STAT Signaling in the Pathogenesis and Treatment of Cancer

Cytokine Signaling in Pediatric Kidney Tumor Cell Lines WT-CLS1, WT-3ab and G-401

Renal tumors comprise ~7% of all malignant pediatric tumors. Approximately 90% of pediatric kidney tumors comprise Wilms tumors, and the remaining 10% include clear cell sarcoma of the kidney, malignant rhabdoid tumor of the kidney, renal cell carcinoma and other rare renal tumors. Over the last 30 years, the role of cytokines and their receptors has been considerably investigated in both cancer progression and anti-cancer therapy. However, more effective immunotherapies require the cytokine profiling of each tumor type and comprehensive understanding of tumor biology. In this study, we aimed to investigate the activation of signaling pathways in response to cytokines in three pediatric kidney tumor cell lines, in WT-CLS1 and WT-3ab cells (both are Wilms tumors), and in G-401 cells (a rhabdoid kidney tumor, formerly classified as Wilms tumor). We observed that interferon-alpha (IFN-α) and interferon-gamma (IFN-γ) very strongly induced the activation of the STAT1 protein, whereas IL-6 and IFN-α activated STAT3 and IL-4 activated STAT6 in all examined tumor cell lines. STAT protein activation was examined by flow cytometry and Western blot using phospho-specific anti-STAT antibodies which recognize only activated (phosphorylated) STAT proteins. Nuclear translocation of phospho-STAT proteins upon activation with specific cytokines was furthermore confirmed by immunofluorescence. Our results also showed that both IFN-α and IFN-γ caused upregulation of major histocompatibility complex (MHC) class I proteins, however, these cytokines did not have any effect on the expression of MHC class II proteins. We also observed that pediatric kidney tumor cell lines exhibit the functional expression of an additional cytokine signaling pathway, the tumor necrosis factor (TNF)-α-mediated activation of nuclear factor kappa B (NF-κB). In summary, our data show that human pediatric renal tumor cell lines are responsive to stimulation with various human cytokines and could be used as in vitro models for profiling cytokine signaling pathways.

Cytokines Activate JAK-STAT Signaling Pathway in MG-63 Cells on Titanium and Zirconia

Although titanium has been traditionally used as the gold standard for dental implants, recent years have seen the widespread application of zirconia implants given their superiority with regards to reduced bacterial adhesion, inflammation and cellular-interaction in terms of bio-compatibility. The JAK-STAT signaling pathway plays an important role in bone remodeling and formation. The aim of the study was to investigate the activation of the JAK-STAT pathway through different cytokines in osteoblast-like cells (MG-63) on zirconia in comparison to titanium discs. IFN-γ induced the very strong activation of STAT1 protein, IFN-α activated both STAT1 and STAT3 molecules, IL-6 activated STAT3 and IL-4 induced the activation of STAT6 on both surfaces. The activation of STAT proteins was confirmed by western blot, immunofluorescence and flow cytometry using phospho-specific anti-STAT antibodies, which recognize only phosphorylated STAT proteins. The incubation of MG-63 cells with IFN-γ caused the upregulation of MHC class I and class II proteins when MG-63 cells were grown on zirconia and titanium discs. In sum, the present study shows that the JAK-STAT pathway is activated in MG-63 cells when they are incubated on titanium or zirconia surfaces.

In silico Prediction on the PI3K/AKT/mTOR Pathway of the Antiproliferative Effect of O. joconostle in Breast Cancer Models

The search for new cancer treatments from traditional medicine involves developing studies to understand at the molecular level different cell signaling pathways involved in cancer development. In this work, we present a model of the PI3K/Akt/mTOR pathway, which plays a key role in cell cycle regulation and is related to cell survival, proliferation, and growth in cancer, as well as resistance to antitumor therapies, so finding drugs that act on this pathway is ideal to propose a new adjuvant treatment. The aim of this work was to model, simulate and predict in silico using the Big Data-Cellulat platform the possible targets in the PI3K/Akt/mTOR pathway on which the Opuntia joconostle extract acts, as well as to indicate the concentration range to be used to find the mean lethal dose in in vitro experiments on breast cancer cells. The in silico results show that, in a cancer cell, the activation of JAK and STAT, as well as PI3K and Akt is related to the effect of cell proliferation, angiogenesis, and inhibition of apoptosis, and that the extract of O. joconostle has an antiproliferative effect on breast cancer cells by inhibiting cell proliferation, regulating the cell cycle and inhibiting apoptosis through this signaling pathway . In vitro it was demonstrated that the extract shows an antiproliferative effect, causing the arrest of cells in the G2/M phase of the cell cycle. Therefore, it is concluded that the use of in silico tools is a valuable method to perform virtual experiments and discover new treatments. The use of this type of model supports in vitro experimentation, reducing the costs and number of experiments in the real laboratory.

FAK inhibitors as promising anticancer targets: present and future directions

FAK, a nonreceptor tyrosine kinase, has been recognized as a novel target class for the development of targeted anticancer agents. Overexpression of FAK is a common occurrence in several solid tumors, in which the kinase has been implicated in promoting metastases. Consequently, designing and developing potent FAK inhibitors is becoming an attractive goal, and FAK inhibitors are being recognized as a promising tool in our armamentarium for treating diverse cancers. This review comprehensively summarizes the different classes of synthetically derived compounds that have been reported as potent FAK inhibitors in the last three decades. Finally, the future of FAK-targeting smart drugs that are designed to slow down the emergence of drug resistance is discussed.

STAT3 induces the expression of GLI1 in chronic lymphocytic leukemia cells

The glioma associated oncogene-1 (GLI1), a downstream effector of the embryonic Hedgehog pathway, was detected in chronic lymphocytic leukemia (CLL), but not normal adult cells. GLI1 activating mutations were identified in 10% of patients with CLL. However, what induces GLI1 expression in GLI1-unmutated CLL cells is unknown. Because signal transducer and activator of transcription 3 (STAT3) is constitutively activated in CLL cells and sequence analysis detected putative STAT3-binding sites in the GLI1 gene promoter, we hypothesized that STAT3 induces the expression of GLI1. Western immunoblotting detected GLI1 in CLL cells from 7 of 7 patients, flow cytometry analysis confirmed that CD19+/CD5+ CLL cells co-express GLI1 and confocal microscopy showed co-localization of GLI1 and phosphorylated STAT3. Chromatin immunoprecipitation showed that STAT3 protein co-immunoprecipitated GLI1 as well as other STAT3-regulated genes. Transfection of CLL cells with STAT3-shRNA induced a mark decrease in GLI1 levels, suggesting that STAT3 binds to and induces the expression of GLI1 in CLL cells. An electromobility shift assay confirmed that STAT3 binds, and a luciferase assay showed that STAT3 activates the GLI1 gene. Transfection with GLI1-siRNA significantly increased the spontaneous apoptosis rate of CLL cells, suggesting that GLI1 inhibitors might provide therapeutic benefit to patients with CLL.

Progesterone and Estrogen Signaling in the Endometrium: What Goes Wrong in Endometriosis?

In the healthy endometrium, progesterone and estrogen signaling coordinate in a tightly regulated, dynamic interplay to drive a normal menstrual cycle and promote an embryo-receptive state to allow implantation during the window of receptivity. It is well-established that progesterone and estrogen act primarily through their cognate receptors to set off cascades of signaling pathways and enact large-scale gene expression programs. In endometriosis, when endometrial tissue grows outside the uterine cavity, progesterone and estrogen signaling are disrupted, commonly resulting in progesterone resistance and estrogen dominance. This hormone imbalance leads to heightened inflammation and may also increase the pelvic pain of the disease and decrease endometrial receptivity to embryo implantation. This review focuses on the molecular mechanisms governing progesterone and estrogen signaling supporting endometrial function and how they become dysregulated in endometriosis. Understanding how these mechanisms contribute to the pelvic pain and infertility associated with endometriosis will open new avenues of targeted medical therapies to give relief to the millions of women suffering its effects.

Activation of STAT1 by the FRK tyrosine kinase is associated with human glioma growth

PURPOSE

Glioma is a highly aggressive and lethal brain tumor. Signal transducers and activators of transcription (STAT) pathway are widely implicated in glioma carcinogenesis. Our previous study found that the Fynrelated kinase (FRK) gene, plays as a tumor suppressor in the development and progression of glioma. This study aimed to investigate the role of FRK in the activation pathway of STATs and its effect on the growth of glioma.

