Activation of Stat3 by cell confluence reveals negative regulation of Stat3 by cdk2

Exosomes in infectious diseases: insights into leishmaniasis pathogenesis, immune modulation, and therapeutic potential

Leishmaniasis continues to be a critical international health issue due to the scarcity of efficient treatment and the development of drug tolerance. New developments in the research of extracellular vesicles (EVs), especially exosomes, have revealed novel disease management approaches. Exosomes are small vesicles that transport lipids, nucleic acids, and proteins in cell signalling. Its biogenesis depends on several cellular processes, and their functions in immune response, encompassing innate and adaptive immunity, underline their function in the pathogen-host interface. Exosomes play a significant role in the pathogenesis of some parasitic infections, especially Leishmaniasis, by helping parasites escape host immunity and promote disease progression. This article explains that in the framework of parasitic diseases, exosomes can act as master regulators that define the pathogenesis of the disease, as illustrated by the engagement of exosomes in the Leishmaniasis parasite and immune escape processes. Based on many published articles on Leishmaniasis, this review aims to summarize the biogenesis of exosomes, the properties of the cargo in exosomes, and the modulation of immune responses. We delve deeper into the prospect of using exosomes for the therapy of Leishmaniasis based on the possibility of using these extracellular vesicles for drug delivery and as diagnostic and prognostic biomarkers. Lastly, we focus on the recent research perspectives and future developments, underlining the necessity to continue the investigation of exosome-mediated approaches in Leishmaniasis treatment. Thus, this review intends to draw attention to exosomes as a bright new perspective in the battle against this disabling affliction.

Development of Functional Foods: A Comparative Study on the Polyphenols and Anthocyanins Content in Chokeberry and Blueberry Pomace Extracts and Their Antitumor Properties

Developing of functional foods is a promising strategy to reduce the increasing burden of colorectal cancer worldwide. Fruit pomace, particularly polyphenol and anthocyanin-rich chokeberry and blueberry, is a valuable ingredient for functional foods and nutraceuticals. Our study aimed to evaluate the anti-inflammatory and antiproliferative effects of chokeberry and blueberry pomace extracts on C2BBe1 colorectal carcinoma cells and explore the underlying signaling pathways. We analyzed both pomace extracts for total polyphenols and anthocyanins using Folin-Ciocalteu method and ultra-performance liquid chromatography, while antioxidative activity was assessed via the 2,2-diphenyl-1-picrylhydrazyl radical scavenging method. We evaluated the in vitro anti-inflammatory and antiproliferative effects using trypan blue exclusion, MTT and LDH assays, and assessed protein levels of p-Erk1/2, Akt-1, STAT1, STAT3, occludin, oxidized proteins, and MDA-protein adducts through western blotting, as well as analysis of a 37-plex panel of inflammatory markers. Chokeberry extracts exhibited higher total polyphenol content, anthocyanin levels, and antioxidative activity compared to blueberry extracts, however, blueberry extracts effects on cell viability and proliferation in C2BBe1 cells were stronger. Both fruit pomaces induced non-inflammatory cell death characterized by membrane integrity loss, beneficial in cancer therapy. Our data suggests chokeberry's cytotoxicity may be mediated by Erk signaling and Akt-1 inhibition, while blueberry uniquely decreased occludin levels. These berries pomaces' potential to mitigate cancer risks and enhance treatment efficacy is promising, warranting further investigation for functional foods development.

Cell culture-derived extracellular vesicles: Considerations for reporting cell culturing parameters

Cell culture-conditioned medium (CCM) is a valuable source of extracellular vesicles (EVs) for basic scientific, therapeutic and diagnostic applications. Cell culturing parameters affect the biochemical composition, release and possibly the function of CCM-derived EVs (CCM-EV). The CCM-EV task force of the Rigor and Standardization Subcommittee of the International Society for Extracellular Vesicles aims to identify relevant cell culturing parameters, describe their effects based on current knowledge, recommend reporting parameters and identify outstanding questions. While some recommendations are valid for all cell types, cell-specific recommendations may need to be established for non-mammalian sources, such as bacteria, yeast and plant cells. Current progress towards these goals is summarized in this perspective paper, along with a checklist to facilitate transparent reporting of cell culturing parameters to improve the reproducibility of CCM-EV research.

Influence of Long Non-Coding RNA in the Regulation of Cancer Stem Cell Signaling Pathways

Over the past two decades, cancer stem cells (CSCs) have emerged as an immensely studied and experimental topic, however a wide range of questions concerning the topic still remain unanswered; in particular, the mechanisms underlying the regulation of tumor stem cells and their characteristics. Understanding the cancer stem-cell signaling pathways may pave the way towards a better comprehension of these mechanisms. Signaling pathways such as WNT, STAT, Hedgehog, NOTCH, PI3K/AKT/mTOR, TGF-β, and NF-κB are responsible not only for modulating various features of CSCs but also their microenvironments. Recently, the prominent roles of various non-coding RNAs such as small non-coding RNAs (sncRNAs) and long non-coding RNAs (lncRNAs) in developing and enhancing the tumor phenotypes have been unfolded. This review attempts to shed light on understanding the influence of long non- coding RNAs in the modulation of various CSC-signaling pathways and its impact on the CSCs and tumor properties; highlighting the protagonistic and antagonistic roles of lncRNAs.

Roads to Stat3 Paved with Cadherins

The engagement of cadherins, cell-to-cell adhesion proteins, triggers a dramatic increase in the levels and activity of the Rac/Cdc42 GTPases, through the inhibition of proteasomal degradation. This leads to an increase in transcription and secretion of IL6 family cytokines, activation of their common receptor, gp130, in an autocrine manner and phosphorylation of the signal transducer and activator of transcription-3 (Stat3) on tyrosine-705 by the Jak kinases. Stat3 subsequently dimerizes, migrates to the nucleus and activates the transcription of genes involved in cell division and survival. The Src oncogene also increases Rac levels, leading to secretion of IL6 family cytokines and gp130 activation, which triggers a Stat3-ptyr705 increase. Interestingly, at the same time, Src downregulates cadherins in a quantitative manner, while cadherins are required to preserve gp130 levels for IL6 family signalling. Therefore, a fine balance between Src527F/Rac/IL6 and Src527F/cadherin/gp130 levels is in existence, which is required for Stat3 activation. This further demonstrates the important role of cadherins in the activation of Stat3, through preservation of gp130 function. Conversely, the absence of cadherin engagement correlates with low Stat3 activity: In sparsely growing cells, both gp130 and Stat3-ptyr705 levels are very low, despite the fact that cSrc is active in the FAK (focal adhesion kinase)/cSrc complex, which further indicates that the engagement of cadherins is important for Stat3 activation, not just their presence. Furthermore, the caveolin-1 protein downregulates Stat3 through binding and sequestration of cadherins to the scaffolding domain of caveolin-1. We hypothesize that the cadherins/Rac/gp130 axis may be a conserved pathway to Stat3 activation in a number of systems. This fact could have significant implications in Stat3 biology, as well as in drug testing and development.

