Regulation Of Signal Transducer And Activator Of Transcription 3 Research Articles

Small acid, big hopes: a rosy outlook for formic acid attracts chemical companies

We aimed to investigate regulation of signal transducer and activator of transcription 3 (STAT3) and suppressor of cytokine signaling 3 (SOCS3) by interferon alpha (IFN-α) and to analyze the relationship between STAT3 and SOCS3 during hepatitis C virus (HCV) infection. Changes in STAT3 and SOCS3 were analyzed at both mRNA and protein levels in human hepatoma cells infected with HCV (J6/JFH1). At 72 h of HCV infection, STAT3 expression was decreased with sustained phosphorylation, and IFN-α increased such decrease and phosphorylation. HCV increased SOCS3 expression, while IFN-α impaired such increase, indicating different regulation of STAT3 and SOCS3 by IFN-α. IFN-α-induced expression and phosphorylation of upstream kinases of the JAK/STAT pathway, Tyk2 and Jak1, were suppressed by HCV. Moreover, knockdown of STAT3 by RNA interference led to decreases in HCV RNA replication and viral protein expression, without affecting either the expression of Tyk2 and Jak1 or the SOCS3 induction in response to IFN-α. These results show that IFN-α antagonizes STAT3 and SOCS3 signaling triggered by HCV and that STAT3 regulation correlates inversely with SOCS3 induction by IFN-α, which may be important in better understanding the complex interplay between IFN-α and signal molecules during HCV infection.

Argon mediates protection by interleukin-8 suppression via a TLR2/TLR4/STAT3/NF-κB pathway in a model of apoptosis in neuroblastoma cells invitro and following ischemia-reperfusion injury in rat retina invivo.

Argon has recently come into scientific focus as a neuroprotective agent. The underlying neuroprotective mechanism remains unknown although toll-like receptors were recently suggested to play an important role. We hypothesized that TLR-associated downstream transcription factors are responsible for argon's effects, leading to anti-apoptotic and anti-inflammatory properties. Apoptosis was induced in human neuroblastoma cells. Immediately afterwards, argon treatment (75 Vol% for 2h) was initiated. Cells were analyzed, measuring mitochondrial membrane potential, reactive-oxygen-species, annexin-V/propidium iodide staining, transcription factor phosphorylation and binding activity as well as protein and mRNA expression of interleukins. Argon's invivo effects were analyzed by quantification of retinal ganglion cell density, mRNA expression, serum cytokine analysis and immunohistochemistry after retinal ischemia reperfusion injury (IRI) in rats. Argon diminished rotenone-induced kappa-light-chain-enhancer' of activated B-cells (NF-κB) and signal transducer and activator of transcription 3 (STAT3) but not STAT5 or cAMP-response element-binding protein (CREB) phosphorylation and DNA-binding activity. Argon treatment attenuated apoptosis by preservation of mitochondrial membrane potential and decline in reactive oxygen species (ROS) generation. NF-κB and STAT3 inhibition, as well as TLR2 and TLR4 inhibition reversed argon's effects on IL-8 mRNA expression. Argon attenuated rotenone-induced IL-8 protein and mRNA expression invitro. Inhibition of TLR2 and 4 attenuated argon's protective effect invivo reducing IRI driven retinal IL-8 expression. IL-8 expression was found in the retina in co-localization with Müller cells and retinal ganglion cells. Argon mediates its neuroprotective effects by TLR-mediated regulation of transcription factors NF-κB and STAT3, thus decreasing interleukin-8 expression invitro and invivo. These findings may open up new opportunities to effectively treat cerebral ischemia and reperfusion injury through the inhalation of argon. Argon exerts its protective effects invitro and in vivo via toll-like receptors TLR2 and TLR4 signaling, followed by alteration of downstream enzymes. In conclusion, argon mediates its beneficial effects by suppression of STAT3 and NF-κB phosphorylation and subsequent suppression of interleukin IL-8 protein expression. These novel findings may open up opportunities for argon as a therapeutic agent, particularly in the treatment of neuronal injury. Cover image for this issue: doi: 10.1111/jnc.13334.

Docosahexaenoic acid inhibits Helicobacter pylori-induced STAT3 phosphorylation through activation of PPARγ.

