Altered expression of HSPA5, HSPA8 and PARK7 in spinocerebellar ataxia type 17 identified by 2-dimensional fluorescence difference in gel electrophoresis

Background: Expansion of the CAG repeat of the TATA-box binding protein (TBP) gene has been identified as the causative mutations in spinocerebellar ataxia 17 (SCA17). TBP is ubiquitously expressed in both central nervous system and peripheral tissues. The underlying molecular changes of SCA17 are rarely explored. Methods: To study the molecular mechanisms underlying SCA17, we generated stably induced isogenic 293 cells expressing normal TBP-Q₃₆ and expanded TBP-Q₆₁ and analyzed the expressed proteins using two-dimensional difference in gel electrophoresis (2D-DIGE), followed by mass spectrometry and immunoblotting. Results: Upon induction with doxycycline, the expanded TBP-Q₆₁ formed aggregates with significant increase in the cell population at subG1 phase and cleaved caspase-3. Proteomics study identified a total of 16 proteins with expression changes greater than 1.5 fold. Among the 16 proteins, PARK7, GLRX3, HNRNPA1, GINS1, ENO1, HNRPK and NPM1 are increased, and SERPINA5, HSPA5, VCL, KHSRP, HSPA8, HNRPH1, IMMT, VCP and HNRNPL are decreased in cells expressing TBP-Q₆₁ compared with those expressing TBP-Q₃₆. The altered expression of HSPA5, HSPA8 and PARK7 were further validated by 2D and Western immunoblot analyses. Conclusions: The results illustrate the utility of proteomics to identify alterations of proteins which underlie pathogenesis of SCA17, and may serve as potential therapeutic targets.