BUTHIONINE SULFOXIMINE ENHANCES GLUTATHIONE-BUT ATTENUATES GLUTAMATE-STIMULATED CELL-PROLIFERATION

Buthionine sulfoximine (BSO) inhibits proliferation of human lung carc inoma A549 cells, and exogenous glutathione (GSH) overcomes the antipr oliferative effect. The BSO antiproliferation may result from inhibiti on of cellular uptake of amino acids, and the antagonistic effect of G SH would result from supplementation of amino acids via the gamma-glut amyl cycle. To explore these possibilities, the present study was unde rtaken to determine effects of BSO on glutamate- and GSH-stimulated ce ll proliferation, A549 cells were cultured in a glutamine-deficient Du lbecco's modified Eagle's medium (Gln(-)-DMEM), in which they did not proliferate. Addition of glutamate or GSH in the medium to a concentra tion of 4 mM stimulated cell proliferation, BSO of 0.1 mM enhanced the GSH-stimulated cell proliferation and attenuated the glutamate-stimul ated cell proliferation. This BSO effect correlated with changes in ce llular glutamate levels; that is, BSO increased and decreased glutamat e concentrations, respectively, in GSH- and glutamate-stimulated cells , GSH or glutamate alone significantly increased cellular GSH levels, BSO depleted cellular GSH in both GSH- and glutamate-stimulated cells to the same level. These changes in GSH levels did not correlate with the respective growth modulatory effect. Because BSO inhibits cellular uptake of some amino acids and the A549 cells contain high levels of gamma-glutamyl transpeptidase activity, the results suggest that the B SO inhibition of glutamate-stimulated cell proliferation may result fr om decreased glutamate uptake. GSH would supplement the cells with glu tamate via the gamma-glutamyl pathway to bypass the inhibition of amin o acid uptake and overcome the BSO-antiproliferative effect.