@article{CastroFernandoReegetal.2019,
  author    = {Castro, Jose Pedro and Fernando, Raquel and Reeg, Sandra and Meinl, Walter and Almeida, Henrique and Grune, Tilman},
  title     = {Non-enzymatic cleavage of Hsp90 by oxidative stress leads to actin aggregate formation},
  series = {Redox Biology},
  volume    = {21},
  journal   = {Redox Biology},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {2213-2317},
  doi       = {10.1016/j.redox.2019.101108},
  pages     = {10},
  year      = {2019},
  abstract  = {Aging is accompanied by the accumulation of oxidized proteins. To remove them, cells employ the proteasomal and autophagy-lysosomal systems; however, if the clearance rate is inferior to its formation, protein aggregates form as a hallmark of proteostasis loss. In cells, during stress conditions, actin aggregates accumulate leading to impaired proliferation and reduced proteasomal activity, as observed in cellular senescence. The heat shock protein 90 (Hsp90) is a molecular chaperone that binds and protects the proteasome from oxidative inactivation. We hypothesized that in oxidative stress conditions a malfunction of Hsp90 occurs resulting in the aforementioned protein aggregates. Here, we demonstrate that upon oxidative stress Hsp90 loses its function in a highly specific non-enzymatic iron-catalyzed oxidation event and its breakdown product, a cleaved form of Hsp90 (Hsp90cl), acquires a new function in mediating the accumulation of actin aggregates. Moreover, the prevention of Hsp90 cleavage reduces oxidized actin accumulation, whereas transfection of the cleaved form of Hsp90 leads to an enhanced accumulation of oxidized actin. This indicates a clear role of the Hsp90cl in the aggregation of oxidized proteins.},
  language  = {en}
}
@article{ReegJungCastroetal.2016,
  author    = {Reeg, Sandra and Jung, Tobias and Castro, Jos{\´e} Pedro and Davies, Kelvin J. A. and Henze, Andrea and Grune, Tilman},
  title     = {The molecular chaperone Hsp70 promotes the proteolytic removal of oxidatively damaged proteins by the proteasome},
  series = {Free radical biology and medicine : the official journal of the Oxygen Society, a constituent member of the International Society for Free Radical Research},
  volume    = {99},
  journal   = {Free radical biology and medicine : the official journal of the Oxygen Society, a constituent member of the International Society for Free Radical Research},
  publisher = {Elsevier},
  address   = {New York},
  issn      = {0891-5849},
  doi       = {10.1016/j.freeradbiomed.2016.08.002},
  pages     = {153 -- 166},
  year      = {2016},
  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 20S proteasome, an efficient turnover proteolysis complex. It has previously been shown that upon oxidative stress the 26S proteasome, another form, dissociates into the 20S form. A critical player implicated in its dissociation is the Heat Shock Protein 70 (Hsp70), which promotes an increase in free 20S 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 20S 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 20S 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 20S proteasome, indicating a role of Hsp70 in mediating the interaction of oxidized proteins with the 20S proteasome. Thus, our data clearly implicate an involvement of Hsp70 oxidatively damaged protein degradation by the 20S proteasome. c) 2016 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).},
  language  = {en}
}