Zooming in on Long Non-Coding RNAs in Ewing Sarcoma Pathogenesis.

Ewing sarcoma (ES) is a rare aggressive cancer of bone and soft tissue that is mainly characterized by a reciprocal chromosomal translocation. As a result, about 90% of cases express the EWS-FLI1 fusion protein that has been shown to function as an aberrant transcription factor driving sarcomagenesis. ES is the second most common malignant bone tumor in children and young adults. Current treatment modalities include dose-intensified chemo- and radiotherapy, as well as surgery. Despite these strategies, patients who present with metastasis or relapse still have dismal prognosis, warranting a better understanding of treatment resistant-disease biology in order to generate better prognostic and therapeutic tools. Since the genomes of ES tumors are relatively quiet and stable, exploring the contributions of epigenetic mechanisms in the initiation and progression of the disease becomes inevitable. The search for novel biomarkers and potential therapeutic targets of cancer metastasis and chemotherapeutic drug resistance is increasingly focusing on long non-coding RNAs (lncRNAs). Recent advances in genome analysis by high throughput sequencing have immensely expanded and advanced our knowledge of lncRNAs. They are non-protein coding RNA species with multiple biological functions that have been shown to be dysregulated in many diseases and are emerging as crucial players in cancer development. Understanding the various roles of lncRNAs in tumorigenesis and metastasis would determine eclectic avenues to establish therapeutic and diagnostic targets. In ES, some lncRNAs have been implicated in cell proliferation, migration and invasion, features that make them suitable as relevant biomarkers and therapeutic targets. In this review, we comprehensively discuss known lncRNAs implicated in ES that could serve as potential biomarkers and therapeutic targets of the disease. Though some current reviews have discussed non-coding RNAs in ES, to our knowledge, this is the first review focusing exclusively on ES-associated lncRNAs.

Mechanisms, Diagnosis and Treatment of Bone Metastases.

Bone and bone marrow are among the most frequent metastatic sites of cancer. The occurrence of bone metastasis is frequently associated with a dismal disease outcome. The prevention and therapy of bone metastases is a priority in the treatment of cancer patients. However, current therapeutic options for patients with bone metastatic disease are limited in efficacy and associated with increased morbidity. Therefore, most current therapies are mainly palliative in nature. A better understanding of the underlying molecular pathways of the bone metastatic process is warranted to develop novel, well-tolerated and more successful treatments for a significant improvement of patients' quality of life and disease outcome. In this review, we provide comparative mechanistic insights into the bone metastatic process of various solid tumors, including pediatric cancers. We also highlight current and innovative approaches to biologically targeted therapy and immunotherapy. In particular, we discuss the role of the bone marrow microenvironment in the attraction, homing, dormancy and outgrowth of metastatic tumor cells and the ensuing therapeutic implications. Multiple signaling pathways have been described to contribute to metastatic spread to the bone of specific cancer entities, with most knowledge derived from the study of breast and prostate cancer. However, it is likely that similar mechanisms are involved in different types of cancer, including multiple myeloma, primary bone sarcomas and neuroblastoma. The metastatic rate-limiting interaction of tumor cells with the various cellular and noncellular components of the bone-marrow niche provides attractive therapeutic targets, which are already partially exploited by novel promising immunotherapies.

MITF reprograms the extracellular matrix and focal adhesion in melanoma.

The microphthalmia-associated transcription factor (MITF) is a critical regulator of melanocyte development and differentiation. It also plays an important role in melanoma where it has been described as a molecular rheostat that, depending on activity levels, allows reversible switching between different cellular states. Here, we show that MITF directly represses the expression of genes associated with the extracellular matrix (ECM) and focal adhesion pathways in human melanoma cells as well as of regulators of epithelial-to-mesenchymal transition (EMT) such as CDH2, thus affecting cell morphology and cell-matrix interactions. Importantly, we show that these effects of MITF are reversible, as expected from the rheostat model. The number of focal adhesion points increased upon MITF knockdown, a feature observed in drug-resistant melanomas. Cells lacking MITF are similar to the cells of minimal residual disease observed in both human and zebrafish melanomas. Our results suggest that MITF plays a critical role as a repressor of gene expression and is actively involved in shaping the microenvironment of melanoma cells in a cell-autonomous manner.

User guide to MiT-TFE isoforms and post-translational modifications.

