Expression levels of asparagine synthetase in blasts from children and adults with acute lymphoblastic leukaemia

Abstract

l-asparaginase (l-asp) is an important component in the treatment of childhood acute lymphoblastic leukaemia (ALL).Recently the assumption that leukaemic cells are sensitive to l-asp because of a relative lack of asparagine synthetase (AS) has been questioned (Stams et al, 2003;Krejci et al, 2004). Using a real-time quantitative reverse transcription polymerase chain reaction (RQ RT-PCR) assay with transcription binding protein IID/TATA (TBP) as the internal control we provide evidence to support the original supposition that lymphoblasts have significantly lower levels of expression of AS than normal peripheral blood mononuclear cells (NPBMC). Materials and methodsFollowing ethical approval, diagnostic bone marrow samples were obtained from 59 children (median 5 years; range 0AE6-15AE5 years) and 23 adults (median 29 years; range 17AE7-71 years) with ALL and eight children (median 5AE2 years; range 1-16 years) and 22 adults (median 57; range 17-84 years) with acute myeloid leukaemia (AML). The presence of >80% blasts were confirmed by morphology. NPBMC were obtained from 14 healthy volunteers. Mononuclear cells were isolated by density gradient centrifugation using Lymphoprep (Nycomed Pharma, Oslo, Norway). K562, MOLT-4 and NALM-6 cell lines were grown under standard conditions for use as controls.Total mRNA was extracted using the RNeasy mini kit (Qiagen, Crawley, UK) according to the manufacturer's protocol. Reverse transcription of 200 ng total RNA was performed using a Taqman reverse transcription kit (Applied Biosystems, Warrington, UK) with random hexomers. Primers and Taqman probe for AS RQ RT-PCR, were designed using Primer-Express (Applied Biosystems). Primer and probe sequences were as follows; forward -5¢-TCAGCCCGCCACAT-CAC-3¢-(in exon 1), reverse -5¢-CAATGAAGCTATAAG-CTTTCTTCAAGTG-3¢ (spanning exon 2 and 3), probe, -5¢-CTGACCTGCTTACGCCCAGATTTTCTTCAA-3¢ (spanning exon one and two). Primers and probe for TBP were purchased as a Taqman pre-developed control reagent.Standards containing 75, 18AE75, 4AE69, 1AE17, 0AE29 and 0AE07 ng of K562 total RNA with reverse transcribed Escherichia coli tRNA as a carrier were assayed for AS and TBP in triplicate on 27 separate occasions. Computerised tomography (CT) values (the fractional cycle numbers at which the fluorescence passed the fixed threshold) for each standard were obtained using an ABI Prism 5700 sequence detection system (Applied Biosystems, Warrington, UK) and the average CT for each point plotted against log standard RNA concentration.Reaction mixtures (82AE5 ll) contained 41AE25 ll Taqman PCR universal master mix, 900 nmol/l AS forward primer, 900 nmol/l AS reverse primer, 225 nmol/l AS probe or 4AE13 ll of ready synthesised TBP primers and probe and either 7AE3 ll of sample cDNA, 22AE5 ll of standard cDNA or 3AE2 ll of calibrator cDNA. Aliquots (25 ll) were added to wells of a microplate in triplicate. The thermal cycling conditions were 95°C for 10 min, 40 cycles at 95°C for 15 s and 60°C for 1 min.A calibrator sample was quantified for AS and TBP ...

Asparagine synthetase is partially localized to the plasma membrane and upregulated by L-asparaginase in U937 cells

“…Apart from this well-recognized effect of L-asparaginase in children ALL, recently, a beneficial effect of L-asparaginase on patients with AML, particular on M5 subtype (FAB classification), has also been proposed. Generally, studies on sensitivity to L-asparaginase in leukemia cells and primary leukemic cells focused on the cellular expression of ASNS, and enzyme activity with the test of in vitro resistance to L-asparaginase [5,6,[11][12][13][14][15][16][17][18][19] . Whereas, little research effort has been directed at other features of ASNS, such as its intracellular localization in the relation with chemoresistance.…”

A critical electrostatic interaction mediates inhibitor recognition by human asparagine synthetase

“…11 One prediction of this model is that increased levels of cellular ASNS are the cause of ASNaseresistance in lymphoblasts because sufficient asparagine is made available as a result of increased intracellular asparagine biosynthesis. 8,12,13 Support for this hypothesis has come from studies employing transformed cell lines. For example, in vitro studies with U937 cells demonstrated that ASNase-sensitive cells can be made resistant by persistent exposure to increasing levels of sublethal doses of the drug, and constitutive expression of ASNS in a human ALL cell line (MOLT-4) conferred ASNase-resistance onto sensitive parental cells.…”

The eIF2 Kinase GCN2 Is Essential for the Murine Immune System to Adapt to Amino Acid Deprivation by Asparaginase

“…ASNase catalyzes the hydrolysis of amino acid asparagine to aspartic acid and ammonia, exploiting an Achilles heel in the leukemic lymphoblast, low or absent levels of asparagine synthetase (ASNS) (2). The potency of the drug to induce cell death is a consequence of asparagine starvation and is strength-ened by its intrinsic glutaminase activity, which lowers the levels of glutamine, an essential substrate in the synthesis of asparagine by ASNS (glutamine + aspartate / glutamate + asparagine) (3)(4)(5).…”