title: Comparative resistance of the 20S and 26S proteasome to oxidative stress.
abstract: Oxidatively modified ferritin is selectively recognized and degraded by the 20S proteasome. Concentrations of hydrogen peroxide (H2O2) higher than 10 micromol/mg of protein are able to prevent proteolytic degradation. Exposure of the protease to high amounts of oxidants (H2O2, peroxynitrite and hypochlorite) inhibits the enzymic activity of the 20S proteasome towards the fluorogenic peptide succinyl-leucine-leucine-valine-tyrosine-methylcoumarylamide (Suc-LLVY-MCA), as well as the proteolytic degradation of normal and oxidant-treated ferritin. Fifty per cent inhibition of the degradation of the protein substrates was achieved using 40 micromol of H2O2/mg of proteasome. No change in the composition of the enzyme was revealed by electrophoretic analysis up to concentrations of 120 micromol of H2O2/mg of proteasome. In further experiments, it was found that the 26S proteasome, the ATP- and ubiquitin-dependent form of the proteasomal system, is much more susceptible to oxidative stress. Whereas degradation of the fluorogenic peptide, Suc-LLVY-MCA, by the 20S proteasome was inhibited by 50% with 12 micromol of H2O2/mg, 3 micromol of H2O2/mg was enough to inhibit ATP-stimulated degradation by the 26S proteasome by 50%. This loss in activity could be followed by the loss of band intensity in the non-denaturing gel. Therefore we concluded that the 20S proteasome was more resistant to oxidative stress than the ATP- and ubiquitin-dependent 26S proteasome. Furthermore, we investigated the activity of both proteases in K562 cells after H2O2 treatment. Lysates from K562 cells are able to degrade oxidized ferritin at a higher rate than non-oxidized ferritin, in an ATP-independent manner. This effect could be followed even after treatment of the cells with H2O2 up to a concentration of 2mM. The lactacystin-sensitive ATP-stimulated degradation of the fluorogenic peptide Suc-LLVY-MCA declined, after treatment of the cells with 1mM H2O2, to the same level as that obtained without ATP stimulation. Therefore, we conclude that the regulation of the 20S proteasome by various regulators takes place during oxidative stress. This provides further evidence for the role of the 20S proteasome in the secondary antioxidative defences of mammalian cells.
authors.affiliation: Clinics of Physical Medicine and Rehabilitation, Medical Faculty (Charité), Humboldt University Berlin, Schumannstr. 20/21, D-10098, Berlin, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Reinheckel
authors.forename: N
authors.initials: N
authors.lastname: Sitte
authors.forename: O
authors.initials: O
authors.lastname: Ullrich
authors.forename: U
authors.initials: U
authors.lastname: Kuckelkorn
authors.forename: K J
authors.initials: KJ
authors.lastname: Davies
authors.forename: T
authors.initials: T
authors.lastname: Grune
mesh_terms: D003374:Coumarins / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004912:Erythrocytes / Q000201:enzymology*; D005293:Ferritins / Q000378:metabolism; D005456:Fluorescent Dyes; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D020014:K562 Cells; D007700:Kinetics; D009097:Multienzyme Complexes / Q000378:metabolism*; D009566:Nitrates / Q000494:pharmacology; D009842:Oligopeptides / Q000378:metabolism; D016877:Oxidants / Q000494:pharmacology*; D018384:Oxidative Stress; D010447:Peptide Hydrolases / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D012973:Sodium Hypochlorite / Q000494:pharmacology; D013379:Substrate Specificity
chemical_list: D003374:Coumarins; D005456:Fluorescent Dyes; D009097:Multienzyme Complexes; D009566:Nitrates; D009842:Oligopeptides; D016877:Oxidants; C039642:peroxynitric acid; D005293:Ferritins; C046582:succinyl-leucyl-leucyl-valyl-tyrosyl-methylcoumarinamide; D006861:Hydrogen Peroxide; D012973:Sodium Hypochlorite; D010447:Peptide Hydrolases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease