trichostatin-a and Choriocarcinoma

Trophoblast cells and many cancer cells that harbor foreign antigens may evade immunity by epigenetic silencing of key immune response genes, including MHC class I and II and CD40. Chromatin active agents, such as histone deacetylase inhibitors (HDACi), induce immune response gene expression but often the expression levels are low and the cells lack a robust antigen presentation response. We show here that pre-treatment of trophoblast cells and certain cancer cells with agents that activate stress pathways (Ras oncogene, PMA or H2O2) and induce senescence can substantially enhance the induction of immune response genes (MHC class II, CD40, MICA, MICB) by HDACi and restore a vigorous IFN-gamma response in trophoblast cells and tumor cells. These results could potentially impact the development of novel anti-cancer therapeutic strategies.

Topics: Animals; Antigen Presentation; CD40 Antigens; Cellular Senescence; Choriocarcinoma; Chromatin Assembly and Disassembly; Female; Gene Silencing; Genes, MHC Class I; Genes, MHC Class II; HeLa Cells; Histone Deacetylase Inhibitors; Humans; Hydroxamic Acids; Interferon-gamma; MAP Kinase Signaling System; Mice; Oxidative Stress; Pregnancy; Transcriptional Activation; Trophoblasts; Tumor Escape; Uterine Neoplasms

The 5'-flank of the H19 gene harbors a differentially methylated imprinting control region that represses the maternally derived Igf2 and paternally derived H19 alleles. Here we show that the H19 imprinting control region (ICR) is a potent silencer when positioned in a promoter-proximal position. The silencing effect is not alleviated by trichostatin A treatment, suggesting that it does not involve histone deacetylase functions. When the H19 ICR is separated from the promoter by more than 1.2 +/- 0.3 kb, however, trichostatin A stimulates promoter activity 10-fold. Deletion analyses revealed that the silencing feature extended throughout the ICR segment. Finally, chromatin immunopurification analyses revealed that the H19 ICR prevented trichostatin A-dependent reacetylation of histones in the promoter region in a proximal but not in a distal position. We argue that these features are likely to be side effects of the H19 ICR, rather than explaining the mechanism of silencing of the paternal H19 allele. We issue a cautionary note, therefore, that the interpretation of insulator/silencer data could be erroneous should the distance issue not be taken into consideration.

Topics: Antifungal Agents; Binding Sites; Chloramphenicol O-Acetyltransferase; Choriocarcinoma; DNA Methylation; DNA Primers; Female; Gene Expression Regulation, Neoplastic; Gene Silencing; Genes, Reporter; Genomic Imprinting; Histones; Humans; Hydroxamic Acids; Polymerase Chain Reaction; Pregnancy; Promoter Regions, Genetic; RNA, Long Noncoding; RNA, Untranslated; Transfection; Tumor Cells, Cultured; Uterine Neoplasms

There is a strong correlation between the acetylation status of nucleosomal histones and transcriptional activity. Here we show that the histone deacetylase inhibitor trichostatin A (TSA) activates reporter gene constructs driven by the human platelet-derived growth factor B (PDGF-B) gene promoter. This activation showed an inverse correlation with the cell type-specific transcriptional activities of the promoter. The TSA response was minimal in three tumor cell lines that exhibit high-level promoter activity. In JEG-3 choriocarcinoma cells, however, where the basal promoter activity is considerably lower, there was a strong response to TSA. This was in contrast to constructs that included a PDGF-B enhancer, which were refractory to TSA effects, indicating a possible function of the enhancer in modulating acetylation status. Analysis of PDGF-B promoter mutants with respect to TSA induction revealed no specific TSA-responsive element, but suggested that association of nonacetylated histones to the PDGF-B promoter may be a default process in the absence of enhancer activation. TSA treatment of JEG-3 cells, either alone or in combination with the demethylating agent 5-azacytidine, failed to activate the silenced endogenous PDGF-B transcript, however, which appears to be repressed by additional mechanisms.

Topics: Adenocarcinoma; Breast Neoplasms; Carcinoma, Hepatocellular; Choriocarcinoma; Chromosomes; DNA Methylation; Enhancer Elements, Genetic; Enzyme Inhibitors; Female; Gene Expression Regulation, Neoplastic; Histone Deacetylase Inhibitors; Histone Deacetylases; Humans; Hydroxamic Acids; Introns; Liver Neoplasms; Mutagenesis; Promoter Regions, Genetic; Proto-Oncogene Proteins c-sis; Rhabdomyosarcoma; Transcription, Genetic; Tumor Cells, Cultured