title: Inhibition of glutamine synthetase triggers apoptosis in asparaginase-resistant cells.
abstract: The resistance to L-asparaginase (ASNase) has been associated to the overexpression of asparagine synthetase (AS), although the role played by other metabolic adaptations has not been yet defined. Both in ASNase-sensitive Jensen rat sarcoma cells and in ARJ cells, their ASNase-resistant counterparts endowed with a five-fold increased AS activity, ASNase treatment rapidly depletes intracellular asparagine. Under these conditions, cell glutamine is also severely reduced and the activity of glutamine synthetase (GS) is very low. After 24 h of treatment, while sensitive cells have undergone massive apoptosis, ARJ cells exhibit a marked increase in GS activity, associated with overexpression of GS protein but not of GS mRNA, and a partial restoration of glutamine and asparagine. However, when ARJ cells are treated with both ASNase and L-methionine-sulfoximine (MSO), an inhibitor of GS, no restoration of cell amino acids occurs and the cell population undergoes a typical apoptosis. No toxicity is observed upon MSO treatment in the absence of ASNase. The effects of MSO are not referable to depletion of cell glutathione or inhibition of AS. These findings indicate that, in the presence of ASNase, the inhibition of GS triggers apoptosis. GS may thus constitute a target for the suppression of ASNase-resistant phenotypes.
authors.affiliation: Units of General and Clinical Pathology, Department of Experimental Medicine, Universita degli Studi di Parma, Parma, Italy.
authors.forename: Bianca Maria
authors.initials: BM
authors.lastname: Rotoli
authors.forename: Jacopo
authors.initials: J
authors.lastname: Uggeri
authors.forename: Valeria
authors.initials: V
authors.lastname: Dall'Asta
authors.forename: Rossana
authors.initials: R
authors.lastname: Visigalli
authors.forename: Amelia
authors.initials: A
authors.lastname: Barilli
authors.forename: Rita
authors.initials: R
authors.lastname: Gatti
authors.forename: Guido
authors.initials: G
authors.lastname: Orlandini
authors.forename: Gian C
authors.initials: GC
authors.lastname: Gazzola
authors.forename: Ovidio
authors.initials: O
authors.lastname: Bussolati
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects*; D001215:Asparaginase / Q000494:pharmacology*; D001483:Base Sequence; D015153:Blotting, Western; D002455:Cell Division / Q000187:drug effects; D017931:DNA Primers; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005974:Glutamate-Ammonia Ligase / Q000037:antagonists & inhibitors*; D010641:Phenotype; D016133:Polymerase Chain Reaction
chemical_list: D000596:Amino Acids; D017931:DNA Primers; D004791:Enzyme Inhibitors; D001215:Asparaginase; D005974:Glutamate-Ammonia Ligase