear Ago2 for hUCB-MSCs differentiation and self-renewal via stemness control

AIMS

Argonaute2 (Ago2) has intrinsic endonuclease activity in microRNA processing that plays a fundamental role in gene regulation. In this study, we demonstrate novel functions and molecular mechanisms of nuclear Ago2 in the self-renewal and plasticity of human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs).

RESULTS

Nuclear Ago2 binds to a set of regulatory genes, including Ago2 itself, Oct4, Sox2, Nanog, GATA, STAT3, and β-catenin, that potentially target fundamental functions of stem cells. Direct regulation of the stemness genes by nuclear Ago2 was also crucial for cell self-renewal, survival, and differentiation into various types of tissues or cells, including neural cells and β-cells. Moreover, regulation of Oct4 by Ago2 directly controls the stem cell plasticity-determining signal mediators JAK2/STAT3 and Wnt5A/β-catenin and positively regulates cell proliferation and differentiation via blockage of ROS generation and P38/JNK inactivation. Nuclear Ago2 or stemness expression lead increased stem cell identity and decreased differentiation into a mesodermal lineage but also led to increased neural differentiation and β-cell differentiation in hUCB-MSCs. Nuclear Ago2-mediated stemness expression in hUCB-MSCs is also involved in cell survival, helping cells escape apoptotic cell death via inactivation of P38/JNK, caspase-3, and Bax.

INNOVATION AND CONCLUSION

This study reveals that nuclear Ago2 globally controls stem cell self-renewal and differentiation through direct regulation of stemness genes and important signal mediator activation following inactivation of ROS/P38/JNK and activation of the JAK/STAT3 and Wnt/ β-catenin signal pathways.

Phospho-Ser727 of STAT3 regulates STAT3 activity by enhancing dephosphorylation of phospho-Tyr705 largely through TC45

Signal transducer and activator of transcription 3 (STAT3) is a latent cytoplasmic transcription factor. It is activated by cytokines, including interleukin-6 (IL-6) through phosphorylation at Tyr705 (pY705), which is required for its dimerization and nuclear translocation. However, the role of Ser727 phosphorylation, occurring during activation, remains poorly understood. Using a combination of HepG2-stat3-knockdown cells reconstituted with various STAT3 mutants and protein kinase inhibitors, we showed that phospho-S727 has an intrinsic mechanism for shortening the duration of STAT3 activity, in turn shortening the duration of socs3 mRNA expression. Both STAT3WT and STAT3Ser727Asp (S727D) but not STAT3Ser727Ala (S727A) showed rapid dephosphorylation of pY705 after the inhibition of tyrosine kinases. We found that the nuclear TC45 phosphatase is most likely responsible for the phospho-S727-dependent pY705 dephosphorylation because TC45 knockdown caused prolonged pY705 with sustained socs3 mRNA expression in STAT3WT but not in STAT3S727A, and overexpressed TC45 caused rapid dephosphorylation of pY705 in STAT3WT but not in STAT3S727A. We further showed that phospho-S727 did not affect the interaction of TC45 with STAT3, and that a reported methylation at K140 of STAT3 occurring after phospho-S727 was not involved in the pY705 regulation. These findings indicate that phospho-Ser727 determines the duration of STAT3 activity largely through TC45.

Signal transducers and activators of transcription 3 (STAT3) directly regulates cytokine-induced fascin expression and is required for breast cancer cell migration

The cytokines oncostatin M (OSM) and IL-6 promote breast cancer cell migration and metastasis. Both cytokines activate STAT3, a member of the STAT (signal transducers and activators of transcription) family of transcription factors. Through transcriptional regulation of its target genes, STAT3 controls a wide range of cellular processes, including cellular proliferation, oncogenesis, and cancer metastasis. Fascin is an actin-bundling protein involved in cell migration. Elevated levels of fascin expression are found in many metastatic cancers, and inhibition of fascin function by small chemical compounds leads to a block of tumor metastasis. In this work, we demonstrate that fascin is a direct STAT3 target gene in response to OSM and IL-6 in both mouse and human breast cancer cells. We show that NFκB also binds to the fascin promoter in response to cytokine treatment and this binding is STAT3-dependent. Both STAT3 and NFκB are required for the cytokine-induced expression of fascin in cancer cells. Furthermore, we demonstrate that STAT3, in directly controlling fascin expression, is both necessary and sufficient for breast cancer cell migration.

