Identification of target genes for wild type and truncated HMGA2 in mesenchymal stem-like cells

Enhancing anti-cancer capacity: Novel class I/II HDAC inhibitors modulate EMT, cell cycle, and apoptosis pathways

Cancer has been a leading cause of death over the last few decades in western countries as well as in Taiwan. However, traditional therapies are limited by the adverse effects of chemotherapy and radiotherapy, and tumor recurrence may occur. Therefore, it is critical to develop novel therapeutic drugs. In the field of HDAC inhibitor development, apart from the hydroxamic acid moiety, 2-aminobenzamide also functions as a zinc-binding domain, which is shown in well-known HDAC inhibitors such as Entinostat and Chidamide. With recent successful experiences in synthesizing 1-(phenylsulfonyl)indole-based compounds, in this study, we further combined two features of the above chemical compounds and generated indolyl benzamides. Compounds were screened in different cancer cell lines, and enzyme activity was examined to demonstrate their potential for anti-HDAC activity. Various biological functional assays evidenced that two of these compounds could suppress cancer growth and migration capacity, through regulating epithelial-mesenchymal transition (EMT), cell cycle, and apoptosis mechanisms. Data from 3D cancer cells and the in vivo zebrafish model suggested the potential of these compounds in cancer therapy in the future.

Novel roles for HMGA2 isoforms in regulating oxidative stress and sensitizing to RSL3-Induced ferroptosis in prostate cancer cells

Oxidative stress is increased in several cancers including prostate cancer, and is currently being exploited in cancer therapy to induce ferroptosis, a novel nonapoptotic form of cell death. High mobility group A2 (HMGA2), a non-histone protein up-regulated in several cancers, can be truncated due to chromosomal rearrangement or alternative splicing of HMGA2 gene. The purpose of this study is to investigate the role of wild-type vs. truncated HMGA2 in prostate cancer (PCa). We analyzed the expression of wild-type vs. truncated HMGA2 and showed that prostate cancer patient tissue and some cell lines expressed increasing amounts of both wild-type and truncated HMGA2 with increasing tumor grade, compared to normal epithelial cells. RNA-Seq analysis of LNCaP prostate cancer cells stably overexpressing wild-type HMGA2 (HMGA2-WT), truncated HMGA2 (HMGA2-TR) or empty vector (Neo) control revealed that HMGA2-TR cells exhibited higher oxidative stress compared to HMGA2-WT or Neo control cells, which was also confirmed by analysis of basal reactive oxygen species (ROS) levels using 2', 7'-dichlorofluorescin diacetate (DCFDA) dye, the ratio of reduced glutathione/oxidized glutathione (GSH/GSSG) and NADP/NADPH using metabolomics. This was associated with increased sensitivity to RAS-selective lethal 3 (RSL3)-induced ferroptosis that could be antagonized by ferrostatin-1. Additionally, proteomic and immunoprecipitation analyses showed that cytoplasmic HMGA2 protein interacted with Ras GTPase-activating protein-binding protein 1 (G3BP1), a cytoplasmic stress granule protein that responds to oxidative stress, and that G3BP1 transient knockdown increased sensitivity to ferroptosis even further. Endogenous knockdown of HMGA2 or G3BP1 in PC3 cells reduced proliferation which was reversed by ferrostatin-1. In conclusion, we show a novel role for HMGA2 in oxidative stress, particularly the truncated HMGA2, which may be a therapeutic target for ferroptosis-mediated prostate cancer therapy.

