ABSTRACT
Platinum-based chemotherapy, with cytoreductive surgery, is the cornerstone of treatment of advanced ovarian cancer; however, acquired drug resistance is a major clinical obstacle. It has been proposed that subpopulations of tumor cells with stem cell-like properties, such as so-called side populations (SP) that overexpress ABC drug transporters, can sustain the growth of drug-resistant tumor cells, leading to tumor recurrence following chemotherapy. The histone methyltransferase EZH2 is a key component of the polycomb-repressive complex 2 required for maintenance of a stem cell state, and overexpression has been implicated in drug resistance and shorter survival of ovarian cancer patients. We observed higher percentage SP in ascites from patients that have relapsed following chemotherapy compared with chemonaive patients, consistent with selection for this subpopulation during platinum-based chemotherapy. Furthermore, ABCB1 (P-glycoprotein) and EZH2 are consistently overexpressed in SP compared with non-SP from patients' tumor cells. The siRNA knockdown of EZH2 leads to loss of SP in ovarian tumor models, reduced anchorage-independent growth, and reduced tumor growth in vivo. Together, these data support a key role for EZH2 in the maintenance of a drug-resistant, tumor-sustaining subpopulation of cells in ovarian cancers undergoing chemotherapy. As such, EZH2 is an important target for anticancer drug development.
Subject(s)
Antineoplastic Agents/pharmacology , DNA-Binding Proteins/genetics , DNA-Binding Proteins/metabolism , Gene Expression Regulation, Neoplastic , Neoplastic Stem Cells/drug effects , Neoplastic Stem Cells/metabolism , Ovarian Neoplasms/pathology , Transcription Factors/genetics , Transcription Factors/metabolism , Animals , Ascites/pathology , Carboplatin/pharmacology , Cell Line, Tumor , Enhancer of Zeste Homolog 2 Protein , Female , Gene Expression Profiling , Gene Expression Regulation, Neoplastic/drug effects , Gene Knockdown Techniques , Humans , Mice , Mice, SCID , Polycomb Repressive Complex 2 , RNA, Small Interfering/genetics , RNA, Small Interfering/metabolism , Xenograft Model Antitumor AssaysABSTRACT
Modifications to the core histones are thought to contribute to ESC pluripotency by priming tissue-specific promoters and enhancers for later activation. However, it is unclear how these marks are targeted in ESCs and maintained during differentiation. Here, we show that the ESC factor Sox2 targets H3K4 methylation to monovalent and bivalent domains. In ESCs, Sox2 contributes to the formation of a monovalent mark at an enhancer in the pro/pre-B cell-specific lambda5-VpreB1 locus. Binding of Foxd3 suppresses intergenic transcription of the enhancer and surrounding sequences. In pro-B cells, enhancer activity is dependent on the Sox and Fox binding sites, and the enhancer is bound by Sox4, which is required for efficient expression of lambda5. Our results lead us to propose a factor relay model whereby ESC factors establish active epigenetic marks at tissue specific elements before being replaced by cell type-specific factors as cells differentiate.
Subject(s)
Embryonic Stem Cells/metabolism , Enhancer Elements, Genetic/genetics , Epigenesis, Genetic/physiology , Forkhead Transcription Factors/metabolism , Immunoglobulin Light Chains, Surrogate/genetics , Precursor Cells, B-Lymphoid/metabolism , Repressor Proteins/metabolism , SOXB1 Transcription Factors/metabolism , Animals , Cell Line , Cells, Cultured , Chromatin Immunoprecipitation , DNA Footprinting , Embryonic Stem Cells/cytology , Epigenesis, Genetic/genetics , Forkhead Transcription Factors/genetics , Hemangioblasts/cytology , Mice , Oligonucleotide Array Sequence Analysis , Protein Binding , Repressor Proteins/genetics , Reverse Transcriptase Polymerase Chain Reaction , SOXB1 Transcription Factors/genetics , SOXC Transcription Factors/genetics , SOXC Transcription Factors/metabolismABSTRACT
Huntingtin is a protein of 348 kDa that is mutated in Huntington's disease (HD), a dominantly inherited neurodegenerative disorder. Previous data have led us to propose that aspects of the disease arise from both a loss of the neuroprotective function of the wild-type protein, and a toxic activity gained by the mutant protein. In particular, we have shown that wild-type huntingtin stimulates the production of brain-derived neurotrophic factor (BDNF), a pro-survival factor for the striatal neurons that die in the pathology. Wild-type huntingtin controls BDNF gene transcription in cerebral cortex, which is then delivered to its striatal targets. In the disease state, supply of cortical BDNF to the striatum is strongly reduced, possibly leading to striatal vulnerability. Here we show that a reduction in cortical BDNF messenger level correlates with the progression of the disease in a mouse model of HD. In particular, we show that the progressive loss of mRNAs transcribed from BDNF exon II, III and IV follows a different pattern that may reflect different upstream mechanisms impaired by mutation in huntingtin. On this basis, we also discuss the possibility that delivery of BDNF may represent an useful strategy for Huntington's disease treatment.
