The high-affinity HSP90-CHIP complex recognizes and selectively degrades phosphorylated tau client proteins
Chad A. Dickey, … , Francis Burrows, Leonard Petrucelli
Chad A. Dickey, … , Francis Burrows, Leonard Petrucelli
Published March 1, 2007
Citation Information: J Clin Invest. 2007;117(3):648-658. https://doi.org/10.1172/JCI29715.
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Research Article

The high-affinity HSP90-CHIP complex recognizes and selectively degrades phosphorylated tau client proteins

Abstract

A primary pathologic component of Alzheimer’s disease (AD) is the formation of neurofibrillary tangles composed of hyperphosphorylated tau (p-tau). Expediting the removal of these p-tau species may be a relevant therapeutic strategy. Here we report that inhibition of Hsp90 led to decreases in p-tau levels independent of heat shock factor 1 (HSF1) activation. A critical mediator of this mechanism was carboxy terminus of Hsp70–interacting protein (CHIP), a tau ubiquitin ligase. Cochaperones were also involved in Hsp90-mediated removal of p-tau, while those of the mature Hsp90 refolding complex prevented this effect. This is the first demonstration to our knowledge that blockade of the refolding pathway promotes p-tau turnover through degradation. We also show that peripheral administration of a novel Hsp90 inhibitor promoted selective decreases in p-tau species in a mouse model of tauopathy, further suggesting a central role for the Hsp90 complex in the pathogenesis of tauopathies. When taken in the context of known high-affinity Hsp90 complexes in affected regions of the AD brain, these data implicate a central role for Hsp90 in the development of AD and other tauopathies and may provide a rationale for the development of novel Hsp90-based therapeutic strategies.

Authors

Chad A. Dickey, Adeela Kamal, Karen Lundgren, Natalia Klosak, Rachel M. Bailey, Judith Dunmore, Peter Ash, Sareh Shoraka, Jelena Zlatkovic, Christopher B. Eckman, Cam Patterson, Dennis W. Dickson, N. Stanley Nahman Jr., Michael Hutton, Francis Burrows, Leonard Petrucelli

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Figure 3

Targeted knockdown of primary components of the chaperone pathway promotes robust and rapid reductions in protein levels.

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Targeted knockdown of primary components of the chaperone pathway promot...
(A) HeLa cells were transfected in duplicate with a scrambled nonsilencing siRNA control or 2 independent siRNAs per gene, targeting the indicated components of the chaperone cycle. After 72 hours, the cells were treated with EC102 (1 μM) for an additional 24 hours and harvested for Western analyses. Knockdown efficiency at the protein level for both siRNAs targeting 7 of the 8 genes was greater than 60% and averaged 80%. Only siRNAs targeting Hsp70 had modest reductions of approximately 30%. Induction of Hsps by EC102 was also prevented by their knockdown, with the exception of Hsp70. GAPDH immunoreactivity was assessed on each membrane to control for loading differences. The panel shown is representative for all membranes. Based on similar knockdown efficiencies, these siRNAs were pooled for subsequent studies. Quantitation was assessed by densitometry. (B) HeLa cells were transfected with either nonsilencing siRNA control or 2 siRNA pools targeting Hsp90 or HSF1. The cells were harvested at the indicated time points. Partial knockdown was apparent after 24 hours for both genes, and immunoreactivity decreased further with each additional 24-hour interval. The 72-hour time point was chosen for subsequent studies to avoid issues associated with toxicity.