HMGA2 drives the IGFBP1/AKT pathway to counteract the increase in P27KIP1 protein levels in mtDNA/RNA-less cancer cells

Recent comprehensive analyses of mtDNA and orthogonal RNA-sequencing data revealed that in numerous human cancers, mtDNA copy numbers and mtRNA amounts are significantly reduced, followed by low respiratory gene expression. Under such conditions (called mt-Low), cells encounter severe cell proliferation defects; therefore, they must acquire countermeasures against this fatal disadvantage during malignant transformation. This study elucidated a countermeasure against the mt-Low condition-induced antiproliferative effects in hepatocellular carcinoma (HCC) cells. The mechanism relied on the architectural transcriptional regulator HMGA2, which was preferably expressed in HCC cells of the mt-Low type in vitro and in vivo. Detailed in vitro analyses suggest that HMGA2 regulates insulin-like growth factor binding protein 1 (IGFBP1) expression, leading to AKT activation, which then phosphorylates the cyclin-dependent kinase inhibitor (CKI), P27KIP1, and facilitates its ubiquitin-mediated degradation. Accordingly, intervention in the HMGA2 function by RNAi resulted in an increase in P27KIP1 levels and an induction of senescence-like cell proliferation inhibition in mt-Low-type HCC cells. Conclusively, the HMGA2/IGFBP1/AKT axis has emerged as a countermeasure against P27KIP1 CKI upregulation under mt-Low conditions, thereby circumventing cell proliferation inhibition and supporting the tumorigenic state. Notably, similar to in vitro cell lines, HMGA2 was likely to regulate IGFBP1 expression in HCC in vivo, thereby contributing to poor patient prognosis. Considering the significant number of cases under mt-Low or the threat of CKI upregulation cancer-wide, the axis is noteworthy as a vulnerability of cancer cells or target for tumor-agnostic therapy inducing irreversible cell proliferation inhibition via CKI upregulation in a large population with cancer.

Mechanisms of cancer stem cells drug resistance and the pivotal role of HMGA2

Nowadays, the focus of researchers is on perceiving the heterogeneity observed in a tumor. The researchers studied the role of a specific subset of cancer cells with high resistance to traditional treatments, recurrence, and unregulated metastasis. This small population of tumor cells that have stem-cell-like specifications was named Cancer Stem Cells (CSCs). The unique features that distinguish this type of cancer cell are self-renewing, generating clones of the tumor, plasticity, recurrence, and resistance to therapies. There are various mechanisms that contribute to the drug resistance of CSCs, such as CSCs markers, Epithelial mesenchymal transition, hypoxia, other cells, inflammation, and signaling pathways. Recent investigations have revealed the primary role of HMGA2 in the development and invasion of cancer cells. Importantly, HMGA2 also plays a key role in resistance to treatment through their function in the drug resistance mechanisms of CSCs and challenge it. Therefore, a deep understanding of this issue can provide a clearer perspective for researchers in the face of this problem.

Susceptibility to disease (tropical theileriosis) is associated with differential expression of host genes that possess motifs recognised by a pathogen DNA binding protein

Background

Knowledge of factors that influence the outcome of infection are crucial for determining the risk of severe disease and requires the characterisation of pathogen-host interactions that have evolved to confer variable susceptibility to infection. Cattle infected by Theileria annulata show a wide range in disease severity. Native (Bos indicus) Sahiwal cattle are tolerant to infection, whereas exotic (Bos taurus) Holstein cattle are susceptible to acute disease.

Methodology/Principal findings

We used RNA-seq to assess whether Theileria infected cell lines from Sahiwal cattle display a different transcriptome profile compared to Holstein and screened for altered expression of parasite factors that could generate differences in host cell gene expression.

Significant differences (<0.1 FDR) in the expression level of a large number (2211) of bovine genes were identified, with enrichment of genes associated with Type I IFN, cholesterol biosynthesis, oncogenesis and parasite infection. A screen for parasite factors found limited evidence for differential expression. However, the number and location of DNA motifs bound by the TashAT2 factor (TA20095) were found to differ between the genomes of B. indicus vs. B. taurus, and divergent motif patterns were identified in infection-associated genes differentially expressed between Sahiwal and Holstein infected cells.

