Unknown,Transcriptomics,Genomics,Proteomics

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PAX5 overexpression is not enough to reestablish the mature B-cell phenotype in classical Hodgkin lymphoma

ABSTRACT: In lymphomas derived from mature B cells the expression of the transcription factor PAX5 is maintained whereas classical Hodgkin lymphoma displays significantly reduced PAX5 expression despite its derivation from mature B cells. To elucidate the functional role of PAX5 in classical Hodgkin lymphoma, we re-established the PAX5 expression in the Hodgkin cell line L428 with and without epigenetic modulation. To this end, we stably transfected the Hodgkin cell line L428 with an inducible PAX5 expression construct. Although the overexpressed PAX5 was transcriptionally active as demonstrated by synthetic reporter constructs, no induction of the B-cell phenotype was achieved. PAX5 chromatin immunoprecipitation with subsequent next generation sequencing in B-cell lines and the PAX5 overexpressing L428 cell line showed different binding patterns. Since epigenetic restrictions might affect PAX5 binding, combined DNA demethylation and histone acetylation was performed. However, no re-expression of B-cell genes was observed also under these conditions. Thus, PAX5 is not sufficient for the re-activation of the B-cell program in Hodgkin cells despite epigenetic opening of the chromatin. This clearly indicates that the repression of the B-cell identity of the Hodgkin cells is caused and secured by complex molecular mechanisms. 2 Burkitt lymphoma cell lines (Raji, Namalwa), the Hodgkin lymphoma cell line L428 and the PAX5-producing L428 (L428-PAX5) with or without 5-aza-2M-bM-^@M-2-deoxycytidine/Trichostatin A treatment were analysed in triplicate.

ORGANISM(S): Homo sapiens

SUBMITTER: Lora Dimitrova

PROVIDER: E-GEOD-44244 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:We examined the biological effects of a potent second-generation proteasome inhibitor, ixazomib, in T-cell lymphoma and Hodgkin lymphoma cell lines and human xenograft models. Ixazomib resulted in time- and dose-dependent cytotoxicity and apoptosis in all cell lines (IC50’s <75nM). In vivo studies via SCID tumor xenografts showed significant inhibition of tumor growth (P<0.001) with significantly improved survival (P<0.001) in Jurkat and L540 models with ixazomib-treated mice versus controls. Through global transcriptome and network analyses, ixazomib-treated Jurkat and L540 cells showed significant overlap in biological functions involved in regulation of cell cycle, chromatin modification, and DNA repair processes with a lack of conservation observed in a relatively ixazomib-resistant cell line, L428. Moreover, the predicted activation and inhibition status of tumor suppressors and oncogenes strongly favored ixazomib inhibition of tumor progression. Most notably, ixazomib down-regulated protein levels of MYC and its target genes. Additionally, chromatin immunoprecipitation showed that histone H3 acetylation affected MYC levels and cell death response to ixazomib. Furthermore, inhibition of MYC with JQ1 resulted in synergistic cell death in L428, which was confirmed utilizing MYC knockout. Collectively, ixazomib down-regulated MYC and downstream substrates in TCL and HL, while resistance appeared mediated through MYC- and CHK1-dependent mechanisms. L428 cells were treated with 25nM ixazomib for 24 hours, RNA was isolated using RNeasy Minikit (Qiagen), following instructions recommended supplied by the manufacturer. Purity and the yield of isolated RNA was determined using Bioanalyzer. These experiments were performed in biological triplicates. Microarray experiment with L428 was performed using Human HT 12 Genechip Illumina. Data for the L428 cell line was corrected through normalization of the housekeeping genes, quantile normalized, and then statistically relevant genes were determined with one-way ANOVA analysis with FDR <0.05.

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PAX5 overexpression is not enough to reestablish the mature B-cell phenotype in classical Hodgkin lymphoma

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