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World J Biol Chem. Jun 26, 2011; 2(6): 108-114
Published online Jun 26, 2011. doi: 10.4331/wjbc.v2.i6.108
Role of Ikaros in T-cell acute lymphoblastic leukemia
Philippe Kastner, Susan Chan
Philippe Kastner, Susan Chan, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch 67400, France;
Philippe Kastner, Susan Chan, INSERM U964, Illkirch 67400, France
Philippe Kastner, Susan Chan, CNRS UMR7104, Illkirch 67400, France; Université de Strasbourg, Strasbourg 67000, France
Author contributions: Kastner P and Chan S wrote the paper.
Supported by Institut National du Cancer, La Ligue Contre le Cancer (équipe labellisée), l’Agence Nationale de la Recherche, l’Association pour la Recherche sur le Cancer and La Fondation de France, with institute funding from INSERM, CNRS and l’Université de Strasbourg
Correspondence to: Philippe Kastner, PhD, Institut de Génétique et de Biologie Moléculaire et Cellulaire, 1 rue Laurent Fries, Illkirch 67404, France. scpk@igbmc.fr
Telephone: +33-3-88653461 Fax: +33-3-88653201
Received: March 22, 2011
Revised: April 27, 2011
Accepted: June 3, 2011
Published online: June 26, 2011

Abstract

Ikaros is a zinc finger transcriptional regulator encoded by the Ikzf1 gene. Ikaros displays crucial functions in the hematopoietic system and its loss of function has been linked to the development of lymphoid leukemia. In particular, Ikaros has been found in recent years to be a major tumor suppressor involved in human B-cell acute lymphoblastic leukemia. Its role in T-cell leukemia, however, has been more controversial. While Ikaros deficiency appears to be very frequent in murine T-cell leukemias, loss of Ikaros appears to be rare in human T-cell acute lymphoblastic leukemia (T-ALL). We review here the evidence linking Ikaros to T-ALL in mouse and human systems.

Key Words: Ikaros, Notch, T-cell leukemia


Citation: Kastner P, Chan S. Role of Ikaros in T-cell acute lymphoblastic leukemia. World J Biol Chem 2011; 2(6): 108-114
INTRODUCTION

Ikaros is a zinc finger transcriptional regulator that binds to specific DNA target sequences harboring the TGGGAA consensus motif[1,2]. How Ikaros regulates its target genes once bound to DNA is not entirely understood, and Ikaros has been found to activate or repress transcription, depending on the target gene. Part of its function may depend on the interaction of Ikaros with chromatin remodeling complexes, which may be recruited by Ikaros to target sites[3,4]. A large number of studies have shown that Ikaros is a key regulator within the hematopoietic system. Ikaros is crucial for controlling the development or the function of almost all hematopoietic cell types (see other reviews in this issue). Mutations or polymorphisms that lead to reduced Ikaros function or expression have also been found to be a major genetic feature in human B-cell acute lymphoblastic leukemia (B-ALL)[5-8]. Loss of Ikaros also promotes the development of T-cell lymphoma/leukemia in mice, which suggests that Ikaros acts as a tumor suppressor in T-cell acute lymphoblastic leukemia (T-ALL) and B-ALL. However, evidence linking Ikaros to human T-ALL has been elusive and sometimes contradictory, and only recently has the involvement of Ikaros in a small proportion of human cases of T-ALL become clear. We review below the role of Ikaros in murine and human T-ALL.

ROLE OF IKAROS IN MOUSE T-ALL
Targeted Ikaros mutations lead to T-ALL

Ikaros function in mice has been addressed through several mutant lines. The first mutant allele (Ikdn-) generated was a deletion of exons 3 and 4, which encode the DNA binding domain (DBD)[9]. This mutation is dominant-negative, because it allows the synthesis of mutant proteins that retain the C-terminal dimerization domain that can dimerize with, and inhibit, other Ikaros proteins or related proteins (such as Aiolos or Helios). Strikingly, heterozygous Ikdn+/- mice rapidly develop T-cell leukemia, which provided the first genetic demonstration that Ikaros is a tumor suppressor in T cells[10]. A second dominant-negative Ikaros allele, named IkPlastic, was isolated in an ENU mutagenesis screen. This allele harbors a point mutation in the third zinc finger of the DBD. These mutant Ikaros proteins could therefore dimerize with their wild-type (WT) counterparts, but dimers fail to bind DNA[11]. Like Ikdn+/- mice, IkPlastic/+ mice develop T-ALL with a rapid onset. The third mutant allele (Ik-) was later generated by deleting the sequences that encode the C-terminal zinc fingers that are required for dimerization; this is considered a null mutation[12]. Clonal expansion of thymocyte populations occurs in these mice as early as 5 d after birth, which also suggests rapid onset of leukemia. Finally, a hypomorphic allele, IkL, has been generated by Kirstetter et al[13], in which, the LacZ gene was targeted into the second exon. In these mice, in-frame transcripts between exons 1 and 3 are generated, which produce low amounts of truncated Ikaros proteins (lacking the protein segment encoded by exon 2). All homozygote IkL/L mice develop T-cell lymphoma/leukemia in the thymus, with a median survival of 20 wk[14]. Thus, all mice that carry loss-of-function mutations in Ikaros develop T-cell leukemia with high incidence, which highlights a strong tumor suppressor function for Ikaros in the T-cell lineage.

