trichostatin-a and Lymphoma--Large-Cell--Anaplastic

BIM is a proapoptotic member of the Bcl-2 family. Here, we investigated the epigenetic status of the BIM locus in NPM/ALK+ anaplastic large cell lymphoma (ALCL) cell lines and in lymph node biopsies from NPM/ALK+ ALCL patients. We show that BIM is epigenetically silenced in cell lines and lymph node specimens and that treatment with the deacetylase inhibitor trichostatin A restores the histone acetylation, strongly upregulates BIM expression, and induces cell death. BIM silencing occurs through recruitment of MeCP2 and the SIN3a/histone deacetylase 1/2 (HDAC1/2) corepressor complex. This event requires BIM CpG methylation/demethylation with 5-azacytidine that leads to detachment of the MeCP2 corepressor complex and reacetylation of the histone tails. Treatment with the ALK inhibitor PF2341066 or with an inducible shRNA targeting NPM/ALK does not restore BIM locus reacetylation; however, enforced expression of NPM/ALK in an NPM/ALK-negative cell line significantly increases the methylation at the BIM locus. This study demonstrates that BIM is epigenetically silenced in NPM/ALK-positive cells through recruitment of the SIN3a/HDAC1/2 corepressor complex and that NPM/ALK is dispensable to maintain BIM epigenetic silencing but is able to act as an inducer of BIM methylation.

Topics: 5' Untranslated Regions; Acetylation; Apoptosis Regulatory Proteins; Bcl-2-Like Protein 11; Case-Control Studies; Cell Line, Tumor; Cell Survival; Chromatin; CpG Islands; DNA Methylation; Epigenesis, Genetic; Gene Expression Regulation, Neoplastic; Gene Silencing; Histone Deacetylase Inhibitors; Histones; Humans; Hydroxamic Acids; Lymphoma, Large-Cell, Anaplastic; Membrane Proteins; Methyl-CpG-Binding Protein 2; Protein Processing, Post-Translational; Protein-Tyrosine Kinases; Proto-Oncogene Proteins; Repressor Proteins; Sin3 Histone Deacetylase and Corepressor Complex

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.

Topics: Azacitidine; B-Lymphocytes; Cell Line, Tumor; Cluster Analysis; Decitabine; DNA Methylation; Epigenesis, Genetic; Gene Expression Profiling; Gene Expression Regulation, Neoplastic; Gene Silencing; Histones; Humans; Hydroxamic Acids; Inhibitor of Differentiation Protein 2; Lymphoma, Large-Cell, Anaplastic; Phenotype; Promoter Regions, Genetic; T-Lymphocytes; Transcription Factors