The microphthalmia-associated transcription factor (MITF) is at the core of melanocyte and melanoma fate specification. The related factors TFEB and TFE3 have been shown to be instrumental for transcriptional regulation of genes involved in lysosome biogenesis and autophagy, cellular processes important for mediating nutrition signals and recycling of cellular materials, in many cell types. The MITF, TFEB, TFE3, and TFEC proteins are highly related. They share many structural and functional features and are targeted by the same signaling pathways. However, the existence of several isoforms of each factor and the increasing number of residues shown to be post-translationally modified by various signaling pathways poses a difficulty in indexing amino acid residues in different isoforms across the different proteins. Here, we provide a resource manual to cross-reference amino acids and post-translational modifications in all isoforms of the MiT-TFE family in humans, mice, and zebrafish and summarize the protein accession numbers for each isoform of these factors in the different genomic databases. This will facilitate future studies on the signaling pathways that regulate different isoforms of the MiT-TFE transcription factor family.

MITF and TFEB cross-regulation in melanoma cells.

The MITF, TFEB, TFE3 and TFEC (MiT-TFE) proteins belong to the basic helix-loop-helix family of leucine zipper transcription factors. MITF is crucial for melanocyte development and differentiation, and has been termed a lineage-specific oncogene in melanoma. The three related proteins MITF, TFEB and TFE3 have been shown to be involved in the biogenesis and function of lysosomes and autophagosomes, regulating cellular clearance pathways. Here we investigated the cross-regulatory relationship of MITF and TFEB in melanoma cells. Like MITF, the TFEB and TFE3 genes are expressed in melanoma cells as well as in melanoma tumors, albeit at lower levels. We show that the MITF and TFEB proteins, but not TFE3, directly affect each other's mRNA and protein expression. In addition, the subcellular localization of MITF and TFEB is subject to regulation by the mTOR signaling pathway, which impacts their cross-regulatory relationship at the transcriptional level. Our work shows that the relationship between MITF and TFEB is multifaceted and that the cross-regulatory interactions of these factors need to be taken into account when considering pathways regulated by these proteins.

MITF has a central role in regulating starvation-induced autophagy in melanoma.

The MITF transcription factor is a master regulator of melanocyte development and a critical factor in melanomagenesis. The related transcription factors TFEB and TFE3 regulate lysosomal activity and autophagy processes known to be important in melanoma. Here we show that MITF binds the CLEAR-box element in the promoters of lysosomal and autophagosomal genes in melanocytes and melanoma cells. The crystal structure of MITF bound to the CLEAR-box reveals how the palindromic nature of this motif induces symmetric MITF homodimer binding. In metastatic melanoma tumors and cell lines, MITF positively correlates with the expression of lysosomal and autophagosomal genes, which, interestingly, are different from the lysosomal and autophagosomal genes correlated with TFEB and TFE3. Depletion of MITF in melanoma cells and melanocytes attenuates the response to starvation-induced autophagy, whereas the overexpression of MITF in melanoma cells increases the number of autophagosomes but is not sufficient to induce autophagic flux. Our results suggest that MITF and the related factors TFEB and TFE3 have separate roles in regulating a starvation-induced autophagy response in melanoma. Understanding the normal and pathophysiological roles of MITF and related transcription factors may provide important clinical insights into melanoma therapy.

Subcellular localization and stability of MITF are modulated by the bHLH-Zip domain.

Microphthalmia-associated transcription factor (MITF) is a member of the basic helix-loop-helix leucine zipper (bHLH-Zip) family and functions as the master regulator of the melanocytic lineage. MITF-M is the predominant isoform expressed in melanocytes and melanoma cells, and, unlike other MITF isoforms, it is constitutively nuclear. Mutational analysis revealed three karyophilic signals in the bHLH-Zip domain of MITF-M, spanning residues 197-206, 214-217, and 255-265. Structural characterization of the MITF protein showed that basic residues within these signals are exposed for interactions in the absence of DNA. Moreover, our data indicate that neither DNA binding nor dimerization of MITF-M are required for its nuclear localization. Finally, dimerization-deficient MITF-M mutants exhibited a significantly reduced stability in melanoma cells when compared to the wild-type protein. Taken together, we have shown that, in addition to its well-established role in DNA binding and dimer formation, the bHLH-Zip domain of MITF modulates the transcription factor's subcellular localization and stability.

Neuregulin-1-mediated ErbB2-ErbB3 signalling protects human trophoblasts against apoptosis to preserve differentiation.

