The androgen receptor (AR) is a ligand-activated transcription factor and a member of the nuclear receptor superfamily. Mutations in the androgen receptor are associated with androgen insensitivity syndrome (AIS), and a neurodegenerative disease, spinal bulbar muscular atrophy (SBMA). Most of the mutations causing AIS are loss-of-function missense mutations whereas SBMA is caused by a gain-of-function polyglutamine expansion in the N-terminal domain of the protein. Characterization of AR mutations has led to a better understanding of structure-function relationships of the AR and serves as a prototype for steroid receptors mechanisms of action. / In the first paper, we examine the role of an AR mutation in causing mild androgen insensitivity syndrome. We found that this mutation conferred reduced transactivation by AR through impaired interactions with the AR coactivator, TIF2, and impaired homodimerization. / In the second paper, we investigate the role of the AR polyGln expansion mutation in SBMA pathogenesis. Recent evidence has implicated proteolytic degradation of polyGln-expanded proteins and their subsequent intracellular aggregation in polyGn-expanded disease pathogenesis. We examined the role and composition of aggregates using fluorescently-tagged AR and found that proteolysis need not be a prerequisite for aggregation and that aggregation is not necessary for poly-Gln-induced cellular toxicity. / Finally, we characterize the novel heterodimerization of AR and ERalpha. We determined that this direct interaction has functional implications for the transactivational properties of both receptors.

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Spinobulbar muscular atrophy (SBMA) is a neurodegenerative disease caused by the expansion of a polyglutamine (polyGln) tract in the human androgen receptor (hAR). One mechanism by which polyGln-expanded proteins are believed to cause neuronotoxicity is through aberrant interaction(s) with, and possible sequestration of, critical cellular protein(s). / Our goal was to confirm and further characterize the interaction between hAR and cytochrome c oxidase subunit Vb (COXVb), a nuclear-encoded mitochondrial protein. We had previously isolated COXVb as an AR-interacting protein in a yeast two-hybrid search to identify candidates that interact with normal and polyGln-expanded AR. Using the mammalian two-hybrid system, we confirm that COXVb interacts with normal and mutant AR and demonstrate that the COXVb-normal AR interaction is stimulated by heat shock protein 70 (Hsp70). Also, BFP-tagged AR specifically co-localizes with cytoplasmic aggregates formed by GFP-labelled polyGln-expanded AR in androgen-treated cells. / Mitochondrial dysfunction may precede neuropathological findings in polyGln-expanded disorders and may thus represent an early event in neuronotoxicity. Interaction of COXVb and hAR, with subsequent sequestration of COXVb, may provide a mechanism for putative mitochondrial dysfunction in SBMA.

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