Spontaneous Ikaros mutations are frequent in mouse T-ALL

The prevalent role for Ikaros as a tumor suppressor in mouse T-cell leukemia has been underscored by studies that have identified frequent loss-of-function Ikaros mutations in murine thymic lymphoma induced by irradiation, mutagens or deficiency in DNA repair pathways (Table 1). Ikaros mutations have been detected in 20-85% of the tumors, depending on the particular model and study. Two types of defects have been observed: focal genomic deletions (mostly heterozygous) in the proximal part of chromosome 11 where Ikaros is located; and point mutations in the coding regions that are missense mutations leading to amino acid changes in the DBD (and therefore are functionally similar to the Ikplastic mutation), or mutations leading to premature stop codons that probably behave as null alleles. Ikaros has also been identified in several studies as a recurrent locus mutated by retroviral insertion, which cooperates with other primary oncogenic events such as activated Notch1 or K-ras proteins, or p19ARF deficiency (Table 1). These insertions appear to promote abnormal splicing and the synthesis of aberrant, dominant-negative isoforms[15]. Together, these studies indicate that Ikaros is an important tumor suppressor gene whose inactivation can be triggered by several mechanisms in a variety of murine T-cell leukemias.

Table 1 Mutations of Ikaros in murine T-cell lymphomas.
StudyModelAlteration studiedType and frequency of Ikaros anomalies
Matsumoto et al[40], 1998γ-irradiation (Balb/c-MSM F1 hybrids)Genome-wide LOH mapping (microsatellites)Allelic loss in proximal chromosome 11 region: 40% (8/20)
Okano et al[41], 1999γ-irradiation (Balb/c-MSM F1 hybrids)LOH (polymorphic restriction site)Allelic loss: 54% (99/182)
Mutation analysis (SSCP and cDNA sequencing)Homozygous deletions: 8/1081
Missense point mutations in DBD: 5/1081
Frame-shift or stop codon point mutations: 6/1081
Shimada et al[42], 2000X-ray-induced thymic lymphomasLOH (microsatellite mapping)Distal region of chromosome 11 containing the Ikzf1 gene identified as a common deleted region in 50% of cases
Kakinuma et al[43], 2002X-ray-induced thymic lymphomasLOH RNA expression (RT-PCR) Protein expression (Western blotting) Point mutationsLOH for Ikzf1 in 20/37 tumors
No or dn transcripts in 9/37 tumors (correlated with absence of Ikaros proteins or presence of dn Ikaros proteins)
Point mutations in 9/37 tumors (mostly zinc finger point mutations)2
Karlsson et al[44], 2002Mutagen-induced thymic lymphomaPoint mutation analysis (SSCA and sequencing) Deletions (Southern) Allelic loss (microsatellite)8 DBD point mutations (8/104)
3 frame-shift mutations (3/104)
27% allelic loss (12/40)
3 homozygous deletions (3/68)
Beverly et al[15], 2003Notch1-IC transgenic micecooperating retroviral insertions40% (synthesis of dn proteins)
López-Nieva et al[18], 2004γ-irradiation (C57Bl6-Balb/c hybrids)LOH (polymorphic restriction site)42% (32/75) of LOH (1 homozygous deletion)
Point mutations (SSCP and sequencing)1 missense mutation in DBD
Kakinuma et al[45], 2005Mutagen-induced thymic lymphomaLOHLOH: 2/27
Point mutationsPoint mutations: 5/27 (all in zn finger regions)
Kang et al[46], 2006γ-irradiation (C57BL/6)CGH-array (BAC)Focal loss of chromosome 11: 20% (2/10)
Kakinuma et al[47], 2007Mlh1-deficient mice (20 spontaneous or radiation-induced lymphomas)Point mutation analysisFrame-shift point mutations: 85% (17/20)
Western blottingLack of Ikaros protein: 75% (15/20)
Ohi et al[48], 2007γ-irradiation (Balb/c-MSM F1 hybrids)LOH (polymorphic restriction site)43% (15/35)
Yoshida et al[49], 2007X-irradiation (C57Bl6-C3H F1 hybrids)KaryotypeInterstitial deletion of the proximal chromosome 11: 27% (7/15)
Uren et al[19], 2008p19ARF- and p53- deficient miceCommon retroviral insertions (CIS)33/5103 (mostly in p19ARF-deficient mice; strong association with Notch1 activation
Dail et al[20], 2010KrasG12D-induced thymic lymphomasRetroviral insertional mutagenesis30% (9/30) insertions into Ikaros gene leading to synthesis of dn proteins
Function of Ikaros in murine T-cell leukemogenesis

