The molecular chaperone Hsp70 promotes the proteolytic removal of oxidatively damaged proteins by the proteasome

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.

Happily (n)ever after: Aging in the context of oxidative stress, proteostasis loss and cellular senescence

“…Substrate recognition is assumed to be similar to the proteasome: exposed hydrophobic protein-sequences. Reeg et al [122] demonstrated an interaction of Hsp70 with both, oxidatively damaged substrate proteins and the 20S proteasome, indicating a role of Hsp70 in the proteasomal degradation after mild oxidative stress. Besides this, Hsp70 is involved in proper protein folding during de novo synthesis.…”

“…Such aggregates can be incorporated into an autophagosome and fusing with lysosomes, resulting in proteolytic degradation by lysosomal proteases, or they can be removed from the cell via excretion as exosome. Modified from [115] and according to [122].…”

Repeated anodal trans‐spinal direct current stimulation results in long‐term reduction of spasticity in mice with spinal cord injury

“…As described above, a-tsDCS reduced expression of NKCC1 protein, yet did not affect the level of NKCCC1 mRNA. These results suggested involvement of a degradation process, and HSP70 has been shown to enhance proteasomal and lysosomal pathways of protein degradation (Reeg et al 2016). Therefore, expression of HSP70 was investigated following a-tsDCS to strengthen and explain the qPCR and western blot data for NKCC1 levels.…”

Oxidised protein metabolism: recent insights

“…Substrate binding is mediated by the two outermost α rings and main proteolytic chamber is between the two β rings (Pickering and Davies, 2012;Jung and Grune, 2013). Recently, it was found that the molecular chaperone heat shock protein 70 (Hsp70) is induced following protein oxidation and forms a substrate with the oxidised protein that promotes the removal of oxidised proteins by the 20S proteasome (Reeg and Grune, 2015;Reeg et al, 2016). However, the 20S system is limited by its requirement for protein unfolding and exposed hydrophobic surface structures to stick to the α binding domain (Pickering and Davies, 2012).…”