Lysyl oxidase is downregulated by the EWS/FLI1 oncoprotein and its propeptide domain displays tumor supressor activities in Ewing sarcoma cells

Genetic analyses identify evidence for a causal relationship between Ewing sarcoma and hernias

Knowledge of Ewing sarcoma (EWS) risk factors is exceedingly limited; however, multiple small, independent studies have suggested a possible connection between hernia and EWS. By leveraging hernia summary statistics from the UK Biobank and a recently published genome-wide association study of EWS (733 EWS cases and 1,346 controls), we conducted a genetic investigation of the relationship of 5 hernia types (diaphragmatic, inguinal, umbilical, femoral, and ventral) and EWS. We discovered a positive causal relationship between inguinal hernia and EWS (OR 1.27, 95% confidence interval [CI] 1.01-1.59, and p = 0.041) through Mendelian randomization analysis. Further analyses suggested shared pathways through three genes: HMGA2, LOX, and FBXW7. Diaphragmatic hernia showed a stronger causal relationship with EWS among all of the hernia types (OR 2.26, 95% CI 1.30-3.95, p = 0.004), but no statistically significant local correlation pattern was observed. No evidence of a causal or genetic relationship was observed between EWS and the other three hernia types, including umbilical hernia, despite a previous report indicating an OR as high as 3.3. The finding of our genetic analysis provided additional support to the hypothesis that EWS and hernias may share a common origin.

Targeted Therapy for EWS-FLI1 in Ewing Sarcoma

Ewing sarcoma (EwS) is a rare and predominantly pediatric malignancy of bone and soft tissue in children and adolescents. Although international collaborations have greatly improved the prognosis of most EwS, the occurrence of macrometastases or relapse remains challenging. The prototypic oncogene EWS-FLI1 acts as an aberrant transcription factor that drives the cellular transformation of EwS. In addition to its involvement in RNA splicing and the DNA damage response, this chimeric protein directly binds to GGAA repeats, thereby modifying the transcriptional profile of EwS. Direct pharmacological targeting of EWS-FLI1 is difficult because of its intrinsically disordered structure. However, targeting the EWS-FLI1 protein complex or downstream pathways provides additional therapeutic options. This review describes the EWS-FLI1 protein partners and downstream pathways, as well as the related target therapies for the treatment of EwS.

CD44 Modulates Cell Migration and Invasion in Ewing Sarcoma Cells

The chimeric EWSR1::FLI1 transcription factor is the main oncogenic event in Ewing sarcoma. Recently, it has been proposed that EWSR1::FLI1 levels can fluctuate in Ewing sarcoma cells, giving rise to two cell populations. EWSR1::FLI1^low cells present a migratory and invasive phenotype, while EWSR1::FLI1^high cells are more proliferative. In this work, we described how the CD44 standard isoform (CD44s), a transmembrane protein involved in cell adhesion and migration, is overexpressed in the EWSR1::FLI1^low phenotype. The functional characterization of CD44s (proliferation, clonogenicity, migration, and invasion ability) was performed in three doxycycline-inducible Ewing sarcoma cell models (A673, MHH-ES1, and CADO-ES1). As a result, CD44s expression reduced cell proliferation in all the cell lines tested without affecting clonogenicity. Additionally, CD44s increased cell migration in A673 and MHH-ES1, without effects in CADO-ES1. As hyaluronan is the main ligand of CD44s, its effect on migration ability was also assessed, showing that high molecular weight hyaluronic acid (HMW-HA) blocked cell migration while low molecular weight hyaluronic acid (LMW-HA) increased it. Invasion ability was correlated with CD44 expression in A673 and MHH-ES1 cell lines. CD44s, upregulated upon EWSR1::FLI1 knockdown, regulates cell migration and invasion in Ewing sarcoma cells.

Fli1 and Tissue Fibrosis in Various Diseases

Being initially described as a factor of virally-induced leukemias, Fli1 (Friend leukemia integration 1) has attracted considerable interest lately due to its role in both healthy physiology and a variety of pathological conditions. Over the past few years, Fli1 has been found to be one of the crucial regulators of normal hematopoiesis, vasculogenesis, and immune response. However, abnormal expression of Fli1 due to genetic predisposition, epigenetic reprogramming (modifications), or environmental factors is associated with a few diseases of different etiology. Fli1 hyperexpression leads to malignant transformation of cells and progression of cancers such as Ewing's sarcoma. Deficiency in Fli1 is implicated in the development of systemic sclerosis and hypertensive disorders, which are often accompanied by pronounced fibrosis in different organs. This review summarizes the initial findings and the most recent advances in defining the role of Fli1 in diseases of different origin with emphasis on its pro-fibrotic potential.

