SOCS-3 is frequently silenced by hypermethylation and suppresses cell growth in human lung cancer

Targeting the STAT3 signaling pathway in cancer: role of synthetic and natural inhibitors

Signal transducers and activators of transcription (STATs) comprise a family of cytoplasmic transcription factors that mediate intracellular signaling that is usually generated at cell surface receptors and thereby transmit it to the nucleus. Numerous studies have demonstrated constitutive activation of STAT3 in a wide variety of human tumors, including hematological malignancies (leukemias, lymphomas, and multiple myeloma) as well as diverse solid tumors (such as head and neck, breast, lung, gastric, hepatocellular, colorectal and prostate cancers). There is strong evidence to suggest that aberrant STAT3 signaling promotes initiation and progression of human cancers by either inhibiting apoptosis or inducing cell proliferation, angiogenesis, invasion, and metastasis. Suppression of STAT3 activation results in the induction of apoptosis in tumor cells, and accordingly its pharmacological modulation by tyrosine kinase inhibitors, antisense oligonucleotides, decoy nucleotides, dominant negative proteins, RNA interference and chemopreventive agents have been employed to suppress the proliferation of various human cancer cells in culture and tumorigenicity in vivo. However, the identification and development of novel drugs that can target deregulated STAT3 activation effectively remains an important scientific and clinical challenge. This review presents the evidence for critical roles of STAT3 in oncogenesis and discusses the potential for development of novel cancer therapies based on mechanistic understanding of STAT3 signaling cascade.

SOCS3-mediated blockade reveals major contribution of JAK2/STAT5 signaling pathway to lactation and proliferation of dairy cow mammary epithelial cells in vitro

Suppressor of cytokine signaling 3 (SOCS3) is a cytokine-induced negative feedback-loop regulator of cytokine signaling. More and more evidence has proved it to be an inhibitor of signal transducers and activators of transcription 5 (STAT5). Here, we used dairy cow mammary epithelial cells (DCMECs) to analyze the function of SOCS3 and the interaction between SOCS3 and STAT5a. The expression of SOCS3 was found in cytoplasm and nucleus of DCMECs by fluorescent immunostaining. Overexpression and inhibition of SOCS3 brought a remarkable milk protein synthesis change through the regulation of JAK2/STAT5a pathway activity, and SOCS3 expression also decreased SREBP-1c expression and fatty acid synthesis. Inhibited STAT5a activation correlated with reduced SOCS3 expression, which indicated that SOCS3 gene might be one of the targets of STAT5a activation, DCMECs treated with L-methionine (Met) resulted in a decrease of SOCS3 expression. SOCS3 could also decrease cell proliferation and viability by CASY-TT detection. Together, our findings indicate that SOCS3 acts as an inhibitor of JAK2/STAT5a pathway and disturbs fatty acid synthesis by decreasing SREBP-1c expression, which validates its involvement in both milk protein synthesis and fat synthesis. In aggregate, these results reveal that low SOCS3 expression is required for milk synthesis and proliferation of DCMECs in vitro.

Methylation profiling of SOCS1, SOCS2, SOCS3, CISH and SHP1 in Philadelphia-negative myeloproliferative neoplasm

Janus kinase-signal transducer and activator of transcription (JAK/STAT) signalling, pivotal in Philadelphia-negative (Ph-ve) myeloproliferative neoplasm (MPN), is negatively regulated by molecules including SOCSs, CISH and SHP1. SOCS1, SOCS2 and SOCS3 methylation have been studied in MPN with discordant results. Herein, we studied the methylation status of SOCS1, SOCS2 and SOCS3, CISH and SHP1 by methylation-specific polymerase chain reaction (MSP) in cell lines and 45 diagnostic marrow samples of Ph-ve MPN. Moreover, we attempted to explain the discordance of methylation frequency by mapping the studied MSP primers to the respective genes. Methylation was detected in normal controls using SOCS2 MSP primers in the 3′translated exonic sequence, but not primers around the transcription start site in the 5′ untranslated regions (5′UTR). SOCS1, SOCS2, SOCS3 and CISH were completely unmethylated in primary MPN samples and cell lines. In contrast, methylation of SHP1 was detected in 8.9% primary marrow samples. Moreover, SHP1 was completely methylated in K562 cell line, leading to reversible SHP1 silencing. A review of methylation studies of SOCS1 and SOCS3 showed that spuriously high rates of SOCS methylation had been reported using MSP primers targeting CpG sites in the 3′translated exonic sequence, which is also methylated in normal controls. However, using MSP primers localized to the 5′UTR, methylation of SOCS1, SOCS2 and SOCS3 is infrequent across all studies. In summary, methylation of SOCS1, SOCS2, SOCS3 and CISH is infrequent in Ph-ve MPN. Appropriate MSP primers are important for accurate estimation of the methylation frequency. The role of SHP1 methylation in the pathogenesis of MPN warrants further investigation.

Determinants of the extent and duration of STAT3 signaling

Multiple molecular mechanisms have been identified that are responsible for the deregulation of the quantitative aspects of JAK-STAT signaling. These mechanisms enhance the extent and the duration of, e.g., STAT3 activation and have profound consequences on the phenotypes of the affected cells. The fine tuning of STAT3 signaling is required to maintain its physiological functions and its deregulation is associated with diverse pathological states. Deregulation can be exerted by the gain of function of components mediating the activation of STAT3 or the loss of function of molecules involved in the deactivation steps of STAT3. Gain of function mutations can involve tyrosine kinases that phosphorylate STAT3, mutations in cytokine and growth factor receptors causing their ligand independent activation, mutations in STAT3 that enhance and prolong its tyrosine phosphorylation and the autocrine or paracrine production and secretion of cytokines, most notably IL-6. Diminished deactivation of phosphorylated STAT3 can be due to the reduced expression of tyrosine phosphatases, inactivating mutations in these enzymes, silencing or functional inactivation of SOCS molecules, post-transcriptional inhibition of PIAS3 expression or deletion mutations in the lymphocyte adaptor protein, LNK. STAT3 variants that exhibit autonomous transactivation potential have been detected in 40% of patients with T-cell large granular lymphocytic leukemia in clonally expanded CD8⁺ T cells. These patients also were preferentially affected by neutropenia and rheumatoid disorders and the results suggest that activating STAT3 mutations in T lymphocytes could be a cause of autoimmune diseases.

SOCS, inflammation, and cancer

Signal transduction pathways elicited by cytokines and hormones have been shown to regulate distinct stages of development. Suppressor of cytokine signaling (SOCS) proteins are negative feedback regulators of cytokine signaling mediated by the JAK-STAT signaling pathway. In particular, SOCS1 and SOCS3 are potent inhibitors of JAKs and can play pivotal roles in inflammation, as well as in the development and progression of cancers. Abnormal expression of SOCS1 and SOCS3 in cancer cells has been reported in human carcinoma associated with dysregulation of signals from cytokine receptors, Toll-like receptors (TLRs), and hormone receptors, resulting in malignancies. In this review, we focus on the role of SOCS1 and SOCS3 in cancer development. In addition, the potential of SOCS as a therapeutic target and diagnostic aid will be discussed.

Interleukin-11 is the dominant IL-6 family cytokine during gastrointestinal tumorigenesis and can be targeted therapeutically

Among the cytokines linked to inflammation-associated cancer, interleukin (IL)-6 drives many of the cancer "hallmarks" through downstream activation of the gp130/STAT3 signaling pathway. However, we show that the related cytokine IL-11 has a stronger correlation with elevated STAT3 activation in human gastrointestinal cancers. Using genetic mouse models, we reveal that IL-11 has a more prominent role compared to IL-6 during the progression of sporadic and inflammation-associated colon and gastric cancers. Accordingly, in these models and in human tumor cell line xenograft models, pharmacologic inhibition of IL-11 signaling alleviated STAT3 activation, suppressed tumor cell proliferation, and reduced the invasive capacity and growth of tumors. Our results identify IL-11 signaling as a potential therapeutic target for the treatment of gastrointestinal cancers.