The studies of murine T-ALL models have implicated certain molecular pathways associated with the tumor suppressive activity of Ikaros. Several reports have found a strong link between Ikaros deficiency and the activation of the Notch pathway; the latter of which plays a crucial role in human and murine T-ALL development. (1) High levels of Notch target gene expression, as well as frequent selection of activating mutations in the Notch1 gene, have been documented in T-cell lymphoma from the mouse models with germline Ikaros deficiencies[14,16,17]; (2) The selection of secondary Ikaros mutations appears to be strongly associated with Notch1 mutations in mice[15,18-20]; and (3) Loss of Ikaros function directly cooperates with Notch activation to promote leukemia[15]. At the molecular level, Ikaros appears to bind similar DNA sequences as RBP-J, the transcriptional mediator of Notch signaling[14,15], and Ikaros expression inhibits the proliferation of leukemic cells and represses the expression of Notch target genes such as Hes1[14,17]. Furthermore, Ikaros has been shown to silence some Notch target gene transcription during T-cell differentiation, which suggests that increased sensitivity to Notch signals is crucial for promoting the outgrowth of Notch-dependent leukemic cells[14,21,22]. Ikaros-mediated silencing of Notch target gene expression appears to be particularly important at the DN4 stage of T-cell differentiation; a stage at which Notch target genes are downregulated and Ikaros expression is strongly upregulated[21]. In this respect, Kleinmann and coworkers have shown at the single cell level that WT DN4 cells can no longer transcribe Hes1 in response to Notch signaling, and that this desensitization to Notch is crucially dependent on Ikaros function[21]. Indeed, the DN4 compartment is expanded in the thymus of Ikaros-deficient mice, which suggests that Ikaros-regulated cell proliferation in this compartment might be particularly relevant to tumor suppression[21,23].

Recently, three groups have addressed the in vivo role of Notch signaling in Ikaros-deficient T-ALL, by deleting floxed RBP-J alleles in the T cells of mice carrying various Ikaros mutations. Chari et al[24] have studied the impact of RBP-J deletion on the expansion of clonal populations in Ikaros null mice. Germline disruption of RBP-J is lethal in utero, therefore, RBP-J was deleted specifically in DN4/DP (CD4+CD8+) thymocytes via CD4-Cre-mediated deletion of floxed RBP-J alleles. Surprisingly, clonal populations still emerge in RBP-J-deleted thymuses within the same time-frame as in RBP-J-proficient thymuses. However, these cells do not expand as efficiently as those from mice with undeleted RBP-J alleles, which suggests that RBP-J (and thus Notch signaling) is required for the expansion but not the initiation of Ikaros-deficient T-ALL. These results, however, must be interpreted with caution, as RBP-J levels were not measured in the clonal populations, and transformation may occur in cells with partially deleted RBP-J alleles. Similarly, we deleted RBP-J in IkL/L mice with the CD4-Cre transgene[25]. In this case, RBP-J deletion significantly delays leukemia onset, and the leukemias that develop in these mice still carry the undeleted RBP-J alleles, which suggests a selection of cells that express RBP-J. Finally, Gómez-del Arco et al[26] have deleted RBP-J in Ikdn+/- and Ik-/- mice using the CD2-Cre transgene, which deletes at the early thymic progenitor stage, and have also observed a significant decrease in leukemia incidence. Altogether, these results suggest an essential role for RBP-J and Notch signaling in the development of Ikaros-deficient T-ALL.

We and Gómez-del Arco et al[26] have further addressed the role of Notch1 in Ikaros-deficient thymocytes by deleting floxed Notch1 alleles that correspond to 3.5 kb of the Notch1 promoter and exon 1[25]. Surprisingly, this deletion greatly accelerates, rather than delays, leukemia development in both studies. Although the Notch1 alleles are efficiently deleted in T cells, truncated Notch1 proteins are generated from de novo transcripts that arise from cryptic intragenic promoters located between exons 25 and 27, or upstream of the deleted canonical promoter. Activation of the cryptic 3’ promoters is a direct consequence of the deletion of the canonical promoter, and an unexpected pro-oncogenic event[25]. Importantly, spontaneous Rag-mediated deletions of the Notch1 promoter region are common in murine T-ALL, including 75% of IkL/L leukemias[25,27,28]. Ikaros binds to both the 5’ and the intragenic cryptic promoters in WT thymocytes[25,26], which suggests that it plays a role in repressing their activity. If so, Ikaros deficiency may cooperate with Notch1 promoter deletions in promoting the activation of these alternative promoters. This hypothesis however awaits experimental demonstration.

