Interacting regions in Stat3 and c-Jun that participate in cooperative transcriptional activation

C-terminally phosphorylated p27 activates self-renewal driver genes to program cancer stem cell expansion, mammary hyperplasia and cancer

In many cancers, a stem-like cell subpopulation mediates tumor initiation, dissemination and drug resistance. Here, we report that cancer stem cell (CSC) abundance is transcriptionally regulated by C-terminally phosphorylated p27 (p27pT157pT198). Mechanistically, this arises through p27 co-recruitment with STAT3/CBP to gene regulators of CSC self-renewal including MYC, the Notch ligand JAG1, and ANGPTL4. p27pTpT/STAT3 also recruits a SIN3A/HDAC1 complex to co-repress the Pyk2 inhibitor, PTPN12. Pyk2, in turn, activates STAT3, creating a feed-forward loop increasing stem-like properties in vitro and tumor-initiating stem cells in vivo. The p27-activated gene profile is over-represented in STAT3 activated human breast cancers. Furthermore, mammary transgenic expression of phosphomimetic, cyclin-CDK-binding defective p27 (p27CK-DD) increases mammary duct branching morphogenesis, yielding hyperplasia and microinvasive cancers that can metastasize to liver, further supporting a role for p27pTpT in CSC expansion. Thus, p27pTpT interacts with STAT3, driving transcriptional programs governing stem cell expansion or maintenance in normal and cancer tissues.

Physical interaction between STAT3 and AP1 in cervical carcinogenesis: Implications in HPV transcription control

The constitutive activation and aberrant expression of Signal Transducer and Activator of Transcription 3 (STAT3) plays a key role in initiation and progression of cervical cancer (CaCx). How STAT3 influences HPV transcription is poorly defined. In the present study, we probed direct and indirect interactions of STAT3 with HPV16/18 LCR. In silico assessment of cis-elements present on LCR revealed the presence of potential STAT3 binding motifs. However, experimental validation by ChIP-PCR could not confirm any specific STAT3 binding on HPV16 LCR. Protein-protein interaction (PPI) network analysis of STAT3 with other host transcription factors that bind LCR, highlighted the physical association of STAT3 with c-FOS and c-JUN. This was further confirmed in vitro by co-immunoprecipitation, where STAT3 co-immunoprecipitated with c-FOS and c-JUN in CaCx cells. The result was supported by immunocytochemical analysis and colocalization of STAT3 with c-FOS and c-JUN. Positive signals in proximity ligation assay validated physical interaction and colocalization of STAT3 with AP1. Colocalization of STAT3 with c-FOS and c-JUN increased upon IL-6 treatment and decreased post-Stattic treatment. Alteration of STAT3 expression affected the subcellular localization of c-FOS and c-JUN, along with the expression of viral oncoproteins (E6 and E7) in CaCx cells. High expression of c-JUN in tumor tissues correlated with poor prognosis in both HPV16 and HPV18 CaCx cohort whereas high expression of STAT3 correlated with poor prognosis in HPV18 CaCx lesions only. Overall, the data suggest an indirect interaction of STAT3 with HPV LCR via c-FOS and c-JUN and potentiate transcription of viral oncoproteins.

IL-13-induced STAT3-dependent signaling networks regulate esophageal epithelial proliferation in eosinophilic esophagitis

BACKGROUND

Basal zone hyperplasia (BZH) and dilated intercellular spaces (DISs) are thought to contribute to the clinical manifestations of eosinophilic esophagitis (EoE); however, the molecular pathways that drive BZH remain largely unexplored.

OBJECTIVE

We sought to define the role of IL-13-induced transcriptional programs in esophageal epithelial proliferation in EoE.

METHODS

We performed RNA sequencing, bioinformatics, Western blot, reverse transcriptase quantitative PCR, and histologic analyses on esophageal biopsies from healthy control and patients with EoE, primary esophageal cells derived from patients with EoE, and IL-13-stimulated esophageal epithelial keratinocytes grown at the air-liquid interface (EPC2-ALI). Genetic (shRNA) and pharmacologic (proteolysis-targeting chimera degrader) approaches and in vivo model of IL-13-induced esophageal epithelial remodeling (Krt5-rtTA x tetO-IL-13Tg) were used to define the role of signal transducer and activator of transcription 3 (STAT3) and STAT6 and secreted frizzled-related protein 1 (SFRP1) in esophageal epithelial proliferation.

RESULTS

RNA-sequencing analysis of esophageal biopsies (healthy control vs EoE) and EPC2-ALI revealed 82 common differentially expressed genes that were enriched for putative STAT3 target genes. In vitro and in vivo analyses revealed a link between IL-13-induced STAT3 and STAT6 phosphorylation, SFRP1 mRNA expression, and esophageal epithelial proliferation. In vitro studies showed that IL-13-induced esophageal epithelial proliferation was STAT3-dependent and regulated by the STAT3 target SFRP1. SFRP1 mRNA is increased in esophageal biopsies from patients with active EoE compared with healthy controls or patients in remission and identifies an esophageal suprabasal epithelial cell subpopulation that uniquely expressed the core EoE proinflammatory transcriptome genes (CCL26, ALOX15, CAPN14, ANO1, and TNFAIP6).

CONCLUSIONS

These studies identify SFRP1 as a key regulator of IL-13-induced and STAT3-dependent esophageal proliferation and BZH in EoE and link SFRP1+ esophageal epithelial cells with the proinflammatory and epithelial remodeling response in EoE.

MORA and EnsembleTFpredictor: An ensemble approach to reveal functional transcription factor regulatory networks

MOTIVATION

Our study aimed to identify biologically relevant transcription factors (TFs) that control the expression of a set of co-expressed or co-regulated genes.

RESULTS

We developed a fully automated pipeline, Motif Over Representation Analysis (MORA), to detect enrichment of known TF binding motifs in any query sequences. MORA performed better than or comparable to five other TF-prediction tools as evaluated using hundreds of differentially expressed gene sets and ChIP-seq datasets derived from known TFs. Additionally, we developed EnsembleTFpredictor to harness the power of multiple TF-prediction tools to provide a list of functional TFs ranked by prediction confidence. When applied to the test datasets, EnsembleTFpredictor not only identified the target TF but also revealed many TFs known to cooperate with the target TF in the corresponding biological systems. MORA and EnsembleTFpredictor have been used in two publications, demonstrating their power in guiding experimental design and in revealing novel biological insights.

The opportunities and challenges in immunotherapy: Insights from the regulation of PD-L1 in cancer cells

The immunosuppressive molecule programmed death-ligand 1 (PD-L1) is frequently upregulated in human cancers. Binding of PD-L1 to its receptor, programmed death-1 (PD-1), on activated T cells facilitates cancer cells to evade the host immune system. Antibody-based PD-1/PD-L1 inhibitors can inhibit PD-1/PD-L1 interaction allowing reactivate cytotoxic T cells to eradicate advanced cancer cells. However, the majority of cancer patients fail to respond to anti-PD-1/PD-L1 therapies and the molecular mechanisms for this remain poorly understood. Recent studies show that PD-L1 expression level on tumor cells affect the clinical efficacy of immune checkpoint therapies. Thus, furthering our understanding of the regulatory mechanisms of PD-L1 expression in cancer cells will be critical to improve clinical response rates and the efficacy of PD-1/PD-L1 immune therapies. Here we review recent studies, primarily focusing on the mechanisms that regulate PD-L1 expression at the transcriptional, post-transcriptional and protein level, with the purpose to drive the development of more targeted and effective anti-PD-1/PD-L1 cancer therapies.