METHODS

The U251 and U87 cells with stable FRK overexpression were generated by lentivirus technique. The effects of FRK on the related proteins of STAT signaling pathway were detected by western blotting. Coimmunoprecipitation was used to detect the association of FRK and STAT1. The effects of STAT1 on the proliferation of glioma cells were detected by CCK8 or Edu cell proliferation assays. The expressions and correlation of FRK and p-STAT1 in glioma tissues were detectd by western blotting or immunohistochemistry. The effect of FRK on the growth of glioma was investigated in vivo mouse model.

RESULTS

The level of p-JAK2 and p-STAT1 increased after FRK overexpression, while they decreased after FRK downregulation both in U251 and U87 cells. However, FRK had no effect on STAT3 phosphorylation. FRK-induced STAT1 activation was not dependent on JAK2. FRK associated with STAT1, induced STAT1 nuclear translocation and regulated the expressions of STAT1-related target genes. STAT1 overexpression suppressed the proliferation of glioma cells. In contrast, STAT1 knockdown by siRNA promoted glioma cell growth. Importantly, down-regulation of STAT1 partially attenuated FRK-induced growth suppression. The clinical sample-based study indicated that the expression of FRK was significantly correlated with the expression of p-STAT1. FRK significantly inhibited glioma tumor growth in vivo.

CONCLUSIONS

Our findings highlighted a critical role of FRK in tumor suppression ability through promoting STAT1 activation, and provided a potential therapeutic target for glioma.

STAT1-mediated inhibition of FOXM1 enhances gemcitabine sensitivity in pancreatic cancer

Forkhead box protein M1 (FOXM1) was identified as an oncogenic transcription factor and master regulator of tumor progression and metastasis. FOXM1 expression often correlates with poor prognosis and chemotherapy resistance. In the present study, we investigated the association of FOXM1 expression and chemoresistance in pancreatic cancer. Elevated FOXM1 protein levels were associated with gemcitabine chemoresistance in patients with pancreatic cancer. In gemcitabine resistance cell line models of pancreatic cancer, FOXM1 expression increased, which induced gemcitabine chemoresistance in vitro. In pancreatic cancer cells treated with gemcitabine, FOXM1 affected nuclear factor κB (NF-κB) signaling activity. Immunohistochemical analysis demonstrated a negative association of FOXM1 expression and the level of phosphorylated signal transducer and activator of transcription 1 (pSTAT1) in human pancreatic cancer tissues. Dual-luciferase reporter assays and chromatin-immunoprecipitation assays demonstrated that pSTAT1 directly binds to the FOXM1 promoter to down-regulate its transcription. Interferon γ (IFNγ) promoted gemcitabine-induced cell apoptosis and inhibited cell proliferation in vitro and in vivo by FOXM1 inhibition. These data suggested that FOXM1 enhances chemoresistance to gemcitabine in pancreatic cancer. IFNγ could be used to down-regulate the expression of FOXM1 through STAT1 phosphorylation, thereby increasing the sensitivity of pancreatic cancer cells to gemcitabine. These studies suggested the sensitization by IFNγ in pancreatic ductal adenocarcinoma (PDAC) chemotherapy, which requires further clinical studies.

EGFR and KRAS mutations do not enrich for the activation of IL-6, JAK1 or phosphorylated STAT3 in resected lung adenocarcinoma

Resistance to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) against EGFR mutant lung adenocarcinoma develops after a median of nine to thirteen months. Upregulation of the interleukin-6 (IL-6)/Janus kinase (JAK)/signal transducers and activators of transcription (STAT) pathway may be a potential source of resistance to EGFR TKIs. We undertook a detailed assessment of the IL-6/JAK1/phosphorylated STAT3 (pSTAT3) pathway in resected lung adenocarcinoma specimens, with special interest in whether the presence of an EGFR mutation enriched for pSTAT3 positivity. Tumours from 143 patients with resected lung adenocarcinoma were assessed. EGFR and KRAS mutation status were scanned for with high-resolution melting and confirmed by polymerase chain reaction. Immunohistochemisty (IHC) was performed for IL-6, gp130, JAK1 and pSTAT3. Two methods for assigning IHC positivity were assessed (the presence of any positivity, and the presence of positivity at an H score >40). We found statistically significant associations between IL-6, JAK1 and pSTAT3 measured by IHC, consistent with the activation of the pathway in clinical specimens. No relationship was demonstrated between members of this pathway and oncogenic mutations in EGFR or KRAS. However, a proportion of tumours with EGFR mutations showed staining for IL-6, JAK1 and pSTAT3. No correlations with clinicopathologic features or survival outcomes were found for IL-6, JAK1 or pSTAT3 staining. The presence of EGFR or KRAS mutations did not enrich for the activation of IL-6, JAK1 or pSTAT3. pSTAT3 may still play a role in resistance to EGFR TKIs in clinical practice.

Prostaglandin E1 reduces the keratinocyte toxicity of sorafenib by maintaining signal transducer and activator of transcription 3 (STAT3) activity and enhancing the cAMP response element binding protein (CREB) activity

Hand-foot skin reaction (HFSR) is a common side effect of multiple tyrosine kinase inhibitors (mTKIs). HFSR can necessitate dose reductions or interruption of therapy owing to its negative effect on the quality of life. Therefore, effective use of mTKIs requires measures to prevent HFSR. We evaluated the effect of prostaglandin E₁ (PGE₁) on HFSR, because PGE₁ is already used to treat bed sores and skin ulcers and has established angiogenic and antiproliferative effects in keratinocytes. We found that the pathogenesis of sorafenib-induced HFSR is characterized by a decrease in levels of a phosphorylated signal transducer and activator of transcription 3 (STAT3). We investigated the effect of PGE₁ on the sorafenib-mediated reduction in phosphorylated STAT3 levels in HaCaT human epidermal keratinocytes. In cells treated with sorafenib, phosphorylated STAT3 levels decreased in a concentration-dependent manner, and this effect was blocked in cells treated with sorafenib and PGE₁. Furthermore, the expression of phosphorylated STAT3, the antiapoptotic proteins myeloid cell leukemia-1 (Mcl-1) and survivin decreased in cells pretreated with an inhibitor of cAMP response element binding protein (CREB). Cell viability increased in cells treated with sorafenib and PGE₁ compared with that in cells treated with sorafenib alone, and these effects were not observed in STAT3 knockdown HaCaT cells. Collectively, these findings indicate that PGE₁ blocks the inhibitory effects of sorafenib on cell growth by maintaining the activity of STAT3 and enhancing the CREB activity. Therefore, PGE₁ might represent an effective treatment for the prevention of sorafenib-induced HFSR.

Epigenetic switch drives the conversion of fibroblasts into proinvasive cancer-associated fibroblasts

Carcinoma-associated fibroblasts (CAF) mediate the onset of a proinvasive tumour microenvironment. The proinflammatory cytokine LIF reprograms fibroblasts into a proinvasive phenotype, which promotes extracellular matrix remodelling and collective invasion of cancer cells. Here we unveil that exposure to LIF initiates an epigenetic switch leading to the constitutive activation of JAK1/STAT3 signalling, which results in sustained proinvasive activity of CAF. Mechanistically, p300-histone acetyltransferase acetylates STAT3, which, in turn, upregulates and activates the DNMT3b DNA methyltransferase. DNMT3b methylates CpG sites of the SHP-1 phosphatase promoter, which abrogates SHP-1 expression, and results in constitutive phosphorylation of JAK1. Sustained JAK1/STAT3 signalling is maintained by DNA methyltransferase DNMT1. Consistently, in human lung and head and neck carcinomas, STAT3 acetylation and phosphorylation are inversely correlated with SHP-1 expression. Combined inhibition of DNMT activities and JAK signalling, in vitro and in vivo, results in long-term reversion of CAF-associated proinvasive activity and restoration of the wild-type fibroblast phenotype.

Carcinoma-associated fibroblasts are key components of solid tumours and associated with poor clinical outcome. Here the authors show that the cytokine LIF initiates an epigenetic switch which results in the sustained invasive activity of the tumour cells.