The health beneficial effects of docosahexaenoic acid (DHA) have been attributed to its anti-inflammatory properties. However, the molecular mechanism underlying anti-inflammatory effects of DHA remains largely elusive. In the present study, DHA was found to suppress the phosphorylation and nuclear translocation of signal transducer and activator of transcription 3 (STAT3) induced by Helicobacter pylori infection in human gastric cancer AGS cells. Notably, DHA induced expression of suppressor of cytokine signaling 3 (SOCS3), a negative regulator of STAT3. Knockdown of SOCS3 abolished the suppressive effect of DHA on STAT3(Tyr705) phosphorylation induced by H. pylori infection. DHA also induced nuclear translocation, DNA binding, and transcriptional activities of peroxisome proliferator-activated receptor gamma (PPARγ) in AGS cells. Knockdown of PPARγ inhibited the transcription of SOCS3 and attenuated the suppressive effect of DHA on phosphorylation of STAT3(Tyr705) induced by H. pylori. The PPARγ antagonist bisphenol A diglycidyl ether also mitigated the suppressive effect of DHA on H. pylori-induced phosphorylation of STAT3(Tyr705) . In addition, DHA inhibited the expression of c-Myc, which was attenuated in the AGS cells harboring SOCS3 specific siRNA. DHA also markedly decreased anchorage-independent growth of AGS cells infected by H. pylori. DHA inhibits H. pylori-induced STAT3 phosphorylation in a PPARγ/SOCS3-dependent manner.

Signal transducer and activator of transcription 3 (STAT-3) is a critical transcription factor in regulating germinal center IgE+ B-cell class switching

Abstract A mutation in the Signal Transducer and Activator of Transcription 3 (STAT-3) has been linked to incidence of Autosomal Dominant Hyper Immunoglobulin E Syndrome (AD-HIES), a disease characterized by elevated serum IgE antibody and susceptibility to respiratory and skin infection. However, how this genetic mutation leads to the phenotype has not been fully understood. In this study we investigated the specific role of STAT-3 in the germinal center (GC), the site of B-cell proliferation and isotype switching. Through the use of CD2-Cre or CD19-Cre driven STAT-3 conditional knockout (cKO) mice in a Th2-type immunization model, we aimed to determine the specific cell subset(s) and signaling mechanism by which STAT-3 mediated isotype switching is regulated. We demonstrated in vivo and in vitro that CD2-Cre driven STAT-3 cKO mice showed elevated IgE and decreased IgG1 in the serum, and a reduction in GC formation. Within the GC, IgG1+ GC B cells were decreased while IgE+ GC B cells were more prevalent. Additionally, these mice exhibited reduced IgG1 and elevated IgE populations of antibody-producing plasma cells. Subsequent experiments using a CD19-Cre B-cell specific cKO mouse established this effect to be B-cell dependent. Our data also revealed other transcription factors, including Bcl-6 and Aicda, function as downstream signals of STAT-3 regulation. This model suggests a role for STAT-3 in regulating class switching of the GC B cells from the IgG1 to the IgE producing state, which may serve as a potential therapeutic target for treatment of AD-HIES and other immune disorders.

Interferon alpha antagonizes STAT3 and SOCS3 signaling triggered by hepatitis C virus

We aimed to investigate regulation of signal transducer and activator of transcription 3 (STAT3) and suppressor of cytokine signaling 3 (SOCS3) by interferon alpha (IFN-α) and to analyze the relationship between STAT3 and SOCS3 during hepatitis C virus (HCV) infection. Changes in STAT3 and SOCS3 were analyzed at both mRNA and protein levels in human hepatoma cells infected with HCV (J6/JFH1). At 72h of HCV infection, STAT3 expression was decreased with sustained phosphorylation, and IFN-α increased such decrease and phosphorylation. HCV increased SOCS3 expression, while IFN-α impaired such increase, indicating different regulation of STAT3 and SOCS3 by IFN-α. IFN-α-induced expression and phosphorylation of upstream kinases of the JAK/STAT pathway, Tyk2 and Jak1, were suppressed by HCV. Moreover, knockdown of STAT3 by RNA interference led to decreases in HCV RNA replication and viral protein expression, without affecting either the expression of Tyk2 and Jak1 or the SOCS3 induction in response to IFN-α. These results show that IFN-α antagonizes STAT3 and SOCS3 signaling triggered by HCV and that STAT3 regulation correlates inversely with SOCS3 induction by IFN-α, which may be important in better understanding the complex interplay between IFN-α and signal molecules during HCV infection.

