Over-expression of the dominant-negative isoform of Ikaros confers resistance to dexamethasone-induced and anti-IgM-induced apoptosis

Myeloid cell-based delivery of IFN-γ reprograms the leukemia microenvironment and induces anti-tumoral immune responses

The immunosuppressive microenvironment surrounding tumor cells represents a key cause of treatment failure. Therefore, immunotherapies aimed at reprogramming the immune system have largely spread in the past years. We employed gene transfer into hematopoietic stem and progenitor cells to selectively express anti-tumoral cytokines in tumor-infiltrating monocytes/macrophages. We show that interferon-γ (IFN-γ) reduced tumor progression in mouse models of B-cell acute lymphoblastic leukemia (B-ALL) and colorectal carcinoma (MC38). Its activity depended on the immune system's capacity to respond to IFN-γ and drove the counter-selection of leukemia cells expressing surrogate antigens. Gene-based IFN-γ delivery induced antigen presentation in the myeloid compartment and on leukemia cells, leading to a wave of T cell recruitment and activation, with enhanced clonal expansion of cytotoxic CD8+ T lymphocytes. The activity of IFN-γ was further enhanced by either co-delivery of tumor necrosis factor-α (TNF-α) or by drugs blocking immunosuppressive escape pathways, with the potential to obtain durable responses.

MYBL2 Gene Polymorphism Is Associated With Acute Lymphoblastic Leukemia Susceptibility in Children

Purpose

Although MYBL2 had been validated to participate in multiple cancers including leukemia, the role of MYBL2 polymorphisms in acute lymphoblastic leukemia (ALL) was still not clear. In this study, we aimed to evaluate the association between MYBL2 single nucleotide polymorphisms (SNPs) and ALL risk in children.

Methods

A total of 687 pediatric ALL cases and 971 cancer-free controls from two hospitals in South China were recruited. A case-control study by genotyping three SNPs in the MYBL2 gene (rs285162 C>T, rs285207 A>C, and rs2070235 A>G) was conducted. The associations were assessed by odds ratios (ORs) with corresponding 95% confidence intervals (CIs). Subgroup and stratification analyses were conducted to explore the association of rs285207 with ALL risk in terms of age, sex, immunophenotype, risk level, and other clinical characteristics. The false-positive report probability (FPRP) analysis was performed to verify each significant finding. Functional analysis in silico was used to evaluate the probability that rs285207 might influence the regulation of MYBL2 .

Results

Our study demonstrated that rs285207 was related to a decreased ALL risk (adjusted OR = 0.78; 95% CI = 0.63-0.97, P = 0.022) in the dominant model. The associations of rs285207 with ALL risk appeared stronger in patients with pre B ALL (adjusted OR=0.56; 95% CI=0.38-0.84, P=0.004), with normal diploid (adjusted OR=0.73; 95% CI=0.57-0.95, P=0.017), with low risk (adjusted OR=0.68; 95% CI=0.49-0.94, P=0.021), with lower WBC (adjusted OR=0.62; 95% CI=0.43-0.87, P=0.007) or lower platelet level (adjusted OR=0.76; 95% CI=0.59-0.96, P=0.023). With FPRP analysis, the significant association between the rs285207 polymorphism and decreased ALL risk was still noteworthy (FPRP=0.128). Functional analysis showed that IKZF1 bound to DNA motif overlapping rs285207 and had a higher preference for the risk allele A. As for rs285162 C>T and rs2070235 A>G, no significant was found between them and ALL risk.

Conclusion

In this study, we revealed that rs285207 polymorphism decreased the ALL risk in children, and rs285207 might alter the binding to IKZF1, which indicated that the MYBL2 gene polymorphism might be a potential biomarker of childhood 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.

Alternative Splice Variants Modulates Dominant-Negative Function of Helios in T-Cell Leukemia

The molecular defects which lead to multistep incidences of human T-cell leukemia have yet to be identified. The DNA-binding protein Helios (known as IKZF2), a member of the Ikaros family of Krüppel-like zinc-finger proteins, functions pivotally in T-cell differentiation and activation. In this study, we identify three novel short Helios splice variants which are T-cell leukemic specific, and demonstrate their dominant-negative function. We then test the cellular localization of distinct Helios isoforms, as well as their capability to form heterodimer with Ikaros, and the association with complexes comprising histone deacetylase (HDAC). In addition, the ectopic expression of T-cell leukemic Helios isoforms interferes with T-cell proliferation and apoptosis. The gene expression profiling and pathway analysis indicated the enrichment of signaling pathways essential for gene expression, translation, cell cycle checkpoint, and response to DNA damage stimulus. These data indicate the molecular function of Helios to be involved in the leukemogenesis and phenotype of T-cell leukemia, and also reveal Helios deregulation as a novel marker for T-cell leukemia.

