Inhibition of Notch3 signalling induces rhabdomyosarcoma cell differentiation promoting p38 phosphorylation and p21(Cip1) expression and hampers tumour cell growth in vitro and in vivo

Novel small molecule DMAMCL induces differentiation in rhabdomyosarcoma by downregulating of DLL1

Rhabdomyosarcoma (RMS), a mesenchymal tumor occurring in the soft tissue of children, is associated with a defect in differentiation. This study unveils a novel anti-tumor mechanism of dimethylaminomicheliolide (DMAMCL), which is a water-soluble derivative of Micheliolide. First, we demonstrate that DMAMCL inhibits RMS cell growth without obvious cell death, leading to morphological alterations, enhanced expression of muscle differentiation markers, and a shift from a malignant to a more benign metabolic phenotype. Second, we detected decreased expression of DLL1 in RMS cells after DMAMCL treatment, known as a pivotal ligand in the Notch signaling pathway. Downregulation of DLL1 inhibits RMS cell growth and induces morphological changes similar to the effects of DMAMCL. Furthermore, DMAMCL treatment or loss of DLL1 expression also inhibits RMS xenograft tumor growth and augmented the expression of differentiation markers. Surprisingly, in C2C12 cells DMAMCL treatment or DLL1 downregulation also induces cell growth inhibition and an elevation in muscle differentiation marker expression. These data indicated that DMAMCL induced RMS differentiation and DLL1 is an important factor for RMS differentiation, opening a new window for the clinical use of DMAMCL as an agent for differentiation-inducing therapy for RMS treatment.

A SNAI2/CTCF Interaction is Required for NOTCH1 Expression in Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is a pediatric malignancy of the muscle with characteristics of cells blocked in differentiation. NOTCH1 is an oncogene that promotes self-renewal and blocks differentiation in the fusion negative-RMS sub-type. However, how NOTCH1 expression is transcriptionally maintained in tumors is unknown. Analyses of SNAI2 and CTCF chromatin binding and HiC analyses revealed a conserved SNAI2/CTCF overlapping peak downstream of the NOTCH1 locus marking a sub-topologically associating domain (TAD) boundary. Deletion of the SNAI2-CTCF peak showed that it is essential for NOTCH1 expression and viability of FN-RMS cells. Reintroducing constitutively activated NOTCH1-ΔE in cells with the SNAI2-CTCF peak deleted restored cell-viability. Ablation of SNAI2 using CRISPR/Cas9 reagents resulted in the loss of majority of RD and SMS-CTR FN-RMS cells. However, the few surviving clones that repopulate cultures have recovered NOTCH1. Cells that re-establish NOTCH1 expression after SNAI2 ablation are unable to differentiate robustly as SNAI2 shRNA knockdown cells; yet, SNAI2-ablated cells continued to be exquisitely sensitive to ionizing radiation. Thus, we have uncovered a novel mechanism by which SNAI2 and CTCF maintenance of a sub-TAD boundary promotes rather than represses NOTCH1 expression. Further, we demonstrate that SNAI2 suppression of apoptosis post-radiation is independent of SNAI2/NOTCH1 effects on self-renewal and differentiation.

Identification and targeting of a HES1‐YAP1‐CDKN1C functional interaction in fusion‐negative rhabdomyosarcoma

Rhabdomyosarcoma (RMS), a cancer characterized by features of skeletal muscle, is the most common soft‐tissue sarcoma of childhood. With 5‐year survival rates among high‐risk groups at < 30%, new therapeutics are desperately needed. Previously, using a myoblast‐based model of fusion‐negative RMS (FN‐RMS), we found that expression of the Hippo pathway effector transcriptional coactivator YAP1 (YAP1) permitted senescence bypass and subsequent transformation to malignant cells, mimicking FN‐RMS. We also found that YAP1 engages in a positive feedback loop with Notch signaling to promote FN‐RMS tumorigenesis. However, we could not identify an immediate downstream impact of this Hippo‐Notch relationship. Here, we identify a HES1‐YAP1‐CDKN1C functional interaction, and show that knockdown of the Notch effector HES1 (Hes family BHLH transcription factor 1) impairs growth of multiple FN‐RMS cell lines, with knockdown resulting in decreased YAP1 and increased CDKN1C expression. In silico mining of published proteomic and transcriptomic profiles of human RMS patient‐derived xenografts revealed the same pattern of HES1‐YAP1‐CDKN1C expression. Treatment of FN‐RMS cells in vitro with the recently described HES1 small‐molecule inhibitor, JI130, limited FN‐RMS cell growth. Inhibition of HES1 in vivo via conditional expression of a HES1‐directed shRNA or JI130 dosing impaired FN‐RMS tumor xenograft growth. Lastly, targeted transcriptomic profiling of FN‐RMS xenografts in the context of HES1 suppression identified associations between HES1 and RAS‐MAPK signaling. In summary, these in vitro and in vivo preclinical studies support the further investigation of HES1 as a therapeutic target in FN‐RMS.

MET Inhibition Sensitizes Rhabdomyosarcoma Cells to NOTCH Signaling Suppression

Rhabdomyosarcoma (RMS) is a pediatric myogenic soft tissue sarcoma. The Fusion-Positive (FP) subtype expresses the chimeric protein PAX3-FOXO1 (P3F) while the Fusion-Negative (FN) is devoid of any gene translocation. FP-RMS and metastatic FN-RMS are often unresponsive to conventional therapy. Therefore, novel therapeutic approaches are needed to halt tumor progression. NOTCH signaling has oncogenic functions in RMS and its pharmacologic inhibition through γ-secretase inhibitors blocks tumor growth in vitro and in vivo. Here, we show that NOTCH signaling blockade resulted in the up-regulation and phosphorylation of the MET oncogene in both RH30 (FP-RMS) and RD (FN-RMS) cell lines. Pharmacologic inhibition of either NOTCH or MET signaling slowed proliferation and restrained cell survival compared to control cells partly by increasing Annexin V and CASP3/7 activation. Co-treatment with NOTCH and MET inhibitors significantly amplified these effects and enhanced PARP1 cleavage in both cell lines. Moreover, it severely hampered cell migration, colony formation, and anchorage-independent growth compared to single-agent treatments in both cell lines and significantly prevented the growth of FN-RMS cells grown as spheroids. Collectively, our results unveil the overexpression of the MET oncogene by NOTCH signaling targeting in RMS cells and show that MET pathway blockade sensitizes them to NOTCH inhibition.

Interaction between SNAI2 and MYOD enhances oncogenesis and suppresses differentiation in Fusion Negative Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is an aggressive pediatric malignancy of the muscle, that includes Fusion Positive (FP)-RMS harboring PAX3/7-FOXO1 and Fusion Negative (FN)-RMS commonly with RAS pathway mutations. RMS express myogenic master transcription factors MYOD and MYOG yet are unable to terminally differentiate. Here, we report that SNAI2 is highly expressed in FN-RMS, is oncogenic, blocks myogenic differentiation, and promotes growth. MYOD activates SNAI2 transcription via super enhancers with striped 3D contact architecture. Genome wide chromatin binding analysis demonstrates that SNAI2 preferentially binds enhancer elements and competes with MYOD at a subset of myogenic enhancers required for terminal differentiation. SNAI2 also suppresses expression of a muscle differentiation program modulated by MYOG, MEF2, and CDKN1A. Further, RAS/MEK-signaling modulates SNAI2 levels and binding to chromatin, suggesting that the differentiation blockade by oncogenic RAS is mediated in part by SNAI2. Thus, an interplay between SNAI2, MYOD, and RAS prevents myogenic differentiation and promotes tumorigenesis.

