Molecular Mechanisms and Clinical Implications of Reversible Protein S -Glutathionylation

Abstract

Sulfhydryl chemistry plays a vital role in normal biology and in defense of cells against oxidants, free radicals, and electrophiles. Modification of critical cysteine residues is an important mechanism of signal transduction, and perturbation of thiol–disulfide homeostasis is an important consequence of many diseases. A prevalent form of cysteine modification is reversible formation of protein mixed disulfides (protein–SSG) with glutathione (GSH). The abundance of GSH in cells and the ready conversion of sulfenic acids and S-nitroso derivatives to S-glutathione mixed disulfides suggests that reversible S-glutathionylation may be a common feature of redox signal transduction and regulation of the activities of redox sensitive thiol-proteins. The glutaredoxin enzyme has served as a focal point and important tool for evolution of this regulatory mechanism, because it is a specific and efficient catalyst of protein–SSG deglutathionylation. However, mechanisms of control of intracellular Grx activity in response to various stimuli are not well understood, and delineation of specific mechanisms and enzyme(s) involved in formation of protein–SSG intermediates requires further attention. A large number of proteins have been identified as potentially regulated by reversible S-glutathionylation, but only a few studies have documented glutathionylation-dependent changes in activity of specific proteins in a physiological context. Oxidative stress is a hallmark of many diseases which may interrupt or divert normal redox signaling and perturb protein–thiol homeostasis. Examples involving changes in S-glutathionylation of specific proteins are discussed in the context of diabetes, cardiovascular and lung diseases, cancer, and neurodegenerative diseases. Antioxid. Redox Signal, 10, 1941–1988.

Introduction

Potential Mechanisms of Protein–SSG Formation

• Thiol-disulfide exchange

• Sulfenic acid intermediates

• Sulfenylamide intermediates

• Thiyl radical intermediates

• Thiosulfinate intermediates

• S-Nitrosylated intermediates

Potential Catalysis of Protein Glutathionylation

• GSTπ

• Grx

• Flavoprotein sulfhydryl oxidease (QSOX)

• Other potential mechanisms of catalysis/control of protein S-glutathionylation

Proteomics of Discovery of Potential Protein–SSG Intermediates

Deglutathionylation (Reversal) of Protein–SSG: Properties of the Glutaredoxin Enzymes

Glutaredoxin Mechanism of Action

Modualtion of Grx Expression

Diabetes and Implications of Changes in S-Glutathionylation Status

• Mechanism of hyperglycemic damage and ROS

• Glucose metabolism: aldose reductase–SSG (Fig. 3, step 1a)

• K⁺ channels: Grx regulated (Fig. 3, step 2a)

• Ca²⁺ channels: SERCA-SSG and Grx-reversible RyR-SSG (Fig. 3, step 3a)

• Insulin exocytosis: Grx regulated (Fig. 3 step 6a)

• Insulin receptor: Grx-reversible PTP1B-SSG (Fig. 3, step 6b)

• Signal transduction [Fig. 3, Ras-SSG (step 7b), MEKK-SSG (step 8b), c-Jun-SSG (step 9b), Akt-SSG (step 10b), IKK-SSG (step 11b), NF-κB(p50)-SSG (steps 5a and 12b), and PKC-SSG (step 4a)]

• Summary and discussion: Grx as a therapeutic target in diabetic complications

Cardiovascular Diseases and Alterations in Protein-S-Glutathionylation Status

• Myocardial infarction

• Preconditioning

• Nonspecific oxidative injury

• Cardiac hypertrophy

• Atherosclerosis

Implications of Protein S-Glutathionylation in Lung Disease

• Tobacco exposure

• Hyperoxic injury

• Inflammation

• Fibrotic and granulomatous diseases

• Chronic obstructuve pulmonary disease (COPD)

• Summary

Implications of Reversible Protein S-Glutathionylation in Cancer

• Thiol oxidation and cancer

• S-Glutathionylation and signal transduction in cancer

• S-Glutathionylation and modulation of kinase/phosphatase signaling pathways

• S-Glutathionylation and modulation of the proteasome pathway

• S-Glutathionylation and modulation of transcription factors (c-Jun, NF-κB, p53, AP-1)

• Modulation of S-glutathionylation as a chemotherapeutic strategy for cancer

• Conclusions

Implications of Protein S-Glutathionylation in Neurodegenerative Diseases

• Oxidative stress and neurodegeneration

• Sources of reactive oxygen and nitrogen species in brain

• Glutaredoxin and neurodegeneration

• Proteins associated with neurodegeneration that are redox regulated through S-glutathionylation

Summary and Conclusions

Frontier Areas of Investigation