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Glucocorticoid resistance in two key models of acute lymphoblastic leukemia occurs at the level of the glucocorticoid receptor

Stefan Schmidt^*,1,2, Julie A. E. Irving^,1, Lynne Minto, Elizabeth Matheson, Lindsay Nicholson, Andreas Ploner^*, Walther Parson, Anita Kofler^*, Melanie Amort^*, Martin Erdel, Andy Hall and Reinhard Kofler^*,||

^* Tyrolean Cancer Research Institute, Innsbruck, Austria;

Northern Institute for Cancer Research, Newcastle upon Tyne, United Kingdom;

Institute of Legal Medicine, Innsbruck Medical University, Innsbruck, Austria;

Division of Human Genetics, Innsbruck Medical University, Innsbruck, Austria;

^|| Division of Molecular Pathophysiology, Biocenter, Innsbruck Medical University, Innsbruck, Austria

²Correspondence: Tyrolean Cancer Research Institute, Innrain 66, A-6020 Innsbruck, Austria. E-mail: stefan.schmidt{at}i-med.ac.at

ABSTRACT

Glucocorticoids (GCs) specifically induce apoptosis in malignant lymphoblasts and are thus pivotal in the treatment of acute lymphoblastic leukemia (ALL). However, GC-resistance is a therapeutic problem with an unclear molecular mechanism. We generated 70 GC-resistant sublines from a GC-sensitive B- and a T-ALL cell line and investigated their mechanisms of resistance. In response to GCs, all GC-resistant subclones analyzed by real-time polymerase chain reaction (PCR) showed a deficient up-regulation of the GC-receptor (GR) and its downstream target, GC-induced leucine zipper. This deficiency in GR up-regulation was confirmed by Western blotting and on retroviral overexpression of GR in resistant subclones GC-sensitivity was restored. All GC-resistant subclones were screened for GR mutations using denaturing high-pressure liquid chromatography (DHPLC), DNA-fingerprinting, and fluorescence in situ hybridization (FISH). Among the identified mutations were some previously not associated with GC resistance: A484D, P515H, L756N, Y663H, L680P, and R714W. This approach revealed three genotypes, complete loss of functional GR in the mismatch repair deficient T-ALL model, apparently normal GR genes in B-ALLs, and heterozygosity in both. In the first genotype, deficiency in GR up-regulation was fully explained by mutational events, in the second by a putative regulatory defect, and in the third by a combination thereof. In all instances, GC-resistance occurred at the level of the GR in both models.—Schmidt, S., Irving, J. A. E., Minto, L., Matheson, E., Nicholson, L., Ploner, A., Parson, W., Kofler, A., Amort, M., Erdel, M., Hall, A., Kofler, R. Glucocorticoid resistance in two key models of acute lymphoblastic leukemia occurs at the level of the glucocorticoid receptor.

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