ABSTRACT
Loss of 5-hydroxymethylcytosine (5hmC) has been associated with mutations of the ten-eleven translocation (TET) enzymes in several types of cancer. However, tumors with wild-type TET genes can also display low 5hmC levels, suggesting that other mechanisms involved in gene regulation might be implicated in the decline of this epigenetic mark. Here we show that DNA hypermethylation and loss of DNA hydroxymethylation, as well as a marked reduction of activating histone marks in the TET3 gene, impair TET3 expression and lead to a genome-wide reduction in 5hmC levels in glioma samples and cancer cell lines. Epigenetic drugs increased expression of TET3 in glioblastoma cells and ectopic overexpression of TET3 impaired in vitro cell growth and markedly reduced tumor formation in immunodeficient mice models. TET3 overexpression partially restored the genome-wide patterns of 5hmC characteristic of control brain samples in glioblastoma cell lines, while elevated TET3 mRNA levels were correlated with better prognosis in glioma samples. Our results suggest that epigenetic repression of TET3 might promote glioblastoma tumorigenesis through the genome-wide alteration of 5hmC.
Subject(s)
Brain Neoplasms/genetics , Carcinogenesis/genetics , Dioxygenases/genetics , Epigenesis, Genetic , Gene Expression Regulation, Neoplastic , Glioblastoma/genetics , 5-Methylcytosine/analogs & derivatives , 5-Methylcytosine/metabolism , Animals , Biopsy , Brain Neoplasms/mortality , Brain Neoplasms/pathology , Cell Line, Tumor , DNA Methylation , Down-Regulation , Glioblastoma/mortality , Glioblastoma/pathology , Histone Code/genetics , Humans , Mice , Prognosis , RNA, Messenger/metabolism , Survival Analysis , Xenograft Model Antitumor AssaysABSTRACT
Histone H4 acetylation at Lysine 16 (H4K16ac) is a key epigenetic mark involved in gene regulation, DNA repair and chromatin remodeling, and though it is known to be essential for embryonic development, its role during adult life is still poorly understood. Here we show that this lysine is massively hyperacetylated in peripheral neutrophils. Genome-wide mapping of H4K16ac in terminally differentiated blood cells, along with functional experiments, supported a role for this histone post-translational modification in the regulation of cell differentiation and apoptosis in the hematopoietic system. Furthermore, in neutrophils, H4K16ac was enriched at specific DNA repeats. These DNA regions presented an accessible chromatin conformation and were associated with the cleavage sites that generate the 50 kb DNA fragments during the first stages of programmed cell death. Our results thus suggest that H4K16ac plays a dual role in myeloid cells as it not only regulates differentiation and apoptosis, but it also exhibits a non-canonical structural role in poising chromatin for cleavage at an early stage of neutrophil cell death.
Subject(s)
Apoptosis , Cell Differentiation , Chromatin/metabolism , Histones/metabolism , Lysine/metabolism , Myeloid Cells/metabolism , Acetylation , Animals , Cells, Cultured , Chromatin/genetics , Epigenesis, Genetic , Humans , Mice, Inbred C57BL , Mice, Knockout , Myeloid Cells/cytology , Protein Processing, Post-Translational , Transcription, GeneticABSTRACT
Ten-eleven translocation (TET) enzymes are frequently deregulated in cancer, but the underlying molecular mechanisms are still poorly understood. Here we report that TET2 shows frequent epigenetic alterations in human glioblastoma including DNA hypermethylation and hypo-hydroxymethylation, as well as loss of histone acetylation. Ectopic overexpression of TET2 regulated neural differentiation in glioblastoma cell lines and impaired tumor growth. Our results suggest that epigenetic dysregulation of TET2 plays a role in human glioblastoma.