FAK Signaling in Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of children and adolescents. The fusion-positive (FP)-RMS variant expressing chimeric oncoproteins such as PAX3-FOXO1 and PAX7-FOXO1 is at high risk. The fusion negative subgroup, FN-RMS, has a good prognosis when non-metastatic. Despite a multimodal therapeutic approach, FP-RMS and metastatic FN-RMS often show a dismal prognosis with 5-year survival of less than 30%. Therefore, novel targets need to be discovered to develop therapies that halt tumor progression, reducing long-term side effects in young patients. Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that regulates focal contacts at the cellular edges. It plays a role in cell motility, survival, and proliferation in response to integrin and growth factor receptors’ activation. FAK is often dysregulated in cancer, being upregulated and/or overactivated in several adult and pediatric tumor types. In RMS, both in vitro and preclinical studies point to a role of FAK in tumor cell motility/invasion and proliferation, which is inhibited by FAK inhibitors. In this review, we summarize the data on FAK expression and modulation in RMS. Moreover, we give an overview of the approaches to inhibit FAK in both preclinical and clinical cancer settings.

CDK9 as a Valuable Target in Cancer: From Natural Compounds Inhibitors to Current Treatment in Pediatric Soft Tissue Sarcomas

Cyclin-Dependent Kinases (CDKs) are well-known reliable targets for cancer treatment being often deregulated. Among them, since the transcription-associated CDK9 represents the sentry of cell transcriptional homeostasis, it can be a valuable target for managing cancers in which the transcriptional machinery is dysregulated by tumor-driver oncogenes. Here we give an overview of some natural compounds identified as CDK inhibitors with reported activity also against CDK9, that were taken as a model for the development of highly active synthetic anti-CDK9 agents. After, we summarize the data on CDK9 inhibition in a group of rare pediatric solid tumors such as rhabdomyosarcoma, Ewing’s sarcoma, synovial sarcoma and malignant rhabdoid tumors (soft tissue sarcomas), highlighting the more recent results in this field. Finally, we discuss the perspective and challenge of CDK9 modulation in cancer.

Current and Future Treatment Strategies for Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children, and can be subcategorized histologically and/or based on PAX-FOXO1 fusion gene status. Over the last four decades, there have been no significant improvements in clinical outcomes for advanced and metastatic RMS patients, underscoring a need for new treatment options for these groups. Despite significant advancements in our understanding of the genomic landscape and underlying biological mechanisms governing RMS that have informed the identification of novel therapeutic targets, development of these therapies in clinical trials has lagged far behind. In this review, we summarize the current frontline multi-modality therapy for RMS according to pediatric protocols, highlight emerging targeted therapies and immunotherapies identified by preclinical studies, and discuss early clinical trial data and the implications they hold for future clinical development.

Insights into pediatric rhabdomyosarcoma research: Challenges and goals

Overall survival rates for pediatric patients with high-risk or relapsed rhabdomyosarcoma (RMS) have not improved significantly since the 1980s. Recent studies have identified a number of targetable vulnerabilities in RMS, but these discoveries have infrequently translated into clinical trials. We propose streamlining the process by which agents are selected for clinical evaluation in RMS. We believe that strong consideration should be given to the development of combination therapies that add biologically targeted agents to conventional cytotoxic drugs. One example of this type of combination is the addition of the WEE1 inhibitor AZD1775 to the conventional cytotoxic chemotherapeutics, vincristine and irinotecan.

Comparison of cachectic and non-cachectic sarcoma patients reveals an important role of Notch signaling in metastasis and myogenesis

Cancer-associated cachexia is a wasting syndrome that affects up to 50% of cancer patients. It is defined as unintentional weight loss ≥5% over 6 months and characterized by muscle atrophy, fatigue, and anorexia that are refractory to nutritional support. Sarcoma describes a diverse group of malignancies arising from the connective tissues. Sarcoma patients are uniquely susceptible to cancer-associated cachexia given its origins in the musculoskeletal system. Our previous research suggests that sarcoma cells may contribute to sarcoma-associated cachexia (SAC) via establishment of TNF-α-mediated inflammation and dysregulation of muscle homeostasis by abnormal Notch signaling. Here, we examine the role of the Notch pathway and pro-inflammatory cytokines in cells derived from cachectic and non-cachectic human sarcoma patients. We observed increased expression of Notch pathway genes in the cachexia group while no differences in pro-inflammatory cytokines were observed. Co-culture of muscle-derived stem cells (MDSCs) and sarcoma cells demonstrated the inhibition of MDSC maturation with both cachectic and non-cachectic patient cells, corresponding to elevated Pax7 and Notch pathway expression in MDSCs. Our findings suggest that there is no difference in inflammatory profile between cachexia and non-cachexia sarcoma samples. However, Cachectic sarcoma samples express increased Notch that mediates muscle wasting possibly through inhibition of myogenesis.

Genetics, epigenetics and redox homeostasis in rhabdomyosarcoma: Emerging targets and therapeutics

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma accounting for 5-8% of malignant tumours in children and adolescents. Children with high risk disease have poor prognosis. Anti-RMS therapies include surgery, radiation and combination chemotherapy. While these strategies improved survival rates, they have plateaued since 1990s as drugs that target differentiation and self-renewal of tumours cells have not been identified. Moreover, prevailing treatments are aggressive with drug resistance and metastasis causing failure of several treatment regimes. Significant advances have been made recently in understanding the genetic and epigenetic landscape in RMS. These studies have identified novel diagnostic and prognostic markers and opened new avenues for treatment. An important target identified in high throughput drug screening studies is reactive oxygen species (ROS). Indeed, many drugs in clinical trials for RMS impact tumour progression through ROS. In light of such emerging evidence, we discuss recent findings highlighting key pathways, epigenetic alterations and their impacts on ROS that form the basis of developing novel molecularly targeted therapies in RMS. Such targeted therapies in combination with conventional therapy could reduce adverse side effects in young survivors and lead to a decline in long-term morbidity.

Twist2 amplification in rhabdomyosarcoma represses myogenesis and promotes oncogenesis by redirecting MyoD DNA binding

Li et al. show that TWIST2 shapes the epigenetic landscape to drive chromatin opening at oncogenic loci and chromatin closing at myogenic loci. These epigenetic changes redirect MyoD binding from myogenic genes toward oncogenic, metabolic, and growth genes.

Rhabdomyosarcoma (RMS) is an aggressive pediatric cancer composed of myoblast-like cells. Recently, we discovered a unique muscle progenitor marked by the expression of the Twist2 transcription factor. Genomic analyses of 258 RMS patient tumors uncovered prevalent copy number amplification events and increased expression of TWIST2 in fusion-negative RMS. Knockdown of TWIST2 in RMS cells results in up-regulation of MYOGENIN and a decrease in proliferation, implicating TWIST2 as an oncogene in RMS. Through an inducible Twist2 expression system, we identified Twist2 as a reversible inhibitor of myogenic differentiation with the remarkable ability to promote myotube dedifferentiation in vitro. Integrated analysis of genome-wide ChIP-seq and RNA-seq data revealed the first dynamic chromatin and transcriptional landscape of Twist2 binding during myogenic differentiation. During differentiation, Twist2 competes with MyoD at shared DNA motifs to direct global gene transcription and repression of the myogenic program. Additionally, Twist2 shapes the epigenetic landscape to drive chromatin opening at oncogenic loci and chromatin closing at myogenic loci. These epigenetic changes redirect MyoD binding from myogenic genes toward oncogenic, metabolic, and growth genes. Our study reveals the dynamic interplay between two opposing transcriptional regulators that control the fate of RMS and provides insight into the molecular etiology of this aggressive form of cancer.

The Role of Notch3 in Cancer

The Notch family is a highly conserved gene group that regulates cell-cell interaction, embryogenesis, and tissue commitment. This review article focuses on the third Notch family subtype, Notch3. Regulation via Notch3 signaling was first implicated in vasculogenesis. However, more recent findings suggest that Notch3 signaling may play an important role in oncogenesis, tumor maintenance, and resistance to chemotherapy. Its role is mainly oncogenic, although in some cancers it appears to be tumor suppressive. Despite the wealth of published literature, it remains relatively underexplored and requires further research to shed more light on its role in cancer development, determine its tissue-specific function, and elaborate novel treatment strategies. Herein we summarize the role of Notch3 in cancer, possible mechanisms of its action, and current cancer treatment strategies targeting Notch3 signaling.