Loss of signal transducer and activator of transcription 1 is associated with prostate cancer recurrence

STAT1 loss has previously been implicated in cell line studies to modify prostate cancer cell growth and survival, however the clinical significance of this has not previously been established. This study investigated if STAT1 loss was associated with patient outcome measures and the phenotypic consequence of STAT1 silencing. STAT1 expression was assessed in two patient cohorts with localised (n = 78) and advanced prostate cancer at initial diagnosis (n = 39) by immunohistochemistry (IHC). Impact of STAT1 silencing on prostate cancer cells lines was assessed using Cell Death detection ELISA, TLDA gene signature apoptosis arrays, WST-1 assay, xCELLigence system, clonogenic assay, and wound healing assay. In the localised patient cohort, low expression of STAT1 was associated with shorter time to disease recurrence (3.8 vs 7.3 years, P = 0.02) and disease specific survival (6.6 vs 9.3 years, P = 0.05). In the advanced patient cohort, low expression was associated with shorter time to disease recurrence (2.0 vs 3.9 years, P = 0.001). When STAT1 was silenced in PC3 cells (AR negative) and LNCaP cells (AR positive) silencing did not influence levels of apoptosis in either cell line and had little effect on cell viability in the LNCaP cells. In contrast, STAT1 silencing in the PC3 cells resulted in a pronounced increase in cell viability (WST-1 assay: mock silenced vs STAT1 silenced, P < 0.001), clonagenicity (clonogenic assay: mock silenced vs STAT1 silenced, P < 0.001), and migration (wound healing: mock silenced vs STAT1 silenced, P < 0.001). In conclusion, loss of STAT1 may promote prostate cancer recurrence in AR negative patients via increasing cell viability. © 2015 Wiley Periodicals, Inc.

The JAK/STAT signaling cascade in gastric carcinoma (Review)

Gastric carcinoma remains one of the most prevalent forms of cancer worldwide, despite the decline in incidence rates, increased awareness of the disease and advancement in treatment strategies. Helicobacter pylori infection, dietary factors, lifestyle influences and various genetic aberrations have been shown to contribute to the development and progression of gastric cancer. Recent studies on the genomic landscape of gastric adenocarcinoma have identified several key signaling molecules, including epidermal growth factor receptor family (ErbB) members, vascular endothelial growth factor receptor family (VEGFR) members and PI3K/Akt/mTOR pathway components, that have been implicated in the molecular pathogenesis of gastric cancers. However, clinical trials with compounds that target these molecules have failed to show a significant improvement in overall survival rates when supplemented with conventional therapies. Therefore, it is essential to identify effective prognostic and/or diagnostic biomarkers and develop molecular targeted therapies. The JAK/STAT cascade is a principal signal transduction pathway in cytokine and growth factor signaling, regulating various cellular processes such as cell proliferation, differentiation, migration and survival. Numerous in vivo and in vitro studies have shown that dysregulated JAK/STAT signaling is a driving force in the pathogenesis of various solid cancers as well as hematopoietic malignancies. Hence, a large number of preclinical and clinical studies of drugs targeting this pathway are currently underway. Notably, aberrant JAK/STAT signaling has also been implicated in gastric cancers. In this review, we focus on the ongoing research on the JAK/STAT cascade in gastric carcinoma and discuss the therapeutic potential of targeting JAK/STAT signaling for the treatment of gastric cancer.

STAT1 Activation Is Enhanced by Cisplatin and Variably Affected by EGFR Inhibition in HNSCC Cells

Cisplatin is a cytotoxic chemotherapeutic drug frequently used to treat many solid tumors, including head and neck squamous cell carcinoma (HNSCC). EGF receptor (EGFR) inhibitors have also shown efficacy as alternatives to cisplatin in some situations. However, large clinical trials have shown no added survival benefit from the use of these two drugs in combination. Possible explanations for this include overlapping downstream signaling cascades. Using in vitro studies, we tested the hypothesis that cisplatin and EGFR inhibitors rely on the activation of the tumor suppressor STAT1, characterized by its phosphorylation at serine (S727) or tyrosine (Y701) residues. Cisplatin consistently increased the levels of p-S727-STAT1, and STAT1 siRNA knockdown attenuated cisplatin-induced cell death. EGFR stimulation also activated p-S727-STAT1 and p-Y701-STAT1 in a subset of cell lines, whereas EGFR inhibitors alone decreased levels of p-S727-STAT1 and p-Y701-STAT1 in these cells. Contrary to our hypothesis, EGFR inhibitors added to cisplatin treatment caused variable effects among cell lines, with attenuation of p-S727-STAT1 and enhancement of cisplatin-induced cell death in some cells and minimal effect in other cells. Using HNSCC tumor specimens from a clinical trial of adjuvant cisplatin plus the anti-EGFR antibody panitumumab, higher intratumoral p-S727-STAT1 appeared to correlate with worse survival. Together, these results suggest that cisplatin-induced cell death is associated with STAT1 phosphorylation, and the addition of anti-EGFR therapy to cisplatin has variable effects on STAT1 and cell death in HNSCC.

Inositol Polyphosphate-5-Phosphatase F (INPP5F) inhibits STAT3 activity and suppresses gliomas tumorigenicity

Glioblastoma (GBM), the most common type of primary malignant brain tumors harboring a subpopulation of stem-like cells (GSCs), is a fast-growing and often fatal tumor. Signal Transducer and Activator of Transcription 3 (STAT3) is one of the major signaling pathways in GSCs maintenance but the molecular mechanisms underlying STAT3 deregulation in GSCs are poorly defined. Here, we demonstrate that Inositol Polyphosphate-5-Phosphatase F (INPP5F), one of the polyphosphoinositide phosphatases, is differentially expressed in GSCs from glioma patients, and is identified as an inhibitor of STAT3 signaling via interaction with STAT3 and inhibition of its phosphorylation. Constitutively expressed INPP5F showed to suppress self-renewal and proliferation potentials of glioblastoma cells and reduced tumorigenicity of glioblastoma. In addition, loss of INPP5F gene in gliomas is significantly correlated with lower overall patient survivals. These findings suggest that INPP5F is a potential tumor suppressor in gliomas via inhibition of STAT3 pathway, and that deregulation of INPP5F may lead to contribution to gliomagenesis.

FSH-induced p38-MAPK-mediated dephosphorylation at serine 727 of the signal transducer and activator of transcription 1 decreases Cyp1b1 expression in mouse granulosa cells

Most mammalian follicles undergo atresia at various stages before ovulation, and granulosa cell apoptosis is a major cause of antral follicular atresia. Estradiol is an essential mitogen for granulosa cell proliferation in vivo and inhibition of apoptosis. The estradiol-producing capacity and metabolism levels are important for follicle health, and sufficient estradiol is necessary for follicle development and ovulation. Cyp1b1, a member of the cytochrome P450 1 subfamily, is responsible for the metabolism of a wide variety of halogenated and polycyclic aromatic hydrocarbons in diverse tissues. In mouse follicles, Cyp1b1 converts estradiol to 4-hydroxyestradiol. We investigated mouse granulosa cells (MGCs) in vivo and in vitro and found that Cyp1b1 played a crucial role in estradiol metabolism in dominant follicles. Follicle-stimulating hormone (FSH) decreased estrogen metabolism by reducing Cyp1b1 mRNA and protein levels in MGCs. Furthermore, FSH regulated signal transducer and activator of transcription 1 (STAT1), a significant transcription factor of Cyp1b1, by mediating the dephosphorylation of STAT1 on serine 727 (Ser(727)) in MGCs. p38 mitogen-activated protein kinase (MAPK) may be involved in the FSH-induced dephosphorylation of STAT1 on Ser(727) in MGCs. These results suggested that FSH functions via p38 MAPK-induced dephosphorylation at Ser(727) of STAT1 to downregulate Cyp1b1 expression and maintain the estradiol levels in mouse dominant follicles.

