The role of dynein mediated transport in the clearance of mutated androgen receptor

Spinal and bulbar muscular atrophy (SBMA) are neurodegenerative disorders characterized by aggregates of mutant androgen receptor (ARpolyQ). In fact, the CAG expansion in the first exons of AR encode for ARpolyQ with aberrant conformation (misfolded) that lead to cell death. Efficient protein quality control (PQC) is required for the maintenance of the physiological and soluble protein pool in affected motoneuron. The balance between autophagy and ubiquitin proteasome system (UPS) prevents protein aggregation and increases degradation of ARpolyQ. Dynein, by binding the co chaperone BAG3, transports the mutant proteins at microtubule organiza- tion center (MTOC) where misfolded proteins interact, aggregate and can be degraded by autophagy. However, heremisfoldedproteinsmayimpairautophagycausingfluxblockage. InNSC34cells,wehaveobservedthat dynein is sequestered into ARpolyQ aggregates. This suggests a defect in autophagy and the role of dynein into aggregates formation process. Unexpectedly, the silencing of dynein heavy chain resulted in a drastic reduction of ARpolyQ retained in filter retardation assay (FRA). Moreover, dynein silencing drastically altered autophagic markers localization (LC3 and p62) by immunofluorescence. Notably, treatment with a dynein inhibitor (EHNA) drastically reduced the retention of ARpolyQ aggregates in FRA. Even when autophagy was inhibit with 3 MA. Conversely UPS blockage with MG132 counteracted the reduction induced by altered dynein transports. RTq PCR on NSC34 cells treated with EHNA showed an increased BAG1:BAG3 ratio that can targeting the misfolded proteins to UPS. Moreover, in NSC34 cells, EHNA increased the degradation of proteasome reporter GFPu, while BAG1 overexpression reduced the level of aggregates retained in FTA. Collectively, these data suggest that, when autophagy is overload, by misfolded proteins, dynein inhibition restores the physiological and soluble protein pool by protein degradation via UPS.