IMPLICATIONS FOR PRACTICE

The Notch family is a highly conserved gene group that regulates cell-cell interaction, embryogenesis, and tissue commitment. This review summarizes the existing data on the third subtype of the Notch family, Notch3. The role of Notch3 in different types of cancers is discussed, as well as implications of its modification and new strategies to affect Notch3 signaling activity.

Dysregulated Myogenesis in Rhabdomyosarcoma

Rhabdomyosarcoma is a mesenchymal malignancy associated with the skeletal muscle lineage and is also the most common pediatric soft tissue cancer. Between the two pediatric subtypes, embryonal and alveolar rhabdomyosarcoma, the alveolar subtype is generally more aggressive and high-risk. Despite intensive multimodal therapy, patients with high-risk rhabdomyosarcoma continue to have poor prognosis. In this chapter we address the mechanisms underlying the dysregulation of myogenesis in rhabdomyosarcoma. We specifically focus on recently identified signaling pathways that function to inhibit myogenesis and how similar functions have been shown to overlap in rhabdomyosarcoma, potentially contributing to the disease.

Pharmacological targeting of the ephrin receptor kinase signalling by GLPG1790 in vitro and in vivo reverts oncophenotype, induces myogenic differentiation and radiosensitizes embryonal rhabdomyosarcoma cells

Background

EPH (erythropoietin-producing hepatocellular) receptors are clinically relevant targets in several malignancies. This report describes the effects of GLPG1790, a new potent pan-EPH inhibitor, in human embryonal rhabdomyosarcoma (ERMS) cell lines.

Methods

EPH-A2 and Ephrin-A1 mRNA expression was quantified by real-time PCR in 14 ERMS tumour samples and in normal skeletal muscle (NSM). GLPG1790 effects were tested in RD and TE671 cell lines, two in vitro models of ERMS, by performing flow cytometry analysis, Western blotting and immunofluorescence experiments. RNA interfering experiments were performed to assess the role of specific EPH receptors. Radiations were delivered using an x-6 MV photon linear accelerator. GLPG1790 (30 mg/kg) in vivo activity alone or in combination with irradiation (2 Gy) was determined in murine xenografts.

Results

Our study showed, for the first time, a significant upregulation of EPH-A2 receptor and Ephrin-A1 ligand in ERMS primary biopsies in comparison to NSM. GLPG1790 in vitro induced G1-growth arrest as demonstrated by Rb, Cyclin A and Cyclin B1 decrease, as well as by p21 and p27 increment. GLPG1790 reduced migratory capacity and clonogenic potential of ERMS cells, prevented rhabdosphere formation and downregulated CD133, CXCR4 and Nanog stem cell markers. Drug treatment committed ERMS cells towards skeletal muscle differentiation by inducing a myogenic-like phenotype and increasing MYOD1, Myogenin and MyHC levels. Furthermore, GLPG1790 significantly radiosensitized ERMS cells by impairing the DNA double-strand break repair pathway. Silencing of both EPH-A2 and EPH-B2, two receptors preferentially targeted by GLPG1790, closely matched the effects of the EPH pharmacological inhibition. GLPG1790 and radiation combined treatments reduced tumour mass by 83% in mouse TE671 xenografts.

Conclusions

Taken together, our data suggest that altered EPH signalling plays a key role in ERMS development and that its pharmacological inhibition might represent a potential therapeutic strategy to impair stemness and to rescue myogenic program in ERMS cells.

A Novel Notch-YAP Circuit Drives Stemness and Tumorigenesis in Embryonal Rhabdomyosarcoma

Rhabdomyosarcoma (RMS), a cancer characterized by skeletal muscle features, is the most common soft-tissue sarcoma of childhood. While low- and intermediate-risk groups have seen improved outcomes, high-risk patients still face a 5-year survival rate of <30%, a statistic that has not changed in over 40 years. Understanding the biologic underpinnings of RMS is critical. The developmental pathways of Notch and YAP have been identified as potent but independent oncogenic signals that support the embryonal variant of RMS (eRMS). Here, the cross-talk between these pathways and the impact on eRMS tumorigenesis is reported. Using human eRMS cells grown as three-dimensional (3D) rhabdospheres, which enriches in stem cells, it was found that Notch signaling transcriptionally upregulates YAP1 gene expression and YAP activity. Reciprocally, YAP transcriptionally upregulates the Notch ligand genes JAG1 and DLL1 and the core Notch transcription factor RBPJ This bidirectional circuit boosts expression of key stem cell genes, including SOX2, which is functionally required for eRMS spheres. Silencing this circuit for therapeutic purposes may be challenging, because the inhibition of one node (e.g., pharmacologic Notch blockade) can be rescued by upregulation of another (constitutive YAP expression). Instead, dual inhibition of Notch and YAP is necessary. Finally, supporting the existence of this circuit beyond a model system, nuclear Notch and YAP protein expression are correlated in human eRMS tumors, and YAP suppression in vivo decreases Notch signaling and SOX2 expression.Implications: This study identifies a novel oncogenic signaling circuit driving eRMS stemness and tumorigenesis, and provides evidence and rationale for combination therapies co-targeting Notch and YAP. Mol Cancer Res; 15(12); 1777-91. ©2017 AACR.

Update on molecular findings in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common malignant soft tissue tumour in children and adolescents. Histologically RMS resembles developing fetal striated skeletal muscle. RMS is stratified into different histological subtypes which appear to influence management plans and patient outcome. Importantly, molecular classification of RMS seems to more accurately capture the true biology and clinical course and prognosis of RMS to guide therapeutic decisions. The identification of PAX-FOXO1 fusion status in RMS is one of the most important updates in the risk stratification of RMS. There are several genes close to PAX that are frequently altered including the RAS family, FGFR4, PIK3CA, CTNNB1, FBXW7, and BCOR. As with most paediatric blue round cell tumours and sarcomas, chemotherapy is the key regimen for RMS therapy. Currently there are no direct inhibitors against PAX-FOXO1 fusion oncoproteins and targeting epigenetic cofactors is limited to clinical trials. Failure of therapy in RMS is usually related to drug resistance and metastatic disease. Through this review we have highlighted most of the molecular aspects in RMS and have attempted to correlate with RMS classification, treatment and prognosis.

Activation of an endothelial Notch1-Jagged1 circuit induces VCAM1 expression, an effect amplified by interleukin-1β

The Notch1 and Notch4 signaling pathways regulate endothelial cell homeostasis. Inflammatory cytokines induce the expression of endothelial adhesion molecules, including VCAM1, partly by downregulating Notch4 signaling. We investigated the role of endothelial Notch1 in this IL-1β-mediated process. Brief treatment with IL-1β upregulated endothelial VCAM1 and Notch ligand Jagged1. IL-1β decreased Notch1 mRNA levels, but levels of the active Notch1ICD protein remained constant. IL-1β-mediated VCAM1 induction was downregulated in endothelial cells subjected to pretreatment with a pharmacological inhibitor of the γ-secretase, which activates Notch receptors, producing NotchICD. It was also downregulated in cells in which Notch1 and/or Jagged1 were silenced.Conversely, the forced expression of Notch1ICD in naïve endothelial cells upregulated VCAM1 per se and amplified IL-1β-mediated VCAM1 induction. Jagged1 levels increased and Notch4 signaling was downregulated in parallel. Finally, Notch1ICD and Jagged1 expression was upregulated in the endothelium of the liver in a model of chronic liver inflammation.In conclusion, we describe here a cell-autonomous, pro-inflammatory endothelial Notch1-Jagged1 circuit (i) triggering the expression of VCAM1 even in the absence of inflammatory cytokines and (ii) enhancing the effects of IL-1β. Thus, IL-1β regulates Notch1 and Notch4 activity in opposite directions, consistent with a selective targeting of Notch1 in inflamed endothelium.