Heteroarylketones inhibit astroglial interleukin-6 expression via a STAT3/NF-κB signaling pathway

Background

Elevated brain levels of the pleiotropic cytokine interleukin-6, which is mainly secreted from activated local astrocytes, contribute to pathological events including neuroinflammation and neurodegeneration. Thus, inhibition of pathological IL-6 expression provides a rationale strategy for targeting the onset or further progression of neurological disorders including Alzheimer's disease, multiple sclerosis, Parkinson's disease and traumatic brain injury. The purpose of this study was to identify and to characterize new potent inhibitors of astrocytic IL-6 expression for further therapeutic development of novel anti-inflammatory and neuroprotective drugs.

Methods

Oncostatin M (OSM)-treated human glioma U343 cells were used as model for induction of astrocytic IL-6 expression. This model was characterized by immunoblotting, siRNA technique, ELISA and qRT-PCR and used to screen low molecular weight compound libraries for IL-6-lowering effects. To validate bioactive compounds identified from library screens, bacterial lipopolysaccharide was used to induce IL-6 expression in cultivated primary astrocytes and in mice in vivo. To dissect underlying molecular mechanisms, protein extracts from OSM-treated U343 cells were analyzed by phospho-specific immunoblotting and immunocytochemistry as well as by co-immunoprecipitation.

Results

OSM-treatment (100 ng/ml; 24 h) led to 30-fold increase of IL-6 secretion from U343 cells. The temporal profile of IL-6 mRNA induction displayed a biphasic induction pattern with peak synthesis at 1 h (6.5-fold) and 16 h (5.5-fold) post stimulation. IL-6 protein release did not show that biphasic pattern and was detected as early as 3 h post stimulation reaching a maximum at 24 h. The screen of compound libraries identified a set of heteroarylketones (HAKs) as potent inhibitors of IL-6 secretion. HAK compounds affected the second peak in IL-6 mRNA synthesis, whereas the first peak was insensitive to HAK treatment. HAK compounds also suppressed lipopolysaccharide-induced IL-6 expression in primary murine astrocytes as well as in brain and plasma samples from lipopolysaccharide-treated mice. Finally, HAK compounds were demonstrated to specifically suppress the OSM-induced phosphorylation of STAT3 at serine 727 and the physical interaction of pSTAT3^S727 with p65.

Conclusion

Heteroarylketone compounds are potent inhibitors of IL-6 expression in vitro and in vivo and may represent a new class of potent anti-inflammatory and neuroprotective drugs.

Roles of IL-6-gp130 Signaling in Vascular Inflammation

Interleukin-6 (IL-6) is a well-established, independent indicator of multiple distinct types of cardiovascular disease and all-cause mortality. In this review, we present current understanding of the multiple roles that IL-6 and its signaling pathways through glycoprotein 130 (gp130) play in cardiovascular homeostasis. IL-6 is highly inducible in vascular tissues through the actions of the angiotensin II (Ang II) peptide, where it acts in a paracrine manner to signal through two distinct mechanisms, the first being a classic membrane receptor initiated pathway and the second, a trans-signaling pathway, being able to induce responses even in tissues lacking the IL-6 receptor. Recent advances and new concepts in how its intracellular signaling pathways operate via the Janus kinase (JAK)-Signal Transducer and Activator of Transcription (STAT) are described. IL-6 has diverse actions in multiple cell types of cardiovascular importance, including endothelial cells, monocytes, platelets, hepatocytes and adipocytes. We discuss central roles of IL-6 in endothelial dysfunction, cellular inflammation by affecting monocyte activation/differentiation, cellular cytoprotective functions from reactive oxygen species (ROS) stress, modulation of pro-coagulant state, myocardial growth control, and its implications in metabolic control and insulin resistance. These multiple actions indicate that IL-6 is not merely a passive biomarker, but actively modulates adaptive and pathological responses to cardiovascular stress.

The STAT3 beacon: IL-6 recurrently activates STAT 3 from endosomal structures

Endocytic trafficking plays an important role in signal transduction. Signal transducer and activator of transcription 3 (STAT3) and mitogen-activate protein kinase (MAPK) have both been localized to endosomal structures and are dependent upon endocytosis for downstream function. While the dependence of MAPK signaling upon endosomes has been well characterized, the involvement of endosomes in regulating STAT3 signaling has not been defined. Consequently, this study evaluated the role of endosomes in the initiation, modulation, amplification and persistence of interleukin-6(IL-6)-induced STAT3 signal transduction and transcription, and utilized IL-6-induced MAPK signaling as a comparator. Using pharmacologic treatment and temperature control of endocytic trafficking, pulse-chase treatments and in vitro kinase assays, STAT3 was found to interact with endosomes in a markedly different fashion than MAPK. STAT3 was activated by direct interaction with internal structures upstream of the late endosome following IL-6 exposure and persistent STAT3 signaling depended upon recurrent activation from endocytic structures. Further, STAT3 subcellular localization was not dependent upon endocytic trafficking. Instead, STAT3 transiently interacted with endosomes and relocated to the nucleus by an endosome-independent mechanism. Finally, endocytic trafficking played a central role in regulating STAT3 serine 727 phosphorylation through crosstalk with the MAPK signaling system. Together, these data reveal endosomes as central to the genesis, course and outcome of STAT3 signal transduction and transcription.

