Concise review: mesenchymal tumors: when stem cells go mad

A current perspective on the role for molecular studies in soft tissue tumor pathology

Soft tissue sarcomas represent an heterogenous group of malignancies. They represent a diagnostic challenge, and their accurate classification impact over treatment options. Sarcomas, similarly to hematologic neoplasm, often harbor relatively specific genetic aberrations, the recognition of which can be used to improved diagnostic accuracy. This review will focus on the clinical relevance of molecular analysis in soft tissue sarcomas, trying to elucidate its role as a diagnostic tool as well as a potential prognostic/predictive marker.

Twist1 is essential in maintaining mesenchymal state and tumor-initiating properties in synovial sarcoma

Synovial sarcoma is an aggressive mesenchymal tumor with dual differentiation; epithelial and mesenchymal differentiation. However, the molecular mechanisms behind tumorigenesis and dual differentiation have remained elusive. In this study, we investigated whether Twist1 is an essential transcription factor for maintaining tumor-initiating cell properties in synovial sarcoma. First, we identified that Twist1 is overexpressed in most cases of synovial sarcoma (SS) samples as well as in two synovial sarcoma cell lines (HSSYII, SW982). Additionally, Twist1 depletion led to down-regulation of mesenchymal markers and up-regulation of epithelial markers in SS cell lines. The migratory and invasive abilities of SS cell lines were also significantly reduced following the loss of Twist1. These results indicate that Twist1 plays an essential role in the maintenance of mesenchymal character in SS. Furthermore, knock-down of Twist1 induced G1 cycle arrest and apoptosis as well as remarkable reduction in the sphere-forming cell subpopulation and side population cells. Moreover, Twist1 knock-down profoundly inhibited the growth of synovial sarcoma xenograft in nude mice compared to controls indicating that Twist1 is essential for tumor initiating cell properties. To explore transcriptional regulation by Twist1 at the genomic level, Chromatin immunoprecipiation-solexa whole genome sequencing (ChIP-SEQ) and cDNA microarray analysis were performed. Mesenchymal differentiation/proliferation and PDGF related genes were found to be affected by Twist1. Finally, depletion of SS18-SSX fusion oncoprotein by RNA inference induced down-regulation of Twist1, implying that Twist1 is regulated by SS18-SSX. Hence, our results suggest that Twist1 is an essential transcription factor for the maintenance of mesenchymal characters and tumor initiating properties of synovial sarcoma.

Autologous hematopoietic stem cell transplantation following high dose chemotherapy for non-rhabdomyosarcoma soft tissue sarcomas

BACKGROUND

Soft tissue sarcomas (STS) are a highly heterogeneous group of rare malignant solid tumors. Non-rhabdomyosarcoma soft tissue sarcomas (NRSTS) comprise all STS except rhabdomyosarcoma. In patients with advanced local or metastatic disease, autologous hematopoietic stem cell transplantation (HSCT) applied after high-dose chemotherapy (HDCT) is a planned rescue therapy for HDCT-related severe hematologic toxicity. The rationale for this update is to determine whether any randomized controlled trials (RCTs) have been conducted and to clarify whether HDCT followed by autologous HSCT has a survival advantage.

OBJECTIVES

To assess the effectiveness and safety of HDCT followed by autologous HSCT for all stages of non-rhabdomyosarcoma soft tissue sarcomas (NRSTS) in children and adults.

SEARCH METHODS

For this update we modified the search strategy to improve the precision and reduce the number of irrelevant hits. All studies included in the original review were considered for re-evaluation in the update. We searched the electronic databases CENTRAL (2012, Issue 11) in The Cochrane Library , MEDLINE and EMBASE (05 December 2012) from their inception using the newly developed search strategy. Online trials registers and reference lists of systematic reviews were searched.

SELECTION CRITERIA

Terms representing STS and autologous HSCT were required in the title or abstract. In studies with aggregated data, participants with NRSTS and autologous HSCT had to constitute at least 80% of the data. Single-arm studies were included in addition to studies with a control arm because the number of comparative studies was expected to be very low.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted study data. Some studies identified in the original review were re-examined and found not to meet the inclusion criteria and were excluded in this update. For studies with no comparator group, we synthesized the results for studies reporting aggregate data and conducted a pooled analysis of individual participant data using the Kaplan-Meyer method. The primary outcomes were overall survival (OS) and treatment-related mortality (TRM).

