Post-translational regulation of Atxn1 in Spinocerebellar Ataxia Type 1
Nitschke L1,2,3, Gennarino VA2,3, Richman R2,3, Lasagna-Reeves CA2,3, Orr HT4 and Zoghbi HY1,2,3,5*
1Program in Integrative Molecular and Biomedical Science, 2Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX; 3Jan and Dan Duncan Neurological Research Institute, Houston, TX; 4Institute for Translational Neuroscience, University of Minnesota, Minneapolis, MN and 5Howard Hughes Medical Institute, Houston, TX *Corresponding author
Spinocerebellar ataxia type 1 (SCA1) is a dominantly inherited neurodegenerative disease characterized by motor dysfunction and breathing and swallowing difficulties. It is caused by the expansion of CAG repeats, encoding a polyglutamine (polyQ) tract in Ataxin-1 (Atxn1). The polyQ tract stabilizes the protein leading to its accumulation in the nucleus of Purkinje cells and brainstem neurons, where it causes toxicity through a gain of function mechanism. While previous studies have shown that decreasing Atxn1 levels or preventing its localization to the nucleus reduces Atxn1's toxicity and rescues SCA1 pathogenesis, the underlying mechanisms of these processes remain largely uncharacterized. To gain further insight into Atxn1's regulation, we performed an immunoprecipitation assay followed by mass spectrometry to identify post-translational modifications of Atxn1 in the mouse brain. We identified seven highly conserved phosphorylation sites in Atxn1 (S82, S88, S239, S406, S694, S776 and S811). To study their functional significance, we generated doxycline-inducible cell lines expressing phosphorylation-deficient Atxn1 constructs and completed an initial in vitro characterization of these phosphorylation sites. We found that phosphorylation of Serine 239 is critical for Atxn1's nuclear localization and confirmed previous studies showing that S776 phosphorylation stabilizes Atxn1. To further test the importance of these two phosphorylation sites in vivo, we then generated phosphorylation-deficient knock-in WT and SCA1 mouse models. Future work aims at characterizing these newly established mouse models on a molecular and behavioral level and elucidating the underlying mechanisms of Atxn1 regulation.