Asparagine synthetase expression alone is sufficient to induce l-asparaginase resistance in MOLT-4 human leukaemia cells.
Childhood acute lymphoblastic leukaemia (ALL) is treated by combination chemotherapy with a number of drugs, always including the enzyme L-asparaginase (ASNase). Although the initial remission rate is quite high, relapse and associated drug resistance are a significant problem. In vitro studies have demonstrated increased asparagine synthetase (AS) expression in ASNase-resistant cells, which has led to the hypothesis that elevated AS activity permits drug-resistant survival. The data presented show that not only is elevated AS expression a property of ASNase-resistant MOLT-4 human leukaemia cells, but that short-term (12 h) treatment of the cells with ASNase causes a relatively rapid induction of AS expression. The results also document that the elevated expression of AS in ASNase-resistant cells is not fully reversible, even 6 weeks after ASNase removal from the culture medium. Furthermore, ASNase resistance, assessed as both drug-insensitive cell growth rates and decreased drug-induced apoptosis, parallels this irreversible AS expression. Mimicking the elevated AS activity in ASNase-resistant cells by overexpression of the human AS protein by stable retroviral transformation of parental MOLT4 cells is sufficient to induce the ASNase-resistance phenotype. These data document that ASNase resistance in ALL cells is a consequence of elevated AS expression and that although other drug-induced metabolic changes occur, they are secondary to the increased asparagine biosynthetic rate.
Aslanian
A M
AM
Department of Biochemistry and Molecular Biology, Box 100245, University of Florida College of Medicine, Gainesville, FL 32610-0245, USA.
Fletcher
B S
BS
Kilberg
M S
MS
D000970:Antineoplastic Agents / Q000633:toxicity*; D017209:Apoptosis / Q000187:drug effects; D001215:Asparaginase / Q000633:toxicity*; D001217:Aspartate-Ammonia Ligase / Q000235:genetics* / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002999:Clone Cells; D019008:Drug Resistance, Neoplasm; D005822:Genetic Vectors; D006801:Humans; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma; D011994:Recombinant Proteins / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D011994:Recombinant Proteins; D001215:Asparaginase; D001217:Aspartate-Ammonia Ligase