PAX7 is a required target for microRNA-206-induced differentiation of fusion-negative rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood. RMS can be parsed based on clinical outcome into two subtypes, fusion-positive RMS (FP-RMS) or fusion-negative RMS (FN-RMS) based on the presence or absence of either PAX3-FOXO1 or PAX7-FOXO1 gene fusions. In both RMS subtypes, tumor cells show histology and a gene expression pattern resembling that of developmentally arrested skeletal muscle. Differentiation therapy is an attractive approach to embryonal tumors of childhood including RMS; however, agents to drive RMS differentiation have not entered the clinic and their mechanisms remain unclear. MicroRNA-206 (miR-206) expression increases through normal muscle development and has decreased levels in RMS compared with normal skeletal muscle. Increasing miR-206 expression drives differentiation of RMS, but the target genes responsible for the relief of the development arrest are largely unknown. Using a combinatorial approach with gene and proteomic profiling coupled with genetic rescue, we identified key miR-206 targets responsible for the FN-RMS differentiation blockade, PAX7, PAX3, NOTCH3, and CCND2. Specifically, we determined that PAX7 downregulation is necessary for miR-206-induced cell cycle exit and myogenic differentiation in FN-RMS but not in FP-RMS. Gene knockdown of targets necessary for miR-206-induced differentiation alone or in combination was not sufficient to phenocopy the differentiation phenotype from miR-206, thus illustrating that miR-206 replacement offers the ability to modulate a complex network of genes responsible for the developmental arrest in FN-RMS. Genetic deletion of miR-206 in a mouse model of FN-RMS accelerated and exacerbated tumor development, indicating that both in vitro and in vivo miR-206 acts as a tumor suppressor in FN-RMS at least partially through downregulation of PAX7. Collectively, our results illustrate that miR-206 relieves the differentiation arrest in FN-RMS and suggests that miR-206 replacement could be a potential therapeutic differentiation strategy.

SRC Family Kinase Inhibition in Ewing Sarcoma Cells Induces p38 MAP Kinase-Mediated Cytotoxicity and Reduces Cell Migration

Ewing sarcoma (ES) is a highly aggressive bone and soft tissue cancer, representing the second most common primary malignant bone tumor in children and adolescents. Although the development of a multimodal therapy, including both local control (surgery and/or radiation) and systemic multidrug chemotherapy, has determined a significant improvement in survival, patients with metastatic and recurrent disease still face a poor prognosis. Moreover, considering that ES primarily affects young patients, there are concerns about long-term adverse effects of the therapy. Therefore, more rational strategies, targeting specific molecular alterations underlying ES, are required. Recent studies suggest that SRC family kinases (SFKs), which are aberrantly activated in most cancer types, could represent key therapeutic targets also for ES. Here, we challenged ES cell lines with a recently developed selective SFK inhibitor (a pyrazolo[3,4-d]pyrimidine derivative, called SI221), which was previously shown to be a valuable proapoptotic agent in other tumor types while not affecting normal cells. We observed that SI221 significantly reduced ES cell viability and proved to be more effective than the well-known SFK inhibitor PP2. SI221 was able to induce apoptosis in ES cells and also reduced ES cell clonogenic potential. Furthermore, SI221 was also able to reduce ES cell migration. At the molecular level, our data suggest that SFK inhibition through SI221 could reduce ES cell viability at least in part by hindering an SFK-NOTCH1 receptor-p38 mitogen-activated protein kinase (MAPK) axis. Overall, our study suggests a potential application of specific SFK inhibition in ES therapy. J. Cell. Physiol. 232: 129-135, 2017. © 2016 Wiley Periodicals, Inc.

Notch Signaling in Neuroendocrine Tumors

Carcinoids and neuroendocrine tumors (NETs) are a heterogeneous group of tumors that arise from the neuroendocrine cells of the GI tract, endocrine pancreas, and the respiratory system. NETs remain significantly understudied with respect to molecular mechanisms of pathogenesis, particularly the role of cell fate signaling systems such as Notch. The abundance of literature on the Notch pathway is a testament to its complexity in different cellular environments. Notch receptors can function as oncogenes in some contexts and tumor suppressors in others. The genetic heterogeneity of NETs suggests that to fully understand the roles and the potential therapeutic implications of Notch signaling in NETs, a comprehensive analysis of Notch expression patterns and potential roles across all NET subtypes is required.

SRC family kinase (SFK) inhibition reduces rhabdomyosarcoma cell growth in vitro and in vivo and triggers p38 MAP kinase-mediated differentiation

Recent data suggest that SRC family kinases (SFKs) could represent potential therapeutic targets for rhabdomyosarcoma (RMS), the most common soft-tissue sarcoma in children. Here, we assessed the effect of a recently developed selective SFK inhibitor (a pyrazolo[3,4-d]pyrimidine derivative, called SI221) on RMS cell lines. SI221, which showed to be mainly effective against the SFK member YES, significantly reduced cell viability and induced apoptosis, without affecting non-tumor cells, such as primary human skin fibroblasts and differentiated C2C12 cells. Moreover, SI221 decreased in vitro cell migration and invasion and reduced tumor growth in a RMS xenograft model. SFK inhibition also induced muscle differentiation in RMS cells by affecting the NOTCH3 receptor-p38 mitogen-activated protein kinase (MAPK) axis, which regulates the balance between proliferation and differentiation. Overall, our findings suggest that SFK inhibition, besides reducing RMS cell growth and invasive potential, could also represent a differentiation therapeutic strategy for RMS.

Histone Deacetylase Inhibitors Antagonize Distinct Pathways to Suppress Tumorigenesis of Embryonal Rhabdomyosarcoma

Embryonal rhabdomyosarcoma (ERMS) is the most common soft tissue cancer in children. The prognosis of patients with relapsed or metastatic disease remains poor. ERMS genomes show few recurrent mutations, suggesting that other molecular mechanisms such as epigenetic regulation might play a major role in driving ERMS tumor biology. In this study, we have demonstrated the diverse roles of histone deacetylases (HDACs) in the pathogenesis of ERMS by characterizing effects of HDAC inhibitors, trichostatin A (TSA) and suberoylanilide hydroxamic acid (SAHA; also known as vorinostat) in vitro and in vivo. TSA and SAHA suppress ERMS tumor growth and progression by inducing myogenic differentiation as well as reducing the self-renewal and migratory capacity of ERMS cells. Differential expression profiling and pathway analysis revealed downregulation of key oncogenic pathways upon HDAC inhibitor treatment. By gain-of-function, loss-of-function, and chromatin immunoprecipitation (ChIP) studies, we show that Notch1- and EphrinB1-mediated pathways are regulated by HDACs to inhibit differentiation and enhance migratory capacity of ERMS cells, respectively. Our study demonstrates that aberrant HDAC activity plays a major role in ERMS pathogenesis. Druggable targets in the molecular pathways affected by HDAC inhibitors represent novel therapeutic options for ERMS patients.