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

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

Generation, secretion and degradation of cancer immunotherapy target PD-L1

Cancer immunotherapy is a rapidly developing and effective method for the treatment of a variety of malignancies in recent years. As a significant immune checkpoint, programmed cell death 1 ligand 1 (PD-L1) and its receptor programmed cell death protein 1 (PD-1) play the most significant role in cancer immune escape and cancer immunotherapy. Though PD-L1 have become an important target for drug development and there have been various approved drugs and clinic trials targeting it, and various clinical response rate and adverse reactions prevent many patients from benefiting from it. In recent years, combination trials have become the main direction of PD-1/PD-L1 antibodies development. Here, we summarized PD-L1 biofunctions and key roles in various cancers along with the development of PD-L1 inhibitors. The regulators that are involved in controlling PD-L1 expression including post-translational modification, mRNA level regulation as well as degradation and exosome secretory pathway of PD-L1 were focused. This systematic summary may provide comprehensive understanding of different regulations on PD-L1 as well as a broad prospect for the search of the important regulator of PD-L1. The regulatory factors of PD-L1 can be potential targets for immunotherapy and increase strategies of immunotherapy in combination.

Epigenetic Signaling of Cancer Stem Cells During Inflammation

Malignant tumors pose a great challenge to human health, which has led to many studies increasingly elucidating the tumorigenic process. Cancer Stem Cells (CSCs) have profound impacts on tumorigenesis and development of drug resistance. Recently, there has been increased interest in the relationship between inflammation and CSCs but the mechanism underlying this relationship has not been fully elucidated. Inflammatory cytokines produced during chronic inflammation activate signaling pathways that regulate the generation of CSCs through epigenetic mechanisms. In this review, we focus on the effects of inflammation on cancer stem cells, particularly the role of signaling pathways such as NF-κB pathway, STAT3 pathway and Smad pathway involved in regulating epigenetic changes. We hope to provide a novel perspective for improving strategies for tumor treatment.

STAT3 as a Potential Target for Tumor Suppressive Effects of 15-Deoxy-Δ12,14-prostaglandin J2 in Triple Negative Breast Cancer

STAT3 plays a prominent role in proliferation and survival of tumor cells. Thus, STAT3 has been considered to be a prime target for development of anti-cancer therapeutics. The electrophilic cyclopentenone prostaglandin,15-deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) has been well recognized for its capability to modulate intracellular signaling pathways involved in cancer cell growth and progression. We previously reported that 15d-PGJ₂ had potent cytotoxicity against harvey-ras transformed human mammary epithelial cells through direct interaction with STAT3. In this study, we have attempted to verify the inhibitory effects of 15d-PGJ₂ on STAT3 signaling in human breast tumor cells. The triple negative breast cancer cell lines, MDA-MB-231 and MDA-MB-468 displaying constitutive phosphorylation of STAT3 on the tyrosine 705 (Tyr705) residue, underwent apoptosis upon inhibition of STAT3 by 15d-PGJ₂. In contrast, estrogen receptor positive MCF-7 breast cancer cells that do not exhibit elevated STAT3 phosphorylation were much less susceptible to 15d-PGJ₂-induced apoptosis as assessed by PARP cleavage. Furthermore, 15d-PGJ₂ inhibited interleukin-6-induced tyrosine phosphorylation of STAT3 in LNCaP cells. According to molecular docking studies, 15d-PGJ₂ may preferentially bind to the cysteine 259 residue (Cys259) present in the coiled-coil domain of STAT3. Site-directed mutagenesis of STAT3 identified Cys259 to be the critical amino acid for the 15d-PGJ₂-induced apoptosis as well as epithelial-to-mesenchymal transition. Taken together, these findings suggest STAT3 inactivation through direct chemical modification of its Cys259 as a potential therapeutic approach for treatment of triple negative breast cancer treatment.

Impact of STAT Proteins in Tumor Progress and Therapy Resistance in Advanced and Metastasized Prostate Cancer

Signal transducers and activators of transcription (STATs) are a family of transcription factors involved in several biological processes such as immune response, cell survival, and cell growth. However, they have also been implicated in the development and progression of several cancers, including prostate cancer (PCa). Although the members of the STAT protein family are structurally similar, they convey different functions in PCa. STAT1, STAT3, and STAT5 are associated with therapy resistance. STAT1 and STAT3 are involved in docetaxel resistance, while STAT3 and STAT5 are involved in antiandrogen resistance. Expression of STAT3 and STAT5 is increased in PCa metastases, and together with STAT6, they play a crucial role in PCa metastasis. Further, expression of STAT3, STAT5, and STAT6 was elevated in advanced and high-grade PCa. STAT2 and STAT4 are currently less researched in PCa. Since STATs are widely involved in PCa, they serve as potential therapeutic targets. Several inhibitors interfering with STATs signaling have been tested unsuccessfully in PCa clinical trials. This review focuses on the respective roles of the STAT family members in PCa, especially in metastatic disease and provides an overview of STAT-inhibitors evaluated in clinical trials.

Divalent Metal Transporter 1 Knock-Down Modulates IL-1β Mediated Pancreatic Beta-Cell Pro-Apoptotic Signaling Pathways through the Autophagic Machinery

Pro-inflammatory cytokines promote cellular iron-import through enhanced divalent metal transporter-1 (DMT1) expression in pancreatic β-cells, consequently cell death. Inhibition of β-cell iron-import by DMT1 silencing protects against apoptosis in animal models of diabetes. However, how alterations of signaling networks contribute to the protective action of DMT1 knock-down is unknown. Here, we performed phosphoproteomics using our sequential enrichment strategy of mRNA, protein, and phosphopeptides, which enabled us to explore the concurrent molecular events in the same set of wildtype and DMT1-silenced β-cells during IL-1β exposure. Our findings reveal new phosphosites in the IL-1β-induced proteins that are clearly reverted by DMT1 silencing towards their steady-state levels. We validated the levels of five novel phosphosites of the potential protective proteins using parallel reaction monitoring. We also confirmed the inactivation of autophagic flux that may be relevant for cell survival induced by DMT1 silencing during IL-1β exposure. Additionally, the potential protective proteins induced by DMT1 silencing were related to insulin secretion that may lead to improving β-cell functions upon exposure to IL-1β. This global profiling has shed light on the signal transduction pathways driving the protection against inflammation-induced cell death in β-cells after DMT1 silencing.

STAT3 couples with 14-3-3σ to regulate BCR signaling, B-cell differentiation, and IgE production

BACKGROUND

STAT3 or dedicator of cytokinesis protein 8 (Dock8) loss-of-function (LOF) mutations cause hyper-IgE syndrome. The role of abnormal T-cell function has been extensively investigated; however, the contribution of B-cell-intrinsic dysfunction to elevated IgE levels is unclear.

OBJECTIVE

We sought to determine the underlying molecular mechanism of how STAT3 regulates B-cell receptor (BCR) signaling, B-cell differentiation, and IgE production.

