A dominant mutation in the Ikaros gene leads to rapid development of leukemia and lymphoma

Ikaros promotes early-born neuronal fates in the cerebral cortex

During cerebral cortex development, a series of projection neuron types is generated in a fixed temporal order. In Drosophila neuroblasts, the transcription factor hunchback encodes first-born identity within neural lineages. One of its mammalian homologs, Ikaros, was recently reported to play an equivalent role in retinal progenitor cells, raising the question as to whether Ikaros/Hunchback proteins could be general factors regulating the development of early-born fates throughout the nervous system. Ikaros is also expressed in progenitor cells of the mouse cerebral cortex, and this expression is highest during the early stages of neurogenesis and thereafter decreases over time. Transgenic mice with sustained Ikaros expression in cortical progenitor cells and neurons have developmental defects, including displaced progenitor cells within the cortical plate, increased early neural differentiation, and disrupted cortical lamination. Sustained Ikaros expression results in a prolonged period of generation of deep layer neurons into the stages when, normally, only late-born upper layer neurons are generated, as well as a delayed production of late-born neurons. Consequently, more early-born and fewer late-born neurons are present in the cortex of these mice at birth. This phenotype was observed in all parts of the cortex, including those with minimal structural defects, demonstrating that it is not secondary to abnormalities in cortical morphogenesis. These data suggest that Ikaros plays a similar role in regulating early temporal fates in the mammalian cerebral cortex as Ikaros/Hunchback proteins do in the Drosophila nerve cord.

Ikaros inhibits megakaryopoiesis through functional interaction with GATA-1 and NOTCH signaling

The transcription factor Ikaros regulates the development of hematopoietic cells. Ikaros-deficient animals fail to develop B cells and display a T-cell malignancy, which is correlated with altered Notch signaling. Recently, loss of Ikaros was associated with progression of myeloproliferative neoplasms to acute myeloid leukemia and increasing evidence shows that Ikaros is also critical for the regulation of myeloid development. Previous studies showed that Ikaros-deficient mice have increased megakaryopoiesis, but the molecular mechanism of this phenomenon remains unknown. Here, we show that Ikaros overexpression decreases NOTCH-induced megakaryocytic specification, and represses expression of several megakaryocytic genes including GATA-1 to block differentiation and terminal maturation. We also demonstrate that Ikaros expression is differentially regulated by GATA-2 and GATA-1 during megakaryocytic differentiation and reveal that the combined loss of Ikzf1 and Gata1 leads to synthetic lethality in vivo associated with prominent defects in erythroid cells and an expansion of megakaryocyte progenitors. Taken together, our observations demonstrate an important functional interplay between Ikaros, GATA factors, and the NOTCH signaling pathway in specification and homeostasis of the megakaryocyte lineage.

Ikaros is a critical target during simultaneous exposure to X-rays and N-ethyl-N-nitrosourea in mouse T-cell lymphomagenesis

Cancer risk associated with radiation exposure is considered the result of concurrent exposure to other natural and manmade carcinogens. Available data on the molecular characteristics of cancer after simultaneous exposure to radiation and chemicals are insufficient. In our study, we used a mouse thymic lymphoma (TL) model that was synergistically induced by simultaneous exposure to X-rays and N-ethyl-N-nitrosourea (ENU) at subcarcinogenic doses and analyzed the mutation frequency and spectrum of the TL-associated genes Ikaros, Notch1, p53 and Kras. We found that the point mutation frequency in Ikaros was significantly increased to 47% for simultaneous exposure compared to 13 and 0% for X-ray and ENU exposure alone, respectively. These mutations were mostly G:C > A:T at non-CpG sites and T:A > C:G, both of which are characteristic of ENU mutagenesis. About half of the point mutations were accompanied by loss of heterozygosity (LOH), typical of X-irradiation. The remaining half did not include LOH, which suggests that they were dominant-negative mutations. In Notch1, the frequency of abnormalities was high (>58%) regardless of the treatment, suggesting that Notch1 aberration may be important for T-cell lymphomagenesis. The p53 and Kras mutation frequencies were low for all treatments (<23%). Importantly, the frequency of TLs containing mutations in multiple genes, especially both Ikaros and Notch1, increased after simultaneous exposure. Thus, after simultaneous exposure, Ikaros is a critical target and is inactivated by ENU-induced point mutations and/or X-ray-induced LOH in T-cell lymphomagenesis. Furthermore, concomitant alterations of multiple tumor-associated genes may contribute to enhanced lymphomagenesis after simultaneous exposure.

Ikaros family transcription factors expression in rat thymus: detection of impaired development

The expression of Ikaros family transcription factors and consequently their signalling pathway is limiting for hematopoietic and lymphocyte development in mice and human. Due to their importance, these transcription factors are highly homologous between species. As an initial approach to examining the possible involvement of Ikaros transcription factors in pathogenesis of rat lymphoid development, we analyzed the expression of all known Ikaros family members, Ikaros, Aiolos, Helios, Eos and Pegasus in the rat thymus. We established a semi-quantitative RT-PCR to detect mRNA of each transcription factor. For the first time we give evidence of the expression of Ikaros family transcription factors in the rat thymus. Further, we evaluated whether their mRNA expression was succumbed to changes when the rats were exposed to ethanol, as a known debilitating agent during development. Therefore we analyzed the thymus of adult rats whose mothers were forced to drink ethanol during gestation, to detect possible changes in thymus mRNA expression levels of Ikaros, Aiolos, Helios, Eos and Pegasus. We found that rats prenatally exposed to ethanol show a slightly higher expression of Ikaros family transcription factors in the adult thymus when compared to control rats, but these differences were not statistically significant. We further studied the distribution of the major lymphocyte subpopulations in the rat thymus according to CD3, CD4 and CD8 expression by four color flow cytometry. We found a higher incidence of CD3 positive cells in the double positive, CD4+CD8+ thymic subpopulation of rats prenatally exposed to ethanol when compared to non-exposed animals. Our findings indicate that ethanol exposure of pregnant rats might influence the development of CD3 positive cells in the thymus of the offspring but this result should be further tackled at the level of transcription factor expression.

