trichostatin-a and Cell-Transformation--Viral

Genome-wide DNA methylation patterns are established and maintained by the coordinated action of three DNA methyltransferases (DNMTs), DNMT1, DNMT3A and DNMT3B. DNMT3B hypomorphic germline mutations are responsible for two-thirds of immunodeficiency, centromere instability, facial anomalies (ICF) syndrome cases, a rare recessive disease characterized by immune defects, instability of pericentromeric satellite 2-containing heterochromatin, facial abnormalities and mental retardation. The molecular defects in transcription, DNA methylation and chromatin structure in ICF cells remain relatively uncharacterized. In the present study, we used global expression profiling to elucidate the role of DNMT3B in these processes using cell lines derived from ICF syndrome and normal individuals. We show that there are significant changes in the expression of genes critical for immune function, development and neurogenesis that are highly relevant to the ICF phenotype. Approximately half the upregulated genes we analyzed were marked with low-level DNA methylation in normal cells that was lost in ICF cells, concomitant with loss of repressive histone modifications, particularly H3K27 trimethylation, and gains in transcriptionally active H3K9 acetylation and H3K4 trimethylation marks. In addition, we consistently observed loss of binding of the SUZ12 component of the PRC2 polycomb repression complex and DNMT3B to derepressed genes, including a number of homeobox genes critical for immune system, brain and craniofacial development. We also observed altered global levels of certain histone modifications in ICF cells, particularly ubiquitinated H2AK119. Therefore, this study provides important new insights into the role of DNMT3B in modulating gene expression and chromatin structure and reveals new connections between DNMT3B and polycomb-mediated repression.

Topics: Abnormalities, Multiple; Acetylation; Azacitidine; B-Lymphocytes; Case-Control Studies; Cell Line, Transformed; Cell Transformation, Viral; Cells, Cultured; Decitabine; DNA (Cytosine-5-)-Methyltransferases; DNA Methylation; DNA Methyltransferase 3B; Enzyme Inhibitors; Epigenesis, Genetic; Female; Gene Expression Profiling; Gene Expression Regulation, Developmental; Genes, Recessive; Histones; Humans; Hydroxamic Acids; Immunologic Deficiency Syndromes; Intellectual Disability; Male; Mutation; Neurons; Oligonucleotide Array Sequence Analysis; Promoter Regions, Genetic; Time Factors

Latent infection of the Epstein-Barr virus (EBV) is strongly associated with the pathogenesis of several human tumor types. The restricted expression of the latent EBV antigens is critical for EBV-associated tumors to escape from immune surveillance. EBV lytic replication can be triggered by various treatments and the induced lytic genes cause strong cytotoxic T lymphocyte (CTL) responses. Histone acetylation or deacetylation is associated with chromatin remodeling and regulates gene expression. Histone deacetylase (HDAC) inhibitors affect cell cycle progression as well as gene expression in a wide variety of transformed cells. We examined whether an HDAC inhibitor, TSA, can affect cell cycle progression and induce EBV lytic replication in EBV-transformed lymphoblastoid cell lines (LCLs). TSA caused cell cycle arrest at low concentrations and induced apoptosis at higher (>300 nM) concentrations in the LCLs and EBV negative BJAB cells. To clarify the underlying mechanism of TSA-induced cell cycle arrest, expression of cell cycle regulatory factors was examined by RNase protection assay and Western blot analysis. Following TSA treatment, a reduced expression of cyclin D2 and an induction of p21 may have played an essential role for G1 arrest in LCLs, while p21 induction might have arrested BJAB cells in G1 phase. A Cdk inhibitor, p57, was increased by 300 nM TSA in both LCLs and BJAB cells, indicating its role in apoptosis. Moreover, immunofluorescene assay and Western blotting showed that TSA induced EBV lytic replication in LCL cells. These results suggest that TSA may exert an enhanced anti-tumor effect for EBV-associated tumors not only by inducing a cell cycle arrest and apoptosis, but also by triggering an EBV lytic cycle.

Topics: Apoptosis; B-Lymphocytes; Blotting, Western; Cell Cycle; Cell Line, Transformed; Cell Line, Tumor; Cell Transformation, Viral; Enzyme Inhibitors; Fluorescent Antibody Technique; Gene Expression; Genes, Viral; Herpesvirus 4, Human; Histone Deacetylase Inhibitors; Humans; Hydroxamic Acids; Reverse Transcriptase Polymerase Chain Reaction

