Serine phosphorylation of STATs

A signal transducers and activators of transcription (STAT) gene from Scylla paramamosain is involved in resistance against mud crab reovirus

A STAT gene from Scylla paramamosain, named SpSTAT, was cloned and characterized. The full length of SpSTAT mRNA contains a 5'untranslated region (UTR) of 238 bp, an open reading frame (ORF) of 2388 bp and a 3' UTR of 326 bp. The SpSTAT protein contains four characteristic STAT domains and showed 84% identity (90% similarity) and 44% identity (64% similarity) to Litopenaeus vannamei STAT protein and Human STAT5a/b protein, respectively. The mRNA of SpSTAT was high expressed in the intestine and eyestalk and low expressed in the heart and muscle. Moreover, expression of SpSTAT was significantly responsive to challenge of mud crab reovirus (MCRV), Poly(I:C), LPS and Staphylococcus aureus. SpSTAT could be activated by Poly(I:C) and LPS to translocate to the nucleus of Drosophila Schneider 2 (S2) cells. SpSTAT could be phosphorylated by interaction with JAK of S. paramamosain (SpJAK) and activated to translocate to the nucleus of S2 cells. Furthermore, Silencing of SpSTAT in vivo resulted in higher mortality rate of MCRV infected mud crab and increased the viral load in tissues, suggesting that SpSTAT could play an important role in defense against MCRV in mud crab.

Natural Sesquiterpene Lactones Enhance Chemosensitivity of Tumor Cells through Redox Regulation of STAT3 Signaling

STAT3 is a nuclear transcription factor that regulates genes involved in cell cycle, cell survival, and immune response. Although STAT3 activation drives cells to physiological response, its deregulation is often associated with the development and progression of many solid and hematological tumors as well as with drug resistance. STAT3 is a redox-sensitive protein, and its activation state is related to intracellular GSH levels. Under oxidative conditions, STAT3 activity is regulated by S-glutathionylation, a reversible posttranslational modification of cysteine residues. Compounds able to suppress STAT3 activation and, on the other hand, to modulate intracellular redox homeostasis may potentially improve cancer treatment outcome. Nowadays, about 35% of commercial drugs are natural compounds that derive from plant extracts used in phytotherapy and traditional medicine. Sesquiterpene lactones are an interesting chemical group of plant-derived compounds often employed in traditional medicine against inflammation and cancer. This review focuses on sesquiterpene lactones able to downmodulate STAT3 signaling leading to an antitumor effect and correlates the anti-STAT3 activity with their ability to decrease GSH levels in cancer cells. These properties make them lead compounds for the development of a new therapeutic strategy for cancer treatment.

STAT3: An Emerging Therapeutic Target for Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a major global health problem and its treatment options have been limited. Signal transducer and activator of transcription 3 (STAT3) is a transcription factor important for various cellular processes. Overexpression and constitutive activation of STAT3 have been frequently found in HCC and associated with poor prognosis. Ample evidence has shown that STAT3 plays pivotal roles in the initiation, progression, metastasis and immune suppression of HCC. Thus, STAT3 has attracted attention as a novel therapeutic target in HCC. Clinical trials have investigated STAT3-targeted therapeutics either as monotherapy or in combination with chemotherapeutic agents, immune checkpoint inhibitors and alternative targeted drugs. Some of these studies have yielded encouraging results. Particularly, napabucasin—a cancer stemness inhibitor targeting STAT3-driven gene transcription—has stood out with its promising clinical efficacy and safety profile. Nonetheless, clinical investigations of STAT3-targeted therapies in HCC are limited and more efforts are strongly urged to evaluate their clinical performance in HCC. Here, we provide a comprehensive review of the roles of STAT3 in HCC and follow by comprehensive analysis of STAT3 targeted strategies.

Fractalkine Induces Hepcidin Expression of BV-2 Microglia and Causes Iron Accumulation in SH-SY5Y Cells

Fractalkine (CX3CL1) is a potent inflammatory mediator of the central nervous system, which is expressed by neurons and regulates microglial functions by binding to fractalkine receptor (CX3CR1). It has been demonstrated that neuroinflammation plays an important role in iron accumulation of the brain leading to neuronal cell death. The major regulator of iron homeostasis is the peptide hormone hepcidin. Hepcidin expression is triggered by inflammatory conditions, which may contribute to the neuronal iron accumulation. In the present study, we established a bilaminar co-culture system of differentiated SH-SY5Y cells and BV-2 microglia as a neuronal model to examine the effect of soluble fractalkine on iron homeostasis of microglia and SH-SY5Y cells. We determined the hepcidin expression of fractalkine-treated microglia which showed significant elevation. We examined the relation between increased hepcidin secretion, the known hepcidin regulators and the signalling pathways controlled by fractalkine receptor. Our data revealed that TMPRSS6 and alpha 1-antitrypsin levels decreased due to fractalkine treatment, as well as the activity of NFκB pathway and the tyrosine phosphorylation of STAT5 factor. Moreover, fractalkine-induced hepcidin production of microglia initiated ferroportin internalisation of SH-SY5Y cells, which contributed to iron accumulation of neurons. Our results demonstrate that soluble form of fractalkine regulates hepcidin expression of BV-2 cells through fractalkine-mediated CX3CR1 internalisation. Moreover, fractalkine indirectly contributes to the iron accumulation of SH-SY5Y cells by activating ferroportin internalisation and by triggering the expressions of divalent metal transporter-1, ferritin heavy chain and mitochondrial ferritin.

IFN-gamma-induced PD-L1 expression in melanoma depends on p53 expression

Background

Immune checkpoint inhibition and in particular anti-PD-1 immunotherapy have revolutionized the treatment of advanced melanoma. In this regard, higher tumoral PD-L1 protein (gene name: CD274) expression is associated with better clinical response and increased survival to anti-PD-1 therapy. Moreover, there is increasing evidence that tumor suppressor proteins are involved in immune regulation and are capable of modulating the expression of immune checkpoint proteins. Here, we determined the role of p53 protein (gene name: TP53) in the regulation of PD-L1 expression in melanoma.

Methods

We analyzed publicly available mRNA and protein expression data from the cancer genome/proteome atlas and performed immunohistochemistry on tumors with known TP53 status. Constitutive and IFN-ɣ-induced PD-L1 expression upon p53 knockdown in wildtype, TP53-mutated or JAK2-overexpressing melanoma cells or in cells, in which p53 was rendered transcriptionally inactive by CRISPR/Cas9, was determined by immunoblot or flow cytometry. Similarly, PD-L1 expression was investigated after overexpression of a transcriptionally-impaired p53 (L22Q, W23S) in TP53-wt or a TP53-knockout melanoma cell line. Immunoblot was applied to analyze the IFN-ɣ signaling pathway.

Results

For TP53-mutated tumors, an increased CD274 mRNA expression and a higher frequency of PD-L1 positivity was observed. Interestingly, positive correlations of IFNG mRNA and PD-L1 protein in both TP53-wt and -mutated samples and of p53 and PD-L1 protein suggest a non-transcriptional mode of action of p53. Indeed, cell line experiments revealed a diminished IFN-ɣ-induced PD-L1 expression upon p53 knockdown in both wildtype and TP53-mutated melanoma cells, which was not the case when p53 wildtype protein was rendered transcriptionally inactive or by ectopic expression of p53^L22Q,W23S, a transcriptionally-impaired variant, in TP53-wt cells. Accordingly, expression of p53^L22Q,W23S in a TP53-knockout melanoma cell line boosted IFN-ɣ-induced PD-L1 expression. The impaired PD-L1-inducibility after p53 knockdown was associated with a reduced JAK2 expression in the cells and was almost abrogated by JAK2 overexpression.

Conclusions

While having only a small impact on basal PD-L1 expression, both wildtype and mutated p53 play an important positive role for IFN-ɣ-induced PD-L1 expression in melanoma cells by supporting JAK2 expression. Future studies should address, whether p53 expression levels might influence response to anti-PD-1 immunotherapy.

Kaempferia parviflora Extract Inhibits STAT3 Activation and Interleukin-6 Production in HeLa Cervical Cancer Cells

Kaempferia parviflora (KP) has been reported to have anti-cancer activities. We previously reported its effects against cervical cancer cells and continued to elucidate the effects of KP on inhibiting the production and secretion of interleukin (IL)-6, as well as its relevant signaling pathways involved in cervical tumorigenesis. We discovered that KP suppressed epidermal growth factor (EGF)-induced IL-6 secretion in HeLa cells, and it was associated with a reduced level of Glycoprotein 130 (GP130), phosphorylated signal transducers and activators of transcription 3 (STAT3), and Mcl-1. Our data clearly showed that KP has no effect on nuclear factor kappa B (NF-κB) localization status. However, we found that KP inhibited EGF-stimulated phosphorylation of tyrosine 1045 and tyrosine 1068 of EGF receptor (EGFR) without affecting its expression level. The inhibition of EGFR activation was verified by the observation that KP significantly suppressed a major downstream MAP kinase, ERK1/2. Consistently, KP reduced the expression of Ki-67 protein, which is a cellular marker for proliferation. Moreover, KP potently inhibited phosphorylation of STAT3, Akt, and the expression of Mcl-1 in response to exogenous IL-6 stimulation. These data suggest that KP suppresses EGF-induced production of IL-6 and inhibits its autocrine IL-6/STAT3 signaling critical for maintaining cancer cell progression. We believe that KP may be a potential alternative anti-cancer agent for suppressing cervical tumorigenesis.

