induced by testosterone, results in its dissociation of chaperone accessory proteins (including Hsp90) and the acquisi- tion of the ?nal active conformation. It has been shown that Hsp90 is absolutely required to stabilize the AR and to allow its interaction with the ligand ( Poletti, 2004; Poletti et al., 2005 ), as well as for the consequent activation of the protein. Therefore, 17-AAG- mediated inhibition of Hsp90 prevents the formation of the AR conformation required to bind testosterone. The AR protein will be thus cleared prior to its activation. This hypothesis is strongly supported by data showing that AR, like other order Pazopanib members of the steroid receptor super- family ( Poletti et al., 1993; Weigel et al., 1995 ), undergoes post- translational modi ?cations, such as phosphorylation ( Pennuto et al., 2009; Poletti, 2004 ), soon after its interaction with testosterone at the AR C-terminus and the consequent dissociation from the chaperone accessory proteins. These post-translational modi ?cations mediate the conformational changes required to activate the AR.
Testosterone- induced phosphorylation has been shown to be altered in the mutant ARpolyQ protein ( LaFevre-Bernt and Ellerby, 2003 ). Therefore, it is conceivable that the elongated polyQ prevents the acquisition of the correct AR conformation, generating protein misfolding and testos- terone dependent aggregation ( Palazzolo et al., 2008; Pennuto et al., 2009 ). 17-AAG, by preventing the interaction of AR with testosterone, also might prevent alterations in the phosphorylation status, as well as the formation of the aberrant conformations described above, and ?nally the aggregation process. Finally, our data also demonstrated that the increased turnover of the AR is thus due to its clearance via the autophagic system. These observations agree with very recent data showing that 17-AAG induces cytoplasmic alpha-synuclein aggregates clearance by induc- tion of purchase Pazopanib autophagy ( Riedel et al., 2010 ), supporting the notion that 17-AAG might directly modulate autophagy in neural cells, via the induction of speci ?c Hsps ( Riedel et al., 2010 ). The effect of the lack of AR from motorneuron of SBMA patients remains to be determined. In fact it is known that AR plays important roles in motorneuronal functions in male ( Pozzi et al., 2003; Marron et al., 2005 ).
On the other hand, the complete blockage of AR action in patients suffering from complete androgen insensitivity syndrome (CAIS) ( Brinkmann, 2001 ) has no effects on motorneuronal survival in CAIS patients. This suggests that 17-AAG induced complete toothbrushes removal of neurotoxic AR in motorneuron will not have a negative impact on motorneurons of SBMA patients, as a consequence of an AR-mediated loss of function. Altogether these data offer a complete molecular view of the bene ?cial effects exerted by 17-AAG in the transgenic mouse model of SBMA ( Katsuno et al., 2005; Tokui et al., 2009; Waza et al., 2005, 2006 ), in which the compound markedly ameliorated motor impair- ments without detectable toxicity. Acknowledgments The ?nancial support of Telethon-Italy (GGP06063, and GGP07063), Fondazione CARIPLO (2008-2307), Italian Ministry of Labour, Health and Social Affairs (2007-36; 2008-15; and convenzione Fondazione Mondino/UNIMI), Fondation Thierry Latran, France (2009), University of Milan are gratefully acknowledged. We thank N.R. Cashman (Department of Medicine, Center for Research Neurodegenerative Pazopanib Diseases, Sunnybrook and Women’s College Health Science Center, University of Toronto, Ontario, Canada) for NSC34 cells.
A. Tolkovsky (Cambridge Centre for Brain Repair and Department of Biochemistry, University of Cambridge, Cambridge, UK) for pmRFP- LC3, E. Buratti (Int Cntr Genetic Eng Biotech, AREA Sci Park, Padriciano, Trieste, Italy) for pFLAG-FL TDP-43 and pFLAG- C TDP-43, R. Kopito (Department of Biological Sciences, Stanford University, Stanford, CA, USA) for GFPu. References Adachi, H., et al., 2003. Heat shock prot