title: Multiple adaptive mechanisms affect asparagine synthetase substrate availability in asparaginase-resistant MOLT-4 human leukaemia cells.
abstract: Childhood acute lymphoblastic leukaemia is treated by combination chemotherapy with a number of drugs, almost always including the enzyme L-asparaginase (ASNase). Although the initial remission rate is quite high, relapse and associated drug resistance remain a problem. In vitro studies have demonstrated an adaptive increase in asparagine synthetase (AS) expression in ASNase-resistant cells, which is believed to permit ASNase-resistant human leukaemia cells to survive in vivo. The present results, obtained with ASNase-sensitive and -resistant human MOLT-4 leukaemia cell lines, illustrate that several other adaptive processes occur to provide sufficient amounts of the AS substrates, aspartate and glutamine, required to support this increased enzymic activity. In both cell populations, aspartate is derived almost exclusively from intracellular sources, whereas the necessary glutamine arises from both intracellular and extracellular sources. Transport of glutamine into ASNase-resistant cells is significantly enhanced compared with the parental cells, whereas amino acid efflux (e.g. asparagine) is reduced. Most of the adaptive change for the amino acid transporters, Systems A, ASC and L, is rapidly (12 h) reversed following ASNase removal. The enzymic activity of glutamine synthetase is also enhanced in ASNase-resistant cells by a post-transcriptional mechanism. The results demonstrate that there are several sites of metabolic adaptation in ASNase-treated leukaemia cells that serve to promote the replenishment of both glutamine and asparagine.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Florida College of Medicine, Gainesville, FL 32610-0245, USA.
authors.forename: A M
authors.initials: AM
authors.lastname: Aslanian
authors.forename: M S
authors.initials: MS
authors.lastname: Kilberg
mesh_terms: D000596:Amino Acids / Q000737:chemistry / Q000378:metabolism; D001215:Asparaginase / Q000494:pharmacology*; D001217:Aspartate-Ammonia Ligase / Q000378:metabolism*; D001224:Aspartic Acid / Q000737:chemistry; D001692:Biological Transport; D002455:Cell Division; D002462:Cell Membrane / Q000378:metabolism; D002470:Cell Survival; D004305:Dose-Response Relationship, Drug; D004351:Drug Resistance / Q000235:genetics; D005434:Flow Cytometry; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D005973:Glutamine / Q000737:chemistry; D006801:Humans; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000201:enzymology*; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D013379:Substrate Specificity; D014407:Tumor Cells, Cultured
chemical_list: D000596:Amino Acids; D012333:RNA, Messenger; D005973:Glutamine; D001224:Aspartic Acid; D012313:RNA; D001215:Asparaginase; D001217:Aspartate-Ammonia Ligase; D005974:Glutamate-Ammonia Ligase