Simultaneous tyrosine and serine phosphorylation of STAT3 transcription factor is involved in Rho A GTPase oncogenic transformation

STAT3 phosphorylation at serine 727 activates specific genetic programs and promotes clear cell renal cell carcinoma (ccRCC) aggressiveness

The signal transducer and activator of transcription 3 (STAT3) is a transcription factor mainly activated by phosphorylation in either tyrosine 705 (Y705) or serine 727 (S727) residues that regulates essential processes such as cell differentiation, apoptosis inhibition, or cell survival. Aberrant activation of STAT3 has been related to development of nearly 50% of human cancers including clear cell renal cell carcinoma (ccRCC). In fact, phosho-S727 (pS727) levels correlate with overall survival of ccRCC patients. With the aim to elucidate the contribution of STAT3 phosphorylation in ccRCC development and progression, we have generated human-derived ccRCC cell lines carrying STAT3 Y705 and S727 phosphomutants. Our data show that the phosphomimetic substitution Ser727Asp facilitates a pro-tumoral phenotype in vitro, in a Y705-phosphorylation-independent manner. Moreover, we describe that STAT3 phosphorylation state determines the expression of different subsets of target genes associated with distinct biological processes, being pS727-dependent genes the most related to cellular hallmarks of cancer. In summary, the present study constitutes the first analysis on the role of overall STAT3 phosphorylation state in ccRCC and demonstrates that pS727 promotes the expression of a specific subset of target genes that might be clinically relevant as novel biomarkers and potential therapeutic targets for ccRCC.

Janus kinase inhibitors are potential therapeutics for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a poorly treated multifactorial neurodegenerative disease associated with multiple cell types and subcellular organelles. As with other multifactorial diseases, it is likely that drugs will need to target multiple disease processes and cell types to be effective. We review here the role of Janus kinase (JAK)/Signal transducer and activator of transcription (STAT) signalling in ALS, confirm the association of this signalling with fundamental ALS disease processes using the BenevolentAI Knowledge Graph, and demonstrate that inhibitors of this pathway could reduce the ALS pathophysiology in neurons, glia, muscle fibres, and blood cells. Specifically, we suggest that inhibition of the JAK enzymes by approved inhibitors known as Jakinibs could reduce STAT3 activation and modify the progress of this disease. Analysis of the Jakinibs highlights baricitinib as a suitable candidate due to its ability to penetrate the central nervous system and exert beneficial effects on the immune system. Therefore, we recommend that this drug be tested in appropriately designed clinical trials for ALS.

Subcellular location defines GPCR signal transduction

Intracellular G protein-coupled receptors (GPCRs) can be activated by permeant ligands, which contributes to agonist selectivity. Opioid receptors (ORs) provide a notable example, where opioid drugs rapidly activate ORs in the Golgi apparatus. Our knowledge on intracellular GPCR function remains incomplete, and it is unknown whether OR signaling in plasma membrane (PM) and Golgi apparatus differs. Here, we assess the recruitment of signal transducers to mu- and delta-ORs in both compartments. We find that Golgi ORs couple to Gαi/o probes and are phosphorylated but, unlike PM receptors, do not recruit β-arrestin or a specific Gα probe. Molecular dynamics simulations with OR-transducer complexes in bilayers mimicking PM or Golgi composition reveal that the lipid environment promotes the location-selective coupling. We then show that delta-ORs in PM and Golgi have distinct effects on transcription and protein phosphorylation. The study reveals that the subcellular location defines the signaling effects of opioid drugs.

Quantitative Proteomic Analysis Reveals the Mechanisms of Sinapine Alleviate Macrophage Foaming

Rapeseed polyphenols have cardiovascular protective effects. Sinapine, one main rapeseed polyphenol, possesses antioxidative, anti-inflammatory, and antitumor properties. However, no research has been published about the role of sinapine in alleviating macrophage foaming. This study aimed to reveal the macrophage foaming alleviation mechanism of sinapine by applying quantitative proteomics and bioinformatics analyses. A new approach was developed to retrieve sinapine from rapeseed meals by using hot-alcohol-reflux-assisted sonication combined with anti-solvent precipitation. The sinapine yield of the new approach was significantly higher than in traditional methods. Proteomics was performed to investigate the effects of sinapine on foam cells, and it showed that sinapine can alleviate foam cell formation. Moreover, sinapine suppressed CD36 expression, enhanced the CDC42 expression, and activated the JAK2 and the STAT3 in the foam cells. These findings suggest that the action of sinapine on foam cells inhibits cholesterol uptake, activates cholesterol efflux, and converts macrophages from pro-inflammatory M1 to anti-inflammatory M2. This study confirms the abundance of sinapine in rapeseed oil by-products and elucidates the biochemical mechanisms of sinapine that alleviates macrophage foaming, which may provide new perspectives for reprocessing rapeseed oil by-products.

Downregulation of CYRI-B promotes migration, invasion and EMT by activating the Rac1-STAT3 pathway in gastric cancer

BACKGROUND

CYRI-B plays key roles in regulating cell motility in nontumor cells. However, the role and function of CYRI-B have rarely been studied in cancer cells, including gastric cancer. The purpose of this study was to investigate the clinical significance, biological function and underlying molecular mechanism of CYRI-B in gastric cancer.

METHOD

CYRI-B protein levels were detected by immunohistochemistry (IHC) and western blotting (WB). Gastric cancer cells and organoid models were evaluated to explore the correlation of CYRI-B with collagen type I. The function of CYRI-B in proliferation, migration, invasion in gastric cancer was evaluated by in vitro and in vivo experiments.

RESULT

CYRI-B protein levels were downregulated in gastric cancer. Low expression of CYRI-B was related to later tumor stage and poorer prognosis. CYRI-B expression was reduced when cells were cultured in collagen type I, which was mediated by collagen receptor DDR1. Knockdown of CYRI-B promoted migration, invasion and EMT in vivo and in vitro. Mechanistically, knockdown of CYRI-B activated the Rac1-STAT3 pathway.

CONCLUSION

Our findings showed that CYRI-B plays an important role in the tumor microenvironment, and is associated with malignant characteristics acquired by gastric cancer. This study may provide new targets for future therapeutic interventions for tumor metastasis.

Activation of STAT3 through combined SRC and EGFR signaling drives resistance to a mitotic kinesin inhibitor in glioblastoma

Inhibitors of the mitotic kinesin Kif11 are anti-mitotics that, unlike vinca alkaloids or taxanes, do not disrupt microtubules and are not neurotoxic. However, development of resistance has limited their clinical utility. While resistance to Kif11 inhibitors in other cell types is due to mechanisms that prevent these drugs from disrupting mitosis, we find that in glioblastoma (GBM), resistance to the Kif11 inhibitor ispinesib works instead through suppression of apoptosis driven by activation of STAT3. This form of resistance requires dual phosphorylation of STAT3 residues Y705 and S727, mediated by SRC and epidermal growth factor receptor (EGFR), respectively. Simultaneously inhibiting SRC and EGFR reverses this resistance, and combined targeting of these two kinases in vivo with clinically available inhibitors is synergistic and significantly prolongs survival in ispinesib-treated GBM-bearing mice. We thus identify a translationally actionable approach to overcoming Kif11 inhibitor resistance that may work to block STAT3-driven resistance against other anti-cancer therapies as well.

The chromosome 21 kinase DYRK1A: emerging roles in cancer biology and potential as a therapeutic target

Dual-specificity tyrosine phosphorylation-regulated kinase 1 A (DYRK1A) is a serine/threonine kinase that belongs to the DYRK family of proteins, a subgroup of the evolutionarily conserved CMGC protein kinase superfamily. Due to its localization on chromosome 21, the biological significance of DYRK1A was initially characterized in the pathogenesis of Down syndrome (DS) and related neurodegenerative diseases. However, increasing evidence has demonstrated a prominent role in cancer through its ability to regulate biologic processes including cell cycle progression, DNA damage repair, transcription, ubiquitination, tyrosine kinase activity, and cancer stem cell maintenance. DYRK1A has been identified as both an oncogene and tumor suppressor in different models, underscoring the importance of cellular context in its function. Here, we review mechanistic contributions of DYRK1A to cancer biology and its role as a potential therapeutic target.

