Dominant-Negative Histone H3 Lysine 27 Mutant Derepresses Silenced Tumor Suppressor Genes and Reverses the Drug-Resistant Phenotype in Cancer Cells

Abstract

Histone modifications and DNA methylation are epigenetic phenomena that play a critical role in many neoplastic processes, including silencing of tumor suppressor genes. One such histone modification, particularly at H3 and H4, is methylation at specific lysine (K) residues. Whereas histone methylation of H3-K9 has been linked to DNA methylation and aberrant gene silencing in cancer cells, no such studies of H3-K27 have been reported. Here, we generated a stable cell line overexpressing a dominant-negative point mutant, H3-K27R, to examine the role of that specific lysine in ovarian cancer. Expression of this construct resulted in loss of methylation at H3-K27, global reduction of DNA methylation, and increased expression of tumor suppressor genes. One of the affected genes, RASSF1, was shown to be a direct target of H3-K27 methylation-mediated silencing. By increasing DNA-platinum adduct formation, indicating increased access of the drug to target DNA sequences, removal of H3-K27 methylation resensitized drug-resistant ovarian cancer cells to the chemotherapeutic agent cisplatin. This increased platinum-DNA access was likely due to relaxation of condensed chromatin. Our results show that overexpression of mutant H3-K27 in mammalian cells represents a novel tool for studying epigenetic mechanisms and the Histone Code Hypothesis in human cancer. Such findings show the significance of H3-K27 methylation as a promising target for epigenetic-based cancer therapies. (Cancer Res 2006; 66(11): 5582-91)

The expression and significance of the enhancer of zeste homolog 2 in lung adenocarcinoma

“…However, LA is less chemosensitive than other NSCLC. Our findings were consistent with another study showing that loss of EZH2-mediated methylation of histone H3 lysine 27 (H3K27) re-sensitized ovarian cancer cells to cisplatin (25). It was demonstrated that overexpression of EZH2 contributed to acquired cisplatin resistance in ovarian cancer cells in vitro and in vivo (26).…”

“…Our results identified EZH2 as an important factor in LA cell chemoresistance for the first time. Abbosh et al (25) found that H3K27 methylation played an important role in drug resistance. EZH2 deletion sensitized pancreatic cancer cells to doxorubicin and gemcitabine (27), because EZH2 mediated H3K27 methylation is a mark of heterochromatin, and loss of chromatin compaction could allow increased DNA damage at lower doxorubicin and gemcitabine doses leading to a decreased survival in EZH2 deleted pancreatic cancer cells.…”

Genetic and epigenetic heterogeneity of epithelial ovarian cancer and the clinical implications for molecular targeted therapy

“…In ovarian cancer, decreased expression of H3K27me3 is significantly associated with high‐grade and advanced‐stage tumours, but not with the histological type 78, predicting resistance to chemotherapy 79 and a poor clinical outcome in ovarian cancer and other malignancies 78. Removal of H3K27 methylation was shown to lead to re‐expression of the RASSF1 tumour suppressor and resensitize drug‐resistant ovarian cancer cells to cisplatin; this increased platinum access to DNA was likely due to relaxation of condensed chromatin 80. Sirtuin1 (SIRT1) is a nicotinamide adenine dinucleotide‐dependent deacetylase and a class III histone deacetyltransferase.…”

Overexpression of EZH2 contributes to acquired cisplatin resistance in ovarian cancer cells in vitro and in vivo

“…7 To explore the mechanism of resistance reversal by EZH2 knockdown, we performed western blotting to examine the level of H3K27me3 in EZH2-knockdown A2780/DDP cells. H3K27me3 level in shEZH2-A2780/ DDP cells was decreased by 50.5% compared with untransfected cells (p < 0.001; Knockdown of EZH2 induces G 2 /M cell cycle arrest in ovarian cancer cells.…”

“…[4][5][6] Recent data indicate that histone H3 lysine 27 (H3K27) methylation plays a important role in drug resistance, opening a novel insight to decipherering epigenetic mechanisms of tumor chemoresistance. 7 enhancer of Zeste homologue 2 (eZh2), a specific histone 3 lysine 27 (h3K27) methyltransferase, plays a critical role in tumorigenesis and cancer progression through epigenetic gene silencing and chromatin remodeling. however, the role of eZh2 in chemotherapy resistance is unknown.…”