Stat3 directly controls the expression of Tbx5, Nkx2.5, and GATA4 and is essential for cardiomyocyte differentiation of P19CL6 cells

The transcription factor Stat3 (signal transducer and activator of transcription 3) mediates many physiological processes, including embryogenesis, stem cell self-renewal, and postnatal survival. In response to gp130 receptor activation, Stat3 becomes phosphorylated by the receptor-associated Janus kinase, forms dimers, and enters the nucleus where it binds to Stat3 target genes and regulates their expression. In this report, we demonstrate that Stat3 binds directly to the promoters and regulates the expression of three genes that are essential for cardiac differentiation: Tbx5, Nkx2.5, and GATA4. We further demonstrate that Tbx5, Nkx2.5, and GATA4 expression is dependent on Stat3 in response to ligand treatment and during ligand-independent differentiation of P19CL6 cells into cardiomyocytes. Finally, we show that Stat3 is necessary for the differentiation of P19CL6 cells into beating cardiomyocytes. All together, these results demonstrate that Stat3 is required for the differentiation of cardiomyocytes through direct transcriptional regulation of Tbx5, Nkx2.5, and GATA4.

Regulation of signal transducer and activator of transcription 3 enhanceosome formation by apurinic/apyrimidinic endonuclease 1 in hepatic acute phase response

The signal transducer and activator of transcription-3 (STAT3) is a latent IL-6 inducible transcription factor that mediates hepatic and vascular inflammation. In this study, we make the novel observation that STAT3 forms an inducible complex with the apurinic/apyrimidinic endonuclease 1 (APE1)/redox effector factor-1 (APE1/Ref-1), an essential multifunctional protein in DNA base excision repair, and studied the role of APE1/Ref-1 in STAT3 function. Using a transfection-coimmunoprecipitation assay, we observed that APE1 selectively binds the NH(2)-terminal acetylation domain of STAT3. Ectopic expression of APE1 potentiated inducible STAT3 reporter activity, whereas knockdown of APE1 resulted in reduced IL-6-inducible acute-phase reactant protein expression (C-reactive protein and serum amyloid P) and monocyte chemotactic protein-1 expression. The mechanism for APE1 requirement in IL-6 signaling was indicated by reduced STAT3 DNA binding activity observed in response to small interfering RNA-mediated APE1 silencing. Consistent with these in vitro studies, we also observed that lipopolysaccharide-induced activation of acute-phase reactant protein expression is significantly abrogated in APE1 heterozygous mice compared with wild-type mice. IL-6 induces both STAT3 and APE1 to bind the suppressor of cytokine signaling-3 and gamma-fibrionogen promoters in their native chromatin environment. Moreover, we observed that APE1 knockdown destabilized formation of the STAT3-inducible enhanceosome on the endogenous gamma-fibrionogen promoter. Taken together, our study indicates that IL-6 induces a novel STAT3-APE1 complex, whose interaction is required for stable chromatin association in the IL-6-induced hepatic acute phase response.

SH2B1beta enhances fibroblast growth factor 1 (FGF1)-induced neurite outgrowth through MEK-ERK1/2-STAT3-Egr1 pathway

Genetic studies have established the crucial roles of FGF signaling, FGF-induced gene expression and morphogenesis during embryogenesis. In this study, we showed that overexpressing a signaling adaptor protein, SH2B1beta, enhanced FGF1-induced neurite outgrowth in PC12 cells. SH2B1beta has previously been shown to promote nerve growth factor (NGF) and glial cell line-derived neurotrophic factor (GDNF)-induced neurite outgrowth, in part, through prolonging NGF and GDNF-induced signaling. To delineate how SH2B1beta promotes FGF1-induced neurite outgrowth, we examined its role in FGF1-dependent signaling. Our data suggest that SH2B1beta enhances and prolongs FGF1-induced MEK-ERK1/2 and PI3K-AKT pathways. We also provided the first evidence that FGF1 induces the phosphorylation of signal transducer and activator of transcription 3 (STAT3) at serine 727 [pSTAT3(S727)] in PC12 cells. SH2B1beta enhances this phosphorylation and the expression of the immediate early gene, Egr1. Through inhibitor assays, we have further shown that MEK-ERK1/2 is required for FGF1-induced neurite outgrowth, pSTAT3(S727) and Egr1 expression. Moreover, inhibiting Rho kinase, ROCK, enhances FGF1-induced neurite outgrowth through pSTAT3(S727)-independent manner. Taken together, our results demonstrate, for the first time, that SH2B1beta enhances FGF1-induced neurite outgrowth in PC12 cells mainly through MEK-ERK1/2-STAT3-Egr1 pathway.

