Effect of neurotoxic metal ions on the proteolytic activities of the 20S proteasome from bovine brain

Abstract

The effect of oxidative stress induced by neurotoxic metal ions on the properties of the brain 20S proteasome or multicatalytic proteinase complex (MPC) has been studied. Exposure of the 20S proteasome to increasing amounts of Fe(III), Fe(II), Cu(II) or Zn(II) affects its main hydrolytic activities: trypsin-like (T-L), chymotrypsin-like (ChT-L), peptidylglutamyl-peptide hydrolase (PGPH), branched-chain amino acid preferring (BrAAP) and caseinolytic activities, although in different ways. T-L activity showed gradual activation by both iron ions but inhibition by Cu(II) and Zn(II). ChT-L and PGPH activities were inhibited whereas BrAAP activity was widely activated by all the tested metal salts except for zinc ions. Moreover, the exposure to ferrous salt increased the degradation rate of casein. The functional effects appear to be linked to oxidation-induced modifications, as demonstrated by an increase of carbonyl groups following the exposure to metal ions. In addition, modifications induced by ferrous salt on the catalytic subunits were also supported by western blot analyses performed using anti-X, anti-Y and anti-Z antibodies. The results obtained clearly indicate that metal-catalyzed oxidation strongly affects the functions of the brain 20S proteasome, even though the catalytic subunits seem to be differently influenced by oxidative phenomena.

Pyrrolidine dithiocarbamate-zinc(II) and -copper(II) complexes induce apoptosis in tumor cells by inhibiting the proteasomal activity

“…It has been published previously that zinc does not have a relevant oxidative strength, while copper caused some level of oxidation (Amici et al, 2002). However, the oxidation found by these authors was induced by milimolar concentrations of copper(II) sulfate pentahydrate, while micromolar range of copper(II) chloride was used in our studies.…”

Analysis of cellular responses of macrophages to zinc ions and zinc oxide nanoparticles: a combined targeted and proteomic approach

“…This would explain in turn why proteasome function is also an important parameter in zinc tolerance. This role of the proteasome may also explain why zinc, acting as a proteasome inhibitor 56 also synergizes with prooxidants 57 , which also induce a strong unfolded protein response. …”

“…In order to investigate the putative implication of this pathway in the response to zinc, we assessed the survival to zinc treatment after proteasome inhibition with the inhibitor MG132. The results, shown on Figure 7, demonstrate that proteasome inhibition increases zinc toxicity, which can be attributed to a synergistic effect between the inhibition of the proteasome by MG132 and the known inhibition of the proteasome by zinc 56 .…”

The proteasomes of two marine decapod crustaceans, European lobster (Homarus gammarus) and Edible crab (Cancer pagurus), are differently impaired by heavy metals

“…borderline and class B metals has been shown to damage and modulate these pathways in vivo with severe negative effects for organisms (Amici et al, 2002;Kim et al, 2004;Pena et al, 2008;Yu et al, 2010;Kanthasamy et al, 2012). Here we show for the first time that the invitro functionality of crustacean proteasomes is impaired by metal ions.…”