Reactive microglia and astrocytes in neonatal intraventricular hemorrhage model are blocked by mesenchymal stem cells

Severe intraventricular hemorrhage (IVH) in premature infants triggers reactive gliosis, causing acute neuronal death and glial scar formation. Transplantation of mesenchymal stem cells (MSCs) has often showed improved CNS recovery in an IVH model, but whether this response is related to reactive glial cells is still unclear. Herein, we suggest that MSCs impede the response of reactive microglia rather than astrocytes, thereby blocking neuronal damage. Astrocytes alone showed mild reactiveness under hemorrhagic conditions mimicked by thrombin treatment, and this was not blocked by MSC-conditioned medium (MSC-CM) in vitro. In contrast, thrombin-induced microglial activation and release of proinflammatory cytokines were inhibited by MSC-CM. Interestingly, astrocytes showed greater reactive response when co-cultured with microglia, and this was abolished in the presence of MSC-CM. Gene expression profiles in microglia revealed that transcript levels of genes for immune response and proinflammatory cytokines were altered by thrombin treatment. This result coincided with the robust phosphorylation of STAT1 and p38 MAPK, which might be responsible for the production and release of proinflammatory cytokines. Furthermore, application of MSC-CM diminished thrombin-mediated phosphorylation of STAT1 and p38 MAPK, supporting the acute anti-inflammatory role of MSCs under hemorrhagic conditions. In line with this, activation of microglia and consequent cytokine release were impaired in Stat1-null mice. However, reactive response in Stat1-deficient astrocytes was maintained. Taken together, our results demonstrate that MSCs mainly block the activation of microglia involving STAT1-mediated cytokine release and subsequent reduction of reactive astrocytes.

Effect of liraglutide on the Janus kinase/signal transducer and transcription activator (JAK/STAT) pathway in diabetic kidney disease in db/db mice and in cultured endothelial cells

BACKGROUND

Emerging evidence demonstrates the involvement of Janus tyrosine kinase/signal transducer and transcription activator (JAK/STAT) proteins in the pathophysiology of diabetic kidney disease (DKD). The JAK/STAT pathway is involved in the inflammatory response and endothelial cell dysfunction observed in DKD. The glucagon-like peptide-1 (GLP-1) analog liraglutide is an effective treatment for type 2 diabetes because it improves the inflammatory changes observed in experimental models of DKD. This study used db/db mice and endothelial cells (ECs) to determine the effect of diabetic environment on the JAK/STAT pathway and to assess the potential effect of liraglutide (200 μg/kg) in both models.

METHODS

Diabetic db/db mice (12 weeks old) were treated with liraglutide for 14 weeks. The kidneys were then perfused with saline and removed for mRNA, protein, and immunohistochemical analyses. Endothelial cells were stimulated advanced glycation end products (AGEs) (200 μg/μL) glucose (200 mg/dL) and liraglutide (100 nM) for 24 hours. Total RNA and protein were extracted and analyzed for expression of JAK/STAT signaling.

RESULTS

Phosphorylated (p-) STAT3 was significantly upregulated in db/db mice compared with non-diabetic mice. Liraglutide significantly downregulated p-STAT3 protein expression in db/db mice. In db/db mice, p-STAT3 was primarily expressed in the glomeruli, whereas p-JAK2 was also expressed in kidney tubules. In ECs, liraglutide treatment prevented increased expression of p-STAT3 and p-JAK2. Liraglutide inhibited the target gene suppressor of cytokine signaling 3 (SOCS3) and sirtuin 1 (SIRT1) in db/db mice and in cultured EC.

CONCLUSIONS

This study suggests that the GLP-1 analog liraglutide inhibits the JAK/STAT pathway, which participates in intracellular processes in experimental models of diabetes.

AXL Inhibition Extinguishes Primitive JAK2 Mutated Myeloproliferative Neoplasm Progenitor Cells

Myeloproliferative neoplasms (MPN) are clonal stem cell associated disorders inclusive of chronic myeloid leukemia (CML), Polycythaemia vera (PV), myelofibrosis (MF), and essential thrombocythemia (ET). They are characterized by increased production of myeloid cells with minimal effects on terminal differentiation but can undergo transformation to acute leukemias. PV is the most common chronic myeloproliferative neoplasm and in the majority of cases is characterized by a V617F point mutation in JAK2. This JAK2 activating mutation is also found in about half the patients with MF and ET. Such aberrant proteins offer great potential for the treatment of these diseases however inhibitors to JAK2 have had limited success in the clinic in terms of curing the disease. We have previously used advanced proteomic techniques to identify drug targets and thus develop novel treatment strategies to distinguish the leukemic clone in both CML and PV. Here, we build on our proteomic data sets to characterize a new target, the receptor tyrosine kinase AXL. AXL is overexpressed in acute myeloid leukemia and importantly small molecule inhibitors have been developed which are currently in clinical trial hence offer the opportunity to repurpose this drug for the treatment of MPNs. We demonstrate that AXL is upregulated and activated in JAK2 associated MPNs. Further we show that inhibition of AXL preferentially kills early hemopoietic stem cells from PV patients and as such represents a promising therapeutic approach for JAK2 driven MPNs.

Urocortin Induces Phosphorylation of Distinct Residues of Signal Transducer and Activator of Transcription 3 (STAT3) via Different Signaling Pathways

BACKGROUND Urocortin (Ucn) is a member of the hypothalamic corticotrophin-releasing factor family and has been shown to reduce cell death in the heart caused by ischemia/reperfusion (I/R) injury. Signal transducer and activator of transcription 3 (STAT3) is a transcription factor known to function as a pro-survival and anti-apoptotic factor, whose activation depends on a variety of cytokines, including IL-6. A recent study demonstrated that urocortin induced IL-6 release from cardiomyocytes in a CRF-R2-dependent manner, suggesting a possible link between CRF-R2 stimulation and STAT3 activation. MATERIAL AND METHODS Experimental work was carried out in HL-1 cardiac myocytes exposed to serum starvation for 16-24 h. RESULTS Ucn stimulation led to IL-6 expression and release from mouse atrial HL-1 cardiomyocytes. Ucn treatment led to rapid phosphorylation of JAK2, which was blocked by the protein synthesis inhibitor cycloheximide or the JAK inhibitor AG490. Urocortin treatment induced STAT3 phosphorylation at Y705 and S727 through transactivation of JAK2 in an IL-6-dependent manner, but had no effect on STAT1 activity. Kinase inhibition experiments revealed that urocortin induces STAT3 S727 phosphorylation through ERK1/2 and Y705 phosphorylation through Src tyrosine kinase. In line with this finding, urocortin failed to induce phosphorylation of Y705 residue in SYF cells bearing null mutation of Src, while phosphorylation of S727 residue was unchanged. CONCLUSIONS Here, we have shown that Ucn induces activation of STAT3 through diverging signaling pathways. Full understanding of these signaling pathways will help fully exploit the cardioprotective properties of endogenous and exogenous Ucn.

Inhibition of IL-13 and IL-13Rα2 Expression by IL-32θ in Human Monocytic Cells Requires PKCδ and STAT3 Association

Interleukin (IL)-32θ, a newly identified IL-32 isoform, has been reported to exert pro-inflammatory effects through the association with protein kinase C delta (PKCδ). In this study, we further examined the effects of IL-32θ on IL-13 and IL-13Rα2 expression and the related mechanism in THP-1 cells. Upon stimulating IL-32θ-expressing and non-expressing cells with phorbol 12-myristate 13-acetate (PMA), the previous microarray analysis showed that IL-13Rα2 and IL-13 mRNA expression were significantly decreased by IL-32θ. The protein expression of these factors was also confirmed to be down-regulated. The nuclear translocation of transcription factors STAT3 and STAT6, which are necessary for IL-13Rα2 and IL-13 promoter activities, was suppressed by IL-32θ. Additionally, a direct association was found between IL-32θ, PKCδ, and signal transducer and activator of transcription 3 (STAT3), but not STAT6, revealing that IL-32θ might act mainly through STAT3 and indirectly affect STAT6. Moreover, the interaction of IL-32θ with STAT3 requires PKCδ, since blocking PKCδ activity eliminated the interaction and consequently limited the inhibitory effect of IL-32θ on STAT3 activity. Interfering with STAT3 or STAT6 binding by decoy oligodeoxynucleotides (ODNs) identified that IL-32θ had additive effects with the STAT3 decoy ODN to suppress IL-13 and IL-13Rα2 mRNA expression. Taken together, our data demonstrate the intracellular interaction of IL-32θ, PKCδ, and STAT3 to regulate IL-13 and IL-13Rα2 synthesis, supporting the role of IL-32θ as an inflammatory modulator.

