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.
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.
Iacobucci
Ilaria
I
Department of Hematology/Oncology, L. and A. Seràgnoli, S. Orsola Malpighi Hospital, University of Bologna, Bologna, Italy.
Lonetti
Annalisa
A
Messa
Francesca
F
Cilloni
Daniela
D
Arruga
Francesca
F
Ottaviani
Emanuela
E
Paolini
Stefania
S
Papayannidis
Cristina
C
Piccaluga
Pier Paolo
PP
Giannoulia
Panagiota
P
Soverini
Simona
S
Amabile
Marilina
M
Poerio
Angela
A
Saglio
Giuseppe
G
Pane
Fabrizio
F
Berton
Giorgio
G
Baruzzi
Anna
A
Vitale
Antonella
A
Chiaretti
Sabina
S
Perini
Giovanni
G
Foà
Robin
R
Baccarani
Michele
M
Martinelli
Giovanni
G
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
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