Systematic multi-omics cell line profiling uncovers principles of Ewing sarcoma fusion oncogene-mediated gene regulation

Ewing sarcoma (EwS) is characterized by EWSR1-ETS fusion transcription factors converting polymorphic GGAA microsatellites (mSats) into potent neo-enhancers. Although the paucity of additional mutations makes EwS a genuine model to study principles of cooperation between dominant fusion oncogenes and neo-enhancers, this is impeded by the limited number of well-characterized models. Here we present the Ewing Sarcoma Cell Line Atlas (ESCLA), comprising whole-genome, DNA methylation, transcriptome, proteome, and chromatin immunoprecipitation sequencing (ChIP-seq) data of 18 cell lines with inducible EWSR1-ETS knockdown. The ESCLA shows hundreds of EWSR1-ETS-targets, the nature of EWSR1-ETS-preferred GGAA mSats, and putative indirect modes of EWSR1-ETS-mediated gene regulation, converging in the duality of a specific but plastic EwS signature. We identify heterogeneously regulated EWSR1-ETS-targets as potential prognostic EwS biomarkers. Our freely available ESCLA (http://r2platform.com/escla/) is a rich resource for EwS research and highlights the power of comprehensive datasets to unravel principles of heterogeneous gene regulation by chimeric transcription factors.

The Transcription Factor FEZF1, a Direct Target of EWSR1-FLI1 in Ewing Sarcoma Cells, Regulates the Expression of Neural-Specific Genes

Ewing sarcoma is a rare pediatric tumor characterized by chromosomal translocations that give rise to aberrant chimeric transcription factors (e.g., EWSR1-FLI1). EWSR1-FLI1 promotes a specific cellular transcriptional program. Therefore, the study of EWSR1-FLI1 target genes is important to identify critical pathways involved in Ewing sarcoma tumorigenesis. In this work, we focused on the transcription factors regulated by EWSR1-FLI1 in Ewing sarcoma. Transcriptomic analysis of the Ewing sarcoma cell line A673 indicated that one of the genes more strongly upregulated by EWSR1-FLI1 was FEZF1 (FEZ family zinc finger protein 1), a transcriptional repressor involved in neural cell identity. The functional characterization of FEZF1 was performed in three Ewing sarcoma cell lines (A673, SK-N-MC, SK-ES-1) through an shRNA-directed silencing approach. FEZF1 knockdown inhibited clonogenicity and cell proliferation. Finally, the analysis of the FEZF1-dependent expression profile in A673 cells showed several neural genes regulated by FEZF1 and concomitantly regulated by EWSR1-FLI1. In summary, FEZF1 is transcriptionally regulated by EWSR1-FLI1 in Ewing sarcoma cells and is involved in the regulation of neural-specific genes, which could explain the neural-like phenotype observed in several Ewing sarcoma tumors and cell lines.

Digital RNA Sequencing of Human Epidermal Keratinocytes Carrying Human Papillomavirus Type 16 E7

High-risk human papillomavirus (HPV) infections are the predominant cause of cervical cancer and its early gene E7 plays an important role in cellular proliferation and cell-cycle progression. While tremendous progress has been made in exploring the molecular mechanisms in late tumorigenesis, many pathways showing how HPV deregulates host gene expression in early inapparent infections and early tumorigenesis still remain undefined. Digital RNA sequencing was performed and a total of 195 differentially expressed genes were identified between the HPV16 E7-transfected NHEKs and control cells (p < 0.05, fold-change > 2). GO enrichment showed that HPV16 E7 primarily affected processes involved in anti-viral and immune responses, while KEGG pathway analysis showed enrichment of gene clusters of associated with HPV infection and MAPK signaling. Of the differentially expressed genes, IFI6, SLC39A9 and ZNF185 showed a strong correlation with tumor progression and patient survival in the OncoLnc database while roles for AKAP12 and DUSP5 in carcinogenesis and poor prognosis have previously been established for other cancer types. Our study identified several novel HPV16 E7-regulated candidate genes with putative functions in tumorigenesis, thus providing new insights into HPV persistence in keratinocytes and early onset of tumorigenesis.