Mechanism for IL-15-Driven B Cell Chronic Lymphocytic Leukemia Cycling: Roles for AKT and STAT5 in Modulating Cyclin D2 and DNA Damage Response Proteins

Clonal expansion of B cell chronic lymphocytic leukemia (B-CLL) occurs within lymphoid tissue pseudofollicles. IL-15, a stromal cell-associated cytokine found within spleens and lymph nodes of B-CLL patients, significantly boosts in vitro cycling of blood-derived B-CLL cells following CpG DNA priming. Both IL-15 and CpG DNA are elevated in microbe-draining lymphatic tissues, and unraveling the basis for IL-15-driven B-CLL growth could illuminate new therapeutic targets. Using CpG DNA-primed human B-CLL clones and approaches involving both immunofluorescent staining and pharmacologic inhibitors, we show that both PI3K/AKT and JAK/STAT5 pathways are activated and functionally important for IL-15→CD122/ɣc signaling in ODN-primed cells expressing activated pSTAT3. Furthermore, STAT5 activity must be sustained for continued cycling of CFSE-labeled B-CLL cells. Quantitative RT-PCR experiments with inhibitors of PI3K and STAT5 show that both contribute to IL-15-driven upregulation of mRNA for cyclin D2 and suppression of mRNA for DNA damage response mediators ATM, 53BP1, and MDC1. Furthermore, protein levels of these DNA damage response molecules are reduced by IL-15, as indicated by Western blotting and immunofluorescent staining. Bioinformatics analysis of ENCODE chromatin immunoprecipitation sequencing data from cell lines provides insight into possible mechanisms for STAT5-mediated repression. Finally, pharmacologic inhibitors of JAKs and STAT5 significantly curtailed B-CLL cycling when added either early or late in a growth response. We discuss how the IL-15-induced changes in gene expression lead to rapid cycling and possibly enhanced mutagenesis. STAT5 inhibitors might be an effective modality for blocking B-CLL growth in patients.

Oncogenic D816V-KIT signaling in mast cells causes persistent IL-6 production

Persistent dysregulation of IL-6 production and signaling have been implicated in the pathology of various cancers. In systemic mastocytosis, increased serum levels of IL-6 associate with disease severity and progression, although the mechanisms involved are not well understood. Since systemic mastocytosis often associates with the presence in hematopoietic cells of a somatic gain-of-function variant in KIT, D816V-KIT, we examined its potential role in IL-6 upregulation. Bone marrow mononuclear cultures from patients with greater D816V allelic burden released increased amounts of IL-6 which correlated with the percentage of mast cells in the cultures. Intracellular IL-6 staining by flow cytometry and immunofluorescence was primarily associated with mast cells and suggested a higher percentage of IL-6 positive mast cells in patients with higher D816V allelic burden. Furthermore, mast cell lines expressing D816V-KIT, but not those expressing normal KIT or other KIT variants, produced constitutively high IL-6 amounts at the message and protein levels. We further demonstrate that aberrant KIT activity and signaling are critical for the induction of IL-6 and involve STAT5 and PI3K pathways but not STAT3 or STAT4. Activation of STAT5A and STAT5B downstream of D816V-KIT was mediated by JAK2 but also by MEK/ERK1/2, which not only promoted STAT5 phosphorylation but also its long-term transcription. Our study thus supports a role for mast cells and D816V-KIT activity in IL-6 dysregulation in mastocytosis and provides insights into the intracellular mechanisms. The findings contribute to a better understanding of the physiopathology of mastocytosis and suggest the importance of therapeutic targeting of these pathways.

Mycobacterium bovis BCG promotes IL-10 expression by establishing a SYK/PKCα/β positive autoregulatory loop that sustains STAT3 activation

Mycobacterium ensures its survival inside macrophages and long-term infection by subverting the innate and adaptive immune response through the modulation of cytokine gene expression profiles. Different Mycobacterium species promote the expression of TGFβ and IL-10, which, at the early stages of infection, block the formation of the phagolysosome, thereby securing mycobacterial survival upon phagocytosis, and at later stages, antagonize IFNγ production and functions. Despite the key role of IL-10 in mycobacterium infection, the signal transduction pathways leading to IL-10 expression in infected macrophages are poorly understood. Here, we report that Mycobacterium bovis BCG promotes IL-10 expression and cytokine production by establishing a SYK/PKCα/β positive feedback loop that leads to STAT3 activation.

IFN/STAT signaling controls tumorigenesis and the drug response in colorectal cancer

Colorectal cancer (CRC) is caused by genetic alterations, and comprehensive sequence analyses have revealed the mutation landscapes. In addition to somatic changes, genetic variations are considered important factors contributing to tumor development; however, our knowledge on this subject is limited. Familial adenomatous polyposis coli (FAP) is an autosomal‐dominant inherited disease caused by germline mutations in the adenomatous polyposis coli (APC) gene. FAP patients are classified into two major groups based on clinical manifestations: classical FAP (CFAP) and attenuated FAP (AFAP). In this study, we established 42 organoids from three CFAP patients and two AFAP patients. Comprehensive gene expression analysis demonstrated a close association between IFN/STAT signaling and the phenotypic features of FAP patients. Genetic disruption of Stat1 in the mouse model of FAP reduced tumor formation, demonstrating that the IFN/STAT pathway is causally associated with the tumor‐forming potential of APC‐deficient tumors. Mechanistically, STAT1 is downstream target of KRAS and is phosphorylated by its activating mutations. We found that enhanced IFN/STAT signaling in CFAP conferred resistance to MEK inhibitors. These findings reveal the crosstalk between RAS signaling and IFN/STAT signaling, which contributes to the tumor‐forming potential and drug response. These results offer a rationale for targeting of IFN/STAT signaling and for the stratification of CRC patients.

Mapping of Signaling Pathways Linked to sIgAD Reveals Impaired IL-21 Driven STAT3 B-Cell Activation

Objectives: It has recently been shown that individuals with selective IgA deficiency (sIgAD) have defective B cell responses both to T cell dependent and independent mimicking stimulations. The complex intracellular signaling pathways from different stimuli leading to IgA isotype switching have not been fully elucidated. Thus, the main objective of this study was to delineate these pathways and their potential role in the immunopathology linked to sIgAD.

Materials and Methods: PBMCs from 10 individuals with sIgAD and 10 healthy controls (HC) were activated in vitro via either a T cell dependent or independent mimicking stimulation. Intracellular phosphorylation of pSTAT3, pSTAT5, pSTAT6, and as pERK1/2 was evaluated in T and B cells using phosphoflow cytometry.

Results: By evaluating T cell dependent cytokine driven pathways linked to IgA isotype induction we identified a defect involving an IL-21 driven STAT3 activation isolated to B cells in sIgAD individuals. However, all other signaling pathways studied were found to be normal compared to HC. In T cell dependent cytokine driven stimulations linked to IgA isotype induction the following patterns emerged: (i) IL-10 led to significant STAT3 activation in both T- and B cells; (ii) IL-4 stimulation was predominantly confined to STAT6 activation in both T- and B cells, with some effects on STAT3 activation in T-cells; (iii) as expected, of tested stimuli, IL-2 alone activated STAT5 and some STAT3 activation though in both cases only in T-cells; (iv) IL-21 induced significant activation of STAT3 in both T- and B cells, with some effects on STAT5 activation in T-cells; and finally (v) synergistic effects were noted of IL-4+IL-10 on STAT5 activation in T-cells, and possibly STAT6 in both T- and B cells. On the other hand, CPG induced T cell independent activation was confined to ERK1/2 activation in B cells.

Conclusion: Our results indicate a diminished STAT3 phosphorylation following IL-21 stimulation solely in B cells from sIgAD individuals. This can represent aberrant germinal center reactions or developmental halt. Thus, our work provides further insight into the unraveling of the previously hypothesized role of IL-21 to reconstitute immunoglobulin production in primary antibody deficiencies.

Cytokines use different intracellular mechanisms to upregulate the membrane expression of CX3CR1 in human monocytes

Membrane expression of fractalkine (CX₃CL1)-receptor (CX₃CR1) is relevant in monocytes (Mo) because CX₃CR1-CX₃CL1 interactions might participate on both, homeostatic and pathologic conditions. We have previously demonstrated that CX₃CR1 levels are decreased during culture and when Mo are differentiated into dendritic cells, but enhanced when differentiated into macrophages. Regarding soluble factors, lipopolysaccharide (LPS) accelerated the loss of CX₃CR1, while interleukin (IL)-10 and Interferon-gamma (IFN-γ) prevented it. However, the comprehensive knowledge about the intracellular pathways that underlay the level of CX₃CR1 expression in Mo is still incomplete. In the current work, we studied the effect of anti-inflammatory cytokines (IL-4, IL-13, IL-10), alone or together with IFN- γ on CX₃CR1 expression. We found that only IL-10 and IFN-γ separately were able to prevent CX₃CR1 down-modulation during culture of human Mo. Besides, Mo incubated with IL-10 plus IFN-γ showed the highest CX₃CR1 expression by cell, suggesting cooperation between two different mechanism used by both cytokines. By studying intracellular mechanisms triggered by IL-10 and IFN-γ, we demonstrated that they specifically induced PI3K-dependent serine-phosphorylation of signal transducer and activator of transcription (STAT)3 or STAT1, respectively. Moreover, chemical inhibitors of STAT1 or STAT3 abrogated IFN-γ or IL-10 effects on CX₃CR1 expression. Strikingly, only IL-10 increased CX₃CR1 mRNA level, as consequence of augmenting mRNA stability. CX₃CR1 mRNA increase was PI3K-dependent, supporting the causal link between the action of IL-10 at the CX₃CR1 transcript and CX₃CR1 protein level on Mo. Thus, both cytokines up-regulate CX₃CR1 expression on human Mo by different intracellular mechanisms.