Inhibition of Notch3 prevents monocrotaline-induced pulmonary arterial hypertension

It has been shown that activation of Notch3 signaling is involved in the development of pulmonary arterial hypertension (PAH) by stimulating pulmonary arteries remodeling, while the molecular mechanisms underlying this are still largely unknown. The aims of this study are to address these issues. Monocrotaline dramatically increased right ventricle systolic pressure to 39.0 ± 2.6 mmHg and right ventricle hypertrophy index to 53.4 ± 5.3% (P < 0.05 versus control) in rats, these were accompanied with significantly increased proliferation and reduced apoptosis of pulmonary vascular cells as well as pulmonary arteries remodeling. Treatment of PAH model with specific Notch inhibitor DAPT significantly reduced right ventricle systolic pressure to 26.6 ± 1.3 mmHg and right ventricle hypertrophy index to 33.5 ± 2.6% (P < 0.05 versus PAH), suppressed proliferation and enhanced apoptosis of pulmonary vascular cells as well as inhibited pulmonary arteries remodeling. Our results further indicated that level of Notch3 protein and NICD3 were increased in MCT-induced model of PAH, this was accompanied with elevation of Skp2 and Hes1 protein level and reduction of P27Kip1. Administration of rats with DAPT-prevented MCT induced these changes. Our results suggest that Notch3 signaling activation stimulated pulmonary vascular cells proliferation by Skp2-and Hes1-mediated P27Kip1 reduction, and Notch3 might be a new target to treat PAH.

MicroRNA-101 is repressed by EZH2 and its restoration inhibits tumorigenic features in embryonal rhabdomyosarcoma

Background

Rhabdomyosarcoma (RMS) is a pediatric soft tissue sarcoma arising from myogenic precursors that have lost their capability to differentiate into skeletal muscle. The polycomb-group protein EZH2 is a Lys27 histone H3 methyltransferase that regulates the balance between cell proliferation and differentiation by epigenetically silencing muscle-specific genes. EZH2 is often over-expressed in several human cancers acting as an oncogene. We previously reported that EZH2 inhibition induces cell cycle arrest followed by myogenic differentiation of RMS cells of the embryonal subtype (eRMS). MiR-101 is a microRNA involved in a negative feedback circuit with EZH2 in different normal and tumor tissues. To that, miR-101 can behave as a tumor suppressor in several cancers by repressing EZH2 expression. We, therefore, evaluated whether miR-101 is de-regulated in eRMS and investigated its interplaying with EZH2 as well as its role in the in vitro tumorigenic potential of these tumor cells.

Results

Herein, we report that miR-101 is down-regulated in eRMS patients and in tumor cell lines compared to their controls showing an inverse pattern of expression with EZH2. We also show that miR-101 is up-regulated in eRMS cells following both genetic and pharmacological inhibition of EZH2. In turn, miR-101 forced expression reduces EZH2 levels as well as restrains the migratory potential of eRMS cells and impairs their clonogenic and anchorage-independent growth capabilities. Finally, EZH2 recruitment to regulatory region of miR-101-2 gene decreases in EZH2-silenced eRMS cells. This phenomenon is associated to reduced H3K27me3 levels at the same regulatory locus, indicating that EZH2 directly targets miR-101 for repression in eRMS cells.

Conclusions

Altogether, our data show that, in human eRMS, miR-101 is involved in a negative feedback loop with EZH2, whose targeting has been previously shown to halt eRMS tumorigenicity. They also demonstrate that the re-induction of miR-101 hampers the tumor features of eRMS cells. In this scenario, epigenetic dysregulations confirm their crucial role in the pathogenesis of this soft tissue sarcoma.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-015-0107-z) contains supplementary material, which is available to authorized users.

Targeting hedgehog signaling reduces self-renewal in embryonal rhabdomyosarcoma

Current treatment regimens for rhabdomyosarcoma (RMS), the most common pediatric soft tissue cancer, rely on conventional chemotherapy, and although they show clinical benefit, there is a significant risk of adverse side effects and secondary tumors later in life. Therefore, identifying and targeting sub-populations with higher tumorigenic potential and self-renewing capacity would offer improved patient management strategies. Hedgehog signaling has been linked to the development of embryonal RMS (ERMS) through mouse genetics and rare human syndromes. However, activating mutations in this pathway in sporadic RMS are rare and therefore the contribution of hedgehog signaling to oncogenesis remains unclear. Here, we show by genetic loss- and gain-of-function experiments and the use of clinically relevant small molecule modulators that hedgehog signaling is important for controlling self-renewal of a subpopulation of RMS cells in vitro and tumor initiation in vivo. In addition, hedgehog activity altered chemoresistance, motility and differentiation status. The core stem cell gene NANOG was determined to be important for ERMS self-renewal, possibly acting downstream of hedgehog signaling. Crucially, evaluating the presence of a subpopulation of tumor-propagating cells in patient biopsies identified by GLI1 and NANOG expression had prognostic significance. Hence, this work identifies novel functional aspects of hedgehog signaling in ERMS, redefines the rationale for its targeting as means to control ERMS self-renewal and underscores the importance of studying functional tumor heterogeneity in pediatric cancers.

Alternative splicing of MEF2C pre-mRNA controls its activity in normal myogenesis and promotes tumorigenicity in rhabdomyosarcoma cells

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children. Many cellular disruptions contribute to the progression of this pediatric cancer, including aberrant alternative splicing. The MEF2 family of transcription factors regulates many developmental programs, including myogenesis. MEF2 gene transcripts are subject to alternate splicing to generate protein isoforms with divergent functions. We found that MEF2Cα1 was the ubiquitously expressed isoform that exhibited no myogenic activity and that MEF2Cα2, the muscle-specific MEF2C isoform, was required for efficient differentiation. We showed that exon α in MEF2C was aberrantly alternatively spliced in RMS cells, with the ratio of α2/α1 highly down-regulated in RMS cells compared with normal myoblasts. Compared with MEF2Cα2, MEF2Cα1 interacted more strongly with and recruited HDAC5 to myogenic gene promoters to repress muscle-specific genes. Overexpression of the MEF2Cα2 isoform in RMS cells increased myogenic activity and promoted differentiation in RMS cells. We also identified a serine protein kinase, SRPK3, that was down-regulated in RMS cells and found that expression of SRPK3 promoted the splicing of the MEF2Cα2 isoform and induced differentiation. Restoration of either MEF2Cα2 or SPRK3 inhibited both proliferation and anchorage-independent growth of RMS cells. Together, our findings indicate that the alternative splicing of MEF2C plays an important role in normal myogenesis and RMS development. An improved understanding of alternative splicing events in RMS cells will potentially reveal novel therapeutic targets for RMS treatment.

The Polycomb group (PcG) protein EZH2 supports the survival of PAX3-FOXO1 alveolar rhabdomyosarcoma by repressing FBXO32 (Atrogin1/MAFbx)

The Polycomb group (PcG) proteins regulate stem cell differentiation via the repression of gene transcription, and their deregulation has been widely implicated in cancer development. The PcG protein Enhancer of Zeste Homolog 2 (EZH2) works as a catalytic subunit of the Polycomb Repressive Complex 2 (PRC2) by methylating lysine 27 on histone H3 (H3K27me3), a hallmark of PRC2-mediated gene repression. In skeletal muscle progenitors, EZH2 prevents an unscheduled differentiation by repressing muscle-specific gene expression and is downregulated during the course of differentiation. In rhabdomyosarcoma (RMS), a pediatric soft-tissue sarcoma thought to arise from myogenic precursors, EZH2 is abnormally expressed and its downregulation in vitro leads to muscle-like differentiation of RMS cells of the embryonal variant. However, the role of EZH2 in the clinically aggressive subgroup of alveolar RMS, characterized by the expression of PAX3-FOXO1 oncoprotein, remains unknown. We show here that EZH2 depletion in these cells leads to programmed cell death. Transcriptional derepression of F-box protein 32 (FBXO32) (Atrogin1/MAFbx), a gene associated with muscle homeostasis, was evidenced in PAX3-FOXO1 RMS cells silenced for EZH2. This phenomenon was associated with reduced EZH2 occupancy and H3K27me3 levels at the FBXO32 promoter. Simultaneous knockdown of FBXO32 and EZH2 in PAX3-FOXO1 RMS cells impaired the pro-apoptotic response, whereas the overexpression of FBXO32 facilitated programmed cell death in EZH2-depleted cells. Pharmacological inhibition of EZH2 by either 3-Deazaneplanocin A or a catalytic EZH2 inhibitor mirrored the phenotypic and molecular effects of EZH2 knockdown in vitro and prevented tumor growth in vivo. Collectively, these results indicate that EZH2 is a key factor in the proliferation and survival of PAX3-FOXO1 alveolar RMS cells working, at least in part, by repressing FBXO32. They also suggest that the reducing activity of EZH2 could represent a novel adjuvant strategy to eradicate high-risk PAX3-FOXO1 alveolar RMS.