Mouse studies have also implicated other pathways associated with Ikaros deficiency. Uren et al[19] have compared cooperating retroviral insertion sites between p19ARF- and p53-deficient tumor models, and have found Ikaros inactivation almost exclusively in p19ARF-deficient tumors, which suggests that loss of Ikaros cooperates selectively with p19ARF inactivation but not with that of p53. Interestingly, Dumortier et al[14] also have detected a big decrease in p19ARF RNA expression in leukemic T cells from IkL/L mice. Furthermore, concomitant loss of Ikaros and of p19ARF (encoded by the Cdkn2a gene) are hallmarks of human Bcr-Abl-positive B-ALL, which suggests a conserved cooperating pathway in lymphoid malignancies[29].

Finally, Winandy et al[23] have addressed the role of T cell receptor (TCR) signaling in the development of T-cell leukemia in Ikdn+/- mice. Leukemia fails to develop when the Ikdn+/- mutation is introduced onto a Rag1-/- background, which indicates an important role for the pre-TCR/TCR in leukemia development. Intriguingly, deletion of the α chain of the TCR dramatically accelerates leukemia progression, while ablation of the TCR β chain promotes the clonal expansion of cells expressing a γδTCR. These data indicate that signals from the pre-TCR or the γδTCR may synergize with Ikaros deficiency to promote the outgrowth of leukemic cells.

IKAROS IN HUMAN T-ALL
Evidence for Ikaros loss-of-function mutations in human T-ALL

The data demonstrating a clear role for Ikaros deficiency in the development of murine T-cell leukemia have prompted investigation into the possibility of a similar role in human T-ALL. A first study by Sun et al[30] has documented a strikingly high prevalence of aberrant, dominant-negative Ikaros isoforms and their cognate transcripts in all 18 cases of pediatric T-ALL studied. Furthermore, aberrant Ikaros proteins were localized in the cytoplasm of the leukemic cells. This study therefore seemed to indicate that Ikaros plays an important role in human T-ALL.

Additional studies by other groups, however, have not confirmed these results. Ikaros status in human T-ALL has now been analyzed by seven other groups over the years, in a total of 134 samples. All together, these studies have revealed six cases with Ikaros anomalies, most often with genomic deletions (Table 2). Several of these studies, however, have employed a limited set of assays, and could thus have missed some defects. Recently, Marçais et al[31] have performed a multi-parameter analysis of 25 T-ALL cases from diverse genetic subtypes, investigating DNA (by CGH-array), RNA (by reverse transcription polymerase chain reaction and cDNA sequencing) and protein (by Western blotting and intracellular localization by immunofluorescence), and found only one case with defective Ikaros. It appears therefore that Ikaros mutations that directly modify the gene and/or proteins are relatively rare in human T-ALL, and occur in approximately 5% of cases. It is unclear why Sun et al[32] have found so many T-ALL cases with aberrant Ikaros. Given the results of the other studies, it appears that the original study may have contained a systematic bias that led to the artefactual detection of aberrant proteins and RNAs. It should be noted that, in another study by the same authors, similarly high frequencies of Ikaros defects were found in B-ALL, which is also at odds with the current estimated frequency of approximatively 30% for these leukemias.

Table 2 Studies of Ikaros status in human T-cell acute lymphoblastic leukemia.
StudyNo. of patientsMethods usedCases with Ikaros abnormalities
Sun et al[30]18 (pediatric)WB, EMSA, IF, RT-PCR18/18
Nakase et al[50]5 (adult)RT-PCR0/5
Ruiz et al[51]9 (pediatric)RT-PCR, WB0/9
Maser et al[52]24 (16 cell lines and 8 primary leukemias)CGH-array2/24
Kuiper et al[53]7 (unknown origin)CGH-array0/7
Meleshko et al[54]14 (pediatric)RT-PCR1/14 (expression of dn Ik6 isoform)
Mullighan et al[6]50 (unknown origin)CGH-array2/50
Marçais et al[31]25 (adult, pediatric)CGH-array, RT-PCR, WB, IF, cDNA sequencing1/25

In addition to direct genetic inactivation, Ikaros can also be inactivated at the functional level. This possibility was suggested by Marçais et al[31] in an intriguing case of Ikaros protein delocalization in leukemic cells (TL92) that had lost one of its Ikaros alleles from a genomic deletion. When analyzed by immunofluorescence, the Ikaros proteins synthesized from the remaining allele appeared to localize to a discrete cytoplasmic location; possibly the centrosome. Unfortunately, the limited material from this patient prevented further characterization of the structure and mechanism involved in this delocalization. This observation suggests that delocalization of Ikaros proteins might contribute to Ikaros inactivation in some T-ALL patients. It will thus be interesting to conduct a systematic investigation of Ikaros localization in primary T-ALL cases.

It has also been suggested that Ikaros can be functionally inactivated following sequestration by the CALM-AF10 fusion protein in the cytoplasm, although this scenario is mostly based on overexpression experiments in cell lines[33]. CALM-AF10 translocation occurs in a subset of T-ALL, therefore, Ikaros localization in three primary T-ALL samples with the CALM-AF10 translocation was studied; no abnormality in Ikaros localization was observed[31]. However, the expression and localization of CALM-AF10 was not analyzed, and further studies are thus required to assess the link between CALM-AF10 and Ikaros in T-ALL.