Conclusions/Significance

We conclude that divergent pathogen-host molecular interactions that influence chromatin architecture of the infected cell are a major determinant in the generation of gene expression differences linked to disease susceptibility.

Methylation-dependent SUMOylation of the architectural transcription factor HMGA2

High mobility group A2 (HMGA2) is a chromatin-associated protein involved in the regulation of stem cell function, embryogenesis and cancer development. Although the protein does not contain a consensus SUMOylation site, it is shown to be SUMOylated. In this study, we demonstrate that the first lysine residue in the reported K₆₆KAE SUMOylation motif in HMGA2 can be methylated in vitro and in vivo by the Set7/9 methyltransferase. By editing the lysine, the increased hydrophobicity of the resulting 6-N-methyl-lysine transforms the sequence into a consensus SUMO motif. This post-translational editing dramatically increases the subsequent SUMOylation of this site. Furthermore, similar putative methylation-dependent SUMO motifs are found in a number of other chromatin factors, and we confirm methylation-dependent SUMOylation of a site in one such protein, the Polyhomeotic complex 1 homolog (PHC1). Together, these results suggest that crosstalk between methylation and SUMOylation is a general mode for regulation of chromatin function.

HMGA2 as a Critical Regulator in Cancer Development

The high mobility group protein 2 (HMGA2) regulates gene expression by binding to AT-rich regions of DNA. Akin to other DNA architectural proteins, HMGA2 is highly expressed in embryonic stem cells during embryogenesis, while its expression is more limited at later stages of development and in adulthood. Importantly, HMGA2 is re-expressed in nearly all human malignancies, where it promotes tumorigenesis by multiple mechanisms. HMGA2 increases cancer cell proliferation by promoting cell cycle entry and inhibition of apoptosis. In addition, HMGA2 influences different DNA repair mechanisms and promotes epithelial-to-mesenchymal transition by activating signaling via the MAPK/ERK, TGFβ/Smad, PI3K/AKT/mTOR, NFkB, and STAT3 pathways. Moreover, HMGA2 supports a cancer stem cell phenotype and renders cancer cells resistant to chemotherapeutic agents. In this review, we discuss these oncogenic roles of HMGA2 in different types of cancers and propose that HMGA2 may be used for cancer diagnostic, prognostic, and therapeutic purposes.

Unravelling the Role of miR-20b-5p, CCNB1, HMGA2 and E2F7 in Development and Progression of Non-Small Cell Lung Cancer (NSCLC)

Lung cancer is a prime cause of worldwide cancer deaths, with non-small cell lung cancer (NSCLC) as a frequent subtype. Surgical resection, chemotherapy are the currently used treatment methods. Delayed detection, poor prognosis, tumor heterogeneity, and chemoresistance make them relatively ineffective. Genomic medicine is a budding aspect of cancer therapeutics, where miRNAs are impressively involved. miRNAs are short ncRNAs that bind to 3′UTR of target mRNA, causing its degradation or translational repression to regulate gene expression. This study aims to identify important miRNA-mRNA-TF interactions in NSCLC using bioinformatics analysis. GEO datasets containing mRNA expression data of NSCLC were used to determine differentially expressed genes (DEGs), and identification of hub genes-BIRC5, CCNB1, KIF11, KIF20A, and KIF4A (all functionally enriched in cell cycle). The FFL network involved, comprised of miR-20b-5p, CCNB1, HMGA2, and E2F7. KM survival analysis determines that these components may be effective prognostic biomarkers and would be a new contemplation in NSCLC therapeutics as they target cell cycle and immunosurveillance mechanisms via HMGA2 and E2F7. They provide survival advantage and evasion of host immune response (via downregulation of cytokines-IL6, IL1R1 and upregulation of chemokines-CXCL13, CXCL14) to NSCLC. The study has provided innovative targets, but further validation is needed to confirm the proposed mechanism.

