Expression of dominant-negative Ikaros isoforms and associated genetic alterations in Chinese adult patients with leukemia

Aberrant ARID5B expression and its association with Ikaros dysfunction in acute lymphoblastic leukemia

Mutations and single nucleotide polymorphisms of AT-rich interactive domain-containing protein 5B (ARID5B) are involved in the oncogenesis of acute lymphoblastic leukemia (ALL) and treatment outcomes. However, ARID5B expression and clinical significance in ALL remain unclear. We found ARID5B is significantly down-regulated in ALL compared to healthy bone marrow controls. ARID5B also interacts with PHD finger protein 2 (PHF2). Low expression of ARID5B (ARID5B^low) or ARID5B and PHF2 (ARID5B^lowPHF2^low) is correlated with the markers of cell proliferation and poor prognosis in ALL patients. Ikaros directly regulates ARID5B expression in ALL. Restoring Ikaros function by Casein Kinase II inhibition also promotes ARID5B expression through recruitment of trimethylation of lysine 4 on histone H3 (H3K4me3) at its promoter region. In summary, our data show that aberrant expression of ARID5B and PHF2 is related to leukemic cell proliferation and several poor prognostic markers. Our data indicate ARID5B^low expression, particularly ARID5B^lowPHF2^low expression, is linked to Ikaros dysfunction and involved in the oncogenic effect of high-risk ALL, which may represent a high-risk subgroup of ALL.

[Effects of minimal residual disease level on day 33 of remission induction and IKZF1 genotype on the survival of children with B-lineage acute lymphoblastic leukemia]

OBJECTIVE

To study the effects of minimal residual disease (MRD) level on day 33 of remission induction and IKZF1 genotype on the survival of children with B-lineage acute lymphoblastic leukemia (B-ALL).

METHODS

A total of 152 children with newly-diagnosed B-ALL who had complete remission after the first cycle of the chemotherapy and had complete follow-up information were enrolled in this study. According to the MRD detection by flow cytometry on day 33 of remission induction, they were divided into three groups: standard-risk (SR) group (MRD <10^-4; n=60), intermediate-risk (IR) group (10^-4≤ MRD <10^-2; n=55), and high-risk (HR) group (MRD ≥10^-2; n=37). Nested RT-PCR was used to determine the IKZF1 genotype of all children before chemotherapy. The effects of MRD level on day 33 of remission induction and IKZF1 genotype on the recurrence-free survival (RFS) of children with B-ALL were analyzed.

RESULTS

There were 7 common IKZF1 subtypes in all the 152 children with B-ALL: IK1, IK2/3, IK4, IK6, IK8, IK9, and IK10. Of the 152 children, 130 had functional subtypes of IKZF1 and 22 had non-functional subtypes of IKZF1. During the follow-up period, relapse occurred in 26 (17%) children, and the recurrence rate was highest in the HR group (P<0.05). However, there was no significant difference in the recurrence rate between the SR group and the IR group (P>0.05). The cumulative recurrence rate of the children with non-functional subtypes of IKZF1 was significantly higher than that of those with functional types of IKZF1 (P<0.01). The predicted 5-year RFS rates in the SR, IR, and HR groups were (94.2±2.9)%, (86.7±3.8)%, and (56.2±4.5)% respectively (P<0.05). The 5-year RFS rate of the children with functional subtypes of IKZF1 was significantly higher than that of those with non-functional subtypes of IKZF1 (P<0.01). There was no significant difference in the predicted 5-year RFS rate between the children with functional subtypes of IKZF1 and those with non-functional subtypes of IKZF1 in the SR group (P>0.05). However, the predicted 5-year RFS rate of the children with functional subtypes of IKZF1 was significantly higher than that of those with non-functional subtypes of IKZF1 in the IR group and the HR group (P<0.05).

CONCLUSIONS

B-ALL children with non-functional subtypes of IKZF1 have a high recurrence rate, and the recurrence rate will be even higher in B-ALL children with non-functional subtypes of IKZF1 and MRD ≥10^-4 on day 33 of chemotherapy.