AGR2, ERp57/GRP58, and some other human protein disulfide isomerases

This review considers the major features of human proteins AGR2 and ERp57/GRP58 and of other members of the protein disulfide isomerase (PDI) family. The ability of both AGR2 and ERp57/GRP58 to catalyze the formation of disulfide bonds in proteins is the parameter most important for assigning them to a PDI family. Moreover, these proteins and also other members of the PDI family have specific structural features (thioredoxin-like domains, special C-terminal motifs characteristic for proteins localized in the endoplasmic reticulum, etc.) that are necessary for their assignment to a PDI family. Data demonstrating the role of these two proteins in carcinogenesis are analyzed. Special attention is given to data indicating the presence of biomarker features in AGR2 and ERp57/GRP58. It is now thought that there is sufficient reason for studies of AGR2 and ERp57/GRP58 for possible use of these proteins in diagnosis of tumors. There are also prospects for studies on AGR2 and ERp57/GRP58 leading to developments in chemotherapy. Thus, we suppose that further studies on different members of the PDI family using modern postgenomic technologies will broaden current concepts about functions of these proteins, and this will be helpful for solution of urgent biomedical problems.

STAT3 inhibitors for cancer therapy: Have all roads been explored?

The signal transducer and activator of transcription STAT3 is a transcription factor which plays a key role in normal cell growth and is constitutively activated in about 70% of solid and hematological cancers. Activated STAT3 is phosphorylated on tyrosine and forms a dimer through phosphotyrosine/src homology 2 (SH2) domain interaction. The dimer enters the nucleus via interaction with importins and binds target genes. Inhibition of STAT3 results in the death of tumor cells, this indicates that it is a valuable target for anticancer strategies; a view that is corroborated by recent findings of activating mutations within the gene. Yet, there is still only a small number of STAT3 direct inhibitors; in addition, the high similarity of STAT3 with STAT1, another STAT family member mostly oriented toward apoptosis, cell death and defense against pathogens, requires that STAT3-inhibitors have no effect on STAT1. Specific STAT3 direct inhibitors consist of SH2 ligands, including G quartet oligodeoxynucleotides (ODN) and small molecules, they induce cell death in tumor cells in which STAT3 is activated. STAT3 can also be inhibited by decoy ODNs (dODN), which bind STAT3 and induce cell death. A specific STAT3 dODN which does not interfere with STAT1-mediated interferon-induced cell death has been designed pointing to the STAT3 DBD as a target for specific inhibition. Comprehensive analysis of this region is in progress in the laboratory to design DBD-targeting STAT3 inhibitors with STAT3/STAT1 discriminating ability.

Screening approaches to generating STAT inhibitors: Allowing the hits to identify the targets

STAT transcription factors are regulators of critical cellular processes such as proliferation, survival, and self-renewal. While the activity of these proteins is tightly regulated under physiological conditions, they can become constitutively activated in a broad range of human cancers. This inappropriate STAT activation leads to enhanced transcription of genes that can directly lead to the malignant phenotype. Since STATs are largely dispensable for normal cell function, this has raised the possibility that STATs might be key targets for cancer therapy. Although a number of structure-based strategies have been used to develop STAT inhibitors, an alternate approach is to use cell-based assays that make use of the transcriptional function of STATs. Employing these systems, one can screen large chemical libraries to identify compounds that specifically block the function of a given STAT. This approach can lead to the identification of compounds that inhibit STATs by a variety of mechanisms, and can suggest novel targets for therapy. This type of functional screening strategy has already identified a drug that potently inhibits STAT3, and which is now being evaluated in a clinical trial for patients with chronic lymphocytic leukemia.

Leelamine mediates cancer cell death through inhibition of intracellular cholesterol transport

Leelamine is a promising compound for the treatment of cancer; however, the molecular mechanisms leading to leelamine-mediated cell death have not been identified. This report shows that leelamine is a weakly basic amine with lysosomotropic properties, leading to its accumulation inside acidic organelles such as lysosomes. This accumulation leads to homeostatic imbalance in the lysosomal endosomal cell compartments that disrupts autophagic flux and intracellular cholesterol trafficking as well as receptor-mediated endocytosis. Electron micrographs of leelamine-treated cancer cells displayed accumulation of autophagosomes, membrane whorls, and lipofuscin-like structures, indicating disruption of lysosomal cell compartments. Early in the process, leelamine-mediated killing was a caspase-independent event triggered by cholesterol accumulation, as depletion of cholesterol using β-cyclodextrin treatment attenuated the cell death and restored the subcellular structures identified by electron microscopy. Protein microarray-based analyses of the intracellular signaling cascades showed alterations in RTK-AKT/STAT/MAPK signaling cascades, which was subsequently confirmed by Western blotting. Inhibition of Akt, Erk, and Stat signaling, together with abnormal deregulation of receptor tyrosine kinases, was caused by the inhibition of receptor-mediated endocytosis. This study is the first report demonstrating that leelamine is a lysosomotropic, intracellular cholesterol transport inhibitor with potential chemotherapeutic properties leading to inhibition of autophagic flux and induction of cholesterol accumulation in lysosomal/endosomal cell compartments. Importantly, the findings of this study show the potential of leelamine to disrupt cholesterol homeostasis for treatment of advanced-stage cancers.

The Role of STAT3 in Non-Small Cell Lung Cancer

Persistent phosphorylation of signal transducer and activator of transcription 3 (STAT3) has been demonstrated in 22%~65% of non-small cell lung cancers (NSCLC). STAT3 activation is mediated by receptor tyrosine kinases, such as epidermal growth factor receptor (EGFR) and MET, cytokine receptors, such as IL-6, and non-receptor kinases, such as Src. Overexpression of total or phosphorylated STAT3 in resected NSCLC leads to poor prognosis. In a preclinical study, overexpression of STAT3 was correlated with chemoresistance and radioresistance in NSCLC cells. Here, we review the role of STAT3 and the mechanisms of treatment resistance in malignant diseases, especially NSCLC. As STAT3 is a critical mediator of the oncogenic effects of EGFR mutations, we discuss STAT3 pathways in EGFR-mutated NSCLC, referring to mechanisms of EGFR tyrosine kinase inhibitor resistance.

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

Background

The JAK/STAT (Janus Tyrosine Kinase, Signal Transducers and Activators of Transcription) pathway is associated with cytokine or growth factor receptors and it is critical for growth control, developmental regulation and homeostasis. The use of porcine ocular cells as putative xenotransplants appears theoretically possible. The aim of this study was to investigate the response of various porcine ocular cells in vitro to human cytokines in regard to the activation of JAK-STAT signaling pathways.

Methods

Porcine lens epithelial cells, pigmented iris epithelial cells and pigmented ciliary body cells were used in this study. These cells were isolated from freshly enucleated porcine eyes by enzymatic digestion. Cultured cells between passages 3–8 were used in all experiments. Electromobility shift assay (EMSA), proliferation assay, immunofluorescence staining and flow cytometry were used to evaluate the JAK-STAT signaling pathway in these cells.

Results

JAK/STAT signaling pathways could be activated in porcine pigmented epithelial ciliary body cells, in pigmented iris epithelial cells and in lens epithelial cells in response to porcine and human interferons and cytokines. All cells showed very strong STAT1 activation upon stimulation with porcine interferon-gamma. Porcine ocular cells also respond to human cytokines; IFN-alpha induced strong activation of STAT1 in EMSA, flow cytometry and immunofluorescence experiments whereas activation of STAT3 was less strong in EMSA, but strong in flow cytometry and immunofluorescence. Human recombinant IL-6 activated STAT3 and human IL-4 activated STAT6. With the help of immunofluorescence assay and flow cytometry we observed nuclear localization of STAT proteins after activation of porcine ocular cells with cytokines and interferons. Human IFN-α had an inhibitory effect on porcine ocular cells in proliferation assays.

Conclusion

Our study demonstrated that some types of human cytokines and interferon activate intracellular JAK-STAT signaling pathways in porcine ocular cells. We hypothesize that direct stimulation of the JAK-STAT pathway in porcine cells in response to human cytokines will lead to complications or failure, if pig-to-human ocular tissue xenotransplantation were to be carried out. For successful xenotransplantation among other obstacles there must be new approaches developed to regulate signaling pathways.