STAT3 inactivation suppresses stemness properties in gastric cancer stem cells and promotes Th17 in Treg/Th17 balance

Signal transducer and activator of transcription 3 (STAT3) has been recognized with dual effects in provision of cancer; either tumor inductive or immune suppressive. Recent findings considering the role of STAT3 in stem cells and cancer stem cell regulation, but its role in gastric cancer stem cells (GCSCs) and modulating the Th17/Treg balance is unknown. In the present study, we aimed to evaluate the role of activated STAT3 in GCSCs and Th17/ Treg cell paradigm. In completion of our previous results, the findings here indicate that gastro-spheroids, as a model of GCSCs, represent higher level of STAT3 activity, up-regulation of TGF-b and VEGF with downregulation of IL-6. On the other hand, treatment of normal naïve T cells with conditioned medium derived from gastro-spheroids promotes T cell differentiation toward cells with a higher level of FOXP3, TGF-b, and IL-10 expression which is indicative of Treg cells. Suppression of STAT3 activation in cancer cells by using Stattic small molecule treatment, decreases stemness features (i.e. spheroid formation and integrity, stemness gene expression and in vivo tumorigenicity capacity) and downregulates TGF-b in the cancer cells. Furthermore, co-culture of conditioned medium of STAT3 inhibited cancer cells with normal PBMCs leads to reduction in the percentage of Treg accompanied with increase of Th17 cells with a decrease in the secretion of TGF-b and increase in IFN-γ in T cells under differentiation. Therefore, targeting the STAT3 pathway in cancer cells seems to control the tumor formation and also impact on immune cells shifting to antitumor Th17 population.

Human Lung Fibroblasts Exhibit Induced Inflammation Memory via Increased IL6 Gene Expression and Release

Fibroblasts of different origins are known to possess stromal memory after inflammatory episodes. However, there are no studies exploring human lung fibroblast memory which may predict a subsequent inflammatory response in chronic respiratory diseases and COVID-19. MRC-5 and HF19 human lung fibroblast cell lines were treated using different primary and secondary stimulus combinations: TNFα–WD–TNFα, Poly (I:C)–WD–TNFα, TNFα–WD–Poly (I:C), or LPS–WD–TNFα with a 24-h rest period (withdrawal period; WD) between the two 24-h stimulations. TLR3 and NF-κB inhibitors were used to determine pathways involved. The effect of SARS-Cov-2 spike protein to inflammatory response of lung fibroblasts was also investigated. mRNA expressions of genes and IL6 release were measured using qRT-PCR and ELISA, respectively. Statistical significance was determined by using one- or two-way ANOVA, followed by Bonferroni’s post hoc analysis for comparison of multiple groups. Preexposure with Poly (I:C) significantly increased TNFα-induced IL6 gene expression and IL6 release in both cell lines, while it affected neither gene expressions of IL1B, IL2, IL8, and MMP8 nor fibrosis-related genes: ACTA2, COL1A1, POSTN, and TGFB1. Inhibition of TLR3 or NF-κB during primary stimulation significantly downregulated IL6 release. Simultaneous treatment of MRC-5 cells with SARS-CoV-2 spike protein further increased TNFα-induced IL6 release; however, preexposure to Poly (I:C) did not affect it. Human lung fibroblasts are capable of retaining inflammatory memory and showed an augmented response upon secondary exposure. These results may contribute to the possibility of training human lung fibroblasts to respond suitably on inflammatory episodes after viral infection.

Emerin Represses STAT3 Signaling through Nuclear Membrane-Based Spatial Control

Emerin is the inner nuclear membrane protein involved in maintaining the mechanical integrity of the nuclear membrane. Mutations in EMD encoding emerin cause Emery–Dreifuss muscular dystrophy (EDMD). Evidence is accumulating that emerin regulation of specific gene expression is associated with this disease, but the exact function of emerin has not been fully elucidated. Here, we show that emerin downregulates Signal transducer and activators of transcription 3 (STAT3) signaling, activated exclusively by Janus kinase (JAK). Deletion mutation experiments show that the lamin-binding domain of emerin is essential for the inhibition of STAT3 signaling. Emerin interacts directly and co-localizes with STAT3 in the nuclear membrane. Emerin knockdown induces STAT3 target genes Bcl2 and Survivin to increase cell survival signals and suppress hydrogen peroxide-induced cell death in HeLa cells. Specifically, downregulation of BAF or lamin A/C increases STAT3 signaling, suggesting that correct-localized emerin, by assembling with BAF and lamin A/C, acts as an intrinsic inhibitor against STAT3 signaling. In C2C12 cells, emerin knockdown induces STAT3 target gene, Pax7, and activated abnormal myoblast proliferation associated with muscle wasting in skeletal muscle homeostasis. Our results indicate that emerin downregulates STAT3 signaling by inducing retention of STAT3 and delaying STAT3 signaling in the nuclear membrane. This mechanism provides clues to the etiology of emerin-related muscular dystrophy and may be a new therapeutic target for treatment.

Importance of stem cell culture conditions for their derived extracellular vesicles therapeutic effect

Stem cell-derived extracellular vesicles (EVs) could be enhanced by modifying specific in vitro parameters when culturing their originating stem cells. Controlling stem cell growth conditions with physical properties, oxygen tension and media preconditioning with soluble factors may influence EVs biogenesis and EVs biological function as well. Unfortunately, many misconceptions and methodological issues have hampered the progress in understanding the biological properties of EVs. In this review we will first discuss the major concerns involved in a suitable EVs production from stem cell culture. Then, we will describe the current techniques for EV isolation, focusing on their advantages and disadvantages, as well as their impact on EVs yield, recovery and functionality. Standardization of the methodology is a prerequisite to compare, to validate and to improve the reliability and credibility of all the different findings reported for the development of EV-based therapeutics.

FMRP regulates STAT3 mRNA localization to cellular protrusions and local translation to promote hepatocellular carcinoma metastasis

Most hepatocellular carcinoma (HCC)-associated mortalities are related to the metastasis of cancer cells. The localization of mRNAs and their products to cell protrusions has been reported to play a crucial role in the metastasis. Our previous findings demonstrated that STAT3 mRNA accumulated in the protrusions of metastatic HCC cells. However, the underlying mechanism and functional significance of this localization of STAT3 mRNA has remained unexplored. Here we show that fragile X mental retardation protein (FMRP) modulates the localization and translation of STAT3 mRNA, accelerating HCC metastasis. The results of molecular analyses reveal that the 3′UTR of STAT3 mRNA is responsible for the localization of STAT3 mRNA to cell protrusions. FMRP is able to interact with the 3′UTR of STAT3 mRNA and facilitates its localization to protrusions. Importantly, FMRP could promote the IL-6-mediated translation of STAT3, and serine 114 of FMRP is identified as a potential phosphorylation site required for IL-6-mediated STAT3 translation. Furthermore, FMRP is highly expressed in HCC tissues and FMRP knockdown efficiently suppresses HCC metastasis in vitro and in vivo. Collectively, our findings provide further insights into the mechanism of HCC metastasis associated with the regulation of STAT3 mRNA localization and translation.

Shen et al. propose a mechanism for the metastasis of hepatocellular carcinoma (HCC) cells through the localization and translation modulation of the STAT3 oncogene by fragile X mental retardation protein (FMRP). To this end, the authors also find that FMRP knockdown efficiently suppresses HCC metastasis in vitro and in vivo.

A Comprehensive Review on Factors Influences Biogenesis, Functions, Therapeutic and Clinical Implications of Exosomes

Exosomes are nanoscale-sized membrane vesicles secreted by almost all cell types into the extracellular environment upon fusion of multivesicular bodies and plasma membrane. Biogenesis of exosomes is a protein quality control mechanism, and once released, exosomes transmit signals to other cells. The applications of exosomes have increased immensely in biomedical fields owing to their cell-specific cargos that facilitate intercellular communications with neighboring cells through the transfer of biologically active compounds. The diverse constituents of exosomes reflect their cell of origin and their detection in biological fluids represents a diagnostic marker for various diseases. Exosome research is expanding rapidly due to the potential for clinical application to therapeutics and diagnosis. However, several aspects of exosome biology remain elusive. To discover the use of exosomes in the biomedical applications, we must better understand the basic molecular mechanisms underlying their biogenesis and function. In this comprehensive review, we describe factors involved in exosomes biogenesis and the role of exosomes in intercellular signaling and cell-cell communications, immune responses, cellular homeostasis, autophagy, and infectious diseases. In addition, we discuss the role of exosomes as diagnostic markers, and their therapeutic and clinical implications. Furthermore, we addressed the challenges and outstanding developments in exosome research, and discuss future perspectives.