The YAP/TAZ Pathway in Osteogenesis and Bone Sarcoma Pathogenesis

YAP and TAZ are intracellular messengers communicating multiple interacting extracellular biophysical and biochemical cues to the transcription apparatus in the nucleus and back to the cell/tissue microenvironment interface through the regulation of cytoskeletal and extracellular matrix components. Their activity is negatively and positively controlled by multiple phosphorylation events. Phenotypically, they serve an important role in cellular plasticity and lineage determination during development. As they regulate self-renewal, proliferation, migration, invasion and differentiation of stem cells, perturbed expression of YAP/TAZ signaling components play important roles in tumorigenesis and metastasis. Despite their high structural similarity, YAP and TAZ are functionally not identical and may play distinct cell type and differentiation stage-specific roles mediated by a diversity of downstream effectors and upstream regulatory molecules. However, YAP and TAZ are frequently looked at as functionally redundant and are not sufficiently discriminated in the scientific literature. As the extracellular matrix composition and mechanosignaling are of particular relevance in bone formation during embryogenesis, post-natal bone elongation and bone regeneration, YAP/TAZ are believed to have critical functions in these processes. Depending on the differentiation stage of mesenchymal stem cells during endochondral bone development, YAP and TAZ serve distinct roles, which are also reflected in bone tumors arising from the mesenchymal lineage at different developmental stages. Efforts to clinically translate the wealth of available knowledge of the pathway for cancer diagnostic and therapeutic purposes focus mainly on YAP and TAZ expression and their role as transcriptional co-activators of TEAD transcription factors but rarely consider the expression and activity of pathway modulatory components and other transcriptional partners of YAP and TAZ. As there is a growing body of evidence for YAP and TAZ as potential therapeutic targets in several cancers, we here interrogate the applicability of this concept to bone tumors. To this end, this review aims to summarize our current knowledge of YAP and TAZ in cell plasticity, normal bone development and bone cancer.

Omic approaches to pediatric bone sarcomas

Over the last decade, next-generation sequencing technologies have improved our ability to assess biological aspects, at genomic and transcriptomic levels, on a large scale- and have been increasingly used for the management of adult cancers. However, their efficacy and feasibility within pediatrics is still under investigation. "Omic" approaches represent an opportunity to understand the oncogenic mechanisms driving the onset and progression of bone sarcoma and improve the clinical management of young patients with bone sarcomas. This review focuses on the current genomic and transcriptomic characteristics of managing pediatric patients, affected by Ewing sarcoma and osteosarcoma.

Sarcoma Tumor Microenvironment

Components of the tumor microenvironment (TME) are known to play an essential role during malignant progression, but often in a context-dependent manner. In bone and soft tissue sarcomas, disease-regulatory activities in the TME remain largely uncharacterized. This chapter introduces the cellular, structural, and chemical composition of the sarcoma TME from a pathobiological and therapeutic perspective.Sarcomas are malignant tumors with diverse features when it comes to primary tumor appearance, metastatic potential, and response to treatment. Many of the classic subtypes are mainly composed of malignant cells and are therefore assumed to be committed to autocrine signaling. Some of the tumors are infiltrated by immune cells and contain necrotic areas or excessive amounts of extracellular matrix (ECM) that regulates tissue stiffness and interstitial fluid pressure. Vascular invasion and blood vessel characteristics can in some instances be considered in the prognostic setting.Further insights into the disease-regulatory activities of the sarcoma TME will provide essential knowledge on how to develop successful combination treatments targeting not only malignant cells, but also their routes of nutrition and ability to shield themselves toward existing therapy.

Divergent roles of lysyl oxidase family members in ornithine decarboxylase- and RAS-transformed mouse fibroblasts and human melanoma cells

We have previously shown that proto-oncoprotein c-Jun is activated in ornithine decarboxylase (ODC)- and RAS-transformed mouse fibroblasts, and that the transformed morphology of these cells can be reversed by expressing the transactivation domain deletion mutant of c-Jun (TAM67). Here, we found that lysyl oxidase (Lox), encoding an extracellular matrix-modifying enzyme, is downregulated in a c-Jun-dependent manner in ODC-transformed fibroblasts (Odc cells). In addition to Lox, the Lox family members Lox-like 1 and 3 (Loxl1 and Loxl3) were found to be downregulated in Odc as well as in RAS-transformed fibroblasts (E4), whereas Lox-like 4 (Loxl4) was upregulated in Odc and downregulated in E4 cells compared to normal N1 fibroblasts. Tetracycline-regulatable LOX re-expression in Odc cells led to inhibition of cell growth and invasion in three-dimensional Matrigel in an activity-independent manner. On the contrary, LOX and especially LOXL2, LOXL3, and LOXL4 were found to be upregulated in several human melanoma cell lines, and LOX inhibitor B-aminopropionitrile inhibited the invasive growth of these cells particularly when co-cultured with fibroblasts in Matrigel. Knocking down the expression of LOX and especially LOXL2 in melanoma cells almost completely abrogated the invasive growth capability. Further, LOXL2 was significantly upregulated in clinical human primary melanomas compared to benign nevi, and high expression of LOXL2 in primary melanomas was associated with formation of metastases and shorter survival of patients. Thus, our studies reveal that inactive pro-LOX (together with Lox propeptide) functions as a tumor suppressor in ODC- and RAS-transformed murine fibroblasts by inhibiting cell growth and invasion, and active LOX and LOXL2 as tumor promoters in human melanoma cells by promoting their invasive growth.