MAIN RESULTS

The selection process was carried out from the start of the search dates for the update. We included 57 studies, from 260 full text articles screened, reporting on 275 participants that were allocated to HDCT followed by autologous HSCT. All studies were not comparable due to various subtypes. We identified a single comparative study, an RCT comparing HDCT followed by autologous HSCT versus standard chemotherapy (SDCT). The overall survival (OS) at three years was 32.7% versus 49.4% with a hazard ratio (HR) of 1.26 (95% confidence interval (CI) 0.70 to 2.29, P value 0.44) and thus not significantly different between the treatment groups. In a subgroup of patients that had a complete response before treatment, OS was higher in both treatment groups and OS at three years was 42.8% versus 83.9% with a HR of 2.92 (95% CI 1.1 to 7.6, P value 0.028) and thus was statistically significantly better in the SDCT group. We did not identify any other comparative studies. We included six single-arm studies reporting aggregate data of cases; three reported the OS at two years as 20%, 48%, and 51.4%. One other study reported the OS at three years as 40% and one further study reported a median OS of 13 months (range 3 to 19 months). In two of the single-arm studies with aggregate data, subgroup analysis showed a better OS in patients with versus without a complete response before treatment. In a survival analysis of pooled individual data of 80 participants, OS at two years was estimated as 50.6% (95% CI 38.7 to 62.5) and at three years as 36.7% (95% CI 24.4 to 49.0). Data on TRM, secondary neoplasia and severe toxicity grade 3 to 4 after transplantation were sparse. The one included RCT had a low risk of bias and the remaining 56 studies had a high risk of bias.

AUTHORS' CONCLUSIONS

A single RCT with a low risk of bias shows that OS after HDCT followed by autologous HSCT is not statistically significantly different from standard-dose chemotherapy. Therefore, HDCT followed by autologous HSCT for patients with NRSTS may not improve the survival of patients and should only be used within controlled trials if ever considered.

Mesenchymal stem cell transformation and sarcoma genesis

MSCs are hypothesized to potentially give rise to sarcomas after transformation and therefore serve as a good model to study sarcomagenesis. Both spontaneous and induced transformation of MSCs have been reported, however, spontaneous transformation has only been convincingly shown in mouse MSCs while induced transformation has been demonstrated in both mouse and human MSCs. Transformed MSCs of both species can give rise to pleomorphic sarcomas after transplantation into mice, indicating the potential MSC origin of so-called non-translocation induced sarcomas. Comparison of expression profiles and differentiation capacities between MSCs and sarcoma cells further supports this. Deregulation of P53- Retinoblastoma-, PI3K-AKT-and MAPK pathways has been implicated in transformation of MSCs. MSCs have also been indicated as cell of origin in several types of chromosomal translocation associated sarcomas. In mouse models the generated sarcoma type depends on amongst others the tissue origin of the MSCs, the targeted pathways and genes and the differentiation commitment status of MSCs. While some insights are glowing, it is clear that more studies are needed to thoroughly understand the molecular mechanism of sarcomagenesis from MSCs and mechanisms determining the sarcoma type, which will potentially give directions for targeted therapies.

Genome-wide analyses on high-grade osteosarcoma: making sense of a genomically most unstable tumor

High-grade osteosarcoma is an extremely genomically unstable tumor. This, together with other challenges, such as the heterogeneity within and between tumor samples, and the rarity of the disease, renders it difficult to study this tumor on a genome-wide level. Now that most laboratories change from genome-wide microarray experiments to Next-Generation Sequencing it is important to discuss the lessons we have learned from microarray studies. In this review, we discuss the challenges of high-grade osteosarcoma data analysis. We give an overview of microarray studies that have been conducted so far on both osteosarcoma tissue samples and cell lines. We discuss recent findings from integration of different data types, which is particularly relevant in a tumor with such a complex genomic profile. Finally, we elaborate on the translation of results obtained with bioinformatics into functional studies, which has lead to valuable findings, especially when keeping in mind that no new therapies with a significant impact on survival have been developed in the past decades.

Peripheral blood mononuclear CD133 mRNA levels correlates with response to treatment in patients with gastrointestinal stromal tumors

BACKGROUND

CD133 is a marker that identifies/enriches cancer stem cell implicated in tumor initiation. We hypothesize that changes in the CD133 mRNA expression levels and vascular endothelial growth factor (VEGF) may correlate tumor response in GIST.

METHODOLOGY/PRINCIPAL FINDINGS

After informed consent, we obtained peripheral blood samples from 24 evaluable patients with gastrointestinal stromal tumors (GIST). There were 7 -paired samples before and after treatment, We measured CD133 mRNA levels by real time RT-PCR method and vascular endothelial growth factor (VEGF) levels by ELISA. All measurements were done in duplicates in two separate experiments. The treatment resulted in significant reduction of CD133 mRNA expression (p = 0.048) as well as the level of VEGF (p = 0.003). The mean CD133 mRNA levels for GIST patients was 615. We found no correlation between the CD133 mRNA levels and VEGF levels. (p = 0.826). Logistic regression analysis suggested a relationship between elevated CD133 mRNA levels and fitted probability of eventual progressive disease (PD) and mixed response at 37% for CD133 mRNA of 2.25, and the probability of eventual PD/MR is 84% for a CD133 of 2072 (p = 0.08).

