Constitutive activation of the nuclear factor-? B (NF-?B) pathway is a hallmark of the activated B-cell-like (ABC) subtype of diffuse large B-cell lymphoma (DLBCL). Recurrent mutations of NF-?B regulators that cause constitutive activity of this oncogenic pathway have been identified. However, it remains unclear how specific target genes are regulated. We identified the atypical nuclear I?B protein I?B-? to be upregulated in ABC compared with germinal center B-cell-like (GCB) DLBCL primary patient samples. Knockdown of I?B-? by RNA interference was toxic to ABC but not to GCB DLBCL cell lines. Gene expression profiling after I?B-? knockdown demonstrated a significant downregulation of a large number of known NF-?B target genes, indicating an essential role of I?B-? in regulating a specific set of NF-?B target genes. To further investigate how I?B-? mediates NF-?B activity, we performed immunoprecipitations and detected a physical interaction of I?B-? with both p50 and p52 NF-?B subunits, indicating that I?B-? interacts with components of both the canonical and the noncanonical NF-?B pathway in ABC DLBCL. Collectively, our data demonstrate that I?B-? is essential for nuclear NF-?B activity in ABC DLBCL, and thus might represent a promising molecular target for future therapies.
MYC is a key transcription factor involved in central cellular processes such as regulation of the cell cycle, histone acetylation and ribosomal biogenesis. It is overexpressed in the majority of human tumors including aggressive B-cell lymphoma. Especially Burkitt lymphoma (BL) is a highlight example for MYC overexpression due to a chromosomal translocation involving the c-MYC gene. However, no genome-wide analysis of MYC-binding sites by chromatin immunoprecipitation (ChIP) followed by next generation sequencing (ChIP-Seq) has been conducted in BL so far.
Epigenetic changes are involved in the extinction of the B-cell gene expression program of classical Hodgkins lymphoma. However, little is known regarding epigenetic similarities between cells of classical Hodgkins lymphoma and plasma cell myeloma, both of which share extinction of the gene expression program of mature B cells.
A characteristic feature of anaplastic large cell lymphoma is the significant repression of the T-cell expression program despite its T-cell origin. The reasons for this down-regulation of T-cell phenotype are still unknown. To elucidate whether epigenetic mechanisms are responsible for the loss of the T-cell phenotype, we treated anaplastic large cell lymphoma and T-cell lymphoma/leukemia cell lines (n=4, each) with epigenetic modifiers to evoke DNA demethylation and histone acetylation. Global gene expression data from treated and untreated cell lines were generated and selected, and differentially expressed genes were evaluated by real-time reverse transcriptase polymerase chain reaction and western blot analysis. Additionally, histone H3 lysine 27 trimethylation was analyzed by chromatin immunoprecipitation. Combined DNA demethylation and histone acetylation of anaplastic large cell lymphoma cells was not able to reconstitute their T-cell phenotype. Instead, the same treatment induced in T cells: (i) an up-regulation of anaplastic large cell lymphoma-characteristic genes (e.g. ID2, LGALS1, c-JUN), and (ii) an almost complete extinction of their T-cell phenotype including CD3, LCK and ZAP70. In addition, suppressive trimethylation of histone H3 lysine 27 of important T-cell transcription factor genes (GATA3, LEF1, TCF1) was present in anaplastic large cell lymphoma cells, which is in line with their absence in primary tumor specimens as demonstrated by immunohistochemistry. Our data suggest that epigenetically activated suppressors (e.g. ID2) contribute to the down-regulation of the T-cell expression program in anaplastic large cell lymphoma, which is maintained by trimethylation of histone H3 lysine 27.
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