Genome-wide identification of Ikaros targets elucidates its contribution to mouse B-cell lineage specification and pre-B-cell differentiation

Ikaros family DNA-binding proteins are critical regulators of B-cell development. Because the current knowledge of Ikaros targets in B-cell progenitors is limited, we have identified genes that are bound and regulated by Ikaros in pre-B cells. To elucidate the role of Ikaros in B-cell lineage specification and differentiation, we analyzed the differential expression of Ikaros targets during the progression of multipotent to lymphoid-restricted progenitors, B- and T-cell lineage specification, and progression along the B-cell lineage. Ikaros targets accounted for one-half of all genes up-regulated during B-cell lineage specification in vivo, explaining the essential role of Ikaros in this process. Expression of the Ikaros paralogs Ikzf1 and Ikzf3 increases incrementally during B-cell progenitor differentiation, and, remarkably, inducible Ikaros expression in cycling pre-B cells was sufficient to drive transcriptional changes resembling the differentiation of cycling to resting pre-Bcells in vivo. The data suggest that Ikaros transcription factor dosage drives the progression of progenitors along a predetermined lineage by regulating multiple targets in key pathways, including pre-B–cell receptor signaling, cell cycle progression, and lymphocyte receptor rearrangement.Our approachmay be of general use to map the contribution of transcription factors to cell lineage commitment and differentiation.

Polycystin-1 regulates the stability and ubiquitination of transcription factor Jade-1

Autosomal-dominant polycystic kidney disease (ADPKD) and von Hippel-Lindau (VHL) disease lead to large kidney cysts that share pathogenetic features. The polycystin-1 (PC1) and pVHL proteins may therefore participate in the same key signaling pathways. Jade-1 is a pro-apoptotic and growth suppressive ubiquitin ligase for beta-catenin and transcriptional coactivator associated with histone acetyltransferase activity that is stabilized by pVHL in a manner that correlates with risk of VHL renal disease. Thus, a relationship between Jade-1 and PC1 was sought. Full-length PC1 bound, stabilized and colocalized with Jade-1 and inhibited Jade-1 ubiquitination. In contrast, the cytoplasmic tail or the naturally occurring C-terminal fragment of PC1 (PC1-CTF) promoted Jade-1 ubiquitination and degradation, suggesting a dominant-negative mechanism. ADPKD-associated PC1 mutants failed to regulate Jade-1, indicating a potential disease link. Jade-1 ubiquitination was mediated by Siah-1, an E3 ligase that binds PC1. By controlling Jade-1 abundance, PC1 and the PC1-CTF differentially regulate Jade-1-mediated transcriptional activity. A key target of PC1, the cyclin-dependent kinase inhibitor p21, is also up-regulated by Jade-1. Through Jade-1, PC1 and PC1 cleaved forms may exert fine control of beta-catenin and canonical Wnt signaling, a critical pathway in cystic renal disease. Thus, Jade-1 is a transcription factor and ubiquitin ligase whose activity is regulated by PC1 in a manner that is physiologic and may correlate with disease. Jade-1 may be an important therapeutic target in renal cystogenesis.

Advances in the molecular pathobiology of B-lymphoblastic leukemia

B-lymphoblastic leukemia/lymphoma, also known as B-acute lymphoblastic leukemia, is derived from B-cell progenitors. B-acute lymphoblastic leukemia occurs predominantly in children, but can occur at any age. Risk-adapted intensive chemotherapy is effective in treating most children with B-acute lymphoblastic leukemia, but this approach is less successful in adults. Recent developments in genome-wide genetic analysis in B-acute lymphoblastic leukemia have provided insights into disease pathogenesis and prognosis. B-acute lymphoblastic leukemia cases usually carry a primary genetic event, often a chromosome translocation, and a constellation of secondary genetic alterations that are acquired and selected dynamically in a nonlinear fashion. These genetic changes commonly affect cellular mechanisms that control B-cell differentiation and proliferation. The cooperative interaction between inactivation of hematopoietic transcription factors involved in differentiation (class II mutation) and activating mutations involved in cell proliferation (class I mutation) is reminiscent of the pathogenic model of acute myeloid leukemia. The resulting improved molecular understanding of B-acute lymphoblastic leukemia is helping to refine disease risk stratification and discover new therapeutic approaches for patients with refractory disease. In this review, we first summarize the clinicopathologic and immunophenotypic features of B-acute lymphoblastic leukemia and introduce current understanding of B-cell development and B-acute lymphoblastic leukemia leukemogenesis. We then focus on recent advances in genetic analysis and gene expression profiling of B-acute lymphoblastic leukemia and discuss the implications of these findings for disease evolution, risk prediction, and possible novel therapeutic approaches.

IKAROS deletions dictate a unique gene expression signature in patients with adult B-cell acute lymphoblastic leukemia

BACKGROUND

Deletions of IKAROS (IKZF1) frequently occur in B-cell precursor acute lymphoblastic leukemia (B-ALL) but the mechanisms by which they influence pathogenesis are unclear. To address this issue, a cohort of 144 adult B-ALL patients (106 BCR-ABL1-positive and 38 B-ALL negative for known molecular rearrangements) was screened for IKZF1 deletions by single nucleotide polymorphism (SNP) arrays; a sub-cohort of these patients (44%) was then analyzed for gene expression profiling.

PRINCIPAL FINDINGS

Total or partial deletions of IKZF1 were more frequent in BCR-ABL1-positive than in BCR-ABL1-negative B-ALL cases (75% vs 58%, respectively, p = 0.04). Comparison of the gene expression signatures of patients carrying IKZF1 deletion vs those without showed a unique signature featured by down-regulation of B-cell lineage and DNA repair genes and up-regulation of genes involved in cell cycle, JAK-STAT signalling and stem cell self-renewal. Through chromatin immunoprecipitation and luciferase reporter assays we corroborated these findings both in vivo and in vitro, showing that Ikaros deleted isoforms lacked the ability to directly regulate a large group of the genes in the signature, such as IGLL1, BLK, EBF1, MSH2, BUB3, ETV6, YES1, CDKN1A (p21), CDKN2C (p18) and MCL1.

CONCLUSIONS

Here we identified and validated for the first time molecular pathways specifically controlled by IKZF1, shedding light into IKZF1 role in B-ALL pathogenesis.