Critical analysis of the potential for targeting STAT3 in human malignancy

The signal transducer and activator of transcription (STAT) family of proteins was originally discovered in the context of normal cell biology where they function to transduce intracellular and extracellular signals to the nucleus, ultimately leading to transcription of specific target genes and downstream phenotypic effects. It was quickly appreciated that the STATs, especially STAT3, play a fundamental role in human malignancy. In contrast to normal biology in which transient STAT3 signaling is strictly regulated by a tightly coordinated network of activators and deactivators, STAT3 is constitutively activated in human malignancies. Constitutive STAT3 signaling has been associated with many cancerous phenotypes across nearly all human cancers, including the upregulation of cell growth, proliferation, survival, and motility, among others. Studies involving candidate preclinical STAT3 inhibitors have further demonstrated that the reversal of these phenotypes results from pharmacologic or genetic inhibition of STAT3, suggesting that STAT3 may be a promising target for clinical interventions. Indeed, a Phase 0 clinical trial involving a STAT3 decoy oligonucleotide demonstrated that STAT3 is a drug-gable target in human tumors. Because of the ubiquity of overactive STAT3 in cancer, its role in promoting a wide variety of cancerous phenotypes, and the strong clinical and preclinical studies performed to date, STAT3 represents a promising target for the development of inhibitors for the treatment of human cancers.

Inhibition of microRNA122 decreases SREBP1 expression by modulating suppressor of cytokine signaling 3 expression

While inhibition of microRNA122 (miR122) function in vivo results in reduced serum cholesterol and fatty acid levels, the molecular mechanisms underlying the link between miR122 function and lipid metabolism remains unclear. Because the expression of SREBP1, a central transcription factor involved in lipid metabolism, is known to be increased by suppressor of cytokine signaling 3 (SOCS3) expression, and because we previously found that SOCS3 expression is regulated by miR122, in this study, we examined the correlation between miR122 status and the expression levels of SOCS3 and SREBP1. SREBP1 expression decreased when SOCS3 expression was reduced by miR122 silencing in vitro. Conversely, SREBP1 expression in miR122-silenced cells was restored by enforced expression of SOCS3. Such correlations were observed in human liver tissues with different miR122 expression levels. These signaling links may explain one of the molecular mechanisms linking inhibition of miR122 function or decreased expression of miR122 to decreased fatty acid and cholesterol levels, in the inhibition of miR122 function, or in pathological status in chronic liver diseases.

Intrinsic and extrinsic mechanisms contribute to maintain the JAK/STAT pathway aberrantly activated in T-type large granular lymphocyte leukemia

The JAK/STAT pathway is altered in T-cell large granular lymphocytic leukemia. In all patients, leukemic LGLs display upregulation of phosphorylated STAT3 (P-STAT3) that activates expression of many antiapoptotic genes. To investigate the mechanisms maintaining STAT3 aberrantly phosphorylated using transcriptional protein and functional assays, we analyzed interleukin (IL)-6 and suppressor of cytokine signaling-3 (SOCS3), 2 key factors of the JAK/STAT pathway that induce and inhibit STAT3 activation, respectively. We showed that IL-6 was highly expressed and released by the patients' peripheral blood LGL-depleted population, accounting for a trans-signaling process. By neutralizing IL-6 or its specific receptor with specific antibodies, a significant reduction of P-STAT3 levels and, consequently, LGL survival was demonstrated. In addition, we found that SOCS3 was down-modulated in LGL and unresponsive to IL-6 stimulation. By treating neoplastic LGLs with a demethylating agent, IL-6-mediated SOCS3 expression was restored with consequent P-STAT3 and myeloid cell leukemia-1 down-modulation. Methylation in the SOCS3 promoter was not detectable, suggesting that an epigenetic inhibition mechanism occurs at a different site. Our data indicate that loss of the inhibitor SOCS3 cooperates with IL-6 to maintain JAK/STAT pathway activation, thus contributing to leukemic LGL survival, and suggest a role of demethylating agents in the treatment of this disorder.

SOCS proteins in development and disease

Cytokine and growth factor signaling mediates essential roles in the differentiation, proliferation, survival and function of a number of cell lineages. This is achieved via specific receptors located on the surface of target cells, with ligand binding activating key intracellular signal transduction cascades to mediate the requisite cellular outcome. Effective resolution of receptor signaling is also essential, with excessive signaling having the potential for pathological consequences. The Suppressor of cytokine signaling (SOCS) family of proteins represent one important mechanism to extinguish cytokine and growth factor receptor signaling. There are 8 SOCS proteins in mammals; SOCS1-7 and the alternatively named Cytokine-inducible SH2-containing protein (CISH). SOCS1-3 and CISH are predominantly associated with the regulation of cytokine receptor signaling, while SOCS4-7 are more commonly involved in the control of Receptor tyrosine kinase (RTK) signaling. Individual SOCS proteins are typically induced by specific cytokines and growth factors, thereby generating a negative feedback loop. As a consequence of their regulatory properties, SOCS proteins have important functions in development and homeostasis, with increasing recognition of their role in disease, particularly their tumor suppressor and anti-inflammatory functions. This review provides a synthesis of our current understanding of the SOCS family, with an emphasis on their immune and hematopoietic roles.

Gene methylation and silencing of SOCS3 in mantle cell lymphoma

The significance of loss of SOCS3, a negative regulator of signalling pathways including those of STAT3 and NF-κB, was examined in mantle cell lymphoma (MCL). The protein expression and gene methylation status of SOCS3 were detected using immunohistochemistry/Western blots and methylation-specific polymerase chain reaction, respectively. To evaluate its functional importance, SOCS3 was restored in two SOCS3-negative MCL cell lines using a lentiviral vector. Loss of SOCS3 protein expression was found in 3/4 MCL cell lines and 18/33 (54.5%) tumours. SOCS3 was found consistently methylated in cell lines (3/4) and tumours (7/7) negative for SOCS3, and was unmethylated in all SOCS3-positive cell line (1/1) and tumours (5/5) examined. Treatment of all three SOCS3-negative cell lines with 2'-deoxy-5-azacytidine restored SOCS3 expression. SOCS3 is biologically important in MCL, as lentiviral transfer of SOCS3 in SOCS3-negative cell lines increased their apoptotic activity, downregulated nuclear factor (NF)-κB-p65, cyclin D1 (CCND1), BCL2 and BCL-XL (BCL2L1), and substantially dampened interleukin 10-induced STAT3 activation. In 19 patients aged ≤ 69 years at time of diagnosis, we found that those that carried SOCS3-negative tumours showed a trend toward a worse outcome (P = 0.1, log-rank).

SOCS3 promotor hypermethylation and STAT3-NF-κB interaction downregulate SOCS3 expression in human coronary artery smooth muscle cells

Suppressor of cytokine signaling-3 (SOCS3) is an intracellular negative regulator of cytokine signaling pathway. We recently found significant reduction in SOCS3 expression in coronary artery smooth muscle cells (CASMCs) of atherosclerotic swine and also in vitro cultured cells. Here, we investigated the underlying mechanisms of SOCS3 downregulation by IGF-1 and TNF-α in human CASMCs(hCASMCs). We propose that hypermethylation of CpG islands in the SOCS3 promoter is responsible for decrease in SOCS3 expression involving STAT3 and NFkB-p65 interaction. Western blot and qPCR data revealed significant upregulation of SOCS3 (6- to 10-fold) in hCASMC when treated individually with TNF-α (100 ng/ml) or IGF-1 (100 ng/ml). However, a significant decrease (5-fold) was observed by the combined treatment with TNF-α and IGF-1 compared with individual stimulation. IGF-1 phosphorylated STAT3 and TNF-α-activated NF-κB in hCASMCs. In the nuclear extract of hCASMCs stimulated with both TNF-α and IGF-1, there was an interaction between NF-κB-p65 and pSTAT3, as determined by co-immunoprecipitation. Knockdown of STAT3 by small interfering RNA abolished SOCS3 expression in response to IGF-1. Methylation-specific PCR confirmed hypermethylation of SOCS3 promoter in hCASMCs stimulated with both TNF-α and IGF-1, and this was positively associated with elevated levels of DNA methyltransferase-I (9- to 10-fold). Knockdown of DNMT1 increased SOCS3 expression in IGF-1+TNF-α-stimulated cells. Downregulation of SOCS3 in the presence of both TNF-α and IGF-1 in hCASMCs is due to SOCS3 promoter hypermethylation involving STAT3-NFkBp65 interaction. Because TNF-α and IGF-1 are released due to mechanical injury during coronary intervention, hypermethylation of SOCS3 gene could be an underlying mechanism of intimal hyperplasia and restenosis.