Nimbolide-Induced Oxidative Stress Abrogates STAT3 Signaling Cascade and Inhibits Tumor Growth in Transgenic Adenocarcinoma of Mouse Prostate Model.

Prostate cancer (PCa) is one of the most commonly diagnosed cancers worldwide. Currently available therapies for metastatic PCa are only marginally effective, hence novel treatment modalities are urgently required. Considerable evidence(s) suggest that deregulated activation of oncogenic transcription factor, signal transducer and activator of transcription 3 (STAT3) plays a pivotal role in the development and progression of PCa. Thus, agents that can abrogate STAT3 activation could form the basis of novel therapy for PCa patients. In the present study, we analyzed whether the potential anticancer effects of nimbolide (NL), a limonoid triterpene derived from Azadirachta indica, against PCa cell lines and transgenic adenocarcinoma of mouse prostate (TRAMP) model are mediated through the negative regulation of STAT3 pathway. Data from the in vitro studies indicated that NL could significantly inhibit cell viability, induce apoptosis, and suppress cellular invasion and migration. Interestingly, NL also abrogated STAT3 activation and this effect was found to be mediated via an increased production of reactive oxygen species (ROS) due to GSH/GSSG imbalance. Oral administration of NL significantly suppressed the tumor growth and metastasis in TRAMP mouse model without exhibiting any significant adverse effects. The present study demonstrates the critical role of GSH/GSSG imbalance-mediated ROS production contributing to the STAT3 inhibitory and tumor-suppressive effect of NL in PCa. Overall, our findings indicate that NL exhibits significant anticancer effects in PCa that may be primarily mediated through the ROS-regulated inhibition of STAT3 signaling cascade.

Correlation between Expression of Signal Transducer and Activator of Transcription 3 and Pituitary Adenoma Subtypes

To investigate the correlation between signal transducer and activator of transcription 3 (STAT3) expression and pituitary adenoma subtypes. The STAT3 expression profiles in different pituitary adenomas from 74 patients were determined using quantificational real-time polymerase chain reaction,Western blot,and immunohistochemistry. Expression of STAT3 was observed in all pituitary adenoma subtypes. The STAT3 expression level was highest in growth hormone adenoma when compared with other tumors including prolactin,follicle-stimulating hormone/luteinizing hormone-secreting adenoma,and adrenocorticotrophic hormone-secreting adenoma. The follicle-stimulating hormone/luteinizing hormone adenomas exhibited the lowest STAT3 expression levels. STAT3 is differentially expressed in pituitary adenoma subtypes, suggesting the cell-specific features of STAT3 regulation,although further investigations are still warranted to clarify the underlying mechanisms.

Constitutive activation of STAT3 in breast cancer cells: A review.

Signal transducer and activator of transcription 3 (STAT3) is constitutively activated in numerous cancer types, including more than 40% of breast cancers. In contrast to tight regulation of STAT3 as a latent transcription factor in normal cells, its signaling in breast cancer oncogenesis is multifaceted. Signaling through the IL-6/JAK/STAT3 pathway initiated by the binding of IL-6 family of cytokines (i.e., IL-6 and IL-11) to their receptors have been implicated in breast cancer development. Receptors with intrinsic kinase activity such as EGFR and VEGFR directly or indirectly induce STAT3 activation in various breast cancer types. Aberrant STAT3 signaling promotes breast tumor progression through deregulation of the expression of downstream target genes which control proliferation (Bcl-2, Bcl-xL, Survivin, Cyclin D1, c-Myc and Mcl-1), angiogenesis (Hif1α and VEGF) and epithelial-mesenchymal transition (Vimentin, TWIST, MMP-9 and MMP-7). These multiple modes of STAT3 regulation therefore make it a central linking point for a multitude of signaling processes. Extensive efforts to target STAT3 activation in breast cancer had no remarkable success in the past because the highly interconnected nature of STAT3 signaling introduces lack of selectivity in pathway identification for STAT3 targeted molecular therapies or because its role in tumorigenesis may not be as critical as it was thought. This review provides a full spectrum of STAT3's involvement in breast cancer by consolidating the knowledge about its role in breast cancer development at multiple levels: its differential regulation by different receptor signaling pathways, its downstream target genes, and modification of its transcriptional activity by its coregulatory transcription factors.

