Unknown,Transcriptomics,Genomics,Proteomics

Dataset Information

Native functions of the androgen receptor are essential to pathogenesis in a Drosophila model of spinobulbar muscular atrophy

ABSTRACT: Spinobulbar muscular atrophy (SBMA) is a neurodegenerative disease caused by expansion of a polyglutamine tract in the androgen receptor (AR). This mutation confers toxic function to AR through unknown mechanisms. Mutant AR toxicity requires binding of its hormone ligand, suggesting that pathogenesis involves ligand-induced changes in AR. However, whether toxicity is mediated by native AR function or a novel AR function is unknown. We systematically investigated events downstream of ligand-dependent AR activation in a Drosophila model of SBMA. We show that nuclear translocation of AR is necessary but not sufficient for toxicity and that DNA binding by AR is necessary for toxicity. Mutagenesis studies demonstrated that a functional AF-2 domain is essential for toxicity, a finding corroborated by a genetic screen that identified AF-2 interactors as dominant modifiers of degeneration. These findings indicate that SBMA pathogenesis is mediated by misappropriation of native protein function, a mechanism that may apply broadly to polyglutamine diseases. We used Affymetrix arrays to generate a molecular phenotype of degeneration in profile flies expressing wild-type or polyglutamine-expanded AR. We also expressed in the fly eye polyglutamine-expanded AR with point mutations affecting the DNA binding domain and the AF-2 domain. In some experiments, GMR-GAL4; UAR-AR flies were crossed to flies carrying a chromosomal duplication of the limpet gene. Transgene expression was induced in the eye using GMR-GAL4. Flies were crossed at 29 deg C on food containing either 1mM DHT or 1% ethanol (vehicle).

ORGANISM(S): Drosophila melanogaster

SUBMITTER: Geoffrey Neale

PROVIDER: E-GEOD-23802 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Native functions of the androgen receptor are essential to pathogenesis in a Drosophila model of spinobulbar muscular atrophy.

Nedelsky Natalia B NB Pennuto Maria M Smith Rebecca B RB Palazzolo Isabella I Moore Jennifer J Nie Zhiping Z Neale Geoffrey G Taylor J Paul JP

Neuron 20100901 6

Spinobulbar muscular atrophy (SBMA) is a neurodegenerative disease caused by expansion of a polyglutamine tract in the androgen receptor (AR). This mutation confers toxic function to AR through unknown mechanisms. Mutant AR toxicity requires binding of its hormone ligand, suggesting that pathogenesis involves ligand-induced changes in AR. However, whether toxicity is mediated by native AR function or a novel AR function is unknown. We systematically investigated events downstream of ligand-depen ...[more]

PMID: 20869592

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Project description:Together with the Estrogen, Progesterone, and Glucocorticoid Receptors, the Androgen Receptor (AR) is a member of the type I nuclear receptor superfamily, a class of transcription factors that are activated by steroid hormones1. Nuclear receptors share a common three-domain structure, comprising a highly variable amino-terminal domain (NTD), with potent transcriptional activator capability, a central two zinc finger motifs DNA-binding domain (DBD), and a well-conserved carboxy-terminal ligand-binding domain (LBD) responsible for interacting with the transcriptional machinery1. Given their modular structure, expression of isoforms resulting from alternative splicing or starting and termination events have profound effects on nuclear receptor activity and function. Several AR variants (AR-Vs) have been identified from prostate cancer clinical specimens, arising from multiple mechanisms, including genomic rearrangements2 and upregulation of splicing factors3. This seminal discovery has provided the molecular basis for a deeper understanding of AR-related diseases, with potential to be translated in identification of novel therapeutic targets and promising prognostic markers4–6. By deeply sequencing the transcriptome of human brains, here we identified AR-2 as the most expressed AR isoform. Furthermore, we found that AR-2 is widely expressed in other human tissues, forms heterodimers with the full length AR and acts as a repressor of its transcriptional activity. Delivery of this isoform via adeno-associated virus (AAV9) resulted in significant amelioration of the disease phenotype in a mouse model of spinal and bulbar muscular atrophy (SBMA), a neuromuscular disease with unmet clinical need caused by a toxic gain of function of polyglutamine-expanded (polyQ) AR7. Collectively, these results establish a physiological role of AR-2 in fine-tuning full length AR activity and demonstrate the feasibility and therapeutic benefit of modulating this variant for treating SBMA and other AR-related diseases.

Project description:Spinocerebellar ataxia type 3 (SCA3) is one of the polyglutamine (polyQ) diseases, which are caused by a CAG repeat expansion within the coding region of the associated genes. The CAG repeat specifies glutamine, and the expanded polyQ domain with mutation confers dominant toxicity on the protein. Traditionally, studies have focused on protein toxicity in polyQ disease mechanisms. Recent findings, however, demonstrate that the CAG repeat RNA, which encodes the toxic polyQ protein, also contributes to the disease in Drosophila. To provide insight into the nature of the RNA toxicity, we extracted brain-enriched RNA from flies expressing a toxic CAG repeat mRNA (CAG100) and a non-toxic interrupted CAA/G mRNA repeat (CAA/G105) for microarray analysis. This approach identified a set of genes that are differentially expressed specifically in CAG100 flies. Four independent replicates of flies expressing CAG0, CAG100, or CAA/G105 by elav-GAL4 were collected at 3 days. The transgenes are DsRed with either (CAG0) no CAG repeat in the 3'UTR, (CAG100) a CAG repeat of 100 CAGs in the 3'UTR, or (CAA/G105) an interrupted CAA CAG repeat in the 3'UTR (ref: Li et al., Nature 453:1107) The transgenes were adjusted to match in mRNA expression such that CAG0 flies had one copy of the transgene, CAG100 flies had 5 copies, and CAA/G105 had two copies. Fly brain tissue (about 20 brains per sample, dissected from head capsule, eyes, lamina and outer medulla removed) was dissected in cold phosphate buffered saline (PBS) and stored in Trizol reagent (Invitrogen Corporation, Carlsbad, CA) at -80Ë?C. Total brain RNA was extracted and purified using TRIzol reagent (Invitrogen) and the RNeasy Mini system (Qiagen), and treated with RNase-free DNase I (Qiagen). To define genes whose expression is altered in response to a toxic CAG repeat RNA, we compared CAG100 flies with age-matched flies expressing CAG0. To exclude transcriptional changes in response to a non-toxic trinucleotide repeat, a second gene list was generated by comparing CAA/G105 flies with age-matched CAG0 flies.

Dataset Information

Native functions of the androgen receptor are essential to pathogenesis in a Drosophila model of spinobulbar muscular atrophy

Publications

Native functions of the androgen receptor are essential to pathogenesis in a Drosophila model of spinobulbar muscular atrophy.

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