High Mobility Group AT-Hook 2 (HMGA2) Oncogenicity in Mesenchymal and Epithelial Neoplasia

High mobility group AT-hook 2 (HMGA2) has been associated with increased cell proliferation and cell cycle dysregulation, leading to the ontogeny of varied tumor types and their metastatic potentials, a frequently used index of disease prognosis. In this review, we deepen our understanding of HMGA2 pathogenicity by exploring the mechanisms by which HMGA2 misexpression and ectopic expression induces mesenchymal and epithelial tumorigenesis respectively and distinguish the pathogenesis of benign from malignant mesenchymal tumors. Importantly, we highlight the regulatory role of let-7 microRNA family of tumor suppressors in determining HMGA2 misexpression events leading to tumor pathogenesis and focused on possible mechanisms by which HMGA2 could propagate lymphangioleiomyomatosis (LAM), benign mesenchymal tumors of the lungs. Lastly, we discuss potential therapeutic strategies for epithelial and mesenchymal tumorigenesis based on targeting the HMGA2 signaling pathway.

12q14 microduplication: a new clinical entity reciprocal to the microdeletion syndrome?

Background

12q14 microdeletion syndrome is characterized by low birth weight and failure to thrive, proportionate short stature and developmental delay. The opposite syndrome (microduplication) has not yet been characterized. Our main objective is the recognition of a new clinical entity - 12q14 microduplication syndrome. - as well as confirming the role of HMGA2 gene in growth regulation.

Case presentation

Array Comparative Genomic Hybridization (CGH), Karyotype, Fluorescence in situ Hybridization, Quantitative-PCR analysis and Whole exome sequencing (WES) were performed in a girl presenting overgrowth and obesity. Array CGH identified a 1.5 Mb 12q14.3 microduplication involving HMGA2, GRIP1, IRAK3, MSRB3 and TMBIM4 genes. Karyotype and FISH showed that duplication was a de novo insertion of 12q14.3 region on chromosome 9p resulting in an interstitial microduplication. Q-PCR confirmed the duplication only in the proband. WES revealed no pathogenic variants.

Conclusions

Phenotypic comparison with patients with 12q14 microdeletion syndrome showed a reciprocal presentation, suggesting a phenotypically recognizable 12q14 microduplication syndrome as well as confirming the role of HMGA2 gene in growth regulation. It is also indicative that other genes, such as IRAK3 and MSRB3 might have of role in weight gain and obesity.

HIT000218960 promotes gastric cancer cell proliferation and migration through upregulation of HMGA2 expression

The aim of the present study was to elucidate whether the long non-coding RNA (lncRNA) HIT000218960 could accelerate the proliferative and migratory ability of gastric cancer (GC) cells by regulating high-mobility group AT-hook 2 (HMGA2) gene. The reverse transcription-quantitative polymerase chain reaction was used to determine HIT000218960 and HMGA2 expression levels in GC tissues and cells. The HMGA2 protein level was detected by western blotting. A χ² test was used to determine the association between the HIT000218960 expression level and the clinical characteristics of patients with GC. GC cells were transfected with small interfering (si)-negative control, si-HIT000218960 and si-HIT000218960+pcDNA-HMGA2, prior to assessing the cell proliferative and migratory ability using the Cell Counting Kit-8 and Transwell assays, respectively. HIT000218960 and HMGA2 were highly expressed in GC tissues compared with in healthy tissues. In addition, HIT000218960 and HMGA2 were positively correlated in GC tissues. The HIT000218960 expression level was associated with tumor size, Tumor-Node-Metastasis staging and lymph node metastasis in patients with GC. HIT000218960 silencing decreased the proliferative and migratory ability of HGC27 and NCI-N87 cells; however, HMGA2 overexpression partly reversed this inhibitory effect. The results of the present study indicated that HIT000218960 could promote HGC27 and NCI-N87 cell proliferation and migration, which may be mediated by HMGA2.