Regulation of STAT3 and its role in cardioprotection by conditioning: focus on non-genomic roles targeting mitochondrial function

Ischemia–reperfusion injury (IRI) is one of the biggest challenges for cardiovascular researchers given the huge death toll caused by myocardial ischemic disease. Cardioprotective conditioning strategies, namely pre- and post-conditioning maneuvers, represent the most important strategies for stimulating pro-survival pathways essential to preserve cardiac health. Conditioning maneuvers have proved to be fundamental for the knowledge of the molecular basis of both IRI and cardioprotection. Among this evidence, the importance of signal transducer and activator of transcription 3 (STAT3) emerged. STAT3 is not only a transcription factor but also exhibits non-genomic pro-survival functions preserving mitochondrial function from IRI. Indeed, STAT3 is emerging as an influencer of mitochondrial function to explain the cardioprotection phenomena. Studying cardioprotection, STAT3 proved to be crucial as an element of the survivor activating factor enhancement (SAFE) pathway, which converges on mitochondria and influences their function by cross-talking with other cardioprotective pathways. Clearly there are still some functional properties of STAT3 to be discovered. Therefore, in this review, we highlight the evidence that places STAT3 as a promoter of the metabolic network. In particular, we focus on the possible interactions of STAT3 with processes aimed at maintaining mitochondrial functions, including the regulation of the electron transport chain, the production of reactive oxygen species, the homeostasis of Ca²⁺ and the inhibition of opening of mitochondrial permeability transition pore. Then we consider the role of STAT3 and the parallels between STA3/STAT5 in cardioprotection by conditioning, giving emphasis to the human heart and confounders.

RhoGTPase Signalling in Cancer Progression and Dissemination

Rho GTPases are a family of small G proteins that regulate a wide array of cellular processes related to their key roles controlling the cytoskeleton. On the other hand, cancer is a multi-step disease caused by the accumulation of genetic mutations and epigenetic alterations, from the initial stages of cancer development when cells in normal tissues undergo transformation, to the acquisition of invasive and metastatic traits, responsible for a large number of cancer related deaths. In this review, we discuss the role of Rho GTPase signalling in cancer in every step of disease progression. Rho GTPases contribute to tumour initiation and progression, by regulating proliferation and apoptosis, but also metabolism, senescence and cell stemness. Rho GTPases play a major role in cell migration, and in the metastatic process. They are also involved in interactions with the tumour microenvironment and regulate inflammation, contributing to cancer progression. After years of intensive research, we highlight the importance of relevant models in the Rho GTPase field, and we reflect on the therapeutic opportunities arising for cancer patients.

Proteogenomic characterization of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive cancer with poor patient survival. Toward understanding the underlying molecular alterations that drive PDAC oncogenesis, we conducted comprehensive proteogenomic analysis of 140 pancreatic cancers, 67 normal adjacent tissues, and 9 normal pancreatic ductal tissues. Proteomic, phosphoproteomic, and glycoproteomic analyses were used to characterize proteins and their modifications. In addition, whole-genome sequencing, whole-exome sequencing, methylation, RNA sequencing (RNA-seq), and microRNA sequencing (miRNA-seq) were performed on the same tissues to facilitate an integrated proteogenomic analysis and determine the impact of genomic alterations on protein expression, signaling pathways, and post-translational modifications. To ensure robust downstream analyses, tumor neoplastic cellularity was assessed via multiple orthogonal strategies using molecular features and verified via pathological estimation of tumor cellularity based on histological review. This integrated proteogenomic characterization of PDAC will serve as a valuable resource for the community, paving the way for early detection and identification of novel therapeutic targets.

Activation of STAT transcription factors by the Rho-family GTPases

The Rho-family of small GTPases are biological molecular switches that are best known for their regulation of the actin cytoskeleton. Through their activation and stimulation of downstream effectors, the Rho-family control pathways involved in cellular morphology, which are commonly activated in cancer cell invasion and metastasis. While this makes them excellent potential therapeutic targets, a deeper understanding of the downstream signalling pathways they influence will be required for successful drug targeting. Signal transducers and activators of transcription (STATs) are a family of transcription factors that are hyper-activated in most cancer types and while STATs are widely understood to be activated by the JAK family of kinases, many additional activators have been discovered. A growing number of examples of Rho-family driven STAT activation, largely of the oncogenic family members, STAT3 and STAT5, are being identified. Cdc42, Rac1, RhoA, RhoC and RhoH have all been implicated in STAT activation, contributing to Rho GTPase-driven changes in cellular morphology that lead to cell proliferation, invasion and metastasis. This highlights the importance and therapeutic potential of the Rho-family as regulators of non-canonical activation of STAT signalling.

Nuclear and cytosolic pS727-STAT3 levels correlate with overall survival of patients affected by clear cell renal cell carcinoma (ccRCC)

Clear cell renal cell carcinoma (ccRCC) is the most frequent and aggressive subtype of renal carcinoma. So far, the basis of its oncogenesis remains unclear resulting in a deficiency of usable and reliable biomarkers for its clinical management. Previously, we showed that nuclear expression of the signal transducer and activator of transcription 3 (STAT3), phosphorylated at its serine 727 (pS727), was inversely proportional to the overall survival of ccRCC patients. Therefore, in the present study, we validated the value of pS727-STAT3 as a clinically relevant biomarker in ccRCC. This work is a retrospective study on 82 ccRCC patients treated with nephrectomy and followed-up for 10 years. Immunohistochemical expression of pS727-STAT3 was analyzed on a tissue microarray and nuclear and cytosolic levels were correlated with clinical outcome of patients. Our results showed that pS727-STAT3 levels, whether in the nucleus (p = 0.002; 95% CI 1.004-1.026) or the cytosol (p = 0.040; 95% CI 1.003-1.042), significantly correlate with patients' survival in an independent-manner of clinicopathological features (Fuhrman grade, risk group, and tumor size). Moreover, we report that patients with high pS727-STAT3 levels who undergone adjuvant therapy exhibited a significant stabilization of the disease (~ 20 months), indicating that pS727-STAT3 can pinpoint a subset of patients susceptible to respond well to treatment. In summary, we demonstrated that high pS727-STAT3 levels (regardless of their cellular location) correlate with low overall survival of ccRCC patients, and we suggested the use of pS727-STAT3 as a prognostic biomarker to select patients for adjuvant treatment to increase their survival.

The Mevalonate Pathway, a Metabolic Target in Cancer Therapy

A hallmark of cancer cells includes a metabolic reprograming that provides energy, the essential building blocks, and signaling required to maintain survival, rapid growth, metastasis, and drug resistance of many cancers. The influence of tumor microenviroment on cancer cells also results an essential driving force for cancer progression and drug resistance. Lipid-related enzymes, lipid-derived metabolites and/or signaling pathways linked to critical regulators of lipid metabolism can influence gene expression and chromatin remodeling, cellular differentiation, stress response pathways, or tumor microenviroment, and, collectively, drive tumor development. Reprograming of lipid metabolism includes a deregulated activity of mevalonate (MVA)/cholesterol biosynthetic pathway in specific cancer cells which, in comparison with normal cell counterparts, are dependent of the continuous availability of MVA/cholesterol-derived metabolites (i.e., sterols and non-sterol intermediates) for tumor development. Accordingly, there are increasing amount of data, from preclinical and epidemiological studies, that support an inverse association between the use of statins, potent inhibitors of MVA biosynthetic pathway, and mortality rate in specific cancers (e.g., colon, prostate, liver, breast, hematological malignances). In contrast, despite the tolerance and therapeutic efficacy shown by statins in cardiovascular disease, cancer treatment demands the use of relatively high doses of single statins for a prolonged period, thereby limiting this therapeutic strategy due to adverse effects. Clinically relevant, synergistic effects of tolerable doses of statins with conventional chemotherapy might enhance efficacy with lower doses of each drug and, probably, reduce adverse effects and resistance. In spite of that, clinical trials to identify combinatory therapies that improve therapeutic window are still a challenge. In the present review, we revisit molecular evidences showing that deregulated activity of MVA biosynthetic pathway has an essential role in oncogenesis and drug resistance, and the potential use of MVA pathway inhibitors to improve therapeutic window in cancer.