During placentation, foetal trophoblasts invade deeply into maternal tissue to establish a foeto-maternal circulation. We have previously shown that extravillous trophoblast (EVT) lineage cells express ErbB2 and ErbB3, of which the potential as an oncogenic unit is well established. However, a physiological function of this receptor combination in humans remains a puzzling question. Here, we demonstrate neuregulin 1 (NRG1) expression and secretion by human decidual stromal cells. Stimulation of human primary trophoblasts with exogenous NRG1 induced phosphorylation of ErbB2, ErbB3 and related downstream effectors. Co-immunoprecipitation experiments confirmed the formation of ErbB2-ErbB3 dimers upon ligand engagement. Along this line, receptor knockdown and ErbB3 neutralization strongly diminished NRG1-dependent activation of the signalling complex. Functional studies revealed that NRG1 promotes EVT formation in placental explant cultures. Although, in the presence of NRG1, basal and camptothecin-induced trophoblast apoptosis was significantly repressed, this effect was abolished upon ErbB3 inhibition. Notably, camptothecin provoked a strong reduction of trophoblast cell column size, whereas NRG1-treated explants were refractory to the compound. Taken together, our findings newly identify a physiological function of the NRG1-ErbB2-ErbB3 axis in trophoblast survival during human placental development.

Trophoblast subtype-specific EGFR/ERBB4 expression correlates with cell cycle progression and hyperplasia in complete hydatidiform moles.

STUDY QUESTION: Do trophoblast subtypes differ in their expression of erythroblastic leukaemia viral oncogene homologue (ERBB) receptor family members and responsiveness towards specific growth factor ligands? SUMMARY ANSWER: Our data reveal a reciprocal expression pattern of epidermal growth factor receptor (EGFR)/ERBB4 in proliferative and ERBB2/ERBB3 in invasive trophoblast subtypes, as well as a restricted responsiveness to epidermal growth factor (EGF) and heparin-binding (HB)-EGF. WHAT IS KNOWN ALREADY: EGFR is expressed by villous cytotrophoblasts (vCTBs), but absent from extravillous trophoblasts (EVTs), which specifically up-regulate ERBB2. STUDY DESIGN, SIZE, DURATION: Tissue samples of human first trimester placentae (n = 50) and deciduae (n = 5) obtained from elective pregnancy terminations were used to study trophoblast subtype-specific ERBB receptor expression and responsiveness to recombinant human EGF and HB-EGF. Age-matched complete hydatidiform mole (CHM) placentae (n = 12) were assessed for EGFR and ERBB4 expression in proliferation-competent regions. PARTICIPANTS/MATERIALS, SETTING, METHODS: ERBB receptor expression was analysed in primary trophoblast cell isolates by means of microarray, quantitative real-time PCR and western blotting, as well as immunofluorescence stainings of placental and decidual tissue sections. EGF and HB-EGF were tested for their potential to activate ERBB receptors in purified EGFR(+) and HLA-G(+) trophoblasts. 5-Ethynyl-2'-deoxyuridine incorporation assays were performed to study the effect of both ligands on the proliferative capacity of primary trophoblasts as well as of vCTBs and proximal cell column trophoblasts (pCCTs) in placental floating explants. Finally, the average number of EGFR(+) vCTB and pCCT layers was determined in CHM placentae and compared with healthy age-matched controls. MAIN RESULTS AND THE ROLE OF CHANCE: Proliferative vCTBs and pCCTs co-express EGFR and ERBB4, but are devoid of ERBB2 and ERBB3. In contrast, HLA-G(+) trophoblast subtypes exhibit an EGFR/ERBB4(-) and ERBB2/ERBB3(+) phenotype. EGF and HB-EGF activate EGFR, ERBB4, AKT and extracellular signal-regulated kinase 1/2 in EGFR(+) primary trophoblasts; however, they do not show an effect on HLA-G(+) EVTs. Both ligands strongly induce cell cycle progression in primary trophoblasts (P < 0.05) and placental explant-associated vCTBs (P < 0.05) and pCCTs (P < 0.05). Notably, EGFR(+) vCTB (P < 0.0001) and pCCT (P < 0.0001) layers are significantly expanded in CHM placentae when compared with healthy controls. LIMITATIONS, REASONS FOR CAUTION: Cells were removed from their physiological context and may therefore respond differently to various stimuli. WIDER IMPLICATIONS OF THE FINDINGS: In this study we define EGFR as a marker for proliferative trophoblast subtypes within the human placenta. Manipulation of EGFR signalling might thus offer a promising therapeutic avenue for the treatment of molar pregnancies associated with trophoblast hyperplasia. STUDY FUNDING/COMPETING INTERESTS: This study was supported by the Austrian Science Fund (grant P-25187-B13 to J.P.). There are no competing interests to declare.

Extravillous trophoblast-associated ADAM12 exerts pro-invasive properties, including induction of integrin beta 1-mediated cellular spreading.

