S-Glutathionylation of the Rpn2 Regulatory Subunit Inhibits 26 S Proteasomal Function

Abstract

Although increased intracellular concentrations of hydrogen peroxide (H 2 O 2 ) are associated with inhibition of 26 S proteasomal activity, the mechanisms responsible for such effects have not been well delineated. In the present studies, we found that direct exposure of purified 26 S proteasomes to H 2 O 2 had negligible effects on their activity, whereas incubation with glutathione and H 2 O 2 produced >80% decrease in chymotrypsin-like and trypsin-like activities. Rpn1 and Rpn2, which are subunits of the 19 S regulatory particle, undergo S-glutathionylation after exposure of purified 26 S proteasomes to glutathione and H 2 O 2 , as well as in HEK 293 cells and neutrophils incubated with H 2 O 2 . Increased oxidation of Rpn1 and Rpn2 cysteine thiols was also found in lung extracts from mice in which catalase was inactivated, a condition associated with augmented intracellular concentrations of H 2 O 2 and diminished 26 S proteasomal activity. Although unoxidized Rpn2 enhanced 20 S proteolytic function in vitro, such potentiation was not found when the 20 S core particle was incubated with oxidized Rpn2. The composition of 26 S proteasomes was not altered after exposure to glutathione and H 2 O 2 , with similar amounts of Rpn1 and Rpn2 in control or oxidized 26 S proteasomal complexes. These findings identify S-glutathionylation of Rpn2 as a contributory mechanism for H 2 O 2 -induced inhibition of 26 S proteasomal function.The ubiquitin-proteasomal system is a major pathway for protein degradation and is involved in multiple cellular processes, including cell cycle control, expression of cell surface receptors, and regulation of intracellular levels of structural and regulatory proteins and transcription factors (1-6). The 26 S proteasome is composed of two main components, a proteolytic 20 S core particle (CP) 2 and an ATPase containing 19 S regulatory particle (RP) (7-10). Ubiquitinated proteins are unfolded in the 19 S RP and then translocated into the 20 S CP where they are degraded. The 20 S CP is composed of four heptameric rings of ␣ and ␤ subunits, with the two inner ␤ rings having proteolytic activity. The 19 S RP consists of a lid and base subcomplex, with the base subcomplex, including the nonenzymatic Rpn1 and Rpn2 toroids, surrounded by six AAA-type ATPases. Rpn1 and Rpn2 appear to play a major regulatory role by modulating the translocation and subsequent degradation of ubiquitinated substrates in the proteolytic core of the 20 S CP (7,(11)(12)(13)(14)(15).Decreased 26 S proteasomal activity, resulting in the accumulation of intracellular proteins, has been associated with aging (16, 17) and with pathophysiologic processes, including heart failure, neurodegenerative diseases, and alcohol induced liver injury (18 -20). A number of recent studies have shown that time-limited inhibition of the 26 S proteasome is beneficial as a therapeutic intervention for malignancies, such as multiple myeloma, and in reducing inflammation and cell injury associated with ischemia-reperfusion injury and transplanta...

Oxidative Stress Inhibits Vascular KATP Channels by S-Glutathionylation

“…The Kir6.1 S-glutathionylation was further tested with the streptavidin pull-down assay (26). The A10 vascular smooth muscle cell line, in which the Kir6.1/SUR2B channel was endogenously expressed (17,27), was loaded with BioGEE (250 M) for 1 h followed by an H 2 O 2 (750 M) challenge for 15 min.…”

S-glutathionylation: relevance in diabetes and potential role as a biomarker

“…S-glutathionylation of S100A9 regulates its inflammatory activity in neutrophils (Lim et al, 2010). In another study, it was found that increased levels of H 2 O 2 results in diminished proteasomal activity of 26S proteasome via S-glutathionylation of its regulatory subunit Rpn2 (Zmijewski et al, 2009). A recent report describes how stimulated neutrophils present deglutathionylated actin and associated polymerization, neutrophil polarization, chemotaxis, adhesion and phagocytosis.…”

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