MiR-125b suppresses the carcinogenesis of osteosarcoma cells via the MAPK-STAT3 pathway

The microRNA (miRNA) miR-125b is abnormally expressed in many different types of tumors, including osteosarcoma (OS). How aberrantly expressed miR-125b participates in regulating the initiation and progression of OS is still poorly understood. In the current study, we found that in OS, miR-125b can suppress the expression of MAP kinase kinase 7 (MKK7), which can dephosphorylate and inactivate signal transducer and activator of transcription 3 (STAT3). We also identified an elevated expression level of MKK7 in OS and an association between MKK7 expression and poor prognosis. Further, miR-125b inhibited OS cell proliferation and invasion by targeting and downregulating MKK7 in vitro and suppressed tumor formation in vivo. Moreover, using Western blot analysis, we preliminarily proved that the activation (phosphorylation) of STAT3 was regulated by MKK7 at the epigenetic level. MKK7 was overexpressed in OS and associated with poor clinical results. The miR-125b-MAPK-STAT3 axis may be one of the mechanisms of OS oncogenesis and a potential target for the treatment of OS.

Understanding the cancer stem cell phenotype: A step forward in the therapeutic management of cancer

The experimental validation of the existence of cancer stem cells (CSC) has had a significant impact on our understanding of the cellular mechanisms and signaling networks involved in the process of carcinogenesis and its progression. These findings provide insights into the critical role that tumor microenvironment and metabolism play in the acquisition of the drug resistance phenotype as well as provide potential targets for therapeutic exploitation. Here we briefly review the literature on the involvement of key signaling pathways such as Wnt/β-catenin, Notch, Hedgehog and STAT3 in the appearance of cancer cells with stem cells-like characteristics. In addition, we also highlight some of the recent therapeutic strategies used to target these pathways as well as approaches aiming to specifically target CSCs through their distinctive metabolic features.

Endothelin-1 stimulates expression of cyclin D1 and S-phase kinase-associated protein 2 by activating the transcription factor STAT3 in cultured rat astrocytes

Brain injury-mediated induction of reactive astrocytes often leads to glial scar formation in damaged brain regions. Activation of signal transducer and activator of transcription 3 (STAT3), a member of the STAT family of transcription factors, plays a pivotal role in inducing reactive astrocytes and glial scar formation. Endothelin-1 (ET-1) is a vasoconstrictor peptide, and its levels increase in brain disorders and promote astrocytic proliferation through ETB receptors. To clarify the mechanisms underlying ET-1-mediated astrocytic proliferation, here we examined its effects on STAT3 in cultured rat astrocytes. ET-1 treatment stimulated Ser-727 phosphorylation of STAT3 in the astrocytes, but Tyr-705 phosphorylation was unaffected, and ET-induced STAT3 Ser-727 phosphorylation was reduced by the ET_B antagonist BQ788. ET-1 stimulated STAT3 binding to its consensus DNA-binding motifs. Monitoring G₁/S phase cell cycle transition through bromodeoxyuridine (BrdU) incorporation, we found that ET-1 increases BrdU incorporation into the astrocytic nucleus, indicating cell cycle progression. Of note, STAT3 chemical inhibition (with stattic or 5,15-diphenyl-porphine (5,15-DPP)) or siRNA-mediated STAT3 silencing reduced ET-induced BrdU incorporation. Moreover, ET-1 increased astrocytic expression levels of cyclin D1 and S-phase kinase-associated protein 2 (SKP2), which were reduced by stattic, 5,15-DPP, and STAT3 siRNA. ChIP-based PCR analysis revealed that ET-1 promotes the binding of SAT3 to the 5'-flanking regions of rat cyclin D1 and SKP2 genes. Our results suggest that STAT3-mediated regulation of cyclin D1 and SKP2 expression underlies ET-induced astrocytic proliferation.

Novel STAT3 Inhibitor LDOC1 Targets Phospho-JAK2 for Degradation by Interacting with LNX1 and Regulates the Aggressiveness of Lung Cancer

Meta-analysis revealed that Leucine Zipper Down-Regulated In Cancer 1 (LDOC1) increased methylation more in people with lung tumors than in those who were healthy and never smoked. Quantitative methylation-specific PCR revealed that cigarette smoke condensate (CSC) exposure drives LDOC1 promoter hypermethylation and silence in human bronchial cells. Immunohistochemistry studies showed that LDOC1 downregulation is associated with poor survival of patients with lung cancer. Loss and gain of LDOC1 functions enhanced and attenuated aggressive phenotypes in lung adenocarcinoma A549 and non⁻small cell lung carcinoma H1299 cell lines, respectively. We found that LDOC1 deficiency led to reinforcing a reciprocal loop of IL-6/JAK2/STAT3, through which LDOC1 mediates the cancer progression. LDOC1 knockdown considerably augmented tumorigenesis and the phosphorylation of JAK2 and STAT3 in vivo. Results from immunoprecipitation and immunofluorescent confocal microscopy indicated that LDOC1 negatively regulates JAK2 activity by forming multiple protein complexes with pJAK2 and E3 ubiquitin-protein ligase LNX1, and in turn, LDOC1 targets pJAK2 to cause ubiquitin-dependent proteasomal degradation. LDOC1 deficiency attenuates the interactions between LNX1 and pJAK2, leading to ineffective ubiquitination of pJAK2, which activates STAT3. Overall, our results elucidated a crucial role of LDOC1 in lung cancer and revealed how LDOC1 acts as a bridge between tobacco exposure and the IL-6/JAK2/STAT3 loop in this human malignancy.

Cellular Substrates for Cell-Based Tissue Engineering of Human Corneal Endothelial Cells

Corneal endothelial tissue engineering aims to find solutions for blindness due to endothelial dysfunction. A suitable combination of endothelial cells, substrates and environmental cues should be deployed for engineering functional endothelial tissues. This manuscript reviews up-to-date topics of corneal endothelial tissue engineering with special emphasis on biomaterial substrates and their properties, efficacy, and mechanisms of supporting functional endothelial cells in vitro.

Activating mutations of the gp130/JAK/STAT pathway in human diseases

Cytokines of the interleukin-6 (IL-6) family are involved in numerous physiological and pathophysiological processes. Dysregulated and increased activities of its members can be found in practically all human inflammatory diseases including cancer. All cytokines activate several intracellular signaling cascades, including the Jak/STAT, MAPK, PI3K, and Src/YAP signaling pathways. Additionally, several mutations in proteins involved in these signaling cascades have been identified in human patients, which render these proteins constitutively active and result in a hyperactivation of the signaling pathway. Interestingly, some of these mutations are associated with or even causative for distinct human diseases, making them interesting targets for therapy. This chapter describes the basic biology of the gp130/Jak/STAT pathway, summarizes what is known about the molecular mechanisms of the activating mutations, and gives an outlook how this knowledge can be exploited for targeted therapy in human diseases.

Targeting STATs in neuroinflammation: The road less traveled!

JAK/STAT transduction pathway is a highly conserved pathway implicated in regulating cellular proliferation, differentiation, survival and apoptosis. Dysregulation of this pathway is involved in the onset of autoimmune, haematological, oncological, metabolic and neurological diseases. Over the last few years, the research of anti-neuroinflammatory agents has gained considerable attention. The ability to diminish the STAT-induced transcription of inflammatory genes is documented for both natural compounds (such as polyphenols) and chemical drugs. Among polyphenols, quercetin and curcumin directly inhibit STAT, while Berberis vulgaris L. and Sophora alopecuroides L extracts act indirectly. Also, the Food and Drug Administration has approved several JAK/STAT inhibitors (direct or indirect) for treating inflammatory diseases, indicating STAT can be considered as a therapeutic target for neuroinflammatory pathologies. Considering the encouraging data obtained so far, clinical trials are warranted to demonstrate the effectiveness and potential use in the clinical practice of STAT inhibitors to treat inflammation-associated neurodegenerative pathologies.

