trichostatin-a and Precursor-Cell-Lymphoblastic-Leukemia-Lymphoma

Aberrant epigenetic regulation has recently been implicated in the downregulation of tumour suppressor microRNAs (miRNAs). Histone modification and DNA methylation can have different roles in gene silencing in cancer. To investigate whether histone modifications would contribute to the dysregulation of miRNAs in acute lymphoblastic leukaemia (ALL), the effect of a histone deacetylase inhibitor, trichostatin A (TSA), on miRNA expression profile was analysed by microarray assay in a precursor B-cell ALL cell line NALM-6. A total of 10 miRNAs were downregulated and 31 were upregulated significantly following TSA treatment. Among TSA-upregulated miRNAs, MIR22 is an extronic miRNA and resides in the second exon of the non-coding transcript MGC14376. Upregulation of MIR22 transcription was found in both NALM-6 cells and primary human ALL malignant cells treated with TSA. Whereas a CpG island was identified within the promoter element of MIR22, no promoter DNA methylation was detected in these cells. In contrast, accumulation of the repressive histone marker H3K27 trimethylation (H3K27triM) was identified around the transcriptional start point of the gene, which was reduced by TSA treatment. Thus, accumulation of H3K27triM independent of promoter DNA methylation may be a novel epigenetic mechanism for MIR22 silencing in ALL.

Topics: Azacitidine; CpG Islands; Decitabine; DNA Methylation; DNA, Neoplasm; Epigenesis, Genetic; Gene Expression Profiling; Gene Expression Regulation, Neoplastic; Gene Silencing; Genes, Neoplasm; Histone Deacetylase Inhibitors; Histones; Humans; Hydroxamic Acids; MicroRNAs; Polymerase Chain Reaction; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Promoter Regions, Genetic; Tumor Cells, Cultured

We recently reported that butyrate, an inhibitor of histone deacetylases, is capable of inducing Fas-independent apoptosis in the acute lymphoblastic leukemia cell line CCRF-CEM. Here we demonstrate that butyrate enhances Fas-induced apoptosis in this cell line. The application of different histone deacetylase inhibitors revealed that tetra-acetylated histone H4 is associated with the amplifying effect of butyrate on Fas-induced cell death. FasL, Fas, FADD, RIP, caspase-8, caspase-3, Bid, FLIP(S+L), FLASH and FAP-1, proteins known to act within the Fas-apoptosis cascade, showed no changes in their expression levels in cells treated with butyrate compared with untreated cells. Analyses of Fas-oligomerization and Western blotting as well as enzyme activity assays of caspase-2, caspase-3 and caspase-8 suggest that butyrate enhances Fas-induced apoptosis downstream of Fas but upstream of caspase-8 activation. In immunoprecipitation experiments a 37 kD butyrate-regulated protein was detected which specifically interacts with caspase-8.

Topics: Apoptosis; Butyrates; Caspase 2; Caspase 3; Caspase 8; Caspase 9; Caspases; Drug Synergism; Enzyme Inhibitors; fas Receptor; Fatty Acids; Histone Deacetylase Inhibitors; Humans; Hydroxamic Acids; Kinetics; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Signal Transduction; Tumor Cells, Cultured; Tumor Necrosis Factor-alpha