Elsevier

Molecular Aspects of Medicine

Volume 24, Issues 4–5, August–October 2003, Pages 195-204
Molecular Aspects of Medicine

The proteasomal system and HNE-modified proteins

https://doi.org/10.1016/S0098-2997(03)00014-1Get rights and content

Abstract

Metabolic processes and environmental conditions cause the constant formation of oxidizing species over the lifetime of cells and organisms. This leads to a continuous oxidation of intracellular components, including lipids, DNA and proteins. During the extensively studied process of lipid peroxidation, several reactive low-molecular weight products are formed, including reactive aldehydes as 4-hydroxynonenal (HNE). These aldehydic lipid peroxidation products in turn are able to modify proteins. The degradation of oxidized and oxidatively modified proteins is an essential part of the oxidant defenses of cells. The major proteolytic system responsible for the removal of oxidized cytosolic and nuclear proteins is the proteasomal system. The proteasomal system by itself is a multicomponent system responsible for the degradation of the majority of intracellular proteins. It has been shown that some, mildly cross-linked, HNE-modified proteins are preferentially degraded by the proteasome, but extensive modification with this cross-linking aldehyde leads to the formation of protein aggregates, that can actually inhibit the proteasome. This review summarizes our knowledge of the interactions between lipid peroxidation products, proteins, and the proteasomal system.

Introduction

Protein oxidation is a continuous process that occurs at low rates during the normal metabolism of aerobic cells and at increased rates in several pathological situations. The degree of protein oxidation caused by oxidants is dependent on several factors, including the nature, relative location, and flux rate of the oxidant, and the presence (or absence) of antioxidants. Both the oxidation of free amino acids and the oxidation of peptides and proteins have been studied by many laboratories. Numerous amino acids are known to be susceptible to oxidation. Besides the oxidation of amino acid side chains in proteins several changes can occur in the protein backbone, such as fragmentation of polypeptide chains, and both intra- and intermolecular cross-linking (Davies, 1987; Davies and Delsignore, 1987; Davies et al., 1987a, Davies et al., 1987b; Stadtman, 1993; Vogt, 1995).

Proteins may also be oxidatively modified via secondary mechanisms resulting from reactions of free radicals with other cellular constituents, such as lipids, carbohydrates, and nucleic acids. The process of lipid peroxidation has been intensively studied and it is known today that numerous products, some of them very reactive, are formed during this fascinating chain reaction. Reactive aldehydes, like malondialdehyde and 4-hydroxynonenal, are of special importance due to their formation rate, their frequent measurement by many laboratories, and their high reactivity with proteins. Of particular interest is the fact that both aldehydes are bi-functional compounds, which are able to form protein cross-links (Grune et al., 1997; Stadtman, 1993).

4-Hydroxynonenal is extensively metabolized, possibly in order to prevent the reaction of this aldehyde with proteins (Grune et al., 1994; Siems et al., 1997). Therefore, only a small share of the aldehyde formed actually reacts with proteins. In experimental models this amount is between 0.5% and 10% of the aldehyde present (Grune et al., 1994; Siems et al., 1997). This rate is actually probably higher than in the real in vivo situation due to the high 4-hydroxynonenal concentrations used in these experiments. Various chemical reactions of 4-hydroxynonenal with proteins have been carefully studied (Esterbauer et al., 1991; Grune et al., 1994; Siems et al., 1997; Uchida et al., 1994, Uchida et al., 1993). It is quite clear that 4-hydroxynonenal (HNE) can inhibit enzymes (Esterbauer et al., 1991) by chemical modification, which raises interesting questions about the fate of these 4-hydroxynonenal modified proteins. Since it is known that oxidized proteins are selectively degraded in mammalian cells, one may reasonably postulate that oxidatively (or 4-hydroxynonenal) modified proteins might be degraded by the same proteolytic machinery, the proteasomal system.

Section snippets

The proteasome

Mammalian cells appear to possess several major pathways for general protein degradation: lysosomal proteases, calcium-dependent proteases, and the proteasomal system. Proteins that enter cells from the outside as well as several intracellular proteins, especially long-lived ones or proteins from various organelles, are degraded within lysosomes. True intracellular proteins are degraded by the intracellular proteasomal system (Rock et al., 1994). The proteasomal system consists of the so called

Degradation of oxidized proteins

Oxidation can induce many changes in proteins, including amino acid modification, fragmentation or aggregation (Berlett and Stadtman, 1997; Davies, 1986; Davies, 1987; Davies and Delsignore, 1987; Davies et al., 1987a, Davies et al., 1987b; Dean et al., 1997; Grune et al., 1997; Huang et al., 1995; Shang et al., 1994; Stadtman, 1993). Some of these oxidative modifications cause an increased susceptibility of oxidized proteins towards proteolysis, possibly due to an increase in surface

HNE-modified proteins and the proteasomal degradation

Unfortunately the literature about the degradation of HNE-modified proteins is very limited. We performed some studies ourselves, demonstrating, that HNE-modified histones are degraded preferentially by the proteasomal system (Table 1). Obviously the recognition and the degradation of HNE-modified isolated histones is concentration dependent. In our experiments we were able to find a maximal degradation of histones (1 mg/ml) treated with 5 μM HNE. Such a bell-shaped proteolytic response by the

