The TGF-ß Family in Glioblastoma.

Members of the transforming growth factor ß (TGF-ß) family have been implicated in the biology of several cancers. In this review, we focus on the role of TGFß and bone morphogenetic protein (BMP) signaling in glioblastoma. Glioblastoma (GBM) is the most common malignant brain tumor in adults; it presents at a median age of 64 years, but can occur at any age, including childhood. Unfortunately, there is no cure, and even patients undergoing current treatments (surgical resection, radiotherapy, and chemotherapy) have a median survival of 15 months. There is a great need to identify new therapeutic targets to improve the treatment of GBM patients. TGF-ßs signaling promotes tumorigenesis in glioblastoma, while BMPs suppress tumorigenic potential by inducing tumor cell differentiation. In this review, we discuss the actions of TGF-ßs and BMPs on cancer cells as well as in the tumor microenvironment, and their use in potential therapeutic intervention.

The long non-coding RNA LINC00707 interacts with Smad proteins to regulate TGFß signaling and cancer cell invasion.

BACKGROUND: Long non-coding RNAs (lncRNAs) regulate cellular processes by interacting with RNAs or proteins. Transforming growth factor ß (TGFß) signaling via Smad proteins regulates gene networks that control diverse biological processes, including cancer cell migration. LncRNAs have emerged as TGFß targets, yet, their mechanism of action and biological role in cancer remain poorly understood. METHODS: Whole-genome transcriptomics identified lncRNA genes regulated by TGFß. Protein kinase inhibitors and RNA-silencing, in combination with cDNA cloning, provided loss- and gain-of-function analyses. Cancer cell-based assays coupled to RNA-immunoprecipitation, chromatin isolation by RNA purification and protein screening sought mechanistic evidence. Functional validation of TGFß-regulated lncRNAs was based on new transcriptomics and by combining RNAscope with immunohistochemical analysis in tumor tissue. RESULTS: Transcriptomics of TGFß signaling responses revealed down-regulation of the predominantly cytoplasmic long intergenic non-protein coding RNA 707 (LINC00707). Expression of LINC00707 required Smad and mitogen-activated protein kinase inputs. By limiting the binding of Krüppel-like factor 6 to the LINC00707 promoter, TGFß led to LINC00707 repression. Functionally, LINC00707 suppressed cancer cell invasion, as well as key fibrogenic and pro-mesenchymal responses to TGFß, as also attested by RNA-sequencing analysis. LINC00707 also suppressed Smad-dependent signaling. Mechanistically, LINC00707 interacted with and retained Smad proteins in the cytoplasm. Upon TGFß stimulation, LINC00707 dissociated from the Smad complex, which allowed Smad accumulation in the nucleus. In vivo, LINC00707 expression was negatively correlated with Smad2 activation in tumor tissues. CONCLUSIONS: LINC00707 interacts with Smad proteins and limits the output of TGFß signaling, which decreases LINC00707 expression, thus favoring cancer cell invasion. Video Abstract.

Cystathionine gamma-lyase (CTH) inhibition attenuates glioblastoma formation.

PURPOSE: Glioblastoma (GBM) is the most common type of adult brain tumor with extremely poor survival. Cystathionine-gamma lyase (CTH) is one of the main Hydrogen Sulfide (H2S) producing enzymes and its expression contributes to tumorigenesis and angiogenesis but its role in glioblastoma development remains poorly understood. METHODS: and Principal Results: An established allogenic immunocompetent in vivo GBM model was used in C57BL/6J WT and CTH KO mice where the tumor volume and tumor microvessel density were blindly measured by stereological analysis. Tumor macrophage and stemness markers were measured by blinded immunohistochemistry. Mouse and human GBM cell lines were used for cell-based analyses. In human gliomas, the CTH expression was analyzed by bioinformatic analysis on different databases. In vivo, the genetic ablation of CTH in the host led to a significant reduction of the tumor volume and the protumorigenic and stemness transcription factor sex determining region Y-box 2 (SOX2). The tumor microvessel density (indicative of angiogenesis) and the expression levels of peritumoral macrophages showed no significant changes between the two genotypes. Bioinformatic analysis in human glioma tumors revealed that higher CTH expression is positively correlated to SOX2 expression and associated with worse overall survival in all grades of gliomas. Patients not responding to temozolomide have also higher CTH expression. In mouse or human GBM cells, pharmacological inhibition (PAG) or CTH knockdown (siRNA) attenuates GBM cell proliferation, migration and stem cell formation frequency. MAJOR CONCLUSIONS: Inhibition of CTH could be a new promising target against glioblastoma formation.