Finally, Ikaros has been shown to be the target of secondary modifications that could alter its activity, such as phosphorylation and sumoylation[34,35], and the possible relevance of altered post-translational modifications in suppressing Ikaros function in leukemic cells has been proposed[36]. The role of indirect mechanisms that inactivate Ikaros will be important to investigate in the future.

Is loss of Ikaros important in human T-ALL?

Despite the low prevalence, Ikaros loss of function is clearly a recurrent anomaly in human T-ALL. Thus, Ikaros inactivation is unlikely to be a bystander defect and could play a causal role in disease progression in a subset of T-ALL cases. T-ALL is a particularly heterogeneous disease with multiple subtypes, therefore, it will be important to determine if loss of Ikaros is associated with a specific class of T-ALL, or if Ikaros defects spread across molecular subtypes.

Given the strong link between Ikaros inactivation and Notch activation in murine T-ALL, a possible role for Ikaros loss in promoting Notch activation in human T-ALL is obviously of interest. However, Notch target gene activation is not particularly elevated in the TL92 case when compared with others[31]. Conversely, cases with high Notch target gene expression appear to express normal Ikaros[31]. Thus, Ikaros deficiency in human T-ALL may not be as strongly associated with Notch activation as it is in mice, and other pathways might be critical in human T-ALL. It will therefore be essential to achieve a better understanding of how Ikaros suppresses leukemogenesis independent of Notch. In this respect, insights gained from the role of Ikaros mutations in B-ALL will be relevant, as Notch has so far not been implicated in these leukemias.

CONCLUSION

The importance of Ikaros as a tumor suppressor in murine T-cell leukemia has been known for about 15 years, but it is only becoming clear that Ikaros inactivation is a recurrent event in human T-ALL. Given that Ikaros is also a major tumor suppressor in human B-ALL[6,37,38], and that reduced Ikaros function dramatically accelerates B-cell leukemia development in mice[39], we hypothesize that Ikaros functions via common mechanisms to suppress B-ALL and T-ALL. Defining these mechanisms will be the central aim of future research on the role of Ikaros in lymphoid malignancies.

Footnotes

Peer reviewers: Mehrdad Mohri, DVM, DVSc, Professor of Veterinary Clinical Pathology, Department of Clinical Sciences, School of Veterinary Medicine, Ferdowsi University of Mashhad, PO Box 91775-1793, Mashhad, Iran; Martin Götte, PhD, Assistant Professor of Medical Biochemistry, Department of Gynecology and Obstetrics, Muenster University Hospital, Domagkstr. 11, D-48149 Muenster, Germany

