title: Expression of spliced oncogenic Ikaros isoforms in Philadelphia-positive acute lymphoblastic leukemia patients treated with tyrosine kinase inhibitors: implications for a new mechanism of resistance.
abstract: Ikaros plays an important role in the control of differentiation and proliferation of all lymphoid lineages. The expression of short isoforms lacking DNA-binding motifs alters the differentiation capacities of hematopoietic progenitors, arresting lineage commitment. We sought to determine whether molecular abnormalities involving the IKZF1 gene were associated with resistance to tyrosine kinase inhibitors (TKIs) in Ph+ acute lymphoblastic leukemia (ALL) patients. Using reverse-transcribed polymerase chain reaction, cloning, and nucleotide sequencing, only the non-DNA-binding Ik6 isoform was detected in 49% of Ph+ ALL patients. Ik6 was predominantly localized to the cytoplasm versus DNA-binding Ik1 or Ik2 isoforms, which showed nuclear localization. There was a strong correlation between nonfunctional Ikaros isoforms and BCR-ABL transcript level. Furthermore, patient-derived leukemia cells expressed oncogenic Ikaros isoforms before TKI treatment, but not during response to TKIs, and predominantly at the time of relapse. In vitro overexpression of Ik6 strongly increased DNA synthesis and inhibited apoptosis in TKI-sensitive cells. Genomic sequence and computational analyses of exon splice junction regions of IKZF1 in Ph+ ALL patients predicted several mutations that may alter alternative splicing. These results establish a previously unknown link between specific molecular defects that involve alternative splicing of the IKZF1 gene and the resistance to TKIs in Ph+ ALL patients.
authors.affiliation: Department of Hematology/Oncology, L. and A. Seràgnoli, S. Orsola Malpighi Hospital, University of Bologna, Bologna, Italy.
authors.forename: Ilaria
authors.initials: I
authors.lastname: Iacobucci
authors.forename: Annalisa
authors.initials: A
authors.lastname: Lonetti
authors.forename: Francesca
authors.initials: F
authors.lastname: Messa
authors.forename: Daniela
authors.initials: D
authors.lastname: Cilloni
authors.forename: Francesca
authors.initials: F
authors.lastname: Arruga
authors.forename: Emanuela
authors.initials: E
authors.lastname: Ottaviani
authors.forename: Stefania
authors.initials: S
authors.lastname: Paolini
authors.forename: Cristina
authors.initials: C
authors.lastname: Papayannidis
authors.forename: Pier Paolo
authors.initials: PP
authors.lastname: Piccaluga
authors.forename: Panagiota
authors.initials: P
authors.lastname: Giannoulia
authors.forename: Simona
authors.initials: S
authors.lastname: Soverini
authors.forename: Marilina
authors.initials: M
authors.lastname: Amabile
authors.forename: Angela
authors.initials: A
authors.lastname: Poerio
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Saglio
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Pane
authors.forename: Giorgio
authors.initials: G
authors.lastname: Berton
authors.forename: Anna
authors.initials: A
authors.lastname: Baruzzi
authors.forename: Antonella
authors.initials: A
authors.lastname: Vitale
authors.forename: Sabina
authors.initials: S
authors.lastname: Chiaretti
authors.forename: Giovanni
authors.initials: G
authors.lastname: Perini
authors.forename: Robin
authors.initials: R
authors.lastname: Foà
authors.forename: Michele
authors.initials: M
authors.lastname: Baccarani
authors.forename: Giovanni
authors.initials: G
authors.lastname: Martinelli
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D017398:Alternative Splicing; D000970:Antineoplastic Agents / Q000493:pharmacokinetics; D001483:Base Sequence; D001549:Benzamides; D045744:Cell Line, Tumor; D017931:DNA Primers / Q000235:genetics; D004273:DNA, Neoplasm / Q000235:genetics; D000069439:Dasatinib; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D016313:Genes, abl; D006801:Humans; D051740:Ikaros Transcription Factor / Q000235:genetics*; D000068877:Imatinib Mesylate; D008875:Middle Aged; D009154:Mutation; D010677:Philadelphia Chromosome; D010879:Piperazines / Q000494:pharmacology; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy* / Q000235:genetics* / Q000473:pathology; D020033:Protein Isoforms / Q000235:genetics; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011743:Pyrimidines / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology
chemical_list: D000970:Antineoplastic Agents; D001549:Benzamides; D017931:DNA Primers; D004273:DNA, Neoplasm; C497239:IKZF1 protein, human; D010879:Piperazines; D020033:Protein Isoforms; D047428:Protein Kinase Inhibitors; D011743:Pyrimidines; D013844:Thiazoles; D051740:Ikaros Transcription Factor; D000068877:Imatinib Mesylate; D011505:Protein-Tyrosine Kinases; D000069439:Dasatinib