High CRLF2 expression associates with IKZF1 dysfunction in adult acute lymphoblastic leukemia without CRLF2 rearrangement

Overexpression of cytokine receptor-like factor 2 (CRLF2) due to chromosomal rearrangement has been observed in acute lymphoblastic leukemia (ALL) and reported to contribute to oncogenesis and unfavorable outcome in ALL. We studied B-ALL and T-ALL patients without CRLF2 rearrangement and observed that CRLF2 is significantly increased in a subset of these patients. Our study shows that high CRLF2expression correlates with high-risk ALL markers, as well as poor survival. We found that the IKZF1-encoded protein, Ikaros, directly binds to the CRLF2 promoter and regulates CRLF2 expression in leukemia cells. CK2 inhibitor, which can increase Ikaros activity, significantly increases Ikaros binding in ALL cells and suppresses CRLF2 expression in an Ikaros-dependent manner. CRLF2 expression is significantly higher in patients with IKZF1 deletion as compared to patients without IKZF1 deletion. Treatment with CK2 inhibitor also results in an increase in IKZF1 binding to the CRLF2 promoter and suppression of CRLF2 expression in primary ALL cells. We further observed that CK2 inhibitor induces increased H3K9me³ histone modifications in the CRLF2 promoter in ALL cell lines and primary cells. Taken together, our results demonstrate that high expression of CRLF2 correlates with high-risk ALL and short survival in patients without CRLF2 rearrangement. Our results are the first to demonstrate that the IKZF1-encoded Ikaros protein directly suppresses CRLF2 expression through enrichment of H3K9me³ in its promoter region. Our data also suggest that high CRLF2 expression works with the IKZF1 deletion to drive oncogenesis of ALL and has significance in an integrated prognostic model for adult high-risk ALL.

Overexpression of dominant-negative Ikaros 6 isoform is associated with resistance to TKIs in patients with Philadelphia chromosome positive acute lymphoblastic leukemia

The clinical significance of the dominant-negative Ikaros 6 (DN-IK6) in the treatment of patients with Philadelphia-positive acute lymphoblastic leukemia (Ph⁺-ALL) with tyrosine kinase inhibitors (TKIs) remains elusive. In the present study, it was demonstrated that DN-IK6 was overexpressed in B-cell (B)-ALL cases compared with T cell-ALL cases at the mRNA and protein levels. Furthermore, nucleotide sequencing revealed that DN-IK6 was due to the deletion of IKAROS family zinc finger 1 exons 4-7. The outcome of patients with Ph⁺-B-ALL with DN-IK6, and treated with TKIs and hyper-cyclophosphamide/vincristine/doxorubicin/dexamethasone regimen were restrospectively evaluated in a 2 year follow-up. The results demonstrated that those with the DN isoform exhibited significantly lower incidences of remission, shorter median cumulative incidence of relapse times (P<0.05) and shorter median overall survival times (P<0.05) compared with those without the DN isoform. In conclusion, the results of the present study demonstrated that DN-IK6 is overexpressed in the majority of patients with Ph⁺-ALL, and is significantly associated with resistance to TKI therapy.

ETS-related gene is a novel prognostic factor in childhood acute lymphoblastic leukemia

The ETS-related gene (ERG) has been demonstrated to be associated with overall survival in cytogenetically normal acute myeloid leukemia and acute T cell-lymphoblastic leukemia (T-ALL) in adult patients. However, there are no data available regarding the impact of ERG expression on childhood ALL. In the present study, ERG expression levels were analyzed in bone marrow samples from 119 ALL pediatric patients. ALL patients demonstrated higher ERG expression compared with the controls (P<0.0001). In addition, low ERG expression identified a group of patients with higher white blood cell counts (P=0.011), higher percentages of T-ALL immunophenotype (P=0.027), and higher relapse rates (P=0.009). Survival analyses demonstrated that low ERG expression was associated with inferior relapse-free survival (RFS) in childhood ALL (P=0.036) and was an independent prognostic factor in multivariable analyses for RFS. In conclusion, low ERG expression is associated with poor outcomes and may be used to serve as a molecular prognostic marker to identify patients with a high risk of relapse in childhood ALL.