Chemoresistance and the Self-Maintaining Tumor Microenvironment

The progression of cancer is associated with alterations in the tumor microenvironment, including changes in extracellular matrix (ECM) composition, matrix rigidity, hypervascularization, hypoxia, and paracrine factors. One key malignant phenotype of cancer cells is their ability to resist chemotherapeutics, and elements of the ECM can promote chemoresistance in cancer cells through a variety of signaling pathways, inducing changes in gene expression and protein activity that allow resistance. Furthermore, the ECM is maintained as an environment that facilitates chemoresistance, since its constitution modulates the phenotype of cancer-associated cells, which themselves affect the microenvironment. In this review, we discuss how the properties of the tumor microenvironment promote chemoresistance in cancer cells, and the interplay between these external stimuli. We focus on both the response of cancer cells to the external environment, as well as the maintenance of the external environment, and how a chemoresistant phenotype emerges from the complex signaling network present.

STAT1 regulates macrophage number and phenotype and prevents renal fibrosis after ischemia-reperfusion injury

Renal ischemia-reperfusion injury (IRI) leads to acute kidney injury or delayed allograft function, which predisposes to fibrosis in the native kidney or kidney transplant. Here we investigated the role of the signal transducer and activator of transcription 1 (STAT1) in inflammatory responses following renal IRI. Our study showed that a subsequent stimulation of Janus-activated kinase 2/STAT1 and Toll-like receptor 4 pathways led to greater STAT1 activation followed by increased cytokine transcription compared with single-pathway stimulation in murine renal tubular cells. Moreover, we observed increased activation of STAT1 under hypoxic conditions. In vivo, STAT1^-/- mice displayed less acute tubular necrosis and decreased macrophage infiltration 24 h after renal ischemia. However, investigation of the healing phase (30 days after IRI) revealed significantly more fibrosis in STAT1^-/- than in wild-type kidneys. In addition, we demonstrated increased macrophage infiltration in STAT1^-/- kidneys. Flow cytometry analysis revealed that STAT1 deficiency drives an alternatively activated macrophage phenotype, which is associated with downregulated cluster of differentiation 80 expression, decreased intracellular reactive oxygen species production, and enhanced ability for phagocytosis. Furthermore, we detected immunohistochemically enhanced STAT1 expression in human renal allograft biopsies with no interstitial fibrosis/tubular atrophy (IF/TA) compared with specimens with severe IF/TA without specific etiology. Thus, STAT1 activation drives macrophages toward an alternatively activated phenotype and enhances fibrogenesis indicating a potential STAT1-driven protective mechanism in tissue repair after ischemic injury.

STAT3 suppresses Wnt/β-catenin signaling during the induction phase of primary Myf5+ brown adipogenesis

Thermogenic fat is a promising target for new therapies in diabetes and obesity. Understanding how thermogenic fat develops is important to develop rational strategies to treat obesity. Previously, we have shown that Tyk2 and STAT3, part of the JAK-STAT pathway, are necessary for proper development of classical brown fat. Using primary preadipocytes isolated from newborn mice we demonstrate that STAT3 is required for differentiation and robust expression of Uncoupling Protein 1 (UCP1). We also confirm that STAT3 is necessary during the early induction stage of differentiation and is dispensable during the later terminal differentiation stage. The inability of STAT3-/- preadipocytes to differentiate can be rescued using Wnt ligand secretion inhibitors when applied during the induction stage. Through chemical inhibition and RNAi, we show that it is the canonical β-catenin pathway that is responsible for the block in differentiation; inhibition or knockdown of β-catenin can fully rescue adipogenesis and UCP1 expression in the STAT3-/- adipocytes. During the induction stage, Wnts 1, 3a, and 10b have increased expression in the STAT3-/- adipocytes, potentially explaining the increased levels and activity of β-catenin. Our results for the first time point towards an interaction between the JAK/STAT pathway and the Wnt/β-catenin pathway during the early stages of in-vitro adipogenesis.

The fungal metabolite cyclonerodiol inhibits IL-4/IL-13 induced Stat6-signaling through blocking the association of Stat6 with p38, ERK1/2 and p300

The IL-4/IL-13/Stat6 pathway is the key driver of asthma pathophysiology. Therefore the development of inhibitors that specifically modulate IL-13/IL-4 or the downstream signaling molecules like Stat6 may be useful as a therapeutic strategy for the treatment of asthma and multiple allergic diseases. We have previously identified the fungal 2,6-cyclofarnesane cyclonerodiol as an inhibitor of IL-4 induced Stat6-dependent signaling in the alveolar epithelial cell line A549 using a transcriptional reporter. In this study we investigated the underlying mode of action of cyclonerodiol on the IL-4/IL-13/Stat6 pathway. Cyclonerodiol failed to interfere with activation, nuclear transport or binding of Stat6 to the corresponding consensus sequence on the DNA. Our results showed that cyclonerodiol blocked serine phosphorylation of Stat6 by affecting its association with p38 and Erk1/2. Cyclonerodiol also prevented the recruitment of the transcriptional coactivator p300 and Stat6 acetylation. These findings suggest that cyclonerodiol affects IL-4/IL-13 induced expression of asthma related marker genes by blocking transcriptional activation.

Protein Tyrosine Phosphatases as Potential Regulators of STAT3 Signaling

The signal transducer and activator of transcription 3 (STAT3) protein is a major transcription factor involved in many cellular processes, such as cell growth and proliferation, differentiation, migration, and cell death or cell apoptosis. It is activated in response to a variety of extracellular stimuli including cytokines and growth factors. The aberrant activation of STAT3 contributes to several human diseases, particularly cancer. Consequently, STAT3-mediated signaling continues to be extensively studied in order to identify potential targets for the development of new and more effective clinical therapeutics. STAT3 activation can be regulated, either positively or negatively, by different posttranslational mechanisms including serine or tyrosine phosphorylation/dephosphorylation, acetylation, or demethylation. One of the major mechanisms that negatively regulates STAT3 activation is dephosphorylation of the tyrosine residue essential for its activation by protein tyrosine phosphatases (PTPs). There are seven PTPs that have been shown to dephosphorylate STAT3 and, thereby, regulate STAT3 signaling: PTP receptor-type D (PTPRD), PTP receptor-type T (PTPRT), PTP receptor-type K (PTPRK), Src homology region 2 (SH-2) domain-containing phosphatase 1(SHP1), SH-2 domain-containing phosphatase 2 (SHP2), MEG2/PTP non-receptor type 9 (PTPN9), and T-cell PTP (TC-PTP)/PTP non-receptor type 2 (PTPN2). These regulators have great potential as targets for the development of more effective therapies against human disease, including cancer.

Targeting a phospho-STAT3-miRNAs pathway improves vesicular hepatic steatosis in an in vitro and in vivo model

Non-alcoholic fatty liver disease (NAFLD) is a leading cause of chronic liver disease. Although genetic predisposition and epigenetic factors contribute to the development of NAFLD, our understanding of the molecular mechanism involved in the pathogenesis of the disease is still emerging. Here we investigated a possible role of a microRNAs-STAT3 pathway in the induction of hepatic steatosis. Differentiated HepaRG cells treated with the fatty acid sodium oleate (fatty dHepaRG) recapitulated features of liver vesicular steatosis and activated a cell-autonomous inflammatory response, inducing STAT3-Tyrosine-phosphorylation. With a genome-wide approach (Chromatin Immunoprecipitation Sequencing), many phospho-STAT3 binding sites were identified in fatty dHepaRG cells and several STAT3 and/or NAFLD-regulated microRNAs showed increased expression levels, including miR-21. Innovative CARS (Coherent Anti-Stokes Raman Scattering) microscopy revealed that chemical inhibition of STAT3 activity decreased lipid accumulation and deregulated STAT3-responsive microRNAs, including miR-21, in lipid overloaded dHepaRG cells. We were able to show in vivo that reducing phospho-STAT3-miR-21 levels in C57/BL6 mice liver, by long-term treatment with metformin, protected mice from aging-dependent hepatic vesicular steatosis. Our results identified a microRNAs-phosphoSTAT3 pathway involved in the development of hepatic steatosis, which may represent a molecular marker for both diagnosis and therapeutic targeting.

Toxoplasma gondii stabilises tetrameric complexes of tyrosine-phosphorylated signal transducer and activator of transcription-1 and leads to its sustained and promiscuous DNA binding

Toxoplasma gondii is an obligate intracellular parasite that infects up to 30% of humans worldwide. It can lead to severe diseases particularly in individuals with immature or defective immune responses. Control of T. gondii relies on the IFN-γ-induced signal transducer and activator of transcription-1 (STAT1) pathway. T. gondii, however, largely inactivates STAT1-mediated gene transcription by T. gondii inhibitor of STAT1-dependent transcription (TgIST), a parasite effector protein binding to STAT1. Here, we have analysed requirements of STAT1 to bind TgIST and characterised downstream effects on STAT1 signalling. TgIST bound to STAT1 dimers but more efficiently assembled with STAT1 tetramers, which are essential for effective IFN-γ responsiveness. Such binding was abrogated in N-terminal, but not C-terminal deletion mutants of STAT1. Furthermore, TgIST did not bind to the STAT1^F77A substitution mutant that cannot form STAT1 tetramers, resulting in a complete unresponsiveness of parasite-infected STAT1^F77A -expressing cells to IFN-γ. Remarkably, binding of TgIST considerably increased the affinity of the aberrant STAT1 tetramers for DNA consensus sequence binding motifs and even enabled binding to nonconsensus sequences. Consistent with the increased DNA binding, STAT1 from parasite-infected cells remained phosphorylated at Tyr⁷⁰¹ and Ser⁷²⁷ and was retained within the nucleus in a DNA-bound state. The sustained and promiscuous binding activity particularly of STAT1 tetramers to unspecific DNA sites lacking a consensus STAT1-binding motif is an as yet unrecognised mechanism contributing to the defective IFN-γ-mediated signalling in T. gondii-infected cells.

