Casein Kinase 2 Interacts With And Phosphorylates Ataxin-3

Neurodegenerative diseases are chronic disorders caused by the deterioration of certain neurons. Changes in these neurons cause a function disorder, eventually lead to neuronal cell death. Machado-Joseph disease (MJD)/Spinocerebellar ataxia type 3 (SCA3) is an autosomal dominant neurodegenerative disorder caused by an expansion of polyglutamine tract near the C-terminus of the MJD1 gene product, ataxin-3. The expanded ataxin-3 forms nuclear inclusions in MJD brain. The precise mechanism of the MJD/SCA3 pathogenesis remains unclear.It was reported that post-translational modifications of desease proteins play an important role in the nuclear inclusions in MJD brain. Post-translational modifications of proteins are crucial to protein maturation, protein structure and protein functions. Post-translational modifications, such as phophorylation, methylation, ubiquitination and SUMOylation, are important for the regulation of protein functions, activities or localizations after their synthesis has been completed. Recent studies show that phosphorylation of some polyglutamine disease proteins, such as huntingtin, ataxin-1 and DRPLA, plays an important role in regulating pathogenesis. However, few kinases are known to phosphorylate ataxin-3.In this thesis, we mainly focus on the relationship between casein kinase 2 (CK2) and ataxin-3. The interaction between ataxin-3 and CK2 was identified by glutathione S-transferase (GST) pull-down assay and co-immunoprecipition assay. The phosphorylation of ataxin-3 by CK2 was measured by in vitro phosphorylation assays. The main results are below: (1) Both wild type and expanded ataxin-3 interacted with CK2αand CK2βin vitro. (2) In 293 cells, both wild type and expanded ataxin-3 interacted with CK2β, but not CK2α. (3) CK2 phosphorylated wild type and expanded ataxin-3.Taking together, we can draw a conclusion that ataxin-3 is a substrate of protein kinase CK2.