Induction of cystine-glutamate transporter xc- by human immunodeficiency virus type 1 transactivator protein tat in retinal pigment epithelium.
OBJECTIVE
The transactivator protein Tat encoded by the human immunodeficiency virus-1 (HIV-1) genome reduces glutathione levels in mammalian cells. Because the retina contains large amounts of glutathione, a study was undertaken to determine the influence of Tat on glutathione levels, gamma-glutamyl transpeptidase activity, and the expression and activity of the cystine-glutamate transporter xc- in the human retinal pigment epithelial cell line ARPE-19 and in retina from Tat-transgenic mice.


METHODS
The transport function of xc- was measured as glutamate uptake in the absence of Na+. mRNA levels for xCT and 4F2hc, the two subunits of system xc-, were monitored by RT-PCR and Northern blot and protein levels by Western blot. The expression pattern of xCT and 4F2hc in the mouse retina was analyzed by immunofluorescence.


RESULTS
Expression of Tat in ARPE-19 cells led to a decrease in glutathione levels and an increase in gamma-glutamyl transpeptidase activity. The transport function of xc- was upregulated, and this increase was accompanied by increases in the levels of mRNAs for xCT and 4F2hc and in corresponding protein levels. The influence of Tat on the expression of xc- was independent of the cellular status of glutathione. Most of these findings were confirmed in the retina of Tat-transgenic mice.


CONCLUSIONS
Expression of HIV-1 Tat in the retina decreases glutathione levels and increases gamma-glutamyl transpeptidase activity. Tat also upregulates the expression of system xc-. Glutathione levels may be decreased and the expression of xc- enhanced in the retina of patients with HIV-1 infection, leading to oxidative stress and excitotoxicity.
Department of Biochemistry, Medical College of Georgia, Augusta 30912-9947, USA.
Christy C
CC
Bridges
Huankai
H
Hu
Seiji
S
Miyauchi
Umapathy N
UN
Siddaramappa
Malliga E
ME
Ganapathy
Leszek
L
Ignatowicz
Dennis M
DM
Maddox
Sylvia B
SB
Smith
Vadivel
V
Ganapathy
D027182:Amino Acid Transport System y+ / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D027282:Fusion Regulatory Protein 1, Heavy Chain / Q000235:genetics / Q000378:metabolism; D015696:Gene Products, tat / Q000235:genetics / Q000502:physiology*; D005721:Glutamate-Cysteine Ligase / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D015497:HIV-1 / Q000378:metabolism*; D006706:Homeostasis; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D008822:Mice, Transgenic / Q000235:genetics; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000378:metabolism / Q000821:virology*; D012333:RNA, Messenger / Q000378:metabolism; D012160:Retina / Q000378:metabolism; D015854:Up-Regulation; D005723:gamma-Glutamyltransferase / Q000378:metabolism; D054322:tat Gene Products, Human Immunodeficiency Virus
D027182:Amino Acid Transport System y+; D027282:Fusion Regulatory Protein 1, Heavy Chain; D015696:Gene Products, tat; D007527:Isoenzymes; D012333:RNA, Messenger; C118895:SLC7A11 protein, human; C492255:Slc7a11 protein, mouse; D054322:tat Gene Products, Human Immunodeficiency Virus; D005723:gamma-Glutamyltransferase; D005721:Glutamate-Cysteine Ligase; D005978:Glutathione