Reciprocal control of miR-197 and IL-6/STAT3 pathway reveals miR-197 as potential therapeutic target for hepatocellular carcinoma

Signal transducer and activator of transcription 3 (STAT3) is one of the key players in liver cancer. Increased levels of phosphorylated STAT3 (p-STAT3) have been detected in many cancers including hepatocellular carcinoma (HCC), and are usually associated with a more aggressive phenotype and poor prognosis. In addition to aberrant activation of STAT3, upregulation of total STAT3 was also detected in HCC, for which the underlying mechanisms and significance remain to be fully elucidated. Here we report that a reciprocal regulation exists between miR-197 and the IL-6/STAT3 inflammatory signaling pathway in HCC. We found that IL-6 stimulation increased total STAT3 expression at protein level but not mRNA level in HCC cells, suggesting the existence of post-transcriptional regulation of STAT3. Our study showed that IL-6/STAT3 pathway decreases expression of miR-197 in HCC, which amplifies IL-6/STAT3 pathway and contributes to HCC progression. miR-197 can significantly inhibit HCC growth both in vitro and in vivo. In addition, IL-6/STAT3-induced downregulation of miR-197 in HCC may be via affecting Drosha binding to primary miR-197 (pri-miR-197) and thus reducing mature miR-197 generation. Our study suggests that miR-197 may serve as a potential therapeutic target for interfering with the IL-6/STAT3 inflammatory pathway in HCC.

Anti-tumor activity of miR-17 in melanoma

A large body of evidence suggests that the crosstalk between cancer cells and the surrounding microenvironment plays a critical role in primary tumor establishment and its dissemination to distant sites. Such interplay is important for sustaining an adaptive microenvironment for tumor cells encountering different conditions during tumor dissemination. MicroRNAs are a small class of non-coding RNAs that have important roles in cancer progression through downregulation of the expression of their target mRNAs. Accumulating evidence shows that abnormal expression of miRNAs in tumors can lead to changes in the intrinsic properties of cancer cells, which include cell proliferation, migration, apoptosis, and cellular senescence.1 Recent research from our lab has implicated the importance of miR-17 expression in the adaptability of tumor cells to environmental fluctuations using the glioblastoma cell line. These cells, which are highly adaptive and over-express miR-17, appeared to adopt a new strategy to cope with the lack of nutrition in the environment by lowering their metabolic rate. Interestingly, reduced metabolism not only enabled them to survive better in serum-free conditions, but also helped them to resist chemotherapeutic drug toxicity, as these drugs are designed to eradicate fast growing tumor cells.2 This adaptability to environmental conditions conferred to tumor cells by miR-17, led us to investigate the immune response properties of these cells. Our previous study showed that B-cell and T-cell development was impaired in miR-17 transgenic mice, indicating the importance of miR-17 in lymphomagenesis and lymphopoiesis.3 In the current study, we observed that transgenic mice over-expressing miR-17 developed fewer tumors compared to wild type mice when they were challenged with B16 melanoma cells. Systemic analysis of CD45+ and CD8+ T-cells, in peripheral blood and spleen, had revealed that there was a significant increase in the percentage of CD8+ T-Cells in transgenic mice compared to control, directly following tumor implantation. In contrast, the percentage of CD8+ T-cells was initially lower in transgenic mice compared to control mice before the tumor was implanted. The expansion of CD8+ T-cell populations and the subsequent infiltration of T-cells into the tumors, suggest that the miR-17 transgenic mice were able to induce a stronger anti-tumor immune response compared to control. But, how is miR-17 able to instigate this rapid adaptive immune response by expansion of CD8+ T-cells in these transgenic mice? CD8+ or cytotoxic T-cells are tumor-specific effector T-cells that are capable of attacking and eliminating cancer cells. However, the ability of CD8+ T-cells to eliminate cancerous cells relies on the tumor microenvironment, but due to the presence of immunosuppressive factors, tumor environment is hostile to T-cell proliferation and activation. So, to explain the increase in T-cells seen in transgenic mice, we reasoned there is an important signaling molecule or transcription factor – promoting immune suppression in the tumor environment – that has been targeted by miR-17. Hence, the down-regulation of this molecule by miR-17, is allowing the increased immune response. A fascinating candidate is Signal Transducer and Activator of Transcription 3 (STAT3), which is commonly activated both in tumor cells and in immune cells of the microenvironment. STAT3 is known to promote tumor-mediated immunosuppression at many levels.4 For instance, STAT3 signaling can lead to the secretion of immunosuppressive cytokines IL-2 and IFN-γ; therefore, it is a negative regulator of CD8+ T-cell proliferation and activation.5 In addition, miR-17 over-expression in Jurkat cells can lead to their faster proliferation and better survival in the presence of B16 melanoma cells, owing to the blockade of STAT3. Furthermore, after being co-cultured with B16 melanoma cells, Jurkat cells over-expressing miR-17 remained in G1 phase for a longer duration, and stayed in S phase for less, thus, indicating their fast mitosis. This data suggest that microRNA-17 can be a negative regulator of STAT3 and therefore facilitate an anti-tumor response through a complex interconnected network.6 Despite recent advances in immunotherapy for cancer, this modality still suffers from a number of limitations. As discussed, failure to initiate a proper anti-tumor immune response by host cells and the development of immune tolerance by cancer cells are 2 key factors in limiting the success of cancer immunotherapy. However, targeting STAT3 by inhibitors has emerged as a potential strategy in providing immunotherapy for cancer.7 Conversely, our study revealed that over expressing miR-17 can be used as an alternative to direct STAT3 inhibition to potentially restore T-cell activation in the microenvironment. Ultimately, this may induce a tumor specific immune response, allowing the hosts own immune system to battle cancer cells more effectively, thus, impacting the outcome of the therapy positively.