Acetylation-dependent glutamate receptor GluR signalosome formation for STAT3 activation in both transcriptional and metabolism regulation

Besides their original regulating roles in the brain, spinal cord, retina, and peripheral nervous system for mediating fast excitatory synaptic transmission, glutamate receptors consisting of metabotropic glutamate receptors (GluRs) and ionotropic glutamate receptors (iGluRs) have emerged to have a critical role in the biology of cancer initiation, progression, and metastasis. However, the precise mechanism underpinning the signal transduction mediated by ligand-bound GluRs is not clearly elucidated. Here, we show that iGluRs, GluR1 and GluR2, are acetylated by acetyltransferase CREB-binding protein upon glutamate stimulation of cells, and are targeted by lysyl oxidase-like 2 for deacetylation. Acetylated GluR1/2 recruit β-arrestin1/2 and signal transducer and activator of transcription 3 (STAT3) to form a protein complex. Both β-arrestin1/2 and STAT3 are subsequently acetylated and activated. Simultaneously, activated STAT3 acetylated at lysine 685 translocates to mitochondria to upregulate energy metabolism-related gene transcription. Our results reveal that acetylation-dependent formation of GluR1/2-β-arrestin1/2-STAT3 signalosome is critical for glutamate-induced cell proliferation.

ARHGAP6 Promotes Apoptosis and Inhibits Glycolysis in Lung Adenocarcinoma Through STAT3 Signaling Pathway

Objective

Constitutively activated signal transducer and activator of transcription 3 (STAT3) has been linked to cisplatin (DDP)-resistance in a wide range of cancers. Recent work has indicated that Rho GTPase-activating protein 6 (ARHGAP6) promotes cell cycle arrest and apoptosis in cervical and breast cancers. However, the role of ARHGAP6 in lung adenocarcinoma and DDP-resistance remains unknown.

Materials and Methods

Bioinformatic analysis, quantitative RT-PCR and IHC staining were used to explore ARHGAP6 expression patterns in The Cancer Genome Atlas (TCGA) dataset and patient samples. Statistical analysis was performed to establish the association of ARHGAP6 expression with the resistance to DDP-based chemotherapy in lung adenocarcinoma patients. Functional assays were then conducted to examine the effect of ARHGAP6 on the apoptosis and glycolysis in DDP-resistant/sensitive A549/DPP cells in vitro. Finally, the effects of ARHGAP6 on the chemosensitivity of DDP were explored in vivo.

Results

We show that decreased ARHGAP6 levels are a reliable marker of lung adenocarcinoma across published datasets, cell culture lines, and clinical samples. Low ARHGAP6 expression was linked to decreased apoptosis and increased metabolic activity, which highlights ARHGAP6’s role as a tumor suppressor. Furthermore, activated p-STAT3 levels increased dramatically in the absence of ARHGAP6, which suggests that ARHGAP6 can inhibit the STAT3 pathway. In agreement with previous studies that linked p-STAT3 levels to DDP-resistance, our in vitro and in vivo data indicate that tumors became more resistant to DDP-therapy with reduced ARHGAP6 levels and an associated increase in p-STAT3.

Conclusion

ARHGAP6 presents a novel study target for overcoming p-STAT3-associated DDP-resistance in lung adenocarcinoma and potentially other cancers.

Maresin1 ameliorates sepsis-associated lung injury by inhibiting the activation of the JAK2/STAT3 and MAPK/ NF-κB signaling pathways

Sepsis-associated acute lung injury (ALI) is a clinically critical disease that carries a high mortality rate. The pathogenesis of sepsis-associated ALI has not yet been precisely elucidated and there is a lack of effective treatment. As a new endogenous docosahexaenoic acid (DHA)-derived lipid mediators, Maresin1 has a significant dual role of anti-inflammatory and promoting inflammation regression. In this study, we established the sepsis model by the cecal ligation and puncture method (CLP) to explore the effect of Maresin1 on sepsis-induced lung injury. We found that the intervention of Maresin1 could significantly attenuate the sepsis-induced inflammatory responses, characterized by the down-regulation of the level of IL-1β, IL-6, TNF-α, MPO, etc. Maresin1 could also significantly decrease the number of neutrophils in lung tissue, thus improving the related lung injury indicators. Our experiment clarified that the protective effect of Maresin1 on sepsis-associated lung injury is closely related to its inhibition function of JAK2/STAT3 and MAPK/NF-κB signaling pathways. Our findings provide new research directions and therapeutic targets for sepsis-associated ALI.

Catecholamines suppress fatty acid re-esterification and increase oxidation in white adipocytes via STAT3

Catecholamines stimulate the mobilization of stored triglycerides in adipocytes to provide fatty acids (FAs) for other tissues. However, a large proportion is taken back up and either oxidized or re-esterified. What controls the disposition of these FAs in adipocytes remains unknown. Here, we report that catecholamines redirect FAs for oxidation through the phosphorylation of signal transducer and activator of transcription 3 (STAT3). Adipocyte STAT3 is phosphorylated upon activation of β-adrenergic receptors, and in turn suppresses FA re-esterification to promote FA oxidation. Adipocyte-specific Stat3 KO mice exhibit normal rates of lipolysis, but exhibit defective lipolysis-driven oxidative metabolism, resulting in reduced energy expenditure and increased adiposity when they are on a high-fat diet. This previously unappreciated, non-genomic role of STAT3 explains how sympathetic activation can increase both lipolysis and FA oxidation in adipocytes, revealing a new regulatory axis in metabolism.

G721-0282 inhibits cell growth and induces apoptosis in human osteosarcoma through down-regulation of the STAT3 pathway

Osteosarcoma (OS) is considered the most common type of primary malignant bone tumor, which has an urgent need for more effective treatment. Recently, chitinase 3 like 1 (Chi3L1) expression has been found in a variety of cancer cells. However it is not known whether Chi3L1 regulates the STAT3 pathway in OS cells. Herein, we examined the effects of the G721-0282, a ligand of Chi3L1, in vitro and in vivo against OS cells. G721-0282 inhibited the proliferation of OS cells and induced apoptosis. This apoptosis was accompanied by upregulation of apoptotic proteins (PARP and procaspase-3), but downregulation of anti-apoptotic proteins (Survivin and Bcl-2). G721-0282 induced the inactivation of mitogen-activated protein kinases (MAPKs) with a decrease in the phosphorylation of Src and STAT3 in OS cells. Importantly, overexpression of Chi3L1 potentiated the effects of G721-0282, while knockdown of Chi3L1 attenuated the effects of G721-0282. Docking model study also showed that G721-0282 interacted with Chi3L1. In addition, G721-0282 inhibited cell migration, invasion, and colony formation. Furthermore, the anti-tumor effects of G721-0282 were observed in an xenograft in vivo model in association with the reduced expression of Chi3L1, PCNA, Cyclin D1, p-STAT3, as well as the increased expression of Chi3L1 was correlated with the p-STAT3 level in human bone tumor tissues. Taken together, a Chi3L1 ligand, G721-0282 may be an attractive therapeutic strategy for OS, especially in vitro and in vivo anti-proliferative effects against OS cells through the inhibition of the STAT3 pathway, and suggest the potentially therapeutic application of G721-0282 in the treatment of OS.