METHODS

We used samples from patients with STAT3 LOF mutation and samples from the STAT3 B-cell-specific knockout (KO) mice Mb1CreStat3flox/flox mice (B-STAT3 KO) to investigate the mechanism of hyper-IgE syndrome.

RESULTS

We found that the peripheral B-cell homeostasis in B-STAT3 KO mice mimicked the phenotype of patients with STAT3 LOF mutation, having decreased levels of follicular and germinal center B cells but increased levels of marginal zone and IgE+ B cells. Furthermore, B-STAT3 KO B cells had reduced BCR signaling following antigenic stimulation owing to reduced BCR clustering and decreased accumulation of Wiskott-Aldrich syndrome protein and F-actin. Excitingly, a central hub protein, 14-3-3σ, which is essential for the increase in IgE production, was enhanced in the B cells of B-STAT3 KO mice and patients with STAT3 LOF mutation. The increase of 14-3-3σ was associated with increased expression of the upstream mediator, microRNA146A. Inhibition of 14-3-3σ with R18 peptide in B-STAT3 KO mice rescued the BCR signaling, follicular, germinal center, and IgE+ B-cell differentiation to the degree seen in wild-type mice.

CONCLUSIONS

Altogether, our study has established a novel regulatory pathway of STAT3-miRNA146A-14-3-3σ to regulate BCR signaling, peripheral B-cell differentiation, and IgE production.

PDCD4-mediated downregulation of Listeria monocytogenes burden in macrophages

Introduction

Macrophages are effector cells of the innate immune system and defend against invading pathogens. Previous reports have shown that infection with Listeria monocytogenes upregulates miR-21a expression in macrophages.

Aim of the study

We aimed to verify whether programmed cell death 4 (PDCD4) is involved in the high bacterial burden observed in macrophages during late-stage L. monocytogenes infections.

Material and methods

We examined the expression of miR-21a and its known target PDCD4 in macrophages after L. monocytogenes infection. The macrophages’ uptake ability of L. monocytogenes was measured using FluoSpheres Carboxylate-modified microspheres. We depleted PDCD4 by transfecting macrophages with siPDCD4.

Results

In macrophages, PDCD4 protein was downregulated 5 h, but not 2 h, after L. monocytogenes infection. Our results validated the hypothesis that PDCD4-depleted macrophages present a higher L. monocytogenes burden. Moreover, we found that the activation of c-Jun and STAT3 accompanied PDCD4 downregulation.

Conclusions

Our results showed that PDCD4 mediated the suppression of L. monocytogenes infection in macrophages via c-Jun/STAT3 signalling activation.

15-Deoxy-Δ12,14 -prostaglandin J2 binds and inactivates STAT3 via covalent modification of cysteine 259 in H-Ras-transformed human breast epithelial cells

Signal transducer and activator of transcription 3 (STAT3) has been considered as a potential target for development of anticancer therapeutics. Here, we report a novel mechanism by which the cyclopentenone prostaglandin, 15-deoxy-Δ^12,14 -prostaglandin J₂ (15d-PGJ₂ ) functions as an allosteric inhibitor of STAT3. 15d-PGJ₂ inhibits phosphorylation, dimerization, nuclear translocation, and transcriptional activity of STAT3 in H-Ras-transformed human mammary epithelial cells (MCF10A-Ras) through the Michael addition reaction at cysteine 259 of STAT3. Comparative studies with 15d-PGJ₂ analogues reveal that both C12-C13 and C9-C10 double bonds conjugated to the carbonyl group in the cyclopentenone ring of 15d-PGJ₂ are essential for STAT3 binding. Antiproliferative and pro-apoptotic activities of 15d-PGJ₂ in MCF10A-Ras cells are attributable to covalent modification of STAT3 on Cys259, and mimic the effects induced by mutation of this amino acid.

Batf Pioneers the Reorganization of Chromatin in Developing Effector T Cells via Ets1-Dependent Recruitment of Ctcf

The basic leucine zipper transcription factor activating transcription factor-like (Batf) contributes to transcriptional programming of multiple effector T cells and is required for T helper 17 (Th17) and T follicular helper (Tfh) cell development. Here, we examine mechanisms by which Batf initiates gene transcription in developing effector CD4 T cells. We find that, in addition to its pioneering function, Batf controls developmentally regulated recruitment of the architectural factor Ctcf to promote chromatin looping that is associated with lineage-specific gene transcription. The chromatin-organizing actions of Batf are largely dependent on Ets1, which appears to be indispensable for the Batf-dependent recruitment of Ctcf. Moreover, most of the Batf-dependent sites to which Ctcf is recruited lie outside of activating protein-1-interferon regulatory factor (Ap-1-Irf) composite elements (AICEs), indicating that direct involvement of Batf-Irf complexes is not required. These results identify a cooperative role for Batf, Ets1, and Ctcf in chromatin reorganization that underpins the transcriptional programming of effector T cells.

Exogenous dihydrosphingosine 1 phosphate mediates collagen synthesis in cardiac fibroblasts through JAK/STAT signalling and regulation of TIMP1

Cardiac fibrosis and myocyte hypertrophy are hallmarks of the cardiac remodelling process in cardiomyopathies such as heart failure (HF). Dyslipidemia or dysregulation of lipids contribute to HF. The dysregulation of high density lipoproteins (HDL) could lead to altered levels of other lipid metabolites that are bound to it such as sphingosine-1- phosphate (S1P). Recently, it has been shown that S1P and its analogue dihydrosphingosine-1-phosphate (dhS1P) are bound to HDL in plasma. The effects of dhS1P on cardiac cells have been obscure. In this study, we show that extracellular dhS1P is able to increase collagen synthesis in neonatal rat cardiac fibroblasts (NCFs) and cause hypertrophy of neonatal cardiac myocytes (NCMs). The janus kinase/signal transducer and activator (JAK/STAT) signalling pathway was involved in the increased collagen synthesis by dhS1P, through sustained increase of tissue inhibitor of matrix metalloproteinase 1 (TIMP1). Extracellular dhS1P increased phosphorylation levels of STAT1 and STAT3 proteins, also caused an early increase in gene expression of transforming growth factor-β (TGFβ), and sustained increase in TIMP1. Inhibition of JAKs led to inhibition of TIMP1 and TGFβ gene and protein expression. We also show that dhS1P is able to cause NCM hypertrophy through S1P-receptor-1 (S1PR1) signalling which is opposite to that of its analogue, S1P. Taken together, our results show that dhS1P increases collagen synthesis in cardiac fibroblasts causing fibrosis through dhS1P-JAK/STAT-TIMP1 signalling.

Role of JAK/STAT3 Signaling in the Regulation of Metastasis, the Transition of Cancer Stem Cells, and Chemoresistance of Cancer by Epithelial-Mesenchymal Transition

The JAK/STAT3 signaling pathway plays an essential role in various types of cancers. Activation of this pathway leads to increased tumorigenic and metastatic ability, the transition of cancer stem cells (CSCs), and chemoresistance in cancer via enhancing the epithelial–mesenchymal transition (EMT). EMT acts as a critical regulator in the progression of cancer and is involved in regulating invasion, spread, and survival. Furthermore, accumulating evidence indicates the failure of conventional therapies due to the acquisition of CSC properties. In this review, we summarize the effects of JAK/STAT3 activation on EMT and the generation of CSCs. Moreover, we discuss cutting-edge data on the link between EMT and CSCs in the tumor microenvironment that involves a previously unknown function of miRNAs, and also discuss new regulators of the JAK/STAT3 signaling pathway.