Protein cross-linking by HNE

As already mentioned, a fairly broad spectrum of protein aggregate formation initially occurs not due to covalent cross-links, but because of new hydrophobic and electrostatic interactions (Davies, 1987; Davies and Delsignore, 1987; Davies et al., 1987a, Davies et al., 1987b; Grune et al., 1997; Sommerburg et al., 1998). This aggregated material can then be chemically modified by a great variety of cellular metabolites, including aldehydic lipid peroxidation products (Grune et al., 1997;

Proteasome inhibition by HNE-cross-linked proteins

Interestingly HNE-modified proteins actually become poor substrates for the proteasome, after cross-linking reactions. This was revealed by studies from our group (Table 1), and others. We have reported that heavily oxidized and cross-linked protein aggregates accumulate in cells because they inhibit the proteasome (Sitte et al., 2000a, Sitte et al., 2000b, Sitte et al., 2000c). HNE-cross-linked proteins are also able to inhbit the turnover of other proteins by inhibiting the proteasome (

Conclusions

As discussed in this mini-review, HNE is a highly reactive lipid peroxidation product able to modify proteins and form intermolecular cross-linked protein aggregates. Whereas moderately HNE-modified proteins are degraded by the proteasomal system, extensively modified proteins form extensive cross-links and are poor substrates for proteasomal degradation. Moreover, such cross-linked proteins are able to inhibit the proteasome, and further impair cellular protein turnover. Despite our present

Acknowledgments

T.G. was supported by the DFG. K.J.A.D. was partially supported by NIH/NIEHS grant number ES03598.

References (69)

  • J. Gieche et al.

    Protein oxidation and proteolysis in RAW264.7 macrophages: Effects of PMA activation

    Biochim. Biophys. Acta

    (2001)
  • T. Grune et al.

    Peroxynitrite increases the degradation of aconitase and other cellular proteins by proteasome

    J. Biol. Chem.

    (1998)
  • T. Grune et al.

    Protein oxidation and proteolysis by the nonradical oxidants singlet oxygen or peroxynitrite

    Free Radic. Biol. Med.

    (2001)
  • T. Grune et al.

    Proteolysis in cultured liver epithelial cells during oxidative stress: Role of the multicatalytic proteinase complex, proteasome

    J. Biol. Chem.

    (1995)
  • T. Grune et al.

    Degradation of oxidized proteins in K562 human hematopoietic cells by proteasome

    J. Biol. Chem.

    (1996)
  • W. Hilt et al.

    Proteasomes: destruction as a programme

    TIBS

    (1996)
  • L.L. Huang et al.

    Degradation of differentially oxidized α-crystallins in bovine lens epithelial cells

    Exp. Eye Res.

    (1995)
  • J. Jahngen-Hodge et al.

    Regulation of ubiquitin-conjugating enzymes by glutathione following oxidative stress

    J. Biol. Chem.

    (1997)
  • P. Lasch et al.

    Hydrogen peroxide-induced structural alterations of Rnase A

    J. Biol. Chem.

    (2001)
  • D. Mahaffey et al.

    Discrimination between ubiquitin-dependent and ubiquitin-independent proteolytic pathways by the 26S proteasome subunit 5a

    FEBS Lett.

    (1999)
  • K. Okada et al.

    4-Hydroxy-2-nonenal-mediated impairment of intracellular proteolysis during oxidative stress

    J. Biol. Chem.

    (1999)
  • R.E. Pacifici et al.

    Protein degradation as an index of oxidative stress

    Meth. Enzymol.

    (1990)
  • R.E. Pacifici et al.

    Macroxyproteinase (MOP): A 670 kDa proteinase comlex that degrades oxidatively denatured proteins in red blood cells

    Free Radic. Biol. Med.

    (1989)
  • R.E. Pacifici et al.

    Hydrophobicity as the signal for selective degradation of hydroxyl radical modified hemoglobin by the multicatalytic proteinase complex, proteasome

    J. Biol. Chem.

    (1993)
  • J.M. Peters

    Proteasomes. Protein degradation machines of the cell

    TIBS

    (1994)
  • M. Rechsteiner et al.

    The multicatalytic and the 26S proteases

    J. Biol. Chem.

    (1993)
  • T. Reinheckel et al.

    Differential impairment of 20S and 26S proteasome activities in human hematopoietic K562 cells during oxidative stress

    Arch. Biochem. Biophys.

    (2000)
  • A.J. Rivett

    Intracellular distribution of proteasomes

    Curr. Opin. Immunol.

    (1998)
  • K.L. Rock et al.

    Inhibitors of proteasome block the degradation of most cell proteins and the generation of peptides on MHC class I molecules

    Cell

    (1994)
  • D.C. Salo et al.

    Superoxide dismutase undergoes proteolysis and fragmentation following oxidative modification and inactivation

    J. Biol. Chem.

    (1990)
  • R. Shringarpure et al.

    Ubiquitin conjugation is not required for the degradation of oxidised proteins by proteasome

    J. Biol. Chem.

    (2003)
  • W. Siems et al.

    Metabolic fate of 4-hydroxynonenal in hepatocytes: 1,4-Dihydroxynonene is not the main product

    J. Lip. Res.

    (1997)
  • N. Sitte et al.

    Proteasome-dependent degradation of oxidized proteins in MRC-5 fibroblasts

    FEBS Lett.

    (1998)
  • O. Sommerburg et al.

    Dose- and wavelength-dependent oxidation of crystallins by UV light – selective recognition and degradation by the 20S proteasome

    Free Radic. Biol. Med.

    (1998)
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