S- Editor Cheng JX L- Editor Kerr C E- Editor Zheng XM

References
1.  Molnár A, Georgopoulos K. The Ikaros gene encodes a family of functionally diverse zinc finger DNA-binding proteins. Mol Cell Biol. 1994;14:8292-8303.  [PubMed]  [DOI]
2.  Hahm K, Ernst P, Lo K, Kim GS, Turck C, Smale ST. The lymphoid transcription factor LyF-1 is encoded by specific, alternatively spliced mRNAs derived from the Ikaros gene. Mol Cell Biol. 1994;14:7111-7123.  [PubMed]  [DOI]
3.  Kim J, Sif S, Jones B, Jackson A, Koipally J, Heller E, Winandy S, Viel A, Sawyer A, Ikeda T. Ikaros DNA-binding proteins direct formation of chromatin remodeling complexes in lymphocytes. Immunity. 1999;10:345-355.  [PubMed]  [DOI]
4.  Sridharan R, Smale ST. Predominant interaction of both Ikaros and Helios with the NuRD complex in immature thymocytes. J Biol Chem. 2007;282:30227-30238.  [PubMed]  [DOI]
5.  Tonnelle C, Imbert MC, Sainty D, Granjeaud S, N'Guyen C, Chabannon C. Overexpression of dominant-negative Ikaros 6 protein is restricted to a subset of B common adult acute lymphoblastic leukemias that express high levels of the CD34 antigen. Hematol J. 2003;4:104-109.  [PubMed]  [DOI]
6.  Mullighan CG, Miller CB, Radtke I, Phillips LA, Dalton J, Ma J, White D, Hughes TP, Le Beau MM, Pui CH. BCR-ABL1 lymphoblastic leukaemia is characterized by the deletion of Ikaros. Nature. 2008;453:110-114.  [PubMed]  [DOI]
7.  Papaemmanuil E, Hosking FJ, Vijayakrishnan J, Price A, Olver B, Sheridan E, Kinsey SE, Lightfoot T, Roman E, Irving JA. Loci on 7p12.2, 10q21.2 and 14q11.2 are associated with risk of childhood acute lymphoblastic leukemia. Nat Genet. 2009;41:1006-1010.  [PubMed]  [DOI]
8.  Treviño LR, Yang W, French D, Hunger SP, Carroll WL, Devidas M, Willman C, Neale G, Downing J, Raimondi SC. Germline genomic variants associated with childhood acute lymphoblastic leukemia. Nat Genet. 2009;41:1001-1005.  [PubMed]  [DOI]
9.  Georgopoulos K, Bigby M, Wang JH, Molnar A, Wu P, Winandy S, Sharpe A. The Ikaros gene is required for the development of all lymphoid lineages. Cell. 1994;79:143-156.  [PubMed]  [DOI]
10.  Winandy S, Wu P, Georgopoulos K. A dominant mutation in the Ikaros gene leads to rapid development of leukemia and lymphoma. Cell. 1995;83:289-299.  [PubMed]  [DOI]
11.  Papathanasiou P, Perkins AC, Cobb BS, Ferrini R, Sridharan R, Hoyne GF, Nelms KA, Smale ST, Goodnow CC. Widespread failure of hematolymphoid differentiation caused by a recessive niche-filling allele of the Ikaros transcription factor. Immunity. 2003;19:131-144.  [PubMed]  [DOI]
12.  Wang JH, Nichogiannopoulou A, Wu L, Sun L, Sharpe AH, Bigby M, Georgopoulos K. Selective defects in the development of the fetal and adult lymphoid system in mice with an Ikaros null mutation. Immunity. 1996;5:537-549.  [PubMed]  [DOI]
13.  Kirstetter P, Thomas M, Dierich A, Kastner P, Chan S. Ikaros is critical for B cell differentiation and function. Eur J Immunol. 2002;32:720-730.  [PubMed]  [DOI]
14.  Dumortier A, Jeannet R, Kirstetter P, Kleinmann E, Sellars M, dos Santos NR, Thibault C, Barths J, Ghysdael J, Punt JA. Notch activation is an early and critical event during T-Cell leukemogenesis in Ikaros-deficient mice. Mol Cell Biol. 2006;26:209-220.  [PubMed]  [DOI]
15.  Beverly LJ, Capobianco AJ. Perturbation of Ikaros isoform selection by MLV integration is a cooperative event in Notch(IC)-induced T cell leukemogenesis. Cancer Cell. 2003;3:551-564.  [PubMed]  [DOI]
16.  Mantha S, Ward M, McCafferty J, Herron A, Palomero T, Ferrando A, Bank A, Richardson C. Activating Notch1 mutations are an early event in T-cell malignancy of Ikaros point mutant Plastic/+ mice. Leuk Res. 2007;31:321-327.  [PubMed]  [DOI]
17.  Kathrein KL, Chari S, Winandy S. Ikaros directly represses the notch target gene Hes1 in a leukemia T cell line: implications for CD4 regulation. J Biol Chem. 2008;283:10476-10484.  [PubMed]  [DOI]
18.  López-Nieva P, Santos J, Fernández-Piqueras J. Defective expression of Notch1 and Notch2 in connection to alterations of c-Myc and Ikaros in gamma-radiation-induced mouse thymic lymphomas. Carcinogenesis. 2004;25:1299-1304.  [PubMed]  [DOI]
19.  Uren AG, Kool J, Matentzoglu K, de Ridder J, Mattison J, van Uitert M, Lagcher W, Sie D, Tanger E, Cox T. Large-scale mutagenesis in p19(ARF)- and p53-deficient mice identifies cancer genes and their collaborative networks. Cell. 2008;133:727-741.  [PubMed]  [DOI]