ADAM12, consisting of a membrane-bound (ADAM12L) and a secreted (ADAM12S) form, is expressed exclusively in regenerating and developing tissue as well as in certain cancer types. Strong ADAM12 expression levels have been noticed in the human placenta, and deregulated ADAM12S levels were associated with various pregnancy-related disorders including pre-eclampsia and intrauterine growth restriction. However, the role of ADAM12 in trophoblast motility has not been investigated so far. Hence, the present study aimed to investigate the specific function of the protease by using different primary trophoblast cell models. Immunofluorescence and Western blot analyses of first trimester placental tissue and differentiating primary first trimester cytotrophoblasts (CTBs) indicated strong upregulation of both of the ADAM12 isoforms during extravillous trophoblast differentiation. Functional assays involving short interfering RNA (siRNA)-mediated knockdown studies in primary CTBs and first trimester explant cultures revealed a significant repression of trophoblast motility upon partial loss of ADAM12. Conversely, isoform-specific overexpression in the ADAM12-negative trophoblast cell line SGHPL-5 enhanced the invasive capacity of these cells. We further confirmed proteolytic activity of trophoblast-derived ADAM12S by demonstrating its potential to degrade insulin-like growth factor-binding protein 3. Finally, we suggest that ADAM12S exerts its pro-migratory function in trophoblasts by inducing integrin beta 1-mediated cellular spreading.

Macrophage-derived IL-33 is a critical factor for placental growth.

IL-33, the most recently discovered member of the IL-1 superfamily and ligand for the transmembrane form of ST2 (ST2L), has been linked to several human pathologies including rheumatoid arthritis, asthma, and cardiovascular disease. Deregulated levels of soluble ST2, the natural IL-33 inhibitor, have been reported in sera of preeclamptic patients. However, the role of IL-33 during healthy pregnancy remains elusive. In the current study, IL-33 was detected in the culture supernatants of human placental and decidual macrophages, identifying them as a major source of secreted IL-33 in the uteroplacental unit. Because flow cytometry and immunofluorescence stainings revealed membranous ST2L expression on specific trophoblast populations, we hypothesized that IL-33 stimulates trophoblasts in a paracrine manner. Indeed, BrdU incorporation assays revealed that recombinant human IL-33 significantly increased proliferation of primary trophoblasts as well as of villous cytotrophoblasts and cell column trophoblasts in placental explant cultures. These effects were fully abolished upon addition of soluble ST2. Interestingly, Western blot and immunofluorescence analyses demonstrated that IL-33 activates AKT and ERK1/2 in primary trophoblasts and placental explants. Inhibitors against PI3K (LY294002) and MEK1/2 (UO126) efficiently blocked IL-33-induced proliferation in all model systems used. In summary, with IL-33, we define for the first time, to our knowledge, a macrophage-derived regulator of placental growth during early pregnancy.

Endostatin suppresses IGF-II-mediated signaling and invasion of human extravillous trophoblasts.

Endostatin, a biological active fragment of the extracellular matrix protein collagen XVIII, is known to interfere with cellular motility in the context of pathological angiogenesis. However, the physiological role of endostatin remains largely elusive. Recent evidence suggested that the inhibitor is produced in human decidual cells of early pregnancy, indicating that endostatin could be involved in diverse reproductive processes, such as implantation and/or placental differentiation. To gain more insights into the role of endostatin, we here analyzed its effects on trophoblast motility, proliferation, and signaling using purified primary trophoblasts, first-trimester villous explant cultures, and trophoblastic SGHPL-5 cells. In vitro Transwell assays demonstrated that purified endostatin inhibited both basal and IGF-II-induced migration and invasion as well as outgrowth from villous explant cultures. In contrast, basal and IGF-II-stimulated proliferation was unaffected upon addition of the inhibitor. Analyses of IGF-II-associated downstream signaling events showed that endostatin interfered with activation of various signaling kinases such as ERK1/2, protein kinase B (Akt)/mammalian target of rapamycin/p70 S6 kinase, and focal adhesion kinase. Furthermore, virus-mediated, stable gene silencing of Akt1 in SGHPL-5 cells using a micro-RNA-adapted short hairpin RNA-expressing plasmid revealed that endostatin-mediated inhibition of IGF-II-induced Akt phosphorylation was critically dependent on the expression of the particular isoform. In conclusion, the data suggest that endostatin could be a physiological inhibitor of IGF-II-dependent trophoblast cell motility by suppressing focal adhesion kinase/Akt/mammalian target of rapamycin/p70 S6 kinase signaling.