Varying the concentration of selected factors alters the induction properties of steroid receptors by changing the position of the dose-response curve (or the value for half-maximal induction=EC(50)) and the amount of partial agonist activity of antisteroids. We now describe a rudimentary mathematical model that predicts a simple Michaelis-Menten curve for the multi-step process of steroid-regulated gene induction. This model suggests that steps far downstream from receptor binding to steroid can influence the EC(50) of agonist-complexes and partial agonist activity of antagonist-complexes. We therefore asked whether inhibitors of three possible downstream steps can reverse the effects of increased concentrations of two factors: glucocorticoid receptors (GRs) and Ubc9. The downstream steps (with inhibitors in parentheses) are protein deacetylation (TSA and VPA), DNA unwinding (CPT), and CTD phosphorylation of RNA polymerase II (DRB and H8). None of the inhibitors mimic or prevent the effects of added GRs. However, inhibitors of DNA unwinding and CTD phosphorylation do reverse the effects of Ubc9 with high GR concentrations. These results support our earlier conclusion that different rate-limiting steps operate at low and high GR concentrations versus high GR with Ubc9. The present data also suggest that downstream steps can modulate the EC(50) of GR-mediated induction, thus both supporting the utility of our mathematical model and widening the field of biochemical processes that can modify the EC(50).

Topics: Acetylation; Animals; Cell Line; Cell Line, Transformed; Cell Transformation, Viral; Chlorocebus aethiops; Dexamethasone; Dichlororibofuranosylbenzimidazole; DNA; Dose-Response Relationship, Drug; Enzyme Inhibitors; Glucocorticoids; Hydroxamic Acids; Isoquinolines; Kinetics; Models, Theoretical; Phosphorylation; Plasmids; Receptors, Glucocorticoid; RNA Polymerase II; Trans-Activators; Transcriptional Activation; Transfection; Ubiquitin-Conjugating Enzymes; Valproic Acid

Immortal cell lines and tumors maintain their telomeres via the telomerase pathway or via a telomerase-independent pathway, referred to as alternative lengthening of telomeres (ALT). Here, we show the reversible conversion of the human papillomavirus type 16 E6-induced immortal human fibroblasts E6 Cl 6 from telomerase-positive (Tel(+)) to telomerase-negative (Tel(-)) cells. Tel(+) cells converted spontaneously to Tel(-) cells that reverted to Tel(+) cells following treatment with trichostatin A (TSA) and/or 5-aza-2'-deoxycytidine (5-AZC), which induced the reversion from complete to partial methylation of the CpG islands of the human telomerase reverse transcriptase (hTERT) promoter in Tel(-) E6 Cl 6 cells. Tel(-) E6 Cl 6 cells lacked the phenotypes characteristic of ALT cell lines such as very long and heterogenous telomeres and ALT-associated promyelocytic leukemia nuclear bodies (APB) but grew for >240 population doublings (PD) after they became telomerase negative. The ratios of histone H3 (H3) lysine (K) 9 methylation to each of H3-K4 methylation, H3-K9 acetylation, and H3-K14 acetylation of the chromatin containing the hTERT promoter in Tel(-) E6 Cl 6 cells and ALT cell lines were greater than those in Tel(+) cells and decreased following treatment with TSA and/or 5-AZC, inversely corresponding to telomerase activity. Our findings suggest the possibility that human tumors may be able to reversibly interconvert their telomere maintenance phenotypes by chromatin structure-mediated regulation of hTERT expression.

Topics: Acetylation; Azacitidine; Cell Line, Transformed; Cell Line, Tumor; Cell Transformation, Viral; Chromatin; Decitabine; DNA Methylation; DNA-Binding Proteins; Fibroblasts; Humans; Hydroxamic Acids; Oncogene Proteins, Viral; Polymorphism, Restriction Fragment Length; Promoter Regions, Genetic; Repressor Proteins; Telomerase; Telomere

CREB-binding protein (CBP) regulates gene expression by binding to certain components of basal transcription machinery and by histone acetylation. In addition, it integrates various cellular signaling pathways through binding to multiple transcription factors, including the Myb proteins. We report in this study that CBP can partially suppress function of the v-Myb oncoprotein in leukemic cells. Although originally described as an activator of v-Myb function, we show that CBP can also act as a v-Myb suppressor. Ectopic expression of murine CBP in v-Myb-transformed chicken monoblasts reduced transcriptional activation abilities of the v-Myb protein and increased sensitivity to differentiation inducers such as phorbol ester or trichostatin A. In addition, exogenous CBP affected morphology of differentiated cells derived from BM2 monoblasts. These results indicate that cellular context is an important factor determining whether CBP will activate or suppress the protein it targets.