High mobility group A2 (HMGA2) promotes EMT via MAPK pathway in prostate cancer

Studies have shown that High mobility group A2 (HMGA2), a non-histone protein, can promote epithelial-mesenchymal transition (EMT), which plays a critical role in prostate cancer progression and metastasis. Interestingly, full-length or wild-type HMGA2 and truncated (lacking the 3'UTR) HMGA2 isoforms are overexpressed in several cancers. However, there are no studies investigating the expression and differential roles of WT vs truncated HMGA2 isoforms in prostate cancer. Immunohistochemical staining of prostate tissue microarray revealed low membrane expression in normal epithelial prostate cells, and that expression increased with tumor grade as well as a switch from predominantly cytoplasmic HMGA2 in lower tumor grades, to mostly nuclear in high grade and bone metastatic tissue. LNCaP cells stably overexpressing wild-type HMGA2 displayed nuclear localization of HMGA2 and induction of EMT associated with increased Snail, Twist and vimentin expression compared to LNCaP Neo control cells, as shown by immunofluorescence and western blot analyses. This was associated with increased cell migration on collagen shown using boyden chamber assay. Conversely, LNCaP cells overexpressing truncated HMGA2 showed cytoplasmic HMGA2 expression that did not induce EMT yet displayed increased cell proliferation and migration compared to LNCaP Neo. Both wild-type and truncated HMGA2 increased levels of phospho-ERK, and interestingly, treatment with U0126, MAPK inhibitor, antagonized wild-type HMGA2-mediated EMT and cell migration, but did not affect truncated HMGA2-mediated cell proliferation or migration. Therefore, although both wild-type and truncated HMGA2 may promote prostate tumor progression, wild-type HMGA2 acts by inducing EMT via MAPK pathway.

Genomic profiling of dedifferentiated liposarcoma compared to matched well-differentiated liposarcoma reveals higher genomic complexity and a common origin

Well-differentiated (WD) liposarcoma is a low-grade mesenchymal tumor with features of mature adipocytes and high propensity for local recurrence. Often, WD patients present with or later progress to a higher-grade nonlipogenic form known as dedifferentiated (DD) liposarcoma. These DD tumors behave more aggressively and can metastasize. Both WD and DD liposarcomas harbor neochromosomes formed from amplifications and rearrangements of Chr 12q that encode oncogenes (MDM2, CDK4, and YEATS2) and adipocytic differentiation factors (HMGA2 and CPM) However, genomic changes associated with progression from WD to DD have not been well-defined. Therefore, we selected patients with matched WD and DD tumors for extensive genomic profiling in order to understand their clonal relationships and to delineate any defining alterations for each entity. Exome and transcriptomic sequencing was performed for 17 patients with both WD and DD diagnoses. Somatic point and copy-number alterations were integrated with transcriptional analyses to determine subtype-associated genomic features and pathways. The results were, on average, that only 8.3% of somatic mutations in WD liposarcoma were shared with their cognate DD component. DD tumors had higher numbers of somatic copy-number losses, amplifications involving Chr 12q, and fusion transcripts than WD tumors. HMGA2 and CPM rearrangements occur more frequently in DD components. The shared somatic mutations indicate a clonal origin for matched WD and DD tumors and show early divergence with ongoing genomic instability due to continual generation and selection of neochromosomes. Stochastic generation and subsequent expression of fusion transcripts from the neochromosome that involve adipogenesis genes such as HMGA2 and CPM may influence the differentiation state of the subsequent tumor.

