Interaction of Huntington Disease Protein with Transcriptional Activator Sp1

Abstract

Polyglutamine expansion causes Huntington disease (HD) and at least seven other neurodegenerative diseases. In HD, N-terminal fragments of huntingtin with an expanded glutamine tract are able to aggregate and accumulate in the nucleus. Although intranuclear huntingtin affects the expression of numerous genes, the mechanism of this nuclear effect is unknown. Here we report that huntingtin interacts with Sp1, a transcription factor that binds to GC-rich elements in certain promoters and activates transcription of the corresponding genes. In vitro binding and immunoprecipitation assays show that polyglutamine expansion enhances the interaction of N-terminal huntingtin with Sp1. In HD transgenic mice (R6/2) that express N-terminal-mutant huntingtin, Sp1 binds to the soluble form of mutant huntingtin but not to aggregated huntingtin. Mutant huntingtin inhibits the binding of nuclear Sp1 to the promoter of nerve growth factor receptor and suppresses its transcriptional activity in cultured cells. Overexpression of Sp1 reduces the cellular toxicity and neuritic extension defects caused by intranuclear mutant huntingtin. These findings suggest that the soluble form of mutant huntingtin in the nucleus may cause cellular dysfunction by binding to Sp1 and thus reducing the expression of Sp1-regulated genes.Huntington disease (HD) is an autosomally dominant degenerative disorder resulting from expansion (Ͼ37 units) of a polyglutamine repeat in huntingtin, a 350-kDa protein of unknown function (15). The polyglutamine repeat is localized in the N-terminal region of huntingtin and is encoded by exon1 of the HD gene. Full-length huntingtin is predominantly distributed in the cytoplasm, whereas N-terminal fragments of huntingtin with expanded polyglutamine tracts accumulate in the nucleus (7,8,10). N-terminal huntingtin fragments containing expanded polyglutamine tracts are also toxic to cells. For example, transgenic mice expressing N-terminal fragments of mutant huntingtin develop rapidly progressing neurological symptoms (7, 37) that are more severe than those of mice expressing full-length mutant huntingtin (13,34). Smaller Nterminal huntingtin fragments, when transfected into cultured cells, kill more cells than do larger huntingtin fragments (11,27).The mechanisms for the cellular pathology associated with N-terminal-mutant huntingtin are unknown. N-terminal fragments of mutant huntingtin also form intranuclear aggregates (7, 8, 10, 37), a pathological hallmark that is found in many other polyglutamine diseases (43). Recent studies suggest that nuclear polyglutamine inclusions recruit transcription factors and that this recruitment affects gene expression (29, 39). Indeed, intranuclear huntingtin alters the expression of a number of genes, both in HD cells (22) and in transgenic animals (3, 26). The nuclear effect of mutant huntingtin may stem from its interactions with a number of transcription factors, such as the nuclear receptor corepressor (N-CoR) (2), cyclic AMP-responsive element-binding protein (CREB)-binding prote...

Functional roles for the striatal-enriched transcription factor, Bcl11b, in the control of striatal gene expression and transcriptional dysregulation in Huntington's disease

“…Scanning the putative promoter regions of these 100 genes for other transcription factors revealed the presence of many sites for known transcription factors, including consensus binding sites for the ubiquitous transcription factors, COUP-TF, which has been shown to interact with Bcl11b (Lin et al, 1999), Sp1, TBP and CREB. Transcriptional control by the latter factors is disrupted by the presence of mutant htt protein, with Sp1 and CBP specifically interacting with htt protein (McCampbell et al 2000;Steffan et al, 2000;Dunah et al 2002;Li et al 2002). Nonetheless, binding sites for these and other transcription factors were equally represented in striatal and non-striatal gene groups (p values ranging from 0.16 to 1.0) ( Table 2), suggesting that these transcription factors have less of a contribution to the specific control of striatal gene expression.…”

“…Studies have shown that mutant htt interacts with ubiquitous transcription factors such as the cAMP response element-binding protein-(CREB)-binding protein (CBP), Specificity protein 1 (Sp1), TATA binding box protein (TBP) and widely expressed components of the basal polymerase II transcriptional machinery such as the transcription initiation factor complexes TFIID and TFIIF, and the TATA box binding protein (TBP)-associated factor (TAF4; a.k.a. TAFII130) (McCampbell et al, 2000;Shimohata et al, 2000;Dunah et al, 2002;Li et al, 2002;van Roon-Mom et al, 2002;Zhai et al, 2005). However, other mechanisms of transcription factor disruption due to mutant htt have been proposed (Chen-Plotkin et al, 2006;Sadri-Vakili et al, 2007).…”

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

“…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)(2)(3)(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)(6)(7)(8).…”

Rapamycin prevents the mutant huntingtin-suppressed GLT-1 expression in cultured astrocytes

“…Consistent with prior research, we have provided direct evidence that mutant Htt-552 in glial cells reduced the expression of GLT-1 but not of GLAST and decreased glutamate uptake in astrocytes, which was mainly caused by decreased expression of GLT-1. Because there are Sp1-binding sites in the promoter of GLT-1 and the transcription of GLT-1 is Sp1-dependent [24,25] , previous reports of mutant Htt binding more Sp1 and reducing Sp1-mediated GLT-1 expression in astrocytes may explain this www.chinaphar.com Chen LL et al Acta Pharmacologica Sinica npg phenomenon [10] .…”