mTORC1 inhibition restricts inflammation-associated gastrointestinal tumorigenesis in mice

Gastrointestinal cancers are frequently associated with chronic inflammation and excessive secretion of IL-6 family cytokines, which promote tumorigenesis through persistent activation of the GP130/JAK/STAT3 pathway. Although tumor progression can be prevented by genetic ablation of Stat3 in mice, this transcription factor remains a challenging therapeutic target with a paucity of clinically approved inhibitors. Here, we uncovered parallel and excessive activation of mTOR complex 1 (mTORC1) alongside STAT3 in human intestinal-type gastric cancers (IGCs). Furthermore, in a preclinical mouse model of IGC, GP130 ligand administration simultaneously activated mTORC1/S6 kinase and STAT3 signaling. We therefore investigated whether mTORC1 activation was required for inflammation-associated gastrointestinal tumorigenesis. Strikingly, the mTORC1-specific inhibitor RAD001 potently suppressed initiation and progression of both murine IGC and colitis-associated colon cancer. The therapeutic effect of RAD001 was associated with reduced tumor vascularization and cell proliferation but occurred independently of STAT3 activity. We analyzed the mechanism of GP130-mediated mTORC1 activation in cells and mice and revealed a requirement for JAK and PI3K activity but not for GP130 tyrosine phosphorylation or STAT3. Our results suggest that GP130-dependent activation of the druggable PI3K/mTORC1 pathway is required for inflammation-associated gastrointestinal tumorigenesis. These findings advocate clinical application of PI3K/mTORC1 inhibitors for the treatment of corresponding human malignancies.

SOCS-3 is downregulated in progressive CKD patients and regulates proliferation in human renal proximal tubule cells in a STAT1/3 independent manner

Proliferation and the sequence of epithelial to mesenchymal transition (EMT) and mesenchymal to epithelial transition (MET), called epithelial-mesenchymal-epithelial (EME) cycling are pivotal mechanisms of kidney repair and fibrosis. Furthermore, data suggest that dedifferentiation (EMT) is a prerequisite for proliferation of tubule cells. These processes have been shown to be regulated by STAT1/3 signaling. Suppressor of cytokine signaling-3 (SOCS-3) is a negative regulator of STAT1/3 signaling. Using a transcriptomics data set of patients with proteinuric kidney diseases we found that low levels of SOCS-3 RNA were associated with high-serum creatinine values in the long-term follow-up, which suggested a role of SOCS-3, regulated signaling in progression of chronic kidney disease. This result was validated in an independent cohort of patients with proteinuric nephropathies on protein level. In addition ∼60% of STAT target genes were differentially expressed in relation to stable kidney disease patients. Using two renal cellular models and SOCS-3 knockdown by short interfering RNA we investigated SOCS-3 effects on oncostatin M-induced STAT activation, differentiation and proliferation. SOCS-3 knockdown resulted in enhanced pSTAT1/3 phosphorylation and epithelial differentiation. The latter effect was only slightly enhanced by OSM treatment. Cellular proliferation was inhibited after SOCS-3 knockdown. This effect could not be further stimulated by OSM. Effects of SOCS-3 knockdown were not enhanced by downregulation of STAT1/3, suggesting a STAT independent effect on cell cycle regulators. Indeed, knockdown and overexpression of SOCS-3 were associated with decrease and increase of cyclin D1, -E and proliferation, respectively. In summary, SOCS-3 inhibits phosphorylation of pSTAT1/3 in renal tubule cells. Additionally, we show for the first time that-in vivo-loss of SOCS-3 is associated with unfavorable prognosis. In vitro, downregulation of SOCS-3 inhibits dedifferentiation (EMT) and cellular proliferation in kidney proximal tubule cells.

CancerMA: a web-based tool for automatic meta-analysis of public cancer microarray data

The identification of novel candidate markers is a key challenge in the development of cancer therapies. This can be facilitated by putting accessible and automated approaches analysing the current wealth of 'omic'-scale data in the hands of researchers who are directly addressing biological questions. Data integration techniques and standardized, automated, high-throughput analyses are needed to manage the data available as well as to help narrow down the excessive number of target gene possibilities presented by modern databases and system-level resources. Here we present CancerMA, an online, integrated bioinformatic pipeline for automated identification of novel candidate cancer markers/targets; it operates by means of meta-analysing expression profiles of user-defined sets of biologically significant and related genes across a manually curated database of 80 publicly available cancer microarray datasets covering 13 cancer types. A simple-to-use web interface allows bioinformaticians and non-bioinformaticians alike to initiate new analyses as well as to view and retrieve the meta-analysis results. The functionality of CancerMA is shown by means of two validation datasets.

ANT2 suppression by shRNA may be able to exert anticancer effects in HCC further by restoring SOCS1 expression

Suppressor of cytokine signaling 1 (SOCS1) is a negative regulator of Janus kinase and the signal transducer and activation of transcription (Jak-STAT) pathway. SOCS-1 is known to be silenced by aberrant promoter methylation in human hepatocellular carcinoma (HCC) during early tumorigenesis, therefore, a strategy to restore SOCS1 expression can be utilized for cancer therapy. Here, we examined the influence of adenine nucleotide translocase 2 (ANT2) suppression by short-hairpin RNA (shRNA) on SOCS1 expression and its downstream effect in HCC. ANT2 shRNA treatment led to restoration of SOCS1 expression along with its promoter demethylation in Hep3B cells, which was accompanied by decreased DNA methyltransferase 1 (DNMT1) activity through the suppression of Ras/PI3K/Akt signaling. Restoration of SOCS1 by ANT2 knockdown, subsequently, inhibited STAT3 activity and downregulated the expression of miR-21, which has been reported to be an important onco-miR in HCC. Downregulation of miR-21 efficiently suppressed Hep3B cell proliferation in vitro with a comparable level to ANT2 shRNA treatment. ANT2 suppression by shRNA may be able to exert anticancer effects in HCC further by restoring SOCS1 expression.

Chronic inflammation as a promotor of mutagenesis in essential thrombocythemia, polycythemia vera and myelofibrosis. A human inflammation model for cancer development?

The Philadelphia-negative chronic myeloproliferative neoplasms (MPNs) are acquired stem cell neoplasms, in which a stem cell lesion induces an autonomous proliferative advantage. In addition to the JAK2V617 mutation several other mutations have been described. Recently chronic inflammation has been proposed as a trigger and driver of clonal evolution in MPNs. Herein, it is hypothesized that sustained inflammation may elicit the stem cell insult by inducing a state of chronic oxidative stress with elevated levels of reactive oxygen species (ROS) in the bone marrow, thereby creating a high-risk microenvironment for induction of mutations due to the persistent inflammation-induced oxidative damage to DNA in hematopoietic cells. Alterations in the epigenome induced by the chronic inflammatory drive may likely elicit a "epigenetic switch" promoting persistent inflammation. The perspectives of chronic inflammation as the driver of mutagenesis in MPNs are discussed, including early intervention with interferon-alpha2 and potent anti-inflammatory agents (e.g. JAK1-2 inhibitors, histone deacetylase inhibitors, DNA-hypomethylators and statins) to disrupt the self-perpetuating chronic inflammation state and accordingly eliminating a potential trigger of clonal evolution and disease progression with myelofibrotic and leukemic transformation.

