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The Molecular Chaperone Hsp70 Promotes the Proteolytic Removal of Oxidatively Damaged Proteins by the Proteasome

Research paper by Sandra Reeg, Tobias Jung, José P. Castro, Kelvin J.A. Davies, Andrea Henze, Tilman Grune

Indexed on: 04 Aug '16Published on: 03 Aug '16Published in: Free Radical Biology & Medicine



Abstract

One hallmark of aging is the accumulation of protein aggregates, promoted by the unfolding of oxidized proteins. Unraveling the mechanism by which oxidized proteins are degraded may provide a basis to delay the early onset of features, such as protein aggregate formation, that contribute to the aging phenotype. In order to prevent aggregation of oxidized proteins, cells recur to the 20 S proteasome, an efficient turnover proteolysis complex. It has previously been shown that upon oxidative stress the 26 S proteasome, another form, dissociates into the 20 S form. A critical player implicated in its dissociation is the Heat Shock Protein 70 (Hsp70), which promotes an increase in free 20 S proteasome and, therefore, an increased capability to degrade oxidized proteins. The aim of this study was to test whether or not Hsp70 is involved in cooperating with the 20 S proteasome for a selective degradation of oxidatively damaged proteins. Our results demonstrate that Hsp70 expression is induced in HT22 cells as a result of mild oxidative stress conditions. Furthermore, Hsp70 prevents the accumulation of oxidized proteins and directly promotes their degradation by the 20 S proteasome. In contrast the expression of the Heat shock cognate protein 70 (Hsc70) was not changed in recovery after oxidative stress and Hsc70 has no influence on the removal of oxidatively damaged proteins. We were able to demonstrate in HT22 cells, in brain homogenates from 129/SV mice and in vitro, that there is an increased interaction of Hsp70 with oxidized proteins, but also with the 20 S proteasome, indicating a role of Hsp70 in mediating the interaction of oxidized proteins with the 20 S proteasome. Thus, our data clearly implicate an involvement of Hsp70 oxidatively damaged protein degradation by the 20 S proteasome.

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