CONCLUSIONS/SIGNIFICANCE

CD133 mRNA expression levels in GIST patients measured by real time RT-PCR assay appeared to correlate with tumor response to surgery or imatinib and may be used to predict tumor progression. Additional prospective studies are warranted.

Modulation of the osteosarcoma expression phenotype by microRNAs

Background

Osteosarcomas are the most common primary malignant tumors of bone and show multiple and complex genomic aberrations. miRNAs are non-coding RNAs capable of regulating gene expression at the post transcriptional level, and miRNAs and their target genes may represent novel therapeutic targets or biomarkers for osteosarcoma. In order to investigate the involvement of miRNAs in osteosarcoma development, global microarray analyses of a panel of 19 human osteosarcoma cell lines was performed.

Principal findings

We identified 177 miRNAs that were differentially expressed in osteosarcoma cell lines relative to normal bone. Among these, miR-126/miR-126*, miR-142-3p, miR-150, miR-223, miR-486-5p and members of the miR-1/miR-133a, miR-144/miR-451, miR-195/miR-497 and miR-206/miR-133b clusters were found to be downregulated in osteosarcoma cell lines. All miRNAs in the paralogous clusters miR-17-92, miR-106b-25 and miR-106a-92 were overexpressed. Furthermore, the upregulated miRNAs included miR-9/miR-9*, miR-21*, miR-31/miR-31*, miR-196a/miR-196b, miR-374a and members of the miR-29 and miR-130/301 families. The most interesting inversely correlated miRNA/mRNA pairs in osteosarcoma cell lines included miR-9/TGFBR2 and miR-29/p85α regulatory subunit of PI3K. PTEN mRNA correlated inversely with miR-92a and members of the miR-17 and miR-130/301 families. Expression profiles of selected miRNAs were confirmed in clinical samples. A set of miRNAs, miR-1, miR-18a, miR-18b, miR-19b, miR-31, miR-126, miR-142-3p, miR-133b, miR-144, miR-195, miR-223, miR-451 and miR-497 was identified with an intermediate expression level in osteosarcoma clinical samples compared to osteoblasts and bone, which may reflect the differentiation level of osteosarcoma relative to the undifferentiated osteoblast and fully differentiated normal bone. Significance: This study provides an integrated analysis of miRNA and mRNA in osteosarcoma, and gives new insight into the complex genetic mechanisms of osteosarcoma development and progression.

β-Catenin Does Not Confer Tumorigenicity When Introduced into Partially Transformed Human Mesenchymal Stem Cells

Although osteosarcoma is the most common primary malignant bone tumor in children and adolescents, its cell of origin and the genetic alterations are unclear. Previous studies have shown that serially introducing hTERT, SV40 large TAg, and H-Ras transforms human mesenchymal stem cells into two distinct sarcomas cell populations, but they do not form osteoid. In this study, β-catenin was introduced into mesenchymal stem cells already containing hTERT and SV40 large TAg to analyze if this resulted in a model which more closely recapitulated osteosarcoma. Results. Regardless of the level of induced β-catenin expression in the stable transfectants, there were no marked differences induced in their phenotype or invasion and migration capacity. Perhaps more importantly, none of them formed tumors when injected into immunocompromised mice. Moreover, the resulting transformed cells could be induced to osteogenic and chondrogenic differentiation but not to adipogenic differentiation. Conclusions. β-catenin, although fostering osteogenic differentiation, does not induce the malignant features and tumorigenicity conveyed by oncogenic H-RAS when introduced into partly transformed mesenchymal stem cells. This may have implications for the role of β-catenin in osteosarcoma pathogenesis. It also may suggest that adipogenesis is an earlier branch point than osteogenesis and chondrogenesis in normal mesenchymal differentiation.