CD4 T-cell transcriptome analysis reveals aberrant regulation of STAT3 and Wnt signaling pathways in rheumatoid arthritis: evidence from a case-control study.

IntroductionRheumatoid arthritis (RA) is a systemic autoimmune disease in which T cells play a pivotal role in the pathogenesis. Knowledge in terms of the CD4 T-cell transcriptome in RA is limited. The aim of this study was to examine the whole-genome transcription profile of CD4 T cells in RA by comparing patients with RA to healthy controls.MethodsPeripheral blood CD4 T cells were isolated from 53 RA patients with active disease and 45 healthy individuals; 13 cases and 10 controls were enrolled in microarray analysis. The remaining 40 cases and 35 controls were recruited as an independent cohort for the validation study. Bioinformatics was performed on Gene Ontology (GO), gene-gene interaction networks, and pathway analysis. The gene modules, by combining the results from GO, gene networks, and pathway analysis, were selected for further validation.ResultsThe CD4 T cells showed 1,496 differentially expressed (DE) genes in RA patients relative to healthy individuals. GO analysis revealed that the DE genes were enriched in immune response, T-cell response, apoptosis process, and Wnt receptor signaling. Pathway analysis also identified that ‘Wnt signaling pathway’ was differentially regulated between two groups (P = 2.78 × 10−10). By gene-gene network analysis, we found that the DE genes were enriched in T-cell receptor (TCR), JAK-STAT signaling, and Wnt signaling pathway. By gene module analysis, we found that a number of DE genes overlapped in the three different analyses. In total, 23 genes were selected for further validation, and nine genes were confirmed. Of these, four genes (SOCS3, CBL, IFNAR1, and PIK3CA) were involved in STAT3 (signal transducer and activator of transcription 3) signaling, and three genes (CBL, KLF9, and CSNK2A1) were involved in the Wnt signaling pathway. Additionally, several zinc finger transcription factors (ZEB1, ZNF292, and ZNF644) were confirmed.ConclusionsWe report here the first case–control study of the CD4 T-cell transcriptome profile in RA. Our data provide evidence that CD4 T cells from patients with RA have abnormal functional networks in STAT3 signaling and Wnt signaling. Our results also suggest that the aberrant expression of several zinc finger transcription factors (ZEB1, ZNF292, and ZNF644) may be potential pathogenic factors for RA.Electronic supplementary materialThe online version of this article (doi:10.1186/s13075-015-0590-9) contains supplementary material, which is available to authorized users.

Serine-727 phosphorylation activates hypothalamic STAT-3 independently from tyrosine-705 phosphorylation.