Cell cycle-specific function of Ikaros in human leukemia

BACKGROUND

The loss of Ikaros is associated with the development of B and T cell leukemia. Data on Ikaros function, including its role as a tumor suppressor and a regulator of cell cycle progression, come almost exclusively from murine studies; little is known of the mechanisms that regulate human Ikaros function. Our studies are the first to examine the function and regulation of human Ikaros isoforms during the cell cycle in human ALL.

PROCEDURES

Electromobility shift assay (EMSA), confocal microscopy, and phosphopeptide mapping were used to study Ikaros function during different stages of the cell cycle.

RESULTS

The DNA-binding activity of human Ikaros complexes undergoes dynamic changes as the cell cycle progresses. In S phase, Ikaros DNA-binding affinity for regulatory regions of its target genes decreases, while its binding to pericentromeric heterochromatin is preserved and correlates with Ikaros pericentromeric localization. These S phase-specific changes in Ikaros function are controlled by phosphorylation via the CK2 kinase pathway. During cell cycle progression, the subcellular pericentromeric localization of the largest human Ikaros isoforms is different from that in mouse cells, suggesting unique functions for human Ikaros.

CONCLUSIONS

Our results demonstrate that the function of Ikaros is cell cycle-specific and controlled by CK2-mediated phosphorylation during S phase of the cell cycle in human T-cell and B-cell ALL. The differences we observe in murine and human Ikaros function highlight the importance of using human cells in studies of ALL. These data identify the CK2 pathway as a target for therapies in ALL.

IKZF1: a critical role in the pathogenesis of systemic lupus erythematosus?

Ikaros family zinc finger 1, encoded by IKZF1, are lymphoid-restricted zinc finger transcription factors that share common N-terminal Kruppel-like zinc finger DNA-binding domain. IKZF1 play multiple important roles on regulators of lymphocyte differentiation and hematological tumor suppressor. Our genome-wide association (GWA) studies in systemic lupus erythematosus (SLE) independently identified genetic variants in IKZF1 associated with SLE, which are supported by other studies. Previous studies found that lower expression of IKZF1 may play critical roles in activating some signal pathways involved in SLE, such as signal transducers and activators of transcription (STAT)4 and interferon pathways. In addition, IKZF1 has been implicated in roles involved in some hematologic traits or abnormalities, such as erythrocyte measures, myelofibrosis, and acute lymphoblastic leukemia (ALL), which may be common clinical manifestations or co-occurrence hematological diseases of patients with SLE. All these findings suggest that IKZF1 may play a critical role in the pathogenesis of SLE. In this article, we discuss the existing understanding of the role of IKZF1 on the physiological and pathological functions associated with SLE, providing insights that may assist in the development of new therapeutic strategies based on IKZF1 for patients with SLE.

Illegitimate V(D)J recombination involving nonantigen receptor loci in lymphoid malignancy

V(D)J recombination of antigen receptor loci (IGH, IGK, IGL, TCRA, TCRB, TCRG, and TCRD) is an essential mechanism that confers enormous diversity to the mammalian immune system. However, there are now at least six examples of intrachromosomal interstitial deletions caused by aberrant V(D)J recombination between nonantigen receptor loci; five of out these six are associated with lymphoid malignancy. The SIL-SCL fusion and deletions of CDKN2A, IKZF1, Notch1, and Bcl11b are all associated with lymphoid malignancy. These interstitial deletions seem to be species specific, as the deletions seen in mice are not seen in humans; the converse is true as well. Nucleotide sequence analysis of these rearrangements reveals the hallmarks of V(D)J recombination, including site specificity near cryptic heptamer signal sequences, exonucleolytic "nibbling" at the junction site, and nontemplated "N"-region nucleotide insertion at the junction site. Two of these interstitial deletions (murine Notch1 and Bcl11b deletions) have been detected, at low frequency, in tissues from healthy mice with no evidence of malignancy, similar to the finding of chromosomal translocations in the peripheral blood or tonsils of healthy individuals. The contention that these are mediated via V(D)J recombination is strengthened by in vivo assays using extrachromosomal substrates, and chromatin immunoprecipitation-sequence analysis which shows Rag2 binding at the sites of rearrangement. Although the efficiency of these "illegitimate" recombination events is several orders of magnitude less than that at bona fide antigen receptor loci, the consequence of such deletions, namely activation of proto-oncogenes or deletion of tumor suppressor genes, is devastating, and a major cause for lymphoid malignancy.

Kidney injury accelerates cystogenesis via pathways modulated by heme oxygenase and complement

AKI accelerates cystogenesis. Because cystogenic mutations induce strong transcriptional responses similar to those seen after AKI, these responses may accelerate the progression of cystic renal disease. Here, we modulated the severity of the AKI-like response in Cys1(cpk/cpk) mice, a model that mimics autosomal recessive polycystic kidney disease. Specifically, we induced or inhibited activity of the renoprotective enzyme heme oxygenase (HO) and determined the effects on renal cystogenesis. We found that induction of HO attenuated both renal injury and the rate of cystogenesis, whereas inhibition of HO promoted cystogenesis. HO activity mediated the response of NFκB, which is a hallmark transcriptional feature common to both cystogenesis and AKI. Among the HO-modulated effects we measured, expression of complement component 3 (C3) strongly correlated with cystogenesis, a functionally relevant association as suggested by Cys1(cpk/cpk) mice with genetically induced C3 deficiency. Because both C3 deficiency and HO induction reduce cyst number and cyst areas, these two factors define an injury-stimulated cystogenic pathway that may provide therapeutic targets to slow the formation of new renal cysts and the growth of existing cysts.

Congenital pancytopenia and absence of B lymphocytes in a neonate with a mutation in the Ikaros gene

BACKGROUND

Congenital pancytopenia is a rare and often lethal condition. Current knowledge of lymphoid and hematopoietic development in mice, as well as understanding regulators of human hematopoiesis, have led to the recent discovery of genetic causes of bone marrow failure disorders. However, in the absence of mutations of specific genes or a distinct clinical phenotype, many cases of aplastic anemia are labeled as idiopathic, while congenital immune deficiencies are described as combined immune deficiency.