EGFR inhibition abrogates leiomyosarcoma cell chemoresistance through inactivation of survival pathways and impairment of CSC potential

Background

Tumor cells with stem-like phenotype and properties, known as cancer stem cells (CSC), have been identified in most solid tumors and are presumed to be responsible for driving tumor initiation, chemoresistance, relapse, or metastasis. A subpopulation of cells with increased stem-like potential has also been identified within sarcomas. These cells are endowed with increased tumorigenic potential, chemoresistance, expression of embryonic markers, and side population(SP) phenotype. Leiomyosarcomas (LMS) are soft tissue sarcomas presumably arising from undifferentiated cells of mesenchymal origin, the Mesenchymal Stem Cells (MSC). Frequent recurrence of LMS and chemoresistance of relapsed patients may likely result from the failure to target CSC. Therefore, therapeutic cues coming from the cancer stem cell (CSC) field may drastically improve patient outcome.

Methodology/Principal Findings

We expanded LMS stem-like cells from patient samples in vitro and examined the possibility to counteract LMS malignancy through a stem-like cell effective approach. LMS stem-like cells were in vitro expanded both as “tumor spheres” and as “monolayers” in Mesenchymal Stem Cell (MSC) conditions. LMS stem-like cells displayed MSC phenotype, higher SP fraction, and increased drug-extrusion, extended proliferation potential, self-renewal, and multiple differentiation ability. They were chemoresistant, highly tumorigenic, and faithfully reproduced the patient tumor in mice. Such cells displayed activation of EGFR/AKT/MAPK pathways, suggesting a possibility in overcoming their chemoresistance through EGFR blockade. IRESSA plus Vincristine treatment determined pathway inactivation, impairment of SP phenotype, high cytotoxicity in vitro and strong antitumor activity in stem-like cell-generated patient-like xenografts, targeting both stem-like and differentiated cells.

Conclusions/Significance

EGFR blockade combined with vincristine determines stem-like cell effective antitumor activity in vitro and in vivo against LMS, thus providing a potential therapy for LMS patients.

Immune microenvironment in tumor progression: characteristics and challenges for therapy

The tumor microenvironment plays a critical role in cancer development, progression, and control. The molecular and cellular nature of the tumor immune microenvironment influences disease outcome by altering the balance of suppressive versus cytotoxic responses in the vicinity of the tumor. Recent developments in systems biology have improved our understanding of the complex interactions between tumors and their immunological microenvironment in various human cancers. Effective tumor surveillance by the host immune system protects against disease, but chronic inflammation and tumor “immunoediting” have also been implicated in disease development and progression. Accordingly, reactivation and maintenance of appropriate antitumor responses within the tumor microenvironment correlate with a good prognosis in cancer patients. Improved understanding of the factors that shape the tumor microenvironment will be critical for the development of effective future strategies for disease management. The manipulation of these microenvironmental factors is already emerging as a promising tool for novel cancer treatments. In this paper, we summarize the various roles of the tumor microenvironment in cancer, focusing on immunological mediators of tumor progression and control, as well as the significant challenges for future therapies.

The activities of Smad and Gli mediated signalling pathways in high-grade conventional osteosarcoma

High-grade conventional osteosarcoma is a malignant tumour predominantly affecting adolescents and, despite multimodal intensive therapy, lethal for one third of the patients. Although there is currently detailed knowledge of normal skeletal development, this has not been integrated into research on the genesis of osteosarcoma. Recently we showed that the canonical Wnt pathway is not active in osteosarcoma and that its reactivation is disadvantageous to osteosarcoma cells. Since Wnt is regulating normal skeletogenesis together with other pathways, here we report on the activities of the bone morphogenic protein (BMP), the transforming growth factor beta (TGFβ) and the hedgehog (Hh) pathways in osteosarcoma. Human osteosarcoma samples (n=210), benign bone tumours of osteoblastic lineage called osteoblastoma (n=25) and osteosarcoma cell lines (n=19) were examined. For pathway activity luciferase transcriptional reporter assays and gene and protein expression analyses were performed. Immunohistochemical analysis of phosphorylated Smad1 and Smad2, the intracellular effectors of BMP and TGFβ, respectively, showed nuclear expression of both proteins in 70% of the osteosarcoma samples at levels comparable to osteoblastoma. Interestingly cases with lower expression showed significantly worse disease free survival. This may imply that drugs restoring impaired signalling pathways in osteosarcoma might change the tumour's aggressive clinical course, however targeted pathway modulation in vitro did not affect cell proliferation.

Primary cardiac sarcomas may develop from resident or bone marrow-derived mesenchymal stem cells: use of immunohistochemistry including CD44 and octamer binding protein 3/4

AIMS

To provide evidence that cardiac sarcomas 'not otherwise specified' express markers that might indicate their cellular origin or identify any lines of differentiation.

