EZH2 is essential for glioblastoma cancer stem cell maintenance.

Overexpression of the polycomb group protein enhancer of zeste homologue 2 (EZH2) occurs in diverse malignancies, including prostate cancer, breast cancer, and glioblastoma multiforme (GBM). Based on its ability to modulate transcription of key genes implicated in cell cycle control, DNA repair, and cell differentiation, EZH2 is believed to play a crucial role in tissue-specific stem cell maintenance and tumor development. Here, we show that targeted pharmacologic disruption of EZH2 by the S-adenosylhomocysteine hydrolase inhibitor 3-deazaneplanocin A (DZNep), or its specific downregulation by short hairpin RNA (shRNA), strongly impairs GBM cancer stem cell (CSC) self-renewal in vitro and tumor-initiating capacity in vivo. Using genome-wide expression analysis of DZNep-treated GBM CSCs, we found the expression of c-myc, recently reported to be essential for GBM CSCs, to be strongly repressed upon EZH2 depletion. Specific shRNA-mediated downregulation of EZH2 in combination with chromatin immunoprecipitation experiments revealed that c-myc is a direct target of EZH2 in GBM CSCs. Taken together, our observations provide evidence that direct transcriptional regulation of c-myc by EZH2 may constitute a novel mechanism underlying GBM CSC maintenance and suggest that EZH2 may be a valuable new therapeutic target for GBM management.

Weaver syndrome and EZH2 mutations: Clarifying the clinical phenotype.

Weaver syndrome, first described in 1974, is characterized by tall stature, a typical facial appearance, and variable intellectual disability. In 2011, mutations in the histone methyltransferase, EZH2, were shown to cause Weaver syndrome. To date, we have identified 48 individuals with EZH2 mutations. The mutations were primarily missense mutations occurring throughout the gene, with some clustering in the SET domain (12/48). Truncating mutations were uncommon (4/48) and only identified in the final exon, after the SET domain. Through analyses of clinical data and facial photographs of EZH2 mutation-positive individuals, we have shown that the facial features can be subtle and the clinical diagnosis of Weaver syndrome is thus challenging, especially in older individuals. However, tall stature is very common, reported in >90% of affected individuals. Intellectual disability is also common, present in ~80%, but is highly variable and frequently mild. Additional clinical features which may help in stratifying individuals to EZH2 mutation testing include camptodactyly, soft, doughy skin, umbilical hernia, and a low, hoarse cry. Considerable phenotypic overlap between Sotos and Weaver syndromes is also evident. The identification of an EZH2 mutation can therefore provide an objective means of confirming a subtle presentation of Weaver syndrome and/or distinguishing Weaver and Sotos syndromes. As mutation testing becomes increasingly accessible and larger numbers of EZH2 mutation-positive individuals are identified, knowledge of the clinical spectrum and prognostic implications of EZH2 mutations should improve.

Development of Ewing's sarcoma from primary bone marrow-derived mesenchymal stem cells