PROCEDURE

We describe the case of a 33-week gestation age male with severe polyhydramnios, hydrops, and ascites who was noted to be pancytopenic at birth. Bone marrow examination revealed a hypocellular marrow with absent myelopoiesis. An immune workup demonstrated profound B lymphopenia, near absent NK cells, and normal T cell number. Due to the similarity of the patient's phenotype with the IKAROS knockout mouse, studies were performed on bone marrow and peripheral blood to assess a potential pathogenic role of Ikaros.

RESULTS

DNA studies revealed a point mutation in one allele of the IKAROS gene, resulting in an amino acid substitution in the DNA-binding zinc finger domain. Functional studies demonstrated that the observed mutation decreased Ikaros DNA-binding affinity, and immunofluorescence microscopy revealed aberrant Ikaros pericentromeric localization.

CONCLUSIONS

Our report describes a novel case of congenital pancytopenia associated with mutation of the IKAROS gene. Furthermore, these data suggest a critical role of IKAROS in human hematopoiesis and immune development.

Role of the transcription factor Bcl11b in development and lymphomagenesis

Bcl11b is a lineage-specific transcription factor expressed in various cell types and its expression is important for development of T cells, neurons and others. On the other hand, Bcl11b is a haploinsufficient tumor suppressor and loss of a Bcl11b allele provides susceptibility to mouse thymic lymphoma and human T-cell acute lymphoblastic leukemia. Although there are many transcription factors affecting both cell differentiation and cancer development, Bcl11b has several unique properties. This review describes phenotypes given by loss of Bcl11b and roles of Bcl11b in cell proliferation, differentiation and apoptosis, taking tissue development and lymphomagenesis into consideration.

Harnessing of the nucleosome-remodeling-deacetylase complex controls lymphocyte development and prevents leukemogenesis

Cell fate decisions depend on the interplay between chromatin regulators and transcription factors. Here we show that activity of the Mi-2β nucleosome remodeling and deacetylase (NuRD) complex was controlled by the Ikaros family of lymphoid-lineage determining proteins. Ikaros, an integral component of the NuRD complex in lymphocytes, tethered this complex to active lymphoid differentiation genes. Loss in Ikaros DNA binding activity caused a local increase in Mi-2β chromatin remodeling and histone deacetylation and suppression of lymphoid gene expression. The NuRD complex also redistributed to transcriptionally poised non-Ikaros gene targets, involved in proliferation and metabolism, inducing their reactivation. Thus, release of NuRD from Ikaros regulation blocks lymphocyte maturation and mediates progression to a leukemic state by engaging functionally opposing epigenetic and genetic networks.

Possible involvement of Helios in controlling the immature B cell functions via transcriptional regulation of protein kinase Cs

The transcription factor Ikaros family consists of five zinc-finger proteins: Ikaros, Aiolos, Helios, Eos and Pegasus; these proteins except Pegasus are essential for development and differentiation of lymphocytes. However, in B lymphocytes, the physiological role of Helios remains to be elucidated yet, because its expression level is very low. Here, we generated the Helios-deficient DT40 cells, Helios (-/-), and showed that the Helios-deficiency caused significant increases in transcriptions of four protein kinase Cs (PKCs); PKC-δ, PKC-ε, PKC-η and PKC-ζ, whereas their expressions were drastically down-regulated in the Aiolos-deficient DT40 cells, Aiolos (-/-). In addition, Helios (-/-) was remarkably resistant against phorbol 12-myristate 13-acetate (PMA)/ionomycin treatment, which mimics the B cell receptor (BCR)-mediated stimulation. In the presence of PMA/ionomycin, their viability was remarkably higher than that of DT40, and their DNA fragmentation was less severe than that of DT40 in the opposite manner for the Aiolos-deficiency. The resistance against the PMA/ionomycin-induced apoptosis of Helios (-/-) was sensitive to Rottlerin but not to Go6976. In addition, the Helios-deficiency caused remarkable up-regulation of the Rottlerin-sensitive superoxide (O2 (-))-generating activity. These data suggest that Helios may contribute to the regulation of the BCR-mediated apoptosis and O2 (-)-generating activity, via transcriptional regulation of these four PKCs (especially PKC-δ) in immature B lymphocytes. Together with previous data, our findings may significantly help in the understanding of the B lymphocyte-specific expressions of PKC genes and molecular mechanisms of both the BCR-mediated apoptosis involved in negative selection and the O2 (-)-generating system in immature B lymphocytes.

Cooperation between somatic Ikaros and Notch1 mutations at the inception of T-ALL

To understand the interactions between Notch1 and Ikaros in the evolution of T cell acute lymphoblastic leukemia (T-ALL), we traced the evolution of T-ALL in mice with an inherited Ikaros mutation, Ikzf1(Plstc) which inactivates DNA binding. DNA-binding Ikaros repressed Notch1 response in transfected cell lines and in CD4(+)8(+) (DP) thymocytes from young pre-leukemic Ikzf1(Plstc) heterozygous mice. In DP thymocytes, a 50-1000 fold escalation in mRNA for Notch1 target genes Hes1 and Dtx1 preceded thymic lymphoma or leukemia and was closely correlated with the first detectable differentiation abnormalities, loss of heterozygosity (LOH) eliminating wild-type Ikzf1, and multiple missense and truncating Notch1 mutations. These findings illuminate the early stages of leukemogenesis by demonstrating progressive exaggeration of Notch1 responsiveness at the DP thymocyte stage brought about by multiple mutations acting in concert upon the Notch1 pathway.

