The ectoenzyme gamma-glutamyl transpeptidase regulates antiproliferative effects of S-nitrosoglutathione on human T and B lymphocytes

Expression of the ectoenzyme gamma-glutamyl transpeptidase (GGT) is regulat ed on T lymphocytes. It is present at a low level on naive T cells, at a hi gh level on activated T cells, and at an intermediate level on resting memo ry T cells, GGT cleaves the glutamyl group from glutathione, which is the f irst step in the uptake of extracellular glutathione. In vitro, purified GG T also metabolizes the naturally occurring nitrosothiol, S-nitrosoglutathio ne (GSNO). Because of this relationship, the effects of cellular GGT on the metabolism of and cellular response to GSNO were tested. The GGT-negative lymphoblasts Ramos and SupT1 were transfected with cDNA for human GGT, In t he presence of cells lacking GGT, GSNO is extremely stable. In contrast, GG T-expressing cells rapidly metabolize GSNO leading to nitric oxide release. The nitric oxide causes a rapid (<2-h) inhibition of DNA synthesis. There is a concomitant decrease in the concentration of intracellular deoxyribonu cleotides, suggesting that one effect of the nitric oxide generated from GS NO is the previously described inactivation of the enzyme ribonucleotide re ductase, GSNO also caused a rapid, GGT-dependent cytostatic effect in Hut-7 8, a human T cell lymphoma, as well as in activated peripheral blood T cell s, Although DNA synthesis was decreased to 16% of control values in anti-CD 3-stimulated Hut-78, the production of IL-2 was unchanged by GSNO, These da ta show that GGT, a regulated ectoenzyme on T cells, controls the rate of n itric oxide production from GSNO and thus markedly affects the physiologica l response to this biologically active nitrosothiol.