Regulation ofl-Cystine Transport and Intracellular GSH Level by a Nitric Oxide Donor in Primary Cultured Rabbit Conjunctival Epithelial Cell Layers

Abstract

L-Cystine is transported by both Na(+)-dependent and -independent amino acid transport systems in RCECs. At low substrate concentrations, L-cystine uptake was higher from apical than basolateral fluid. Permeability studies indicated net absorption of L-cystine across RCECs. SNAP caused significant increases in both L-cystine uptake and intracellular GSH level, which occurred concomitantly with elevation of both catalytic and regulatory subunits of GCS. Understanding sulfur amino acid precursor-dependent cellular mechanisms of GSH homeostasis would be of value in devising GSH-based treatment for conjunctival or other ocular disorders.

Expression of the cystine-glutamate exchanger (xc −) in retinal ganglion cells and regulation by nitric oxide and oxidative stress

“…For these experiments cells were treated on the second day following seeding with various NO donors: 3-nitroso-N-acetylpenicillamine (SNAP), S-nitrosoglutathione (SNOG), or 3-morpholinosydnonimine hydrochloride (SIN-1) at concentrations of 10 μM, 50 μM, 100 μM and 500 μM, for 4, 6, 18 or 24 hours. Additional experiments were carried out using three other donors of reactive oxygen species (ROS), since oxidative stress has been shown to upregulate system x c -in other systems [4][5][6][7][8][9]. These ROS were menadione sodium bisulfite [5.4 μM], hydrogen peroxide prepared from a 30% (W/W) solution (final concentration 0.0001%), and xanthine sodium salt/xanthine oxidase (concentrations 10 μM and 2 mU/ml, respectively); the treatment time was 6 h. These concentrations were selected based on earlier reports of toxicity to retinal cells [30].…”

“…As GSH is necessary for protection of cells against oxidative damage, system x c -assumes significance as a transport system closely associated with the cellular antioxidant machinery. The relevance of system x c -to cellular antioxidant processes is underscored by its upregulation in multiple cell types exposed to oxidative stress [4][5][6][7][8][9].…”

Induction of Cystine-Glutamate Transporter xc−by Human Immunodeficiency Virus Type 1 Transactivator Protein Tat in Retinal Pigment Epithelium

“…[5][6][7][8][9] The relevance of this transport system to cellular antioxidant processes is highlighted by the observations that cells exposed to oxidative stress upregulate this transport system. This has been shown in a variety of cell and tissue types, including macrophages, 10 retinal pigment epithelial cells, 7 conjunctival epithelial cells, 11 the blood-brain barrier, 12 and the blood-retinal barrier. 13 The transcription factor Nrf2 participates in this oxidant-induced upregulation of x c Ϫ .…”

Cystine and glutamate transport in renal epithelial cells transfected with human system x—c

“…However, under conditions of oxidative stress, the transport activity of this carrier appears to be upregulated [9,10,[13][14][15][16][17][18][19][20], possibly via an amino acid response element [21]. As a result of this up-regulation, an increased number of cystine molecules could be transported into the cells, which, in turn, would provide (after intracellular reduction) an increased number of molecules of cysteine (the rate-limiting substrate) for glutathione (GSH) synthesis [3,22].…”