title: Glucocorticoid resistance in two key models of acute lymphoblastic leukemia occurs at the level of the glucocorticoid receptor.
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 approximately 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.
authors.affiliation: Tyrolean Cancer Research Institute, Innrain 66, A-6020 Innsbruck, Austria. stefan.schmidt@i-med.ac.at
authors.forename: Stefan
authors.initials: S
authors.lastname: Schmidt
authors.forename: Julie A E
authors.initials: JA
authors.lastname: Irving
authors.forename: Lynne
authors.initials: L
authors.lastname: Minto
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Matheson
authors.forename: Lindsay
authors.initials: L
authors.lastname: Nicholson
authors.forename: Andreas
authors.initials: A
authors.lastname: Ploner
authors.forename: Walther
authors.initials: W
authors.lastname: Parson
authors.forename: Anita
authors.initials: A
authors.lastname: Kofler
authors.forename: Melanie
authors.initials: M
authors.lastname: Amort
authors.forename: Martin
authors.initials: M
authors.lastname: Erdel
authors.forename: Andy
authors.initials: A
authors.lastname: Hall
authors.forename: Reinhard
authors.initials: R
authors.lastname: Kofler
mesh_terms: D045744:Cell Line, Tumor; D053843:DNA Mismatch Repair; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D005938:Glucocorticoids / Q000378:metabolism / Q000627:therapeutic use*; D006801:Humans; D009154:Mutation; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy*; D011965:Receptors, Glucocorticoid / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D005938:Glucocorticoids; D011965:Receptors, Glucocorticoid; C404226:TSC22D3 protein, human; D014157:Transcription Factors