Lysyl oxidase (LOX) limits VSMC proliferation and neointimal thickening through its extracellular enzymatic activity

Lysyl oxidase (LOX) plays a critical role in extracellular matrix maturation and limits VSMC proliferation and vascular remodeling. We have investigated whether this anti-proliferative effect relies on the extracellular catalytically active LOX or on its biologically active propeptide (LOX-PP). High expression levels of both LOX and LOX-PP were detected in the vascular wall from transgenic mice over-expressing the full-length human LOX cDNA under the control of SM22α promoter (TgLOX), which targets the transgene to VSMC without affecting the expression of mouse LOX isoenzymes. TgLOX VSMC also secrete high amounts of both mature LOX and LOX-PP. Wild-type (WT) mouse VSMC exposed to VSMC supernatants from transgenic animals showed reduced proliferative rates (low [³H]-thymidine uptake and expression of PCNA) than those incubated with conditioned media from WT cells, effect that was abrogated by β-aminopropionitrile (BAPN), an inhibitor of LOX activity. Lentiviral over-expression of LOX, but not LOX-PP, decreased human VSMC proliferation, effect that was also prevented by BAPN. LOX transgenesis neither impacted local nor systemic inflammatory response induced by carotid artery ligation. Interestingly, in this model, BAPN normalized the reduced neointimal thickening observed in TgLOX mice. Therefore, extracellular enzymatically active LOX is required to limit both VSMC proliferation and vascular remodeling.

Caveolin-1 promotes Ewing sarcoma metastasis regulating MMP-9 expression through MAPK/ERK pathway

Ewing sarcoma (ES) is a bone and soft tissue sarcoma affecting mostly children and young adults. Caveolin-1 (CAV1) is a well-known target of EWS/FLI1, the main driver of ES, with an oncogenic role in ES. We have previously described how CAV1 is able to induce metastasis in ES via matrix metalloproteinase-9 (MMP-9). In the present study we showed how CAV1 silencing in ES reduced MEK1/2 and ERK1/2 phosphorylation. Accordingly, chemical inhibition of MEK1/2 resulted in reduction in MMP-9 expression and activity that correlated with reduced migration and invasion. IQ Motif Containing GTPase Activating Protein 1 (IQGAP1) silencing reduced MEK1/2 and ERK1/2 phosphorylation and MMP-9 expression. Furthermore, IQGAP1 silenced cells showed a marked decrease in their migratory and invasive capacity. We demonstrated that CAV1 and IQGAP1 localize in close proximity at the cellular edge, thus IQGAP1 could be the connecting node between CAV1 and MEK/ERK in ES metastatic phenotype. Analysis of the phosphorylation profile of CAV1-silenced cells showed a decrease of p-ribosomal protein S6 (RPS6). RPS6 can be phosphorylated by p90 ribosomal S6 kinases (RSK) proteins. CAV1-silenced cells showed reduced levels of p-RSK1 and treatment with U0126 provoked the same effect. Despite not affecting ERK1/2 and RPS6 phosphorylation status neither MMP-9 expression nor activity, RSK1 silencing resulted in a reduced migratory and invasive capacity in vitro and reduced incidence of metastases in vivo in a novel orthotopic model. The present work provides new insights into CAV1-driven metastatic process in ES unveiling novel key nodes.

A polypeptide from the junction region sequence of EWS-FLI1 inhibits Ewing's sarcoma cells, interacts with the EWS-FLI1 and partner proteins

The EWS-FLI1 chimeric protein uniquely expressed in Ewing’s sarcoma has an obligate role in its aetiology. In our previous report we showed that ectopic expression of the DNA sequences form the junction region (a.a 251–280) can inhibit Ewing’s sarcoma cell growth. In the present report, we introduced a peptide (TAT/NLS/EWS-PEP) comprising of thirty amino acids spanning the junction in conjunction with HIV-1-trans-activating (TAT) and nuclear localization signal sequence (NLS). Peptide uptake and localization studies revealed presence of peptide in ~99% of transduced cells and in the nucleus. Peptide transfection induced cytotoxicity relative to untreated and TAT-NLS peptide treated Ewing’s sarcoma cells. The peptide inhibited clonogenicity, cell cycle, bromo-deoxy uridine (BrdU) uptake and invasion capacity of treated cells. The treatment also affected epithelial to mesenchymal transition (EMT) markers and EWS-FLI1 target gene expression levels. Co-immunoprecipitation experiments involving ectopically expressed full-length EWS-FLI1 protein and the peptide revealed an interaction. Additionally, we found that peptide interaction also occurs with the protein-GGAA microsatellite sequences complex known to contain EWS-FLI1. Further, in the pull-down assay, the peptide was found to interact with proteins known to potentially interact with EWS-FLI1. Based on these results we conclude that peptide could be applied in targeting EWS-FLI1 protein.

