Browsing by Person "Cato, Andrew C. B."

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Effects of N-terminal mutations of human androgen receptor on polyglutamine toxicity
(2008) Funderburk, Sarah F.; Cato, Andrew C. B.
Nine neurodegenerative diseases are caused by polyglutamine (polyQ) tract amplification in different proteins. The cytotoxicity of each of these proteins is associated with a misfolding of the mutant protein, resulting in the subsequent alteration of cellular processes and interactions as well as the interrelated formation of insoluble aggregates and other conformationally toxic species. However, the diseases differ in their pathology and tissue specificity of action, which may be due to protein context/regions neighboring the polyQ stretch. For the purpose of the studies presented in ths work, the polyQ containing human androgen receptor (AR) that causes the disorder spinal and bulbar muscular atrophy (SBMA) was used to model polyQ toxicity. In previous investigations, two putative phosphorylation sites of the AR were identified, and it was demonstrated that mutation of these sites appeared to cause conformational change in the protein. Therefore, these N-terminal serine residues were exchanged to alanine in the wild type AR (ARQ22/ARQ22dm) or a receptor with an amplified polyQ stretch (ARQ77/ARQ77dm). These mutants were then used to characterize variance in types of aggregates and the associated toxic profiles due to the different protein conformations that arose from the serine mutations. Evaluating changes in aggregation and toxicity in cultured cells and in a Drosophila model of SBMA, it was found that the effects of the conformational changes differed depending on the length of the polyQ stretch. Mutations in the ARQ22 resulted in a marked increase in aggregation as well as decreased survival rates and altered locomotion behavior in Drosophila. These results were similar but not as severe as the ARQ77/SBMA model. In quite the opposite manner, mutations in the ARQ77 caused a decrease in aggregation and a lessened toxic effect in Drosophila. Moreover, it was found that inhibitor compounds used to ameliorate polyQ toxicity were not as efficient in inhibiting the varied toxicities exhibited by both the ARQ22dm and ARQ77dm. Therefore, two distinct amino acid sites that profoundly modulate polyQ toxicity in the AR have been identified. These results can be further utilized to understand the conformational changes in the AR that lead to aggregation as well as the types of aggregates that lead to toxicity.