Elevation of glutathione in phenylalanine mustard-resistant murine L1210 leukemia cells.
Murine L1210 leukemia cells resistant to the antineoplastic agent L-phenylalanine mustard have a 1.5-2.0-fold elevation in their cellular GSH and GSSG content as compared to drug-sensitive cells. Cellular uptake of L-[U-14C]cystine and its incorporation into GSH of the resistant tumor are correspondingly elevated. Synthesis of gamma-glutamylcysteine, GSH, and GSSG is elevated 1.5-2.0-fold in cell-free preparations of the resistant tumor. This increased synthesis of GSH is attributed to increased cellular content (1.6-fold) of gamma-glutamylcysteine synthetase. GSH synthetase activity is equivalent in both drug-sensitive and -resistant cells. Investigation into the hydrolysis of selected peptides by cell-free preparations of both sensitive and resistant tumors suggest that aminopeptidase M participates in the formation of L-cysteine from L-Cys-Gly. This is supported by the observation that these preparations readily degrade L-Leu-p-nitroanilide and L-Ala-L-Ala-L-Ala, known substrates for aminopeptidase M, but not dipeptidase. The failure of the tumors to degrade Gly-D-Ala, a dipeptidase substrate, and the marked inhibition of L-Ala-Gly, L-Cys-Gly, and L-Ala-L-Ala-L-Ala hydrolysis by Bestatin further support a role for aminopeptidase M in the generation of L-cysteine from L-Cys-Gly. These results suggest that the drug-resistant tumor cell has developed an efficient mechanism for maintenance of elevated GSH which involves both gamma-glutamyl transpeptidase-initiated catabolism of GSH to cysteine and its reutilization by gamma-glutamylcysteine synthetase.
Ahmad
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Laboratory of Pharmacology and Experimental Therapeutics, National Cancer Institute, Bethesda, Maryland 20892.
Okine
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Najarian
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Vistica
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D000818:Animals; D003545:Cysteine / Q000378:metabolism; D004151:Dipeptides / Q000378:metabolism; D004351:Drug Resistance; D005978:Glutathione / Q000031:analogs & derivatives / Q000096:biosynthesis / Q000378:metabolism*; D019803:Glutathione Disulfide; D007700:Kinetics; D007939:Leukemia L1210 / Q000378:metabolism*; D008558:Melphalan / Q000494:pharmacology*; D051379:Mice
D004151:Dipeptides; D005978:Glutathione; D003545:Cysteine; C017341:gamma-glutamylcysteine; D008558:Melphalan; D019803:Glutathione Disulfide