UXT Is a LOX-PP Interacting Protein That Modulates Estrogen Receptor Alpha Activity in Breast Cancer Cells

The lysyl oxidase proenzyme propeptide region (LOX-PP) is a tumor suppressor protein whose mechanism of action is not completely understood. Here, the Ubiquitously expressed Transcript (UXT) was identified in a yeast two-hybrid assay with LOX-PP as bait and confirmed as a novel LOX-PP associating protein. UXT, a prefoldin-like protein, is ubiquitous in human and mouse. Since UXT modulates androgen receptor transcriptional activity in prostate cancer, we studied its role in breast cancer. Breast tumors and derived cell lines overexpressed UXT. UXT was able to associate with the estrogen receptor alpha (ER) and decrease its transcriptional activity and target gene expression. Conversely, UXT knockdown increased ER element-dependent transcriptional activity. Ectopic LOX-PP relocalized UXT to the cytoplasm and decreased its stability. UXT ubiquitination and depletion in the presence of LOX-PP was rescued by a proteasomal inhibitor. In summary, proteasome-mediated turnover of UXT upon interaction with LOX-PP releases repression of ER transcriptional activity. J. Cell. Biochem. 118: 2347-2356, 2017. © 2017 Wiley Periodicals, Inc.

Cell-to-cell heterogeneity of EWSR1-FLI1 activity determines proliferation/migration choices in Ewing sarcoma cells

Ewing sarcoma is characterized by the expression of the chimeric EWSR1-FLI1 transcription factor. Proteomic analyses indicate that the decrease of EWSR1-FLI1 expression leads to major changes in effectors of the dynamics of the actin cytoskeleton and the adhesion processes with a shift from cell-to-cell to cell-matrix adhesion. These changes are associated with a dramatic increase of in vivo cell migration and invasion potential. Importantly, EWSR1-FLI1 expression, evaluated by single-cell RT-ddPCR/immunofluorescence analyses, and activity, assessed by expression of EWSR1-FLI1 downstream targets, are heterogeneous in cell lines and in tumours and can fluctuate along time in a fully reversible process between EWSR1-FLI1^high states, characterized by highly active cell proliferation, and EWSR1-FLI1^low states where cells have a strong propensity to migrate, invade and metastasize. This new model of phenotypic plasticity proposes that the dynamic fluctuation of the expression level of a dominant oncogene is an intrinsic characteristic of its oncogenic potential.

Lysyl Oxidase and the Tumor Microenvironment

The lysyl oxidase (LOX) family of oxidases contains a group of extracellular copper-dependent enzymes that catalyze the cross-linking of collagen and elastin by oxidation, thus maintaining the rigidity and structural stability of the extracellular matrix (ECM). Aberrant expression or activation of LOX alters the cellular microenvironment, leading to many diseases, including atherosclerosis, tissue fibrosis, and cancer. Recently, a number of studies have shown that LOX is overexpressed in most cancers and that it is involved in the regulation of tumor progression and metastasis. In contrast, a few reports have also indicated the tumor-suppressing role of LOX. In this short review, we discuss recent research on the correlations between LOX and cancer. Further, the role of LOX in tumor microenvironment remodeling, tumorigenesis, and metastasis and the underlying mechanisms have also been elucidated.

Identification of Mithramycin Analogues with Improved Targeting of the EWS-FLI1 Transcription Factor

PURPOSE

The goal of this study was to identify second-generation mithramycin analogues that better target the EWS-FLI1 transcription factor for Ewing sarcoma. We previously established mithramycin as an EWS-FLI1 inhibitor, but the compound's toxicity prevented its use at effective concentrations in patients.

EXPERIMENTAL DESIGN

We screened a panel of mithralogs to establish their ability to inhibit EWS-FLI1 in Ewing sarcoma. We compared the IC50 with the MTD established in mice to determine the relationship between efficacy and toxicity. We confirmed the suppression of EWS-FLI1 at the promoter, mRNA, gene signature, and protein levels. We established an improved therapeutic window by using time-lapse microscopy to model the effects on cellular proliferation in Ewing sarcoma cells relative to HepG2 control cells. Finally, we established an improved therapeutic window using a xenograft model of Ewing sarcoma.