METHODS AND RESULTS

We reviewed all 11 cases of primary undifferentiated cardiac sarcomas found in the archives of the Royal Marsden and Royal Brompton Hospitals, London, UK during the period 2000-2009. Five cases with appropriate consent and archived material were investigated using immunohistochemistry. We found that the spindle, pleomorphic or occasionally epithelioid cell sarcomas showed no lineage-specific differentiation other than partial myofibroblastic or 'myoid' differentiation (all cases). All tumours showed some degree of cytoplasmic positivity for the mesenchymal stem cell marker CD44. In contrast, no nuclear octamer binding protein 3/4 (Oct3/4) expression was seen in any of the tumours, although very patchy cytoplasmic positivity was seen in some tumours.

CONCLUSIONS

The cytoplasmic positivity for CD44 and the absence of nuclear Oct3/4 suggest that the cells of these sarcomas may represent 'daughter' stem cells that no longer have the capacity for tumour initiation, but have subsequently developed new lines of partial differentiation. Primary cardiac sarcomas may arise from mesenchymal stem cells with the ability to generate tumours with multilineage differentiation.

An osteosarcoma zebrafish model implicates Mmp-19 and Ets-1 as well as reduced host immune response in angiogenesis and migration

About 40% of osteosarcoma patients die of metastases. Novel strategies to improve treatment of metastatic patients require a better understanding of the processes involved, like angiogenesis, migration, and the immune response. However, the rarity of osteosarcoma and its heterogeneity make this neoplasm difficult to study. Recently we reported malignant transformation of mouse mesenchymal stem cells (MSCs) which formed osteosarcoma upon transplantation into mice. Here we studied these cells in zebrafish embryos and found that transformed MSCs induced angiogenesis and migrated through the bodies of the embryos, but this was never observed with non-transformed normal MSCs (progenitors of the transformed MSCs). Whole genome expression analysis of both the cells and the host showed that angiogenesis and migration-related genes matrix metalloproteinase 19 (Mmp-19) and erythroblastosis virus E26 oncogene homologue 1 (Ets-1) were overexpressed in transformed MSCs compared to normal MSCs. Investigating the host response, embryos injected with transformed MSCs showed decreased expression of immune response-related genes, especially major histocompatibility complex class 1 (mhc1ze), as compared to embryos injected with normal MSCs. These findings contribute to the identification of genetic events involved in angiogenesis, migration, and host response providing targets as well as an appropriate model for high-throughput drug screens.

The MET oncogene transforms human primary bone-derived cells into osteosarcomas by targeting committed osteo-progenitors

The MET oncogene is aberrantly overexpressed in human osteosarcomas. We have previously converted primary cultures of human bone-derived cells into osteosarcoma cells by overexpressing MET. To determine whether MET transforms mesenchymal stem cells or committed progenitor cells, here we characterize distinct MET overexpressing osteosarcoma (MET-OS) clones using genome-wide expression profiling, cytometric analysis, and functional assays. All the MET-OS clones consistently display mesenchymal and stemness markers, but not most of the mesenchymal–stem cell-specific markers. Conversely, the MET-OS clones express genes characteristic of early osteoblastic differentiation phases, but not those of late phases. Profiling of mesenchymal stem cells induced to differentiate along osteoblast, adipocyte, and chondrocyte lineages confirms that MET-OS cells are similar to cells at an initial phase of osteoblastic differentiation. Accordingly, MET-OS cells cannot differentiate into adipocytes or chondrocytes, but can partially differentiate into osteogenic-matrix-producing cells. Moreover, in vitro MET-OS cells form self-renewing spheres enriched in cells that can initiate tumors in vivo. MET kinase inhibition abrogates the self-renewal capacity of MET-OS cells and allows them to progress toward osteoblastic differentiation. These data show that MET initiates the transformation of a cell population that has features of osteo-progenitors and suggest that MET regulates self-renewal and lineage differentiation of osteosarcoma cells.

Human fallopian tube mesenchymal stromal cells enhance bone regeneration in a xenotransplanted model