The Dichotomous Nature of AZ5104 (an EGFR Inhibitor) Towards RORγ and RORγT

The RORC (RAR related orphan receptor C) gene produces two isoforms by alternative promoter usage: RORγ (nuclear receptor ROR-gamma isoform 1) and RORγT (nuclear receptor ROR-gamma isoform 1). Both proteins have distinct tissue distributions and are involved in several physiological processes, including glucose/lipid metabolism and the development of Th17 lymphocytes. Previously, we developed a stably transfected reporter cell line and used it to screen a library of kinase inhibitors. We found that AZ5104 acts as an RORγ agonist at low micromolar concentrations. Molecular docking analysis showed that this compound occupies the ligand binding domain of the receptor with a significant docking score. However, analysis of the biological activity of this compound in Th17 cells revealed that it downregulates RORγT expression and Th17-related cytokine production via inhibition of SRC-ERK-STAT3 (SRC proto-oncogene - extracellular regulated MAP kinase - signal transducer and activator of transcription 3). We thus identified a compound acting as an agonist of RORγ that, due to the inhibition of downstream elements of EGFR (epidermal growth factor receptor) signaling, exerts different biological activity towards a Th17-specific isoform. Additionally, our results may be relevant in the future for the design of treatments targeting signaling pathways that inhibit Th17-related inflammation in certain autoimmune disorders.

Discovery of fluorescent coumarin-benzo[b]thiophene 1, 1-dioxide conjugates as mitochondria-targeting antitumor STAT3 inhibitors

STAT3 has been extensively studied as a potential antitumor target. Though studies on regulating STAT3 mainly focus on the inhibition of STAT3 phosphorylation at Tyr705 residue, the phosphorylation at Ser727 residue of STAT3 protein is also closely associated with the mitochondrial import of STAT3 protein. N, N-diethyl-7-aminocoumarin is a fluorescent mitochondria-targeting probe. In this study, a series of STAT3 inhibitors were developed by connecting N, N-diethyl-7-aminocoumarin fluorophore with benzo [b]thiophene 1, 1-dioxide moiety. All designed compounds displayed potent anti-proliferative activity against cancer cells. The representative compound 7a was mainly accumulated in mitochondria visualized by its fluorescence. STAT3 phosphorylation was inhibited by compound 7a at both Tyr705 and Ser727 residues. Compound 7a inhibited STAT3 phosphorylation whereas had no influence on the phosphorylation levels of STAT1, JAK2, Src and Erk1/2, indicating good selectivity of compound 7a. Moreover, compound 7a down-regulated the expression of STAT3 target genes Bcl-2 and Cyclin D1, increased ROS production and remarkably reduced the mitochondrial membrane potential to induce mitochondrial apoptotic pathway. Furthermore, compound 7ain vivo suppressed breast cancer 4T1 implanted tumor growth. Taken together, these results highlighted that compound 7a might be a promising mitochondria-targeting STAT3 inhibitor for cancer therapy.

Dehydroepiandrosterone attenuates pulmonary artery and right ventricular remodeling in a rat model of pulmonary hypertension due to left heart failure

AIM

Pulmonary hypertension due to left heart failure (PH-LHF) is the most common cause of pulmonary hypertension. However, therapies for PH-LHF are lacking. Therefore, we investigated the effects and potential mechanism of dehydroepiandrosterone (DHEA) treatment in an experimental model of PH-LHF.

MAIN METHOD

PH-LHF was induced in rats via ascending aortic banding. The rats then received daily DHEA from Day 1 to Day 63 for the prevention protocol or from Day 49 to Day 63 for the reversal protocol. Other ascending aortic banding rats were left untreated to allow development of PH and right ventricular (RV) failure. Sham ascending aortic banding rats served as controls.

KEY FINDING

Significant increases in mean pulmonary arterial pressure (mPAP) and right ventricular end-diastolic diameter (RVEDD) were observed in the PH-LHF group. Therapy with DHEA prevented LHF-induced PH and RV failure by preserving mPAP and preventing RV hypertrophy and pulmonary artery remodeling. In preexisting severe PH, DHEA attenuated most lung and RV abnormalities. The beneficial effects of DHEA in PH-LHF seem to result from depression of the STAT3 signaling pathway in the lung.

SIGNIFICANT

DHEA not only prevents the development of PH-LHF and RV failure but also rescues severe preexisting PH-LHF.

Rho GTPase Activating Protein 24 (ARHGAP24) Regulates the Anti-Cancer Activity of Sorafenib Against Breast Cancer MDA-MB-231 Cells via the Signal Transducer and Activator of Transcription 3 (STAT3) Signaling Pathway

BACKGROUND STAT3 has emerged as a novel potential target for sorafenib, a multikinase inhibitor, in the context of cancer therapy. ARHGAP24 is a Rac-specific Rho GTPase-activating protein (Rho GAP), which can convert Rho GTPases to an inactive state. It has been proved to be an oncosuppressor protein in renal cancer. In the present study, we investigated its anti-cancer effect in breast cancer (BC). MATERIAL AND METHODS Quantitative real-time PCR (qRT-PCR) and Western blot analysis were performed to detect the expression of ARHGAP24 in clinical tissue samples. Then, BC MDA-MB-231 cells were virally transduced with ARHGAP24 silencing or overexpression lentiviral vectors in the absence or presence of sorafenib. Cell viability and metastatic ability were evaluated by using the Cell Counting Kit-8 (CCK-8) and Transwell assays. Proteins belonging to the STAT3 pathway were detected by Western blot. RESULTS ARHGAP24 decreased in BC tissues compared with the adjacent normal tissues. Forced expression of ARHGAP24 and sorafenib treatment significantly suppressed the viability, migration, and invasion of MDA-MB-231 cells. Conversely, elimination of the endogenous ARHGAP24 with shRNA promoted cell viability, migration, and invasion. The phosphorylation of STAT3 and the expression of MMP-2 and MMP-9 were attenuated by ARHGAP24 ectopic expression and sorafenib treatment. Furthermore, forced expression of ARHGAP24 significantly enhanced sorafenib-induced decrease of cell viability, migration, and invasion of MDA-MB-231 cells, while elimination of the endogenous ARHGAP24 with shRNA inhibited it. CONCLUSIONS ARHGAP24 can suppress the development of MDA-MB-231 cells via the STAT3 signaling pathway, and sorafenib inhibits cell viability, migration, invasion, and STAT3 activation in MDA-MB-231 cells through ARHGAP24.

Nucleus, Mitochondrion, or Reticulum? STAT3 à La Carte

The transcription factor signal transducer and activator of transcription (STAT)3 mediates the functions of cytokines, growth factors, and oncogenes under both physiological and pathological conditions. Uncontrolled/constitutive STAT3 activity is often detected in tumors of different types, where its role is mostly that of an oncogene, contributing in multiple ways to tumor transformation, growth, and progression. For this reason, many laboratories and pharmaceutical companies are making efforts to develop specific inhibitors. However, STAT3 has also been shown to act as a tumor suppressor in a number of cases, suggesting that its activity is strongly context-specific. Here, we discuss the bases that can explain the multiple roles of this factor in both physiological and pathological contexts. In particular, we focus on the following four features: (i) the distinct properties of the STAT3α and β isoforms; (ii) the multiple post-translational modifications (phosphorylation on tyrosine or serine, acetylation and methylation on different residues, and oxidation and glutathionylation) that can affect its activities downstream of multiple different signals; (iii) the non-canonical functions in the mitochondria, contributing to the maintenance of energy homeostasis under stress conditions; and (iv) the recently discovered functions in the endoplasmic reticulum, where STAT3 contributes to the regulation of calcium homeostasis, energy production, and apoptosis.

