title: The cystine/cysteine cycle: a redox cycle regulating susceptibility versus resistance to cell death.
abstract: The glutathione-dependent system is one of the key systems regulating cellular redox balance, and thus cell fate. Cysteine, typically present in its oxidized form cystine in the extracellular space, is regarded as the rate-limiting substrate for glutathione (GSH) synthesis. Cystine is transported into cells by the highly specific amino-acid antiporter system xc-. Since Burkitt's Lymphoma (BL) cells display limited uptake capacity for cystine, and are thus prone to oxidative stress-induced cell death, we stably expressed the substrate-specific subunit of system xc-, xCT, in HH514 BL cells. xCT-overexpressing cells became highly resistant to oxidative stress, particularly upon GSH depletion. Contrary to previous predictions, the increase of intracellular cysteine did not affect the cellular GSH pool, but concomitantly boosted extracellular cysteine concentrations. Even though cells were depleted of bulk GSH, xCT overexpression maintained cellular integrity by protecting against lipid peroxidation, a very early event in cell death progression. Our results show that system xc- protects against oxidative stress not by elevating intracellular GSH levels, but rather creates a reducing extracellular environment by driving a highly efficient cystine/cysteine redox cycle. Our findings show that the cystine/cysteine redox cycle by itself must be viewed as a discrete major regulator of cell survival.
authors.affiliation: GSF-Forschungszentrum für Umwelt und Gesundheit, Institut für Klinische Molekularbiologie und Tumorgenetik, München, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Banjac
authors.forename: T
authors.initials: T
authors.lastname: Perisic
authors.forename: H
authors.initials: H
authors.lastname: Sato
authors.forename: A
authors.initials: A
authors.lastname: Seiler
authors.forename: S
authors.initials: S
authors.lastname: Bannai
authors.forename: N
authors.initials: N
authors.lastname: Weiss
authors.forename: P
authors.initials: P
authors.lastname: Kölle
authors.forename: K
authors.initials: K
authors.lastname: Tschoep
authors.forename: R D
authors.initials: RD
authors.lastname: Issels
authors.forename: P T
authors.initials: PT
authors.lastname: Daniel
authors.forename: M
authors.initials: M
authors.lastname: Conrad
authors.forename: G W
authors.initials: GW
authors.lastname: Bornkamm
mesh_terms: D027182:Amino Acid Transport System y+ / Q000378:metabolism*; D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D017209:Apoptosis; D015152:Blotting, Northern; D019328:Buthionine Sulfoximine / Q000494:pharmacology; D020169:Caspases / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D003545:Cysteine / Q000378:metabolism*; D003553:Cystine / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D018698:Glutamic Acid / Q000494:pharmacology; D005978:Glutathione / Q000378:metabolism*; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D015151:Immunoblotting; D015227:Lipid Peroxidation / Q000187:drug effects; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D051379:Mice; D016877:Oxidants / Q000494:pharmacology; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D017382:Reactive Oxygen Species / Q000378:metabolism