MicroRNAs and epigenetic mechanisms of rhabdomyosarcoma development

Rhabdomyosarcoma is the most common type of soft tissue sarcoma in children. Two main subtypes of rhabdomyosarcoma with different molecular pattern and distinct clinical behaviour may be identified - embryonal and alveolar rhabdomyosarcoma. All types of rhabdomyosarcoma are believed to be of myogenic origin as they express high levels of myogenesis-related factors. They all, however, fail to undergo a terminal differentiation which results in tumour formation. In the aberrant regulation of myogenesis in rhabdomyosarcoma, microRNAs and epigenetic factors are particularly involved. Indeed, these mediators seem to be even more significant for the development of rhabdomyosarcoma than canonical myogenic transcription factors like MyoD, a master regulatory switch for myogenesis. Therefore, in this review we focus on the regulation of rhabdomyosarcoma progression by microRNAs, and especially on microRNAs of the myo-miRNAs family (miR-1, -133a/b and -206), other well-known myogenic regulators like miR-29, and on microRNAs recently recognized to play a role in the differentiation of rhabdomyosarcoma, such as miR-450b-5p or miR-203. We also review changes in epigenetic modifiers associated with rhabdomyosarcoma, namely histone deacetylases and methyltransferases, especially from the Polycomp Group, like Yin Yang1 and Enhancer of Zeste Homolog2. Finally, we summarize how the functioning of these molecules can be affected by oxidative stress and how antioxidative enzymes can influence the development of this tumour. This article is part of a Directed Issue entitled: Rare Cancers.

Hyper-activation of Notch3 amplifies the proliferative potential of rhabdomyosarcoma cells

Rhabdomyosarcoma (RMS) is a pediatric myogenic-derived soft tissue sarcoma that includes two major histopathological subtypes: embryonal and alveolar. The majority of alveolar RMS expresses PAX3-FOXO1 fusion oncoprotein, associated with the worst prognosis. RMS cells show myogenic markers expression but are unable to terminally differentiate. The Notch signaling pathway is a master player during myogenesis, with Notch1 activation sustaining myoblast expansion and Notch3 activation inhibiting myoblast fusion and differentiation. Accordingly, Notch1 signaling is up-regulated and activated in embryonal RMS samples and supports the proliferation of tumor cells. However, it is unable to control their differentiation properties. We previously reported that Notch3 is activated in RMS cell lines, of both alveolar and embryonal subtype, and acts by inhibiting differentiation. Moreover, Notch3 depletion reduces PAX3-FOXO1 alveolar RMS tumor growth in vivo. However, whether Notch3 activation also sustains the proliferation of RMS cells remained unclear. To address this question, we forced the expression of the activated form of Notch3, Notch3IC, in the RH30 and RH41 PAX3-FOXO1-positive alveolar and in the RD embryonal RMS cell lines and studied the proliferation of these cells. We show that, in all three cell lines tested, Notch3IC over-expression stimulates in vitro cell proliferation and prevents the effects of pharmacological Notch inhibition. Furthermore, Notch3IC further increases RH30 cell growth in vivo. Interestingly, knockdown of Notch canonical ligands JAG1 or DLL1 in RMS cell lines decreases Notch3 activity and reduces cell proliferation. Finally, the expression of Notch3IC and its target gene HES1 correlates with that of the proliferative marker Ki67 in a small cohort of primary PAX-FOXO1 alveolar RMS samples. These results strongly suggest that high levels of Notch3 activation increase the proliferative potential of RMS cells.

Glycogen synthase kinase 3 inhibitors induce the canonical WNT/β-catenin pathway to suppress growth and self-renewal in embryonal rhabdomyosarcoma

Embryonal rhabdomyosarcoma (ERMS) is a common pediatric malignancy of muscle, with relapse being the major clinical challenge. Self-renewing tumor-propagating cells (TPCs) drive cancer relapse and are confined to a molecularly definable subset of ERMS cells. To identify drugs that suppress ERMS self-renewal and induce differentiation of TPCs, a large-scale chemical screen was completed. Glycogen synthase kinase 3 (GSK3) inhibitors were identified as potent suppressors of ERMS growth through inhibiting proliferation and inducing terminal differentiation of TPCs into myosin-expressing cells. In support of GSK3 inhibitors functioning through activation of the canonical WNT/β-catenin pathway, recombinant WNT3A and stabilized β-catenin also enhanced terminal differentiation of human ERMS cells. Treatment of ERMS-bearing zebrafish with GSK3 inhibitors activated the WNT/β-catenin pathway, resulting in suppressed ERMS growth, depleted TPCs, and diminished self-renewal capacity in vivo. Activation of the canonical WNT/β-catenin pathway also significantly reduced self-renewal of human ERMS, indicating a conserved function for this pathway in modulating ERMS self-renewal. In total, we have identified an unconventional tumor suppressive role for the canonical WNT/β-catenin pathway in regulating self-renewal of ERMS and revealed therapeutic strategies to target differentiation of TPCs in ERMS.

Pharmacological inhibition of EZH2 as a promising differentiation therapy in embryonal RMS

Background

Embryonal Rhabdomyosarcoma (RMS) is a pediatric soft-tissue sarcoma derived from myogenic precursors that is characterized by a good prognosis in patients with localized disease. Conversely, metastatic tumors often relapse, leading to a dismal outcome. The histone methyltransferase EZH2 epigenetically suppresses skeletal muscle differentiation by repressing the transcription of myogenic genes. Moreover, de-regulated EZH2 expression has been extensively implied in human cancers. We have previously shown that EZH2 is aberrantly over-expressed in RMS primary tumors and cell lines. Moreover, it has been recently reported that EZH2 silencing in RD cells, a recurrence-derived embryonal RMS cell line, favors myofiber-like structures formation in a pro-differentiation context. Here we evaluate whether similar effects can be obtained also in the presence of growth factor-supplemented medium (GM), that mimics a pro-proliferative microenvironment, and by pharmacological targeting of EZH2 in RD cells and in RD tumor xenografts.

Methods

Embryonal RMS RD cells were cultured in GM and silenced for EZH2 or treated with either the S-adenosylhomocysteine hydrolase inhibitor 3-deazaneplanocin A (DZNep) that induces EZH2 degradation, or with a new class of catalytic EZH2 inhibitors, MC1948 and MC1945, which block the catalytic activity of EZH2. RD cell proliferation and myogenic differentiation were evaluated both in vitro and in vivo.

Results

Here we show that EZH2 protein was abnormally expressed in 19 out of 19 (100%) embryonal RMS primary tumors and cell lines compared to their normal counterparts. Genetic down-regulation of EZH2 by silencing in GM condition reduced RD cell proliferation up-regulating p21^Cip1. It also resulted in myogenic-like differentiation testified by the up-regulation of myogenic markers Myogenin, MCK and MHC. These effects were reverted by enforced over-expression of a murine Ezh2, highlighting an EZH2-specific effect. Pharmacological inhibition of EZH2 using either DZNep or MC inhibitors phenocopied the genetic knockdown of EZH2 preventing cell proliferation and restoring myogenic differentiation both in vitro and in vivo.

Conclusions

These results provide evidence that EZH2 function can be counteracted by pharmacological inhibition in embryonal RMS blocking proliferation even in a pro-proliferative context. They also suggest that this approach could be exploited as a differentiation therapy in adjuvant therapeutic intervention for embryonal RMS.

