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  • Biotechnical Methods Section BTS
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Biotechnical Methods Section (BTS)

mRNA expression levels of methotrexate resistance-related proteins in childhood leukemia as determined by a standardized competitive template-based RT-PCR method

Leukemia volume 14, pages 2166–2175 (2000)Cite this article

Abstract

Drug resistance of leukemic blasts is correlated to event-free survival and might be predicted by mRNA expression of drug resistance-related proteins. Methotrexate (MTX) is an important component in the treatment of childhood leukemia. Mechanisms of MTX resistance include (1) decreased transport via the reduced folate carrier (RFC), (2) altered levels of target enzymes, eg dihydrofolate reductase (DHFR) and thymidylate synthase (TS), (3) decreased ratio of folylpolyglutamate synthetase (FPGS)/folylpolyglutamate hydrolase (FPGH). We designed competitive templates for each of these genes to measure mRNA expression by quantitative RT-PCR and normalized the expression to that of β-actin. T-lineage acute lymphoblastic leukemia (T-ALL), relatively MTX resistant compared to common/preB-ALL, displayed higher mRNA levels of DHFR and TS (three- and four-fold higher, respectively; P < 0.001), while FPGS expression was lower (three-fold, P = 0.006) compared to common/preB-ALL. The ratio of (DHFR × FPGH)/(RFC × FPGS) was more discriminating between T-ALL and c/preB-ALL (eight-fold higher; P < 0.001) than either target independently. Acute myeloid leukemia (AML) cells, considered MTX resistant, expressed two-fold lower levels of FPGS mRNA compared to c/preB-ALL (P = 0.04). The ratio of FPGH/FPGS was more discriminating between AML and c/preB-ALL (four-fold higher; P = 0.001) than either target independently. For the total group of 79 leukemic samples, mRNA expression of DHFR varied 549-fold and paralleled TS mRNA expression (r = 0.80; P < 0.001). Although variations in mRNA expression resembled variations in functional activity, no direct correlations were found for RFC (58-fold variation in mRNA expression), FPGS (95-fold) and FPGH (178-fold). In conclusion, differences in mRNA expression of MTX resistance parameters between leukemic subtypes as detected by competitive RT-PCR are in line with known differences in MTX resistance.

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Acknowledgements

This work was supported by the Dutch Cancer Society (grant VU 94-679).

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Authors and Affiliations

  1. Department of Pediatric Hematology/Oncology, University Hospital Vrije Universiteit, Amsterdam, The Netherlands

    MG Rots, CH Van Zantwijk, AJP Veerman & R Pieters

  2. Department of Medical Oncology, University Hospital Vrije Universiteit, Amsterdam, The Netherlands

    MG Rots, G Jansen, P Noordhuis, E Kuiper & GJ Peters

  3. Department of Medicine, Medical College of Ohio, Toledo, OH, USA

    JC Willey & JP DeMuth

  4. Department of Pediatric Hematology/Oncology, Sophia Children's Hospital, University Hospital Rotterdam, The Netherlands

    R Pieters

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Rots, M., Willey, J., Jansen, G. et al. mRNA expression levels of methotrexate resistance-related proteins in childhood leukemia as determined by a standardized competitive template-based RT-PCR method. Leukemia 14, 2166–2175 (2000). https://doi.org/10.1038/sj.leu.2401943

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