Circulating exosomes in cardiovascular disease: Novel carriers of biological information

Exosomes are a group of nanosized extracellular vesicles that include various bioactive nucleic acids, lipids, and proteins. They originate from membrane invagination and are released by exocytosis, which can transmit signals to target cells to achieve cell-to-cell communication and maintain homeostasis. The heart is a complex multicellular organ that contains resident cell types such as fibroblasts, endothelial cells, and smooth muscle cells. Communication between different cell types and immune systems is essential for the dynamic equilibrium of the cardiac internal environment. Intercellular communication is a universal phenomenon mediated by exosomes and their contents during several pathological processes in cardiovascular diseases, such as cardiomyocyte hypertrophy, apoptosis, and angiogenesis. Therefore, exosomes can be used as novel invasive diagnostic biomarkers in multiple diseases, including atherosclerosis, myocardial ischemia, cardiac fibrosis, and ischemia-reperfusion injury. In addition, the biocompatible nature and low immunogenicity of exosomes make them high-quality nanoparticle drug carriers with potential applications in translational medicine and therapeutic strategies. Here, we focus on the biogenesis, isolation, biological functions, and future application prospects of exosomes in cardiovascular disease.

Emerging Roles of Exosomes in T1DM

Type 1 diabetes mellitus (T1DM) is a complex autoimmune disorder that mainly affects children and adolescents. The elevated blood glucose level of patients with T1DM results from absolute insulin deficiency and leads to hyperglycemia and the development of life-threatening diabetic complications. Although great efforts have been made to elucidate the pathogenesis of this disease, the precise underlying mechanisms are still obscure. Emerging evidence indicates that small extracellular vesicles, namely, exosomes, take part in intercellular communication and regulate interorgan crosstalk. More importantly, many findings suggest that exosomes and their cargo are associated with the development of T1DM. Therefore, a deeper understanding of exosomes is beneficial for further elucidating the pathogenic process of T1DM. Exosomes are promising biomarkers for evaluating the risk of developingty T1DM, monitoring the disease state and predicting related complications because their number and composition can reflect the status of their parent cells. Additionally, since exosomes are natural carriers of functional proteins, RNA and DNA, they can be used as therapeutic tools to deliver these molecules and drugs. In this review, we briefly introduce the current understanding of exosomes. Next, we focus on the relationship between exosomes and T1DM from three perspectives, i.e., the pathogenic role of exosomes in T1DM, exosomes as novel biomarkers of T1DM and exosomes as therapeutic tools for T1DM.

Osteogenically-induced exosomes stimulate osteogenesis of human adipose-derived stem cells

Exosomes exhibit great therapeutic potential in bone tissue engineering. The study aimed to investigate whether the exosomes derived from human adipose-derived stem cells (hADSCs-Exos) during different time-span of osteogenic differentiation could promote osteogenesis. The appropriate concentrations of hADSCs-Exos to enhance the proliferation, migration and osteogenesis of hADSCs-Exos were also examined. PKH67 labelled hADSCs-Exos was used to detect the internalization ability of hADSCs. The osteogenic differentiation abilities of hADSCs after treatment with hADSCs-Exos was evaluated by Alizarin red staining (ARS). The proliferation and migration of hADSCs was examined by cell counting kit-8 and wound healing assay, respectively. The expression of exosomal surface markers and osteoblast-related protein of hADSCs was assessed by Western blot. PKH67-labelled exosomes were internalized by hADSCs after 4 h incubation. ARS showed that the amount of mineralized nodules in Exo^1−14d group was significantly higher than that in Exo^15−28d group. hADSCs-Exos could promote the proliferation and migration capacity of hADSCs. Western blot analysis showed that after hADSCs-Exos treatment, ALP and RUNX2 were significantly enhanced. Specially, the Exo^1−14d group of 15 μg/mL significantly upregulated the expression of RUNX2 than the other exosomes treated groups. Our findings suggest that exosomes secreted by hADSCs during osteogenic induction for 1–14 days could be efficiently internalized by hADSCs and could induce osteogenic differentiation of hADSCs. Moreover, administration of Exo^1−14d at 15 μg/mL promoted the proliferation and migration of hADSCs. In conclusion, our research confirmed that comprised of hADSCs-Exos and hADSCs may provide a new therapeutic paradigm for bone tissue engineering.

Targeting of EZH2 inhibits epithelial‑mesenchymal transition in head and neck squamous cell carcinoma via regulating the STAT3/VEGFR2 axis

Tumor metastasis regulated by epithelial‑mesenchymal transition (EMT) plays a significant role in the development of human cancers, whereas the molecular mechanisms of this process in head and neck squamous cell carcinoma (HNSCC) remain elusive. In this study, we found that inhibition of enhancer of zeste homolog 2 (EZH2) resulted in suppressed EMT in HNSCC in vitro and in vivo. We reported that signal transducer and activator of transcription factor 3 (STAT3)/vascular endothelial growth factor receptor 2 (VEGFR2) axis served as the downstream signaling of EZH2 and mediated EMT in HNSCC. EZH2 inhibition downregulated the expression of key molecules of the STAT3/VEGFR2 axis and EMT‑related markers, while the expression of E‑cadherin was upregulated in HNSCC cells. Targeting the EZH2/STAT3/VEGFR2 axis significantly reduced motility of HNSCC cells. Furthermore, EZH2 knockdown reduced the growth of xenograft HNSCC tumors via inhibiting the EZH2/STAT3/VEGFR2 axis. In conclusion, we proposed that EZH2 regulates EMT and tumor invasion and metastasis in HNSCC by governing the STAT3/VEGFR2 axis. These findings provide a rationale for developing novel strategies to treat invasive and metastatic HNSCC via targeting the EZH2/STAT3/VEGFR2 pathway.

Review of the Isolation, Characterization, Biological Function, and Multifarious Therapeutic Approaches of Exosomes

Exosomes are extracellular vesicles that contain a specific composition of proteins, lipids, RNA, and DNA. They are derived from endocytic membranes and can transfer signals to recipient cells, thus mediating a novel mechanism of cell-to-cell communication. They are also thought to be involved in cellular waste disposal. Exosomes play significant roles in various biological functions, including the transfer of biomolecules such as RNA, proteins, enzymes, and lipids and the regulation of numerous physiological and pathological processes in various diseases. Because of these properties, they are considered to be promising biomarkers for the diagnosis and prognosis of various diseases and may contribute to the development of minimally invasive diagnostics and next generation therapies. The biocompatible nature of exosomes could enhance the stability and efficacy of imaging probes and therapeutics. Due to their potential use in clinical applications, exosomes have attracted much research attention on their roles in health and disease. To explore the use of exosomes in the biomedical arena, it is essential that the basic molecular mechanisms behind the transport and function of these vesicles are well-understood. Herein, we discuss the history, biogenesis, release, isolation, characterization, and biological functions of exosomes, as well as the factors influencing their biogenesis and their technical and biological challenges. We conclude this review with a discussion on the future perspectives of exosomes.

