ESET/SETDB1 gene expression and histone H3 (K9) trimethylation in Huntington's disease

Abstract

Chromatin remodeling and transcription regulation are tightly controlled under physiological conditions. It has been suggested that altered chromatin modulation and transcription dysfunction may play a role in the pathogenesis of Huntington's disease (HD). Increased histone methylation, a well established mechanism of gene silencing, results in transcriptional repression. ERG-associated protein with SET domain (ESET), a histone H3 (K9) methyltransferase, mediates histone methylation. We show that ESET expression is markedly increased in HD patients and in transgenic R6/2 HD mice. Similarly, the protein level of trimethylated histone H3 (K9) was also elevated in HD patients and in R6/2 mice. We further demonstrate that both specificity protein 1 (Sp1) and specificity protein 3 (Sp3) act as transcriptional activators of the ESET promoter in neurons and that mithramycin, a clinically approved guanosine-cytosine-rich DNA binding antitumor antibiotic, interferes with the DNA binding of these Sp family transcription factors, suppressing basal ESET promoter activity in a dose dependent manner. The combined pharmacological treatment with mithramycin and cystamine down-regulates ESET gene expression and reduces hypertrimethylation of histone H3 (K9). This polytherapy significantly ameliorated the behavioral and neuropathological phenotype in the R6/2 mice and extended survival over 40%, well beyond any existing reported treatment in HD mice. Our data suggest that modulation of gene silencing mechanisms, through regulation of the ESET gene is important to neuronal survival and, as such, may be a promising treatment in HD patients. H untington's disease (HD) is an autosomal-dominant inherited neurological disorder caused by expanded stretches of CAG repeats coding for glutamine in the Huntingtin (Htt) gene. Polyglutamine [poly(Q)] expansions of mutant Htt (mtHtt) protein lead to a number of cellular abnormalities that include altered nucleosome dynamics and subsequent transcriptional dysregulation (1-4). Consistent with transcriptional repression playing a role in the pathogenesis of HD, decreased acetylation and increased methylation of histones, well established mechanisms of gene activation and silencing, have been found in HD experimental models (5-8). Histone acetylation is involved in the regulation of gene expression and is regulated by the opposing activities of histone acetyltransferases and histone deacetylases (HDACs) (9). The poly(Q) stretches in mtHtt interact physically with CREB binding protein (CBP), a transcriptional coactivator, and block intrinsic CBP histone acetyltransferase activity (2, 5). These specific interactions have led to a model in which mtHtt, by harboring extra glutamines, becomes a hyperactive glutamine-containing corepressor (10). Transcriptional repression may also be attributable to epigenetic modifications, such as histone methylation and histone deacetylation (11). Thus, transcriptional dysfunction has been proposed to play an important role in the neuronal cell death of HD and has be...

Sprouty2 inhibits BDNF-induced signaling and modulates neuronal differentiation and survival

“…We blocked the activity of CREB and SP1 by using respectively, ICER, a dominant negative form of CREB, and mithramycin A, a drug that inhibits the activity of the transcription factors of the SP1 family. 28,29 Separately, ICER and mithramycin reduced by approximately 50% the induction of the spry2 promoter by BDNF, whereas Figure 3d). These results suggest that BDNF stimulates spry2 expression by regulating its promoter through cooperation between CREB and SP1.…”

Epigenetic Mechanisms of Neurodegeneration in Huntington's Disease

“…Indeed, the condensation of H3K9me3-dependent heterochromatin structure has been shown to be a prominent pathological feature of HD. Our group found that the levels of SETDB1 protein and histone H3K9me3 are elevated in striatal neurons of HD patients and HD transgenic animal models [66]. These data suggest that neuronal levels of SETDB1 and H3K9me3 may be predictive markers of nucleosomal dysfunction in HD [32].…”

“…Impaired neurogenesis results in cognitive dysfunction and could be an important epigenetic marker of neurodegeneration in HD HAT activity [50,64]. Accordingly, the sequestration of CBP protein by mthtt expression causes the hypermethylation and hypo-acetylation of histone proteins, and the subsequent transcriptional dysfunction of neurons in HD [56,59,61,65,66]. These specific interactions and transcriptional dysfunction are attributable to pathological epigenetic modifications [51].…”

“…4). Altered expression of HMT and elevated H3K9me3 are linked to upstream transcriptional deregulation in both animal models of HD and in HD patients [65,66,70]. Thus, the increase of H3K9me3 level has been correlated with the formation of large constitutive heterochromatin domains and is thought to promote gene silencing in both global and local repression of transcription, including CHRM1 [68,71].…”

“…HDAC inhibitors have been preclinically tested in many neurodegenerative conditions, including animal models of HD, amyotrophic lateral sclerosis, and multiple sclerosis [55,56,65,66,89,90]. Suberoylanilide hydroxamic acid and sodium butyrate are the first compounds that provide the efficacy of HDAC inhibition and histone modification in HD transgenic mice [91,92].…”