A requirement for SOCS-1 and SOCS-3 phosphorylation in Bcr-Abl-induced tumorigenesis

Suppressors of cytokine signaling 1 and 3 (SOCS-1 and SOCS-3) are inhibitors of the Janus tyrosine kinase (JAK)/signal transducers and activators of transcription (STAT) pathway and function in a negative feedback loop during cytokine signaling. Abl transformation is associated with constitutive activation of JAK/STAT-dependent signaling. However, the mechanism by which Abl oncoproteins bypass SOCS inhibitory regulation remains poorly defined. Here, we demonstrate that coexpression of Bcr-Abl with SOCS-1 or SOCS-3 results in tyrosine phosphorylation of these SOCS proteins. Interestingly, SOCS-1 is highly tyrosine phosphorylated in one of five primary chronic myelogenous leukemia samples. Bcr-Abl-dependent tyrosine phosphorylation of SOCS-1 and SOCS-3 occurs mainly on Tyr 155 and Tyr 204 residues of SOCS-1 and on Tyr 221 residue of SOCS-3. We observed that phosphorylation of these SOCS proteins was associated with their binding to Bcr-Abl. Bcr-Abl-dependent phosphorylation of SOCS-1 and SOCS-3 diminished their inhibitory effects on the activation of JAK and STAT5 and thereby enhanced JAK/STAT5 signaling. Strikingly, disrupting the tyrosine phosphorylation of SOCS-1 or SOCS-3 impaired the expression of Bcl-X(L) protein and sensitized K562 leukemic cells to undergo apoptosis. Moreover, selective mutation of tyrosine phosphorylation sites of SOCS-1 or SOCS-3 significantly blocked Bcr-Abl-mediated tumorigenesis in nude mice and inhibited Bcr-Abl-mediated murine bone marrow transformation. Together, these results reveal a mechanism of how Bcr-Abl may overcome SOCS-1 and SOCS-3 inhibition to constitutively activate the JAK/STAT-dependent signaling, and suggest that Bcr-Abl may critically requires tyrosine phosphorylation of SOCS-1 and SOCS-3 to mediate tumorigenesis when these SOCS proteins are present in cells.

Hypoxia-induced decreases in SOCS3 increase STAT3 activation and upregulate VEGF gene expression

Signal transducer and activator of transcription (STAT) 3 has been described as a master regulator of the signaling pathways that are involved in the mesenchymal transition of glioblastomas, which are the most aggressive type of tumors and which result in poor prognoses. Hypoxia, which is a strong inducer of vascular endothelial growth factor (VEGF), results in angiogenesis and the bulky growth of tumors. Here, we show that hypoxia induces VEGF gene expression through a STAT3 signaling cascade. Hypoxia increases the levels of aberrantly activated STAT3 by decreasing the levels of the suppressor of cytokine signaling (SOCS) 3, which is a negative regulator of the STAT3 signaling cascade. Activated STAT3 binds to the hypoxia-responsible element that is located -914 to -905 bp upstream of the transcription initiation site in the VEGF promoter and that transcriptionally regulates VEGF gene expression. This sequence closely resembled the previously defined sis-inducible element in the STAT3-binding sequences. The enforced overexpression of SOCS3 abolished the hypoxia-induced STAT3 activation and the STAT3-mediated transcriptional upregulation of the VEGF gene. In addition, activated STAT3 was found around necrotic foci in surgical specimens. These observations suggest that STAT3 is a molecular target of antiangiogenesis.

Mutational screening of the SOCS3 gene promoter in metastatic colorectal cancer patients

Cytokine-induced expression of suppressors of cytokine signalling (SOCS) molecules is important for the negative feedback control of STAT-dependent cytokine signalling. The aim of this study was to investigate possible association between the promoter region polymorphisms of the SOCS3 gene and metastatic colorectal carcinoma in a Turkish population. The DNA samples obtained from 103 patients and 109 healthy individuals were analyzed by polymerase chain reaction/single-strand conformation polymorphism (SSCP), and nucleotide sequence analysis. Five sets of primers designed for the SOCS3 gene were used, and we did not detect significant differences in genotype frequencies for any of these polymorphisms between the study groups. Only the S3P1 region showed polymorphism and displayed three (1,2,4, 2,3,4 and 2,4) genotypes. Interestingly, 2,3,4 genotype was observed in 3 patients, but not in controls. Moreover, the sequence analysis revealed that the nucleotides positioned at -914 and -1031 nt had the polymorphisms. Nucleotide sequence analysis of SSCP band 1 and band 3 revealed C-914A (rs12953258) and T-1031C (rs111033850) polymorphisms, respectively. The T-1031C polymorphism lies in the border of the STAT-binding site. The T-1031C polymorphism (rs111033850) is a newly identified single nucleotide polymorphism with this study, and we submitted this to the NCBI database. However, these results suggested that there is no marked association between SOCS3 gene promoter region polymorphisms and the risk of developing metastatic colorectal cancer.

Pien Tze Huang suppresses IL-6-inducible STAT3 activation in human colon carcinoma cells through induction of SOCS3

IL-6/STAT3 is one of the most critical cellular signal transduction pathways known to malfunction in colorectal cancer (CRC). As a target gene of signal transducer and activator of transcription 3 (STAT3) signaling, suppressor of cytokine signaling 3 (SOCS3) can be quickly induced by interleukin-6 (IL-6) stimulation but it then strongly inhibits IL-6-mediated STAT3 activation, functioning as a negative feedback regulator of the IL-6/STAT3 pathway. Aberrant activation of STAT3 and/or reduced expression of SOCS are strongly correlated with carcinogenesis, which therefore becomes a promising target for the development of novel anticancer chemotherapies. Pien Tze Huang (PZH) is a well-known traditional Chinese formula that was first prescribed by a royal physician 450 years ago in the Ming Dynasty. It has been used in China and Southeast Asia for centuries as a folk remedy for various types of cancer including CRC. However, the precise mechanism of its antitumor activity remains largely unclear. In the present study, we found that PZH could significantly and dose-dependently inhibit IL-6-mediated increase of STAT3 phosphorylation levels and transcriptional activity in the human colon carcinoma HT-29 cells, resulting in the suppression of cell proliferation and the induction of apoptosis. In addition, PZH treatment profoundly inhibited IL-6-induced upregulation of cyclin D1 and Bcl-2, two key target genes of the STAT3 pathway. Moreover, PZH treatment increased the expression of SOCS3. These results suggest that PZH could effectively inhibit proliferation and promote apoptosis of human colon carcinoma cells via modulation of the IL-6/STAT3 signaling pathway and its target genes.

Loss of expression and function of SOCS3 is an early event in HNSCC: altered subcellular localization as a possible mechanism involved in proliferation, migration and invasion

Background

Suppressor of cytokine signaling 3 (SOCS3) is an inducible endogenous negative regulator of signal transduction and activator of transcription 3 (STAT3). Epigenetic silencing of SOCS3 has been shown in head and neck squamous cell carcinoma (HNSCC), which is associated with increased activation of STAT3. There is scarce information on the functional role of the reduction of SOCS3 expression and no information on altered subcellular localization of SOCS3 in HNSCC.

