Rb targets histone H3 methylation and HP1 to promoters.
ABSTRACT In eukaryotic cells the histone methylase SUV39H1 and the methyl-lysine binding protein HP1 functionally interact to repress transcription at heterochromatic sites. Lysine 9 of histone H3 is methylated by SUV39H1 (ref. 2), creating a binding site for the chromo domain of HP1 (refs 3, 4). Here we show that SUV39H1 and HP1 are both involved in the repressive functions of the retinoblastoma (Rb) protein. Rb associates with SUV39H1 and HP1 in vivo by means of its pocket domain. SUV39H1 cooperates with Rb to repress the cyclin E promoter, and in fibroblasts that are disrupted for SUV39, the activity of the cyclin E and cyclin A2 genes are specifically elevated. Chromatin immunoprecipitations show that Rb is necessary to direct methylation of histone H3, and is necessary for binding of HP1 to the cyclin E promoter. These results indicate that the SUV39H1-HP1 complex is not only involved in heterochromatic silencing but also has a role in repression of euchromatic genes by Rb and perhaps other co-repressor proteins.
Full-textDOI: · Available from: Ron Firestein, Jun 21, 2015
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ABSTRACT: Seizures cannot be medically controlled in approximately 40% of people with epilepsy. Although we are beginning to understand how to better treat certain seizure types, we still do not know the regulatory events that determine antiepileptic drug resistance. Proposed pathoetiologic mechanisms include altered expression of drug targets (i.e., receptor or ion channel modifications), endothelial drug transporter activation (i.e., increasing drug clearance), or intrinsic severity factors. The latter hypothesis results from an often confirmed clinical observation, that seizure severity is a reliable predictor for the development of pharmacoresistance (PR) in epilepsy. Herein, we propose, that genome modifications that do not involve changes to the DNA sequence per se (i.e., epigenetic changes) could confer PR in patients with epilepsy. Seizures cause excessive neuronal membrane depolarization, which can influence the cellular nucleus; we thus hypothesize that seizures can mediate epigenetic modifications that result in persistent genomic methylation, histone density, and posttranslational modifications, as well as noncoding RNA-based changes. Although experimental evidence is lacking in epilepsy, such mechanisms are well characterized in cancer, either as a result of anticancer drugs themselves or cancer-related intrinsic signals (i.e., noncoding RNAs). We suggest that similar mechanisms also play a role in PR epilepsies. Addressing such epigenetic mechanisms may be a successful strategy to increase the brain's sensitivity to antiepileptic drugs and may even act as disease-modifying treatment.Epilepsia 05/2013; 54 Suppl 2:41-7. DOI:10.1111/epi.12183 · 4.58 Impact Factor
- Future Aspects of Tumor Suppressor Gene, Edited by Yue Cheng, 01/2013: chapter Chapter 2: pages pp17-43; InTech Open Access Publisher., ISBN: 980-953-307-910-8
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ABSTRACT: The expansion of repressive epigenetic marks has been implicated in heterochromatin formation during embryonic development, but the general applicability of this mechanism is unclear. Here we show that nuclear rearrangement of repressive histone marks H3K9me3 and H3K27me3 into nonoverlapping structural layers characterizes senescence-associated heterochromatic foci (SAHF) formation in human fibroblasts. However, the global landscape of these repressive marks remains unchanged upon SAHF formation, suggesting that in somatic cells, heterochromatin can be formed through the spatial repositioning of pre-existing repressively marked histones. This model is reinforced by the correlation of presenescent replication timing with both the subsequent layered structure of SAHFs and the global landscape of the repressive marks, allowing us to integrate microscopic and genomic information. Furthermore, modulation of SAHF structure does not affect the occupancy of these repressive marks, nor vice versa. These experiments reveal that high-order heterochromatin formation and epigenetic remodeling of the genome can be discrete events.Molecular cell 07/2012; 47(2):203-14. DOI:10.1016/j.molcel.2012.06.010 · 14.46 Impact Factor