Role of Glutamine Depletion in Directing Tissue-specific Nutrient Stress Responses to L-Asparaginase

Abstract

L-Asparaginase is important in the induction regimen for treating acute lymphoblastic leukemia. Cytotoxic complications are clinically significant problems lacking mechanistic insight. To reveal tissue-specific molecular responses to this drug, mice were administered asparaginase from either Escherichia coli (clinically used) or Wolinella succinogenes (novel, glutaminasefree form). Both enzymes abolished serum asparagine, but only the E. coli form reduced circulating glutamine. E. coli asparaginase reduced protein synthesis in liver and spleen but not pancreas via increased phosphorylation of the translation factor eIF2. In contrast, treatment with Wolinella caused no untoward changes in protein synthesis in any tissue examined. Treating mice deleted for the eIF2 kinase, GCN2, with the E. coli enzyme showed eIF2 phosphorylation to be GCN2-dependent, but only initially. Furthermore, although eIF2 phosphorylation was not increased in the pancreas or by Wolinella asparaginase, expression of the amino acid stress response genes, asparagine synthetase and CHOP/GADD153, increased as a result of both enzymes, even in tissues demonstrating no change in eIF2 phosphorylation. Finally, signaling downstream of the mammalian target of rapamycin kinase was repressed in liver and pancreas by E. coli but not Wolinella asparaginase. These data demonstrate that the nutrient stress response to asparaginase is tissuespecific and exacerbated by glutamine depletion. Importantly, increased expression of asparagine synthetase and CHOP does not require eIF2 phosphorylation, signifying alternate or auxiliary means of inducing gene expression under conditions of amino acid depletion in the whole animal.

Glucocorticoid resistance in T-lineage acute lymphoblastic leukaemia is associated with a proliferative metabolism

“…Finally, GLUL expression is induced by GCs (Harmon and Thompson, 1982) and we have recently reported that reduced expression of this gene is associated with adverse outcome in B-lineage ALL (Hoffmann et al, 2008). The importance of glutamine in ALL is highlighted by the fact that a significant proportion of the clinical efficacy of L-asparaginase, a cornerstone of therapy for this disease, is actually due to the glutaminase activity contained within such preparations (Reinert et al, 2006). The current data suggest that changes to amino-acid metabolism are not only fundamental to the leukemic phenotype but may also contribute to GC resistance.…”

GCN2 Protein Kinase Is Required to Activate Amino Acid Deprivation Responses in Mice Treated with the Anti-cancer Agent l-Asparaginase

“…Not PERK-Previously, we showed that treatment with asparaginase activates p-eIF2 in liver and spleen but not pancreas (4). In that study, a slight increase in p-eIF2 was detectable in the liver of GCN2 Ϫ/Ϫ mice 1-6 h after asparaginase injection.…”

“…Measurement of L-Asparaginase Activity-The activity of experimental L-asparaginase derived from E. coli (Elspar product from Merck) was determined by the Nesslerization technique, as described previously (4,19). Briefly, the production of ammonia by L-asparaginase over time was expressed relative to the slope of known ammonia standards.…”

“…Asparaginase reduces protein synthesis by increasing phosphorylation of eukaryotic initiation factor 2 (eIF2) 2 (4). Phosphorylation of eIF2 (p-eIF2) is catalyzed by a family of four protein kinases that are differentially sensitive to various cell stressors (7).…”

Pharmacokinetic, pharmacodynamic and intracellular effects of PEG-asparaginase in newly diagnosed childhood acute lymphoblastic leukemia: results from a single agent window study

“…35 Disturbances in hemostasis due to amino-acid depletion are probably a local effect, that is, in the liver only. 53,54 Outcome and prognostic factors Both the clinical response to PEG-asparaginase window and the in vitro sensitivity to L-asparaginase are predictive for outcome. The prognostic relevance of the in vitro sensitivity has been previously shown.…”