ATM Is Required for the Prolactin-Induced HSP90-Mediated Increase in Cellular Viability and Clonogenic Growth After DNA Damage

Prolactin (PRL) acts as a survival factor for breast cancer cells, but the PRL signaling pathway and the mechanism are unknown. Previously, we identified the master chaperone, heat shock protein 90 (HSP90) α, as a prolactin-Janus kinase 2 (JAK2)-signal transducer and activator of transcription 5 (STAT5) target gene involved in survival, and here we investigated the role of HSP90 in the mechanism of PRL-induced viability in response to DNA damage. The ataxia-telangiectasia mutated kinase (ATM) protein plays a critical role in the cellular response to double-strand DNA damage. We observed that PRL increased viability of breast cancer cells treated with doxorubicin or etoposide. The increase in cellular resistance is specific to the PRL receptor, because the PRL receptor antagonist, Δ1-9-G129R-hPRL, prevented the increase in viability. Two different HSP90 inhibitors, 17-allylamino-17-demethoxygeldanamycin and BIIB021, reduced the PRL-mediated increase in cell viability of doxorubicin-treated cells and led to a decrease in JAK2, ATM, and phosphorylated ATM protein levels. Inhibitors of JAK2 (G6) and ATM (KU55933) abolished the PRL-mediated increase in cell viability of DNA-damaged cells, supporting the involvement of each, as well as the crosstalk of ATM with the PRL pathway in the context of DNA damage. Drug synergism was detected between the ATM inhibitor (KU55933) and doxorubicin and between the HSP90 inhibitor (BIIB021) and doxorubicin. Short interfering RNA directed against ATM prevented the PRL-mediated increase in cell survival in two-dimensional cell culture, three-dimensional collagen gel cultures, and clonogenic cell survival, after doxorubicin treatment. Our results indicate that ATM contributes to the PRL-JAK2-STAT5-HSP90 pathway in mediating cellular resistance to DNA-damaging agents.

RhoE/ROCK2 regulates chemoresistance through NF-κB/IL-6/ STAT3 signaling in hepatocellular carcinoma

Small Rho GTPase (Rho) and its immediate effector Rho kinase (ROCK) are reported to regulate cell survival, but the detailed molecular mechanism remains largely unknown. We had previously shown that Rho/ROCK signaling was highly activated in hepatocellular carcinoma (HCC). In this study, we further demonstrated that downregulation of RhoE, a RhoA antagonist, and upregulation of ROCK enhanced resistance to chemotherapy in HCC in both in vitro cell and in vivo murine xenograft models, whereas a ROCK inhibitor was able to profoundly sensitize HCC tumors to cisplatin treatment. Specifically, the ROCK2 isoform but not ROCK1 maintained the chemoresistance in HCC cells. Mechanistically, we demonstrated that activation of ROCK2 enhanced the phosphorylation of JAK2 and STAT3 through increased expression of IL-6 and the IL-6 receptor complex. We also identified IKKβ as the direct downstream target of Rho/ROCK, and activation of ROCK2 significantly augmented NF-κB transcription activity and induced IL-6 expression. These data indicate that Rho/ROCK signaling activates a positive feedback loop of IKKβ/NF-κB/IL-6/STAT3 which confers chemoresistance to HCC cells and is a potential molecular target for HCC therapy.

TYK2-induced phosphorylation of Y640 suppresses STAT3 transcriptional activity

STAT3 is a pleiotropic transcription factor involved in homeostatic and host defense processes in the human body. It is activated by numerous cytokines and growth factors and generates a series of cellular effects. Of the STAT-mediated signal transduction pathways, STAT3 transcriptional control is best understood. Jak kinase dependent activation of STAT3 relies on Y705 phosphorylation triggering a conformational switch that is stabilized by intermolecular interactions between SH2 domains and the pY705 motif. We here show that a second tyrosine phosphorylation within the SH2 domain at position Y640, induced by Tyk2, negatively controls STAT3 activity. The Y640F mutation leads to stabilization of activated STAT3 homodimers, accelerated nuclear translocation and superior transcriptional activity following IL-6 and LIF stimulation. Moreover, it unlocks type I IFN-dependent STAT3 signalling in cells that are normally refractory to STAT3 transcriptional activation.

STAT3 in cancer: A double edged sword

The transcription factor signal transducer and activator of transcription (STAT) 3 is activated downstream of cytokines, growth factors and oncogenes to mediate their functions under both physiological and pathological conditions. In particular, aberrant/unrestrained STAT3 activity is detected in a wide variety of tumors, driving multiple pro-oncogenic functions. For that, STAT3 is widely considered as an oncogene and is the object of intense translational studies. One of the distinctive features of this factor is however, its ability to elicit different and sometimes contrasting effects under different conditions. In particular, STAT3 activities have been shown to be either pro-oncogenic or tumor-suppressive according to the tumor aetiology/mutational landscape, suggesting that the molecular bases underlining its functions are still incompletely understood. Here we discuss some of the properties that may provide the bases to explain STAT3 heterogeneous functions, and in particular how post-translational modifications contribute shaping its sub-cellular localization and activities, the cross talk between these activities and cell metabolic conditions, and finally how its functions can control the behaviour of both tumor and tumor microenvironment cell populations.

Isoliquiritigenin inhibits the proliferation of human renal carcinoma Caki cells through the ROS-mediated regulation of the Jak2/STAT3 pathway

Isoliquiritigenin (ISL) is a flavonoid with chalcone structure that has been noted in licorice and shallot, which are generally used in traditional Chinese medicine. ISL has demonstrated various pharmacological effects including antioxidant, anti-inflammatory and antitumor activity. However, the molecular mechanisms underlying the anticancer effects of ISL remain poorly understood. The present study revealed that ISL significantly decreased viability and induced apoptosis in human renal carcinoma Caki cells. The ISL-induced apoptosis was associated with the cleavage of caspase-9, -7 and -3, and that of PARP. Moreover, ISL increased the expression of pro-apoptotic protein Bax and diminished the expression of anti-apoptotic protein Bcl-2, and Bcl-xl, thereby increasing cytochrome c release. Treatment of cells with ISL also induced the expression of p53 through downregulation of murine double minute 2 (Mdm2). Furthermore, ISL generated reactive oxygen species (ROS), and pretreatment with ROS scavenger N-acetyl cysteine (NAC) and NADPH oxidase inhibitor diphenyleneiodonium abrogated the ISL-induced apoptosis. One of the key oncogenic signaling pathways is mediated through signal transducer and activator of transcription 3 (STAT3), which promotes abnormal cell proliferation. Incubation of cells with ISL markedly diminished phosphorylation and DNA binding activity of STAT3, and reduced expression of STAT3 responsive gene products, such as cyclin D1 and D2. ISL also attenuated constitutive phosphorylation of upstream kinase, Janus-activated kinase 2 (Jak2). Pretreatment with NAC abrogated the inhibitory effect of ISL on activation of STAT3 and blocked the cleavage of caspase-9, -7 and -3, and that of PARP in Caki cells. Taken together, the present study provides the first report that ISL induces apoptosis in Caki cells via generation of ROS, which causes induction of p53 and inhibition of the STAT3 signaling pathway.

A novel STAT3 inhibitor negatively modulates platelet activation and aggregation

The signal transducer and activator of transcription 3 (STAT3) plays a critical role in platelet functions. This study sought to understand the effects of the STAT3 inhibitor SC99 on platelet activation and aggregation. Immunoblotting assays were applied to measure the effects of SC99 on the STAT3 signaling pathway. A ChronoLog aggregometer was used to evaluate platelet aggregation. A flow cytometer was used to evaluate P-selectin expression in the presence of SC99. AlamarBlue and Annexin-V staining were used to evaluate platelet viability and apoptosis, respectively. A fluorescence microscope was applied to analyze platelet spreading. SC99 inhibited the phosphorylation of JAK2 and STAT3 in human platelets but had no effects on the phosphorylation of AKT, p65 or Src, all of which are involved in platelet activation. Further studies revealed that SC99 inhibited human platelet aggregation induced by collagen and thrombin in a dose-dependent manner. SC99 inhibited thrombin-induced P-selectin expression and fibrinogen binding to single platelets. Moreover, SC99 inhibited platelet spreading on fibrinogen and clot retraction mediated by outside-in signaling. SC99 inhibited platelet aggregation in mice but it did not significantly prolong the bleeding time. Taken together, the present study revealed that SC99 inhibited platelet activation and aggregation as a STAT3 inhibitor. This agent can be developed as a promising treatment for thrombotic disorders.