STAT3 is activated in multicellular spheroids of colon carcinoma cells and mediates expression of IRF9 and interferon stimulated genes

Three-dimensional cell cultures, such as multicellular spheroids (MCS), reflect the in vivo architecture of solid tumours and multicellular drug resistance. We previously identified interferon regulatory factor 9 (IRF9) to be responsible for the up-regulation of a subset of interferon (IFN)-stimulated genes (ISGs) in MCS of colon carcinoma cells. This set of ISGs closely resembled a previously identified IFN-related DNA-damage resistance signature (IRDS) that was correlated to resistance to chemo- and radiotherapy. In this study we found that transcription factor STAT3 is activated upstream of IRF9 and binds to the IRF9 promoter in MCS of HCT116 colorectal carcinoma cells. Transferring conditioned media (CM) from high cell density conditions to non-confluent cells resulted in STAT3 activation and increased expression of IRF9 and a panel of IRDS genes, also observed in MCS, suggesting the involvement of a soluble factor. Furthermore, we identified gp130/JAK signalling to be responsible for STAT3 activation, IRF9, and IRDS gene expression in MCS and by CM. Our data suggests a novel mechanism where STAT3 is activated in high cell density conditions resulting in increased expression of IRF9 and, in turn, IRDS genes, underlining a mechanism by which drug resistance is regulated.

Notch signaling regulates cell density-dependent apoptosis of NIH 3T3 through an IL-6/STAT3 dependent mechanism

Apoptosis is a physiological process that plays a critical maintenance role in cellular homeostasis. Previous reports have demonstrated that cells undergo apoptosis in a cell density-dependent manner, which is regulated, in part, by signal transducers and activators of transcription (STAT) 3. The molecular mechanisms regulating cell density-dependent apoptosis, however, has not been thoroughly investigated to date. Since Notch signaling is activated via direct cell-to-cell contact and plays a pivotal role in cell fate decisions, we examined the role of Notch signaling in cell density-dependent apoptosis of mouse embryonic fibroblasts NIH 3T3 cells. With the increase in cell density, IL-6 expression was induced, which was necessary for STAT3 activation as well as apoptosis regulation. Notch signaling was also activated in a cell-density dependent manner. Blocking Notch signaling either through siRNA-mediated targeting of Jagged1 expression or γ-secretase inhibitor treatment demonstrated that Notch signaling activation was necessary for IL-6 induction. Constitutive activation of Notch signaling via the overexpression of Notch1 intracellular domain was sufficient for the induction of IL-6, which was mediated via direct transcriptional activation. Taken together, our study indicates that Notch signaling regulates cell density-dependent apoptosis through IL-6/STAT3-dependent mechanism. Consequently, Notch signaling might represent a novel therapeutic target in diseases characterized by dysregulated apoptosis.

Gjb4 serves as a novel biomarker for lung cancer and promotes metastasis and chemoresistance via Src activation

Most lung cancer patients are diagnosed late with metastasis, which is the major cause of cancer-related death and recurrent tumors that often exhibit chemoresistance. In the present study, we initially identified gap junction beta-4 protein (Gjb4) to be overexpressed in highly metastatic cancer cells selected by their enhanced binding to serum components. Overexpression or knockdown of Gjb4 increased or decreased lung metastasis of syngeneic mice, respectively. We found that Gjb4 expression was higher in lung tumors than normal tissues (p = 0.0026), and Gjb4 levels in blood buffy coat samples showed significant performance in diagnosing stage I-III (p = 0.002814) and stage IV (p < 0.0001) lung cancer. Moreover, high Gjb4 expression levels were correlated with poor prognosis (p = 1.4e-4) and recurrence (p = 1.9e-12). Using syngeneic mouse model, we observed that Gjb4 was able to promote tumor growth. High molecular weight serum fraction containing the major growth factor component IGF1 was able to induce Gjb4 via PKC pathway. Gjb4 activated Src signaling via MET, and overexpression of Gjb4 enhanced sphere-forming ability and anchorage-independent growth, which were reversed by inhibition of Src. In addition, we demonstrated that Gjb4-mediated Src activation enhanced chemoresistance of cancer cells toward gemcitabine and etoposide. The combination of Gjb4 knockdown, gemcitabine, and dasatinib further enhanced the inhibition of cancer cell viability. Together, our study has identified Gjb4 as a potential novel diagnostic and prognostic biomarker for lung cancer. Targeting Gjb4 may be exploited as a modality for improving lung cancer therapy.

STAT3 labels a subpopulation of reactive astrocytes required for brain metastasis

The brain microenvironment imposes a particularly intense selective pressure on metastasis-initiating cells, but successful metastases bypass this control through mechanisms that are poorly understood. Reactive astrocytes are key components of this microenvironment that confine brain metastasis without infiltrating the lesion. Here, we describe that brain metastatic cells induce and maintain the co-option of a pro-metastatic program driven by signal transducer and activator of transcription 3 (STAT3) in a subpopulation of reactive astrocytes surrounding metastatic lesions. These reactive astrocytes benefit metastatic cells by their modulatory effect on the innate and acquired immune system. In patients, active STAT3 in reactive astrocytes correlates with reduced survival from diagnosis of intracranial metastases. Blocking STAT3 signaling in reactive astrocytes reduces experimental brain metastasis from different primary tumor sources, even at advanced stages of colonization. We also show that a safe and orally bioavailable treatment that inhibits STAT3 exhibits significant antitumor effects in patients with advanced systemic disease that included brain metastasis. Responses to this therapy were notable in the central nervous system, where several complete responses were achieved. Given that brain metastasis causes substantial morbidity and mortality, our results identify a novel treatment for increasing survival in patients with secondary brain tumors.

Tissue-Engineered Bone Immobilized with Human Adipose Stem Cells-Derived Exosomes Promotes Bone Regeneration

Exosomes, nanoscale extracellular vesicles functioning as cell-to-cell communicators, are an emerging promising therapeutic in the field of bone tissue engineering. Here, we report the construction and evaluation of a novel cell-free tissue-engineered bone that successfully accelerated the restoration of critical-sized mouse calvarial defects through combining exosomes derived from human adipose-derived stem cells (hASCs) with poly(lactic-co-glycolic acid) (PLGA) scaffolds. The exosomes were immobilized on the polydopamine-coating PLGA (PLGA/pDA) scaffolds under mild chemical conditions. Specifically, we investigated the effects of hASC-derived exosomes on the osteogenic, proliferation, and migration capabilities of human bone marrow-derived mesenchymal stem cells in vitro and optimized their osteoinductive effects through osteogenic induction. Furthermore, an in vitro assay showed exosomes could release from PLGA/pDA scaffold slowly and consistently and in vivo results showed this cell-free system enhanced bone regeneration significantly, at least partially through its osteoinductive effects and capacities of promoting mesenchymal stem cells migration and homing in the newly formed bone tissue. Therefore, overall results demonstrated that our novel cell-free system comprised of hASC-derived exosomes and PLGA/pDA scaffold provides a new therapeutic paradigm for bone tissue engineering and showed promising potential in repairing bone defects.

Inhibition of STAT3/VEGF/CDK2 axis signaling is critically involved in the antiangiogenic and apoptotic effects of arsenic herbal mixture PROS in non-small lung cancer cells

Despite the antitumor effects of asrsenic trioxide (As2O3), tetraarsenic hexoxide (As4O6 or PR) and tetraarsenic tetrasulfide (As4S4) in several cancers, their adverse poisoning, toxicity and resistance are still hot issues for effective cancer therapy. Here, antitumor mechanism of arsenic herbal mixture PROS including PR and OS (Oldenlandia diffusa and Salvia miltiorrhiza extract) was elucidated in non-small cell lung cancer cells (NSCLCs), since PR alone showed resistant cytotoxicity in NSCLCs compared to other cancers. PROS exerted significant cytotoxicity, induced sub-G1 phase and S phase arrest, increased apoptotic bodies, and attenuated the expression of pro-PARP, Bcl-2, Cyclin E, Cyclin A, CDK2, E2F1, p-Src, p-STAT3, p-ERK, p-AKT, COX-2 and SOCS-1 in A549 and H460 cells along with disrupted binding of STAT3 with CDK2 or VEGF. Notably, PROS inhibited VEGF induced proliferation, migration and tube formation in HUVECs and suppressed angiogenesis in chorioallantoic membrane (CAM) assay via reduced phosphorylation of VEGFR2, Src and STAT3. Consistently, PROS reduced the growth of H460 cells implanted in BALB/c athymic nude mice via inhibition of STAT3, and VEGF and activation of caspase 3. Overall, these findings suggest that PROS exerts antiangiogenic and apoptotic effects via inhibition of STAT3/ VEGF/ CDK2 axis signaling as a potent anticancer agent for lung cancer treatment.