The liver kinase B1 supports mammary epithelial morphogenesis by inhibiting critical factors that mediate epithelial-mesenchymal transition.

The liver kinase B1 (LKB1) controls cellular metabolism and cell polarity across species. We previously established a mechanism for negative regulation of transforming growth factor ß (TGFß) signaling by LKB1. The impact of this mechanism in the context of epithelial polarity and morphogenesis remains unknown. After demonstrating that human mammary tissue expresses robust LKB1 protein levels, whereas invasive breast cancer exhibits significantly reduced LKB1 levels, we focused on mammary morphogenesis studies in three dimensional (3D) acinar organoids. CRISPR/Cas9-introduced loss-of-function mutations of STK11 (LKB1) led to profound defects in the formation of 3D organoids, resulting in amorphous outgrowth and loss of rotation of young organoids embedded in matrigel. This defect was associated with an enhanced signaling by TGFß, including TGFß auto-induction and induction of transcription factors that mediate epithelial-mesenchymal transition (EMT). Protein marker analysis confirmed a more efficient EMT response to TGFß signaling in LKB1 knockout cells. Accordingly, chemical inhibition of the TGFß type I receptor kinase largely restored the morphogenetic defect of LKB1 knockout cells. Similarly, chemical inhibition of the bone morphogenetic protein pathway or the TANK-binding kinase 1, or genetic silencing of the EMT factor SNAI1, partially restored the LKB1 knockout defect. Thus, LKB1 sustains mammary epithelial morphogenesis by limiting pathways that promote EMT. The observed downregulation of LKB1 expression in breast cancer is therefore predicted to associate with enhanced EMT induced by SNAI1 and TGFß family members.

Aporphine and isoquinoline derivatives block glioblastoma cell stemness and enhance temozolomide cytotoxicity.

Glioblastoma (GBM) is the most aggressive and common primary malignant brain tumor with limited available therapeutic approaches. Despite improvements in therapeutic options for GBM patients, efforts to develop new successful strategies remain as major unmet medical needs. Based on the cytotoxic properties of aporphine compounds, we evaluated the biological effect of 12 compounds obtained through total synthesis of ( ±)-apomorphine hydrochloride (APO) against GBM cells. The compounds 2,2,2-trifluoro-1-(1-methylene-3,4-dihydroisoquinolin-2(1H)-yl)ethenone (A5) and ( ±)-1-(10,11-dimethoxy-6a,7-dihydro-4H-dibenzo[de,g]quinolin-6(5H)-yl)ethenone (C1) reduced the viability of GBM cells, with 50% inhibitory concentration ranging from 18 to 48 µM in patient-derived GBM cultures. Our data show that APO, A5 or C1 modulate the expression of DNA damage and apoptotic markers, impair 3D-gliomasphere growth and reduce the expression of stemness markers. Potential activity and protein targets of A5, C1 or APO were predicted in silico based on PASS and SEA software. Dopamine receptors (DRD1 and 5), CYP2B6, CYP2C9 and ABCB1, whose transcripts were differentially expressed in the GBM cells, were among the potential A5 or C1 target proteins. Docking analyses (HQSAR and 3D-QSAR) were performed to characterize possible interactions of ABCB1 and CYP2C9 with the compounds. Notably, A5 or C1 treatment, but not temozolomide (TMZ), reduced significantly the levels of extracellular ATP, suggesting ABCB1 negative regulation, which was correlated with stronger cytotoxicity induced by the combination of TMZ with A5 or C1 on GBM cells. Hence, our data reveal a potential therapeutic application of A5 and C1 as cytotoxic agents against GBM cells and predicted molecular networks that can be further exploited to characterize the pharmacological effects of these isoquinoline-containing substances.