Glycogen synthase kinase 3β represses MYOGENIN function in alveolar rhabdomyosarcoma

MYOGENIN is a member of the muscle regulatory factor family that orchestrates an obligatory step in myogenesis, the terminal differentiation of skeletal muscle cells. A paradoxical feature of alveolar rhabdomyosarcoma (ARMS), a prevalent soft tissue sarcoma in children arising from cells with a myogenic phenotype, is the inability of these cells to undergo terminal differentiation despite the expression of MYOGENIN. The chimeric PAX3-FOXO1 fusion protein which results from a chromosomal translocation in ARMS has been implicated in blocking cell cycle arrest, preventing myogenesis from occurring. We report here that PAX3-FOXO1 enhances glycogen synthase kinase 3β (GSK3β) activity which in turn represses MYOGENIN activity. MYOGENIN is a GSK3β substrate in vitro on the basis of in vitro kinase assays and MYOGENIN is phosphorylated in ARMS-derived RH30 cells. Constitutively active GSK3β(S9A) increased the level of a phosphorylated form of MYOGENIN on the basis of western blot analysis and this effect was reversed by neutralization of the single consensus GSK3β phosphoacceptor site by mutation (S160/164A). Congruently, GSK3β inhibited the trans-activation of an E-box reporter gene by wild-type MYOGENIN, but not MYOGENIN with the S160/164A mutations. Functionally, GSK3β repressed muscle creatine kinase (MCK) promoter activity, an effect which was reversed by the S160/164A mutated MYOGENIN. Importantly, GSK3β inhibition or exogenous expression of the S160/164A mutated MYOGENIN in ARMS reduced the anchorage independent growth of RH30 cells in colony-formation assays. Thus, sustained GSK3β activity represses a critical regulatory step in the myogenic cascade, contributing to the undifferentiated, proliferative phenotype in alveolar rhabdomyosarcoma (ARMS).

TBX2 blocks myogenesis and promotes proliferation in rhabdomyosarcoma cells

Rhabdomyosarcomas (RMSs) are the most frequent soft tissue sarcomas in children that share many features of developing skeletal muscle. We have discovered that a T-box family member, TBX2, is highly upregulated in tumor cells of both major RMS subtypes. TBX2 is a repressor that is often overexpressed in cancer cells and is thought to function in bypassing cell growth control, including repression of p14 and p21. The cell cycle regulator p21 is required for the terminal differentiation of skeletal muscle cells and is silenced in RMS cells. We have found that TBX2 interacts with the myogenic regulatory factors MyoD and myogenin and inhibits the activity of these factors. TBX2 is expressed in primary myoblasts and C2C12 cells, but is strongly downregulated upon differentiation. TBX2 recruits the histone deacetylase HDAC1 and is a potent inhibitor of the expression of muscle-specific genes and the cell cycle regulators, p21 and p14. TBX2 promotes the proliferation of RMS cells and either depletions of TBX2 or dominant negative TBX2 upregulate p21- and muscle-specific genes. Significantly, depletion or interference with TBX2 completely inhibits tumor growth in a xenograft assay, highlighting the oncogenic role of TBX2 in RMS cells. Thus, the data demonstrate that elevated expression of TBX2 contributes to the pathology of RMS cells by promoting proliferation and repressing differentiation-specific gene expression. These results show that deregulated TBX2 serves as an oncogene in RMS, suggesting that TBX2 may serve as a new diagnostic marker or therapeutic target for RMS tumors.

Expression of notch family proteins in placentas from patients with early-onset severe preeclampsia

OBJECTIVES

This study is aimed to identify the expression of Notch family proteins in placentas from patients with early-onset severe preeclampsia.

STUDY DESIGN

The expression of Notch family proteins in placentas was investigated by immunohistochemistry, Western blotting, and real-time reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

The profile of distribution of all Notch family proteins in placentas from patients with early-onset severe preeclampsia is similar to that in normal placentas. All Notch family proteins are expressed in placental trophoblasts. Moreover, Notch1 and Jagged1 (Jag1) are detected in placental endothelial cells. Real-time RT-PCR showed that messenger RNA levels of Notch2 and Delta-like4 (Dll4) in placentas from patients with early-onset severe preeclampsia are lower than that of normal placentas. Western blotting showed a significant increase in Notch3 expression and a significant decrease in Notch2 expression in placentas from patients with early-onset severe preeclampsia relative to those in normal placentas.

CONCLUSION

The results suggest that Notch2 and Notch3 may play some roles in the pathogenesis of preeclampsia.

Loss of MEF2D expression inhibits differentiation and contributes to oncogenesis in rhabdomyosarcoma cells

Background

Rhabdomyosarcoma (RMS) is a highly malignant pediatric cancer that is the most common form of soft tissue tumors in children. RMS cells have many features of skeletal muscle cells, yet do not differentiate. Thus, our studies have focused on the defects present in these cells that block myogenesis.

Methods

Protein and RNA analysis identified the loss of MEF2D in RMS cells. MEF2D was expressed in RD and RH30 cells by transient transfection and selection of stable cell lines, respectively, to demonstrate the rescue of muscle differentiation observed. A combination of techniques such as proliferation assays, scratch assays and soft agar assays were used with RH30 cells expressing MEF2D to demonstrate the loss of oncogenic growth in vitro and xenograft assays were used to confirm the loss of tumor growth in vivo.

Results

Here, we show that one member of the MEF2 family of proteins required for normal myogenesis, MEF2D, is largely absent in RMS cell lines representing both major subtypes of RMS as well as primary cells derived from an embryonal RMS model. We show that the down regulation of MEF2D is a major cause for the failure of RMS cells to differentiate. We find that MyoD and myogenin are bound with their dimerization partner, the E proteins, to the promoters of muscle specific genes in RMS cells. However, we cannot detect MEF2D binding at any promoter tested. We find that exogenous MEF2D expression can activate muscle specific luciferase constructs, up regulate p21 expression and increase muscle specific gene expression including the expression of myosin heavy chain, a marker for skeletal muscle differentiation. Restoring expression of MEF2D also inhibits proliferation, cell motility and anchorage independent growth in vitro. We have confirmed the inhibition of tumorigenicity by MEF2D in a tumor xenograft model, with a complete regression of tumor growth.

Conclusions

Our data indicate that the oncogenic properties of RMS cells can be partially attributed to the loss of MEF2D expression and that restoration of MEF2D may represent a useful therapeutic strategy to decrease tumorigenicity.

Cyclin D1 is a major target of miR-206 in cell differentiation and transformation

miR-206, a member of the so-called myomiR family, is largely acknowledged as a specific, positive regulator of skeletal muscle differentiation. A growing body of evidence also suggests a tumor suppressor function for miR-206, as it is frequently downregulated in various types of cancers. In this study, we show that miR-206 directly targets cyclin D1 and contributes to the regulation of CCND1 gene expression in both myogenic and non-muscle, transformed cells. We demonstrate that miR-206, either exogenous or endogenous, reduces cyclin D1 levels and proliferation rate in C2C12 cells without promoting differentiation, and that miR-206 knockdown in terminally differentiated C2C12 cells leads to cyclin D1 accumulation in myotubes, indicating that miR-206 might be involved in the maintenance of the post-mitotic state. Targeting of cyclin D1 might also account, at least in part, for the tumor-suppressor activity suggested for miR-206 in previous studies. Accordingly, the analysis of neoplastic and matched normal lung tissues reveals that miR-206 downregulation in lung tumors correlates, in most cases, with higher cyclin D1 levels. Moreover, gain-of-function experiments with cancer-derived cell lines and with in vitro transformed cells indicate that miR-206-mediated cyclin D1 repression is directly coupled to growth inhibition. Altogether, our data highlight a novel activity for miR-206 in skeletal muscle differentiation and identify cyclin D1 as a major target that further strengthens the tumor suppressor function proposed for miR-206.