Methodology/Principal Findings

We assessed endogenous SOCS3 expression in different HNSCC cell lines by RT-qPCR and western blot. Immunofluorescence and western blot were used to study the subcellular localization of endogenous SOCS3 induced by IL-6. Overexpression of SOCS3 by CMV-driven plasmids and siRNA-mediated inhibition of endogenous SOCS3 were used to verify the role of SOCS3 on tumor cell proliferation, viability, invasion and migration in vitro. In vivo relevance of SOCS3 expression in HNSCC was studied by quantitative immunohistochemistry of commercially-available tissue microarrays. Endogenous expression of SOCS3 was heterogeneous in four HNSCC cell lines and surprisingly preserved in most of these cell lines. Subcellular localization of endogenous SOCS3 in the HNSCC cell lines was predominantly nuclear as opposed to cytoplasmic in non-neoplasic epithelial cells. Overexpression of SOCS3 produced a relative increase of the protein in the cytoplasmic compartment and significantly inhibited proliferation, migration and invasion, whereas inhibition of endogenous nuclear SOCS3 did not affect these events. Analysis of tissue microarrays indicated that loss of SOCS3 is an early event in HNSCC and was correlated with tumor size and histological grade of dysplasia, but a considerable proportion of cases presented detectable expression of SOCS3.

Conclusion

Our data support a role for SOCS3 as a tumor suppressor gene in HNSCC with relevance on proliferation and invasion processes and suggests that abnormal subcellular localization impairs SOCS3 function in HNSCC cells.

Interleukin-6: a multifunctional targetable cytokine in human prostate cancer

Several cytokines are involved in regulation of cellular events in prostate cancer. Interleukin-6 (IL-6) was frequently investigated in prostate cancer models because of its increased expression in cancer tissue at early stages of the disease. In patients with metastatic prostate cancer, it is well-known that IL-6 levels increase in serum. High levels of IL-6 were measured in the supernatants of cells which do not respond to androgenic stimulation. IL-6 expression in prostate cancer increases due to enhanced expression of transforming growth factor-beta, and members of the activating protein-1 complex, and loss of the retinoblastoma tumour suppressor. IL-6 activation of androgen receptor (AR) may contribute to progression of a subgroup of prostate cancers. Results obtained with two prostate cancer cell lines, LNCaP and MDA PCa 2b, indicate that IL-6 activation of AR may cause either stimulatory or inhibitory responses on proliferation. Interestingly, prolonged treatment with IL-6 led to establishment of an IL-6 autocrine loop, suppressed signal transducer and activator of transcription (STAT)3 activation, and increased mitogen-activated protein kinase phosphorylation. In several cell lines IL-6 acts as a survival molecule through activation of the signalling pathway of phosphotidylinositol 3-kinase. Expression of suppressors of cytokine signalling (SOCS) has been studied in prostate cancer. SOCS-3 prevents phosphorylation of STAT3 and is an important anti-apoptotic factor in AR-negative prostate cancer cells. Experimental therapy against IL-6 in prostate cancer is based on the use of the monoclonal antibody siltuximab which may be used for personalised therapy coming in the future.

Platelet factor 4 induces cell apoptosis by inhibition of STAT3 via up-regulation of SOCS3 expression in multiple myeloma

Platelet factor 4 (PF4) is an angiostatic chemokine that suppresses tumor growth and metastasis. We previously revealed frequent transcriptional silencing of PF4 in multiple myeloma, but the functional roles of this chemokine are still unknown. We studied the apoptotic effects of PF4 on myeloma cell lines and primary myeloma in vitro, and investigated the involved signaling pathway. The in vivo effects were also studied using a mouse model. PF4 not only suppressed myeloma-associated angiogenesis, but also inhibited growth and induced apoptosis in myeloma cells. We found that PF4 negatively regulated STAT3 and concordantly inhibited constitutive and interleukin-6-induced phosphorylation of STAT3, and down-regulated the expression of STAT3 target genes (Mcl-1, survivin and VEGF). Overexpression of constitutively activated STAT3 could rescue PF4-induced apoptotic effects. Furthermore, we found that PF4 induced the expression of SOCS3, a STAT3 inhibitor, and gene silencing of SOCS3 abolished its ability to inhibit STAT3 activation, suggesting a critical role of SOCS3 in PF4-induced STAT3 inhibition. Knockdown of LRP1, a putative PF4 receptor, could also abolish PF4-induced apoptosis and STAT3 inhibition. Finally, the tumor growth inhibitory effect of PF4 was confirmed by in vivo mouse models. Immunostaining of rabbit bone xenografts from PF4-treated mice showed induction of apoptosis of myeloma cells and inhibition of angiogenesis, which was associated with suppression of STAT3 activity. Together, our preclinical data indicate that PF4 may be a potential new targeting agent for the treatment of myeloma.

The role of DNA methyltransferase 3b in esophageal squamous cell carcinoma

BACKGROUND

The identification of potential tumor markers can improve therapeutic planning and patient management. The objective of this study was to highlight the role of DNA methyltransferase 3b (DNMT3b) in esophageal squamous cell carcinoma (SCC).

METHODS

One hundred seventy-three esophageal SCC samples were analyzed using immunohistochemical staining to correlate the expression of DNMT3b with clinical outcome. Furthermore, a human esophageal SCC cell line, CE81T, was selected for cellular and animal experiments to investigate changes in tumor behavior and treatment response after the manipulation of DNMT3b expression.

RESULTS

The incidence of nuclear DNMT3b immunoreactivity in esophageal cancer specimens was significantly higher than in nonmalignant epithelium, and this incidence was linked positively to developing distant metastasis (56% in localized disease vs 80% in distant metastasis; P = .002). Furthermore, increased expression of DNMT3b was linked significantly to lower treatment response rates (P = .002) and reduced survival rates (P = .000). Inhibition of DNMT3b expression resulted in slower cellular proliferation, increased cell death, a less invasive capacity, and less epithelial-mesenchymal-transition changes. Moreover, DNMT3b silencing vectors sensitized esophageal cancer cells to irradiation and cisplatin treatment. The current results also indicated that constitutional activation of signal transducer and activator of transcription 3 (STAT3) signaling associated with inhibited expression of suppressor of cytokine signaling 3 (SOCS3) may be the mechanism underlying more aggressive tumor growth in DNMT3b-positive esophageal cancer.

CONCLUSIONS

DNMT3b was linked significantly to a poor prognosis for patients with esophageal cancer. Moreover, the current results indicated that targeting this enzyme may be a promising strategy for treating esophageal cancer, as evidenced by inhibited aggressive tumor behavior and treatment resistance.

SOCS3 in immune regulation of inflammatory bowel disease and inflammatory bowel disease-related cancer

Inflammatory bowel disease (IBD) has unclear pathogenesis and it is related to the increasing risk of developing colorectal cancer (CRC). Recent studies have uncovered the molecular mechanism of intracellular signaling pathways of inflammatory cytokines such as tumor necrosis factor (TNF)-α, interferon (IFN)-γ and interleukin (IL)-6. The major transcription factors including STAT3 have been shown to play a major role in transmitting inflammatory cytokine signals to the nucleus. The suppressors of cytokine signaling (SOCS) 3 protein is the key physiological regulators of cytokine-mediated STAT3 signaling. As such it influences the development of inflammatory and malignant disorders like this associated with IBD. Here we review the complex function of SOCS3 in innate and adaptive immunity, different cell types (macrophages, neutrophils, dendritic cells, B cells, T cells and intestinal epithelial cells) and the role of SOCS3 on the pathogenesis of inflammatory bowel disease (IBD) and IBD-related cancer. Finally, we explore how this knowledge may open novel avenues for the rational treatment of IBD and IBD-related cancer.

Suppressor of cytokine signaling 4 detected as a novel gastric cancer suppressor gene using double combination array analysis

BACKGROUND

Molecular mechanisms behind the oncogenesis of gastric cancer (GC) have yet to be identified.

METHODS

A novel candidate tumor-suppressor gene, which is also associated with inhibition of epidermal growth factor (EGF), was sought by means of double combination array analysis for use as a prognostic marker of GC. This consisted of expression array and single nucleotide polymorphism array analysis, along with a literature search. Cancerous and noncancerous tissues from an 82-year-old man with GC were analyzed simultaneously.