20.  Dail M, Li Q, McDaniel A, Wong J, Akagi K, Huang B, Kang HC, Kogan SC, Shokat K, Wolff L. Mutant Ikzf1, KrasG12D, and Notch1 cooperate in T lineage leukemogenesis and modulate responses to targeted agents. Proc Natl Acad Sci U S A. 2010;107:5106-5111.  [PubMed]  [DOI]
21.  Kleinmann E, Geimer Le Lay AS, Sellars M, Kastner P, Chan S. Ikaros represses the transcriptional response to Notch signaling in T-cell development. Mol Cell Biol. 2008;28:7465-7475.  [PubMed]  [DOI]
22.  Chari S, Winandy S. Ikaros regulates Notch target gene expression in developing thymocytes. J Immunol. 2008;181:6265-6274.  [PubMed]  [DOI]
23.  Winandy S, Wu L, Wang JH, Georgopoulos K. Pre-T cell receptor (TCR) and TCR-controlled checkpoints in T cell differentiation are set by Ikaros. J Exp Med. 1999;190:1039-1048.  [PubMed]  [DOI]
24.  Chari S, Umetsu SE, Winandy S. Notch target gene deregulation and maintenance of the leukemogenic phenotype do not require RBP-J kappa in Ikaros null mice. J Immunol. 2010;185:410-417.  [PubMed]  [DOI]
25.  Jeannet R, Mastio J, Macias-Garcia A, Oravecz A, Ashworth T, Geimer Le Lay AS, Jost B, Le Gras S, Ghysdael J, Gridley T. Oncogenic activation of the Notch1 gene by deletion of its promoter in Ikaros-deficient T-ALL. Blood. 2010;116:5443-5454.  [PubMed]  [DOI]
26.  Gómez-del Arco P, Kashiwagi M, Jackson AF, Naito T, Zhang J, Liu F, Kee B, Vooijs M, Radtke F, Redondo JM. Alternative promoter usage at the Notch1 locus supports ligand-independent signaling in T cell development and leukemogenesis. Immunity. 2010;33:685-698.  [PubMed]  [DOI]
27.  Ashworth TD, Pear WS, Chiang MY, Blacklow SC, Mastio J, Xu L, Kelliher M, Kastner P, Chan S, Aster JC. Deletion-based mechanisms of Notch1 activation in T-ALL: key roles for RAG recombinase and a conserved internal translational start site in Notch1. Blood. 2010;116:5455-5464.  [PubMed]  [DOI]
28.  Tsuji H, Ishii-Ohba H, Noda Y, Kubo E, Furuse T, Tatsumi K. Rag-dependent and Rag-independent mechanisms of Notch1 rearrangement in thymic lymphomas of Atm(-/-) and scid mice. Mutat Res. 2009;660:22-32.  [PubMed]  [DOI]
29.  Mullighan CG, Williams RT, Downing JR, Sherr CJ. Failure of CDKN2A/B (INK4A/B-ARF)-mediated tumor suppression and resistance to targeted therapy in acute lymphoblastic leukemia induced by BCR-ABL. Genes Dev. 2008;22:1411-1415.  [PubMed]  [DOI]
30.  Sun L, Crotty ML, Sensel M, Sather H, Navara C, Nachman J, Steinherz PG, Gaynon PS, Seibel N, Mao C. Expression of dominant-negative Ikaros isoforms in T-cell acute lymphoblastic leukemia. Clin Cancer Res. 1999;5:2112-2120.  [PubMed]  [DOI]
31.  Marçais A, Jeannet R, Hernandez L, Soulier J, Sigaux F, Chan S, Kastner P. Genetic inactivation of Ikaros is a rare event in human T-ALL. Leuk Res. 2010;34:426-429.  [PubMed]  [DOI]
32.  Sun L, Heerema N, Crotty L, Wu X, Navara C, Vassilev A, Sensel M, Reaman GH, Uckun FM. Expression of dominant-negative and mutant isoforms of the antileukemic transcription factor Ikaros in infant acute lymphoblastic leukemia. Proc Natl Acad Sci U S A. 1999;96:680-685.  [PubMed]  [DOI]
33.  Greif PA, Tizazu B, Krause A, Kremmer E, Bohlander SK. The leukemogenic CALM/AF10 fusion protein alters the subcellular localization of the lymphoid regulator Ikaros. Oncogene. 2008;27:2886-2896.  [PubMed]  [DOI]
34.  Gómez-del Arco P, Maki K, Georgopoulos K. Phosphorylation controls Ikaros's ability to negatively regulate the G(1)-S transition. Mol Cell Biol. 2004;24:2797-2807.  [PubMed]  [DOI]
35.  Gurel Z, Ronni T, Ho S, Kuchar J, Payne KJ, Turk CW, Dovat S. Recruitment of ikaros to pericentromeric heterochromatin is regulated by phosphorylation. J Biol Chem. 2008;283:8291-8300.  [PubMed]  [DOI]
36.  Dovat S, Payne KJ. Tumor suppression in T cell leukemia--the role of Ikaros. Leuk Res. 2010;34:416-417.  [PubMed]  [DOI]
37.  Trageser D, Iacobucci I, Nahar R, Duy C, von Levetzow G, Klemm L, Park E, Schuh W, Gruber T, Herzog S. Pre-B cell receptor-mediated cell cycle arrest in Philadelphia chromosome-positive acute lymphoblastic leukemia requires IKAROS function. J Exp Med. 2009;206:1739-1753.  [PubMed]  [DOI]