Metabolic determinants of stemness in medulloblastoma.

Medulloblastomas (MBs) are the most prevalent brain tumours in children. They are classified as grade IV, the highest in malignancy, with about 30% metastatic tumours at the time of diagnosis. Cancer stem cells (CSCs) are a small subset of tumour cells that can initiate and support tumour growth. In MB, CSCs contribute to tumour initiation, metastasis, and therapy resistance. Metabolic differences among the different MB groups have started to emerge. Sonic hedgehog tumours show enriched lipid and nucleic acid metabolism pathways, whereas Group 3 MBs upregulate glycolysis, gluconeogenesis, glutamine anabolism, and glut athione-mediated anti-oxidant pathways. Such differences impact the clinical behaviour of MB tumours and can be exploited therapeutically. In this review, we summarise the existing knowledge about metabolic rewiring in MB, with a particular focus on MB-CSCs. Finally, we highlight some of the emerging metabolism-based therapeutic strategies for MB.

NOX4 regulates TGFß-induced proliferation and self-renewal in glioblastoma stem cells.

Glioblastoma (GBM) is the most aggressive and common glioma subtype, with a median survival of 15 months after diagnosis. Current treatments have limited therapeutic efficacy; thus, more effective approaches are needed. The glioblastoma tumoural mass is characterised by a small cellular subpopulation - glioblastoma stem cells (GSCs) - that has been held responsible for glioblastoma initiation, cell invasion, proliferation, relapse and resistance to chemo- and radiotherapy. Targeted therapies against GSCs are crucial, as is understanding the molecular mechanisms that govern the GSCs. Transforming growth factor ß (TGFß) signalling and reactive oxygen species (ROS) production are known to govern and regulate cancer stem cell biology. Among the differentially expressed genes regulated by TGFß in a transcriptomic analysis of two different patient-derived GSCs, we found NADPH oxidase 4 (NOX4) as one of the top upregulated genes. Interestingly, when patient tissues were analysed, NOX4 expression was found to be higher in GSCs versus differentiated cells. A functional analysis of the role of NOX4 downstream of TGFß in several patient-derived GSCs showed that TGFß does indeed induce NOX4 expression and increases ROS production in a NOX4-dependent manner. NOX4 downstream of TGFß regulates GSC proliferation, and NOX4 expression is necessary for TGFß-induced expression of stem cell markers and of the transcription factor nuclear factor erythroid 2-related factor 2 (NRF2), which in turn controls the cell's antioxidant and metabolic responses. Interestingly, overexpression of NOX4 recapitulates the effects induced by TGFß in GSCs: enhanced proliferation, stemness and NRF2 expression. In conclusion, this work functionally establishes NOX4 as a key mediator of GSC biology.

The protein kinase LKB1 promotes self-renewal and blocks invasiveness in glioblastoma.

