The high-affinity HSP90-CHIP complex recognizes and selectively degrades phosphorylated tau client proteins
J. Clin. Invest. Chad A. Dickey, et al. 117:648 doi:10.1172/JCI29715 [Go to this article.]

Figure 5
Other components of the constitutive chaperone system are required to facilitate degradation of aberrant tau species by Hsp90 inhibitors; in turn, refolding machinery prevents p-tau degradation. (A) HeLa cells were transfected in duplicate with nonsilencing control, CHIP, Hop, Hsp40, or Hsp70 siRNA pools for 72 hours, then transfected with V5-tau and harvested after 24 hours’ EC102 exposure. EC102 caused robust reductions in p-tau immunoreactivity in control-transfected cells, while chaperone knockdown prevented such reductions. (B) Densitometric values, shown as percent optical density of nontransfected, vehicle-treated (Veh) control cells after GAPDH normalization (dashed line). (C) P23 and Pin1 siRNA pools mimicked EC102 treatment. P23 knockdown reduced tau to an extent similar to that of EC102, whereas Pin1 knockdown reduced p-tau levels by nearly 75%. These siRNAs had no apparent effect on drug efficacy. (D) Effects of chaperone knockdown on total tau levels regardless of EC102 treatment were assessed by V5 immunoreactivity (including Hsp90 and HSF1 from Figure 4A). Densitometric values are shown as percent optical density of V5 immunoreactivity in nonsilencing siRNA–transfected cells after GAPDH normalization. Hsp90, CHIP, Hop, and Hsp40 all caused tau levels to accumulate by approximately 40%. HSF1 and Hsp70 had no effect on tau accumulation. P23 and Pin1 reduced total tau by approximately 35% and 75%, respectively. (E) These results suggest that dephosphorylation and refolding of p-tau is initially facilitated by an Hsp90/P23/Pin1 complex, preventing degradation; however, when refolding is subverted by Hsp90 inhibition or P23/Pin1 knockdown, p-tau is transferred to the Hsp70/CHIP complex, and polyubiquitination mediates degradation.