38.  Iacobucci I, Storlazzi CT, Cilloni D, Lonetti A, Ottaviani E, Soverini S, Astolfi A, Chiaretti S, Vitale A, Messa F. Identification and molecular characterization of recurrent genomic deletions on 7p12 in the IKZF1 gene in a large cohort of BCR-ABL1-positive acute lymphoblastic leukemia patients: on behalf of Gruppo Italiano Malattie Ematologiche dell'Adulto Acute Leukemia Working Party (GIMEMA AL WP). Blood. 2009;114:2159-2167.  [PubMed]  [DOI]
39.  Virely C, Moulin S, Cobaleda C, Lasgi C, Alberdi A, Soulier J, Sigaux F, Chan S, Kastner P, Ghysdael J. Haploinsufficiency of the IKZF1 (IKAROS) tumor suppressor gene cooperates with BCR-ABL in a transgenic model of acute lymphoblastic leukemia. Leukemia. 2010;24:1200-1204.  [PubMed]  [DOI]
40.  Matsumoto Y, Kosugi S, Shinbo T, Chou D, Ohashi M, Wakabayashi Y, Sakai K, Okumoto M, Mori N, Aizawa S. Allelic loss analysis of gamma-ray-induced mouse thymic lymphomas: two candidate tumor suppressor gene loci on chromosomes 12 and 16. Oncogene. 1998;16:2747-2754.  [PubMed]  [DOI]
41.  Okano H, Saito Y, Miyazawa T, Shinbo T, Chou D, Kosugi S, Takahashi Y, Odani S, Niwa O, Kominami R. Homozygous deletions and point mutations of the Ikaros gene in gamma-ray-induced mouse thymic lymphomas. Oncogene. 1999;18:6677-6683.  [PubMed]  [DOI]
42.  Shimada Y, Nishimura M, Kakinuma S, Okumoto M, Shiroishi T, Clifton KH, Wakana S. Radiation-associated loss of heterozygosity at the Znfn1a1 (Ikaros) locus on chromosome 11 in murine thymic lymphomas. Radiat Res. 2000;154:293-300.  [PubMed]  [DOI]
43.  Kakinuma S, Nishimura M, Sasanuma S, Mita K, Suzuki G, Katsura Y, Sado T, Shimada Y. Spectrum of Znfn1a1 (Ikaros) inactivation and its association with loss of heterozygosity in radiogenic T-cell lymphomas in susceptible B6C3F1 mice. Radiat Res. 2002;157:331-340.  [PubMed]  [DOI]
44.  Karlsson A, Söderkvist P, Zhuang SM. Point mutations and deletions in the znfn1a1/ikaros gene in chemically induced murine lymphomas. Cancer Res. 2002;62:2650-2653.  [PubMed]  [DOI]
45.  Kakinuma S, Nishimura M, Kubo A, Nagai JY, Amasaki Y, Majima HJ, Sado T, Shimada Y. Frequent retention of heterozygosity for point mutations in p53 and Ikaros in N-ethyl-N-nitrosourea-induced mouse thymic lymphomas. Mutat Res. 2005;572:132-141.  [PubMed]  [DOI]
46.  Kang HM, Jang JJ, Langford C, Shin SH, Park SY, Chung YJ. DNA copy number alterations and expression of relevant genes in mouse thymic lymphomas induced by gamma-irradiation and N-methyl-N-nitrosourea. Cancer Genet Cytogenet. 2006;166:27-35.  [PubMed]  [DOI]
47.  Kakinuma S, Kodama Y, Amasaki Y, Yi S, Tokairin Y, Arai M, Nishimura M, Monobe M, Kojima S, Shimada Y. Ikaros is a mutational target for lymphomagenesis in Mlh1-deficient mice. Oncogene. 2007;26:2945-2949.  [PubMed]  [DOI]
48.  Ohi H, Mishima Y, Kamimura K, Maruyama M, Sasai K, Kominami R. Multi-step lymphomagenesis deduced from DNA changes in thymic lymphomas and atrophic thymuses at various times after gamma-irradiation. Oncogene. 2007;26:5280-5289.  [PubMed]  [DOI]
49.  Yoshida MA, Nakata A, Akiyama M, Kakinuma S, Sado T, Nishimura M, Shimada Y. Distinct structural abnormalities of chromosomes 11 and 12 associated with loss of heterozygosity in X-ray-induced mouse thymic lymphomas. Cancer Genet Cytogenet. 2007;179:1-10.  [PubMed]  [DOI]
50.  Nakase K, Ishimaru F, Avitahl N, Dansako H, Matsuo K, Fujii K, Sezaki N, Nakayama H, Yano T, Fukuda S. Dominant negative isoform of the Ikaros gene in patients with adult B-cell acute lymphoblastic leukemia. Cancer Res. 2000;60:4062-4065.  [PubMed]  [DOI]
51.  Ruiz A, Jiang J, Kempski H, Brady HJ. 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. Br J Haematol. 2004;125:31-37.  [PubMed]  [DOI]
52.  Maser RS, Choudhury B, Campbell PJ, Feng B, Wong KK, Protopopov A, O'Neil J, Gutierrez A, Ivanova E, Perna I. Chromosomally unstable mouse tumours have genomic alterations similar to diverse human cancers. Nature. 2007;447:966-971.  [PubMed]  [DOI]
53.  Kuiper RP, Schoenmakers EF, van Reijmersdal SV, Hehir-Kwa JY, van Kessel AG, van Leeuwen FN, Hoogerbrugge PM. High-resolution genomic profiling of childhood ALL reveals novel recurrent genetic lesions affecting pathways involved in lymphocyte differentiation and cell cycle progression. Leukemia. 2007;21:1258-1266.  [PubMed]  [DOI]
54.  Meleshko AN, Movchan LV, Belevtsev MV, Savitskaja TV. Relative expression of different Ikaros isoforms in childhood acute leukemia. Blood Cells Mol Dis. 2008;41:278-283.  [PubMed]  [DOI]