Binding of high mobility group A proteins to the mammalian genome occurs as a function of AT-content

Genomic location can inform on potential function and recruitment signals for chromatin-associated proteins. High mobility group (Hmg) proteins are of similar size as histones with Hmga1 and Hmga2 being particularly abundant in replicating normal tissues and in cancerous cells. While several roles for Hmga proteins have been proposed we lack a comprehensive description of their genomic location as a function of chromatin, DNA sequence and functional domains. Here we report such a characterization in mouse embryonic stem cells in which we introduce biotin-tagged constructs of wild-type and DNA-binding domain mutants. Comparative analysis of the genome-wide distribution of Hmga proteins reveals pervasive binding, a feature that critically depends on a functional DNA-binding domain and which is shared by both Hmga proteins. Assessment of the underlying queues instructive for this binding modality identifies AT richness, defined as high frequency of A or T bases, as the major criterion for local binding. Additionally, we show that other chromatin states such as those linked to cis-regulatory regions have little impact on Hmga binding both in stem and differentiated cells. As a consequence, Hmga proteins are preferentially found at AT-rich regions such as constitutively heterochromatic regions but are absent from enhancers and promoters arguing for a limited role in regulating individual genes. In line with this model, we show that genetic deletion of Hmga proteins in stem cells causes limited transcriptional effects and that binding is conserved in neuronal progenitors. Overall our comparative study describing the in vivo binding modality of Hmga1 and Hmga2 identifies the proteins’ preference for AT-rich DNA genome-wide and argues against a suggested function of Hmga at regulatory regions. Instead we discover pervasive binding with enrichment at regions of higher AT content irrespective of local variation in chromatin modifications.

We investigated the chromosomal location of a group of highly abundant nuclear proteins. Our genome-wide results for Hmga1 and Hmga2 reveal a unique binding modality indicating preference for DNA rich in A or T bases in vivo. Importantly this preferential binding to AT-rich sequences occurs throughout the genome irrespectively of other local chromatin features. Genomic location and loss of function experiments challenge the view that Hmga proteins act as local modulators of transcriptional regulation but rather argue for a role as structural components of chromatin.

Generation and characterisation of a canine EGFP-HMGA2 prostate cancer in vitro model

The architectural transcription factor HMGA2 is abundantly expressed during embryonic development. In several malignant neoplasias including prostate cancer, high re-expression of HMGA2 is correlated with malignancy and poor prognosis. The let-7 miRNA family is described to regulate HMGA2 negatively. The balance of let-7 and HMGA2 is discussed to play a major role in tumour aetiology. To further analyse the role of HMGA2 in prostate cancer a stable and highly reproducible in vitro model system is precondition. Herein we established a canine CT1258-EGFP-HMGA2 prostate cancer cell line stably overexpressing HMGA2 linked to EGFP and in addition the reference cell line CT1258-EGFP expressing solely EGFP to exclude EGFP-induced effects. Both recombinant cell lines were characterised by fluorescence microscopy, flow cytometry and immunocytochemistry. The proliferative effect of ectopically overexpressed HMGA2 was determined via BrdU assays. Comparative karyotyping of the derived and the initial CT1258 cell lines was performed to analyse chromosome consistency. The impact of the ectopic HMGA2 expression on its regulator let-7a was analysed by quantitative real-time PCR. Fluorescence microscopy and immunocytochemistry detected successful expression of the EGFP-HMGA2 fusion protein exclusively accumulating in the nucleus. Gene expression analyses confirmed HMGA2 overexpression in CT1258-EGFP-HMGA2 in comparison to CT1258-EGFP and native cells. Significantly higher let-7a expression levels were found in CT1258-EGFP-HMGA2 and CT1258-EGFP. The BrdU assays detected an increased proliferation of CT1258-HMGA2-EGFP cells compared to CT1258-EGFP and native CT1258. The cytogenetic analyses of CT1258-EGFP and CT1258-EGFP-HMGA2 resulted in a comparable hyperdiploid karyotype as described for native CT1258 cells. To further investigate the impact of recombinant overexpressed HMGA2 on CT1258 cells, other selected targets described to underlie HMGA2 regulation were screened in addition. The new fluorescent CT1258-EGFP-HMGA2 cell line is a stable tool enabling in vitro and in vivo analyses of the HMGA2-mediated effects on cells and the development and pathogenesis of prostate cancer.