Role of STAT signaling and autocrine action of chemokines during H2 O 2 induced HTR-8/SVneo trophoblastic cells invasion

During pregnancy, regulated generation of reactive oxygen species (ROS) is important for activation of signaling pathways and placentation. In the current study, the effect of H₂ O₂ on invasion of HTR-8/SVneo cells, a human extravillous trophoblast cell line, is investigated. Treatment of HTR-8/SVneo cells for 24 hr with H ₂ O₂ (25 µM) leads to a significant increase in invasion without affecting cell proliferation, viability, and apoptosis. Concomitantly, a significant increase in the matrix metalloproteinase-9 (MMP-9)/tissue inhibitor of metalloproteinases-1 (TIMP-1) ratio is observed. Further, significant increase in phosphorylation of signal transducer and activator of transcription 1 (STAT-1) and STAT-3 (both at ser727 residue) is observed on treating HTR-8/SVneo cells with 25 µM of H₂ O₂ accompanied by an increase in the secretion of interleukin-8 (IL-8) and macrophage inflammatory protein-1β (MIP-1β). A significant decrease in H₂ O₂ -mediated invasion of HTR-8/SVneo cells and reduced expression of IL-8 and MIP-1β accompanied by decrease in MMP-9/TIMP-1 ratio are observed on inhibiting STAT-1 and STAT-3 by small interfering RNA (siRNA). Inhibition of STAT-1 activity by fludarabine and STAT-3 activity by Stattic also leads to a decrease in H₂ O₂ -mediated increase in HTR-8/SVneo cell invasion. Inhibition of IL-8 and MIP-1β by siRNA also leads to a significant decrease in both basal and H₂ O₂ -mediated invasion. Interestingly, inhibition of MIP-1β by siRNA leads to a significant reduction in H₂ O₂ -mediated increase in IL-8. However, no significant effect of IL-8 silencing on H₂ O₂ -mediated MIP-1β expression was observed. From the above results, it can be concluded that H₂ O₂ activates STAT signaling, MIP-1β & IL-8 secretion and increases MMP-9/TIMP-1 ratio leading to an increased invasion of HTR-8/SVneo cells without affecting their viability.

"Do We Know Jack" About JAK? A Closer Look at JAK/STAT Signaling Pathway

Janus tyrosine kinase (JAK) family of proteins have been identified as crucial proteins in signal transduction initiated by a wide range of membrane receptors. Among the proteins in this family JAK2 has been associated with important downstream proteins, including signal transducers and activators of transcription (STATs), which in turn regulate the expression of a variety of proteins involved in induction or prevention of apoptosis. Therefore, the JAK/STAT signaling axis plays a major role in the proliferation and survival of different cancer cells, and may even be involved in resistance mechanisms against molecularly targeted drugs. Despite extensive research focused on the protein structure and mechanisms of activation of JAKs, and signal transduction through these proteins, their importance in cancer initiation and progression seem to be underestimated. This manuscript is an attempt to highlight the role of JAK proteins in cancer biology, the most recent developments in targeting JAKs, and the central role they play in intracellular cross-talks with other signaling cascades.

O-Glycosylation with O-linked β-N-acetylglucosamine increases vascular contraction: Possible modulatory role on Interleukin-10 signaling pathway

AIMS

The interleukin-10 (IL-10) is an immuno-regulatory cytokine that plays a protective effect in the vasculature. IL-10 binding to its receptor, activating the IL-10/JAK1/STAT3 cascade to exert its effects. Therefore, STAT3 phosphorylation is essential for IL-10 actions. O-Glycosylation with linked β-N-acetylglucosamine (O-GlcNAc) is a post-translational modification able to regulate many proteins by interfering with protein on a phosphorylation level. Our aim was to determine whether O-GlcNAc promotes the inhibition of IL-10-pathway (JAK1/STAT3/IL-10), inactivationg its action in the vasculature.

MAIN METHODS

Mice (C57BL/6) aortic segments were incubated with vehicle or Thiamet G (0.1 mM, for 24 h) to increase global O-GlcNAc levels. Aortas from knockout mice for IL-10 were also used. Vascular reactivity and western blot tests were performed to evaluate protein expression.

KEY FINDINGS

High levels of O-GlcNAc, induced by Thiamet G incubation, increased vascular expression of JAK1, but decreased expression and activity of STAT3. In addition, IL-10 levels were diminished in arteries treated with Thiamet G. Absence of IL-10, as well as augmented O-GlcNAcylation, increased vascular reactivity to constrictor stimuli, an effect that was abolished by ERK 1/2 inhibitor. High levels of O-GlcNAc and the absence of IL-10 also leads to increased vascular expression of ERK1/2.

SIGNIFICANCE

Our data suggest that O-GlcNAc modification seems to (dys)regulate IL-10 signaling pathway and consequently, compromise the protective effect of this cytokine in vasculature. It is possible that there is a promising relationship in pathophysiological conditions where changes in O-GlcNAcylation and IL-10 levels are observed, such as hypertension and diabetes.

Mitophagy in Intestinal Epithelial Cells Triggers Adaptive Immunity during Tumorigenesis

In colorectal cancer patients, a high density of cytotoxic CD8⁺ T cells in tumors is associated with better prognosis. Using a Stat3 loss-of-function approach in two wnt/β-catenin-dependent autochthonous models of sporadic intestinal tumorigenesis, we unravel a complex intracellular process in intestinal epithelial cells (IECs) that controls the induction of a CD8⁺ T cell based adaptive immune response. Elevated mitophagy in IECs causes iron(II)-accumulation in epithelial lysosomes, in turn, triggering lysosomal membrane permeabilization. Subsequent release of proteases into the cytoplasm augments MHC class I presentation and activation of CD8⁺ T cells via cross-dressing of dendritic cells. Thus, our findings highlight a so-far-unrecognized link between mitochondrial function, lysosomal integrity, and MHC class I presentation in IECs and suggest that therapies triggering mitophagy or inducing LMP in IECs may prove successful in shifting the balance toward anti-tumor immunity in colorectal cancer.

spd1672, a novel in vivo-induced gene, affects inflammatory response in a murine model of Streptococcus pneumoniae infection

spd1672, a novel Streptococcus pneumoniae (hereinafter S. pn) gene induced in vivo, has been identified to contribute to the virulence of S. pn; however, the role of spd1672 during host innate immune reaction against S. pn infection is unknown. In the present study, mice were infected with wild-type D39 and mutant D39Δspd1672 strains. Compared with the D39-infected mice, reduced bacterial load and attenuated inflammatory response were observed in the D39Δspd1672-treated mice. The levels of proinflammatory cytokines, including IFN-γ, TNF-α, and IL-1β, in the blood of D39Δspd1672-infected mice were lower than that in the D39-infected group. Additionally, attenuated activation of STAT3 and AKT was observed in the D39Δspd1672-infected mice. In conclusion, our data indicated that spd1672 expression modulates the release of proinflammatory cytokines, and AKT–STAT3 signaling appears to participate in the process. In conclusion, the present study extends our understanding of the role of an in vivo-induced gene in S. pn–host interaction.