Transcriptional activity of signal transducer and activator of transcription-3 (STAT-3) is a key element in the central regulation of appetite and energy homeostasis. Activation of hypothalamic STAT-3 has been attributed to cytokine-promoted phosphorylation at tyrosine-705 (Tyr-705). In nonhypothalamic cells, STAT-3 is also phosphorylated at serine-727 (Ser-727), but the functional significance of Ser-727 in the regulation of hypothalamic STAT-3 is not known. We used 2 hypothalamic cell lines and analyzed the effects of various hormones on STAT-3-dependent reporter gene activity and observed that IFN-γ, epidermal growth factor (EGF), and bradykinin (BK) induce similar STAT-3 reporter activation. EGF and BK solely increased Ser-727 and IFN-γ increased Tyr-705 phosphorylation of STAT-3. Specific inhibition of ERK-1/2 activity blocked EGF- and BK-induced STAT-3 activation and Ser-727 phosphorylation. BK-induced ERK-1/2 activation occurred via EGF receptor transactivation. Consequently, the BK-mediated effects on STAT-3 were blocked by a specific EGF receptor antagonist. Next, we analyzed the effects of IFN-γ and EGF on the expression of the STAT-3-dependent genes thyroliberin-releasing hormone and suppressors of cytokine signaling-3. EGF but not IFN-γ enhanced thyroliberin-releasing hormone expression via STAT-3. With regard to suppressors of cytokine signaling-3, we observed prolonged expression induced by IFN-γ and a transient effect of EGF that required coactivation of the activator protein-1. Thus, EGF-promoted Ser-727 phosphorylation by ERK-1/2 is not only sufficient to fully activate hypothalamic STAT-3, but, in terms of targeted genes and required cofactors, entails distinct modes of STAT-3 actions compared with IFN-γ-induced Tyr-705 phosphorylation.

Role of STAT3 in lung cancer.

Lung cancer remains a challenging disease. It is responsible for the high cancer mortality rates in the US and worldwide. Elucidation of the molecular mechanisms operative in lung cancer is an important first step in developing effective therapies. Accumulating evidence over the last 2 decades suggests a critical role for Signal Transducer and Activator of Transcription 3 (STAT3) as a point of convergence for various signaling pathways that are dysregulated in the disease. In this review, we discuss possible molecular mechanisms involving STAT3 in lung tumorigenesis based on recent literature. We consider possible roles of STAT3 in cancer cell proliferation and survival, in the tumor immune environment, and in epigenetic regulation and interaction of STAT3 with other transcription factors. We also discuss the potential role of STAT3 in tumor suppression, which complicates strategies of targeting STAT3 in cancer therapy.

Erk1/2 activation and modulation of STAT3 signaling in oral cancer.

Constitutive activation of the signal transducer and activator of transcription 3(STAT3) signaling pathway possesses confirmed oncogenic potential in oral squamous cell carcinoma(OSCC). Crosstalk with other molecular pathways contributes to STAT3 regulation in cancer. The effects of mitogen-activated protein kinases(MAPKs) and particularly extracellular signal-regulated kinase 1/2(Erk1/2) on STAT3 signaling in OSCC have not been thoroughly investigated. The present study examined the effects of Erk1/2 modulation on STAT3 signaling and cell growth in OSCC cells. Constitutive expression levels of phosphorylated (tyrosine and serine) and total STAT3, Erk1/2 and cyclinD1 were assessed in OSCC cell lines. Erk1/2 modulation was achieved by pharmacological agents; siRNA silencing against Erk1/2 was also performed. Cell proliferation and viability were assessed. Erk1/2 inhibition with either U0126 treatment or specific siRNA silencing resulted in decreases in p-serSTAT3 and cyclinD1 levels and increases in p-tyr STAT3 in OSCC cells. Moreover, Erk1/2 inhibition resulted in a dose-dependent reduction in OSCC cell growth and viability. Erk1/2 induction had the opposite effects. Taken together, these results are supportive of an active crosstalk between the oncogenic Erk1/2 and STAT3 pathways in OSCC, the significance of which requires further investigation.

Transcriptional regulation of STAT3 by SPTBN1 and SMAD3 in HCC through cAMP-response element-binding proteins ATF3 and CREB2.