HMGA2 and high-grade serous ovarian carcinoma

HMGA2, the High Mobility Group A2 gene, plays a very important role in fetal development and carcinogenesis. As an oncofetal gene, it is upregulated in tumors of both epithelial and mesenchymal tissue origin. Chromosomal translocations of HMGA2 are common in mesenchymal tumors, whereas the regulatory mechanisms of HMGA2 in malignant epithelial tumors are much more complex. As an architectural transcription factor, it is involved in multiple biological pathways by targeting different downstream genes in different cancers. HMGA2 is upregulated in both the early and late stages of high-grade serous ovarian carcinoma (HGSOC) and, according to The Cancer Genomic Atlas, is among a signature of genes overexpressed in ovarian cancer. Recent identification of miR-182 as a mediator of BRCA1 and HMGA2 deregulation in ovarian cancer cells may guide us toward a better understanding of the roles of HMGA2 in ovarian carcinogenesis. In this article, we will review recent developments and findings related to HMGA2, including its regulation, oncogenic properties, major functional pathways associated with the tumorigenesis of HGSOC, and its potential role as a biomarker for clinical application.

Rearrangement of HMGA2 in a case of infantile lipoblastoma without Plag1 alteration

Lipoblastoma is a rare benign adipocytic tumor that occurs usually in children. It can be difficult to distinguish a lipoblastoma from other lipogenic tumors. In such cases, the detection of a rearrangement of the PLAG1 gene by fluorescence in situ hybridization analysis is useful for characterizing a lipoblastoma. We present here a novel case of morphological infantile lipoblastoma showing a rearrangement of HMGA2 instead of the classical PLAG1 alteration. HMGA2 is the main target of clonal aberrations encountered in lipomas. This result supports the hypothesis that benign lipomatous tumors harboring PLAG1 or HMGA2 rearrangement could constitute a unique pathogenetic entity.

Adipocyte differentiation of human bone marrow-derived stromal cells is modulated by microRNA-155, microRNA-221, and microRNA-222

Human mesenchymal stromal cells (hMSCs) are capable of limited self-renewal and multilineage differentiation in vitro. Several studies have demonstrated that microRNAs (miRNAs, miRs), post-transcriptional modifiers of mRNA stability and protein translation, play crucial roles in the regulation of these complex processes. To gain knowledge regarding the role of miRNAs in human adipocyte differentiation, we examined the miRNA expression profile of the immortalized human bone marrow-derived stromal cell line hMSC-Tert20. Such a model system has the advantage of a reproducible and consistent phenotype while maintaining important properties of the primary donor cells, including the potential to differentiate to adipocytes, osteoblasts, and chondrocytes. We identified 12 miRNAs that were differentially expressed during adipogenesis, of which several have been previously shown to play important roles in adipocyte biology. Among these, the expression of miRNA-155, miRNA-221, and miRNA-222 decreased during the adipogenic program of both immortalized and primary hMSCs, suggesting that they act as negative regulators of differentiation. Interestingly, ectopic expression of the miRNAs significantly inhibited adipogenesis and repressed induction of the master regulators PPARγ and CCAAT/enhancer-binding protein alpha. Our study provides the first experimental evidence that miRNA-155, miRNA-221, and miRNA-222 have an important function in human adipocyte differentiation, and that their downregulation is necessary to relieve the repression of genes crucial for this process.