IL6 sensitizes prostate cancer to the antiproliferative effect of IFNα2 through IRF9

Development and progression of prostate cancer (PCa) are associated with chronic inflammation. The cytokine interleukin 6 (IL6) can influence progression, differentiation, survival, and angiogenesis of PCa. To identify novel pathways that are triggered by IL6, we performed a gene expression profiling of two PCa cell lines, LNCaP and MDA PCa 2b, treated with 5 ng/ml IL6. Interferon (IFN) regulatory factor 9 (IRF9) was identified as one of the most prevalent IL6-regulated genes in both cell lines. IRF9 is a mediator of type I IFN signaling and acts together with STAT1 and 2 to activate transcription of IFN-responsive genes. The IL6 regulation of IRF9 was confirmed at mRNA and protein levels by quantitative real-time PCR and western blot respectively in both cell lines and could be blocked by the anti-IL6 antibody Siltuximab. Three PCa cell lines, PC3, Du-145, and LNCaP-IL6+, with an autocrine IL6 loop displayed high expression of IRF9. A tissue microarray with 36 PCa tissues showed that IRF9 protein expression is moderately elevated in malignant areas and positively correlates with the tissue expression of IL6. Downregulation and overexpression of IRF9 provided evidence for an IFN-independent role of IRF9 in cellular proliferation of different PCa cell lines. Furthermore, expression of IRF9 was essential to mediate the antiproliferative effects of IFNα2. We concluded that IL6 is an inducer of IRF9 expression in PCa and a sensitizer for the antiproliferative effects of IFNα2.

Hepatitis delta virus induces specific DNA methylation processes in Huh-7 liver cancer cells

Hepatitis delta virus (HDV) is a small, defective RNA virus that can infect only individuals carrying hepatitis B virus. HBV/HDV co-infection results in more severe liver disease than HBV single infection and more rapid progression to cirrhosis and hepatocellular carcinoma (HCC). The epigenetic events involved in hepatocyte transformation towards malignancy in this context are poorly known. Here we report that, in Huh-7 cells, HDV induces DNMT3b expression and is associated to E2F1 transcription factor hypermethylation. Moreover our cell cycle analysis showed that HDV induces G2/M arrest. These findings suggest that HDV could play a role in HCC development at least in part by altering DNA methylation events. A better understanding of the molecular mechanisms involved in HDV-related carcinogenesis could help to identify new therapeutic targets.

Constitutive activation of signal transducers and activators of transcription 3 correlates with better prognosis, cell proliferation and hypoxia-inducible factor-1α in human gastric cancer

OBJECTIVE

We aimed to investigate the biological significance of signal transducers and activators of transcription 3 (STAT3) in gastric carcinoma.

METHODS

Immunohistochemistry was performed on tissue array slides containing 285 gastric carcinoma specimens. The relationship between the nuclear expression of phospho-Tyr705-STAT3 (pSTAT3), an active form of STAT3, and prognosis, clinicopathological factors, proliferation, cell cycle regulators, apoptosis regulators, or angiogenesis-related proteins was evaluated.

RESULTS

In nonneoplastic gastric mucosa, pSTAT3 was observed primarily in the nuclei of cells in the proliferative zone and intestinal metaplasia. In gastric carcinomas, nuclear STAT3 activation was observed in 36% of cases and was positively correlated with the Ki-67 labeling index and earlier tumor stage, whereas it was inversely correlated with lymphatic metastasis and distant metastasis (p< 0.05). Moreover, survival analyses showed that pSTAT3 expression was an independent prognostic factor of good survival. In addition, the expression of nuclear pSTAT3 positively correlated with that of cyclin D1, p21, p27, hypoxia-inducible factor-1α, or vascular endothelial growth factor (p< 0.05).

CONCLUSIONS

STAT3 activation is an early event in gastric tumorigenesis and significantly correlates with better prognosis, proliferation and angiogenesis. Thus, STAT3 activation may be a valuable prognostic variable and therapeutic target in gastric carcinoma.

SARS-CoV pathogenesis is regulated by a STAT1 dependent but a type I, II and III interferon receptor independent mechanism

Severe acute respiratory syndrome coronavirus (SARS-CoV) infection often caused severe end stage lung disease and organizing phase diffuse alveolar damage, especially in the elderly. The virus-host interactions that governed development of these acute end stage lung diseases and death are unknown. To address this question, we evaluated the role of innate immune signaling in protection from human (Urbani) and a recombinant mouse adapted SARS-CoV, designated rMA15. In contrast to most models of viral pathogenesis, infection of type I, type II or type III interferon knockout mice (129 background) with either Urbani or MA15 viruses resulted in clinical disease outcomes, including transient weight loss, denuding bronchiolitis and alveolar inflammation and recovery, identical to that seen in infection of wildtype mice. This suggests that type I, II and III interferon signaling play minor roles in regulating SARS pathogenesis in mouse models. In contrast, infection of STAT1-/- mice resulted in severe disease, high virus titer, extensive pulmonary lesions and 100% mortality by day 9 and 30 post-infection with rMA15 or Urbani viruses, respectively. Non-lethal in BALB/c mice, Urbani SARS-CoV infection in STAT1-/- mice caused disseminated infection involving the liver, spleen and other tissues after day 9. These findings demonstrated that SARS-CoV pathogenesis is regulated by a STAT1 dependent but type I, II and III interferon receptor independent, mechanism. In contrast to a well documented role in innate immunity, we propose that STAT1 also protects mice via its role as an antagonist of unrestrained cell proliferation.

Reciprocal effects of STAT5 and STAT3 in breast cancer

Breast cancer is often associated with inappropriate activation of transcription factors involved in normal mammary development. Two related transcription factors, signal transducer and activator of transcription (STAT) 5 and STAT3, play important and distinct roles in mammary development and both can be activated in breast cancer. However, the relative contribution of these STATs to mammary tumorigenesis is unknown. We have found that primary human breast tumors displaying activation of both STATs are more differentiated than those with STAT3 activation alone and display more favorable prognostic characteristics. To understand this difference, we have analyzed the effect of these STATs on gene regulation and phenotype of mammary carcinoma cells. STAT5 and STAT3 mediate opposing effects on several key target genes, with STAT5 exerting a dominant role. Using a model system of paired breast cancer cell lines, we found that coactivation of STAT5 and STAT3 leads to decreased proliferation and increased sensitivity to the chemotherapeutic drugs paclitaxel and vinorelbine compared with cells that have only STAT3 activation. Thus, STAT5 can modify the effects of STAT3 from the level of gene expression to cellular phenotype and analysis of the activation state of both STAT5 and STAT3 may provide important diagnostic and prognostic information in breast cancer.

Avicin D: a protein reactive plant isoprenoid dephosphorylates Stat 3 by regulating both kinase and phosphatase activities

Avicins, a class of electrophilic triterpenoids with pro-apoptotic, anti-inflammatory and antioxidant properties, have been shown to induce redox-dependant post-translational modification of cysteine residues to regulate protein function. Based on (a) the cross-talk that occurs between redox and phosphorylation processes, and (b) the role of Stat3 in the process of apoptosis and carcinogenesis, we chose to study the effects of avicins on the processes of phosphorylation/dephosphorylation in Stat3. Avicins dephosphorylate Stat3 in a variety of human tumor cell lines, leading to a decrease in the transcriptional activity of Stat3. The expression of Stat3-regulated proteins such as c-myc, cyclin D1, Bcl2, survivin and VEGF were reduced in response to avicin treatment. Underlying avicin-induced dephosphorylation of Stat3 was dephosphorylation of JAKs, as well as activation of protein phosphatase-1. Downregulation of both Stat3 activity and expression of Stat 3-controlled pro-survival proteins, contributes to the induction of apoptosis in avicin treated tumor cells. Based on the role of Stat3 in inflammation and wounding, and the in vivo inhibition of VEGF by avicins in a mouse skin carcinogenesis model, it is likely that avicin-induced inhibition of Stat3 activity results in the suppression of the pro-inflammatory and pro-oxidant stromal environment of tumors. Activation of PP-1, which also acts as a cellular economizer, combined with the redox regulation by avicins, can aid in redirecting metabolism from growth promoting anabolic to energy sparing pathways.