A novel small molecule agent displays potent anti-myeloma activity by inhibiting the JAK2-STAT3 signaling pathway

The oncogenic STAT3 signaling pathway is emerging as a promising target for the treatment of multiple myeloma (MM). In the present study, we identified a novel STAT3 inhibitor SC99 in a target-based high throughput screen. SC99 inhibited JAK2-STAT3 activation but had no effects on other transcription factors such as NF-κB, and kinases such as AKT, ERK, and c-Src that are in association with STAT3 signaling pathway. Furthermore, SC99 downregulated the expression of STAT3-modulated genes, including Bcl-2, Bcl-xL, VEGF, cyclin D2, and E2F-1. By inhibiting the STAT3 signaling, SC99 induced MM cell apoptosis which could be partly abolished by the ectopic expression of STAT3. Furthermore, SC99 displayed potent anti-MM activity in two independent MM xenograft models in nude mice. Oral administration of SC99 led to marked decrease of tumor growth within 10 days at a daily dosage of 30 mg/kg, but did not raise toxic effects. Taken together, this study identified a novel oral JAK2/STAT3 inhibitor that could be developed as an anti-myeloma agent.

4-Methoxydalbergione suppresses growth and induces apoptosis in human osteosarcoma cells in vitro and in vivo xenograft model through down-regulation of the JAK2/STAT3 pathway

Although the heartwood of Dalbergia odorifera T. Chen (Leguminosae) is an important source of traditional Korean and Chinese medicines, the effects of novel compound methoxydalbergione (4-MD) isolated from Dalbergia odorifera was not reported. Herein, we investigated the effects of the 4-MD in vitro and in vivo against osteosarcoma cells and its molecular mechanisms. 4-MD inhibited the proliferation of osteosarcoma cells and induced apoptosis as evidenced by Annexin V + and TUNEL + cells. This apoptosis was accompanied by upregulation of apoptotic proteins (procaspase-3 and PARP), but downregulation of anti-apoptotic proteins (Bcl-2, Bcl-xL, and Survivin). 4-MD inhibited phosphorylation of JAK2 and STAT3 with the inactivation of mitogen-activated protein kinases (MAPKs) and CREB, and the upregulation of PTEN in osteosarcoma cells. Importantly, 4-MD reduced colony formation in soft agar and inhibited tumor growth in mice xenograft model in association with the reduced expression of PCNA, Ki67, p-STAT3, and Survivin. Taken together, the present study for the first time demonstrates that 4-MD exerts in vitro and in vivo anti-proliferative effects against osteosarcoma cells through the inhibition of the JAK2/STAT3 pathway, and suggest the potential for therapeutic application of 4-MD in the treatment of osteosarcoma.

STAT3 Undergoes Acetylation-dependent Mitochondrial Translocation to Regulate Pyruvate Metabolism

Cytoplasmic STAT3, after activation by growth factors, translocates to different subcellular compartments, including nuclei and mitochondria, where it carries out different biological functions. However, the precise mechanism by which STAT3 undergoes mitochondrial translocation and subsequently regulates the tricarboxylic acid (TCA) cycle-electron transport chain (ETC) remains poorly understood. Here, we clarify this process by visualizing STAT3 acetylation in starved cells after serum reintroduction or insulin stimulation. CBP-acetylated STAT3 undergoes mitochondrial translocation in response to serum introduction or insulin stimulation. In mitochondria, STAT3 associates with the pyruvate dehydrogenase complex E1 (PDC-E1) and subsequently accelerates the conversion of pyruvate to acetyl-CoA, elevates the mitochondrial membrane potential, and promotes ATP synthesis. SIRT5 deacetylates STAT3, thereby inhibiting its function in mitochondrial pyruvate metabolism. In the A549 lung cancer cell line, constitutively acetylated STAT3 localizes to mitochondria, where it maintains the mitochondrial membrane potential and ATP synthesis in an active state.

Immunological and Functional Characterization of RhoGDI3 and Its Molecular Targets RhoG and RhoB in Human Pancreatic Cancerous and Normal Cells

RhoGDI proteins have been implicated in several human cancers; changes in their expression levels have shown pro- or anti-tumorigenic effects. Pancreatic Ductal Adenocarcinoma (PDAC) is a complex pathology, with poor prognosis, and most patients die shortly after diagnosis. Efforts have been focused on understanding the role of RhoGDI's in PDAC, specially, RhoGDI1 and RhoGDI2. However, the role of RhoGDI3 has not been studied in relation to cancer or to PDAC. Here, we characterized the expression and functionality of RhoGDI3 and its target GTPases, RhoG and RhoB in pancreatic cell lines from both normal pancreatic tissue and tissue in late stages of PDAC, and compared them to human biopsies. Through immunofluorescences, pulldown assays and subcellular fractionation, we found a reduction in RhoGDI3 expression in the late stages of PDAC, and this reduction correlates with tumor progression and aggressiveness. Despite the reduction in the expression of RhoGDI3 in PDAC, we found that RhoB was underexpressed while RhoG was overexpressed, suggesting that cancerous cells preserve their capacity to activate this pathway, thus these cells may be more eager to response to the stimuli needed to proliferate and become invasive unlike normal cells. Surprisingly, we found nuclear localization of RhoGDI3 in non-cancerous pancreatic cell line and normal pancreatic tissue biopsies, which could open the possibility of novel nuclear functions for this protein, impacting gene expression regulation and cellular homeostasis.

Senescence Mediated by p16INK4a Impedes Reprogramming of Human Corneal Endothelial Cells into Neural Crest Progenitors

Human corneal endothelial cells (HCECs) have limited proliferative capacity due to “contact-inhibition” at G1 phase. Such contact-inhibition can be delayed from Day 21 to Day 42 by switching EGF-containing SHEM to LIF/bFGF-containing MESCM through transient activation of LIF-JAK1-STAT3 signaling that delays eventual nuclear translocation of p16^INK4a. Using the latter system, we have reported a novel tissue engineering technique by implementing 5 weekly knockdowns with p120 catenin (p120) and Kaiso siRNAs since Day 7 to achieve effective expansion of HCEC monolayers to a transplantable size with a normal HCEC density, through reprogramming of HCECs into neural crest progenitors by activating p120-Kaiso-RhoA-ROCK-canonical BMP signaling. Herein, we noted that a single knockdown with p120-Kaiso siRNAs at Day 42 failed to achieve such reprogramming when contact inhibition transitioned to senescence with nuclear translocation of p16^INK4a. In contrast, 5 weekly knockdowns with p120-Kaiso siRNAs since Day 7 precluded senescence mediated by p16^INK4a by inducing nuclear translocation of Bmi1 because of sustained activation of JAK2-STAT3 signaling downstream of p120-Kaiso-RhoA-ROCK signaling. STAT3 or Bmi1 siRNA impeded nuclear exclusion of p16^INK4a and suppressed the reprogramming induced by p120-Kaiso siRNAs, suggesting that another important engineering strategy of HCEC lies in prevention of senescence mediated by nuclear translocation of p16^INK4a.

STAT3 in the systemic inflammation of cancer cachexia

Weight loss is diagnostic of cachexia, a debilitating syndrome contributing mightily to morbidity and mortality in cancer. Most research has probed mechanisms leading to muscle atrophy and adipose wasting in cachexia; however cachexia is a truly systemic phenomenon. Presence of the tumor elicits an inflammatory response and profound metabolic derangements involving not only muscle and fat, but also the hypothalamus, liver, heart, blood, spleen and likely other organs. This global response is orchestrated in part through circulating cytokines that rise in conditions of cachexia. Exogenous Interleukin-6 (IL6) and related cytokines can induce most cachexia symptomatology, including muscle and fat wasting, the acute phase response and anemia, while IL-6 inhibition reduces muscle loss in cancer. Although mechanistic studies are ongoing, certain of these cachexia phenotypes have been causally linked to the cytokine-activated transcription factor, STAT3, including skeletal muscle wasting, cardiac dysfunction and hypothalamic inflammation. Correlative studies implicate STAT3 in fat wasting and the acute phase response in cancer cachexia. Parallel data in non-cancer models and disease states suggest both pathological and protective functions for STAT3 in other organs during cachexia. STAT3 also contributes to cancer cachexia through enhancing tumorigenesis, metastasis and immune suppression, particularly in tumors associated with high prevalence of cachexia. This review examines the evidence linking STAT3 to multi-organ manifestations of cachexia and the potential and perils for targeting STAT3 to reduce cachexia and prolong survival in cancer patients.