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, CK2 kinase, and the road to leukemia

Ikaros encodes a zinc finger protein that is essential for hematopoiesis and that acts as a tumor suppressor in leukemia. Ikaros function depends on its ability to localize to pericentromeric-heterochromatin (PC-HC). Ikaros protein binds to the upstream regulatory elements of target genes, aids in their recruitment to PC-HC, and regulates their transcription via chromatin remodeling. We identified four novel Ikaros phosphorylation sites that are phosphorylated by CK2 kinase. Using Ikaros phosphomimetic and phosphoresistant mutants of the CK2 phosphorylation sites, we demonstrate that (1) CK2-mediated phosphorylation inhibits Ikaros' localization to PC-HC; (2) dephosphorylation of Ikaros at CK2 sites increases its binding to the promoter of the terminal deoxynucleotidetransferase (TdT) gene, leading to TdT repression during thymocyte differentiation; and (3) hyperphosphorylation of Ikaros promotes its degradation by the ubiquitin/proteasome pathway. We show that Ikaros is dephosphorylated by Protein Phosphatase 1 (PP1) via interaction at a consensus PP1-binding motif, RVXF. Point mutations that abolish Ikaros-PP1 interaction result in functional changes in DNA-binding affinity and subcellular localization, similar to those observed in hyperphosphorylated Ikaros and/or Ikaros phosphomimetic mutants. Phosphoresistant Ikaros mutations at CK2 sites restored Ikaros' DNA-binding activity and localization to PC-HC and prevented accelerated Ikaros degradation. These results demonstrate the role of CK2 kinase in lymphocyte differentiation and in regulation of Ikaros' function, and suggest that CK2 promotes leukemogenesis by inhibiting the tumor suppressor activity of Ikaros. We propose a model whereby a balance between CK2 kinase and PP1 phosphatase is essential for normal lymphocyte differentiation and for the prevention of malignant transformation.

Ikaros isoforms: The saga continues

Through alternate splicing, the Ikaros gene produces multiple proteins. Ikaros is essential for normal hematopoiesis and possesses tumor suppressor activity. Ikaros isoforms interact to form dimers and potentially multimeric complexes. Diverse Ikaros complexes produced by the presence of different Ikaros isoforms are hypothesized to confer distinct functions. Small dominant-negative Ikaros isoforms have been shown to inhibit the tumor suppressor activity of full-length Ikaros. Here, we describe how Ikaros activity is regulated by the coordinated expression of the largest Ikaros isoforms IK-1 and IK-H. Although IK-1 is described as full-length Ikaros, IK-H is the longest Ikaros isoform. IK-H, which includes residues coded by exon 3B (60 bp that lie between exons 3 and 4), is abundant in human but not murine hematopoietic cells. Specific residues that lie within the 20 amino acids encoded by exon 3B give IK-H DNA-binding characteristics that are distinct from those of IK-1. Moreover, IK-H can potentiate or inhibit the ability of IK-1 to bind DNA. IK-H binds to the regulatory regions of genes that are upregulated by Ikaros, but not genes that are repressed by Ikaros. Although IK-1 localizes to pericentromeric heterochromatin, IK-H can be found in both pericentromeric and non-pericentromeric locations. Anti-silencing activity of gamma satellite DNA has been shown to depend on the binding of IK-H, but not other Ikaros isoforms. The unique features of IK-H, its influence on Ikaros activity, and the lack of IK-H expression in mice suggest that Ikaros function in humans may be more complex and possibly distinct from that in mice.

Regulator of myeloid differentiation and function: The secret life of Ikaros

Ikaros (also known as Lyf-1) was initially described as a lymphoid-specific transcription factor. Although Ikaros has been shown to regulate hematopoietic stem cell renewal, as well as the development and function of cells from multiple hematopoietic lineages, including the myeloid lineage, Ikaros has primarily been studied in context of lymphoid development and malignancy. This review focuses on the role of Ikaros in myeloid cells. We address the importance of post-transcriptional regulation of Ikaros function; the emerging role of Ikaros in myeloid malignancy; Ikaros as a regulator of myeloid differentiation and function; and the selective expression of Ikaros isoform-x in cells with myeloid potential. We highlight the challenges of dissecting Ikaros function in lineage commitment decisions among lymphoid-myeloid progenitors that have emerged as a major myeloid differentiation pathway in recent studies, which leads to reconstruction of the traditional map of murine and human hematopoiesis.

Regulation of Ikaros function by casein kinase 2 and protein phosphatase 1

The Ikaros gene encodes a zinc finger, DNA-binding protein that regulates gene transcription and chromatin remodeling. Ikaros is a master regulator of hematopoiesis and an established tumor suppressor. Moderate alteration of Ikaros activity (e.g. haploinsufficiency) appears to be sufficient to promote malignant transformation in human hematopoietic cells. This raises questions about the mechanisms that normally regulate Ikaros function and the potential of these mechanisms to contribute to the development of leukemia. The focus of this review is the regulation of Ikaros function by phosphorylation/dephosphorylation. Site-specific phosphorylation of Ikaros by casein kinase 2 (CK2) controls Ikaros DNA-binding ability and subcellular localization. As a consequence, the ability of Ikaros to regulate cell cycle progression, chromatin remodeling, target gene expression, and thymocyte differentiation are controlled by CK2. In addition, hyperphosphorylation of Ikaros by CK2 leads to decreased Ikaros levels due to ubiquitin-mediated degradation. Dephosphorylation of Ikaros by protein phosphatase 1 (PP1) acts in opposition to CK2 to increase Ikaros stability and restore Ikaros DNA binding ability and pericentromeric localization. Thus, the CK2 and PP1 pathways act in concert to regulate Ikaros activity in hematopoiesis and as a tumor suppressor. This highlights the importance of these signal transduction pathways as potential mediators of leukemogenesis via their role in regulating the activities of Ikaros.

Ikaros in B cell development and function

The zinc finger transcription factor, Ikaros, is a central regulator of hematopoiesis. It is required for the development of the earliest B cell progenitors and at later stages for VDJ recombination and B cell receptor expression. Mature B cells rely on Ikaros to set the activation threshold for various stimuli, and to choose the correct antibody isotype during class switch recombination. Thus, Ikaros contributes to nearly every level of B cell differentiation and function.

Up a lymphoid blind alley: Does CALM/AF10 disturb Ikaros during leukemogenesis?

The Ikaros gene is required for normal development of lymphocytes and frequent intragenic deletions of Ikaros have been identified in acute lymphoblastic leukemia. However, little is known about the role of Ikaros in myeloid malignancies. Here we discuss the role of Ikaros as a lineage master regulator during the onset and progression of myeloid leukemias, namely CALM-AF10 positive acute myeloid leukemia and chronic myeloid leukemia. Alterations of Ikaros at the gene or protein level may act as a bi-directional lineage switch subverting developmental plasticity for malignant transformation. Finally, we propose that promiscuous signaling involving Ikaros and FOXO transcription factors might be a critical link between early lineage fate and uncontrolled proliferation.

