Unknown,Transcriptomics,Genomics,Proteomics

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MicroRNA profiling of murine lymphoma model harboring the MYC transgene in a Tet-off system reveals MYC stimulates EZH2 expression by repression of its negative regulator miR-26a

ABSTRACT: The MYC oncogene, which is commonly mutated/amplified in tumors, represents an important regulator of cell growth owing to its ability to induce both proliferation and apoptosis. Recent evidence links MYC to altered miRNA expression, thereby suggesting that MYC-regulated miRNAs might contribute to tumorigenesis. To further analyze the impact of MYC-regulated miRNAs we investigated a murine lymphoma model harboring the MYC transgene in a Tet-off system in order to control its expression. Microarray-based miRNA expression profiling revealed both known and novel MYC targets. Among the miRNAs repressed by MYC we identified the potential tumor suppressor miR-26a, which possessed the ability to attenuate proliferation in MYC-dependent cells. Interestingly, miR-26a was also found to be deregulated in primary human Burkitt lymphoma samples, thereby likely being of clinical relevance. While today only few miRNA targets have been identified in human disease, we could show that ectopic expression of miR-26a influenced cell cycle progression by targeting the bona fide oncogene EZH2, a Polycomb protein and global regulator of gene expression yet unknown to be regulated by miRNAs. Thus, in addition to directly targeting protein-coding genes, MYC modulates genes important to oncogenesis via deregulation of miRNAs, thereby vitally contributing to MYC-induced lymphomagenesis. Experiment Overall Design: Gene expression profiling (GEP) was performed in six cell line samples using Affymetrix microarray technology according to the manufacturerâs recommendations (Human Genome U133 Plus 2.0 Array, Affymetrix). Fluorescence ratios were normalized by applying the RMA algorithm using the BRB Array Tools software package. For subsequent analyses, we only included probe sets whose expression varied as previously determined.

ORGANISM(S): Homo sapiens

SUBMITTER: Lars Bullinger

PROVIDER: E-GEOD-12278 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Background: MYC is a transcription factor encoded by the c-MYC gene (thereafter termed MYC). MYC is key transcription factor involved in many central cellular processes including ribosomal biogenesis. MYC is overexpressed in the majority of human tumours including aggressive B-cell lymphoma especially Burkitt's lymphoma. Although Burkitt's lymphoma is a highlight example for MYC overexpression due to a chromosomal translocation, no global analysis of MYC binding sites by chromatin immunoprecipitation (ChIP) followed by global next generation sequencing (ChIP-Seq) has been conducted so far in Burkitt's lymphoma. Methodology/Principal Findings: ChIP-Seq was performed with a MYC-specific antibody giving rise to 7,054 predicted MYC binding sites after bioinformatics analysis of a total of 19 million sequence reads. In line with previous findings, binding sites accumulate in gene sets known to be involved in the ribosomal biogenesis, histone acetyltransferase and methyltransferase complexes and the cell cycle demonstrating a regulatory role of MYC in these processes. Unexpectedly, MYC binding sites also accumulate in genes typically expressed in mature B-cells. To assess the functional consequences of altered MYC binding, the ChIP-Seq data were supplemented with siRNA mediated knock-downs of MYC in BL cell lines followed by gene expression profiling. Interestingly, amongst others, genes involved in B-cell function were up-regulated in response to MYC silencing. Conclusion/Significance: The 7,054 MYC-binding sites identified by our ChIP-Seq approach greatly extend the knowledge regarding MYC binding in Burkitt's lymphoma and sheds further light on the enormous complexity of the MYC regulatory network. Especially our observation that (i) many B-cell relevant genes are targeted by MYC and (ii) that MYC down-regulation leads to an up-regulation of B-cell genes highlights an interesting aspect of BurkittM-BM-4s lymphoma biology. [ChIP-Seq] Analysis of MYC DNA binding sites by ChiP-Seq in 5 BurkittM-BM-4s lymphoma cell lines (Raji, Ramos, Blue1, BL41, CA46) [mRNA expression profiling] siRNA-mediated knock-down of MYC was done employing the BL cell lines Raji, BL41 and Blue1 in order to detect MYC-driven gene expression changes. For this purpose, the cells were Amaxa-transfected using MYC smart pool siRNA and control siRNA (Thermo Scientific/Dharmacon, Erembodegem, Belgium), respectively.

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MicroRNA profiling of murine lymphoma model harboring the MYC transgene in a Tet-off system reveals MYC stimulates EZH2 expression by repression of its negative regulator miR-26a

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