RESULTS

The expression array and literature search identified that the suppressor of cytokine signaling 4 (SOCS4), a negative feedback regulator of EGF signaling, had significantly attenuated expression in tumor tissue. Although chromosomal deletion was not found at 14q22 where SOCS4 is located, numerous CpG sites were observed in the promoter region of the SOCS4 gene. Several GC cell lines showed reactivation of SOCS4 mRNA expression after treatment with 5-aza-2'-deoxycytidine. Using surgically resected specimens, we found that 40 of 50 (80%) tumor tissues exhibited promoter hypermethylation of the SOCS4 gene. Consequently, SOCS4 expression in tumor tissues was significantly weaker than in noncancerous counterparts (P < 0.0001). In the survival analysis, SOCS4 hypermethylation was associated with a poor prognosis of GC patients (P = 0.0320).

CONCLUSIONS

Double combination array analysis suggested that SOCS4 could be a novel candidate for further exploration as a tumor-suppressor gene in GC. Hypermethylation was the mechanism by which SOCS4 was silenced and was implicated in the development of GC. SOCS4 methylation might be an informative marker in predicting the prognosis.

Suppressor of cytokine signaling 3 inhibits breast tumor kinase activation of STAT3

Breast tumor kinase (Brk) was originally isolated from a human metastatic breast tumor, but also is found expressed in other epithelial tumors and in a subset of normal epithelia. Brk is a tyrosine kinase and its expression in breast carcinoma has been linked to tumor progression. The signal transducer and activator of transcription 3 (STAT3) is one of the substrate targets of Brk, and elevated tyrosine phosphorylation of STAT3 is known to contribute to oncogenesis. Conventional activation of STAT3 occurs in response to cytokine stimulation of Janus tyrosine kinases (JAK). One of the negative regulators discovered in cytokine signaling of the JAK-STAT pathway is the suppressor of cytokine signaling 3 (SOCS3). In this report we describe the finding that SOCS3 can also inhibit the unconventional target, Brk. Investigation of the mechanism by which SOCS3 inhibits Brk reveals the SOCS3 protein binds to Brk primarily via its SH2 domain, and its main inhibitory effect is mediated by the SOCS3 kinase inhibitory region (KIR). SOCS3 has only a modest effect on promoting Brk degradation, and this requires the C-terminal SOCS box domain. SOCS3 is the only known inhibitor of Brk, and knowledge of the mechanisms by which SOCS3 inhibits Brk may lead to methods that block Brk in cancer progression.

Biology and significance of the JAK/STAT signalling pathways

Since its discovery two decades ago, the activation of the Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway by numerous cytokines and growth factors has resulted in it becoming one of the most well-studied intracellular signalling networks. The field has progressed from the identification of the individual components to high-resolution crystal structures of both JAK and STAT, and an understanding of the complexities of the molecular activation and deactivation cycle which results in a diverse, yet highly specific and regulated pattern of transcriptional responses. While there is still more to learn, we now appreciate how disruption and deregulation of this pathway can result in clinical disease and look forward to adoption of the next generation of JAK inhibitors in routine clinical treatment.

Prognostic significance of phosphorylated signal transducer and activator of transcription 3 and suppressor of cytokine signaling 3 expression in human cutaneous melanoma

Cutaneous malignant melanoma is one of the most common and aggressive forms of human cancers and has a poor prognosis. Activation of signal transducer and activator of transcription 3 (STAT3) has been found in several human cancers and is thought to correlate aggressive disease and poor response. In this study, we investigated the clinical role of STAT3 and its natural inhibitor, suppressor of cytokine signaling 3 (SOCS3), in human cutaneous melanoma development and progression. Immunohistochemical analysis of pSTAT3, SOCS3, matrix metalloproteinase (MMP)-2, and MMP-9 expression was performed on 90 primary melanomas and 43 common melanocytic nevi specimens. The expression of STAT3 mRNA was further detected by in-situ hybridization in the same cohort of patients. The association of STAT3 mRNA, pSTAT3, and SOCS3 protein expression with clinicopathological parameters and patient survival was analyzed. Altered expression of STAT3 mRNA, pSTAT3, and SOCS3 protein was observed in melanoma specimens, compared with benign melanocytic nevi. High expression of pSTAT3 was correlated to large tumor diameter, depth of tumor invasion, tumor lymph node metastasis, MMP-2 and MMP-9 expression, and poor patient survival. Decreased expression of SOCS3 was correlated to depth of tumor invasion, tumor lymph node metastasis, the expression of MMP-2, MMP-9, and pSTAT3, and poor patient survival. Moreover, the expression of pSTAT3 was conversely correlated to SOCS3 expression in melanoma. Our results indicate that deregulated expression of pSTAT3 and SOCS3 might possess potential roles in the development and progression of human cutaneous melanoma.

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

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

Extracellular signal-regulated kinase mitogen-activated protein kinase-dependent SOCS-3 gene induction requires c-Jun, signal transducer and activator of transcription 3, and specificity protein 3 transcription factors

SOCS-3 gene induction by cAMP-elevating agents or the protein kinase C (PKC) activator, phorbol 12-myristate 13-acetate (PMA), in primary HUVECs was found to require PKCη- and PKCε-dependent extracellular signal-regulated kinase (ERK) activation. The minimal, ERK-responsive element of the SOCS-3 promoter was localized to a region spanning nucleotides -107 to the transcription start site and contains conserved binding sites for AP-1 and SP1/SP3 transcription factors, as well as proximal and distal signal transducer and activator of transcription (pSTAT and dSTAT) binding elements. All three classes of transcription factor were activated in response to ERK activation. Moreover, representative protein components of each of these transcription factor binding sites, namely c-Jun, STAT3, and SP3, were found to undergo ERK-dependent phosphorylation within their respective transactivation domains. Mutational analysis demonstrated an absolute requirement for the SP1/SP3 binding element in controlling basal transcriptional activity of the minimal SOCS-3 promoter. In addition AP-1, pSTAT, and SP1/SP3 binding sites were required for ERK-dependent, PMA-stimulated SOCS-3 gene activation. The dSTAT site seems to be important for supporting activity of the AP-1 site, because combined deletion of both sites completely blocks transcriptional activation of SOCS-3 by PMA. Together these results describe novel, ERK-dependent regulation of transcriptional activity that requires codependent activation of multiple transcription factors within the same region of the SOCS-3 gene promoter.

STAT3 is activated by JAK2 independent of key oncogenic driver mutations in non-small cell lung carcinoma

Constitutive activation of STAT3 is a common feature in many solid tumors including non-small cell lung carcinoma (NSCLC). While activation of STAT3 is commonly achieved by somatic mutations to JAK2 in hematologic malignancies, similar mutations are not often found in solid tumors. Previous work has instead suggested that STAT3 activation in solid tumors is more commonly induced by hyperactive growth factor receptors or autocrine cytokine signaling. The interplay between STAT3 activation and other well-characterized oncogenic “driver” mutations in NSCLC has not been fully characterized, though constitutive STAT3 activation has been proposed to play an important role in resistance to various small-molecule therapies that target these oncogenes. In this study we demonstrate that STAT3 is constitutively activated in human NSCLC samples and in a variety of NSCLC lines independent of activating KRAS or tyrosine kinase mutations. We further show that genetic or pharmacologic inhibition of the gp130/JAK2 signaling pathway disrupts activation of STAT3. Interestingly, treatment of NSCLC cells with the JAK1/2 inhibitor ruxolitinib has no effect on cell proliferation and viability in two-dimensional culture, but inhibits growth in soft agar and xenograft assays. These data demonstrate that JAK2/STAT3 signaling operates independent of known driver mutations in NSCLC and plays critical roles in tumor cell behavior that may not be effectively inhibited by drugs that selectively target these driver mutations.