Epigenetic inhibition of the tumor suppressor ARHI by light at night-induced circadian melatonin disruption mediates STAT3-driven paclitaxel resistance in breast cancer

Disruption of circadian time structure and suppression of circadian nocturnal melatonin (MLT) production by exposure to dim light at night (dLAN), as occurs with night shift work and/or disturbed sleep-wake cycles, is associated with a significantly increased risk of breast cancer and resistance to tamoxifen and doxorubicin. Melatonin inhibition of human breast cancer chemoresistance involves mechanisms including suppression of tumor metabolism and inhibition of kinases and transcription factors which are often activated in drug-resistant breast cancer. Signal transducer and activator of transcription 3 (STAT3), frequently overexpressed and activated in paclitaxel (PTX)-resistant breast cancer, promotes the expression of DNA methyltransferase one (DNMT1) to epigenetically suppress the transcription of tumor suppressor Aplasia Ras homolog one (ARHI) which can sequester STAT3 in the cytoplasm to block PTX resistance. We demonstrate that breast tumor xenografts in rats exposed to dLAN and circadian MLT disrupted express elevated levels of phosphorylated and acetylated STAT3, increased DNMT1, but reduced sirtuin 1 (SIRT1) and ARHI. Furthermore, MLT and/or SIRT1 administration blocked/reversed interleukin 6 (IL-6)-induced acetylation of STAT3 and its methylation of ARH1 to increase ARH1 mRNA expression in MCF-7 breast cancer cells. Finally, analyses of the I-SPY 1 trial demonstrate that elevated MT₁ receptor expression is significantly correlated with pathologic complete response following neo-adjuvant therapy in breast cancer patients. This is the first study to demonstrate circadian disruption of MLT by dLAN driving intrinsic resistance to PTX via epigenetic mechanisms increasing STAT3 expression and that MLT administration can reestablish sensitivity of breast tumors to PTX and drive tumor regression.

Recent Findings in the Regulation of Programmed Death Ligand 1 Expression

With the recent approvals for the application of monoclonal antibodies that target the well-characterized immune checkpoints, immune therapy shows great potential against both solid and hematologic tumors. The use of these therapeutic monoclonal antibodies elicits inspiring clinical results with durable objective responses and improvements in overall survival. Agents targeting programmed cell death protein 1 (PD-1; also known as PDCD1) and its ligand (PD-L1) achieve a great success in immune checkpoints therapy. However, the majority of patients fail to respond to PD-1/PD-L1 axis inhibitors. Expression of PD-L1 on the membrane of tumor and immune cells has been shown to be associated with enhanced objective response rates to PD-1/PD-L1 inhibition. Thus, an improved understanding of how PD-L1 expression is regulated will enable us to better define its role as a predictive marker. In this review, we summarize recent findings in the regulation of PD-L1 expression.

Antitumor activity of Raddeanin A is mediated by Jun amino-terminal kinase activation and signal transducer and activator of transcription 3 inhibition in human osteosarcoma

Osteosarcoma is the most common primary malignant bone tumor. Raddeanin A (RA) is an active oleanane‐type triterpenoid saponin extracted from the traditional Chinese herb Anemone raddeana Regel that exerts antitumor activity against several cancer types. However, the effect of RA on osteosarcoma remains unclear. In the present study, we showed that RA inhibited proliferation and induced apoptosis of osteosarcoma cells in a dose‐ and time‐dependent way in vitro and in vivo. RA treatment resulted in excessive reactive oxygen species (ROS) generation and JNK and ERK1/2 activation. Apoptosis induction was evaluated by the activation of caspase‐3, caspase‐8, and caspase‐9 and poly‐ADP ribose polymerase (PARP) cleavage. RA‐induced cell death was significantly restored by the ROS scavenger glutathione (GSH), the pharmacological inhibitor of JNK SP600125, or specific JNK knockdown by shRNA. Additionally, signal transducer and activator of transcription 3 (STAT3) activation was suppressed by RA in human osteosarcoma, and this suppression was restored by GSH, SP600125, and JNK‐shRNA. Further investigation showed that STAT3 phosphorylation was increased after JNK knockdown. In a tibial xenograft tumor model, RA induced osteosarcoma apoptosis and notably inhibited tumor growth. Taken together, our results show that RA suppresses proliferation and induces apoptosis by modulating the JNK/c‐Jun and STAT3 signaling pathways in human osteosarcoma. Therefore, RA may be a promising candidate antitumor drug for osteosarcoma intervention.

Therapeutically exploiting STAT3 activity in cancer - using tissue repair as a road map

The tightly orchestrated temporal and spatial control of signal transducer and activator of transcription 3 (STAT3) activity in epithelial, immune and stromal cells is critical for wound healing and tissue repair. Excessive STAT3 activation within cancer cells and cells of the tumour microenvironment can be viewed as a neoplastic mimic of an inflammation-driven repair response that collectively promotes tumour progression. In addition to the canonical transcriptional pathways by which STAT3 promotes stem cell-like characteristics, survival, proliferation, metastatic potential and immune evasion, cytoplasmic STAT3 activity fuels tumour growth by metabolic and other non-transcriptional mechanisms. Here, we review the tumour-modulating activities of STAT3 in light of its role as a signalling node integrating inflammatory responses during wound healing. Accordingly, many of the cytokines that contribute to the para-inflammatory state of most solid malignancies converge on and underpin dysregulated STAT3 activity. Targeting of these cytokines, their cognate receptors and associated signalling cascades in clinical trials is beginning to demonstrate therapeutic efficacy, given that interference with STAT3 activity is likely to simultaneously curb the growth of cancer cells and augment antitumour immunity.

Chromatin Accessibility and Interactions in the Transcriptional Regulation of T Cells

During T cell differentiation and activation, specific stimuli, and a network of transcription factors (TFs) are involved in orchestrating chromatin accessibility, establishing enhancer-promoter interactions, and regulating gene expression. Over the past few years, there have been new insights into how chromatin interactions coordinate differentiation during T cell development and how regulatory elements are programmed to allow T cells to differentially respond to distinct stimuli. In this review, we discuss recent advances related to the roles of TFs in establishing the regulatory chromatin landscapes that orchestrate T cell development and differentiation. In particular, we focus on the role of TFs (e.g., TCF-1, BCL11B, PU.1, STAT3, STAT5, AP-1, and IRF4) in mediating chromatin accessibility and interactions and in regulating gene expression in T cells, including gene expression that is dependent on IL-2 and IL-21. Furthermore, we discuss the state of knowledge on enhancer-promoter interactions and how autoimmune disease risk variants can be linked to molecular functions of putative target genes.

Regulation and Function of the PD-L1 Checkpoint

Expression of programmed death-ligand 1 (PD-L1) is frequently observed in human cancers. Binding of PD-L1 to its receptor PD-1 on activated T cells inhibits anti-tumor immunity by counteracting T cell-activating signals. Antibody-based PD-1-PD-L1 inhibitors can induce durable tumor remissions in patients with diverse advanced cancers, and thus expression of PD-L1 on tumor cells and other cells in the tumor microenviroment is of major clinical relevance. Here we review the roles of the PD-1-PD-L1 axis in cancer, focusing on recent findings on the mechanisms that regulate PD-L1 expression at the transcriptional, posttranscriptional, and protein level. We place this knowledge in the context of observations in the clinic and discuss how it may inform the design of more precise and effective cancer immune checkpoint therapies.

