Tumor necrosis factor stimulates system XAG- transport activity in human endothelium.
System xAG- is responsible for the carrier-mediated Na(+)-independent transport of anionic amino acids such as glutamate and aspartate across the plasma membrane of cells. In order to examine a possible role for cytokines in regulating System xAG- activity, the effect of TNF on [3H]glutamate transport in cultured human umbilical vein endothelial cells (HUVECs) was studied. Carrier-mediated glutamate uptake was accomplished by two high-affinity carriers, predominantly by a Na(+)-independent carrier (System xAG-, 75% of total glutamate uptake) and, to a lesser extent by a Na(+)-dependent carrier (System XAG-, 24% of total uptake). TNF treatment (10 ng/ml for 10 hr) resulted in an 80% increase in Na(+)-independent glutamate transport activity with no change in System XAG- activity. The TNF stimulatory effect was blocked by actinomycin D and cycloheximide. TNF treatment increased System xAG- glutamate transporter Vmax by 51% (control Vmax = 2359 +/- 345 pmole/mg protein/min vs TNF Vmax = 3569 +/- 436 pmole/mg protein/min, P < 0.01) without altering transporter affinity (control Km, 229 +/- 40 microM glutamate vs TNF Km = 224 +/- 60 microM glutamate, P = NS). The protein kinase C (PKC) inhibitor chelerythrine chloride had no effect on the TNF-stimulated glutamate transport, indicating that the augmented glutamate transport was not mediated by PKC activation. These data indicate that the TNF-stimulated glutamate transport in HUVECs requires do novo protein synthesis, possibly of the System xAG- transporter protein itself. Accelerated glutamate transport provides a precursor for the biosynthesis of macromolecules and glutamine.
Pan
M
M
Division of Surgical Oncology, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA.
Wasa
M
M
Souba
W W
WW
D001692:Biological Transport / Q000187:drug effects; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism*; D006801:Humans; D012964:Sodium / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D014409:Tumor Necrosis Factor-alpha; D018698:Glutamic Acid; D012964:Sodium