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Global Long Terminal Repeat activation participates in establishing the unique gene expression program of classical Hodgkin Lymphoma [ChIP-Seq]

ABSTRACT: Long terminal repeat (LTR) elements are wide-spread in the human genome and have the potential to act as promoters and enhancers. Their expression is therefore under tight epigenetic control. We previously reported that a member of the THE1B class of LTR elements in classical Hodgkin Lymphoma (cHL) acted as a promoter for the growth factor receptor gene CSF1R and that expression of this gene is required for tumor survival. However, to which extent and how such elements participate in globally shaping the unique cHL gene expression program is unknown. To address this question we mapped the genome-wide activation of THE1-LTRs in cHL cells using a targeted next generation sequencing approach (RACE-Seq). Integration of these data with global gene expression data from cHL and control B cell lines showed a unique pattern of LTR activation impacting on gene expression, including genes associated with the cHL phenotype. We also show that global LTR activation is induced by strong inflammatory stimuli. Together these results demonstrate that LTR activation provides an additional layer of gene deregulation in classical Hodgkin lymphoma and highlight the potential impact of genome-wide LTR activation in other inflammatory diseases.

ORGANISM(S): Homo sapiens

PROVIDER: GSE120538 | GEO | 2018/12/13

REPOSITORIES: GEO

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Project description:Background Epigenetic changes are involved in the extinction of the B-cell gene expression program of classical Hodgkin lymphoma. However, little is known regarding epigenetic similarities between classical Hodgkin lymphoma and plasma cell myeloma cells, both of which share an extinction of the gene expression program of mature B-cells. Design and methods Global histone H3 acetylation patterns were determined in cell lines derived from classical Hodgkin lymphoma, plasma cell myeloma and B-cell lymphoma by chromatin immunoprecipitation and subsequent hybridization onto promoter tiling arrays. H3K27 trimethylation was analyzed by chromatin immunoprecipitation and real-time DNA-PCR for selected genes. Epigenetic modifications were compared to gene expression data. Results B-cell characteristic genes were hypoacetylated in classical Hodgkin lymphoma and plasma cell myeloma cell lines, as demonstrated by comparison of their histone H3 acetylation patterns to those of B-cell lines. However, the number of genes jointly hyperacetylated and expressed in classical Hodgkin lymphoma and plasma cell myeloma cell lines, such as IFR4/MUM1 and RYBP, is limited. Moreover, H3K27 trimethylation for selected B-cell characteristic genes revealed that this additional epigenetic silencing is much more prevalent in classical Hodgkin lymphoma as compared to plasma cell myeloma. Conclusion Our epigenetic data support the view that classical Hodgkin lymphoma is characterized by an abortive plasma cell differentiation with a down-regulation of B-cell characteristic genes but without activation of most plasma cell typical genes. Gene expression analysis of Hodgkin lymphoma (cHL) and B-cell lines: Microarray data for three Hodgkin lymphoma cell lines (KM-H2, L1236, L428) and the B-cell line Namalwa that were published previously by our group (GEO accession GSE8388) were analyzed together with newly generated data for the B-cell lines SU-DHL4 and SU-DHL6. For all cell lines, RNA was isolated according to standard protocols (Qiagen, Hilden, Germany) and used for Affymetrix GeneChip hybridization (HG-U133A). Microarrays were normalized using RMA, and differential expression was calculated using moderated t-test. The gene expression profiles of the cell lines were generated in duplicates.