Transcriptional Regulation of Emergency Granulopoiesis in Leukemia

Neutropenic conditions are prevalent in leukemia patients and are often associated with increased susceptibility to infections. In fact, emergency granulopoiesis (EG), a process regulating neutrophil homeostasis in inflammatory conditions and infections, may occur improperly in leukemic conditions, leading to reduced neutrophil counts. Unfortunately, the mechanisms central to dysfunctional EG remain understudied in both leukemia patients and leukemic mouse models. However, despite no direct studies on EG response in leukemia are reported, recently certain transcription factors (TFs) have been found to function at the crossroads of leukemia and EG. In this review, we present an update on TFs that can potentially govern the fate of EG in leukemia. Transcriptional control of Fanconi DNA repair pathway genes is also highlighted, as well as the newly discovered role of Fanconi proteins in innate immune response and EG. Identifying the TFs regulating EG in leukemia and dissecting their underlying mechanisms may facilitate the discovery of therapeutic drugs for the treatment of neutropenia.

microRNA-133a attenuates cardiomyocyte hypertrophy by targeting PKCδ and Gq

During the past decade, microRNAs have continuously been suggested as a promising therapeutic tool due to their beneficial effects, such as their multi-targets and multi-functions in pathologic conditions. As a pathologic phenotype is generally regulated by multiple signaling pathways, in this study we identified a microRNA regulating multiple target genes within cardiac hypertrophic signaling pathways. microRNA-133a is known to play a crucial role in cardiac hypertrophy. However, the role of microRNA-133a, which may regulate several signaling pathways in norepinephrine-induced cardiac hypertrophy via multi-targeting, has not been investigated. In the current study, we showed that microRNA-133a can protect cardiomyocyte hypertrophy against norepinephrine stimulation in neonatal rat ventricular cardiomyocytes via new targets, PKCδ and Gq, all of which are related to downstream signaling pathways of the α₁-adrenergic receptor. Taken together, these results suggest the advantages of the therapeutic use of microRNAs as an effective potential drug regulating multiple signaling pathways under pathologic conditions.

Discovery and validation of information theory-based transcription factor and cofactor binding site motifs

Data from ChIP-seq experiments can derive the genome-wide binding specificities of transcription factors (TFs) and other regulatory proteins. We analyzed 765 ENCODE ChIP-seq peak datasets of 207 human TFs with a novel motif discovery pipeline based on recursive, thresholded entropy minimization. This approach, while obviating the need to compensate for skewed nucleotide composition, distinguishes true binding motifs from noise, quantifies the strengths of individual binding sites based on computed affinity and detects adjacent cofactor binding sites that coordinate with the targets of primary, immunoprecipitated TFs. We obtained contiguous and bipartite information theory-based position weight matrices (iPWMs) for 93 sequence-specific TFs, discovered 23 cofactor motifs for 127 TFs and revealed six high-confidence novel motifs. The reliability and accuracy of these iPWMs were determined via four independent validation methods, including the detection of experimentally proven binding sites, explanation of effects of characterized SNPs, comparison with previously published motifs and statistical analyses. We also predict previously unreported TF coregulatory interactions (e.g. TF complexes). These iPWMs constitute a powerful tool for predicting the effects of sequence variants in known binding sites, performing mutation analysis on regulatory SNPs and predicting previously unrecognized binding sites and target genes.

Negative Regulation of Hepatic Inflammation by the Soluble Resistance-Related Calcium-Binding Protein via Signal Transducer and Activator of Transcription 3

Host immune response is tightly controlled by negative regulators to avoid excessive immune reactions for homeostasis. Some pathogens may take advantage of host negative regulating system to evade host defense. Our previous report showed that foot-and-mouth disease virus (FMDV) VP1 inhibited TNF-α- and SeV-induced type I interferon response via interaction with cellular protein soluble resistance-related calcium-binding protein (sorcin). Conversely, TNF-α- or SeV-induced type I interferon response increased when sorcin knocked down, leading to inhibition of vesicular stomatitis virus replication. However, the exact role of sorcin in regulation of the immune response is still not clear. Here, we show that mice deficient of sorcin (sorcin^-/-) display enhanced ConA-induced hepatitis. Importantly, splenocytes from sorcin^-/- mice produced more IL-2, IL-4, IL-17, and IFN-γ than that of littermate controls (sorcin^+/+) in response to anti-CD3/28 stimulation. Furthermore, our data indicate that sorcin interacts with signal transducer and activator of transcription 3 (STAT3) and enhances its phosphorylation and that STAT3 acts as an immediate downstream molecule of sorcin in the negative regulation of NF-κB signaling. Thus, sorcin, in association with STAT3, negatively regulates hepatic inflammation.

Hippocalcin Is Required for Astrocytic Differentiation through Activation of Stat3 in Hippocampal Neural Precursor Cells

Hippocalcin (Hpca) is a neuronal calcium sensor protein expressed in the mammalian brain. However, its function in neural stem/precursor cells has not yet been studied. Here, we clarify the function of Hpca in astrocytic differentiation in hippocampal neural precursor cells (HNPCs). When we overexpressed Hpca in HNPCs in the presence or absence of bFGF, expression levels of nerve-growth factors such as neurotrophin-3 (NT-3), neurotrophin-4/5 (NT-4/5), and brain-derived neurotrophic factor (BDNF), together with the proneural basic helix loop helix (bHLH) transcription factors NeuroD and neurogenin 1 (Ngn1), increased significantly. In addition, there was an increase in the number of cells expressing glial fibrillary acidic protein (GFAP), an astrocyte marker, and in branch outgrowth, indicating astrocytic differentiation of the HNPCs. Downregulation of Hpca by transfection with Hpca siRNA reduced expression of NT-3, NT-4/5, BDNF, NeuroD, and Ngn1 as well as levels of GFAP protein. Furthermore, overexpression of Hpca increased the phosphorylation of STAT3 (Ser727), and this effect was abolished by treatment with a STAT3 inhibitor (S3I-201), suggesting that STAT3 (Ser727) activation is involved in Hpca-mediated astrocytic differentiation. As expected, treatment with Stat3 siRNA or STAT3 inhibitor caused a complete inhibition of astrogliogenesis induced by Hpca overexpression. Taken together, this is the first report to show that Hpca, acting through Stat3, has an important role in the expression of neurotrophins and proneural bHLH transcription factors, and that it is an essential regulator of astrocytic differentiation and branch outgrowth in HNPCs.

Role of STAT3 in Genesis and Progression of Human Malignant Gliomas

Signal transducer and activator of transcription 3 (STAT3) is aberrantly activated in glioblastoma and has been identified as a relevant therapeutic target in this disease and many other human cancers. After two decades of intensive research, there is not yet any approved STAT3-based glioma therapy. In addition to the canonical activation by tyrosine 705 phosphorylation, concordant reports described a potential therapeutic relevance of other post-translational modifications including mainly serine 727 phosphorylation. Such reports reinforce the need to refine the strategy of targeting STAT3 in each concerned disease. This review focuses on the role of serine 727 and tyrosine 705 phosphorylation of STAT3 in glioma. It explores their contribution to glial cell transformation and to the mechanisms that make glioma escape to both immune control and standard treatment.