The cytoskeletal protein Spectrin, beta, non-erythrocytic 1 (SPTBN1), an adapter protein to SMAD3 in TGF-β signaling, may prevent hepatocellular carcinoma (HCC) development by downregulating the expression of signal transducer and activator of transcription 3 (STAT3). To elucidate the as yet undefined mechanisms that regulate this process, we demonstrate that higher levels of STAT3 transcription are found in livers of heterozygous SPTBN1(+/-) mice as compared to that of wild type mice. We also found increased levels of STAT3 mRNA, STAT3 protein, and p-STAT3 in human HCC cell-lines after knockdown of SPTBN1 or SMAD3, which promoted cell colony formation. Inhibition of STAT3 overrode the increase in cell colony formation due to knockdown of SPTBN1 or SMAD3. We also found that inhibition of SPTBN1 or SMAD3 upregulated STAT3 promoter activity in HCC cell-lines, which is dependent upon the cAMP-response element (CRE) and STAT-binding element (SBE) sites of the STAT3 promoter. Mechanistically, suppression of SPTBN1 and SMAD3 augmented the transcription of STAT3 by upregulating the CRE-binding proteins ATF3 and CREB2 and augmented the binding of those proteins to the regions within or upstream of the CRE site of the STAT3 promoter. Finally, in human HCC tissues, SPTBN1 expression correlated negatively with expression levels of STAT3, ATF3, and CREB2; SMAD3 expression correlated negatively with STAT3 expression; and the level of phosphorylated SMAD3 (p-SMAD3) correlated negatively with ATF3 and CREB2 protein levels. SPTBN1 and SMAD3 collaborate with CRE-binding transcription factors to inhibit STAT3, thereby preventing HCC development.

Regulation of signal transducer and activator of transcription 3 and apoptotic pathways by betaine attenuates isoproterenol-induced acute myocardial injury in rats.

The present study was designed to investigate the cardioprotective effects of betaine on acute myocardial ischemia induced experimentally in rats focusing on regulation of signal transducer and activator of transcription 3 (STAT3) and apoptotic pathways as the potential mechanism underlying the drug effect. Male Sprague Dawley rats were treated with betaine (100, 200, and 400 mg/kg) orally for 40 days. Acute myocardial ischemic injury was induced in rats by subcutaneous injection of isoproterenol (85 mg/kg), for two consecutive days. Serum cardiac marker enzyme, histopathological variables and expression of protein levels were analyzed. Oral administration of betaine (200 and 400 mg/kg) significantly reduced the level of cardiac marker enzyme in the serum and prevented left ventricular remodeling. Western blot analysis showed that isoproterenol-induced phosphorylation of STAT3 was maintained or further enhanced by betaine treatment in myocardium. Furthermore, betaine (200 and 400 mg/kg) treatment increased the ventricular expression of Bcl-2 and reduced the level of Bax, therefore causing a significant increase in the ratio of Bcl-2/Bax. The protective role of betaine on myocardial damage was further confirmed by histopathological examination. In summary, our results showed that betaine pretreatment attenuated isoproterenol-induced acute myocardial ischemia via the regulation of STAT3 and apoptotic pathways.

Regulation and function of signal transducer and activator of transcription 3.

Signal transducer and activator of transcription 3 (STAT3), a member of the STAT family, is a key regulator of many physiological and pathological processes. Significant progress has been made in understanding the transcriptional control, posttranslational modification, cellular localization and functional regulation of STAT3. STAT3 can translocate into the nucleus and bind to specific promoter sequences, thereby exerting transcriptional regulation. Recent studies have shown that STAT3 can also translocate into mitochondria, participating in aerobic respiration and apoptosis. In addition, STAT3 plays an important role in inflammation and tumorigenesis by regulating cell proliferation, differentiation and metabolism. Conditional knockout mouse models make it possible to study the physiological function of STAT3 in specific tissues and organs. This review summarizes the latest advances in the understanding of the expression, regulation and function of STAT3 in physiological and tumorigenic processes.

CXCR4 Negatively Regulates Keratinocyte Proliferation in IL-23-Mediated Psoriasiform Dermatitis

CXCR4 is expressed by basal keratinocytes (KCs), but little is known about its function in inflamed skin. We crossed K14-Cre and CXCR4flox/flox (f/f) transgenic mice, resulting in mice with specific loss of the CXCR4 gene in K14-expressing cells (K14-CXCR4KO), including basal KCs. K14-CXCR4KO pups had no obvious skin defects. We compared K14-CXCR4KO and CXCR4f/f control mice in an IL-23-mediated psoriasisform dermatitis model and measured skin edema, histologic, and immunohistological changes. IL-23-treated K14-CXCR4KO mice showed a 1.3-fold increase in mean ear swelling, 2-fold increase in epidermal thickness, and greater parakeratosis. IL-23-treated WT mice showed weak CXCR4 expression in areas of severe epidermal hyperplasia, but strong CXCR4 expression in non-hyperplastic regions, suggesting CXCR4 may regulate keratinocyte proliferation. To test this hypothesis, we overexpressed CXCR4 in HaCaT keratinocyte cells and treated them with IL-22 and/or CXCL12. CXCL12 blocked IL-22-mediated HaCaT cell proliferation in vitro and synergized with IL-22 in upregulating SOCS3, a key regulator of STAT3. SOCS3 was required for CXCR4-mediated growth inhibition. In human psoriatic skin, both CXCR4 and SOCS3 were upregulated in the junctional region at the border of psoriatic plaques. Thus, CXCR4 plays an unexpected role in inhibiting KC proliferation and mitigating the effects of proliferative Th17 cytokines.