Role of Ikaros in T-cell acute lymphoblastic leukemia

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.

Vasoactive intestinal peptide signaling axis in human leukemia

The vasoactive intestinal peptide (VIP) signaling axis constitutes a master “communication coordinator” between cells of the nervous and immune systems. To date, VIP and its two main receptors expressed in T lymphocytes, vasoactive intestinal peptide receptor (VPAC)1 and VPAC2, mediate critical cellular functions regulating adaptive immunity, including arresting CD4 T cells in G₁ of the cell cycle, protection from apoptosis and a potent chemotactic recruiter of T cells to the mucosa associated lymphoid compartment of the gastrointestinal tissues. Since the discovery of VIP in 1970, followed by the cloning of VPAC1 and VPAC2 in the early 1990s, this signaling axis has been associated with common human cancers, including leukemia. This review highlights the present day knowledge of the VIP ligand and its receptor expression profile in T cell leukemia and cell lines. Also, there will be a discussion describing how the anti-leukemic DNA binding transcription factor, Ikaros, regulates VIP receptor expression in primary human CD4 T lymphocytes and T cell lymphoblastic cell lines (e.g. Hut-78). Lastly, future goals will be mentioned that are expected to uncover the role of how the VIP signaling axis contributes to human leukemogenesis, and to establish whether the VIP receptor signature expressed by leukemic blasts can provide therapeutic and/or diagnostic information.

Evolutionary history of the cancer immunity antigen MAGE gene family

The evolutionary mode of a multi-gene family can change over time, depending on the functional differentiation and local genomic environment of family members. In this study, we demonstrate such a change in the melanoma antigen (MAGE) gene family on the mammalian X chromosome. The MAGE gene family is composed of ten subfamilies that can be categorized into two types. Type I genes are of relatively recent origin, and they encode epitopes for human leukocyte antigen (HLA) in cancer cells. Type II genes are relatively ancient and some of their products are known to be involved in apoptosis or cell proliferation. The evolutionary history of the MAGE gene family can be divided into four phases. In phase I, a single-copy state of an ancestral gene and the evolutionarily conserved mode had lasted until the emergence of eutherian mammals. In phase II, eight subfamily ancestors, with the exception for MAGE-C and MAGE-D subfamilies, were formed via retrotransposition independently. This would coincide with a transposition burst of LINE elements at the eutherian radiation. However, MAGE-C was generated by gene duplication of MAGE-A. Phase III is characterized by extensive gene duplication within each subfamily and in particular the formation of palindromes in the MAGE-A subfamily, which occurred in an ancestor of the Catarrhini. Phase IV is characterized by the decay of a palindrome in most Catarrhini, with the exception of humans. Although the palindrome is truncated by frequent deletions in apes and Old World monkeys, it is retained in humans. Here, we argue that this human-specific retention stems from negative selection acting on MAGE-A genes encoding epitopes of cancer cells, which preserves their ability to bind to highly divergent HLA molecules. These findings are interpreted with consideration of the biological factors shaping recent human MAGE-A genes.

A cooperative microRNA-tumor suppressor gene network in acute T-cell lymphoblastic leukemia (T-ALL)

The importance of individual microRNAs (miRNAs) has been established in specific cancers. However, a comprehensive analysis of the contribution of miRNAs to the pathogenesis of any specific cancer is lacking. Here we show that in T-cell acute lymphoblastic leukemia (T-ALL), a small set of miRNAs is responsible for the cooperative suppression of several tumor suppressor genes. Cross-comparison of miRNA expression profiles in human T-ALL with the results of an unbiased miRNA library screen allowed us to identify five miRNAs (miR-19b, miR-20a, miR-26a, miR-92 and miR-223) that are capable of promoting T-ALL development in a mouse model and which account for the majority of miRNA expression in human T-ALL. Moreover, these miRNAs produce overlapping and cooperative effects on tumor suppressor genes implicated in the pathogenesis of T-ALL, including IKAROS (also known as IKZF1), PTEN, BIM, PHF6, NF1 and FBXW7. Thus, a comprehensive and unbiased analysis of miRNA action in T-ALL reveals a striking pattern of miRNA-tumor suppressor gene interactions in this cancer.

From trees to the forest: genes to genomics

Crick, Watson, and colleagues revealed the genetic code in 1953, and since that time, remarkable progress has been made in understanding what makes each of us who we are. Identification of single genes important in disease, and the development of a mechanistic understanding of genetic elements that regulate gene function, have cast light on the pathophysiology of many heritable and acquired disorders. In 1990, the human genome project commenced, with the goal of sequencing the entire human genome, and a "first draft" was published with astonishing speed in 2001. The first draft, although an extraordinary achievement, reported essentially an imaginary haploid mix of alleles rather than a true diploid genome. In the years since 2001, technology has further improved, and efforts have been focused on filling in the gaps in the initial genome and starting the huge task of looking at normal variation in the human genome. This work is the beginning of understanding human genetics in the context of the structure of the genome as a complete entity, and as more than simply the sum of a series of genes. We present 3 studies in this review that apply genomic approaches to leukemia and to transplantation to improve and extend therapies.

Signaling proteins and transcription factors in normal and malignant early B cell development

B cell development starts in bone marrow with the commitment of hematopoietic progenitors to the B cell lineage. In murine models, the IL-7 and preBCR receptors, and the signaling pathways and transcription factors that they regulate, control commitment and maintenance along the B cell pathway. E2A, EBF1, PAX5, and Ikaros are among the most important transcription factors controlling early development and thereby conditioning mice homeostatic B cell lymphopoiesis. Importantly, their gain or loss of function often results in malignant development in humans, supporting conserved roles for these transcription factors. B cell acute lymphoblastic leukemia is the most common cause of pediatric cancer, and it is characterized by unpaired early B cell development resulting from genetic lesions in these critical signaling pathways and transcription factors. Fine mapping of these genetic abnormalities is allowing more specific treatments, more accurately predicting risk profiles for this disease, and improving survival rates.