Signal Transducers and Activators of Transcription: Insights into the Molecular Basis of Oral Cancer

Recent efforts on developing more direct and effective targets for cancer therapy have revolved around a family of transcription factors known as STATs (signal transducers and activators of transcription). STAT proteins are latent cytoplasmic transcription factors that become activated in response to extracellular signaling proteins. STAT proteins have been convincingly reported to possess oncogenic properties in a plethora of human cancers, including oral and oropharyngeal cancer. Signal transduction pathways mediated by these oncogenic transcription factors and their regulation in oral cancer are the focus of this review.

Stat3 contributes to cancer progression by regulating Jab1/Csn5 expression

Our previous studies demonstrated that Jab1/Csn5 overexpression is correlated with low survival rates in cancer patients, including nasopharyngeal carcinoma (NPC), breast cancer and hepatocellular carcinoma, and contributes to NPC's resistance to radiotherapy and cisplatin by regulating DNA damage and repair pathways. However, the molecular mechanism by which Jab1/Csn5 expression is upregulated in NPCs has yet to be determined. In the present study, we identified the upstream regulator of Jab1/Csn5 expression and demonstrated its role in intrinsic resistance of NPC cells to treatment with cisplatin. Signal transducer and activator of transcription-3 (Stat3) expression correlates with and contributes to Jab1/Csn5 transcription. Consistently, silencing of Stat3 in tumors reduced Jab1/Csn5 expression, thereby sensitizing NPC cells to cisplatin-induced apoptosis both in vitro and in vivo. Mechanistically, Stat3 transcriptionally regulated Jab1/Csn5. Furthermore, high mRNA expression levels of Stat3 or Jab1 in colon cancer, breast cancer and glioblastoma are associated with significantly shorter survival times from the R2 online database. These findings identify a novel Stat3-Jab1/Csn5 signaling axis in cancer pathogenesis with therapeutic and prognostic relevance.

PARD3 Inactivation in Lung Squamous Cell Carcinomas Impairs STAT3 and Promotes Malignant Invasion

Correct apicobasal polarization and intercellular adhesions are essential for the appropriate development of normal epithelia. Here, we investigated the contribution of the cell polarity regulator PARD3 to the development of lung squamous cell carcinomas (LSCC). Tumor-specific PARD3 alterations were found in 8% of LSCCs examined, placing PARD3 among the most common tumor suppressor genes in this malignancy. Most PAR3-mutant proteins exhibited a relative reduction in the ability to mediate formation of tight junctions and actin-based protrusions, bind atypical protein kinase C, activate RAC1, and activate STAT3 at cell confluence. Thus, PARD3 alterations prevented the formation of contacts between neighboring cells and the subsequent downstream signaling. Notably, reconstituting PAR3 activity in vivo reduced tumor-invasive and metastatic properties. Our findings define PARD3 as a recurrently inactivated cell polarity regulator in LSCC that affects tumor aggressiveness and metastasis.

Systematic review of factors influencing extracellular vesicle yield from cell cultures

The potential therapeutic utility of extracellular vesicles (EVs) has spawned an interest into a scalable production, where the quantity and purity of EV samples is sufficient for clinical applications. EVs can be isolated using several different protocols; however, these isolation protocols and the subsequent methods of quantifying the resulting EV yield have not been sufficiently standardized. Therefore, the possibility of comparing different studies with respect to these parameters is limited. In this review, we have presented factors that might influence the yield and function of EVs from cell culture supernatants. The methods of isolation, downstream quantification, and culture conditions of the EV producing cells have been discussed. In order to examine the inter-study coherency of EV yields, 259 studies were initially screened, and 46 studies were included for extensive downstream analysis of EV yields where information pertaining to the isolation protocols and quantification methods was obtained from each study. Several other factors influencing yield were compared, such as cell type producing EVs, cell confluence level, and cell stimulation. In conclusion, various factors may impact the resulting EV yield, including technical aspects such as EV isolation and quantification procedures, and biological aspects such as cell type and culture conditions. The reflections presented in this review might aid in future standardization of the workflow in EV research.

Review of STAT3 (Signal Transducers and Activators of Transcription) in head and neck cancer

STATs can be activated independently of JAKs, most notably by c-Src kinases. In cancer cells, STAT3 and STAT5 activation leads to the increased expression of downstream target genes, leading to increased cell proliferation, cell survival, angiogenesis, and immune system evasion. STAT3 and STAT5 are expressed and activated in head and neck squamous cell carcinoma where they contribute to cell survival and proliferation. STATs can be activated by a number of signal transduction pathways, including the epidermal growth factor receptor (EGFR), nicotinic receptor, interleukin (IL) receptor, and erythropoietin receptor pathways. Identifying agents that inhibit STAT-3, a cytosolic transcription factor involved in the activation of various genes implicated in tumor progression is a promising strategy for cancer chemoprevention. Several approaches have been used to inhibit STAT3 in the hope of developing an antitumor agent. Although several STAT3-specific agents are promising, none are in clinical development, mostly because of drug delivery and stability issues.

Cyclin A2 and its associated kinase activity are required for optimal induction of progesterone receptor target genes in breast cancer cells

A role for the cell cycle protein cyclin A2 in regulating progesterone receptor (PR) activity is emerging. This study investigates the role of cyclin A2 in regulating endogenous PR activity in T47D breast cancer cells by depleting cyclin A2 expression and measuring PR target genes using q-RT-PCR. Targets examined included genes induced by the PR-B isoform more strongly than PR-A (SGK1, FKBP5), a gene induced predominantly by PR-A (HEF1), genes induced via PR tethering to other transcription factors (p21, p27), a gene induced in part via extra-nuclear PR signaling mechanisms (cyclin D1) and PR-repressed genes (DST, IL1R1). Progestin induction of target genes was reduced following cyclin A2 depletion. However, cyclin A2 depletion did not diminish progestin target gene repression. Furthermore, inhibition of the associated Cdk2 kinase activity of cyclin A2 also reduced progestin induction of target genes, while Cdk2 enhanced the interaction between PR and cyclin A2. These results demonstrate that cyclin A2 and its associated kinase activity are important for progestin-induced activation of endogenous PR target genes in breast cancer cells.

A negative feedback loop mediated by STAT3 limits human Th17 responses

The transcription factor STAT3 is critically required for the differentiation of Th17 cells, a T cell subset involved in various chronic inflammatory diseases. In this article, we report that STAT3 also drives a negative-feedback loop that limits the formation of IL-17-producing T cells within a memory population. By activating human memory CD4(+)CD45RO(+) T cells at a high density (HiD) or a low density (LoD) in the presence of the pro-Th17 cytokines IL-1β, IL-23, and TGF-β, we observed that the numbers of Th17 cells were significantly higher under LoD conditions. Assessment of STAT3 phosphorylation revealed a more rapid and stronger STAT3 activation in HiD cells than in LoD cells. Transient inhibition of active STAT3 in HiD cultures significantly enhanced Th17 cell numbers. Expression of the STAT3-regulated ectonucleotidase CD39, which catalyzes ATP hydrolysis, was higher in HiD, than in LoD, cell cultures. Interestingly, inhibition of CD39 ectonucleotidase activity enhanced Th17 responses under HiD conditions. Conversely, blocking the ATP receptor P2X7 reduced Th17 responses in LoD cultures. These data suggest that STAT3 negatively regulates Th17 cells by limiting the availability of ATP. This negative-feedback loop may provide a safety mechanism to limit tissue damage by Th17 cells during chronic inflammation. Furthermore, our results have relevance for the design of novel immunotherapeutics that target the STAT3-signaling pathway, because inhibition of this pathway may enhance, rather than suppress, memory Th17 responses.