We have recently reported that human fallopian tubes, which are discarded during surgical procedures of women submitted to sterilization or hysterectomies, are a rich source of human fallopian tube mesenchymal stromal cells (htMSCs). It has been previously shown that human mesenchymal stromal cells may be useful in enhancing the speed of bone regeneration. This prompted us to investigate whether htMSCs might be useful for the treatment of osteoporosis or other bone diseases, since they present a pronounced capacity for osteogenic differentiation in vitro. Based on this prior knowledge, our aim was to evaluate, in vivo, the osteogenic capacity of htMSCs to regenerate bone through an already described xenotransplantation model: nonimmunosuppressed (NIS) rats with cranial defects. htMSCs were obtained from five 30-50 years old healthy women and characterized by flow cytometry and for their multipotenciality in vitro capacity (osteogenic, chondrogenic and adipogenic differentiations). Two symmetric full-thickness cranial defects on each parietal region of seven NIS rats were performed. The left side (LS) of six animals was covered with CellCeram (Scaffdex)-a bioabsorbable ceramic composite scaffold that contains 60% hydroxyapatite and 40% β-tricalciumphosphate-only, and the right side (RS) with the CellCeram and htMSCs (10(6) cells/scaffold). The animals were euthanized at 30, 60 and 90 days postoperatively and cranial tissue samples were taken for histological analysis. After 90 days we observed neobone formation in both sides. However, in animals euthanized 30 and 60 days after the procedure, a mature bone was observed only on the side with htMSCs. PCR and immunofluorescence analysis confirmed the presence of human DNA and thus that human cells were not rejected, which further supports the imunomodulatory property of htMSCs. In conclusion, htMSCs can be used successfully to enhance bone regeneration in vivo, opening a new field for future treatments of osteoporosis and bone reconstruction.

Sarcomas as a mise en abyme of mesenchymal stem cells: exploiting interrelationships for cell mediated anticancer therapy

Mise en abyme meaning "placed into abyss or infinite recurrence" is an apt paradigm for the relentless growth of sarcoma cells. Its alternative meaning, "self-reflexive embedding" fits the central role attributed to cancer stem cells (CSCs). Diversely sourced and defined, mesenchymal stem cells (MSCs) may be the cells of sarcoma origin, evolve a CSC phenotype and/or contribute to tumor growth through inherent qualities for homing, neovascularization, paracrine cross-feeding, microvesicle secretion, cell fusion, entosis and immune modulation. Exploiting these qualities, MSC expressing modified forms of the TNF-related apoptosis-inducing ligand (Apo2L/TRAIL) are being developed to complement more conventional radiation and chemotherapy.

Myxoid liposarcoma-associated EWSR1-DDIT3 selectively represses osteoblastic and chondrocytic transcription in multipotent mesenchymal cells

Background

Liposarcomas are the most common class of soft tissue sarcomas, and myxoid liposarcoma is the second most common liposarcoma. EWSR1-DDIT3 is a chimeric fusion protein generated by the myxoid liposarcoma-specific chromosomal translocation t(12;22)(q13;q12). Current studies indicate that multipotent mesenchymal cells are the origin of sarcomas. The mechanism whereby EWSR1-DDIT3 contributes to the phenotypic selection of target cells during oncogenic transformation remains to be elucidated.

Methodology/Principal Findings

Reporter assays showed that the EWSR1-DDIT3 myxoid liposarcoma fusion protein, but not its wild-type counterparts EWSR1 and DDIT3, selectively repressed the transcriptional activity of cell lineage-specific marker genes in multipotent mesenchymal C3H10T1/2 cells. Specifically, the osteoblastic marker Opn promoter and chondrocytic marker Col11a2 promoter were repressed, while the adipocytic marker Ppar-γ2 promoter was not affected. Mutation analyses, transient ChIP assays, and treatment of cells with trichostatin A (a potent inhibitor of histone deacetylases) or 5-Aza-2′-deoxycytidine (a methylation-resistant cytosine homolog) revealed the possible molecular mechanisms underlying the above-mentioned selective transcriptional repression. The first is a genetic action of the EWSR1-DDIT3 fusion protein, which results in binding to the functional C/EBP site within Opn and Col11a2 promoters through interaction of its DNA-binding domain and subsequent interference with endogenous C/EBPβ function. Another possible mechanism is an epigenetic action of EWSR1-DDIT3, which enhances histone deacetylation, DNA methylation, and histone H3K9 trimethylation at the transcriptional repression site. We hypothesize that EWSR1-DDIT3-mediated transcriptional regulation may modulate the target cell lineage through target gene-specific genetic and epigenetic conversions.

Conclusions/Significance

This study elucidates the molecular mechanisms underlying EWSR1-DDIT3 fusion protein-mediated phenotypic selection of putative target multipotent mesenchymal cells during myxoid liposarcoma development. A better understanding of this process is fundamental to the elucidation of possible direct lineage reprogramming in oncogenic sarcoma transformation mediated by fusion proteins.

