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Epigenetic upregulation of B-cell inappropriate genes induces extinction of B-cell program in classical Hodgkin lymphoma

ABSTRACT: A unique feature of the tumour cells (Hodgkin/Reed-Sternberg (HRS)) of classical Hodgkin lymphoma (cHL) is the loss of their B-cell phenotype despite their B-cell origin. Several lines of evidence suggest that epigenomic events, especially promoter DNA-methylation, are involved in this silencing of many B-cell associated genes. Here we show that DNA-demethylation alone or in conjunction with histone-acetylation is not able to reconstitute the B-cell gene expression program in cultured HRS cells. Instead, combined DNA-demethylation and histone-acetylation of B cells induce a nearly complete extinction of their B-cell expression program and a tremendous up-regulation of numerous cHL characteristic genes including key players such as Id2 known to be involved in the suppression of the B-cell phenotype. Since the up-regulation of cHL characteristic genes and the extinction of the B-cell expression program occurred simultaneously, epigenetic changes may also be responsible for the malignant transformation of cHL. The epigenetic up-regulation of cHL characteristic genes thus play - in addition to promoter DNA-hypermethylation of B-cell associated genes – a pivotal role for the reprogramming of HRS cells and explain why DNA-demethylation alone is unable to reconstitute the B-cell expression program in HRS cells. Keywords: Epigenetic modification

ORGANISM(S): Homo sapiens

PROVIDER: GSE8388 | GEO | 2007/11/01

SECONDARY ACCESSION(S): PRJNA101427

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.

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Epigenetic upregulation of B-cell inappropriate genes induces extinction of B-cell program in classical Hodgkin lymphoma

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