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

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

Antifibrotic effects of roscovitine in normal and scleroderma fibroblasts

Heightened production of collagen and other matrix proteins underlies the fibrotic phenotype of systemic sclerosis (SSc). Roscovitine is an inhibitor of cyclin-dependent kinases that promote cell cycling (CDK1, 2), neuronal development (CDK5) and control transcription (CDK7,9). In an in vivo glomerulonephritis model, roscovitine treatment decreased mesangial cell proliferation and matrix proteins [1]. We investigated whether roscovitine could regulate fibrotic protein production directly rather than through cell cycling. Our investigations revealed that roscovitine coordinately inhibited the expression of collagen, fibronectin, and connective tissue growth factor (CTGF) in normal and SSc fibroblasts. This effect occurred on a transcriptional basis and did not result from roscovitine-mediated cell cycle inhibition. Roscovitine-mediated suppression of matrix proteins could not be reversed by the exogenous profibrotic cytokines TGF-β or IL-6. To our knowledge, we are the first to report that roscovitine modulates matrix protein transcription. Roscovitine may thus be a viable treatment option for SSc and other fibrosing diseases.

Arecoline downregulates levels of p21 and p27 through the reactive oxygen species/mTOR complex 1 pathway and may contribute to oral squamous cell carcinoma

Arecoline, the major alkaloid of areca nut, has been shown to cause strong genotoxicity and is considered a potential carcinogen. However, the detailed mechanism for arecoline-induced carcinogenesis remains obscure. In this study, we noticed that the levels of p21 and p27 increased in two oral squamous cell carcinoma cell lines with high confluence. Furthermore, when treated with arecoline, elevated levels of p21 and p27 could be downregulated through the reactive oxygen species/mTOR complex 1 (ROS/mTORC1) pathway. Although arecoline decreased the activity of mTORC1, the amounts of autophagosome-like vacuoles or type II LC3 remained unchanged, suggesting that the downregulation of p21 and p27 was independent of autophagy-mediated protein destruction. Arecoline also caused DNA damage through ROS, indicating that the reduced levels of p21 and p27 might facilitate G (1) /S transition of the cell cycle and subsequently lead to error-prone DNA replication. In conclusion, these data have provided a possible mechanism for arecoline-induced carcinogenesis in subcytolytic doses in vivo.

The R(h)oads to Stat3: Stat3 activation by the Rho GTPases

The signal transducer and activator of transcription-3 (Stat3) is a member of the STAT family of cytoplasmic transcription factors. Overactivation of Stat3 is detected with high frequency in human cancer and is considered a molecular abnormality that supports the tumor phenotype. Despite concerted investigative efforts, the molecular mechanisms leading to the aberrant Stat3 activation and Stat3-mediated transformation and tumorigenesis are still not clearly defined. Recent evidence reveals a crosstalk close relationship between Stat3 signaling and members of the Rho family of small GTPases, including Rac1, Cdc42 and RhoA. Specifically, Rac1, acting in a complex with the MgcRacGAP (male germ cell RacGAP), promotes tyrosine phosphorylation of Stat3 by the IL6-receptor family/Jak kinase complex, as well as its translocation to the nucleus. Studies have further revealed that the mutational activation of Rac1 and Cdc42 results in Stat3 activation, which occurs in part through the upregulation of IL6 family cytokines that in turn stimulates Stat3 through the Jak kinases. Interestingly, evidence also shows that the engagement of cadherins, cell to cell adhesion molecules, specifically induces a striking increase in Rac1 and Cdc42 protein levels and activity, which in turn results in Stat3 activation. In this review we integrate recent findings clarifying the role of the Rho family GTPases in Stat3 activation in the context of malignant progression.

Master stem cell transcription factors and signaling regulation

The present article reviews master stem cell transcription factors, their expression regulation network, and related signaling pathways with the aim of understanding the molecular mechanisms of pluripotent cell fate decisions. Oct4, Sox2, and Nanog are master transcription factors for maintenance of the undifferentiated state and self-renewal of embryonic stem cells (ESCs). In the mouse, they form a regulatory circuitry with coregulators, such as beta-catenin, Stat3, Myc, Klfs, Sall4, and Esrrb to control the expression of pluripotency-related genes including themselves. The threshold expression of Oct4, Sox2, and Nanog for sustaining ESC properties depends on the synergistic effects among Stat3, beta-catenin, and Smad signaling pathway under the specific conditions of the ESC cytoplasmic microenvironment. Some of the salient differences in human ESC signaling pathways affecting their fate commitment are highlighted.

ZIP4 regulates pancreatic cancer cell growth by activating IL-6/STAT3 pathway through zinc finger transcription factor CREB

PURPOSE

Recent studies indicate a strong correlation of zinc transporter ZIP4 and pancreatic cancer progression; however, the underlying mechanisms are unclear. We have recently found that ZIP4 is overexpressed in pancreatic cancer. In this study, we investigated the signaling pathway through which ZIP4 regulates pancreatic cancer growth.

EXPERIMENTAL DESIGN

The expression of cyclin D1, interleukin 6 (IL-6), and signal transducer and activator of transcription 3 (STAT3) in pancreatic cancer xenografts and cells were examined by real-time PCR, Bio-Plex cytokine assay, and Western blot, respectively. The activity of cAMP response element-binding protein (CREB) is examined by a promoter activity assay.

RESULTS

Cyclin D1 was significantly increased in the ZIP4 overexpressing MIA PaCa-2 cells (MIA-ZIP4)-injected orthotopic xenografts and was downregulated in the ZIP4-silenced ASPC-1 (ASPC-shZIP4) group. The phosphorylation of STAT3, an upstream activator of cyclin D1, was increased in MIA-ZIP4 cells and decreased in ASPC-shZIP4 cells. IL-6, a known upstream activator for STAT3, was also found to be significantly increased in the MIA-ZIP4 cells and xenografts and decreased in the ASPC-shZIP4 group. Overexpression of ZIP4 led to a 75% increase of IL-6 promoter activity and caused increased phosphorylation of CREB.

CONCLUSIONS

Our study suggest that ZIP4 overexpression causes increased IL-6 transcription through CREB, which in turn activates STAT3 and leads to increased cyclin D1 expression, resulting in increased cell proliferation and tumor progression in pancreatic cancer. These results elucidated a novel pathway in ZIP4-mediated pancreatic cancer growth and suggest new therapeutic targets, including ZIP4, IL-6, and STAT3, in pancreatic cancer treatment.

Beyond structure, to survival: activation of Stat3 by cadherin engagement

Cells in normal tissues or in tumors have extensive opportunities for adhesion to their neighbors and the importance of cell to cell contact in the study of fundamental cellular processes is beginning to emerge. In this review, we discuss recent evidence of dramatic changes in the activity of an important signal transducer found to be profoundly affected by cell to cell adhesion, the signal transducer and activator of transcription-3 (Stat3). Direct cadherin engagement, growth of cells to postconfluence, or formation of multicellular aggregates were found to induce a striking increase in the levels of Stat3 activity, Rac1/Cdc42, and members of the IL6 receptor family in different settings. This activation was specific to Stat3, in that the levels of the extracellular signal regulated kinase (Erk1/2), a signal transducer often coordinately activated with Stat3 by a number of growth factors or oncogenes, remained unaffected by cell density. Density-dependent Stat3 activation may play a key role in survival, and could contribute to the establishment of cell polarity. It is clear that at any given time the total Stat3 activity levels in a cell are the sum of the effects of cell to cell adhesion plus the conventional Stat3 activating factors present.