The role of liver kinase B1 (LKB1) in glioblastoma (GBM) development remains poorly understood. LKB1 may regulate GBM cell metabolism and has been suggested to promote glioma invasiveness. After analyzing LKB1 expression in GBM patient mRNA databases and in tumor tissue via multiparametric immunohistochemistry, we observed that LKB1 was localized and enriched in GBM tumor cells that co-expressed SOX2 and NESTIN stemness markers. Thus, LKB1-specific immunohistochemistry can potentially reveal subpopulations of stem-like cells, advancing GBM patient molecular pathology. We further analyzed the functions of LKB1 in patient-derived GBM cultures under defined serum-free conditions. Silencing of endogenous LKB1 impaired 3D-gliomasphere frequency and promoted GBM cell invasion in vitro and in the zebrafish collagenous tail after extravasation of circulating GBM cells. Moreover, loss of LKB1 function revealed mitochondrial dysfunction resulting in decreased ATP levels. Treatment with the clinically used drug metformin impaired 3D-gliomasphere formation and enhanced cytotoxicity induced by temozolomide, the primary chemotherapeutic drug against GBM. The IC50 of temozolomide in the GBM cultures was significantly decreased in the presence of metformin. This combinatorial effect was further enhanced after LKB1 silencing, which at least partially, was due to increased apoptosis. The expression of genes involved in the maintenance of tumor stemness, such as growth factors and their receptors, including members of the platelet-derived growth factor (PDGF) family, was suppressed after LKB1 silencing. The defect in gliomasphere growth caused by LKB1 silencing was bypassed after supplementing the cells with exogenous PFDGF-BB. Our data support the parallel roles of LKB1 in maintaining mitochondrial homeostasis, 3D-gliomasphere survival, and hindering migration in GBM. Thus, the natural loss of, or pharmacological interference with LKB1 function, may be associated with benefits in patient survival but could result in tumor spread.

The polarity protein Par3 coordinates positively self-renewal and negatively invasiveness in glioblastoma.

Glioblastoma (GBM) is a brain malignancy characterized by invasiveness to the surrounding brain tissue and by stem-like cells, which propagate the tumor and may also regulate invasiveness. During brain development, polarity proteins, such as Par3, regulate asymmetric cell division of neuro-glial progenitors and neurite motility. We, therefore, studied the role of the Par3 protein (encoded by PARD3) in GBM. GBM patient transcriptomic data and patient-derived culture analysis indicated diverse levels of expression of PARD3 across and independent from subtypes. Multiplex immunolocalization in GBM tumors identified Par3 protein enrichment in SOX2-, CD133-, and NESTIN-positive (stem-like) cells. Analysis of GBM cultures of the three subtypes (proneural, classical, mesenchymal), revealed decreased gliomasphere forming capacity and enhanced invasiveness upon silencing Par3. GBM cultures with suppressed Par3 showed low expression of stemness (SOX2 and NESTIN) but higher expression of differentiation (GFAP) genes. Moreover, Par3 silencing reduced the expression of a set of genes encoding mitochondrial enzymes that generate ATP. Accordingly, silencing Par3 reduced ATP production and concomitantly increased reactive oxygen species. The latter was required for the enhanced migration observed upon silencing of Par3 as anti-oxidants blocked the enhanced migration. These findings support the notion that Par3 exerts homeostatic redox control, which could limit the tumor cell-derived pool of oxygen radicals, and thereby the tumorigenicity of GBM.

Glucose and Amino Acid Metabolic Dependencies Linked to Stemness and Metastasis in Different Aggressive Cancer Types.

Malignant cells are commonly characterised by being capable of invading tissue, growing self-sufficiently and uncontrollably, being insensitive to apoptosis induction and controlling their environment, for example inducing angiogenesis. Amongst them, a subpopulation of cancer cells, called cancer stem cells (CSCs) shows sustained replicative potential, tumor-initiating properties and chemoresistance. These characteristics make CSCs responsible for therapy resistance, tumor relapse and growth in distant organs, causing metastatic dissemination. For these reasons, eliminating CSCs is necessary in order to achieve long-term survival of cancer patients. New insights in cancer metabolism have revealed that cellular metabolism in tumors is highly heterogeneous and that CSCs show specific metabolic traits supporting their unique functionality. Indeed, CSCs adapt differently to the deprivation of specific nutrients that represent potentially targetable vulnerabilities. This review focuses on three of the most aggressive tumor types: pancreatic ductal adenocarcinoma (PDAC), hepatocellular carcinoma (HCC) and glioblastoma (GBM). The aim is to prove whether CSCs from different tumour types share common metabolic requirements and responses to nutrient starvation, by outlining the diverse roles of glucose and amino acids within tumour cells and in the tumour microenvironment, as well as the consequences of their deprivation. Beyond their role in biosynthesis, they serve as energy sources and help maintain redox balance. In addition, glucose and amino acid derivatives contribute to immune responses linked to tumourigenesis and metastasis. Furthermore, potential metabolic liabilities are identified and discussed as targets for therapeutic intervention.

