COL11A2 collagen gene transcription is differentially regulated by EWS/ERG sarcoma fusion protein and wild-type ERG

A specific t(21;22) chromosomal translocation creates the chimeric EWS/ERG gene in some cases of Ewing's sarcoma. In the resultant EWS/ERG fusion protein, the N-terminal part of the ETS family protein ERG is replaced by the N terminus of the RNA-binding protein EWS. We found that both the EWS/ERG and COL11A2 genes are expressed in the Ewing's sarcoma cell line, CADO-ES1. To investigate a potential role for EWS/ERG in COL11A2 gene expression, we characterized the COL11A2 promoter and tested the ability of wild-type ERG and EWS/ERG sarcoma fusion protein to transactivate COL11A2 promoter using a luciferase assay. We found that expression of EWS/ERG, but not wild-type ERG, transactivated the COL11A2 promoter and that this transactivation required not only the N-terminal region of EWS but also an intact DNA-binding domain from ERG. Electrophoretic mobility shift assay using COL11A2 promoter sequence showed involvement of EWS/ERG in the formation of DNA-protein complexes, and chromatin immunoprecipitation assay revealed direct interaction between COL11A2 promoter and EWS/ERG fusion protein in vivo. EWS/ERG, but not wild-type ERG, bound to RNA polymerase II. Treatment of cells with the histone deacetylase inhibitor trichostatin A enabled ERG to transactivate the COL11A2 promoter, therefore abolishing the differential effects of EWS/ERG and ERG. Taken together, these findings indicate that the COL11A2 gene is regulated both by potential ERG association with a histone deacetylase complex and by direct EWS/ERG recruitment of RNA polymerase II.     

Establishment and proteomic characterization of patient-derived clear cell sarcoma xenografts and cell lines

Clear cell sarcoma (CCS) is an aggressive mesenchymal malignancy characterized by the unique chimeric EWS-ATF1 fusion gene. Patient-derived cancer models are essential tools for the understanding of tumorigenesis and the development of anti-cancer drugs; however, only a limited number of CCS cell lines exist. The objective of this study was to establish patient-derived CCS models. We established patient-derived CCS models from a 43-yr-old female patient. We prepared the patient-derived xenografts (PDXs) from tumor tissues obtained through biopsy or surgery and isolated stable cell lines from PDXs and the original tumor tissue. The presence of gene fusions was examined by RT-PCR, and Sanger sequencing. The established cell lines were characterized by short tandem repeat, viability, colony and spheroid formation, and invasion analyses. Differences in gene enrichment between the primary tumor and cell lines were examined by mass spectrometry and KEGG pathway analysis. The cell lines were maintained for more than 80 passages, and had tumorigenic characteristics such as colony and spheroid formation and invasion. Mass spectrometric proteome analysis demonstrated that the cell lines were enriched for similar but distinct molecular pathways, compared to those in the xenografts and original tumor tissue. Next, tyrosine kinase inhibitors were screened for their suppressive effects on viability. We found that ponatinib, vandetanib, and doxorubicin suppressed the growth of cell lines, and had equivalent IC₅₀ values. Further in-depth investigation and understanding of drug-sensitivity mechanisms will be important for the clinical applications of our cell lines.     

Serum- and glucocorticoid-regulated kinase 1 (SGK1) induction by the EWS/NOR1(NR4A3) fusion protein

The NR4A3 nuclear receptor (also known as NOR1) is involved in tumorigenesis by the t(9;22) chromosome translocation encoding the EWS/NOR1 fusion protein found in approximately 75% of all cases of extraskeletal myxoid chondrosarcomas (EMC). Several observations suggest that one role of EWS/NOR1 in tumorigenesis may be to deregulate the expression of specific target genes. We have shown previously that constitutive expression of EWS/NOR1 in CFK2 fetal rat chondrogenic cells induces their transformation as measured by growth beyond confluency and growth in soft agar. To identify genes regulated by the fusion protein in this model, we have generated a CFK2 cell line in which the expression of EWS/NOR1 is controlled by tetracycline. Using the differential display technique, we have identified the serum- and glucocorticoid-regulated kinase 1 (SGK1) mRNA as being up-regulated in the presence of EWS/NOR1. Co-immunocytochemistry confirmed over-expression of the SGK1 protein in cells expressing EWS/NOR1. Significantly, immunohistochemistry of 10 EMC tumors positive for EWS/NOR1 showed that all of them over-express the SGK1 protein in contrast to non-neoplastic cells in the same biopsies and various other sarcoma types. These results strongly suggest that SGK1 may be a genuine in vivo target of EWS/NOR1 in EMC.     

