Accumulation of the PX domain mutant Frank-ter Haar syndrome protein Tks4 in aggresomes

Abstract

Background: Cells deploy quality control mechanisms to remove damaged or misfolded proteins. Recently, we have reported that a mutation (R43W) in the Frank-ter Haar syndrome protein Tks4 resulted in aberrant intracellular localization. Results: Here we demonstrate that the accumulation of Tks4R43W depends on the intact microtubule network. Detergent-insoluble Tks4 mutant colocalizes with the centrosome and its aggregate is encaged by the intermediate filament protein vimentin. Both the microtubule inhibitor nocodazole and the histone deacetylase inhibitor Trichostatin A inhibit markedly the aggresome formation in cells expressing Tks4R43W. Finally, pretreatment of cells with the proteasome inhibitor MG132 markedly increases the level of aggresomes formed by Tks4R43W. Furthermore, two additional mutant Tks4 proteins (Tks41-48 or Tks41-341) have been investigated. Whereas the shorter Tks4 mutant, Tks41-48, shows no expression at all, the longer Tks4 truncation mutant accumulates in the nuclei of the cells. Conclusions: Our results suggest that misfolded Frank-ter Haar syndrome protein Tks4R43W is transported via the microtubule system to the aggresomes. Lack of expression of Tks41-48 or aberrant intracellular expressions of Tks4R43W and Tks41-341 strongly suggest that these mutations result in dysfunctional proteins which are not capable of operating properly, leading to the development of FTHS.