Epigenetic and epigenomic mechanisms shape sarcoma and other mesenchymal tumor pathogenesis

Sarcomas comprise a large number of rare, histogenetically heterogeneous, mesenchymal tumors. Cancers such as Ewing's sarcoma, liposarcoma, rhabdomyosarcoma and synovial sarcoma can be generated by the transduction of mesenchymal stem cell progenitors with sarcoma-pathognomonic oncogenic fusions, a neoplastic transformation process accompanied by profound locus-specific and pangenomic epigenetic alterations. The epigenetic activities of histone-modifying and chromatin-remodeling enzymes such as SUV39H1/KMT1A, EZH2/KMT6A and BMI1 are central to epigenetic-regulated transformation, a property we coin oncoepigenic. Sarcoma-specific oncoepigenic aberrations modulate critical signaling pathways that control cell growth and differentiation including several miRNAs, Wnt, PI3K/AKT, Sav-RASSF1-Hpo and regulators of the G1 and G2/M checkpoints of the cell cycle. Herein an overview of the current knowledge of this rapidly evolving field that will undoubtedly uncover additional oncoepigenic mechanisms and yield druggable targets in the near future is discussed.

Role of mesenchymal stem cell therapy in Crohn's disease

Many trials of mesenchymal stem cells (MSCs) have been published in the past 5-6 y. MSCs inhibit T-cell alloreactivity in vitro by soluble factors and direct cell-to-cell contact. They are safe to infuse in humans with no acute toxicity and no ectopic tissue formation. Promising results of MSC infusion for graft-vs.-host disease and fistulizing Crohn's disease (CD) have been published. Treatment of CD requires a comprehensive treatment approach to maintain symptomatic control, improve health-related quality-of-life measures, and minimize complications from the disease. In this review, we will discuss the results of clinical trials using a novel treatment in the form of MSCs for treatment of CD and related complications. Success of these phase I, II, and III trials have set the stage for usage of this novel treatment for children with CD.

Identification of osteosarcoma driver genes by integrative analysis of copy number and gene expression data

High-grade osteosarcoma is a tumor with a complex genomic profile, occurring primarily in adolescents with a second peak at middle age. The extensive genomic alterations obscure the identification of genes driving tumorigenesis during osteosarcoma development. To identify such driver genes, we integrated DNA copy number profiles (Affymetrix SNP 6.0) of 32 diagnostic biopsies with 84 expression profiles (Illumina Human-6 v2.0) of high-grade osteosarcoma as compared with its putative progenitor cells, i.e., mesenchymal stem cells (n = 12) or osteoblasts (n = 3). In addition, we performed paired analyses between copy number and expression profiles of a subset of 29 patients for which both DNA and mRNA profiles were available. Integrative analyses were performed in Nexus Copy Number software and statistical language R. Paired analyses were performed on all probes detecting significantly differentially expressed genes in corresponding LIMMA analyses. For both nonpaired and paired analyses, copy number aberration frequency was set to >35%. Nonpaired and paired integrative analyses resulted in 45 and 101 genes, respectively, which were present in both analyses using different control sets. Paired analyses detected >90% of all genes found with the corresponding nonpaired analyses. Remarkably, approximately twice as many genes as found in the corresponding nonpaired analyses were detected. Affected genes were intersected with differentially expressed genes in osteosarcoma cell lines, resulting in 31 new osteosarcoma driver genes. Cell division related genes, such as MCM4 and LATS2, were overrepresented and genomic instability was predictive for metastasis-free survival, suggesting that deregulation of the cell cycle is a driver of osteosarcomagenesis.

Osteosarcoma models: from cell lines to zebrafish

High-grade osteosarcoma is an aggressive tumor most commonly affecting adolescents. The early age of onset might suggest genetic predisposition; however, the vast majority of the tumors are sporadic. Early onset, most often lack of a predisposing condition or lesion, only infrequent (<2%) prevalence of inheritance, extensive genomic instability, and a wide histological heterogeneity are just few factors to mention that make osteosarcoma difficult to study. Therefore, it is sensible to design and use models representative of the human disease. Here we summarize multiple osteosarcoma models established in vitro and in vivo, comment on their utilities, and highlight newest achievements, such as the use of zebrafish embryos. We conclude that to gain a better understanding of osteosarcoma, simplification of this extremely complex tumor is needed. Therefore, we parse the osteosarcoma problem into parts and propose adequate models to study them each separately. A better understanding of osteosarcoma provides opportunities for discovering and assaying novel effective treatment strategies.

“Sometimes the model is more interesting than the original disease”

PJ Hoedemaeker (1937–2007).

Putative multifunctional signature of lung metastases in dedifferentiated chondrosarcoma

Chondrosarcomas are among the most malignant skeletal tumors. Dedifferentiated chondrosarcoma is a highly aggressive subtype of chondrosarcoma, with lung metastases developing within a few months of diagnosis in 90% of patients. In this paper we performed comparative analyses of the transcriptomes of five individual metastatic lung lesions that were surgically resected from a patient with dedifferentiated chondrosarcoma. We document for the first time a high heterogeneity of gene expression profiles among the individual lung metastases. Moreover, we reveal a signature of “multifunctional” genes that are expressed in all metastatic lung lesions. Also, for the first time, we document the occurrence of massive macrophage infiltration in dedifferentiated chondrosarcoma lung metastases.