Loss of STAT5 causes liver fibrosis and cancer development through increased TGF-{beta} and STAT3 activation

The molecular mechanisms underlying the development of hepatocellular carcinoma are not fully understood. Liver-specific signal transducer and activator of transcription (STAT) 5A/B–null mice (STAT5-LKO) were treated with carbon tetrachloride (CCl₄), and histological analyses revealed liver fibrosis and tumors. Transforming growth factor (TGF)–β levels and STAT3 activity were elevated in liver tissue from STAT5-LKO mice upon CCl₄ treatment. To define the molecular link between STAT5 silencing and TGF-β up-regulation, as well as STAT3 activation, we examined STAT5-null mouse embryonic fibroblasts and primary hepatocytes. These cells displayed elevated TGF-β protein levels, whereas messenger RNA levels remained almost unchanged. Protease inhibitor studies revealed that STAT5 deficiency enhanced the stability of mature TGF-β. Immunoprecipitation and immunohistochemistry analyses demonstrated that STAT5, through its N-terminal sequences, could bind to TGF-β and that retroviral-mediated overexpression of STAT5 decreased TGF-β levels. To confirm the in vivo significance of the N-terminal domain of STAT5, we treated mice that expressed STAT5 lacking the N terminus (STAT5-ΔN) with CCl₄. STAT5-ΔN mice developed CCl₄-induced liver fibrosis but no tumors. In conclusion, loss of STAT5 results in elevated TGF-β levels and enhanced growth hormone–induced STAT3 activity. We propose that a deregulated STAT5–TGF-β–STAT3 network contributes to the development of chronic liver disease.

Three LIF-dependent signatures and gene clusters with atypical expression profiles, identified by transcriptome studies in mouse ES cells and early derivatives

Background

Mouse embryonic stem (ES) cells remain pluripotent in vitro when grown in the presence of the cytokine Leukaemia Inhibitory Factor (LIF). Identification of LIF targets and of genes regulating the transition between pluripotent and early differentiated cells is a critical step for understanding the control of ES cell pluripotency.

Results

By gene profiling studies carried out with mRNAs from ES cells and their early derivatives treated or not with LIF, we have identified i) LIF-dependent genes, highly expressed in pluripotent cells, whose expression level decreases sharply upon LIF withdrawal [Pluri genes], ii) LIF induced genes [Lifind genes] whose expression is differentially regulated depending upon cell context and iii) genes specific to the reversible or irreversible committed states. In addition, by hierarchical gene clustering, we have identified, among eight independent gene clusters, two atypical groups of genes, whose expression level was highly modulated in committed cells only. Computer based analyses led to the characterization of different sub-types of Pluri and Lifind genes, and revealed their differential modulation by Oct4 or Nanog master genes. Individual knock down of a selection of Pluri and Lifind genes leads to weak changes in the expression of early differentiation markers, in cell growth conditions in which these master genes are still expressed.

Conclusion

We have identified different sets of LIF-regulated genes depending upon the cell state (reversible or irreversible commitment), which allowed us to present a novel global view of LIF responses. We are also reporting on the identification of genes whose expression is strictly regulated during the commitment step. Furthermore, our studies identify sub-networks of genes with a restricted expression in pluripotent ES cells, whose down regulation occurs while the master knot (composed of OCT4, SOX2 and NANOG) is still expressed and which might be down-regulated together for driving cells towards differentiation.

Molecular and chromosomal alterations: new therapies for relapsed acute myeloid leukemia

Acute myeloid leukemia (AML) remains the most common form of leukemia and the most common cause of leukemia death. Although conventional chemotherapy can cure between 25 and 45% of AML patients, the majority of patients die after relapse or of complications associated with treatment. Thus, more specific and less toxic treatments for AML patients are needed, especially for elderly patients. An indispensable prerequisite to investigate tailored approaches for AML is the recent progress in the understanding the molecular features that distinguish leukemia progenitors from normal hematopoietic counterparts and the identification of a variety of dysregulated molecular pathways. This in turn would allow the identification of tumor-specific characteristics that provide a rational basis for the development of more tailored, and hence potentially more effective and less toxic, therapeutic approaches. In this review, we describe some of the signaling pathways that are aberrantly regulated in AML, with a specific focus on their pathogenetic and therapeutic significance, and we examine some recent therapies directed against these targets, used in clinical trial for relapsed patients or unfit for conventional chemotherapy.

ephrinB1 signals from the cell surface to the nucleus by recruitment of STAT3

The Eph (erythropoietin-producing hepatoma) family of receptor tyrosine kinases and their membrane-bound ligands, the ephrins, have been implicated in regulating cell adhesion and migration during development by mediating cell-to-cell signaling events. The transmembrane ephrinB (Eph receptor interactor B) protein is a bidirectional signaling molecule that sends a forward signal through the activation of its cognate receptor tyrosine kinase, residing on another cell. A reverse signal can be transduced into the ephrinB-expressing cell via tyrosine phosphorylation of its conserved C-terminal cytoplasmic domain. Although some insight has been gained regarding how ephrinB may send signals affecting cytoskeletal components, little is known about how ephrinB1 reverse signaling affects transcriptional processes. Here we report that signal transducer and activator of transcription 3 (STAT3) can interact with ephrinB1 in a phosphorylation-dependent manner that leads to enhanced activation of STAT3 transcriptional activity. This activity depends on the tyrosine kinase Jak2, and two tyrosines within the intracellular domain of ephrinB1 are critical for the association with STAT3 and its activation. The recruitment of STAT3 to ephrinB1, and its resulting Jak2-dependent activation and transcription of reporter targets, reveals a signaling pathway from ephrinB1 to the nucleus.

Hepatitis C virus NS3/4A protein interacts with ATM, impairs DNA repair and enhances sensitivity to ionizing radiation

Hepatitis C virus (HCV) infection is frequently associated with the development of hepatocellular carcinomas and non-Hodgkin's B-cell lymphomas. Nonstructural protein 3 (NS3) of HCV possesses serine protease, nucleoside triphosphatase, and helicase activities, while NS4A functions as a cofactor for the NS3 serine protease. Here, we show that HCV NS3/4A interacts with the ATM (ataxia-telangiectasia mutated), a cellular protein essential for cellular response to irradiation. The expression of NS3/4A caused cytoplasmic translocation of either endogenous or exogenous ATM and delayed dephosphorylation of the phosphorylated ATM and gamma-H2AX following ionizing irradiation. As a result, the irradiation-induced gamma-H2AX foci persisted longer in the NS3/4A-expressing cells. Furthermore, these cells showed increased comet tail moment in single-cell electrophoresis assay, indicating increased double-strand DNA breaks. The cells harboring an HCV replicon also exhibited cytoplasmic localization of ATM and increased sensitivity to irradiation. These results demonstrate that NS3/4A impairs the efficiency of DNA repair by interacting with ATM and renders the cells more sensitive to DNA damage. This effect may contribute to HCV oncogenesis.

KIT oncogenic signaling mechanisms in imatinib-resistant gastrointestinal stromal tumor: PI3-kinase/AKT is a crucial survival pathway

Most gastrointestinal stromal tumor (GIST) patients respond to KIT inhibition with imatinib, yet will eventually exhibit resistance. Imatinib-resistance mechanisms are heterogeneous, and little is known about KIT functional roles in imatinib-resistant GIST. Biological consequences of biochemical inhibition of KIT, phosphatidyl-inositol-3-kinase (PI3-K), PLCgamma, MAPK/ERK kinase/mitogen-activated protein kinase (MEK/MAPK), mammalian target of rapamycin (mTOR) and JAK were determined by immunoblotting for protein activation, and by cell proliferation and apoptosis assays in GIST cell lines from imatinib-sensitive GIST (GIST882), imatinib-resistant GISTs (GIST430 and GIST48) and KIT-negative GIST (GIST62). KIT activation was 3- to 6-fold higher in GIST430 and GIST48 than in GIST882, whereas total KIT expression was comparable in these three GIST lines. In addition to the higher set point for KIT activation, GIST430 and GIST48 had intrinsic imatinib resistance. After treatment with 1 muM imatinib, residual KIT activation was 6- and 2.8-fold higher in GIST430 and GIST48, respectively, compared to GIST882. In all GIST lines, cell growth arrest resulted from PI3-K inhibition, and - to a lesser extent - from MEK/MAPK and mTOR inhibition. Inhibition of JAK/STAT or PLCgamma did not affect cell proliferation. Similarly, only PI3-K inhibition resulted in substantial apoptosis in the imatinib-resistant GISTs. We conclude that GIST secondary KIT mutations can be associated with KIT hyperactivation and imatinib resistance. Targeting critical downstream signaling proteins, such as PI3-K, is a promising therapeutic strategy in imatinib-resistant GISTs.