SUMMARY : Ewing's sarcoma is a member of Ewing's family tumors (ESPY) and the second most common solid bone and soft tissue malignancy of children and young adults. It is associated in 85% of cases with the t(11;22)(q24:q12) chromosomal translocation that generates fusion of the 5' segment of the EWSR1 gene with the 3' segment of the ETS family gene FLI-1. The EWSR1-FLI-1 fusion protein behaves as an aberrant transcriptional activator and is believed to contribute to ESFT development. However, EWSR1-FLI-1 induces growth arrest and apoptosis in normal fibroblasts, and primary cells that are pemissive for its putative oncogenic properties have not been discovered, hampering basic understanding of ESFT biology. Here, we show that EWSR1-FLI-1 alone can transform mouse primary bone marrow-derived mesenchymal progenitor cells and generate tumors that display hallmarks of Ewing's sarcoma, including a small round cell phenotype, expression of ESFT-associated markers, insulin like growth factor-I dependence, and induction or repression of numerous EWSR1-FLI-1 target genes. Consistent with this finding, we tested the possibility that human mesenchymal stem cells (hMSC) might also provide a permissive cellular environment for EWSR1-FLI-1, and could represent the first adequate primary human cellular background for the oncogenic properties of the fusion protein. Indeed, expression of EWSR1-FLI-1 in human mesenchymal stem cells (hMSC) was not only stably maintained without inhibiting proliferation, but induced a gene expression profile bearing striking similarity to that of ESFT, including genes that are among the highest ESFT discriminators. Expression of EWSR1-FLI-1 in hMSCs may recapitulate the initial steps of Ewing's sarcoma development, allowing identification of genes that play an important role early in its pathogenesis. Among relevant candidate transcripts induced by EWSR1-FL/-1 in hMSC we found the polycomb group gene EZH2 which we show to play a critical role in Ewing's sarcoma growth. These observations provide the first identification of candidate primary cells from which ESFTs originate and suggest that EWSR1-FLI-1 expression may constitute the initiating event in ESFT pathogenesis. Le sarcome d' Ewing est un membre de la famille des tumeurs Ewing (ESFT) et représente la deuxième tumeur maligne solide de l'os et des tissus mous chez les enfants et les jeunes adultes. Cette tumeur est associée dans 85% des cas avec la translocation chromosomique t(11;22)(g24:g12), qui génère la fusion entre le segment 5' du gène EWSR1 avec le segment 3' du gène FLI-1, appartenant à la famille des facteurs de transcription ETS. La protéine de fusion EWSR1-FLI-1 qui en dérive joue le rSle d'un facteur de transcription aberrant, et est supposée contribuer de manière décisive au processus de développement des ESFTs. Néanmoins, l'expression de EWSR1-FLI-1 dans des fibroblastes normaux induit un arrêt de croissance et leur apoptose, et les cellules primaires permissives pour les propriétés oncogéniques attribuées à la translocation n'ont pas encore été identifiées, empêchant la compréhension de la biologie de base du sarcome d'Ewing. Dans ce travail on montre que l'expression de EWSR1-FLI-1 uniquement est capable de transformer des cellules souches mésenchymateuses dérivées de la moelle osseuse de la souris, pour générer des tumeurs qui présentent les caractéristiques du sarcome d' Ewing humain, et notamment une morphologie de petites cellules bleues et rondes, l'expression de marqueurs associés aux ESFTs, une dépendance du facteur de croissance IGF-1, et l'induction ou la répression de nombreux gènes cibles connus de EWSR1-FLI-1. Sur la base de ces observations, on a testé la possibilité que les cellules souches mésenchymateuses humaines (hMSCs) puissent aussi fournir un environnement cellulaire permissif pour EWSR1-FLI-1 ; et représenter le premier background cellulaire humain adéquat pour la manifestation du pouvoir oncogénique de la protéine de fusion. En effet, l'expression de EWSR1-FLI-1 dans des cellules souches mésenchymateuses humaines s'est révélée non seulement maintenue, mais elle a induit un profil d'expression génétique étonnamment similaire à celui des ESFTs humains, incluant les gènes qui ont été rapportés comme étant les plus discriminatifs pour ces tumeurs. L'expression de EWSR1-FLI-1 dans les hMSCs pourrait récapituler les étapes initiales du développement du sarcome d' Ewing, et de ce fait consentir à identifier les gènes qui jouent un rôle crucial dans sa pathogenèse précoce. Parmi les transcrits relevant indults par EWSR1-FL/-9 dans les hMSCs nous avons découvert le gène du groupe des polycomb EZH2, que nous avons par la suite démontré jouer un rôle essentiel dans la croissance du sarcome de Ewing. Ces observations apportent pour la première fois l'identification d'une cellule primaire candidate pour représenter la cellule d'origine des ESFTs, et en même temps suggèrent que l'expression de EWSR1-FLI-1 peut constituer l'événement initial dans la pathogenèse du sarcome d' Ewing.

Gene expression profiling of isolated tumour cells from anaplastic large cell lymphomas: insights into its cellular origin, pathogenesis and relation to Hodgkin lymphoma.

Anaplastic large cell lymphoma (ALCL) is a main type of T-cell lymphomas and comprises three distinct entities: systemic anaplastic lymphoma kinase (ALK) positive, systemic ALK(-) and cutaneous ALK(-) ALCL (cALCL). Little is known about their pathogenesis and their cellular origin, and morphological and immunophenotypical overlap exists between ALK(-) ALCL and classical Hodgkin lymphoma (cHL). We conducted gene expression profiling of microdissected lymphoma cells of five ALK(+) and four ALK(-) systemic ALCL, seven cALCL and sixteen cHL, and of eight subsets of normal T and NK cells. The analysis supports a derivation of ALCL from activated T cells, but the lymphoma cells acquired a gene expression pattern hampering an assignment to a CD4(+), CD8(+) or CD30(+) T-cell origin. Indeed, ALCL display a down-modulation of many T-cell characteristic molecules. All ALCL types show significant expression of NFkappaB target genes and upregulation of genes involved in oncogenesis (e.g. EZH2). Surprisingly, few genes are differentially expressed between systemic and cALCL despite their different clinical behaviour, and between ALK(-) ALCL and cHL despite their different cellular origin. ALK(+) ALCL are characterized by expression of genes regulated by pathways constitutively activated by ALK. This study provides multiple novel insights into the molecular biology and pathogenesis of ALCL.