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Ikzf1 alterations contribute to the pathogenesis of BCR-ABL1 positive acute lymphoblastic leukemia (400K CGH)

ABSTRACT: Alterations of IKZF1, encoding the lymphoid transcription factor IKAROS, are a hallmark of high risk acute lymphoblastic leukemia (ALL), however the role of IKZF1 alterations in ALL pathogenesis is poorly understood. Here we show that in mouse models of BCR-ABL1 leukemia, Ikzf1 and Arf alterations synergistically promote the development of an aggressive lymphoid leukemia. Ikzf1 alterations were associated with acquisition of stem cell-like features, including self-renewal and increased bone marrow stromal adhesion. Rexinoid receptor agonists reversed this phenotype, in part by inducing expression of IKZF1, resulting in abrogation of adhesion and self-renewal, cell cycle arrest and attenuation of proliferation without direct cytotoxicity. Retinoids potentiated the activity of dasatinib in mouse and human BCR-ABL1 ALL, providing a new therapeutic option in IKZF1-mutated ALL. Significance: The outcome of therapy for high-risk acute lymphoblastic leukemia remains suboptimal despite contemporary chemotherapy and the advent of targeted therapeutic approaches. Recent genomic studies have identified deletions or mutations of IKZF1 as a hallmark of high-risk ALL, but an understanding of how IKZF1 alteration contribute to leukemia development are lacking. Here we show that IKZF1 alterations drive lymphoid lineage, a stem cell-like phenotype, abnormal bone marrow adhesion, and poor responsiveness to tyrosine kinase inhibitor (TKI) therapy. Using a high-content screen, we show that retinoids reverse this phenotype in part by inducing expression of wild type IKZF1, and increase responsiveness to TKIs. These findings provide new insight into the pathogenesis of high-risk ALL and potential new therapeutic approaches.

ORGANISM(S): Mus musculus

PROVIDER: GSE54821 | GEO | 2015/09/04

SECONDARY ACCESSION(S): PRJNA237751

REPOSITORIES: GEO

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Project description:We studied a cohort of 221 high-risk pediatric B-progenitor ALL patients that excluded known high risk ALL subtypes (BCR-ABL1 and infant ALL), using Affymetrix single nucleotide polymorphism microarrays, gene expression profiling and candidate gene resequencing. A CNA poor outcome predictor was identified using a semi-supervised principal components approach, and tested in an independent validation cohort of 258 pediatric B-progenitor ALL cases. Over 50 regions of recurring somatically acquired CNA, with the most frequently targeted genes encoding regulators of B-lymphoid development (66.8% of cases; with PAX5 targeted in 31.7% and IKZF1 in 28.6%). A CNA classifier identified a very poor outcome subgroup in the high-risk cohort (P=4.2x10-5) and was strongly associated with the presence of deletions involving IKZF1, which encodes the early lymphoid transcription factor IKAROS. This classifier, and IKZF1 deletions, also predicted poor outcome and elevated minimal residual disease at the end of induction therapy in the validation cohort. The gene expression signature of the poor outcome group was characterized by reduced expression of B lineage specific genes, and was highly related to the expressing signature of BCR-ABL1 ALL, a known high-risk ALL subtype also characterized by a high frequency of IKZF1 deletion.Somatically acquired deletions involving IKZF1 identify a very poor outcome subgroup of pediatric ALL patients. Incorporation of molecular tests to identify IKZF1 deletion in diagnostic leukemic blasts should improve the ability to accurately risk stratify patients for appropriate therapy. Affymetrix U133A arrays were performed according to the maufacturers directions on RNA extracted from cryopreserved diagnostic bone marrow or peripheral blood samples. Samples with less than 80% blasts were flow sorted prior to RNA extraction Experiment Overall Design: One hundred seventy five pediatric B-progenitor ALL samples were studied using either Affymetrix U133A