Notch inhibitors for cancer treatment

Notch signaling is an evolutionarily conserved cell signaling pathway involved in cell fate during development, stem cell renewal and differentiation in postnatal tissues. Roles for Notch in carcinogenesis, in the biology of cancer stem cells and tumor angiogenesis have been reported. These features identify Notch as a potential therapeutic target in oncology. Based on the molecular structure of Notch receptor, Notch ligands and Notch activators, a set of Notch pathway inhibitors have been developed. Most of these inhibitors had shown anti-tumor effects in preclinical studies. At the same time, the combinatorial effect of these inhibitors with current chemotherapeutical drugs is still under study in different clinical trials. In this review, we describe the basics of Notch signaling and the role of Notch in normal and cancer stem cells as a logic way to develop different Notch inhibitors and their current stage of progress for cancer patient's treatment.

Failure to downregulate the BAF53a subunit of the SWI/SNF chromatin remodeling complex contributes to the differentiation block in rhabdomyosarcoma

Rhabdomyosarcoma (RMS), the most common soft tissue sarcoma in children and young adults, is characterized by a partially differentiated myogenic phenotype. We have previously shown that the blocking of tumor growth and resumption of differentiation can be achieved by re-expression of miR-206, a muscle-enriched microRNA missing in RMS. In this work, we focused on BAF53a, one of the genes downregulated in miR-206-expressing RMS cells, which codes for a subunit of the SWI/SNF chromatin remodeling complex. Here we show that the BAF53a transcript is significantly higher in primary RMS tumors than in normal muscle, and is a direct target of miR-206. Sustained expression of BAF53a interferes with differentiation in myogenic cells, whereas its silencing in RMS cells increases expression of myogenic markers and inhibits proliferation and anchorage-independent growth. Accordingly, BAF53a silencing also impairs embryonal RMS and alveolar RMS tumor growth, inducing their morphological and biochemical differentiation. These results indicate that failure to downregulate the BAF53a subunit may contribute to the pathogenesis of RMS, and suggest that BAF53a may represent a novel therapeutic target for this tumor.

Involvement of α2-antiplasmin in dendritic growth of hippocampal neurons

The α2-Antiplasmin (α2AP) protein is known as a principal physiological inhibitor of plasmin, but we previously demonstrated that it acts as a regulatory factor for cellular functions independent of plasmin. α2AP is highly expressed in the hippocampus, suggesting a potential role for α2AP in hippocampal neuronal functions. However, the role for α2AP was unclear. This study is the first to investigate the involvement of α2AP in the dendritic growth of hippocampal neurons. The expression of microtubule-associated protein 2, which contributes to neurite initiation and neuronal growth, was lower in the neurons from α2AP⁻/⁻ mice than in the neurons from α2AP⁺/⁺ mice. Exogenous treatment with α2AP enhanced the microtubule-associated protein 2 expression, dendritic growth and filopodia formation in the neurons. This study also elucidated the mechanism underlying the α2AP-induced dendritic growth. Aprotinin, another plasmin inhibitor, had little effect on the dendritic growth of neurons, and α2AP induced its expression in the neurons from plaminogen⁻/⁻ mice. The activation of p38 MAPK was involved in the α2AP-induced dendritic growth. Therefore, our findings suggest that α2AP induces dendritic growth in hippocampal neurons through p38 MAPK activation, independent of plasmin, providing new insights into the role of α2AP in the CNS.

Proof-of-concept rare cancers in drug development: the case for rhabdomyosarcoma

Rare diseases typically affect fewer than 200,000 patients annually, yet because thousands of rare diseases exist, the cumulative impact is millions of patients worldwide. Every form of childhood cancer qualifies as a rare disease-including the childhood muscle cancer, rhabdomyosarcoma (RMS). The next few years promise to be an exceptionally good era of opportunity for public-private collaboration for rare and childhood cancers. Not only do certain governmental regulation advantages exist, but these advantages are being made permanent with special incentives for pediatric orphan drug-product development. Coupled with a growing understanding of sarcoma tumor biology, synergy with pharmaceutical muscle disease drug-development programs, and emerging publically available preclinical and clinical tools, the outlook for academic-community-industry partnerships in RMS drug development looks promising.

Notch signaling in pediatric soft tissue sarcomas

Pediatric soft tissue sarcomas are rare tumors of childhood, frequently characterized by specific chromosome translocations. Despite improvements in treatment, their clinical management is often challenging due to the low responsiveness of metastatic forms and aggressive variants to conventional therapeutic approaches, which leads to poor overall survival. It is widely thought that soft tissue sarcomas derive from mesenchymal progenitor cells that, during embryonic life, have developed chromosomal aberrations with de-regulation of the main pathways governing tissue morphogenesis. The Notch signaling pathway is one of the most important molecular networks involved in differentiation processes. Emerging evidence highlights the role of Notch signaling de-regulation in the biology of these pediatric sarcomas. In this review, we present an outline of recently gathered evidence on the role of Notch signaling in soft tissue sarcomas, highlighting its importance in tumor cell biology. The potential challenges and opportunities of targeting Notch signaling in the treatment of pediatric soft tissue sarcomas are also discussed.

Notch3 and Mef2c proteins are mutually antagonistic via Mkp1 protein and miR-1/206 microRNAs in differentiating myoblasts

BACKGROUND

Notch3 is expressed in myogenic precursors, but its function is not well known.

RESULTS

Notch3 represses the activity of Mef2c and is in turn inhibited by the microRNAs-1 and -206.

CONCLUSION

Notch3 serves as a regulator for preventing premature myogenic differentiation.

SIGNIFICANCE

Understanding how precocious differentiation is prevented is critical for designing therapy for skeletal muscle regeneration. The Notch signaling pathway is a well known regulator of skeletal muscle stem cells known as satellite cells. Loss of Notch1 signaling leads to spontaneous myogenic differentiation. Notch1, normally expressed in satellite cells, is targeted for proteasomal degradation by Numb during differentiation. A homolog of Notch1, Notch3, is also expressed in these cells but is not inhibited by Numb. We find that Notch3 is paradoxically up-regulated during the early stages of differentiation by an enhancer that requires both MyoD and activated Notch1. Notch3 itself strongly inhibits the myogenic transcription factor Mef2c, most likely by increasing the p38 phosphatase Mkp1, which inhibits the Mef2c activator p38 MAP kinase. Active Notch3 decreases differentiation. Mef2c, however, induces microRNAs miR-1 and miR-206, which directly down-regulate Notch3 and allow differentiation to proceed. Thus, the myogenic differentiation-induced microRNAs miR-1 and -206 are important for differentiation at least partly because they turn off Notch3. We suggest that the transient expression of Notch3 early in differentiation generates a temporal lag between myoblast activation by MyoD and terminal differentiation into myotubes directed by Mef2c.

New therapeutic targets in soft tissue sarcoma

Soft tissue sarcomas are an uncommon and diverse group of more than 50 mesenchymal malignancies. The pathogenesis of many of these is poorly understood, but others have begun to reveal the secrets of their underlying mechanisms. With considerable effort over recent years, soft tissue sarcomas have increasingly been classified on the basis of underlying molecular alterations. In turn, this has allowed the development and application of targeted agents in several specific, molecularly defined, sarcoma subtypes. This review will focus on the rationale for targeted therapy in sarcoma, with emphasis on the relevance of specific molecular factors and pathways in both translocation-associated sarcomas and in genetically complex tumors. In addition, we will address some of the early successes in sarcoma-targeted therapy as well as a few challenges and disappointments in this field. Finally, we will discuss several possible opportunities represented by poorly understood, but potentially promising new therapeutic targets, as well as several novel biological agents currently in preclinical and early phase I/II trials. This will provide the reader with the context for understanding the current state of this field and a sense of where it may be headed in the coming years.