RESULTS

EC-8105 was found to be the most potent analogue and was able to suppress EWS-FLI1 activity at concentrations nontoxic to other cell types. EC-8042 was substantially less toxic than mithramycin in multiple species but maintained suppression of EWS-FLI1 at similar concentrations. Both compounds markedly suppressed Ewing sarcoma xenograft growth and inhibited EWS-FLI1 in vivo

CONCLUSIONS

These results provide a basis for the continued development of EC-8042 and EC-8105 as EWS-FLI1 inhibitors for the clinic. Clin Cancer Res; 22(16); 4105-18. ©2016 AACR.

EWS-FLI1-mediated suppression of the RAS-antagonist Sprouty 1 (SPRY1) confers aggressiveness to Ewing sarcoma

Ewing sarcoma is characterized by chromosomal translocations fusing the EWS gene with various members of the ETS family of transcription factors, most commonly FLI1. EWS-FLI1 is an aberrant transcription factor driving Ewing sarcoma tumorigenesis by either transcriptionally inducing or repressing specific target genes. Herein, we showed that Sprouty 1 (SPRY1), which is a physiological negative feedback inhibitor downstream of fibroblast growth factor (FGF) receptors (FGFRs) and other RAS-activating receptors, is an EWS-FLI1 repressed gene. EWS-FLI1 knockdown specifically increased the expression of SPRY1, while other Sprouty family members remained unaffected. Analysis of SPRY1 expression in a panel of Ewing sarcoma cells showed that SPRY1 was not expressed in Ewing sarcoma cell lines, suggesting that it could act as a tumor suppressor gene in these cells. In agreement, induction of SPRY1 in three different Ewing sarcoma cell lines functionally impaired proliferation, clonogenic growth and migration. In addition, SPRY1 expression inhibited extracellular signal-related kinase/mitogen-activated protein kinase (MAPK) signaling induced by serum and basic FGF (bFGF). Moreover, treatment of Ewing sarcoma cells with the potent FGFR inhibitor PD-173074 reduced bFGF-induced proliferation, colony formation and in vivo tumor growth in a dose-dependent manner, thus mimicking SPRY1 activity in Ewing sarcoma cells. Although the expression of SPRY1 was low when compared with other tumors, SPRY1 was variably expressed in primary Ewing sarcoma tumors and higher expression levels were significantly associated with improved outcome in a large patient cohort. Taken together, our data indicate that EWS-FLI1-mediated repression of SPRY1 leads to unrestrained bFGF-induced cell proliferation, suggesting that targeting the FGFR/MAPK pathway can constitute a promising therapeutic approach for this devastating disease.

Lysyl Oxidase Isoforms and Potential Therapeutic Opportunities for Fibrosis and Cancer

INTRODUCTION

The lysyl oxidase family of enzymes is classically known as being required for connective tissue maturation by oxidizing lysine residues in elastin and lysine and hydroxylysine residues in collagen precursors. The resulting aldehydes then participate in cross-link formation, which is required for normal connective tissue integrity. These enzymes have biological functions that extend beyond this fundamental biosynthetic role, with contributions to angiogenesis, cell proliferation, and cell differentiation. Dysregulation of lysyl oxidases occurs in multiple pathologies including fibrosis, primary and metastatic cancers, and complications of diabetes in a variety of tissues.

AREAS COVERED

This review summarizes the major findings of novel roles for lysyl oxidases in pathologies, and highlights some of the potential therapeutic approaches that are in development and which stem from these new findings.

EXPERT OPINION

Fundamental questions remain regarding the mechanisms of novel biological functions of this family of proteins, and regarding functions that are independent of their catalytic enzyme activity. However, progress is underway in the development of isoform-specific pharmacologic inhibitors, potential therapeutic antibodies and gaining an increased understanding of both tumor suppressor and metastasis promotion activities. Ultimately, this is likely to lead to novel therapeutic agents.

Inhibition of Lysyl Oxidase and Lysyl Oxidase-Like Enzymes Has Tumour-Promoting and Tumour-Suppressing Roles in Experimental Prostate Cancer

Lysyl oxidase (LOX) and LOX-like (LOXL) enzymes are key players in extracellular matrix deposition and maturation. LOX promote tumour progression and metastasis, but it may also have tumour-inhibitory effects. Here we show that orthotopic implantation of rat prostate AT-1 tumour cells increased LOX and LOXLs mRNA expressions in the tumour and in the surrounding non-malignant prostate tissue. Inhibition of LOX enzymes, using Beta-aminopropionitrile (BAPN), initiated before implantation of AT-1 cells, reduced tumour growth. Conversely, treatment that was started after the tumours were established resulted in unaffected or increased tumour growth. Moreover, treatment with BAPN did not suppress the formation of spontaneous lymph node metastases, or lung tumour burden, when tumour cells were injected intravenously. A temporal decrease in collagen fibre content, which is a target for LOX, was observed in tumours and in the tumour-adjacent prostate tissue. This may explain why early BAPN treatment is more effective in inhibiting tumour growth compared to treatment initiated later. Our data suggest that the enzymatic function of the LOX family is context-dependent, with both tumour-suppressing and tumour-promoting properties in prostate cancer. Further investigations are needed to understand the circumstances under which LOX inhibition may be used as a therapeutic target for cancer patients.