The role of signal transducer and activator of transcription 3 in Rift Valley fever virus infection

Rift Valley fever (RVF) is a zoonotic disease that can cause severe illness in humans and livestock, triggering spontaneous abortion in almost 100% of pregnant ruminants. In this study, we demonstrate that signal transducer and activator of transcription 3 (STAT3) is phosphorylated on its conserved tyrosine residue (Y705) following RVFV infection. This phosphorylation was dependent on a major virulence factor, the viral nonstructural protein NSs. Loss of STAT3 had little effect on viral replication, but rather resulted in cells being more susceptible to RVFV-induced cell death. Phosphorylated STAT3 translocated to the nucleus, coinciding with inhibition of fos, jun, and nr4a2 gene expression, and the presence of STAT3 and NSs at the nr4a2 promoter. NSs was found predominantly in the cytoplasm of STAT3 null cells, indicating that STAT3 influences NSs nuclear localization. Collectively, these data demonstrate that STAT3 functions in a pro-survival capacity through modulation of NSs localization.

Stat3 orchestrates interaction between endothelial and tumor cells and inhibition of Stat3 suppresses brain metastasis of breast cancer cells

Brain metastasis is a major cause of morbidity and mortality in patients with breast cancer. Our previous studies indicated that Stat3 plays an important role in brain metastasis. Here, we present evidence that Stat3 functions at the level of the microenvironment of brain metastases. Stat3 controlled constitutive and inducible VEGFR2 expression in tumor-associated brain endothelial cells. Furthermore, inhibition of Stat3 by WP1066 decreased the incidence of brain metastases and increased survival in a preclinical model of breast cancer brain metastasis. WP1066 inhibited Stat3 activation in tumor-associated endothelial cells, reducing their infiltration and angiogenesis. WP1066 also inhibited breast cancer cell invasion. Our results indicate that WP1066 can inhibit tumor angiogenesis and brain metastasis mediated by Stat3 in endothelial and tumor cells.

Overexpression of ATF3 or the combination of ATF3, c-Jun, STAT3 and Smad1 promotes regeneration of the central axon branch of sensory neurons but without synergistic effects

Peripheral nerve injury results in the activation of a number of transcription factors (TFs) in injured neurons, some of which may be key regulators of the regeneration-associated gene (RAG) programme. Among known RAG TFs, ATF3, Smad1, STAT3 and c-Jun have all been linked to successful axonal regeneration and have known functional and physical interactions. We hypothesised that TF expression would promote regeneration of the central axon branch of DRG neurons in the absence of a peripheral nerve lesion and that simultaneous overexpression of multiple RAG TFs would lead to greater effects than delivery of a single TF. Using adeno-associated viral vectors, we overexpressed either the combination of ATF3, Smad1, STAT3 and c-Jun with farnesylated GFP (fGFP), ATF3 only with fGFP, or fGFP only, in DRG neurons and assessed axonal regeneration after dorsal root transection or dorsal column injury and functional improvement after dorsal root injury. ATF3 alone and the combination of TFs promoted faster regeneration in the injured dorsal root. Surprisingly, however, the combination did not perform better than ATF3 alone. Neither treatment was able to induce functional improvement on sensory tests after dorsal root injury or promote regeneration in a dorsal column injury model. The lack of synergistic effects among these factors indicates that while they do increase the speed of axon growth, there may be functional redundancy between these TFs. Because axon growth is considerably less than that seen after a conditioning lesion, it appears these TFs do not induce the full regeneration programme.

Constitutive control of AKT1 gene expression by JUNB/CJUN in ALK+ anaplastic large-cell lymphoma: a novel crosstalk mechanism

Anaplastic lymphoma kinase-positive (ALK+) anaplastic large-cell lymphoma (ALCL) is an aggressive T-cell non-Hodgkin lymphoma characterized by the t(2;5), resulting in the overexpression of nucleophosmin (NPM)-ALK, which is known to activate the phosphatidylinositol-3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway, resulting in cell cycle and apoptosis deregulation. ALK+ ALCL is also characterized by strong activator protein-1 (AP-1) activity and overexpression of two AP-1 transcription factors, CJUN and JUNB. Here, we hypothesized that a biologic link between AP-1 and AKT kinase may exist, thus contributing to ALCL oncogenesis. We show that JUNB and CJUN bind directly to the AKT1 promoter, inducing AKT1 transcription in ALK+ ALCL. Knockdown of JUNB and CJUN in ALK+ ALCL cell lines downregulated AKT1 mRNA and promoter activity and was associated with lower AKT1 protein expression and activation. We provide evidence that this is a transcriptional control mechanism shared by other cell types even though it may operate in a way that is cell context-specific. In addition, STAT3 (signal transducer and activator of transcription 3)-induced control of AKT1 transcription was functional in ALK+ ALCL and blocking of STAT3 and AP-1 signaling synergistically affected cell proliferation and colony formation. Our findings uncover a novel transcriptional crosstalk mechanism that links AP-1 and AKT kinase, which coordinate uncontrolled cell proliferation and survival in ALK+ ALCL.

Complex interactions of transcription factors in mediating cytokine biology in T cells

T-helper (Th) cells play critical roles within the mammalian immune system, and the differentiation of naive CD4(+) T cells into distinct T-helper subsets is critical for normal immunoregulation and host defense. These carefully regulated differentiation processes are controlled by networks of cytokines, transcription factors, and epigenetic modifications, resulting in the generation of multiple CD4(+) T-cell subsets, including Th1, Th2, Th9, Th17, Treg, and Tfh cells. In this review, we discuss the roles of transcription factors in determining the specific type of differentiation and in particular the role of interleukin-2 (IL-2) in promoting or inhibiting Th differentiation. In addition to discussing master regulators and subset-specific transcription factors for distinct T-helper cell populations, we focus on signal transducer and activator of transcription (STAT) proteins and on the cooperative action of interferon regulatory factor 4 (IRF4) with activator protein 1 (AP-1) family proteins and STAT3 in the assembly of complexes that broadly influence T-cell differentiation.

Ghrelin induces leptin resistance by activation of suppressor of cytokine signaling 3 expression in male rats: implications in satiety regulation

The anorexigenic adipocyte-derived hormone leptin and the orexigenic hormone ghrelin act in opposition to regulate feeding behavior via the vagal afferent pathways. The mechanisms by which ghrelin exerts its inhibitory effects on leptin are unknown. We hypothesized that ghrelin activates the exchange protein activated by cAMP (Epac), inducing increased SOCS3 expression, which negatively affects leptin signal transduction and neuronal firing in nodose ganglia (NG) neurons. We showed that 91 ± 3% of leptin receptor (LRb) -bearing neurons contained ghrelin receptors (GHS-R1a) and that ghrelin significantly inhibited leptin-stimulated STAT3 phosphorylation in rat NG neurons. Studies of the signaling cascades used by ghrelin showed that ghrelin caused a significant increase in Epac and suppressor of cytokine signaling 3 (SOCS3) expression in cultured rat NG neurons. Transient transfection of cultured NG neurons to silence SOCS3 and Epac genes reversed the inhibitory effects of ghrelin on leptin-stimulated STAT3 phosphorylation. Patch-clamp studies and recordings of single neuronal discharges of vagal primary afferent neurons showed that ghrelin markedly inhibited leptin-stimulated neuronal firing, an action abolished by silencing SOCS3 expression in NG. Plasma ghrelin levels increased significantly during fasting. This was accompanied by enhanced SOCS3 expression in the NG and prevented by treatment with a ghrelin antagonist. Feeding studies showed that silencing SOCS3 expression in the NG reduced food intake evoked by endogenous leptin. We conclude that ghrelin exerts its inhibitory effects on leptin-stimulated neuronal firing by increasing SOCS3 expression. The SOCS3 signaling pathway plays a pivotal role in ghrelin's inhibitory effect on STAT3 phosphorylation, neuronal firing, and feeding behavior.

