Expression of the cystine-glutamate exchanger (xc-) in retinal ganglion cells and regulation by nitric oxide and oxidative stress.
The cystine-glutamate exchanger, system x(c)(-), mediates the Na(+)-independent exchange of cystine into cells, coupled to the efflux of intracellular glutamate. System x(c)(-) plays a critical role in glutathione homeostasis. Early studies of brain suggested that system x(c)(-) was present primarily in astrocytes but not neurons. More recent work indicates that certain brain neurons have an active system x(c)(-). In the retina, system x(c)(-) has been demonstrated in Müller and retinal pigment epithelial cells. We have recently suggested that two protein components of system x(c)(-), xCT and 4F2hc, are present in ganglion cells of the intact retina. Here, we have used (1) molecular and immunohistochemical assays to determine whether system x(c)(-) is present in primary ganglion cells isolated from neonatal mouse retinas and (2) functional assays to determine whether its activity is regulated by oxidative stress in a retinal ganglion cell line (RGC-5). Primary mouse ganglion cells and RGC-5 cells express xCT and 4F2hc. RGC-5 cells take up [(3)H]glutamate in the absence of Na(+), and this uptake is blocked by known substrates of system x(c)(-) (glutamate, cysteine, cystine, quisqualic acid). Treatment of RGC-5 cells with NO and reactive oxygen species donors leads to increased activity of system x(c)(-) associated with an increase in the maximal velocity of the transporter with no significant change in the substrate affinity. This is the first report of system x(c)(-) in primary retinal ganglion cells and RGC-5 cells. Oxidative stress upregulates this transport system in RGC-5 cells, and the process is associated with an increase in xCT mRNA and protein but no change in 4F2hc mRNA or protein.
Dun
Y
Y
Department of Cellular Biology and Anatomy, Medical College of Georgia, 1459 Laney-Walker Blvd., CB 2820, Augusta, GA 30912-2000, USA.
Mysona
B
B
Van Ells
T
T
Amarnath
L
L
Ola
M Shamsul
MS
Ganapathy
V
V
Smith
S B
SB
D027182:Amino Acid Transport System y+ / Q000235:genetics* / Q000378:metabolism*; D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D001483:Base Sequence; D002460:Cell Line; D002478:Cells, Cultured; D017931:DNA Primers / Q000235:genetics; D027282:Fusion Regulatory Protein 1, Heavy Chain / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D005978:Glutathione / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D009569:Nitric Oxide / Q000494:pharmacology*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D018384:Oxidative Stress; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017382:Reactive Oxygen Species / Q000494:pharmacology; D012165:Retinal Ganglion Cells / Q000187:drug effects* / Q000378:metabolism*; D026423:S-Nitroso-N-Acetylpenicillamine / Q000494:pharmacology
D027182:Amino Acid Transport System y+; D000975:Antioxidants; D017931:DNA Primers; D027282:Fusion Regulatory Protein 1, Heavy Chain; D020030:Nitric Oxide Donors; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; C492255:Slc7a11 protein, mouse; D009569:Nitric Oxide; D026423:S-Nitroso-N-Acetylpenicillamine; D005978:Glutathione