Activated Rac1 requires gp130 for Stat3 activation, cell proliferation and migration

Rac1 (Rac) is a member of the Rho family of small GTPases which controls cell migration by regulating the organization of actin filaments. Previous results suggested that mutationally activated forms of the Rho GTPases can activate the Signal Transducer and Activator of Transcription-3 (Stat3), but the exact mechanism is a matter of controversy. We recently demonstrated that Stat3 activity of cultured cells increases dramatically following E-cadherin engagement. To better understand this pathway, we now compared Stat3 activity levels in mouse HC11 cells before and after expression of the mutationally activated Rac1 (Rac(V12)), at different cell densities. The results revealed for the first time a dramatic increase in protein levels and activity of both the endogenous Rac and Rac(V12) with cell density, which was due to inhibition of proteasomal degradation. In addition, Rac(V12)-expressing cells had higher Stat3, tyrosine-705 phosphorylation and activity levels at all densities, indicating that Rac(V12) is able to activate Stat3. Further examination of the mechanism of Stat3 activation showed that Rac(V12) expression caused a surge in mRNA of Interleukin-6 (IL6) family cytokines, known potent Stat3 activators. Knockdown of gp130, the common subunit of this family reduced Stat3 activity, indicating that these cytokines may be responsible for the Stat3 activation by Rac(V12). The upregulation of IL6 family cytokines was required for cell migration and proliferation induced by Rac(V12), as shown by gp130 knockdown experiments, thus demonstrating that the gp130/Stat3 axis represents an essential effector of activated Rac for the regulation of key cellular functions.

Differential expression of alpha-2,3-sialyltransferases and alpha-1,3/4-fucosyltransferases regulates the levels of sialyl Lewis a and sialyl Lewis x in gastrointestinal carcinoma cells

Sialyl Lewis x and sialyl Lewis a expression depends on sialyltransferases and fucosyltransferases. In this study, we screened for major variations of sialyltransferases and fucosyltransferases involved in the synthesis and regulation of sialyl Lewis x and sialyl Lewis a epitopes in gastrointestinal carcinoma cells. Our results show that expression of ST3Gal IV in several gastrointestinal cell lines is correlated with the expression of sialyl Lewis x at the cell surface. ST3Gal IV overexpressed in the gastric MKN45 cell line, showed exclusive enzymatic activity towards glycoproteins containing terminal Galbeta1-4GlcNAc structure. On the other hand, when ST3Gal III was overexpressed in MKN45, an increase in the expression levels of both sialyl Lewis epitopes was observed. ST3Gal III and ST3Gal IV lead to de novo synthesis of sialyl Lewis x determinant on different molecular weight glycoproteins of MKN45 cells suggesting that each enzyme used different substrates within the available glycoproteome. The final glycosylation step in sialyl Lewis x and sialyl Lewis a biosynthesis in MKN45 cell line was shown to be associated to FUT5, which efficiently fucosylated sialyl Lewis precursors on glycoproteins. Moreover we demonstrate that the expression of sialyl Lewis epitopes in the MKN45 was induced by cell confluence, which can be regarded as a model to study altered glycosylation during tumour progression. This increase was observed together with an increase in mRNA levels of ST3GAL3, FUT5 and FUT6, and a decrease in FUT4 transcript levels in MKN45 confluent cells, suggesting a possible control at the transcriptional level.

Cadherin-cadherin engagement promotes cell survival via Rac1/Cdc42 and signal transducer and activator of transcription-3

Signal transducer and activator of transcription-3 (Stat3) is activated by a number of receptor and nonreceptor tyrosine kinases, whereas a constitutively active form of Stat3 alone is sufficient to induce neoplastic transformation. In the present report, we show that Stat3 can also be activated through homophilic interactions by the epithelial (E)-cadherin. Indeed, by plating cells onto surfaces coated with fragments encompassing the two outermost domains of this cadherin, we clearly show that cadherin engagement can activate Stat3, even in the absence of direct cell-to-cell contact. Most importantly, our results also reveal for the first time an unexpected and dramatic surge in total Rac1 and Cdc42 protein levels triggered by cadherin engagement and an increase in Rac1 and Cdc42 activity, which is responsible for the Stat3 stimulation observed. Inhibition of cadherin interactions using a peptide, a soluble cadherin fragment, or genetic ablation induced apoptosis, points to a significant role of this pathway in cell survival signaling, a finding that could also have important therapeutic implications. (Mol Cancer Res 2009;7(8):1310-27).

Reduced expression of a gene proliferation signature is associated with enhanced malignancy in colon cancer

The association between cell proliferation and the malignant potential of colon cancer is not well understood. Here, we evaluated this association using a colon-specific gene proliferation signature (GPS). The GPS was derived by combining gene expression data obtained from the analysis of a cancer cell line model and a published colon crypt profile. The GPS was overexpressed in both actively cycling cells in vitro and the proliferate compartment of colon crypts. K-means clustering was used to independantly stratify two cohorts of colon tumours into two groups with high and low GPS expression. Notably, we observed a significant association between reduced GPS expression and an increased likelihood of recurrence (P<0.05), leading to shorter disease-free survival in both cohorts. This finding was not a result of methodological bias as we verified the well-established association between breast cancer malignancy and increased proliferation, by applying our GPS to public breast cancer data. In this study, we show that reduced proliferation is a biological feature characterizing the majority of aggressive colon cancers. This contrasts with many other carcinomas such as breast cancer. Investigating the reasons underlying this unusual observation may provide important insight into the biology of colon cancer progression and putative novel therapy options.

Cell confluency-induced Stat3 activation regulates NHE3 expression by recruiting Sp1 and Sp3 to the proximal NHE3 promoter region during epithelial dome formation

Activation of signal transducer and activator of transcription-3 (Stat3) during cell confluency is related to its regulatory roles in cell growth arrest- or survival-related physiological or developmental processes. We previously demonstrated that this signaling event triggers epithelial dome formation by transcriptional augmentation of sodium hydrogen exchanger-3 (NHE3) expression. However, the detailed molecular mechanism remained unclear. By using serial deletions, site-directed mutagenesis, and EMSA analysis, we now demonstrate Stat3 binding to an atypical Stat3-response element in the rat proximal NHE3 promoter, located adjacent to a cluster of Sp cis-elements (SpA/B/C), within -77/-36 nt of the gene. SpB (-58/-55 nt) site was more effective than SpA (-72/-69 nt) site for cooperative binding of Sp1/Sp3. Increasing cell density had no effect on Sp1/Sp3 expression but resulted in their increased binding to the SpA/B/C probe along with Stat3 and concurrently with enhanced nuclear pTyr705-Stat3 level. Immunoprecipitation performed with the nuclear extracts demonstrated physical interaction of Stat3 and Sp1/Sp3 triggered by cell confluency. Stat3 inhibition by overexpression of dominant-negative Stat3-D mutant in MDCK cells or by small interfering RNA-mediated knockdown in Caco-2 cells resulted in inhibition of the cell density-induced NHE3 expression, Sp1/Sp3 binding, and NHE3 promoter activity and in decreased dome formation. Thus, during confluency, ligand-independent Stat3 activation leads to its interaction with Sp1/Sp3, their recruitment to the SpA/B/C cluster in a Stat3 DNA-binding domain-dependent fashion, increased transcription, and expression of NHE3, to coordinate cell density-mediated epithelial dome formation.

