Journal Article

Polycomb Mediated Epigenetic Silencing and Replication Timing at the INK4a/ARF Locus during Senescence

Verthuy, Christophe, Serrano, Manuel, Gaussmann-Wenger, Anne, Agherbi, Hanane, Chasson, Lionel, Djabali, Malek

2009

Overview

The INK4/ARF locus encodes three tumor suppressor genes (p15(Ink4b), Arf and p16(Ink4a)) and is frequently inactivated in a large number of human cancers. Mechanisms regulating INK4/ARF expression are not fully characterized. Here we show that in young proliferating embryonic fibroblasts (MEFs) the Polycomb Repressive Complex 2 (PRC2) member EZH2 together with PRC1 members BMI1 and M33 are strongly expressed and localized at the INK4/ARF regulatory domain (RD) identified as a DNA replication origin. When cells enter senescence the binding to RD of both PRC1 and PRC2 complexes is lost leading to a decreased level of histone H3K27 trimethylation (H3K27me3). This loss is accompanied with an increased expression of the histone demethylase Jmjd3 and with the recruitment of the MLL1 protein, and correlates with the expression of the Ink4a/Arf genes. Moreover, we show that the Polycomb protein BMI1 interacts with CDC6, an essential regulator of DNA replication in eukaryotic cells. Finally, we demonstrate that Polycomb proteins and associated epigenetic marks are crucial for the control of the replication timing of the INK4a/ARF locus during senescence. We identified the replication licencing factor CDC6 as a new partner of the Polycomb group member BMI1. Our results suggest that in young cells Polycomb proteins are recruited to the INK4/ARF locus through CDC6 and the resulting silent locus is replicated during late S-phase. Upon senescence, Jmjd3 is overexpressed and the MLL1 protein is recruited to the locus provoking the dissociation of Polycomb from the INK4/ARF locus, its transcriptional activation and its replication during early S-phase. Together, these results provide a unified model that integrates replication, transcription and epigenetics at the INK4/ARF locus.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Animals / Cell Aging / Cell Biology/Gene Expression / Cell cycle / Cell Cycle Proteins / Cell Cycle Proteins - metabolism / Cell growth / Cellular Senescence / Chromatin / Cyclin-Dependent Kinase Inhibitor p16 / Cyclin-Dependent Kinase Inhibitor p16 - chemistry / Cyclin-Dependent Kinase Inhibitor p16 - genetics / Cyclin-Dependent Kinase Inhibitor p16 - metabolism / Cyclin-dependent kinase inhibitors / Deoxyribonucleic acid / Dissociation / DNA / DNA biosynthesis / DNA replication / DNA Replication Timing / Drosophila / Embryo fibroblasts / Embryo, Mammalian / Embryo, Mammalian - cytology / Embryos / Enhancer of Zeste Homolog 2 Protein / Epigenetic inheritance / Epigenetics / Fibroblasts / Fibroblasts - cytology / Fibroblasts - metabolism / Gene expression / Gene Silencing / Genes / Genetics and Genomics/Epigenetics / Genetics and Genomics/Gene Expression / Genomes / Histone-Lysine N-Methyltransferase / Histone-Lysine N-Methyltransferase - metabolism / Histones / Histones - metabolism / Immunology / INK4 protein / INK4a protein / Insects / Life Sciences / Loci / Methylation / Mice / Models, Biological / Myeloid-Lymphoid Leukemia Protein / Myeloid-Lymphoid Leukemia Protein - metabolism / NIH 3T3 Cells / Nuclear Proteins / Nuclear Proteins - metabolism / Oncology / p16 Protein / Pilot projects / Polycomb group proteins / Polycomb Repressive Complex 1 / Polycomb Repressive Complex 2 / Protein Binding / Protein Structure, Tertiary / Proteins / Proto-Oncogene Proteins / Proto-Oncogene Proteins - metabolism / Recruitment / Replication / Replication origins / Repressor Proteins / Repressor Proteins - metabolism / Senescence / Stem cells / Transcription activation / Tumor suppressor genes