Selective oral ROCK2 inhibitor down-regulates IL-21 and IL-17 secretion in human T cells via STAT3-dependent mechanism

Rho-associated kinase 2 (ROCK2) regulates the secretion of proinflammatory cytokines and the development of autoimmunity in mice. Data from a phase 1 clinical trial demonstrate that oral administration of KD025, a selective ROCK2 inhibitor, to healthy human subjects down-regulates the ability of T cells to secrete IL-21 and IL-17 by 90% and 60%, respectively, but not IFN-γ in response to T-cell receptor stimulation in vitro. Pharmacological inhibition with KD025 or siRNA-mediated inhibition of ROCK2, but not ROCK1, significantly diminished STAT3 phosphorylation and binding to IL-17 and IL-21 promoters and reduced IFN regulatory factor 4 and nuclear hormone RAR-related orphan receptor γt protein levels in T cells derived from healthy subjects or rheumatoid arthritis patients. Simultaneously, treatment with KD025 also promotes the suppressive function of regulatory T cells through up-regulation of STAT5 phosphorylation and positive regulation of forkhead box p3 expression. The administration of KD025 in vivo down-regulates the progression of collagen-induced arthritis in mice via targeting of the Th17-mediated pathway. Thus, ROCK2 signaling appears to be instrumental in regulating the balance between proinflammatory and regulatory T-cell subsets. Targeting of ROCK2 in man may therefore restore disrupted immune homeostasis and have a role in the treatment of autoimmunity.

Critical functions of RhoB in support of glioblastoma tumorigenesis

BACKGROUND

RhoB is a member of the Rho small GTPase family that regulates cytoskeletal dynamics and vesicle trafficking. The RhoB homologs, RhoA and RhoC, have been shown to promote cancer progression and metastasis. In contrast, the functions of RhoB in human cancers are context dependent. Although expression of RhoB inversely correlates with disease progression in several epithelial cancers, recent data suggest that RhoB may support malignant phenotypes in certain cancer types.

METHODS

We assessed RhoB protein levels in glioma surgical specimens and patient-derived xenografts. The roles of RhoB in glioblastoma were determined by loss-of-function and gain-of-function assays in vitro and in vivo. The impact on p53 and STAT3 signaling was investigated.

RESULTS

RhoB expression was similar in tumor specimens compared with normal neural tissues obtained from epilepsy surgery. RhoB was expressed in the vast majority of xenograft tumors and spheroid cultures. Knockdown of RhoB induced cell-cycle arrest and apoptosis and compromised in vivo tumorigenic potential. However, overexpression of wild-type RhoB or a constitutively active mutant (RhoB-V14) did not significantly affect cell growth, which suggests that RhoB is not a rate-limiting oncogenic factor and is consistent with the scarcity of RhoB mutations in human cancer. Knockdown of RhoB reduced basal STAT3 activity and impaired cytokine-induced STAT3 activation. In glioblastoma tumors retaining wild-type p53, depletion of RhoB also activated p53 and induced expression of p21(CIP1) (/WAF1).

CONCLUSIONS

Our data suggest that RhoB belongs to an emerging class of "nononcogene addiction" factors that are essential for maintenance of malignant phenotypes in human cancers.

Comprehensive molecular characterization of gastric adenocarcinoma

Gastric cancer is a leading cause of cancer deaths, but analysis of its molecular and clinical characteristics has been complicated by histological and aetiological heterogeneity. Here we describe a comprehensive molecular evaluation of 295 primary gastric adenocarcinomas as part of The Cancer Genome Atlas (TCGA) project. We propose a molecular classification dividing gastric cancer into four subtypes: tumours positive for Epstein-Barr virus, which display recurrent PIK3CA mutations, extreme DNA hypermethylation, and amplification of JAK2, CD274 (also known as PD-L1) and PDCD1LG2 (also known as PD-L2); microsatellite unstable tumours, which show elevated mutation rates, including mutations of genes encoding targetable oncogenic signalling proteins; genomically stable tumours, which are enriched for the diffuse histological variant and mutations of RHOA or fusions involving RHO-family GTPase-activating proteins; and tumours with chromosomal instability, which show marked aneuploidy and focal amplification of receptor tyrosine kinases. Identification of these subtypes provides a roadmap for patient stratification and trials of targeted therapies.

STAT3 Activities and Energy Metabolism: Dangerous Liaisons

STAT3 mediates cytokine and growth factor receptor signalling, becoming transcriptionally active upon tyrosine 705 phosphorylation (Y-P). Constitutively Y-P STAT3 is observed in many tumors that become addicted to its activity, and STAT3 transcriptional activation is required for tumor transformation downstream of several oncogenes. We have recently demonstrated that constitutively active STAT3 drives a metabolic switch towards aerobic glycolysis through the transcriptional induction of Hif-1α and the down-regulation of mitochondrial activity, in both MEF cells expressing constitutively active STAT3 (Stat3^C/C) and STAT3-addicted tumor cells. This novel metabolic function is likely involved in mediating pre-oncogenic features in the primary Stat3^C/C MEFs such as resistance to apoptosis and senescence and rapid proliferation. Moreover, it strongly contributes to the ability of primary Stat3^C/C MEFs to undergo malignant transformation upon spontaneous immortalization, a feature that may explain the well known causative link between STAT3 constitutive activity and tumor transformation under chronic inflammatory conditions. Taken together with the recently uncovered role of STAT3 in regulating energy metabolism from within the mitochondrion when phosphorylated on Ser 727, these data place STAT3 at the center of a hub regulating energy metabolism under different conditions, in most cases promoting cell survival, proliferation and malignant transformation even though with distinct mechanisms.

Plasmid transfer of plasminogen K1-5 reduces subcutaneous hepatoma growth by affecting inflammatory factors

There is evidence that plasminogen K1-5 (PlgK1-5) directly affects tumour cells and inflammation. Therefore, we analysed if PlgK1-5 has immediate effects on hepatoma cells and inflammatory factors in vitro and in vivo. In vitro, effects of plasmid encoding PlgK1-5 (pK1-5) on Hepa129, Hepa1-6, and HuH7 cell viability, apoptosis, and proliferation as well as VEGF and TNF-alpha expression and STAT3-phosphorylation were investigated. In vivo, tumour growth, proliferation, vessel density, and effects on vascular endothelial growth factor (VEGF) and tumour necrosis factor alpha (TNF-alpha) expression were examined following treatment with pK1-5. In vivo, pK1-5 halved cell viability; cell death was increased by up to 15% compared to the corresponding controls. Proliferation was not affected. VEGF, TNF-alpha, and STAT3-phosphorylation were affected following treatment with pK1-5. In vivo, ten days after treatment initiation, pK1-5 reduced subcutaneous tumour growth by 32% and mitosis by up to 77% compared to the controls. Vessel density was reduced by 50%. TNF-alpha levels in tumour and liver tissue were increased, whereas VEGF levels in tumours and livers were reduced after pK1-5 treatment. Taken together, plasmid gene transfer of PlgK1-5 inhibits hepatoma (cell) growth not only by reducing vessel density but also by inducing apoptosis, inhibiting proliferation, and triggering inflammation.