Mesenchymal niches of bone marrow in cancer

Over the last decade, genetic and cell biology studies have indicated that tumour growth is not only determined by malignant cancer cells themselves, but also by the tumour microenvironment. Cells present in the tumour microenvironment include fibroblasts, vascular, smooth muscle, adipocytes, immune cells and mesenchymal stem cells (MSC). The nature of the relationship between MSC and tumour cells appears dual and whether MSC are pro- or anti-tumorigenic is a subject of controversial reports. This review is focused on the role of MSC and bone marrow (BM) niches in cancer.

Epiphyseal growth plate and secondary peripheral chondrosarcoma: the neighbours matter

Chondrocytes interact with their neighbours through their cartilaginous extracellular matrix (ECM). Chondrocyte-matrix interactions compensate the lack of cell-cell contact and are modulated by proteoglycans and other molecules. The epiphyseal growth plate is a highly organized tissue responsible for long bone elongation. The growth plate is regulated by gradients of morphogens that are established by proteoglycans. Morphogens diffuse across the ECM, creating short- and long-range signalling that lead to the formation of a polarized tissue. Mutations affecting genes that modulate cell-matrix interactions are linked to several human disorders. Homozygous mutations of EXT1/EXT2 result in reduced synthesis and shortened heparan sulphate chains on both cell surface and matrix proteoglycans. This disrupts the diffusion gradients of morphogens and signal transduction in the epiphyseal growth plate, contributing to loss of cell polarity and osteochondroma formation. Osteochondromas are cartilage-capped bony projections arising from the metaphyses of endochondral bones adjacent to the growth plate. The osteochondroma cap is formed by cells with homozygous mutation of EXT1/EXT2 and committed stem cells/wild-type chondrocytes. Osteochondroma serves as a niche (a permissive environment), which facilitates the committed stem cells/wild-type chondrocytes to acquire secondary genetic changes to form a secondary peripheral chondrosarcoma. In such a scenario, the micro-environment is the site of the initiating processes that ultimately lead to cancer.

Modeling sarcomagenesis using multipotent mesenchymal stem cells

Because of their unique properties, multipotent mesenchymal stem cells (MSCs) represent one of the most promising adult stem cells being used worldwide in a wide array of clinical applications. Overall, compelling evidence supports the long-term safety of ex vivo expanded human MSCs, which do not seem to transform spontaneously. However, experimental data reveal a link between MSCs and cancer, and MSCs have been reported to inhibit or promote tumor growth depending on yet undefined conditions. Interestingly, solid evidence based on transgenic mice and genetic intervention of MSCs has placed these cells as the most likely cell of origin for certain sarcomas. This research area is being increasingly explored to develop accurate MSC-based models of sarcomagenesis, which will be undoubtedly valuable in providing a better understanding about the etiology and pathogenesis of mesenchymal cancer, eventually leading to the development of more specific therapies directed against the sarcoma-initiating cell. Unfortunately, still little is known about the mechanisms underlying MSC transformation and further studies are required to develop bona fide sarcoma models based on human MSCs. Here, we comprehensively review the existing MSC-based models of sarcoma and discuss the most common mechanisms leading to tumoral transformation of MSCs and sarcomagenesis.

Turning round: multipotent stromal cells, a three-dimensional revolution?

Mesenchymal stromal cells (MSC) can be isolated from adult tissues and induced to differentiate into skeletal cells, such as osteoblasts, chondrocytes and adipocytes. Consequently, ex vivo MSC are valuable systems for studying the mechanisms that control tissue-context lineage commitment and may offer broad therapeutic applications in the orthopedic theater and beyond. To date, most of these studies have used MSC grown on two-dimensional (2-D) plastic surfaces. The use of three-dimensional (3-D) in vitro growth techniques for MSC may accelerate these areas of research by providing a more representative 'in vivo-like' environment, where cells interact with each other and their cellular products, rather than a plastic surface. We introduce some of the techniques used for 3-D in vitro cultures and how they relate to the MSC field. We will present evidence of how MSC grown as 3-D spheroids not only permits appropriate MSC-like behavior, but appears to promote their stem-cell attributes and therapeutic benefit in applications ranging from regenerative medicine to anti-inflammatory treatments and cancer therapy. 3-D culture techniques also allow de/reconstruction of the specialized in vivo niche of the tissue-resident stem cell where microenvironmental influences can be recognized.