Effects of plasmid-based Stat3-specific short hairpin RNA and GRIM-19 on PC-3M tumor cell growth

PURPOSE

Persistent activation of signal transducers and activators of transcription 3 (Stat3) and its overexpression contribute to the progression and metastasis of several different tumor types. For this reason, Stat3 is a reasonable target for RNA interference-mediated growth inhibition. Blockade of Stat3 using specific short hairpin RNAs (shRNA) can significantly reduce prostate tumor growth in mice. However, RNA interference does not fully ablate target gene expression in vivo, owing to the idiosyncrasies associated with shRNAs and their targets. To enhance the therapeutic efficacy of Stat3-specific shRNA, we applied a combination treatment involving gene associated with retinoid-IFN-induced mortality 19 (GRIM-19), another inhibitor of STAT3, along with shRNA.

EXPERIMENTAL DESIGN

The coding sequences for GRIM-19, a cellular STAT3-specific inhibitor, and Stat3-specific shRNAs were used to create a dual expression plasmid vector and used for prostate cancer therapy in vitro and in mouse xenograft models in vivo.

RESULTS

The coexpressed Stat3-specific shRNA and GRIM-19 synergistically and more effectively suppressed prostate tumor growth and metastases when compared with treatment with either single agent alone.

CONCLUSION

The simultaneous use of two specific, but mechanistically different, inhibitors of STAT3 activity exerts enhanced antitumor effects.

Cell density dependent increase of constitutive signal transducers and activators of transcription 3 activity in melanoma cells is mediated by Janus kinases

Signal transducers and activators of transcriptions (STAT) are key mediators of cytokine signaling. Moreover, these transcription factors play a crucial role in oncogenic signaling where inappropriate and sustained activation of STATs, especially STAT3, is a trait of many different cancers and their derived cell lines. Constitutively active STAT3 has been reported to prevent programmed cell death and enhance cell proliferation, whereas the disruption of STAT3 signaling can inhibit tumor growth. The physiologic activation of STAT3 by cytokines has been well established; however, little is known about altered, stimulation-independent STAT3 activation. Here, we show that, in most but not all melanoma cell lines, STAT3 phosphorylation increased substantially with cell density and that this STAT3 was able to bind to DNA and to activate transcription. Inhibitor studies showed that the cell density-dependent STAT3 activation relies on Janus kinases (JAK) rather than Src kinases. Using a specific JAK inhibitor, sustained STAT3 activation was completely abrogated in all tested melanoma lines, whereas inhibition of Src or mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 1/2 had no effect on constitutively tyrosine-phosphorylated STAT3 levels. Although STAT3 activation was completely blocked with JAK inhibitor I and to a lesser extent with the common JAK inhibitor AG490, only the latter compound markedly decreased proliferation and induced apoptosis. Taken together, variations in cell density can profoundly modify the extent of JAK-mediated persistent STAT3 phosphorylation; however, STAT3 activation was not sufficient to provide critical growth and survival signals in melanoma cell lines.

STAT3 signaling is induced by intercellular adhesion in squamous cell carcinoma cells

The signal transducer and activator of transcription-3 (STAT3) frequently activated during tumor progression has been linked to enhanced cell growth. In squamous cell carcinoma of the head and neck (HNSCC), STAT3 signaling has been shown to inhibit apoptosis and induce a more aggressive phenotype through the activation of specific signaling pathways. In the present study, we have examined the potential mechanism by which cell-cell contact initiates STAT3 activation. Using a panel of HNSCC cell lines, Ca(+2)-dependent cell-cell adhesion and adherens junction formation in multicellular aggregates triggered phosphorylation of STAT3-Y705 and STAT1-Y701. This intercellular adhesion-induced STAT3 activation was mediated by JAK and Src signaling and partially by EGFR signaling. In addition, immunolocalization studies revealed initial formation of phosphorylated STAT3-Y705 at nascent E-cadherin cell junctions with eventual translocation to the nucleus in cell aggregates. Adhesion-mediated STAT activation in monolayer and cell aggregate cultures required functional E-cadherin. These results indicate that, in HNSCC cells, cadherin-mediated intercellular adhesion induces STAT signaling that may modulate cell survival and resistance to apoptosis during tumor progression.

Tumors Initiated by Constitutive Cdk2 Activation Exhibit Transforming Growth Factor β Resistance and Acquire Paracrine Mitogenic Stimulation during Progression

Cyclin D1/cyclin-dependent kinase 2 (Cdk2) complexes are present at high frequency in human breast cancer cell lines, but the significance of this observation is unknown. This report shows that expression of a cyclin D1-Cdk2 fusion protein under the control of the mouse mammary tumor virus (MMTV) promoter results in mammary gland hyperplasia and fibrosis, and mammary tumors. Cell lines isolated from MMTV-cyclin D1-Cdk2 (MMTV-D1K2) tumors exhibit Rb and p130 hyperphosphorylation and up-regulation of the protein products of E2F-dependent genes. These results suggest that cyclin D1/Cdk2 complexes may mediate some of the transforming effects that result from cyclin D1 overexpression in human breast cancers. MMTV-D1K2 cancer cells express the hepatocyte growth factor (HGF) receptor, c-Met. MMTV-D1K2 cancer cells also secrete transforming growth factor beta (TGFbeta), but are relatively resistant to TGFbeta antiproliferative effects. Fibroblasts derived from MMTV-D1K2 tumors secrete factors that stimulate the proliferation of MMTV-D1K2 cancer cells, stimulate c-Met tyrosine phosphorylation, and stimulate the phosphorylation of the downstream signaling intermediates p70(s6k) and Akt on activating sites. Together, these results suggest that deregulation of the Cdk/Rb/E2F axis reprograms mammary epithelial cells to initiate a paracrine loop with tumor-associated fibroblasts involving TGFbeta and HGF, resulting in desmoplasia. The MMTV-D1K2 mice should provide a useful model system for the development of therapeutic approaches to block the stromal desmoplastic reaction that likely plays an important role in the progression of multiple types of human tumors.

Cell confluence-induced activation of signal transducer and activator of transcription-3 (Stat3) triggers epithelial dome formation via augmentation of sodium hydrogen exchanger-3 (NHE3) expression

Cell confluence induces the activation of signal transducer and activator of transcription-3 (Stat3) in various cancer and epithelial cells, yet the biological implications and the associated regulatory mechanisms remain unclear. Because confluent polarized epithelia demonstrate dome formation and sodium influx that mimic the onset of differentiation, we sought to elucidate the role of Stat3 in association with the regulation of selective epithelial transporters in this biological phenomenon. This study established the correlation between Stat3 activation and cell confluence-induced dome formation in Madin-Darby canine kidney cells (MDCK) by following Stat3 activation events in dome-forming cells. Epifluorescent and confocal microscopy provided evidence showing specific localization of phosphorylated Stat3 Tyr(705) in the nuclei of dome-forming cells at initial stages. The relationship was further elucidated by the establishment of tetracycline-inducible expression of constitutive Stat3 mutant (Stat3-C) in MDCK cells or expression of dominant negative Stat3 (Stat3-D) stable cell lines (MDCK and NMuMG). Dome formation was promoted by the expression of Stat3-C but inhibited by Stat3-D. Two trans-epithelial transporters, NHE3 and ENaC alpha-subunit, were found to be increased during cell confluence. Interestingly, NHE3 expression could be specifically up-regulated by Stat3-C but inhibited by Stat3-D through promoter regulation, whereas NHE1 and ENaC alpha-subunit were not affected by Stat3 expression. Application of NHE3 shRNA, NHE3 inhibitors (EIPA and S3226) suppressed confluence-induced dome formation in MDCK or NMuMG cells. These results demonstrate a cell confluence-induced Stat3 signaling pathway in epithelial cells in triggering dome formation through NHE3 augmentation.