A signal transducer and activator of transcription 3·Nuclear Factor κB (Stat3·NFκB) complex is necessary for the expression of fascin in metastatic breast cancer cells in response to interleukin (IL)-6 and tumor necrosis factor (TNF)-α

IL-6 mediated activation of Stat3 is a major signaling pathway in the process of breast cancer metastasis. One important mechanism by which the IL-6/Stat3 pathway promotes metastasis is through transcriptional regulation of the actin-bundling protein fascin. In this study, we further analyzed the transcriptional regulation of the fascin gene promoter. We show that in addition to IL-6, TNF-α increases Stat3 and NFκB binding to the fascin promoter to induce its expression. We also show that NFκB is required for Stat3 recruitment to the fascin promoter in response to IL-6. Furthermore, Stat3 and NFκB form a protein complex in response to cytokine stimulation. Finally, we demonstrate that an overlapping STAT/NFκB site in a highly conserved 160-bp region of the fascin promoter is sufficient and necessary to induce transcription in response to IL-6 and TNF-α.

Breast cancer cells condition lymphatic endothelial cells within pre-metastatic niches to promote metastasis

Breast cancer metastasis involves lymphatic dissemination in addition to hematogenous spreading. Although stromal lymphatic vessels (LVs) serve as initial metastatic routes, roles of organ-residing LVs are under-investigated. Here we show that lymphatic endothelial cells (LECs), a component of LVs within pre-metastatic niches, are conditioned by triple-negative breast cancer (TNBC) cells to accelerate metastasis. LECs within the lungs and lymph nodes, conditioned by tumor-secreted factors express CCL5 that is not expressed either in normal LECs or cancer cells, and direct tumor dissemination into these tissues. Moreover, tumor-conditioned LECs promote angiogenesis in these organs, allowing tumor extravasation and colonization. Mechanistically, tumor cell-secreted IL6 causes Stat3 phosphorylation in LECs. This pStat3 induces HIF-1α and VEGF, and a pStat3-pc-Jun-pATF-2 ternary complex induces CCL5 expression in LECs. This study demonstrates anti-metastatic activities of multiple repurposed drugs, blocking a self-reinforcing paracrine loop between breast cancer cells and LECs.

Cross-talk between KLF4 and STAT3 regulates axon regeneration

Cytokine-induced activation of signal transducer and activator of transcription 3 (STAT3) promotes the regrowth of damaged axons in the adult central nervous system (CNS). Here we show that KLF4 physically interacts with STAT3 upon cytokine-induced phosphorylation of tyrosine 705 (Y705) on STAT3. This interaction suppresses STAT3-dependent gene expression by blocking its DNA-binding activity. The deletion of KLF4 in vivo induces axon regeneration of adult retinal ganglion cells (RGCs) via Janus kinase (JAK)-STAT3 signalling. This regeneration can be greatly enhanced by exogenous cytokine treatment, or removal of an endogenous JAK-STAT3 pathway inhibitor called suppressor of cytokine signalling 3 (SOCS3). These findings reveal an unexpected cross-talk between KLF4 and activated STAT3 in the regulation of axon regeneration that might have therapeutic implications in promoting repair of injured adult CNS.

STAT1β is not dominant negative and is capable of contributing to gamma interferon-dependent innate immunity

The transcription factor STAT1 is essential for interferon (IFN)-mediated immunity in humans and mice. STAT1 function is tightly regulated, and both loss- and gain-of-function mutations result in severe immune diseases. The two alternatively spliced isoforms, STAT1α and STAT1β, differ with regard to a C-terminal transactivation domain, which is absent in STAT1β. STAT1β is considered to be transcriptionally inactive and to be a competitive inhibitor of STAT1α. To investigate the functions of the STAT1 isoforms in vivo, we generated mice deficient for either STAT1α or STAT1β. As expected, the functions of STAT1α and STAT1β in IFN-α/β- and IFN-λ-dependent antiviral activity are largely redundant. In contrast to the current dogma, however, we found that STAT1β is transcriptionally active in response to IFN-γ. In the absence of STAT1α, STAT1β shows more prolonged IFN-γ-induced phosphorylation and promoter binding. Both isoforms mediate protective, IFN-γ-dependent immunity against the bacterium Listeria monocytogenes, although with remarkably different efficiencies. Our data shed new light on the potential contributions of the individual STAT1 isoforms to STAT1-dependent immune responses. Knowledge of STAT1β's function will help fine-tune diagnostic approaches and help design more specific strategies to interfere with STAT1 activity.

STAT3 and MCL-1 associate to cause a mesenchymal epithelial transition

Embryo implantation is effected by a myriad of signaling cascades acting on the embryo-endometrium axis. Here we show, by using MALDI TOF analysis, far-western analysis and colocalization and co-transfection studies, that STAT3 and MCL-1 are interacting partners during embryo implantation. We show in vitro that the interaction between the two endogenous proteins is strongly regulated by estrogen and progesterone. Implantation, pregnancy and embryogenesis are distinct from any other process in the body, with extensive, but controlled, proliferation, cell migration, apoptosis, cell invasion and differentiation. Cellular plasticity is vital during the early stages of development for morphogenesis and organ homeostasis, effecting the epithelial to mesenchymal transition (EMT) and, the reverse process, mesenchymal to epithelial transition (MET). STAT3 functionally associates with MCL-1 in the mammalian breast cancer cell line MCF7 that overexpresses STAT3 and MCL-1, which leads to an increased rate of apoptosis and decreased cellular invasion, disrupting the EMT. Association of MCL-1 with STAT3 modulates the normal, anti-apoptotic, activity of MCL-1, resulting in pro-apoptotic effects. Studying the impact of the association of STAT3 with MCL-1 on MET could lead to an enhanced understanding of pregnancy and infertility, and also metastatic tumors.

Role of IL-9 and STATs in hematological malignancies (Review)

Although interleukin-9 (IL-9) exhibits pleiotropic functions in the immune system, it remains a well-known cytokine in hematological malignancies. Previous cell culture and animal model studies have revealed that the Janus kinase-signal transducer and activator of transcription signaling pathway, which may be activated by a number of cytokines including IL-9, is critical in hematological malignancies. The current review summarizes the characterization of the biological activities of IL-9, highlights the clearly defined roles of the cytokine, and outlines questions with regard to the functions of IL-9 that require further exploration and their downstream signaling proteins, signal transducers and activators of transcription.