The noncoding MIR100HG RNA enhances the autocrine function of transforming growth factor ß signaling.

Activation of the transforming growth factor ß (TGFß) pathway modulates the expression of genes involved in cell growth arrest, motility, and embryogenesis. An expression screen for long noncoding RNAs indicated that TGFß induced mir-100-let-7a-2-mir-125b-1 cluster host gene (MIR100HG) expression in diverse cancer types, thus confirming an earlier demonstration of TGFß-mediated transcriptional induction of MIR100HG in pancreatic adenocarcinoma. MIR100HG depletion attenuated TGFß signaling, expression of TGFß-target genes, and TGFß-mediated cell cycle arrest. Moreover, MIR100HG silencing inhibited both normal and cancer cell motility and enhanced the cytotoxicity of cytostatic drugs. MIR100HG overexpression had an inverse impact on TGFß signaling responses. Screening for downstream effectors of MIR100HG identified the ligand TGFß1. MIR100HG and TGFB1 mRNA formed ribonucleoprotein complexes with the RNA-binding protein HuR, promoting TGFß1 cytokine secretion. In addition, TGFß regulated let-7a-2-3p, miR-125b-5p, and miR-125b-1-3p expression, all encoded by MIR100HG intron-3. Certain intron-3 miRNAs may be involved in TGFß/SMAD-mediated responses (let-7a-2-3p) and others (miR-100, miR-125b) in resistance to cytotoxic drugs mediated by MIR100HG. In support of a model whereby TGFß induces MIR100HG, which then enhances TGFß1 secretion, analysis of human carcinomas showed that MIR100HG expression correlated with expression of TGFB1 and its downstream extracellular target TGFBI. Thus, MIR100HG controls the magnitude of TGFß signaling via TGFß1 autoinduction and secretion in carcinomas.

The TGFB2-AS1 lncRNA Regulates TGF-ß Signaling by Modulating Corepressor Activity.

Molecular processes involving lncRNAs regulate cell function. By applying transcriptomics, we identify lncRNAs whose expression is regulated by transforming growth factor ß (TGF-ß). Upon silencing individual lncRNAs, we identify several that regulate TGF-ß signaling. Among these lncRNAs, TGFB2-antisense RNA1 (TGFB2-AS1) is induced by TGF-ß through Smad and protein kinase pathways and resides in the nucleus. Depleting TGFB2-AS1 enhances TGF-ß/Smad-mediated transcription and expression of hallmark TGF-ß-target genes. Increased dose of TGFB2-AS1 reduces expression of these genes, attenuates TGF-ß-induced cell growth arrest, and alters BMP and Wnt pathway gene profiles. Mechanistically, TGFB2-AS1, mainly via its 3' terminal region, binds to the EED adaptor of the Polycomb repressor complex 2 (PRC2), promoting repressive histone H3K27me3 modifications at TGF-ß-target gene promoters. Silencing EED or inhibiting PRC2 methylation activity partially rescues TGFB2-AS1-mediated gene repression. Thus, the TGF-ß-induced TGFB2-AS1 lncRNA exerts inhibitory functions on TGF-ß/BMP signaling output, supporting auto-regulatory negative feedback that balances TGF-ß/BMP-mediated responses.

Downregulation of Epidermal Growth Factor Receptor in hepatocellular carcinoma facilitates Transforming Growth Factor-ß-induced epithelial to amoeboid transition.