Emerging Roles of Extracellular Hsp90 in Cancer

Heat shock protein 90 (Hsp90) is a highly expressed chaperone that modulates the function and stability of hundreds of cellular client proteins. In this capacity, Hsp90 impacts human health in myriad ways and it is accordingly a high-interest molecular target in the oncology setting. This interest has led to a large number of clinical trials to evaluate the potential benefit of Hsp90 inhibitors in cancer treatment and, more recently, in combination with chemotherapeutic agents. Although these studies are still ongoing, some issues have arisen, such as toxicity effects associated with administration of these agents. We and others have identified a novel role for Hsp90 outside of cancer cells. This extracellular Hsp90 (eHsp90) was shown to be critical for the regulation of tumor invasiveness and metastasis, central processes associated with cancer lethality. Since these initial papers, a considerable cohort of studies has expanded upon this role, implicating eHsp90 in the activation of a number of proteins that support tumor cell invasion. As eHsp90 is preferentially detected on the surface of tumor cells, and within their surrounding microenvironment, it is possible that drugs capable of selectively targeting eHsp90 may exploit this differential expression. This selectivity may, in turn, enable treatment regimens with reduced target-related toxicity. This review will focus on our current understanding of eHsp90, particularly in cancer, and we will discuss the relevance of eHsp90 as a biomarker for invasive cancer and its potential as a drug target.

Lysyl oxidase propeptide stimulates osteoblast and osteoclast differentiation and enhances PC3 and DU145 prostate cancer cell effects on bone in vivo

Lysyl oxidase pro-enzyme is secreted by tumor cells and normal cells as a 50 kDa pro-enzyme into the extracellular environment where it is cleaved into the ~30 kDa mature enzyme (LOX) and 18 kDa pro-peptide (LOX-PP). Extracellular LOX enzyme activity is required for normal collagen and elastin extracellular cross-linking and maturation of the extracellular matrix. Extracellular LOX-PP acts as a tumor suppressor and can re-enter cells from the extracellular environment to induce its effects. The underlying hypothesis is that LOX-PP has the potential to promote bone cell differentiation, while inhibiting cancer cell effects in bone. Here we investigate the effect of LOX-PP on bone marrow cell proliferation and differentiation towards osteoblasts or osteoclasts, and LOX-PP modulation of prostate cancer cell conditioned media-induced alterations of proliferation and differentiation of bone marrow cells in vitro. Effects of overexpression of rLOX-PP in DU145 and PC3 prostate cancer cell lines on bone structure in vivo after intramedullary injections were determined. Data show that prostate cancer cell conditioned media inhibited osteoblast differentiation in bone marrow-derived cells, which was reversed by rLOX-PP treatment. Prostate cancer conditioned media stimulated osteoclast differentiation which was further enhanced by rLOX-PP treatment. rLOX-PP stimulated osteoclast differentiation by inhibiting OPG expression, up-regulating CCN2 expression, and increasing osteoclast fusion. In vivo studies indicate that rLOX-PP expression by PC3 cells implanted into the tibia of mice further enhanced PC3 cell ability to resorb bone, while rLOX-PP expression in DU145 cells resulted in non-significant increases in net bone formation. rLOX-PP enhances both osteoclast and osteoblast differentiation. rLOX-PP may serve to enhance coupling interactions between osteoclasts and osteoblasts helping to maintain a normal bone turnover in health, while contributing to bone abnormalities in disease.

EWS/FLI1 Target Genes and Therapeutic Opportunities in Ewing Sarcoma

Ewing sarcoma is an aggressive bone malignancy that affect children and young adults. Ewing sarcoma is the second most common primary bone malignancy in pediatric patients. Although significant progress has been made in the treatment of Ewing sarcoma since it was first described in the 1920s, in the last decade survival rates have remained unacceptably invariable, thus pointing to the need for new approaches centered in the molecular basis of the disease. Ewing sarcoma driving mutation, EWS–FLI1, which results from a chromosomal translocation, encodes an aberrant transcription factor. Since its first characterization in 1990s, many molecular targets have been described to be regulated by this chimeric transcription factor. Their contribution to orchestrate Ewing sarcoma phenotype has been reported over the last decades. In this work, we will focus on the description of a selection of EWS/FLI1 targets, their functional role, and their potential clinical relevance. We will also discuss their role in other types of cancer as well as the need for further studies to be performed in order to achieve a broader understanding of their particular contribution to Ewing sarcoma development.