Let-7a is a direct EWS-FLI-1 target implicated in Ewing's sarcoma development

Ewing's sarcoma family tumors (ESFT) are the second most common bone malignancy in children and young adults, characterized by unique chromosomal translocations that in 85% of cases lead to expression of the EWS-FLI-1 fusion protein. EWS-FLI-1 functions as an aberrant transcription factor that can both induce and suppress members of its target gene repertoire. We have recently demonstrated that EWS-FLI-1 can alter microRNA (miRNA) expression and that miRNA145 is a direct EWS-FLI-1 target whose suppression is implicated in ESFT development. Here, we use miRNA arrays to compare the global miRNA expression profile of human mesenchymal stem cells (MSC) and ESFT cell lines, and show that ESFT display a distinct miRNA signature that includes induction of the oncogenic miRNA 17–92 cluster and repression of the tumor suppressor let-7 family. We demonstrate that direct repression of let-7a by EWS-FLI-1 participates in the tumorigenic potential of ESFT cells in vivo. The mechanism whereby let-7a expression regulates ESFT growth is shown to be mediated by its target gene HMGA2, as let-7a overexpression and HMGA2 repression both block ESFT cell tumorigenicity. Consistent with these observations, systemic delivery of synthetic let-7a into ESFT-bearing mice restored its expression in tumor cells, decreased HMGA2 expression levels and resulted in ESFT growth inhibition in vivo. Our observations provide evidence that deregulation of let-7a target gene expression participates in ESFT development and identify let-7a as promising new therapeutic target for one of the most aggressive pediatric malignancies.

Concise review: mesenchymal tumors: when stem cells go mad

Sarcomas are nonepithelial, nonhematopoietic malignant tumors that arise from the embryonic mesoderm. Despite their rarity, less than 10% of all cancers, sarcomas are accountable for relatively high morbidity and mortality especially in children and adolescents. Although there are some hereditary conditions predisposing sarcoma, such as the Li-Fraumeni and Retinoblastoma syndrome, the vast majority of these tumors are sporadic. Based on their histological morphology, sarcomas have been divided into a broad spectrum of subtypes recognized in the 2002 WHO classification of tumors. This wide lineage range suggests that sarcomas originate from either many committed different cell types or from a multipotent cell, subsequently driven into a certain lineage. Mesenchymal stem cells (MSCs) are able to differentiate into many cell types needed to create mature structures like vessels, muscle, and bone. These multipotent cells can be isolated from several adult human tissues and massively expanded in culture, making them both of use for research as well as potential beneficial therapeutical agents. For this reason MSCs are being extensively studied, however, concerns have raised about whether they are the putative originating cells of sarcoma and their questionable role in cancer progression. Recent accomplishments in the field have broadened our knowledge of MSCs in relation to sarcoma origin, sarcoma treatment and the safety of MSCs usage in therapeutic settings.

Identification of altered MicroRNA expression patterns in synovial sarcoma

MicroRNAs (miRNAs) are noncoding small RNAs that function as an endogenous regulator of gene expression. Their dysregulation has been implicated in the development of several cancers. However, the status of miRNA in soft tissue sarcomas has not yet been thoroughly investigated. This study examined the global miRNA expression in synovial sarcoma and compared the results to those in another translocation-associated sarcoma, the Ewing family of tumors, and in normal skeletal muscle. The 3D-Gene miRNA microarray platform (Toray, Kamakura, Japan) and unsupervised hierarchical clustering revealed a distinct expression pattern of miRNAs in synovial sarcoma from Ewing tumors and skeletal muscle. Thirty-five of the more than 700 miRNAs analyzed were differentially expressed in synovial sarcomas in comparison to other tissue types. There were 21 significantly up-regulated miRNAs, including some miRNAs, such as let-7e, miR-99b, and miR-125a-3p, clustered within the same chromosomal loci. Quantitative reverse transcription-polymerase chain reaction also demonstrated that these miRNAs were over-expressed in synovial sarcomas. The down-regulation of let-7e and miR-99b by anti-miR miRNA inhibitors resulted in the suppression of the proliferation of synovial sarcoma cells, and modulated the expression of their putative targets, HMGA2 and SMARCA5, suggesting that these molecules have a potential oncogenic role. The unique miRNA expression pattern including the over-expressed miRNA clusters in synovial sarcoma warrants further investigation to develop a better understanding of the oncogenic mechanisms and future therapeutic strategies for synovial sarcoma.