Topics: Animals; Avian Myeloblastosis Virus; Cell Differentiation; Cell Line, Transformed; Cell Transformation, Viral; Chickens; CREB-Binding Protein; Hydroxamic Acids; Mice; Monocytes; Nuclear Proteins; Oncogene Proteins v-myb; Phagocytosis; Phorbol Esters; Trans-Activators

BM2 cells are chicken monoblasts transformed by the v-myb oncogene of avian myeloblastosis virus. The constitutively high v-myb expression interferes with the terminal differentiation of BM2 cells, but these cells can be induced to differentiate into macrophage-like cells by phorbol esters. Histone acetylation plays an important role in regulation of transcription and is particularly relevant to the regulation and pathology of hematopoiesis. In the present study, we examined the contribution of elevated histone acetylation to the differentiation of BM2 cells. Inhibition of the activity of endogenous histone deacetylases by trichostatin A (TSA) resulted in histone hyperacetylation causing cell cycle arrest and differentiation of BM2 cells into macrophage polykaryons. TSA did not affect the level of v-Myb protein in BM2 cells, but it downregulated its transcription activation capability. This suggests that chromatin remodeling can be significantly engaged in regulation of proliferation and differentiation of leukemic cells.

Topics: Acetylation; Animals; Cell Cycle; Cell Differentiation; Cell Line, Transformed; Cell Transformation, Viral; Chickens; Chromatin Assembly and Disassembly; Genes, myb; Histone Deacetylases; Histones; Hydroxamic Acids; Macrophages

Increased histone acetylation has been associated with activated gene transcription and decreased acetylation with repression. However, there is a growing number of genes known, which are downregulated by histone deacetylase (HDAC) inhibitors through unknown mechanisms. This study examines the mechanism by which the mouse mammary tumor virus (MMTV) promoter is repressed by the HDAC inhibitor, trichostatin A (TSA). We find that this repression is transcriptional in nature and that it occurs in the presence and absence of glucocorticoids. TSA decreases MMTV transcription at a rapid rate, reaching maximum in 30-60 min. In contrast with previous reports, the repression does not correlate with an inhibition of glucocorticoid-induced nuclease hypersensitivity or NF1-binding at the MMTV promoter. Surprisingly, TSA does not induce sizable increases in histone acetylation at the MMTV promoter nor does it inhibit histone deacetylation, which accompanies deactivation of the glucocorticoid-activated MMTV promoter. Repression of MMTV transcription by TSA does not depend on the chromatin organization of the promoter because a transiently transfected MMTV promoter construct with a disorganized nucleoprotein structure was also repressed by TSA treatment. Mutational analysis of the MMTV promoter indicates that repression by TSA is mediated through the TATA box region. These results suggest a novel mechanism that involves acetylation of nonhistone proteins necessary for basal transcription.

Topics: Acetylation; Adenocarcinoma; Animals; Cell Transformation, Viral; Chromatin; Dexamethasone; Enzyme Inhibitors; Female; Genes, Reporter; Histone Deacetylase Inhibitors; Histones; Hydroxamic Acids; Mammary Neoplasms, Experimental; Mammary Tumor Virus, Mouse; Mice; Nucleosomes; Promoter Regions, Genetic; Protein Processing, Post-Translational; Recombinant Fusion Proteins; Sequence Deletion; TATA Box; Terminal Repeat Sequences; Transcription, Genetic; Transfection

Mesotheliomas are tumors arising from mesothelial cells and are associated with asbestos exposure and approximately 50% contain simian virus 40 (SV40) DNA sequences. SV40 infection of human mesothelial cells (HM) causes early cellular immortalization and late transformation. Aberrant methylation is a major mech-anism for loss of function of tumor suppressor genes (TSGs). We recently reported that of seven genes frequently methylated in epithelial tumors, only RASSF1A gene was frequently methylated in mesotheliomas, and its methylation was correlated with loss of RASSF1A expression and the presence of SV40. We studied whether SV40 infection of normal HM induces aberrant methylation of the genes previously studied in mesotheliomas. Of six infected foci examined at early passages (passages 8-30) there was no methylation of the seven genes examined. Of two foci examined at late passages (passages 51-86) after the appearance of morphological changes suggestive of transformation, methylation and loss of expression of RASSF1A was detected. Sequencing of the CpG dense region around the transcription start site and semi-quantitative real-time methylation specific PCR (MSP) assay for RASSF1A methylation demonstrated progressive methylation during late passages. Exposure to the demethylating agent 5-aza-2'-deoxycytidine restored RASSF1A expression, while exposure to the histone deacetylation inhibitor trichostatin A had no effect. These data, together with our previous findings, support a causal relationship between SV40 infection, progressive RASSF1A methylation and its silencing, and the pathogenesis of mesothelioma.

Topics: Alleles; Azacitidine; Cell Line, Transformed; Cell Transformation, Viral; Cocarcinogenesis; CpG Islands; Decitabine; DNA Methylation; DNA, Neoplasm; Gene Expression Regulation; Gene Silencing; Genes, Tumor Suppressor; Humans; Hydroxamic Acids; Mesothelioma; Neoplasm Proteins; Polymerase Chain Reaction; Promoter Regions, Genetic; Simian virus 40; Tumor Suppressor Proteins