Structural basis for recruitment of CBP/p300 coactivators by STAT1 and STAT2 transactivation domains

CBP/p300 transcriptional coactivators mediate gene expression by integrating cellular signals through interactions with multiple transcription factors. To elucidate the molecular and structural basis for CBP-dependent gene expression, we determined structures of the CBP TAZ1 and TAZ2 domains in complex with the transactivation domains (TADs) of signal transducer and activator of transcription 2 (STAT2) and STAT1, respectively. Despite the topological similarity of the TAZ1 and TAZ2 domains, subtle differences in helix packing and surface grooves constitute major determinants of target selectivity. Our results suggest that TAZ1 preferentially binds long TADs capable of contacting multiple surface grooves simultaneously, whereas smaller TADs that are restricted to a single contiguous binding surface form complexes with TAZ2. Complex formation for both STAT TADs involves coupled folding and binding, driven by intermolecular hydrophobic and electrostatic interactions. Phosphorylation of S727, required for maximal transcriptional activity of STAT1, does not enhance binding to any of the CBP domains. Because the different STAT TADs recognize different regions of CBP/p300, there is a potential for multivalent binding by STAT heterodimers that could enhance the recruitment of the coactivators to promoters.

The STAT3 NH2-terminal domain stabilizes enhanceosome assembly by interacting with the p300 bromodomain

Signal transducer and activator of transcription 3 (STAT3) is a latent transcription factor mainly activated by the interleukin-6 cytokine family. Previous studies have shown that activated STAT3 recruits p300, a coactivator whose intrinsic histone acetyltransferase activity is essential for transcription. Here we investigated the function of the STAT3 NH(2)-terminal domain and how its interaction with p300 regulates STAT3 signal transduction. In STAT3(-/-) mouse embryonic fibroblasts, a stably expressed NH(2) terminus-deficient STAT3 mutant (STAT3-DeltaN) was unable to efficiently induce either STAT3-mediated reporter activity or endogenous mRNA expression. Chromatin immunoprecipitation assays were performed to determine whether the NH(2)-terminal domain regulates p300 recruitment or stabilizes enhanceosome assembly. Despite equivalent levels of STAT3 binding, cells expressing the STAT3-DeltaN mutant were unable to recruit p300 and RNA polymerase II to the native socs3 promoter as efficiently as those expressing STAT3-full length. We previously reported that the STAT3 NH(2)-terminal domain is acetylated by p300 at Lys-49 and Lys-87. By introducing K49R/K87R mutations, here we found that the acetylation status of the STAT3 NH(2)-terminal domain regulates its interaction with p300. In addition, the STAT3 NH(2)-terminal binding site maps to the p300 bromodomain, a region spanning from amino acids 995 to 1255. Finally a p300 mutant lacking the bromodomain (p300-DeltaB) exhibited a weaker binding to STAT3, and the enhanceosome formation on the socs3 promoter was inhibited when p300-DeltaB was overexpressed. Taken together, our data suggest that the STAT3 NH(2)-terminal domain plays an important role in the interleukin-6 signaling pathway by interacting with the p300 bromodomain, thereby stabilizing enhanceosome assembly.

Identification of novel direct Stat3 target genes for control of growth and differentiation

Signal transducer and activator of transcription 3 (Stat3) is a key regulator of gene expression in response to signaling of the glycoprotein 130 (gp130) family cytokines, including interleukin 6, oncostatin M, and leukemia inhibitory factor. Many efforts have been made to identify Stat3 target genes and to understand the mechanism of how Stat3 regulates gene expression. Using the microarray technique, hundreds of genes have been documented to be potential Stat3 target genes in different cell types. However, only a small fraction of these genes have been proven to be true direct Stat3 target genes. Here we report the identification of novel direct Stat3 target genes using a genome-wide screening procedure based on the chromatin immunoprecipitation method. These novel Stat3 target genes are involved in a diverse array of biological processes such as oncogenesis, cell growth, and differentiation. We show that Stat3 can act as both a repressor and activator on its direct target genes. We further show that most of the novel Stat3 direct target genes are dependent on Stat3 for their transcriptional regulation. In addition, using a physiological cell system, we demonstrate that Stat3 is required for the transcriptional regulation of two of the newly identified direct Stat3 target genes important for muscle differentiation.