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.

Ikaros: master of hematopoiesis, agent of leukemia

Ikaros is the founding member of a family of zinc finger transcription factors whose function during early hematopoietic development is required for differentiation into the three major hematopoietic lineages. Ikaros deletions have been described in human malignancies, particularly precursor B-cell leukemia. Deletions of this transcription factor appear to mediate leukemogenesis, although the exact mechanism is unclear. This article reviews the structure and function of Ikaros proteins in chromatin remodeling and gene expression as well as the current knowledge of Ikaros deletions in human malignancies. A new proteomic platform, mass cytometry, is introduced which allows measurements of greater than 30 parameters at the single-cell level and should thus provide a greater level of detail to unravel the mechanistic consequences of Ikaros dysfunction in leukemia.

Expression of Ikaros isoform 6 in chinese children with acute lymphoblastic leukemia

Ikaros is a zinc-finger transcription factor that plays an important role in the differentiation and proliferation of lymphocytes. Dominant-negative Ikaros isoform 6 (Ik6), one of its common subtypes, is overexpressed in leukemia patients and is associated with unfavorable prognosis in childhood B-cell progenitor acute lymphoblastic leukemia (ALL). This study was to identify specific isoforms, especially Ik6, in Chinese pediatric patients with ALL. The mRNA expression of Ikaros was detected in 88 children with previously untreated ALL by nested reverse transcription-polymerase chain reaction (RT-PCR). Sequencing of the PCR products was performed to identify specific isoforms. The expression of fusion genes was determined by using multiplex RT-PCR. The functional isoforms Ik1, Ik2/3, and dominant negative isoforms Ik4, 6, 8, 9, 10 identified by nested RT-PCR were further confirmed by sequence analysis. In the 88 cases, the Ik6 was found to be overexpressed in 8 of 70 cases of B-lineage ALL and in 1 of 18 cases of T-lineage ALL patients. Among Ik6 B-lineage ALL patients, 3 had expression of BCR/ABL fusion gene and 1 had HOX11 expression. Ik6 overexpression was independent of age, white blood cell count at diagnosis, risk group, and expression of the fusion genes currently measured in China except BCR/ABL (P<0.01). And it was strongly associated with elevated levels of minimal residual disease at day 28 (P<0.01). Ik6 can be included as a high-risk factor at diagnosis. In developing countries with limited resources, it can be economically detected by nested RT-PCR.

Ikaros increases normal apoptosis in adult erythroid cells

Ikaros is a critical transcriptional regulator of hematopoietic cell differentiation. In addition to its effects on the lymphoid system and hematopoietic stem-cell compartment, we have previously shown that Ikaros is also required for normal erythroid development. In this report, we compare Ikaros-dependent gene expression in erythroid cells of mice lacking the Ikaros protein with that of normal mice in purified adult bone-marrow erythroid cells (BMRC). Gene expression, measured by Affymetrix microarray analysis, indicates that in the BMRC of Ikaros-null mice, there is significant up-regulation of SMADs 6 and 7, serine protease inhibitor 3, and immediate-early protein 3 (IER3), all proteins that play a modulating role in apoptosis. We investigate the role of Ikaros in oxidative stress-induced apoptosis using Annexin-V staining and FACS analysis. We find a decrease in apoptosis in the BMRC of Ikaros-null mice compared to normal mice. This effect is also seen in nonerythroid cells but is stronger in BMRC. We conclude that normal Ikaros function increases normal apoptosis in erythroid cells. The data also suggest that Ikaros plays a role in apoptosis-mediated events in other normal hematopoietic cell lineages.