Organophosphate pesticide chlorpyrifos impairs STAT1 signaling to induce dopaminergic neurotoxicity: Implications for mitochondria mediated oxidative stress signaling events

The organophosphate (OP) pesticide chlorpyrifos (CPF), used in agricultural settings, induces developmental and neurological impairments. Recent studies using in vitro cell culture models have reported CPF exposure to have a positive association with mitochondria-mediated oxidative stress response and dopaminergic cell death; however, the mechanism by which mitochondrial reactive oxygen species (ROS) contribute to dopaminergic cell death remains unclear. Therefore, we hypothesized that STAT1, a transcription factor, causes apoptotic dopaminergic cell death via mitochondria-mediated oxidative stress mechanisms. Here we show that exposure of dopaminergic neuronal cells such as N27 cells (immortalized murine mesencephalic dopaminergic cells) to CPF resulted in a dose-dependent increase in apoptotic cell death as measured by MTS assay and DNA fragmentation. Similar effects were observed in CPF-treated human dopaminergic neuronal cells (LUHMES cells), with an associated increase in mitochondrial dysfunction. Moreover, CPF (10 μM) induced time-dependent increase in STAT1 activation coincided with the collapse of mitochondrial transmembrane potential, increase in ROS generation, proteolytic cleavage of protein kinase C delta (PKCδ), inhibition of the mitochondrial basal oxygen consumption rate (OCR), with a concomitant reduction in ATP-linked OCR and reserve capacity, increase in Bax/Bcl-2 ratio and enhancement of autophagy. Additionally, by chromatin immunoprecipitation (ChIP), we demonstrated that STAT1 bound to a putative regulatory sequence in the NOX1 and Bax promoter regions in response to CPF in N27 cells. Interestingly, overexpression of non-phosphorylatable STAT1 mutants (STAT1Y701F and STAT1S727A) but not STAT1 WT construct attenuated the cleavage of PKCδ and ultimately cell death in CPF-treated cells. Furthermore, small interfering RNA knockdown demonstrated STAT1 to be a critical regulator of autophagy and mitochondria-mediated proapoptotic cell signaling events after CPF treatment in N27 cells. Finally, oral administration of CPF (5 mg/kg) in postnatal rats (PNDs 27-61) induced motor deficits, and nigrostriatal dopaminergic neurodegeneration with a concomitant induction of STAT1-dependent proapoptotic cell signaling events. Conversely, co-treatment with mitoapocynin (a mitochondrially-targeted antioxidant) and CPF rescued motor deficits, and restored dopaminergic neuronal survival via abrogation of STAT1-dependent proapoptotic cell signaling events. Taken together, our study identifies a novel mechanism by which STAT1 regulates mitochondria-mediated oxidative stress response, PKCδ activation and autophagy. In this context, the phosphorylation of Tyrosine 701 and Serine 727 in STAT1 was found to be essential for PKCδ cleavage. By attenuating mitochondrial-derived ROS, mitoapocynin may have therapeutic applications for reversing CPF-induced dopaminergic neurotoxicity and associated neurobehavioral deficits as well as neurodegenerative diseases.

Cooperative STAT/NF-κB signaling regulates lymphoma metabolic reprogramming and aberrant GOT2 expression

Knowledge of stromal factors that have a role in the transcriptional regulation of metabolic pathways aside from c-Myc is fundamental to improvements in lymphoma therapy. Using a MYC-inducible human B-cell line, we observed the cooperative activation of STAT3 and NF-κB by IL10 and CpG stimulation. We show that IL10 + CpG-mediated cell proliferation of MYC^low cells depends on glutaminolysis. By ¹³C- and ¹⁵N-tracing of glutamine metabolism and metabolite rescue experiments, we demonstrate that GOT2 provides aspartate and nucleotides to cells with activated or aberrant Jak/STAT and NF-κB signaling. A model of GOT2 transcriptional regulation is proposed, in which the cooperative phosphorylation of STAT3 and direct joint binding of STAT3 and p65/NF-κB to the proximal GOT2 promoter are important. Furthermore, high aberrant GOT2 expression is prognostic in diffuse large B-cell lymphoma underscoring the current findings and importance of stromal factors in lymphoma biology.

Metabolic rewiring of cancer cells can be driven by both extrinsic and intrinsic factors. Here the authors show that microenvironmental factors induce metabolic rewiring of B-cell lymphoma through activation of STAT3 and NF-ΚB resulting in upregulation of the aminotransferase GOT2 and glutamine addiction.

STAT3 activation by E6 is essential for the differentiation-dependent HPV18 life cycle

Human papillomaviruses (HPV) activate a number of host factors to control their differentiation-dependent life cycles. The transcription factor signal transducer and activator of transcription (STAT)-3 is important for cell cycle progression and cell survival in response to cytokines and growth factors. STAT3 requires phosphorylation on Ser727, in addition to phosphorylation on Tyr705 to be transcriptionally active. In this study, we show that STAT3 is essential for the HPV life cycle in undifferentiated and differentiated keratinocytes. Primary human keratinocytes containing high-risk HPV18 genomes display enhanced STAT3 phosphorylation compared to normal keratinocytes. Expression of the E6 oncoprotein is sufficient to induce the dual phosphorylation of STAT3 at Ser727 and Tyr705 by a mechanism requiring Janus kinases and members of the MAPK family. E6-mediated activation of STAT3 induces the transcription of STAT3 responsive genes including cyclin D1 and Bcl-xL. Silencing of STAT3 protein expression by siRNA or inhibition of STAT3 activation by small molecule inhibitors, or by expression of dominant negative STAT3 phosphorylation site mutants, results in blockade of cell cycle progression. Loss of active STAT3 impairs HPV gene expression and prevents episome maintenance in undifferentiated keratinocytes and upon differentiation, lack of active STAT3 abolishes virus genome amplification and late gene expression. Organotypic raft cultures of HPV18 containing keratinocytes expressing a phosphorylation site STAT3 mutant display a profound reduction in suprabasal hyperplasia, which correlates with a loss of cyclin B1 expression and increased differentiation. Finally, increased STAT3 expression and phosphorylation is observed in HPV positive cervical disease biopsies compared to control samples, highlighting a role for STAT3 activation in cervical carcinogenesis. In summary, our data provides evidence of a critical role for STAT3 in the HPV18 life cycle.

STAT3 as a potential immunotherapy biomarker in oncogene-addicted non-small cell lung cancer

Immune checkpoint blockade has modified the treatment landscape for many types of tumors, including lung cancer. Still our knowledge on the biology of the interaction between tumor cells and the microenvironment is limited, preventing the optimal use of these new compounds and the maximum benefit that the patients can derive from them. We have actively worked on the role of STAT3, a transcriptional factor that causes innate resistance to targeted therapies in oncogene-addicted tumors. In this short review we take the opportunity to express our opinion and review existing knowledge on the immune role of STAT3 and the possible implications that this may have for the discovery of new biomarkers to predict response to immunotherapy, as well as new partners to combine with and increase the efficacy of immune checkpoint inhibitors.

Inhibitory effects of bee venom on mast cell-mediated allergic inflammatory responses

Although bee venom (BV) is a toxin that causes bee stings to be painful, it has been widely used clinically for the treatment of certain immune‑associated diseases. BV has been used traditionally for the treatment of chronic inflammatory diseases. In this regard, the present study analyzed the effect of BV on the regulation of inflammatory mediator production by mast cells and their allergic inflammatory responses in an animal model. HMC‑1 cells were treated with BV prior to stimulation with phorbol‑12‑myristate 13‑acetate plus calcium ionophore A23187 (PMACI). The production of allergy‑associated pro‑inflammatory mediators was examined, and the underlying mechanisms were investigated. Furthermore, to investigate whether BV exhibits anti‑inflammatory effects associated with anti‑allergic effects in vivo, a compound 48/80‑induced anaphylaxis model was used. BV inhibited histamine release, mRNA expression and production of cytokines in the PMACI‑stimulated HMC‑1 cells. Furthermore, the inhibitory effects of BV on mitogen‑activated protein kinase (MAPK), MAPK kinase, signal transducer and activator of transcription 3 (STAT3) and Akt were demonstrated. The present study also investigated the ability of BV to inhibit compound 48/80‑induced systemic anaphylaxis in vivo. BV protected the mice against compound 48/80‑induced anaphylactic‑associated mortality. Furthermore, BV suppressed the mRNA expression levels of pro‑inflammatory cytokines, and suppressed the activation of MAPK and STAT3 in this model. These results provide novel insights into the possible role of BV as a modulator for mast cell‑mediated allergic inflammatory disorders.

Reactive oxygen species released from astrocytes treated with amyloid beta oligomers elicit neuronal calcium signals that decrease phospho-Ser727-STAT3 nuclear content

The transcription factor STAT3 has a crucial role in the development and maintenance of the nervous system. In this work, we treated astrocytes with oligomers of the amyloid beta peptide (AβOs), which display potent synaptotoxic activity, and studied the effects of mediators released by AβOs-treated astrocytes on the nuclear location of neuronal serine-727-phosphorylated STAT3 (pSerSTAT3). Treatment of mixed neuron-astrocyte cultures with 0.5µMAβOs induced in neurons a significant decrease of nuclear pSerSTAT3, but not of phosphotyrosine-705 STAT3, the other form of STAT3 phosphorylation. This decrease did not occur in astrocyte-poor neuronal cultures revealing a pivotal role for astrocytes in this response. To test if mediators released by astrocytes in response to AβOs induce pSerSTAT3 nuclear depletion, we used conditioned medium derived from AβOs-treated astrocyte cultures. Treatment of astrocyte-poor neuronal cultures with this medium caused pSerSTAT3 nuclear depletion but did not modify overall STAT3 levels. Extracellular catalase prevented the pSerSTAT3 nuclear depletion caused by astrocyte-conditioned medium, indicating that reactive oxygen species (ROS) mediate this response. This conditioned medium also increased neuronal oxidative tone, leading to a ryanodine-sensitive intracellular calcium signal that proved to be essential for pSerSTAT3 nuclear depletion. In addition, this depletion decreased BCL2 and Survivin transcription and significantly increased BAX/BCL2 ratio. This is the first description that ROS generated by AβOs-treated astrocytes and neuronal calcium signals jointly regulate pSerSTAT3 nuclear distribution in neurons. We propose that astrocytes release ROS in response to AβOs, which by increasing neuronal oxidative tone, generate calcium signals that cause pSerSTAT3 nuclear depletion and loss of STAT3 protective transcriptional activity.