Lysyl oxidase in cancer research

Metastasis is the main reason for cancer-associated deaths and therapies are desperately needed to target the progression of cancer. Lysyl oxidase (LOX) plays a pivotal role in cancer progression, including metastasis, and is therefore is an attractive therapeutic target. In this review we will breakdown the process of cancer progression and the various roles that LOX plays has in the advancement of cancer. We will highlight why LOX is an exciting therapeutic target for the future.

Effects of tumor-suppressor lysyl oxidase propeptide on prostate cancer xenograft growth and its direct interactions with DNA repair pathways

Lysyl oxidase (LOX) is a multifunctional protein required for normal collagen and elastin biosynthesis and maturation. In addition, LOX has complex roles in cancer in which the lysyl oxidase propeptide (LOX-PP) domain of secreted pro-LOX has tumor-suppressor activity, while the active enzyme promotes metastasis. In prostate cancer cell lines, recombinant LOX-PP (rLOX-PP) inhibits the growth of PC3 cells in vitro by mechanisms that were not characterized, while in DU145 cells rLOX-PP targeted fibroblast growth factor signaling. Because rLOX-PP can enhance effects of a genotoxic chemotherapeutic on breast cancer cell apoptosis, we reasoned that rLOX-PP could target DNA repair pathways typically elevated in cancer. Here we demonstrate for the first time that rLOX-PP inhibits prostate xenograft growth in vivo and that activating phosphorylations of the key DNA repair molecules ataxia-telangiectasia mutated (ATM) and checkpoint kinase 2 (CHK2) are inhibited by rLOX-PP expression in vivo. In addition, in vitro studies showed that rLOX-PP inhibits radiation-induced activating phosphorylations of ATM and CHK2 and that exogenously added rLOX-PP protein can localize to the nucleus in both DU145 and PC3 cells. rLOX-PP pull-down studies resulted in detection of a protein complex with the nuclear DNA repair regulator MRE11 in both cell lines, and rLOX-PP localized to radiation-induced nuclear DNA repair foci. Finally, rLOX-PP was shown to sensitize both DU145 and PC3 cells to radiation-induced cell death determined in colony-formation assays. These data provide evidence that rLOX-PP has a nuclear mechanism of action in which it directly interacts with DNA repair proteins to sensitize prostate cancer cells to the effects of ionizing radiation.

Blocking the road, stopping the engine or killing the driver? Advances in targeting EWS/FLI-1 fusion in Ewing sarcoma as novel therapy

INTRODUCTION

Ewing sarcoma (ES) represents the paradigm of an aberrant E-twenty-six (ETS) oncogene-driven cancer. It is characterized by specific rearrangements of one of five alternative ETS family member genes with EWSR1. There is experimental evidence that the resulting fusion proteins act as aberrant transcription factors driving ES pathogenesis. The transcriptional gene regulatory network driven by EWS-ETS proteins provides the oncogenic engine to the tumor. Therefore, EWS-ETS and their downstream machinery are considered ideal tumor-specific therapeutic targets.

AREAS COVERED

This review critically discusses the literature on the development of EWS-ETS-directed ES targeting strategies considering current knowledge of EWS-ETS biology and cellular context. It focuses on determinants of EWS-FLI1 function with an emphasis on interactions with chromatin structure. We speculate about the relevance of poorly investigated aspects in ES research such as chromatin remodeling and DNA damage repair for the development of targeted therapies.

EXPERT OPINION

This review questions the specificity of signature-based screening approaches to the identification of EWS-FLI1-targeted compounds. It challenges the view that targeting the downstream gene regulatory network carries potential for therapeutic breakthroughs because of resistance-inducing network rewiring. Instead, we propose to combine targeting of the fusion protein with epigenetic therapy as a future treatment strategy in ES.

The potential for targeting extracellular LOX proteins in human malignancy

The extracellular matrix (ECM) is the physical scaffold where cells are organized into tissues and organs. The ECM may be modified during cancer to allow and promote proliferation, invasion, and metastasis. The family of lysyl oxidase (LOX) enzymes cross-links collagens and elastin and, therefore, is a central player in ECM deposition and maturation. Extensive research has revealed how the LOX proteins participate in every stage of cancer progression, and two family members, LOX and LOX-like 2, have been linked to metastasis, the final stage of cancer responsible for over 90% of cancer patient deaths. However, LOX biosynthesis results in by-product with antiproliferative properties in certain cancers, and LOX enzymes may have different effects depending on the molecular network in which they are active. Therefore, the design of therapies targeting the LOX family needs to be guided by the molecular makeup of the individual disease and will probably require other agents to act on both the LOX enzymes and their associated network.