Interplay between Menin and K-Ras in Regulating Lung Adenocarcinoma

MEN1, which encodes the nuclear protein menin, acts as a tumor suppressor in lung cancer and is often inactivated in human primary lung adenocarcinoma. Here, we show that the inactivation of MEN1 is associated with increased DNA methylation at the MEN1 promoter by K-Ras. On one hand, the activated K-Ras up-regulates the expression of DNA methyltransferases and enhances the binding of DNA methyltransferase 1 to the MEN1 promoter, leading to increased DNA methylation at the MEN1 gene in lung cancer cells; on the other hand, menin reduces the level of active Ras-GTP at least partly by preventing GRB2 and SOS1 from binding to Ras, without affecting the expression of GRB2 and SOS1. In human lung adenocarcinoma samples, we further demonstrate that reduced menin expression is associated with the enhanced expression of Ras (p < 0.05). Finally, excision of the Men1 gene markedly accelerates the K-Ras^G12D-induced tumor formation in the Men1^f/f;K-Ras^G12D/+;Cre ER mouse model. Together, these findings uncover a previously unknown link between activated K-Ras and menin, an important interplay governing tumor activation and suppression in the development of lung cancer.     

Genome-wide Epigenetic Data Facilitate Understanding of Disease Susceptibility Association Studies

Complex traits such as susceptibility to diseases are determined in part by variants at multiple genetic loci. Genome-wide association studies can identify these loci, but most phenotype-associated variants lie distal to protein-coding regions and are likely involved in regulating gene expression. Understanding how these genetic variants affect complex traits depends on the ability to predict and test the function of the genomic elements harboring them. Community efforts such as the ENCODE Project provide a wealth of data about epigenetic features associated with gene regulation. These data enable the prediction of testable functions for many phenotype-associated variants.     

Identification of PR-SET7 and EZH2 selective inhibitors inducing cell death in human leukemia U937 cells

Chemical manipulations undertaken on some bis(bromo- and dibromo-phenol) compounds previously reported by us as wide-spectrum epigenetic inhibitors let us to identify bis (bromo- and dibromo-methoxyphenyl) derivatives highly selective for PR-SET7 and EZH2 (compounds 4, 5, 9, and 10). Western blot analyses were carried out in U937 cells to determine the effects of such compounds on the methyl marks related to the tested enzymes (H3K4me1, H3K9me2, H4H20me1, and H3K27me3). The 1,5-bis(3-bromo-4-methoxyphenyl)penta-1,4-dien-3-one 4 (EC₅₀ vs EZH2 = 74.9 μM), tested in U937 cells at 50 μM, induced massive cell death and 28% of granulocytic differentiation, highlighting the potential use of EZH2 inhibitors in cancer.     

Mutations in DNA Methyltransferase (DNMT3A) Observed in Acute Myeloid Leukemia Patients Disrupt Processive Methylation

DNA methylation is a key regulator of gene expression and changes in DNA methylation occur early in tumorigenesis. Mutations in the de novo DNA methyltransferase gene, DNMT3A, frequently occur in adult acute myeloid leukemia patients with poor prognoses. Most of the mutations occur within the dimer or tetramer interface, including Arg-882. We have identified that the most prevalent mutation, R882H, and three additional mutants along the tetramer interface disrupt tetramerization. The processive methylation of multiple CpG sites is disrupted when tetramerization is eliminated. Our results provide a possible mechanism that accounts for how DNMT3A mutations may contribute to oncogenesis and its progression.     

Phenotypic diversity and epigenomic variation - The utility of mass spectrometric analysis of DNA methylation

Epigenomic variation may underlie phenotypic diversity that is not attributable to differences in genomic sequence. Such processes provide an organism the flexibility to respond to changing environmental cues within its lifetime, and perhaps its offspring's lifetime, and would therefore be expected to confer a selective advantage in evolutionary terms. Analysis of epigenomic variation within a population may be both a useful measure of developmental exposures and an indicator of future phenotype. A key molecular indicator of epigenomic variation in organisms is the chemical modification of DNA by methylation at specific nucleotide residues in the genome. Here we discuss how mass spectrometry can be utilised to provide quantitative analysis of DNA methylation patterns across populations. This article is part of a Special Section entitled: Understanding genome regulation and genetic diversity by mass spectrometry.     

Dicentric chromosome formation and epigenetics of centromere formation in plants

Plant centromeres are generally composed of tandem arrays of simple repeats that form a complex chromosome locus where the kinetochore forms and microtubules attach during mitosis and meiosis. Each chromosome has one centromere region, which is essential for accurate division of the genetic material. Recently, chromosomes containing two centromere regions (called dicentric chromosomes) have been found in maize and wheat. Interestingly, some dicentric chromosomes are stable because only one centromere is active and the other one is inactivated. Because such arrays maintain their typical structure for both active and inactive centromeres, the specification of centromere activity has an epigenetic component independent of the DNA sequence. Under some circumstances, the inactive centromeres may recover centromere function, which is called centromere reactivation. Recent studies have highlighted the important changes, such as DNA methylation and histone modification, that occur during centromere inactivation and reactivation.