Project description:Traditional response criteria in MDS and AML are based on bone marrow morphology and may not accurately reflect tumor burden in patients treated with hypomethylating agents. We used massively parallel sequencing of serial bone marrow samples to monitor MDS and AML tumor burden during treatment with epigenetic therapy (decitabine and panobinostat). Serial bone marrow samples (and skin as a source of normal DNA) from 25 MDS and AML patients were sequenced . We observed that responders, including those in complete remission (CR), can have persistent measurable tumor burden for at least one year without disease progression. Using an ultra-sensitive barcode sequencing approach, we detected extremely rare mutations months to years prior to disease relapse. While patients can live with persistent clonal hematopoiesis in a CR or stable disease, ultimately we find evidence that expansion of a rare subclone can drive relapse or progression. Digital sequencing provides an alternative measure of tumor burden and disease response which may augment traditional clinical response criteria in patients treated with hypomethylating agents and its use should be explored in future clinical trials. BCR-ABL1 lymphoblastic leukaemia is characterized by the deletion of Ikaros. The Philadelphia chromosome, encoding BCR-ABL1, is the defining lesion of chronic myelogenous leukemia (CML) and a subset of acute lymphoblastic leukemia (ALL) cases. To define oncogenic lesions that cooperate with BCR-ABL1 to induce ALL, we performed genome-wide analysis of leukemic samples from 23 CML cases and 304 ALL cases, including 43 BCR-ABL1 B-ALL cases. IKZF1 (encoding the transcription factor Ikaros) was deleted in 83.7% of BCR-ABL1 B-ALL cases, but not in chronic phase CML. Deletion of IKZF1 was also identified as an acquired lesion in lymphoid blast crisis of CML. The IKZF1 deletions resulted in haploinsufficiency, expression of a dominant negative Ikaros isoform or the complete loss of Ikaros expression. Sequencing of IKZF1 deletion breakpoints suggested that aberrant V(D)J recombination is responsible for the deletions. These findings suggest that genetic lesions resulting in the loss of Ikaros function are a key event in the development of BCR-ABL1 ALL.

Project description:Deletions within the human IKZF1 gene, which encodes Ikaros, a zinc finger transcription factor critical for lymphopoiesis, appear to be the most prominent recurring lesion in human BCR-ABL1+ (Ph+) B-ALL. Furthermore, IKZF1 mutations correlate with poor prognosis of progenitor B-ALL, further strengthening the notion that IKZF1 is a critical tumor suppressor gene in human B-lineage malignancies. To better understand the relationship between Ikzf1 mutations, BCR-ABL, and B-lineage leukemia, we examined the effect of two newly generated Ikzf1 germline mutation on BCR-ABL-induced proliferation and leukemogenesis in vitro and in vivo. We recently showed that deletion of either the exon encoding the first or the fourth DNA-binding zinc finger of Ikaros (IkZnF1-/- and IkZnF4-/-) led to distinct defects in lymphoid development and tumor suppression with de-regulation of distinct subsets of genes, providing a powerful tool for elucidation of Ikaros target genes and mechanism of function. Importantly, IkZnF4-/- had lost Ikaros tumor suppression function, while not abolishing B-cell development. Retroviral expression of BCR-ABL1 p185 in bone marrow cells from the two Ikzf1 mutant strains demonstrated that loss of ZnF4 resulted in expansion of progenitor B cells, with enhanced proliferation in vitro and a less mature cell surface B-cell phenotype in comparison to transduced wild-type bone marrow. Furthermore, in an in vivo model of BCR-ABL+ B-ALL, leukemias generated in the IkZnF4-/- background were more aggressive than those observed in a wild-type background, with cell phenotype corresponding to the in vitro cell cultures. Genome wide high throughput expression analysis (RNA-Seq) revealed a distinct subset of deregulated genes in the IkZnF4-/- BCR-ABL+ in vitro cell cultures, and molecular analysis demonstrated that this in vitro system is amendable for functional studies. These results establish a mouse model for studying the role of Ikzf1 mutations in B-ALL, and for understanding how BCR-ABL collaborates with Ikzf1 mutations to generate aggressive B-ALL.

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Ikzf1 alterations contribute to the pathogenesis of BCR-ABL1 positive acute lymphoblastic leukemia (400K CGH)

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