The Epidermal Growth Factor Receptor (EGFR) and the Transforming Growth Factor-beta (TGF-ß) are key regulators of hepatocarcinogenesis. Targeting EGFR was proposed as a promising therapy; however, poor success was obtained in human hepatocellular carcinoma (HCC) clinical trials. Here, we describe how EGFR is frequently downregulated in HCC patients while TGF-ß is upregulated. Using 2D/3D cellular models, we show that after EGFR loss, TGF-ß is more efficient in its pro-migratory and invasive effects, inducing epithelial to amoeboid transition. EGFR knock-down promotes loss of cell-cell and cell-to-matrix adhesion, favouring TGF-ß-induced actomyosin contractility and acquisition of an amoeboid migratory phenotype. Moreover, TGF-ß upregulates RHOC and CDC42 after EGFR silencing, promoting Myosin II in amoeboid cells. Importantly, low EGFR combined with high TGFB1 or RHOC/CDC42 levels confer poor patient prognosis. In conclusion, this work reveals a new tumour suppressor function for EGFR counteracting TGF-ß-mediated epithelial to amoeboid transitions in HCC, supporting a rational for targeting the TGF-ß pathway in patients with low EGFR expression. Our work also highlights the relevance of epithelial to amoeboid transition in human tumours and the need to better target this process in the clinic.

TANK-binding kinase 1 is a mediator of platelet-induced EMT in mammary carcinoma cells.

Platelets can promote several stages of the metastatic process and thus contribute to malignant progression. As an example, platelets promote invasive properties of tumor cells by induction of epithelial to mesenchymal transition (EMT). In this study, we show that tumor necrosis factor receptor-associated factor (TRAF) family member-associated NF-κB activator (TANK)-binding kinase 1 (TBK1) is a previously unknown mediator of platelet-induced EMT in mammary carcinoma cells. Coculture of 2 mammary carcinoma cell lines, Ep5 from mice and MCF10A(MII) from humans, with isolated platelets induced morphologic as well as molecular changes characteristic of EMT, which was paralleled with activation of TBK1. TBK1 depletion using small interfering RNA impaired platelet-induced EMT in both Ep5 and MCF10A(MII) cells. Furthermore, platelet-induced activation of the NF-κB subunit p65 was suppressed after TBK1 knockdown, demonstrating that TBK1 mediates platelet-induced NF-κB signaling and EMT. Using an in vivo metastasis assay, we found that depletion of TBK1 from mammary carcinoma cells during in vitro preconditioning with platelets subsequently suppressed the formation of lung metastases in mice. Altogether, these results suggest that TBK1 contributes to tumor invasiveness and may be a driver of metastatic spread in breast cancer.-Zhang, Y., Unnithan, R. V. M., Hamidi, A., Caja, L., Saupe, F., Moustakas, A., Cedervall, J., Olsson, A.-K. TANK-binding kinase 1 is a mediator of platelet-induced EMT in mammary carcinoma cells.

TGF-ß and the Tissue Microenvironment: Relevance in Fibrosis and Cancer.

Transforming growth factor-β (TGF-β) is a cytokine essential for the induction of the fibrotic response and for the activation of the cancer stroma. Strong evidence suggests that a strong cross-talk exists among TGF-β and the tissue extracellular matrix components. TGF-β is stored in the matrix as part of a large latent complex bound to the latent TGF-β binding protein (LTBP) and matrix binding of latent TGF-β complexes, which is required for an adequate TGF-β function. Once TGF-β is activated, it regulates extracellular matrix remodelling and promotes a fibroblast to myofibroblast transition, which is essential in fibrotic processes. This cytokine also acts on other cell types present in the fibrotic and tumour microenvironment, such as epithelial, endothelial cells or macrophages and it contributes to the cancer-associated fibroblast (CAF) phenotype. Furthermore, TGF-β exerts anti-tumour activity by inhibiting the host tumour immunosurveillance. Aim of this review is to update how TGF-β and the tissue microenvironment cooperate to promote the pleiotropic actions that regulate cell responses of different cell types, essential for the development of fibrosis and tumour progression. We discuss recent evidences suggesting the use of TGF-β chemical inhibitors as a new line of defence against fibrotic disorders or cancer.