Ikaros is expressed in human extravillous trophoblasts and involved in their migration and invasion

The transcriptional factor Ikaros was originally found to function as a key regulator of lymphocyte differentiation. In addition, we have reported that Ikaros regulates the human placental leucine aminopeptidase (P-LAP)/insulin-regulated aminopeptidase (IRAP) gene in choriocarcinoma trophoblastic cells, suggesting that Ikaros might be involved in placental development, while even its presence in human placenta remains undetermined. We therefore sought to clarify the location and roles of Ikaros in human placenta. Immunohistochemical analysis showed modest Ikaris expression in syncytium, and intense expression in extravillous trophoblasts (EVTs) in first trimester placenta. Western blot analysis showed that villous trophoblasts principally expressed Ikaros-2/3, while Ikaros-x (Ikx) was predominantly expressed in cultured EVTs. Furthermore, to investigate the functional role of Ikx in EVTs, the EVT cell line HTR-8/SVneo was infected with a retrovirus vector expressing the hemagglutinin (HA)-tagged dominant negative isoform Ikaros-6 (Ik6), which prevents the DNA-binding activity of Ikx. Antibody against HA showed successful transduction of Ik6 in HTR-8/SVneo cells on immunocytochemistry and Western blotting. Transduction of Ik6 significantly reduced the migratory and invasive abilities of HTR-8/SVneo cells. These results suggest that Ikx is involved in migration and invasion of EVTs in early placentation.

Comparison of properties of spontaneous and radiation-induced mouse thymic lymphomas: role of Trp53 and radiation

Mouse thymic lymphomas are readily induced by radiation and also arise without irradiation when the mice are null in Trp53 functions. In the present study, spontaneous thymic lymphomas in Trp53-/- mice were compared to those arising in irradiated Trp53+/- mice, revealing three features characteristic of the spontaneous lymphomas. (1) Mp53D2, a Trp53 modifier that affects the latent period of radiogenic thymic lymphomas in Trp53+/- mice, had no effect on the development of spontaneous lymphomas. (2) A sex difference in the latency was found. (3) A marked difference was noted in the frequency of allelic loss at the Ikaros gene on chromosome 11, encoding a transcription factor required for normal lymphocyte development and differentiation; 2% in the lymphomas of Trp53-/- mice and 78% in the radiogenic lymphomas of Trp53+/- mice, suggesting that loss of Trp53 may reduce the requirement for the loss of Ikaros for lymphomagenesis. Furthermore, allelic loss analysis on chromosome 19 localized a region that may harbor an unknown tumor suppressor gene. These results suggest intricate steps of lymphomagenesis influenced by the presence or absence of Trp53.

Overexpression of the Ikaros 6 isoform is restricted to t(4;11) acute lymphoblastic leukaemia in children and infants and has a role in B-cell survival

The Ikaros transcription factor has been shown to play an important role in the differentiation of both myeloid and lymphoid lineages. Mice heterozygous for a dominant negative (DN) ikaros isoform develop T-cell leukaemia and lymphoma with 100% penetrance. Overexpression of DN Ikaros isoforms has been reported in some forms of leukaemia, such as childhood acute myelomonocytic and monocytic leukaemias, adult B-cell acute lymphoblastic leukaemias (B ALL) and in childhood and adult pre-B ALL. In this study, the expression of Ikaros isoforms in 49 infant and childhood leukaemia patients was analysed by reverse transcription polymerase chain reaction and Western blot analysis. We found overexpression of the DN Ikaros 6 (Ik6) isoform in a subset of leukaemia patients harbouring t(4;11) translocations. To further study the consequences of Ik6 overexpression in B ALL, we inducibly expressed Ik6 in BaF3 cells and found that Ik6 overexpression delayed cell death after interleukin-3 withdrawal, suggesting that overexpression of Ik6 found in t(4;11) B cells could contribute to leukaemogenesis by preventing the apoptosis of cells in an environment with reduced survival factors.

Altered expression of Tfg and Dap3 in Ikaros-defective T-cell lymphomas induced by X-irradiation in B6C3F1 mice

Ikaros is a Kruppel-type zinc finger protein that is essential for normal lymphocyte development and differentiation. Recently, it has been demonstrated that Ikaros is frequently inactivated in both human and mouse leukaemias/lymphomas. Although this inactivation is thought to be involved in leukaemogenesis, little is known about the molecular mechanisms that lead to neoplastic transformation. To identify the genes that may be controlled by Ikaros, we performed differential display analysis of RNAs from mouse 3T3-L1 cells that had been transfected with the Ikaros gene. Two cDNAs, the Trk-fused gene (Tfg) and death-associated protein 3 gene (Dap3) were upregulated in Ikaros-transfected cells. Expression of Tfg and Dap3 was consistently downregulated in radiation-induced T-cell lymphomas that exhibited defective Ikaros expression. These results suggest that Tfg and Dap3 function downstream of Ikaros and may be involved in radiation-induced lymphomagenesis.