Cardiac hormones target nuclear oncogenes c-Fos and c-Jun in carcinoma cells

BACKGROUND

c-Fos is a cellular proto-oncogene which dimerizes with c-Jun proto-oncogene to form AP-1 transcription factor, which upregulates transcription of genes involved in proliferation and cancer formation. Four cardiac hormones, that is, long-acting natriuretic peptide (LANP), vessel dilator, kaliuretic peptide (KP) and atrial natriuretic peptide (ANP) with anticancer effects in vivo are potent inhibitors of the Ras-MEK 1/2-ERK 1/2 kinase cascade and signal transducer and activator of transcription-3 (STAT-3) that activate c-Fos and c-Jun. These four cardiac hormones were investigated for their effects on proto-oncogenes c-Fos and c-Jun within the nucleus of cancer cells.

MATERIALS AND METHODS

Four cardiac hormones were evaluated for their ability to decrease proto-oncogenes c-Fos and c-Jun, measured by ELISA in extracted nuclei of three human cancer cell lines.

RESULTS

Vessel dilator, LANP, KP and ANP over a concentration range of 100 pM-10 μM, maximally decreased c-Fos by 61%, 60%, 61% and 59% in human hepatocellular cancer cells, by 82%, 74%, 78% and 74% in small-cell lung cancer cells, and by 82%, 73%, 78% and 74% in human renal adenocarcinoma cells. c-Jun was maximally reduced by vessel dilator, LANP, KP and ANP by 43%, 31%, 61% and 35% in hepatocellular cancer cells, by 65%, 49%, 59% and 40% in small-cell lung cancer cells, and by 47%, 43%, 57% and 49% in renal cancer cells.

CONCLUSION

Four cardiac hormones are potent inhibitors of c-Fos and c-Jun proto-oncogenes within the nucleus of cancer cells.

Cell-type and transcription factor specific enrichment of transcriptional cofactor motifs in ENCODE ChIP-seq data

Background

Cell type and TF specific interactions between Transcription Factors (TFs) and cofactors are essential for transcriptional regulation through recruitment of general transcription machinery to gene promoter regions and their identification heavily reliant on protein interaction assays.

Results

Using TF targeted chromatin immunoprecipitation coupled with massively parallel sequencing (ChIP-seq) data from Encyclopedia of DNA Elements (ENCODE), we report cell type and TF specific TF-cofactor interactions captured in vivo through enrichments of non target cofactor binding site motifs within ChIP-seq peaks. We observe enrichments in both known and novel cofactor motifs.

Conclusions

Given the regulatory implications which TF and cofactor interactions have on a cell's phenotype, their identification is necessary but challenging. Here we present the findings to our analyses surrounding the investigation of TF-cofactor interactions encoded within TF ChIP-seq peaks. Novel cofactor binding site enrichments observed provides valuable insight into TF and cell type specific interactions driving TF interactions.

Src kinases mediate the interaction of the apical determinant Bazooka/PAR3 with STAT92E and increase signalling efficiency in Drosophila ectodermal cells

Intercellular communication depends on the correct organization of the signal transduction complexes. In many signalling pathways, the mechanisms controlling the overall cell polarity also localize components of these pathways to different domains of the plasma membrane. In the Drosophila ectoderm, the JAK/STAT pathway components are highly polarized with apical localization of the receptor, the associated kinase and the STAT92E protein itself. The apical localization of STAT92E is independent of the receptor complex and is due to its direct association with the apical determining protein Bazooka (Baz). Here, we find that Baz-STAT92E interaction depends on the presence of the Drosophila Src kinases. In the absence of Src, STAT92E cannot bind to Baz in cells or in whole embryos, and this correlates with an impairment of JAK/STAT signalling function. We believe that the requirement of Src proteins for STAT92E apical localization is mediated through Baz, as we can co-precipitate Src with Baz but not with STAT92E. This is the first time that a functional link between cell polarity, the JAK/STAT signalling pathway and the Src kinases has been established in a whole organism.

Bacterial expression, purification, and crystallization of tyrosine phosphorylated STAT proteins

Signal Transducer and Activator of Transcription (STAT) proteins are latent cytoplasmic transcription -factors that become activated by phosphorylation at a C-terminal tyrosine residue. Upon activation STAT proteins translocate to the nucleus and bind to their specific target sites. Here, we describe the recombinant expression of tyrosine phosphorylated STAT proteins in bacteria. This method allows the production of large amounts of activated STAT proteins for structural and biochemical studies including the high-throughput screening of chemical libraries.

Oleic acid stimulates system A amino acid transport in primary human trophoblast cells mediated by toll-like receptor 4

Obese women have an increased risk to deliver large babies. However, the mechanisms underlying fetal overgrowth in these pregnancies are not well understood. Obese pregnant women typically have elevated circulating lipid levels. We tested the hypothesis that fatty acids stimulate placental amino acid transport, mediated via toll-like receptor 4 (TLR4) and mammalian target of rapamycin (mTOR) signaling pathways. Circulating NEFA levels and placental TLR4 expression were assessed in women with varying prepregnancy body mass index (BMI). The effects of oleic acid on system A and system L amino acid transport, and on the activation of the mTOR (4EBP1, S6K1, rpS6), TLR4 (IĸB, JNK, p38 MAPK), and STAT3 signaling pathways were determined in cultured primary human trophoblast cells. Maternal circulating NEFAs (n = 33), but not placental TLR4 mRNA expression (n = 16), correlated positively with BMI (P < 0.05). Oleic acid increased trophoblast JNK and STAT3 phosphorylation (P < 0.05), whereas mTOR activity was unaffected. Furthermore, oleic acid doubled trophoblast system A activity (P < 0.05), without affecting system L activity. siRNA-mediated silencing of TLR4 expression prevented the stimulatory effect of oleic acid on system A activity. Our data suggest that maternal fatty acids can increase placental nutrient transport via TLR4, thereby potentially affecting fetal growth.

BATF-JUN is critical for IRF4-mediated transcription in T cells

Interferon regulatory factor 4 (IRF4) is an IRF family transcription factor with critical roles in lymphoid development and in regulating the immune response^1,2. IRF4 binds DNA weakly due to a C-terminal auto-inhibitory domain, but cooperative binding with factors such as PU.1 or SPIB in B cells increases binding affinity³, allowing IRF4 to regulate genes containing ETS/IRF composite elements (EICEs; 5′-GGAAnnGAAA-3′)¹. Here, we show that in CD4⁺ T cells, where PU.1/SPIB expression is low, and in B cells, where PU.1 is well expressed, IRF4 unexpectedly can cooperate with Activator Protein-1 (AP-1) complexes to bind to AP-1/IRF4 composite (TGAnTCA/GAAA) motifs that we denote as AP-1/IRF composite elements (AICEs). Moreover, BATF/Jun family protein complexes cooperate with IRF4 in binding to AICEs in pre-activated CD4⁺ T cells stimulated with IL-21 and in Th17 differentiated cells. Importantly, BATF binding was diminished in Irf4^−/− T cells and IRF4 binding was diminished in Batf^−/− T cells, consistent with functional cooperation between these factors. Moreover, we show that AP-1 and IRF complexes cooperatively promote transcription of the Il10 gene, which is expressed in Th17 cells and potently regulated by IL-21. These findings reveal that IRF4 can signal via complexes containing ETS or AP-1 motifs depending on the cellular context, thus indicating new approaches for modulating IRF4-dependent transcription.