STAT5 represses BCL6 expression by binding to a regulatory region frequently mutated in lymphomas

Deregulated expression of BCL6 is a pathogenic event in many lymphomas. BCL6 blocks cellular differentiation by repressing transcription of its target genes, and this may promote tumorigenesis. Conversely, the transcription factor signal transducers and activators of transcription (STAT)5 promotes differentiation in many systems. STAT5 upregulates a number of genes repressed by BCL6, raising the possibility that STAT5 and BCL6 have opposing roles in transcriptional regulation. Therefore, we sought to determine the effects of STAT5 activation on BCL6 expression and function. We found that activation of STAT5 downregulates BCL6 expression in B-lymphoma cells and other hematopoietic cell lines. We identified two potential STAT-binding regions in the first exon and first intron of BCL6 that fell within regions of high inter-species homology, suggesting conservation of regulatory function. STAT5 can bind inducibly and regulate transcription at one of these regions, identifying BCL6 as a STAT5 target gene. Additionally, STAT5-mediated downregulation of BCL6 results in loss of BCL6 repression of its target genes, confirming that STAT5 is a negative regulator of BCL6 function. The STAT5 responsive region of the BCL6 gene is mutated frequently in B-cell lymphomas, suggesting that loss of the repressive effects of STAT5 on BCL6 might contribute to the pathogenesis of these cancers.

Deletion of the SOCS3 gene in liver parenchymal cells promotes hepatitis-induced hepatocarcinogenesis

BACKGROUND & AIMS

A recent study has suggested that the methylation silencing of the suppressor of cytokine signaling-3 (SOCS3), a negative regulator of interleukin-6-related cytokines, could be involved in hepatocellular carcinoma (HCC). However, the roles of SOCS3 in hepatocellular carcinogenesis and hepatitis have not been established. We investigated the effect of deleting the SOCS3 gene on the development of hepatitis and HCC in hepatitis C virus-infected patients and mouse models.

METHODS

The expression of SOCS genes in HCC and non-HCC regions of patient samples was determined by real-time reverse-transcription polymerase chain reaction and immunoblotting. The conditional knockout approach in mice was used to determine the hepatocyte-specific roles of SOCS3. To generate a liver-specific deletion, floxed SOCS3 (SOCS3(fl/fl)) mice were crossed with albumin-Cre transgenic mice. Hepatitis and HCC were induced by administering concanavalin A and diethylnitrosamine, respectively.

RESULTS

SOCS3 expression was reduced in the HCC regions compared with the non-HCC regions. Carcinogen-induced hepatic tumor development was enhanced by deletion of the SOCS3 gene, which was associated with higher levels of the targets of signal transducers and activators of transcription (ie, B-cell lymphoma-XL, B-cell lymphoma-2, C-myelocytomatosis, cyclin D1, and vascular endothelial growth factor). In the concanavalin A-mediated hepatitis model, deletion of the SOCS3 gene in the hepatocytes protected against liver injury through suppression of interferon-gamma signaling and induction of the antiapoptotic protein Bcl-XL.

CONCLUSIONS

Deletion of the SOCS3 gene in hepatocytes promotes the activation of STAT3, resistance to apoptosis, and an acceleration of proliferation, resulting in enhanced hepatitis-induced hepatocarcinogenesis.

IL-6 signaling via the STAT3/SOCS3 pathway: functional analysis of the conserved STAT3 N-domain

The conserved N-domain of the STAT proteins has been implicated in several activities crucial to cytokine signaling including receptor recruitment and STAT activation, cooperative DNA binding and STAT-dependent gene expression. We evaluated the role of the STAT3 N-domain in the IL-6 signal transduction pathway leading to Socs3 gene expression, an essential mechanism that controls the quality and magnitude of IL-6-dependent transcriptional responses. Based on the model for STAT N-domain function in cooperative gene expression and the presence of tandem STAT binding motifs in the murine Socs3 promoter, we anticipated that stabilizing interactions between adjacent STAT3 dimers via N-domain sequences might be essential for Socs3 gene expression. This was underscored by the tight conservation in the location and sequence of the tandem STAT binding sites between the murine and human Socs3 promoters. Using reconstitution into Stat3-/- mouse embryonic fibroblasts (Stat3-/- MEFs), we find that a STAT3 N-domain deletion mutant (Delta 133STAT3) is activated by tyrosine phosphorylation in response to IL-6 and then undergoes dephosphorylation with kinetics similar to full-length STAT3. These results highlight important differences compared to other STATs where the N-domain has been shown to mediate activation (STAT4) or dephosphorylation (STAT1). STAT3 binds predominantly to a single STAT consensus site in the Socs3 promoter, despite the presence of an adjacent STAT motif. Significantly, Delta 133STAT3 stimulates expression of the endogenous Socs3 gene in Stat3-/- MEFs upon IL-6 treatment with an activity similar to reconstituted STAT3, demonstrating that the N-domain is dispensable for Socs3 gene expression. We propose that the Socs3 gene in its chromosomal context is activated by the IL-6/STAT3 pathway independent of STAT3 N-domain sequences.

Interferon-gamma, but not interferon-alpha, induces SOCS 3 expression in human melanoma cell lines

The signal transducers and transcription activators (STATs) and their endogenous inhibitors of the suppressors of cytokine signalling (SOCS) family are major proteins harmonizing the transmission of external signals from the surface membrane to target genes in the nucleus. To correlate the induction of SOCS 3 by interferons (IFNs) on messenger RNA and protein levels with STAT 1 phosphorylation in human malignant melanoma cell lines, we used a unique collection of 18 established malignant melanoma cell lines and six human non-malignant normal cells (two melanocytes, two skin keratinocytes and two fibroblasts). IFN-gamma induced SOCS 3 in 83% of melanoma cell lines, whereas IFN-alpha stimulated SOCS 3 expression in only 11% of cases. Similarly, melanocytes showed strong induction of SOCS 3 by IFN-gamma and, to a lesser extent, by IFN-alpha. In most cases, SOCS 3 expression was paralleled by STAT 1 phosphorylation at tyrosine residues (Y701). In several lines, however, SOCS 3 was not induced despite STAT 1 phosphorylation and, in a few lines, SOCS 3 induction occurred without detectable STAT 1 phosphorylation, indicating that STAT 1 might not be an exclusive inducer of SOCS 3. Similarly, non-malignant cells displayed STAT 1 activation and high levels of SOCS 3 expression after IFN-gamma (but not IFN-alpha) treatment. In conclusion, in contrast to IFN-alpha, IFN-gamma appeared to induce SOCS 3 apparently at the transcription level and exhibited higher cytotoxic effects regardless of the cell origin.

Signal transducer and activator of transcription 3 is required for the oncogenic effects of non-small-cell lung cancer-associated mutations of the epidermal growth factor receptor

Somatic mutations in the epidermal growth factor receptor (EGFR) occur frequently in lung cancer and confer sensitivity to EGFR kinase inhibitors gefitinib and erlotinib. These mutations, which occur in the kinase domain of the protein, also render EGFR constitutively active and transforming. Signal transducers and activators of transcription 3 (STAT3) transduces signals from a number of oncogenic tyrosine kinases and contributes to a wide spectrum of human malignancies. Here, we show that STAT3 is activated by mutant EGFRs and is necessary for its downstream phenotypic effects. Inhibiting STAT3 function in fibroblasts abrogates transformation by mutant EGFR. In non-small-cell lung cancer cells, STAT3 activity is regulated by EGFR through modulation of STAT3 serine phosphorylation. Inhibiting STAT3 function increases apoptosis of these cells, suggesting that STAT3 is necessary for their survival. Finally, a group of genes constituting a STAT3 signature is enriched in lung tumors with EGFR mutations. Thus, STAT3 is a critical mediator of the oncogenic effects of somatic EGFR mutations and targeting STAT3 may be an effective strategy for treating tumors characterized by these mutations.