The Ikaros gene family: transcriptional regulators of hematopoiesis and immunity

The Ikaros family of proteins - comprising Ikaros, Aiolos, Helios, Eos and Pegasus - are zinc finger transcription factors. These proteins participate in a complex network of interactions with gene regulatory elements, other family members and a raft of other transcriptional regulators to control gene expression including via chromatin remodelling. In this way, Ikaros family members regulate important cell-fate decisions during hematopoiesis, particularly in the development of the adaptive immune system. Mutation of several family members results in hematological malignancies,especially those of a lymphoid nature. This review describes the key roles of Ikaros proteins in development and disease, their mechanisms of action and gene targets, as well as explaining their evolutionary origins and role in the emergence of adaptive immunity.

Ikaros-Notch axis in host hematopoietic cells regulates experimental graft-versus-host disease

Host hematopoietically derived APCs play a vital role in the initiation of GVH responses. However, the APC autonomous molecular mechanisms that are critical for the induction of GVHD are not known. We report here that the Ikaros-Notch axis in host hematopoietically derived APCs regulates the severity of acute GVHD across multiple clinically relevant murine models of experimental bone marrow transplantation. In the present study, Ikaros deficiency (Ik(-/-)) limited to host hematopoietically derived APCs enhanced donor T-cell expansion and intensified acute GVHD, as determined by survival and other GVHD-specific parameters. The Ik(-/-) conventional CD8(+) and CD8(-)CD11c(+) dendritic cells (DCs), the most potent APCs, showed no increase in the expression of activation markers or in response to TLR stimulation compared with wild-type controls. However, Ik(-/-) DCs demonstrated an enhanced stimulation of allogeneic T cells. Deficiency of Ikaros in the conventional CD8(+) and CD8(-)CD11c(+) DCs was associated with an increase in Notch signaling, the blockade of which mitigated the enhanced in vitro and in vivo allostimulatory capacity. Therefore, the Ikaros-Notch axis is a novel pathway that modulates DC biology in general, and targeting this pathway in host hematopoietically derived APCs may reduce GVHD.

Therapeutic potential of vasopressin V2 receptor antagonist in a mouse model for autosomal dominant polycystic kidney disease: optimal timing and dosing of the drug

BACKGROUND

The renoprotective effect of vasopressin V2 receptor antagonist (V2RA) is currently being tested in a clinical trial in early autosomal dominant polycystic kidney disease (ADPKD). If efficacious, this warrants life-long treatment with V2RA, however, with associated side effects as polydipsia and polyuria. We questioned whether we could reduce the side effects without influencing the renoprotective effect by starting the treatment later in the disease or by lowering drug dosage.

METHODS

To investigate this, we administered V2RA OPC-31260 at a high (0.1%) and low (0.05%) dose to a tamoxifen-inducible kidney epithelium-specific Pkd1-deletion mouse model starting treatment at Day 21 (early) or 42 (advanced). After 3 and 6 weeks of treatment, we monitored physiologic and potential renoprotective effects.

RESULTS

Initiation of V2RA treatment at advanced stage of the disease lacked renoprotective effects and had less pronounced physiologic effects than early initiation. After 3 weeks on a high dose, cyst ratio and kidney weight were reduced versus untreated controls (18 versus 25%, P = 0.05, and 0.33 versus 0.45 g, P = 0.03, respectively). After 6 weeks of treatment, however, this did not reach significance anymore, even at a high dose (cyst ratio 24 versus 27%, P = 0.12, and kidney weight 0.55 versus 0.66 g, P = 0.38).

CONCLUSIONS

Our results suggest that intervention with V2RA should be instituted early in ADPKD and that it might be necessary to further increase the dosage of this drug later in the disease to decrease cyst growth.

Notch is oncogenic dominant in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is a hematologic neoplasm characterized by malignant expansion of immature T cells. Activated NOTCH (Notch(IC)) and c-MYC expression are increased in a large percentage of human T-ALL tumors. Furthermore, c-MYC has been shown to be a NOTCH target gene. Although activating mutations of Notch have been found in human T-ALL tumors, there is little evidence that the c-MYC locus is altered in this neoplasm. It was previously demonstrated that Notch and c-Myc-regulated genes have a broadly overlapping profile, including genes involved in cell cycle progression and metabolism. Given that Notch and c-Myc appear to function similarly in T-ALL, we sought to determine whether these two oncogenes could substitute for each other in T-ALL tumors. Here we report that NOTCH(IC) is able to maintain T-ALL tumors formed in the presence of exogenous NOTCH(IC) and c-MYC when exogenous c-MYC expression is extinguished. In contrast, c-MYC is incapable of maintaining these tumors in the absence of NOTCH(IC). We propose that failure of c-MYC to maintain these tumors is the result of p53-mediated apoptosis. These results demonstrate that T-ALL maintenance is dependent on NOTCH(IC), but not c-MYC, demonstrating that NOTCH is oncogenic dominant in T-ALL tumors.

Alternative promoter usage at the Notch1 locus supports ligand-independent signaling in T cell development and leukemogenesis

Loss of the transcription factor Ikaros is correlated with Notch receptor activation in T cell acute lymphoblastic leukemia (T-ALL). However, the mechanism remains unknown. We identified promoters in Notch1 that drove the expression of Notch1 proteins in the absence of a ligand. Ikaros bound to both canonical and alternative Notch1 promoters and its loss increased permissive chromatin, facilitating recruitment of transcription regulators. At early stages of leukemogenesis, increased basal expression from the canonical and 5'-alternative promoters initiated a feedback loop, augmenting Notch1 signaling. Ikaros also repressed intragenic promoters for ligand-independent Notch1 proteins that are cryptic in wild-type cells, poised in preleukemic cells, and active in leukemic cells. Only ligand-independent Notch1 isoforms were required for Ikaros-mediated leukemogenesis. Notch1 alternative-promoter usage was observed during T cell development and T-ALL progression. Thus, a network of epigenetic and transcriptional regulators controls conventional and unconventional Notch signaling during normal development and leukemogenesis.