STAT3/p53 pathway activation disrupts IFN-β-induced dormancy in tumor-repopulating cells

Dynamic interaction with the immune system profoundly regulates tumor cell dormancy. However, it is unclear how immunological cues trigger cancer cell-intrinsic signaling pathways for entering into dormancy. Here, we show that IFN-β treatment induced tumor-repopulating cells (TRC) to enter dormancy through an indolamine 2,3-dioxygenase/kynurenine/aryl hydrocarbon receptor/p27-dependent (IDO/Kyn/AhR/p27-dependent) pathway. Strategies to block this metabolic circuitry did not relieve dormancy, but led to apoptosis of dormant TRCs in murine and human melanoma models. Specifically, blocking AhR redirected IFN-β signaling to STAT3 phosphorylation through both tyrosine and serine sites, which subsequently facilitated STAT3 nuclear translocation and subsequent binding to the p53 promoter in the nucleus. Upregulation of p53 in turn disrupted the pentose phosphate pathway, leading to excessive ROS production and dormant TRC death. Additionally, in melanoma patients, high expression of IFN-β correlated with tumor cell dormancy. Identification of this mechanism for controlling TRC dormancy by IFN-β provides deeper insights into cancer-immune interaction and potential new cancer immunotherapeutic modalities.

Bilateral activation of STAT3 by phosphorylation at the tyrosine-705 (Y705) and serine-727 (S727) positions and its nuclear translocation in primary sensory neurons following unilateral sciatic nerve injury

Unilateral sciatic nerve compression (SNC) or complete sciatic nerve transection (CSNT), both varying degrees of nerve injury, induced activation of STAT3 bilaterally in the dorsal root ganglia (DRG) neurons of lumbar (L4-L5) as well as cervical (C6-C8) spinal cord segments. STAT3 activation was by phosphorylation at the tyrosine-705 (Y705) and serine-727 (S727) positions and was followed by their nuclear translocation. This is the first evidence of STAT3(S727) activation together with the well-known activation of STAT3(Y705) in primary sensory neurons upon peripheral nerve injury. Bilateral activation of STAT3 in DRG neurons of spinal segments anatomically both associated as well as non-associated with the injured nerve indicates diffusion of STAT3 activation inducers along the spinal cord. Increased levels of IL-6 protein in the CSF following nerve injury as well as activation and nuclear translocation of STAT3 in DRG after intrathecal injection of IL-6 shows that this cytokine, released into the subarachnoid space can penetrate the DRG to activate STAT3. Previous results on increased bilateral IL-6 synthesis and the present manifestation of STAT3 activation in remote DRG following unilateral sciatic nerve injury may reflect a systemic reaction of the DRG neurons to nerve injury.

CD44 and CD24 coordinate the reprogramming of nasopharyngeal carcinoma cells towards a cancer stem cell phenotype through STAT3 activation

Cell surface proteins such as CD44 and CD24 are used to distinguish cancer stem cells (CSCs) from the bulk-tumor population. However, the molecular functionalities of CD24 and CD44, and how these two molecules coordinate in CSCs remain poorly understood. We found that nasopharyngeal carcinoma (NPC) cells with high expression of CD44 and CD24 proteins presented with pronounced CSC properties. Accordingly, a subpopulation of NPC cells with co-expression of CD44 and CD24 were specially enriched in high-stage clinical samples. Furthermore, ectopically expressing the epithelial-mesenchymal transition (EMT) regulator Twist was able to upregulate the stemness factors, and vice versa. This indicates a reciprocal regulation of stemness and EMT. Intriguingly, we found that this reciprocal regulation was differentially orchestrated by CD44 and CD24, and only simultaneous silencing the expression of CD44 and CD24 led to a broad-spectrum suppression of CSC properties. Oppositely, overexpression of CD44 and CD24 induced the reprogramming of parental NPC cells into CSCs through STAT3 activation, which could be blunted by STAT3 inhibition, indicating that CD44 and CD24 collaboratively drive the reprogramming of NPC cells through STAT3-mediated stemness and EMT activation. Consequently, targeting of the CD44/CD24/STAT3 axis may provide a potential therapeutic paradigm for the treatment of NPC through repressing CSC activities.

Prevention of Burn-Induced Inflammatory Responses and Muscle Wasting by GTS-21, a Specific Agonist for α7 Nicotinic Acetylcholine Receptors

INTRODUCTION

Muscle wasting (MW) in catabolic conditions (e.g., burn injury [BI]) is a major risk factor affecting prognosis. Activation of interleukin-1β (IL-1β)/nuclear factor-kappa B (NF-κB), interleukin-6 (IL-6)/signal transducer and activator of transcription 3 (STAT3), and/or forkhead box O transcriptional factor (FOXO)-mediated gene transcription pathways is the pivotal trigger of inflammatory response-induced protein catabolic processes in muscle. The α7 acetylcholine receptors (α7AChRs) are upregulated in macrophages and peripheral tissues including skeletal muscle during MW conditions. Stimulation of α7AChRs mitigates inflammatory responses. Hypothesis tested is that attenuation of inflammation by α7AChR stimulation with specific α7AChR agonist, GTS-21, will reverse BI-induced body mass and MW by modulating inflammatory and proteolytic signals.

METHODS

Body surface area (30%) BI or sham BI mice were treated with GTS-21 or saline. Tibialis anterior (TA) muscle was harvested at 6 h, day 1 or 3 to examine inflammatory and proteolytic signals.

RESULTS

GTS-21 significantly ameliorated the BI-induced increased expression of inflammatory cytokines IL-6, IL-1β, C-X-C motif chemokine ligand 2 (6 h), phosphorylated STAT3, and NF-κB (day 1) in TA muscle. GTS-21 also significantly inhibited BI-induced increase of MuRF1 and FOXO1 (day 1). Consistent with the cytokine and inflammatory mediator changes, BI-induced body weight and TA muscle mass loss at day 3 were mitigated by GTS-21 treatment. The beneficial effect of GTS-21 on BI changes was absent in methyllycaconitine (α7AChR antagonist)-treated wild-type and α7AChR knockout mice.

CONCLUSION

GTS-21 stimulation of α7AChRs, by modulating multiple molecular signals related to inflammation and proteolysis, attenuates protein wasting, evidenced by maintenance of body weight and attenuation of distant muscle mass loss after BI. GTS-21 can be a novel, potent therapeutic option for reversal of BI-induced MW.

Stat3 and CCAAT enhancer-binding protein β (C/ebpβ) activate Fanconi C gene transcription during emergency granulopoiesis

Interferon consensus sequence–binding protein (Icsbp) is required for terminating emergency granulopoiesis, an episodic event responsible for granulocyte production in response to infections and a key component of the innate immune response. Icsbp inhibits the expression of Stat3 and C/ebpβ, transcription factors essential for initiating and sustaining granulopoiesis, and activates transcription of Fanconi C (FANCC), a DNA repair protein. In prior studies, we noted accelerated bone marrow failure in Fancc^−/− mice undergoing multiple episodes of emergency granulopoiesis, associated with apoptosis of bone marrow cells with unrepaired DNA damage. Additionally, we found increased expression of Fanconi C and F proteins during emergency granulopoiesis. These findings suggest that Icsbp protects the bone marrow from DNA damage by increasing activity of the Fanconi DNA repair pathway, but the mechanisms for FANCC activation during initiation of emergency granulopoiesis are unclear. In this study, we observed that Stat3 and C/ebpβ activate FANCC transcription and contribute to DNA repair. Our findings indicate that FancC expression is increased during Stat3- and C/ebpβ-induced initiation of emergency granulopoiesis by these transcription factors and is maintained through termination by Icsbp. Our work reveals that Stat3- and C/ebpβ-mediated FancC expression is a critical component for initiating and sustaining key innate immune responses.

Interaction of suppressor of cytokine signalling 3 with cavin-1 links SOCS3 function and cavin-1 stability

Effective suppression of JAK-STAT signalling by the inducible inhibitor "suppressor of cytokine signalling 3" (SOCS3) is essential for limiting signalling from cytokine receptors. Here we show that cavin-1, a component of caveolae, is a functionally significant SOCS3-interacting protein. Biochemical and confocal imaging demonstrate that SOCS3 localisation to the plasma membrane requires cavin-1. SOCS3 is also critical for cavin-1 stabilisation, such that deletion of SOCS3 reduces the expression of cavin-1 and caveolin-1 proteins, thereby reducing caveola abundance in endothelial cells. Moreover, the interaction of cavin-1 and SOCS3 is essential for SOCS3 function, as loss of cavin-1 enhances cytokine-stimulated STAT3 phosphorylation and abolishes SOCS3-dependent inhibition of IL-6 signalling by cyclic AMP. Together, these findings reveal a new functionally important mechanism linking SOCS3-mediated inhibition of cytokine signalling to localisation at the plasma membrane via interaction with and stabilisation of cavin-1.