The role of protein kinase C δ activation and STAT3 Ser727 phosphorylation in insulin-induced keratinocyte proliferation

Activation of the STAT family of transcription factors is regulated by cytokines and growth factors. STAT tyrosine and serine phosphorylation are linked to the transcriptional activation and function of STAT. We have previously described a unique pathway inducing keratinocyte proliferation, which is mediated by insulin stimulation and depends on protein kinase C δ (PKCδ). In this study, we assessed STAT3 activation downstream of this pathway and characterized the role of PKCδ activation in STAT3 tyrosine and serine phosphorylation and keratinocyte proliferation. Following insulin stimulation, STAT3 interacted with PKCδ but not with any other PKC isoform expressed in skin. Activated forms of PKCδ and STAT3 were essential for insulin-induced PKCδ-STAT3 activation in keratinocyte proliferation. Abrogation of PKCδ activity inhibited insulin-induced STAT3 phosphorylation, PKCδ-STAT3 association and nuclear translocation. In addition, overexpression of STAT3 tyrosine mutant eliminated insulin-induced PKCδ activation and keratinocyte proliferation. Finally, overexpression of a STAT3 serine mutant abrogated insulin-induced STAT3 serine phosphorylation and STAT3-induced keratinocyte proliferation, whereas STAT3 tyrosine phosphorylation was induced and nuclear localization remained intact. This study indicates that PKCδ activation is a primary regulator of STAT3 serine phosphorylation and that PKCδ is essential in directing insulin-induced signaling in keratinocyte proliferation.

Activated STAT 3 in choroidal neovascular membranes of patients with age-related macular degeneration

PURPOSE

The Jak/STAT (Janus tyrosine kinase/signal transducers and activators of transcription) pathway is critical for growth control, developmental regulation and homeostasis. Here we studied the expression of STAT proteins in the proliferative disease of age-related macular degeneration (AMD) with choroidal neovascular membranes (CNVM). The STAT family are of cytoplasmic proteins with roles as signal messengers and transcription factors that participate in normal cellular responses to cytokines and growth factors. Abnormal activity of certain STAT family members, particularly STAT 3 and STAT 5, is associated with a wide variety of human malignancies and other diseases. Here were studied STAT activation in CNVM of patients with AMD.

METHODS

Sections of formalin-fixed, paraffin-embedded samples from 8 eyes with AMD and 5 controls were included in this study. Immunohistochemical staining was performed using antibodies against activated STAT 1, STAT 3 and STAT 5 proteins, and tenascin.

RESULTS

In CNVM, we observed a strong positive staining for tenascin and STAT 3 in retinal pigmented epithelial (RPE) cells restricted to areas of developing scars. In contrast, STAT 3 immunoreactivity failed in areas completely composed of fibrovascular disciform scar material. In addition, no immunoreactivity for both STAT 1 and STAT 5 was detected in all CNVM and in all control samples.

CONCLUSION

In CNVM, activation of STAT 3 appears in RPE cells simultaneously with the formation of scars.

Identification of a genetic signature of activated signal transducer and activator of transcription 3 in human tumors

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that is activated in diverse human tumors and may play a direct role in malignant transformation. However, the full complement of target genes that STAT3 regulates to promote oncogenesis is not known. We created a system to express a constitutively active form of STAT3, STAT3-C, in mouse fibroblasts and used it to identify STAT3 targets. We showed that a subset of these targets, which include transcription factors regulating cell growth, survival, and differentiation, are coexpressed in a range of human tumors. Using immunohistochemical staining of tissue microarrays, we showed that these targets are enriched in breast and prostate tumors harboring activated STAT3. Finally, we showed that STAT3 is required for the expression of these genes in a breast cancer cell line. Taken together, these results identify a cohort of STAT3 targets that may mediate its role in oncogenesis.

Constitutive SOCS-3 expression protects T-cell lymphoma against growth inhibition by IFNα

Signal transducer and activator of transcription (Stat)3 is constitutively activated in cutaneous T-cell lymphoma (CTCL), where it protects tumour cells against apoptosis. The constitutive activation of Stat3 leads to a constitutive expression of suppressor of cytokine signalling (SOCS)-3. In healthy cells, SOCS-3 is transiently expressed following cytokine stimulation and functions as a negative feedback inhibitor of the Stat3-activating kinases. Here, we attempt to resolve the apparent paradox of a simultaneous SOCS-3 expression and Stat3 activation in the same cells. We show that (i) SOCS-3 expression in tumour cells is equal to or higher than in cytokine-stimulated nonmalignant T cells, (ii) SOCS-3 is not mutated in CTCL, (iii) overexpression of SOCS-3 blocks IFNalpha-mediated growth inhibition without affecting Stat3 activation, growth, and apoptosis, and (iv) inhibition of SOCS-3 by a dominant negative Stat3 (Stat3D) increases the IFNalpha-mediated growth inhibition. Taken together, these data show that SOCS-3 does not inhibit Stat3 activation, growth, and survival in CTCL. In contrast, SOCS3 protects tumour cells against growth inhibition by IFNalpha. Unlike SOCS-1, SOCS-3 is therefore not a tumour suppressor but rather a protector of tumour cells.

Anaplastic lymphoma kinase proteins in growth control and cancer

The normal functions of full-length anaplastic lymphoma kinase (ALK) remain to be completely elucidated. Although considered to be important in neural development, recent studies in Drosophila also highlight a role for ALK in gut muscle differentiation. Indeed, the Drosophila model offers a future arena for the study of ALK, its ligands and signalling cascades. The discovery of activated fusion forms of the ALK tyrosine kinase in anaplastic large cell lymphoma (ALCL) has dramatically improved our understanding of the pathogenesis of these lymphomas and enhanced the pathological diagnosis of this subtype of non-Hodgkin's lymphoma (NHL). Likewise, the realisation that a high percentage of inflammatory myofibroblastic tumours express activated-ALK fusion proteins has clarified the causation of these mesenchymal neoplasms and provided for their easier discrimination from other mesenchymal-derived inflammatory myofibroblastic tumour (IMT) mimics. Recent reports of ALK expression in a range of carcinoma-derived cell lines together with its apparent role as a receptor for PTN and MK, both of which have been implicated in tumourigenesis, raise the possibility that ALK-mediated signalling could play a role in the development and/or progression of a number of common solid tumours. The therapeutic targeting of ALK may prove to have efficacy in the treatment of many of these neoplasms.

Novel peptidomimetic inhibitors of signal transducer and activator of transcription 3 dimerization and biological activity

The critical role of signal transducer and activator of transcription 3 (Stat3) in the growth and survival of human tumor cells identifies it as a promising target for cancer drug discovery. We previously identified a Stat3 SH2 domain-binding phosphopeptide, PY*LKTK, and its tripeptide derivatives, PY*L and AY*L (where Y* represents phosphotyrosine), which inhibit Stat3 biochemical activity and biological function. Here, we report novel peptidomimetic compounds based on PY*L (or AY*L) with substitution of the Y-1 residue by benzyl, pyridyl, or pyrazinyl derivatives that are selective and greater than 5-fold more potent in disrupting Stat3 activity in vitro than lead tripeptides. The biological activities of these derivatives mirror that originally observed for peptides. In this context, the representative peptidomimetic ISS 610 with 4-cyanobenzoate substitution inhibits constitutive Stat3 activity in Src-transformed mouse fibroblasts and human breast and lung carcinoma cells. This effect is not evident with the non-phosphorylated counterpart, ISS 610NP, consistent with interaction of peptidomimetics with the SH2 domain of Stat3. Moreover, ISS 610 induces cell growth inhibition and apoptosis of Src-transformed fibroblasts that contain persistently active Stat3. We present the first report of a peptidomimetic approach to design of small-molecule inhibitors of Stat3 that are also among the first examples of disruptors of transcription factor dimerization with the potential for novel cancer therapy.

Oral fludarabine has significant activity in patients with previously untreated chronic lymphocytic leukemia, and leads to increased STAT1 levels in vivo

Fifteen patients with previously untreated chronic lymphocytic leukemia (CLL) were treated with oral fludarabine. Toxicities were mainly hematologic, and the response rate was 80%. To assess the effect of fludarabine on the transcription factor STAT1, blood samples obtained on study entry were treated in vitro with fludarabine for 24 h, and the majority of samples displayed an expected decrease in STAT1. To determine whether similar changes occurred in vivo, we developed a flow cytometric assay to quantitate STAT1 levels. On completion of fludarabine cycle 1, CLL cells showed increased STAT1 in the majority of patients, in contrast to the in vitro findings. This may reflect a survival advantage for cells that express high levels of STAT1. In conclusion, oral fludarabine is highly active and merits further investigation in previously untreated patients with CLL. Larger studies are indicated to determine optimal timing of STAT1 assessment, and if changes in STAT1 represent an in vivo indicator of response to purine analog therapy.