Role of SOCS1 in tumor progression and therapeutic application

SOCS1, a prototype molecule of the SOCS family, was initially defined as a suppressor of cytokine signaling. The molecular mechanisms of SOCS1-mediated functions have been subsequently identified by studies using gene knockout mice and gene silencing technology. As part of a negative feedback regulation, SOCS1 downregulates cytokine signaling through direct inhibition of the JAK tyrosine kinase and the signaling cascade of activated cytokine receptors, thereby attenuating cytokine-initiated signal transduction. Moreover, other studies have demonstrated that SOCS1 also downregulates TLR signaling through direct and indirect mechanisms. Both cytokine receptor and TLR signaling pathways mediate important functions in survival, maturation and differentiation of various types of cells and in the regulation of immune function. Abnormal expression of SOCS1 in tumor cells has been detected in various human cancers, where it is associated with dysregulation of cytokine receptor and TLR signaling to promote cell transformation. Recent studies on the function of SOCS1 in tumor cells have revealed its novel role in carcinogenesis. In this review, we will focus on the mechanism of action of SOCS1 in both tumor cells and antigen-presenting cells in the tumor microenvironment. The potential of using SOCS1 as a diagnostic marker and therapeutic target in tumor diagnosis, prognosis and treatment is discussed.

Inflammation, DNA methylation and colitis-associated cancer

Inflammation can result from a range of sources including microbial infections, exposure to allergens and toxic chemicals, autoimmune disease and obesity. A well-balanced immune response can be anti-tumorigenic; however, a sustained or chronic inflammatory response is generally harmful as the immune response becomes distorted. A causal link between chronic inflammation and cancer is now well accepted and many chronically inflamed organs of the gastrointestinal tract show this association. For example, patients with inflammatory bowel disease (IBD), including both ulcerative colitis and Crohn's disease, have a 2- to 3-fold greater lifetime risk of developing colorectal cancer compared with the general population. The development of colitis-associated cancer (CAC) is thought to be multifaceted and is probably due to a combination of genetic factors, epigenetic factors and the duration, extent and severity of disease. Recently, epigenetic alterations, in particular alterations in DNA methylation, have been observed during inflammation and inflammation-associated carcinogenesis. The mediators of this, the significance of these changes in DNA methylation and the effect this has on gene expression and the malignant transformation of the epithelial cells during IBD and CAC are discussed in this review. The recent advances in technologies to study genome-wide DNA methylation and the therapeutic potential of understanding these molecular mechanisms are also highlighted.

Colorectal cancer mouse models: integrating inflammation and the stroma

Sequences of molecular events that initiate and advance the progression of human colorectal cancer (CRC) are becoming clearer. Accepting that these events, once they are in place, accumulate over time, rapid disease progression might be expected. Yet CRC usually develops slowly over decades. Emerging insights suggest that the tumor cell microenvironment encompassing fibroblasts and endothelial and immune cells dictate when, whether, and how malignancies progress. Signaling pathways that affect the microenvironment and the inflammatory response seem to play a central role in CRC. Indeed, some of these pathways directly regulate the stem/progenitor cell niche at the base of the crypt; it now appears that the survival and growth of neoplastic cells often relies upon their subverted engagement of these pathways. Spurned on by the use of gene manipulation technologies in the mouse, dissecting and recapitulating these complex molecular interactions between the tumor and its microenvironment in the gastrointestinal (GI) tract is a reality. In parallel, our ability to isolate and grow GI stem cells in vitro enables us, for the first time, to complement reductionist in vitro findings with complex in vivo observations. Surprisingly, data suggest that the large number of signaling pathways underpinning the reciprocal interaction between the neoplastic epithelium and its microenvironment converge on a small number of common transcription factors. Here, we review the separate and interactive roles of NFκB, Stat3, and Myb, transcription factors commonly overexpressed or excessively activated in CRC. They confer molecular links between inflammation, stroma, the stem cell niche, and neoplastic cell growth.

Clinical implications of epigenetic alterations in human thoracic malignancies: epigenetic alterations in lung cancer

Besides known genetic aberrations, epigenetic alterations have emerged as common hallmarks of many cancer types, including lung cancer. Epigenetics is a process involved in gene regulation, mediated via DNA methylation, histone modification, chromatin remodeling, and functional noncoding RNAs, which influences the accessibility of the underlying DNA to transcriptional regulatory factors that activate or repress expression. Studies have shown that epigenetic dysregulation is associated with multiple steps during carcinogenesis. Since epigenetic therapy is now in clinical use in hematopoietic diseases and undergoing trials for lung cancer, a better understanding of epigenetic abnormalities is desired. Recent technologies for high-throughput genome-wide analyses for epigenetic modifications are promising and potent tools for understanding the global dysregulation of cancer epigenetics. In this chapter, studies of epigenetic abnormality and its clinical implication in lung cancers are discussed.

Inhibition of DNA methyltransferase induces G2 cell cycle arrest and apoptosis in human colorectal cancer cells via inhibition of JAK2/STAT3/STAT5 signalling

DNA methyltransferase inhibitors (MTIs) have recently emerged as promising chemotherapeutic or preventive agents for cancer, despite their poorly characterized mechanisms of action. The present study shows that DNA methylation is integral to the regulation of SH2-containing protein tyrosine phosphatase 1 (SHP1) expression, but not for regulation of suppressors of cytokine signalling (SOCS)1 or SOCS3 in colorectal cancer (CRC) cells. SHP1 expression correlates with down-regulation of Janus kinase/signal transducers and activators of transcription (JAK2/STAT3/STAT5) signalling, which is mediated in part by tyrosine dephosphorylation events and modulation of the proteasome pathway. Up-regulation of SHP1 expression was achieved using a DNA MTI, 5-aza-2'-deoxycytidine (5-aza-dc), which also generated significant down-regulation of JAK2/STAT3/STAT5 signalling. We demonstrate that 5-aza-dc suppresses growth of CRC cells, and induces G2 cell cycle arrest and apoptosis through regulation of downstream targets of JAK2/STAT3/STAT5 signalling including Bcl-2, p16(ink4a), p21(waf1/cip1) and p27(kip1). Although 5-aza-dc did not significantly inhibit cell invasion, 5-aza-dc did down-regulate expression of focal adhesion kinase and vascular endothelial growth factor in CRC cells. Our results demonstrate that 5-aza-dc can induce SHP1 expression and inhibit JAK2/STAT3/STAT5 signalling. This study represents the first evidence towards establishing a mechanistic link between inhibition of JAK2/STAT3/STAT5 signalling and the anticancer action of 5-aza-dc in CRC cells that may lead to the use of MTIs as a therapeutic intervention for human colorectal cancer.

STAT5A-mediated SOCS2 expression regulates Jak2 and STAT3 activity following c-Src inhibition in head and neck squamous carcinoma

PURPOSE

The inhibition of c-Src results in a striking reduction in cancer cell invasion, but the effect on cell survival is modest. Defining mechanisms that limit apoptosis following c-Src inhibition could result in an ideal therapeutic approach that both inhibits invasion and leads to apoptosis. In this regard, we discovered a novel feedback loop that results in STAT3 reactivation following sustained c-Src inhibition. Here we define the mechanism underlying this feedback loop and examine the effect of inhibiting it in vivo.

EXPERIMENTAL DESIGN

We measured levels and activity of pathway components using PCR, Western blotting, and kinase assays following their manipulation using both molecular and pharmacologic approaches. We used a heterotransplant animal model in which human oral squamous cancer is maintained exclusively in vivo.

RESULTS

Following c-Src inhibition, STAT5 is durably inhibited. The inhibition of STAT5A, but not STAT5B, subsequently reduces the expression of suppressors of cytokine signaling 2 (SOCS2). SOCS2 inhibits Janus kinase 2 (Jak2) activity and Jak2-STAT3 binding. SOCS2 expression is necessary for STAT3 inhibition by c-Src inhibitors. Overexpression of SOCS2 is adequate to prevent STAT3 reactivation and to enhance the cytotoxic effects of c-Src inhibition. Likewise, the combination of Jak and c-Src inhibitors led to significantly more apoptosis than either agent alone in vivo.