Signal integration and gene induction by a functionally distinct STAT3 phosphoform

Aberrant activation of the ubiquitous transcription factor STAT3 is a major driver of solid tumor progression and pathological angiogenesis. STAT3 activity is regulated by numerous posttranslational modifications (PTMs), including Tyr(705) phosphorylation, which is widely used as an indicator of canonical STAT3 function. Here, we report a noncanonical mechanism of STAT3 activation that occurs independently of Tyr(705) phosphorylation. Using quantitative liquid chromatography-tandem mass spectrometry, we have discovered and characterized a novel STAT3 phosphoform that is simultaneously phosphorylated at Thr(714) and Ser(727) by glycogen synthase kinase 3α and -β (GSK-3α/β). Both Thr(714) and Ser(727) are required for STAT3-dependent gene induction in response to simultaneous activation of epidermal growth factor receptor (EGFR) and protease-activated receptor 1 (PAR-1) in endothelial cells. In this combinatorial signaling context, preventing formation of doubly phosphorylated STAT3 by depleting GSK-3α/β is sufficient to disrupt signal integration and inhibit STAT3-dependent gene expression. Levels of doubly phosphorylated STAT3 but not of Tyr(705)-phosphorylated STAT3 are remarkably elevated in clear-cell renal-cell carcinoma relative to adjacent normal tissue, suggesting that the GSK-3α/β-STAT3 pathway is active in the disease. Collectively, our results describe a functionally distinct, noncanonical STAT3 phosphoform that positively regulates target gene expression in a combinatorial signaling context and identify GSK-3α/β-STAT3 signaling as a potential therapeutic target in renal-cell carcinoma.

Functional role and therapeutic potential of the pim-1 kinase in colon carcinoma

PURPOSE

The provirus integration site for Moloney murine leukemia virus 1 (Pim-1) kinase is overexpressed in various tumors and has been linked to poor prognosis. Its role as proto-oncogene is based on several Pim-1 target proteins involved in pivotal cellular processes. Here, we explore the functional relevance of Pim-1 in colon carcinoma.

EXPERIMENTAL DESIGN

RNAi-based knockdown approaches, as well as a specific small molecule inhibitor, were used to inhibit Pim-1 in colon carcinoma cells. The effects were analyzed regarding proliferation, apoptosis, sensitization toward cytostatic treatment, and overall antitumor effect in vitro and in mouse tumor models in vivo.

RESULTS

We demonstrate antiproliferative, proapoptotic, and overall antitumor effects of Pim-1 inhibition. The sensitization to 5-fluorouracil (5-FU) treatment upon Pim-1 knockdown offers new possibilities for combinatorial treatment approaches. Importantly, this also antagonizes a 5-FU-triggered Pim-1 up-regulation, which is mediated by decreased levels of miR-15b, a microRNA we newly identify to regulate Pim-1. The analysis of the molecular effects of Pim-1 inhibition reveals a complex regulatory network, with therapeutic Pim-1 repression leading to major changes in oncogenic signal transduction with regard to p21(Cip1/WAF1), STAT3, c-jun-N-terminal kinase (JNK), c-Myc, and survivin and in the levels of apoptosis-related proteins Puma, Bax, and Bcl-xL.

CONCLUSIONS

We demonstrate that Pim-1 plays a pivotal role in several tumor-relevant signaling pathways and establish the functional relevance of Pim-1 in colon carcinoma. Our results also substantiate the RNAi-mediated Pim-1 knockdown based on polymeric polyethylenimine/small interfering RNA nanoparticles as a promising therapeutic approach.

The Rho GTPase RhoE is a p53-regulated candidate tumor suppressor in cancer cells

Previous studies have shown that RhoE, an atypical member of the Rho GTPase family, may play an opposite role to RhoA in regulating cell proliferation and invasion. To explore the relationship between RhoE and the malignant phenotypes of human cancer, we have determined the expression patterns of RhoE in varying grade of human cancer tissues and tested the effects of RhoE expression in several RhoE underexpressing cancer cell lines. Systemic immunocytochemistry analyses of gastric, colorectal, lung and breast carcinomas, respectively, showed that RhoE protein expression was significantly decreased in most cancer cases compared with that of adjacent normal tissues. Enhanced RhoE expression could markedly inhibit proliferation, migration and invasion and induce apoptosis of the cancer cells which have relatively low levels of endogenous RhoE expression. Wild-type p53 (wt-p53) could strongly increase RhoE expression in p53-transfected cells. Furthermore, the luciferase assays indicated that wt-p53 significantly enhanced the activities of RhoE promoter compared with mutant p53 (mt-p53) in PC3 cells (p53 null). Collectively, data are presented showing that RhoE may participate in human cancer progression and act as a candidate target of p53, and these findings also strongly suggest that RhoE may be a new candidate tumor suppressor and could serve as a potential target in the gene therapy of cancer.

Nitric oxide donors: spermine/NO and diethylenetriamine/NO induce ovarian cancer cell death and affect STAT3 and AKT signaling proteins

The important features of cancer cells are uncontrolled growth and proliferation, as well as the ability to metastasis. These features depend mainly on the constant overexpression and activity of various cell signaling proteins, such as signal transducer and activator of transcription 3 (STAT3) and serine-threonine protein kinase AKT proteins. Nitric oxide (NO) has the potential of being anti-tumoral agent, however the exact character of anti-tumoral action of NO is still a matter of debate. In our research we used two NO donors, belonging to NONOates family, with different half-life times: spermine nitric oxide complex hydrate (SPER/NO t1/2=39min) and diethylenetriamine nitric oxide adduct (DETA/NO, t1/2=20h). We evaluated the cytotoxic effect of aforementioned NO donors on SK-OV-3 and OVCAR-3 ovarian cancer cell lines, as well as their effect on posttranslational modification of STAT3 and AKT proteins in these cells. We found that both NO donors present cytotoxic activity on the cancer cell lines, mainly through the induction of apoptosis. What is more, at the high concentration and longer exposure time they were also capable of inducing late apoptosis/necrosis. Both NO donors inhibited STAT3 and AKT3 proteins phosphorylation and down regulated their cytosolic levels, with DETA/NO being stronger inhibitor. We suggests, that NO donors have the potential to act as anti-tumoral agent through inhibiting cancer cell signaling and reducing their viability.

ROCKing the JAKs

The endocrine cytokine leptin is mainly secreted by white adipose tissue and plasma leptin levels positively correlate with body fat mass. Via its action on neurons in the hypothalamic arcuate nucleus (ARC), leptin regulates body weight by stimulating energy expenditure and inhibiting food intake. The main signaling pathway of the leptin receptor is the JAK2-STAT3 pathway. A recent publication of Huang et al. in Nature Neuroscience shows that leptin’s hypothalamic signaling via JAK2 requires the kinase ROCK1 (Rho-associated coiled-coil-containing protein kinase 1). ROCK1 directly phosphorylates JAK2, and this phosphorylation is required for the JAK2-STAT3 pathway of the leptin receptor. Gene deletion of ROCK1 in ARC neurons targeted by leptin makes these neurons less sensitive to leptin. This is reflected by a pronounced weight gain with hyperphagia, reduced locomotor activity, and increased fat accumulation. In this article we comment on the article of Huang et al. While the mechanism of ROCK1 activation in the neurons remains uncharacterized for the moment, a literature survey suggests that the interplay between ROCK1 and a JAK kinase may be a common theme for receptors that function via a JAK2 and even for other members of the JAK kinase family.

BART inhibits pancreatic cancer cell invasion by Rac1 inactivation through direct binding to active Rac1

We report that Binder of Arl Two (BART) plays a role in inhibiting cell invasion by regulating the activity of the Rho small guanosine triphosphatase protein Rac1 in pancreatic cancer cells. BART was originally identified as a binding partner of ADP-ribosylation factor-like 2, a small G protein implicated as a regulator of microtubule dynamics and folding. BART interacts with active forms of Rac1, and the BART-Rac1 complex localizes at the leading edges of migrating cancer cells. Suppression of BART increases active Rac1, thereby increasing cell invasion. Treatment of pancreatic cancer cells in which BART is stably knocked down with a Rac1 inhibitor decreases invasiveness. Thus, BART-dependent inhibition of cell invasion is likely associated with decreased active Rac1. Suppression of BART induces membrane ruffling and lamellipodial protrusion and increases peripheral actin structures in membrane ruffles at the edges of lamellipodia. The Rac1 inhibitor inhibits the lamellipodia formation that is stimulated by suppression of BART. Our results imply that BART regulates actin-cytoskeleton rearrangements at membrane ruffles through modulation of the activity of Rac1, which, in turn, inhibits pancreatic cancer cell invasion.