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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.

ORGANISM(S): Drosophila melanogaster

PROVIDER: GSE23802 | GEO | 2010/09/23

SECONDARY ACCESSION(S): PRJNA130695

REPOSITORIES: GEO

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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.

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

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