RKIP phosphorylation and STAT3 activation is inhibited by oxaliplatin and camptothecin and are associated with poor prognosis in stage II colon cancer patients

BackgroundA major obstacle in treating colorectal cancer (CRC) is the acquired resistance to chemotherapeutic agents. An important protein in the regulation of cancer cell death and clinical outcome is Raf kinase inhibitor protein (RKIP). In contrast, activated signal transducer and activator of transcription 3 (STAT3) is a protein that promotes tumor cell survival by inhibiting apoptosis and has an important role in cancer progression in many of cancer types. The aim of this study was to evaluate the regulation of RKIP and STAT3 after treatment with clinically relevant chemotherapeutic agents (camptothecin (CPT) and oxaliplatin (OXP)) and the cytokine interleukin-6 (IL-6) in HCT116 colon cancer cells as well as evaluate the association between RKIP and STAT3 with clinical outcome of Stage II colon cancer patients.MethodsHCT-116 colon cancer cells were treated with CPT, OXP, and IL-6 separately or in combination in a time and dose-dependent manner and examined for phosphorylated and non-phosphorylated RKIP and STAT3 via Western blot analysis. STAT3 transcriptional activity was measured via a luciferase reporter assay in HCT116 cells treated with CPT, IL-6 or transfected with JAK 1, 2 separately or in combination. We extended these observations and determined STAT3 and RKIP/ pRKIP in tumor microarrays (TMA) in stage II colon cancer patients.ResultsWe demonstrate IL-6-mediated activation of STAT3 occurs in conjunction with the phosphorylation of RKIP in vitro in human colon cancer cells. OXP and CPT block IL-6 mediated STAT3 activation and RKIP phosphorylation via the inhibition of the interaction of STAT3 with gp130. We determined that STAT3 and nuclear pRKIP are significantly associated with poor patient prognosis in stage II colon cancer patients.ConclusionsIn the analysis of tumor samples from stage II colon cancer patients and the human colon carcinoma cell line HCT116, pRKIP and STAT3, 2 proteins potentially involved in the resistance to conventional treatments were detected. The phosphorylation of pRKIP and STAT3 are induced by the cytokine IL-6 and suppressed by the chemotherapeutic drugs CPT and OXP. Therefore, these results suggest that STAT3 and pRKIP may serve as prognostic biomarkers in stage II colon cancer patients and may improve chemotherapy.

Expression of microRNA-1234 related signal transducer and activator of transcription 3 in patients with diffuse large B-cell lymphoma of activated B-cell like type from high and low infectious disease areas

Diffuse large B-cell lymphoma (DLBCL) is a heterogeneous disease, and infectious agents are suspected to be involved in the tumorigenesis of DLBCL. MicroRNAs (miRNAs) are non-coding RNAs modulating protein expression. We compared miRNA expression profiles in lymph node tissues of patients with DLBCL of the activated B-cell like (ABC) type from two geographical areas with different background exposures, Sweden and Egypt. We showed previously that DLBCL tissues of the ABC-type in Swedish patients had a higher expression of signal transducer and activator of transcription 3 (STAT3) compared to Egyptian patients. Here, we analyzed the involvement of miRNAs in STAT3 regulation. miR-1234 was significantly up-regulated in Egyptian patients with DLBCL compared to Swedish patients (p < 0.03). The miR-1234 expression level correlated inversely with the expression of STAT3. The Stat3 protein was down-regulated in cells transfected with miR-1234, suggesting that STAT3 might be a potential target for miR-1234. miR-1234 and STAT3 might be involved in the tumorigenesis of DLBCL of ABC type and possibly associated with environmental background exposure.