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Identification of C/EBPβ Target Genes in ALK+ Anaplastic Large Cell Lymphoma (ALCL) by Gene Expression Profiling and Chromatin Immunoprecipitation

ABSTRACT: C/EBPβ (CCAAT enhancer binding protein) is a transcription factor that plays a crucial role in survival and transformation of ALK+ anaplastic large cell lymphoma (ALCL). The aim of this study was to identify the downstream targets of C/EBPβ responsible for ALK-mediated oncogenesis. C/EBPβ was knocked down in ALK+ ALCL cell lines with a C/EBPβ-shRNA, followed by gene expression profiling (GEP). GEP analysis revealed a reproducible signature of genes that were significantly regulated by C/EBPβ. Classification into biological categories revealed overrepresentation of genes involved in the immune response, apoptosis and cell proliferation. Transcriptional regulation by C/EBPβ was found in 6 of 11 (BCL2A1, G0S2, TRIB1, S100A9, DDX21 and DDIT4) genes investigated by chromatin immunoprecipitation. We demonstrated that BCL2A1, G0S2 and DDX21 play a crucial role in survival and proliferation of ALK+ ALCL cells. DDX21, a gene involved in rRNA biogenesis, was found differentially overexpressed in primary ALK+ ALCL cases. All three candidate genes were validated in primary ALCL cases by either immunohistochemistry or RT-qPCR. In conclusion, we identified and validated several key C/EBPβ-regulated genes with major impact on survival and cell growth in ALK+ ALCL, supporting the central role of C/EBPβ in ALK-mediated oncogenesis.

ORGANISM(S): Homo sapiens

PROVIDER: GSE23368 | GEO | 2013/07/10

SECONDARY ACCESSION(S): PRJNA133305

REPOSITORIES: GEO

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Project description:Anaplastic Large Cell Lymphomas (ALCL) represent a subset of lymphomas in which the Anaplastic Lymphoma Kinase (ALK) gene is frequently fused to the NPM gene. We previously demonstrated that the constitutive phosphorylation of ALK chimeric proteins is sufficient to induce cellular transformation in vitro and in vivo, and that ALK activity is strictly required for the survival of ALK positive ALCL cells. To elucidate the signaling pathways required for ALK-mediated transformation and tumor maintenance, we analyzed the transcriptomes of multiple ALK positive ALCL cell lines abrogating their ALK-mediated signaling by inducible ALK RNA interference (RNAi) or with potent and cell permeable ALK inhibitors. Transcripts derived from the gene expression profiling (GEP) analysis uncovered a reproducible signature, which included a novel group of ALK-regulated genes. Functional RNAi screening on a set of these ALK transcriptional targets revealed that the transcription factor C/EBPb and the anti-apoptotic protein BCL2A1 are absolutely necessary to induce cell transformation and/or to sustain the growth and survival of ALK positive ALCL cells. Thus, we proved that an experimentally controlled and functionally validated GEP analysis represents a powerful tool to identify novel pathogenetic networks and validate biologically suitable target genes for therapeutic interventions. Experiment Overall Design: This series of microarray experiments contains the gene expression profiles of Anaplastic Large Cell Lymphoma (ALCL) cell lines (TS [a subclone of Sup-M2] and Su-DHL1) engineered to express ALK-A5 shRNA under a doxycycline-inducible promoter or treated with cell permeable pyrrolocarbazole-derived ALK inhibitors. A mutated ALK-A5M shRNA was used as control. Briefly, cells were transduced with pLV-DsRed-tTRKRAB, expanded, and used for transduction with pLVTH-GFP-shRNA lentiviral particles. Cells were induced with doxycycline (1 microg/ml) for 12 hours, double GFP+ DsRed+ cells selected by fluorescence-activated cell sorting. Cells expressing GFP in the absence of the inducer were removed by a second flow cytometry sorting, and expanded. shRNA expression was induced by doxycycline treatment for 72 or 84 hours. Drug treatments (300 nM), were performed in TS cells with ALK inhibitors (A2 or A3), mock compound (A1), or control diluent for 6 hours. 5 micrograms of total RNA was processed and hybridized to the Affymetrix HG-U133A chip following the manufacturer's instructions.

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Identification of C/EBPβ Target Genes in ALK+ Anaplastic Large Cell Lymphoma (ALCL) by Gene Expression Profiling and Chromatin Immunoprecipitation

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