CONCLUSIONS

To our knowledge, ours is the first study that fully defines the mechanism underlying this feedback loop, in which sustained c-Src inhibition leads to diminished SOCS2 expression via sustained inhibition of STAT5A, allowing activation of Jak2 and STAT3, Jak2-STAT3 binding, and survival signals.

Cytokine induction of tumor necrosis factor receptor 2 is mediated by STAT3 in colon cancer cells

The IL-6/STAT3 and TNFα/NFκB pathways are emerging as critical mediators of inflammation-associated colon cancer. TNF receptor (TNFR) 2 expression is increased in inflammatory bowel diseases, the azoxymethane/dextran sodium sulfate (AOM/DSS) model of colitis-associated cancer, and by combined interleukin (IL) 6 and TNFα. The molecular mechanisms that regulate TNFR2 remain undefined. This study used colon cancer cell lines to test the hypothesis that IL-6 and TNFα induce TNFR2 via STAT3 and/or NFκB. Basal and IL-6 + TNFα-induced TNFR2 were decreased by pharmacologic STAT3 inhibition. NFκB inhibition had little effect on IL-6 + TNFα-induced TNFR2, but did inhibit induction of endogenous IL-6 and TNFR2 in cells treated with TNFα alone. Chromatin immunoprecipitation (ChIP) revealed cooperative effects of IL-6 + TNFα to induce STAT3 binding to a -1,578 STAT response element in the TNFR2 promoter but no effect on NFκB binding to consensus sites. Constitutively active STAT3 was sufficient to induce TNFR2 expression. Overexpression of SOCS3, a cytokine-inducible STAT3 inhibitor, which reduces tumorigenesis in preclinical models of colitis-associated cancer, decreased cytokine-induced TNFR2 expression and STAT3 binding to the -1,578 STAT response element. SOCS3 overexpression also decreased proliferation of colon cancer cells and dramatically decreased anchorage-independent growth of colon cancer cells, even cells overexpressing TNFR2. Collectively, these studies show that IL-6- and TNFα-induced TNFR2 expression in colon cancer cells is mediated primarily by STAT3 and provide evidence that TNFR2 may contribute to the tumor-promoting roles of STAT3.

SOCS3 promoter methylation is mutually exclusive to EGFR amplification in gliomas and promotes glioma cell invasion through STAT3 and FAK activation

The suppressor of cytokine signaling 3 (SOCS3) gene is one of eight structurally related genes of the SOCS family and has been suggested to function as a tumor suppressor by inhibition of the JAK/STAT signaling pathway. We investigated 60 human gliomas of different histological types for SOCS3 alterations and found frequent SOCS3 promoter hypermethylation and transcriptional downregulation. However, SOCS3 promoter hypermethylation was virtually absent in primary glioblastomas, which are characterized by frequent epidermal growth factor receptor (EGFR) amplification and overexpression. Assessment of the relationship between SOCS3 and EGFR aberrations revealed that SOCS3 promoter hypermethylation was inversely related to both the EGFR gene dosage as well as the EGFR protein expression, thus suggesting SOCS3 inactivation as a mechanism substituting for EGFR activation in a subset of gliomas. In support of this hypothesis, stable shRNA-mediated SOCS3 knock-down in U251 glioblastoma cells resulted in an activation of EGFR-related signaling pathways, i.e. an increase in the activation levels of STAT3, FAK and to a lesser extent MAPK, while the AKT phosphorylation levels remained unaffected. Functionally, SOCS3-depletion caused strongly increased tumor cell invasion with no obvious effect on tumor cell proliferation. In summary, our findings suggest that SOCS3 inactivation by promoter hypermethylation is mutually exclusive to EGFR activation in gliomas and preferentially promotes glioma cell invasion through STAT3 and FAK activation.

Division of labor by dual feedback regulators controls JAK2/STAT5 signaling over broad ligand range

Cellular signal transduction is governed by multiple feedback mechanisms to elicit robust cellular decisions. The specific contributions of individual feedback regulators, however, remain unclear. Based on extensive time-resolved data sets in primary erythroid progenitor cells, we established a dynamic pathway model to dissect the roles of the two transcriptional negative feedback regulators of the suppressor of cytokine signaling (SOCS) family, CIS and SOCS3, in JAK2/STAT5 signaling. Facilitated by the model, we calculated the STAT5 response for experimentally unobservable Epo concentrations and provide a quantitative link between cell survival and the integrated response of STAT5 in the nucleus. Model predictions show that the two feedbacks CIS and SOCS3 are most effective at different ligand concentration ranges due to their distinct inhibitory mechanisms. This divided function of dual feedback regulation enables control of STAT5 responses for Epo concentrations that can vary 1000-fold in vivo. Our modeling approach reveals dose-dependent feedback control as key property to regulate STAT5-mediated survival decisions over a broad range of ligand concentrations.

The lineage-defining factors T-bet and Bcl-6 collaborate to regulate Th1 gene expression patterns

T-bet acts as a functional repressor in association with Bcl-6 to antagonize SOCS1, SOCS3, TCF-1, and late-stage IFN-γ to regulate Th1 development.

The T-box transcription factor T-bet is important for the differentiation of naive CD4⁺ T helper cells (Th cells) into the Th1 phenotype. Much is known about T-bet’s role as a transcriptional activator, but less is known about the mechanisms by which T-bet functionally represses alternative Th cell genetic programs. In this study, we first identify Socs1, Socs3, and Tcf7 (TCF-1) as gene targets that are negatively regulated by T-bet. Significantly, T-bet’s role in the repression of these genes is through a direct interaction with their promoters. Consistent with this, we identified two T-bet DNA-binding elements in the Socs1 promoter that are functionally used to down-regulate transcription in primary Th1 cells. Importantly, T-bet’s novel role in transcriptional repression is because of its ability to physically associate with, and functionally recruit, the transcriptional repressor Bcl-6 to a subset of promoters. Furthermore, T-bet functionally recruits Bcl-6 to the Ifng locus in late stages of Th1 differentiation to repress its activity, possibly to prevent the overproduction of IFN-γ, which could result in autoimmunity. Collectively, these data establish a novel mechanism for T-bet–mediated gene repression in which two lineage-defining transcription factors, one a classical activator and one a repressor, collaborate to promote and properly regulate Th1 development.

Trichostatin A, a histone deacetylase inhibitor, suppresses JAK2/STAT3 signaling via inducing the promoter-associated histone acetylation of SOCS1 and SOCS3 in human colorectal cancer cells

Aberrant janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling is involved in the oncogenesis of several cancers. Suppressors of cytokine signaling (SOCS) genes and SH2-containing protein tyrosine phosphatase 1 (SHP1) proteins, which are negative regulators of JAK/STAT signaling, have been reported to have tumor suppressor functions. However, in colorectal cancer (CRC) cells, the mechanisms that regulate SOCS and SHP1 genes, and the cause of abnormalities in the JAK/STAT signaling pathway, remain largely unknown. The present study shows that trichostatin A (TSA), a histone deacetylase (HDAC) inhibitor, leads to the hyperacetylation of histones associated with the SOCS1 and SOCS3 promoters, but not the SHP1 promoter in CRC cells. This indicates that histone modifications are involved in the regulation of SOCS1 and SOCS3. Moreover, upregulation of SOCS1 and SOCS3 expression was achieved using TSA, which also significantly downregulated JAK2/STAT3 signaling in CRC cells. We also demonstrate that TSA suppresses the growth of CRC cells, and induces G1 cell cycle arrest and apoptosis through the regulation of downstream targets of JAK2/STAT3 signaling, including Bcl-2, survivin and p16(ink4a) . Therefore, our data demonstrate that TSA may induce SOCS1 and SOCS3 expression by inducing histone modifications and consequently inhibits JAK2/STAT3 signaling in CRC cells. These results also establish a mechanistic link between the inhibition of JAK2/STAT3 signaling and the anticancer action of TSA in CRC cells.