Changing of IKZF1 genotype during Philadelphia-negative precursor-B acute lymphoblastic leukemia progression: a short clinical report

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The case demonstrated a rare event of clonal heterogeneity by IKZF1 gene status in BCRABL1- ALL.

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IKZF1 deletions are secondary events in ALL caused by clonal evolution during the treatment.

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It's prognostic significance could be more crucial in BCR-ABL- rather than in BCR-ABL + ALL.

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IKZF1 gene alterations may be determined and proved at the genome, expression and protein level.

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IKZF1 deletions are suitable for MRD detection but not stable compared to Ig/TCR rearrangement.

Characterization of LEF1 High Expression and Novel Mutations in Adult Acute Lymphoblastic Leukemia

Aberrant activation of the Wnt pathway plays a pathogenetic role in tumors and has been associated with adverse outcome in acute lymphoblastic leukemia (ALL). Lymphoid enhancer binding factor 1 (LEF1), a key mediator of Wnt signaling, has been linked to leukemic transformation, and LEF1 mutations have been identified in T-ALL. Here we found LEF1 is highly expressed in 25.0% adult ALL patients and LEF1 high expression was associated with high-risk leukemia factors (high WBC, Philadelphia chromosome positive, complex karyotype), shorter event-free survival (EFS), and high relapse rates in patients with B-ALL. LEF1 high expression is also associated with high mutation rate of Notch1 and JAK1 in T-ALL. We identified 2 novel LEF1 mutations (K86E and P106L) in 4 of 131 patients with ALL, and those patients with high-risk ALL (high WBC, complex karyotype). These results suggest a role for LEF1 mutations in leukemogenesis. We further explored the effect of the mutations on cell proliferation and found both mutations significantly promoted the proliferation of ALL cells. We also observed the effect of LEF1 and its mutations on the transcription of its targets, c-MYC and Cyclin D1. We found LEF1 increased the promoter activity of its targets c-MYC and Cyclin D1, and LEF1 K86E and P106L mutants further significantly enhanced this effect. We also observed that the c-MYC and Cyclin D1 mRNA levels were significantly increased in patients with LEF1 high expression compared with those with low expression. Taken together, our findings indicate high LEF1 expression and mutation are associated with high-risk leukemia and our results also revealed that LEF1 high expression and/or gain-of-function mutations are involved in leukemogenesis of ALL.

A novel, non-canonical splice variant of the Ikaros gene is aberrantly expressed in B-cell lymphoproliferative disorders

The Ikaros gene encodes a Krüppel-like zinc-finger transcription factor involved in hematopoiesis regulation. Ikaros has been established as one of the most clinically relevant tumor suppressors in several hematological malignancies. In fact, expression of dominant negative Ikaros isoforms is associated with adult B-cell acute lymphoblastic leukemia, myelodysplastic syndrome, acute myeloid leukemia and adult and juvenile chronic myeloid leukemia. Here, we report the isolation of a novel, non-canonical Ikaros splice variant, called Ikaros 11 (Ik11). Ik11 is structurally related to known dominant negative Ikaros isoforms, due to the lack of a functional DNA-binding domain. Interestingly, Ik11 is the first Ikaros splice variant missing the transcriptional activation domain. Indeed, we demonstrated that Ik11 works as a dominant negative protein, being able to dimerize with Ikaros DNA-binding isoforms and inhibit their functions, at least in part by retaining them in the cytoplasm. Notably, we demonstrated that Ik11 is the first dominant negative Ikaros isoform to be aberrantly expressed in B-cell lymphoproliferative disorders, such as chronic lymphocytic leukemia. Aberrant expression of Ik11 interferes with both proliferation and apoptotic pathways, providing a mechanism for Ik11 involvement in tumor pathogenesis. Thus, Ik11 could represent a novel marker for B-cell lymphoproliferative disorders.