Snail regulates BMP and TGFß pathways to control the differentiation status of glioma-initiating cells.

Glioblastoma multiforme is a brain malignancy characterized by high heterogeneity, invasiveness, and resistance to current therapies, attributes related to the occurrence of glioma stem cells (GSCs). Transforming growth factor ß (TGFß) promotes self-renewal and bone morphogenetic protein (BMP) induces differentiation of GSCs. BMP7 induces the transcription factor Snail to promote astrocytic differentiation in GSCs and suppress tumor growth in vivo. We demonstrate that Snail represses stemness in GSCs. Snail interacts with SMAD signaling mediators, generates a positive feedback loop of BMP signaling and transcriptionally represses the TGFB1 gene, decreasing TGFß1 signaling activity. Exogenous TGFß1 counteracts Snail function in vitro, and in vivo promotes proliferation and re-expression of Nestin, confirming the importance of TGFB1 gene repression by Snail. In conclusion, novel insight highlights mechanisms whereby Snail differentially regulates the activity of the opposing BMP and TGFß pathways, thus promoting an astrocytic fate switch and repressing stemness in GSCs.

Snail mediates crosstalk between TGFß and LXRα in hepatocellular carcinoma.

Understanding the complexity of changes in differentiation and cell survival in hepatocellular carcinoma (HCC) is essential for the design of new diagnostic tools and therapeutic modalities. In this context, we have analyzed the crosstalk between transforming growth factor ß (TGFß) and liver X receptor α (LXRα) pathways. TGFß is known to promote cytostatic and pro-apoptotic responses in HCC, and to facilitate mesenchymal differentiation. We here demonstrate that stimulation of the nuclear LXRα receptor system by physiological and clinically useful agonists controls the HCC response to TGFß. Specifically, LXRα activation antagonizes the mesenchymal, reactive oxygen species and pro-apoptotic responses to TGFß and the mesenchymal transcription factor Snail mediates this crosstalk. In contrast, LXRα activation and TGFß cooperate in enforcing cytostasis in HCC, which preserves their epithelial features. LXRα influences Snail expression transcriptionally, acting on the Snail promoter. These findings propose that clinically used LXR agonists may find further application to the treatment of aggressive, mesenchymal HCCs, whose progression is chronically dependent on autocrine or paracrine TGFß.

Transforming growth factor ß as regulator of cancer stemness and metastasis.

Key elements of cancer progression towards metastasis are the biological actions of cancer stem cells and stromal cells in the tumour microenvironment. Cross-communication between tumour and stromal cells is mediated by secreted cytokines, one of which, the transforming growth factor ß (TGFß), regulates essentially every cell within the malignant tissue. In this article, we focus on the actions of TGFß on cancer stem cells, cancer-associated fibroblasts and immune cells that assist the overall process of metastatic dissemination. We aim at illustrating intricate connections made by various cells in the tumour tissue and which depend on the action of TGFß.

Transforming growth factor ß and bone morphogenetic protein actions in brain tumors.

Members of the transforming growth factor ß (TGF-ß) family are implicated in the biology of several cancers. Here we focus on malignancies of the brain and examine the TGFß and the bone morphogenetic protein (BMP) signaling branches of the family. These pathways exhibit context-dependent actions during tumorigenesis, acting either as tumor suppressors or as pro-tumorigenic agents. In the brain, the TGF-ßs associate with oncogenic development and progression to the more malignant state. Inversely, the BMPs suppress tumorigenic potential by acting as agents that induce tumor cell differentiation. The latter has been best demonstrated in grade IV astrocytomas, otherwise known as glioblastoma multiforme. We discuss how the actions of TGF-ßs and BMPs on cancer stem cells may explain their effects on tumor progression, and try to highlight intricate mechanisms that may link tumor cell differentiation to invasion. The focus on TGF-ß and BMP and their actions in brain malignancies provides a rich territory for mechanistic understanding of tumor heterogeneity and suggests ways for improved therapeutic intervention, currently being addressed by clinical trials.