Autophagy-deficient tumor cells rely on extracellular amino acids to survive upon glutamine deprivation

Macroautophagy/autophagy is a unique protein degradation process by which intracellular materials are recycled for energy homeostasis. However, the metabolic status and energy source of autophagy-defective tumor cells is poorly understood. Here in this study, we found ATF4-dependent amino acid transporter (AAT) gene expression and amino acid uptake were increased in autophagy-deficient cells under conditions of Gln deprivation. Notably, inhibition of amino acid uptake reduced the viability of Gln-deprived autophagy-deficient cells, but not significantly in wild-type cells, suggesting the reliance of autophagy-deficient tumor cells on extracellular amino acid uptake.     

Clinical and Biochemical Function of Polymorphic NR0B1 GGAA-Microsatellites in Ewing Sarcoma: A Report from the Children's Oncology Group

Background

The genetics involved in Ewing sarcoma susceptibility and prognosis are poorly understood. EWS/FLI and related EWS/ETS chimeras upregulate numerous gene targets via promoter-based GGAA-microsatellite response elements. These microsatellites are highly polymorphic in humans, and preliminary evidence suggests EWS/FLI-mediated gene expression is highly dependent on the number of GGAA motifs within the microsatellite.

Objectives

Here we sought to examine the polymorphic spectrum of a GGAA-microsatellite within the NR0B1 promoter (a critical EWS/FLI target) in primary Ewing sarcoma tumors, and characterize how this polymorphism influences gene expression and clinical outcomes.

Results

A complex, bimodal pattern of EWS/FLI-mediated gene expression was observed across a wide range of GGAA motifs, with maximal expression observed in constructs containing 20–26 GGAA motifs. Relative to white European and African controls, the NR0B1 GGAA-microsatellite in tumor cells demonstrated a strong bias for haplotypes containing 21–25 GGAA motifs suggesting a relationship between microsatellite function and disease susceptibility. This selection bias was not a product of microsatellite instability in tumor samples, nor was there a correlation between NR0B1 GGAA-microsatellite polymorphisms and survival outcomes.

Conclusions

These data suggest that GGAA-microsatellite polymorphisms observed in human populations modulate EWS/FLI-mediated gene expression and may influence disease susceptibility in Ewing sarcoma.     

Exposure on cell surface and extensive arginine methylation of ewing sarcoma (EWS) protein

In contrast to the knowledge regarding the function of chimeric Ewing sarcoma (EWS) fusion proteins that arise from chromosomal translocation, the cellular function of the RNA binding EWS protein is poorly characterized. EWS protein had been found mainly in the nucleus. In this report we show that EWS protein is not only found in the nucleus and cytosol but also on cell surfaces. After cell-surface biotinylation, isoelectric focusing of membrane fraction, avidin-agarose extraction of biotinylated proteins, and SDS-polyacrylamide gel electrophoresis, EWS protein was identified by matrix-assisted laser desorption ionization and nanoelectrospray tandem mass spectrometry of in-gel-digested peptides. These analyses revealed that the protein, having repeated RGG motifs, is extensively asymmetrically dimethylated on arginine residues, the sites of which have been mapped by mass spectrometric methods. Out of a total of 30 Arg-Gly sequences, 29 arginines were found to be at least partially methylated. The Arg-Gly-Gly sequence was present in 21 of the 29 methylation sites, and in contrast to other methylated proteins, only 11 (38%) methylated arginine residues were found in the Gly-Arg-Gly sequence. The presence of Gly on the C-terminal side of the arginine residue seems to be a prerequisite for recognition by a protein-arginine N-methyltransferase (PRMT) catalyzing this asymmetric dimethylation reaction. One monomethylarginine and no symmetrically methylated arginine residue was found. The present findings imply that RNA-binding EWS protein shuttles from the nucleus to the cell surface in a methylated form, the role of which is discussed.