Essential roles of the histone methyltransferase ESET in the epigenetic control of neural progenitor cells during development

p53 down-regulates SETDB1 gene expression during paclitaxel induced-cell death

Paclitaxel (PTX) is a chemotherapeutic drug which induces tubulin stability and regulates expression of death related genes in human cancer cells. Its anticancer mechanism is well known, however its effects on chromatin remodeling factors are poorly understood. In this study, we examine if PTX affects expression of SETDB1 HMTase during cell death. PTX induces cell death via G2/M arrest in human lung cancer cells. PTX treatment induces the p53 protein, but down-regulates expression of SETDB1 at the transcriptional level as well as the protein level. SETDB1 promoter activity is increased to approximately 30-fold in normal condition, but the activity is significantly inhibited in the PTX treated group. In addition, p53 transfection inhibits SETDB1 promoter activity. The p53 protein directly binds to proximal region of the SETDB1 promoter, and H3K9me3 occupancy in this region also increased in the presence of p53. Immunoprecipitation experiment showed interaction of p53 and SUV39H1, suggesting that association of p53 and SUV39H1 is responsible for increased H3K9me3 occupancy and transcription repression of SETDB1. This result demonstrates that PTX down-regulates SETDB1 gene expression in a p53 dependent manner, and p53 might participate in heterochromatic repression on the promoter regions of SETDB1.

Dynamic changes of the epigenetic landscape during cellular differentiation

Epigenetic mechanisms are crucial to stabilize cell type-specific gene-expression programs. However, during differentiation, these programs need to be modified – a complex process that requires dynamic but tightly controlled rearrangements in the epigenetic landscape. During recent years, the major epigenetic machineries for gene activation and repression have been extensively characterized. Snapshots of the epigenetic landscape in pluripotent versus differentiated cells have further revealed how chromatin can change during cellular differentiation. Although transcription factors are the key drivers of developmental transitions, it became clear that their function is greatly influenced by the chromatin environment. Better insight into the tight interplay between transcription factor networks and the epigenetic landscape is therefore necessary to improve our understanding of cellular differentiation mechanisms. These systems can then be challenged and modified for the development of regenerative therapies.

ESET histone methyltransferase regulates osteoblastic differentiation of mesenchymal stem cells during postnatal bone development

To investigate the effects of histone methyltransferase ESET (also known as SETDB1) on bone metabolism, we analyzed osteoblasts and osteoclasts in ESET knockout animals, and performed osteogenesis assays using ESET-null mesenchymal stem cells. We found that ESET deletion severely impairs osteoblast differentiation but has no effect on osteoclastogenesis, that co-transfection of ESET represses Runx2-mediated luciferase reporter while siRNA knockdown of ESET activates the luciferase reporter in mesenchymal cells, and that ESET is required for postnatal expression of Indian hedgehog protein in the growth plate. As the bone phenotype in ESET-null mice is 100% penetrant, these results support ESET as a critical regulator of osteoblast differentiation during bone development.

Histone methylation in the nervous system: functions and dysfunctions

Chromatin remodeling is a key epigenetic process controlling the regulation of gene transcription. Local changes of chromatin architecture can be achieved by post-translational modifications of histones such as methylation, acetylation, phosphorylation, ubiquitination, sumoylation, and ADP-ribosylation. These changes are dynamic and allow for rapid repression or de-repression of specific target genes. Chromatin remodeling enzymes are largely involved in the control of cellular differentiation, and loss or gain of function is often correlated with pathological events. For these reasons, research on chromatin remodeling enzymes is currently very active and rapidly expanding, these enzymes representing very promising targets for the design of novel therapeutics in different areas of medicine including oncology and neurology. In this review, we focus on histone methylation in the nervous system. We provide an overview on mammalian histone methyltransferases and demethylases and their mechanisms of action, and we discuss their roles in the development of the nervous system and their involvement in neurodevelopmental, neurodegenerative, and behavioral disorders.

MicroRNA9 regulates neural stem cell differentiation by controlling Hes1 expression dynamics in the developing brain

Earlier studies show that Hes1 expression is oscillatory in neural stem cells but sustained and high in the roof plate and the floor plate, and that such different dynamics of Hes1 expression (oscillatory versus sustained) regulate different proliferation and differentiation characteristics of these cells (active in neural stem cells but rather dormant in roof/floor plate cells). The mechanism of how different dynamics of Hes1 expression is controlled remains to be determined. Here, we found that the seed sequence of microRNA-9 (miR-9) is complementary to the 3'-UTR sequence of Hes1 mRNA. MiR-9 is highly expressed in the ventricular zone of the developing brain, which contains neural stem cells, but it is not expressed in the roof plate or the floor plate. Over-expression of miR-9 negatively regulates the Hes1 protein expression by interacting with the 3'-UTR of Hes1 mRNA, thereby inducing cell cycle exit and neuronal differentiation. Conversely, knockdown of miR-9 inhibits neuronal differentiation. Furthermore, knockdown of miR-9 inhibits the oscillatory expression of Hes1 mRNA in neural stem cells. These results indicate that miR-9 regulates the proliferation and differentiation of neural stem cells by controlling the dynamics of Hes1 expression in the developing brain.