Transcriptional repressors, corepressors and chromatin modifying enzymes in T cell development

Gene expression is regulated by the combined action of transcriptional activators and transcriptional repressors. Transcriptional repressors function by recruiting corepressor complexes containing histone-modifying enzymes to specific sites within DNA. Chromatin modifying complexes are subsequently recruited, either directly by transcriptional repressors, or indirectly via corepressor complexes and/or histone modifications, to remodel chromatin into either a transcription-friendly 'open' form or an inhibitory 'closed' form. Transcriptional repressors, corepressors and chromatin modifying complexes play critical roles throughout T cell development. Here, we highlight those genes that function to repress transcription and that have been shown to be required for T cell development.

Copeptin, a surrogate marker of vasopressin, is associated with disease severity in autosomal dominant polycystic kidney disease

BACKGROUND AND OBJECTIVES

Experimental studies suggest a detrimental role for vasopressin in the pathogenesis of autosomal dominant polycystic kidney disease (ADPKD). However, it is unknown whether endogenous vasopressin concentration is associated with disease severity in patients with ADPKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Plasma copeptin concentration (a marker of endogenous vasopressin levels) was measured in 102 ADPKD patients (diagnosis based on Ravine criteria) by an immunoassay. Plasma and urinary osmolarity were also measured. To assess disease severity, GFR and effective renal blood flow were measured by continuous infusion of 125I-iothalamate and 131I-hippuran, total renal volume by magnetic resonance imaging, and 24-hour urinary albumin excretion by nephelometry.

RESULTS

In these ADPKD patients, copeptin was associated with the various markers of disease severity in ADPKD (positively with total renal volume [R=0.47] and albuminuria [R=0.39] and negatively with GFR [R=-0.58] and effective renal blood flow [R=-0.52], all P<0.001). These associations were independent of age, gender, and use of diuretics. Copeptin was furthermore associated with plasma osmolarity (P<0.001) but not with 24-hour urinary volume, 24-hour urinary osmolarity or fractional urea excretion (P=0.7, 0.9, and 0.3, respectively).

CONCLUSIONS

On cross-sectional analysis, copeptin is associated with disease severity in ADPKD patients, supporting the results of experimental studies that suggest that vasopressin antagonists have a renoprotective effect in ADPKD and offering a good prospect for clinical studies with these agents.

Targeting paediatric acute lymphoblastic leukaemia: novel therapies currently in development

Modifications to the treatment of acute lymphoblastic leukaemia (ALL) in children have led to a dramatic increase in survival in the past 40 years. Despite this success, a significant subset of paediatric leukaemia patients either relapse or fail to ever achieve a complete remission. Additionally, some patients necessitate treatment with intensified chemotherapy regimens due to clinical or laboratory findings which identify them as high risk. These patients are unlikely to respond to further minor adjustments to the dosing or timing of administration of the same chemotherapy medications. Many novel targeted therapies for the treatment of childhood ALL provide potential mechanisms to further improve cure rates, and provide the possibility of minimizing toxicity to non-malignant cells, given their specificity to malignant cell phenotypes. This article explores many of the potential targeted therapies in varying stages of development, from those currently in clinical trials to those still being refined in the research laboratory.

Genomic profiling of high-risk acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is a heterogeneous disease comprising multiple subtypes with different genetic alterations and responses to therapy. Recent genome-wide profiling studies of ALL have identified a number of novel genetic alterations that target key cellular pathways in lymphoid growth and differentiation and are associated with treatment outcome. Notably, genetic alteration of the lymphoid transcription factor gene IKZF1 is a hallmark of multiple subtypes of ALL with poor prognosis, including BCR-ABL1-positive lymphoid leukemia and a subset of 'BCR-ABL1-like' ALL cases that, in addition to IKZF1 alteration, harbor genetic mutations resulting in aberrant lymphoid cytokine receptor signaling, including activating mutations of Janus kinases and rearrangement of cytokine receptor-like factor 2 (CRLF2). Recent insights from genome-wide profiling studies of B-progenitor ALL and the potential for new therapeutic approaches in high-risk disease are discussed.

Gene expression in formalin-fixed paraffin-embedded lymph nodes

Elucidation of molecular pathways involved in development of human lymphoma requires efficient methods for tackling gene expression in lymph nodes. Expression studies of transcription factors in these malignancies facilitate understanding the changes occurring in neoplastic transformation and lymphoma development. Excised lymph nodes are routinely fixed in formalin and embedded in paraffin for diagnosis and stored in many hospitals' pathology archives. These tissues represent a precious resource for research since they allow retrospective studies to cover a broad range of human lymphoma even the less frequent types. Reverse transcription polymerase chain reaction (RT-PCR) is a commonly used method for gene expression analysis and a reproducible protocol for RNA isolation from lymph nodes is an inevitable requirement for these studies. However, formalin fixation and paraffin-embedding interfere with the quality of RNA especially when isolated from lymph nodes being the most fragile lymphatic tissues. We present here a simple and fast method for RNA isolation from formalin-fixed paraffin-embedded lymph nodes that can be successfully applied for RT-PCR as well as for quantitative RT-PCR analysis. We tested diverse isolation reagents and combined a range of factors in order to get a high quality RNA for retrospective studies of gene expression in human lymphoma samples. Our modified method of RNA extraction from FFPE provides superior yields and purity based on qPCR data.

Notch target gene deregulation and maintenance of the leukemogenic phenotype do not require RBP-J kappa in Ikaros null mice

Ikaros and Notch are transcriptional regulators essential for normal T cell development. Aberrant activation of Notch target genes is observed in Ikaros-deficient thymocytes as well as leukemia cell lines. However, it is not known whether Notch deregulation plays a preferential or obligatory role in the leukemia that arise in Ikaros null (Ik(-/-)) mice. To answer this question, the expression of the DNA-binding Notch target gene activator RBP-Jkappa was abrogated in Ik(-/-) double-positive thymocytes. This was accomplished through conditional inactivation using CD4-Cre transgenic mice containing floxed RBP-Jkappa alleles (RBPJ(fl/fl)). Ik(-/-) x RBPJ(fl/fl) x CD4-Cre(+) transgenic mice develop clonal T cell populations in the thymus that escape to the periphery, with similar kinetics and penetrance as their CD4-Cre(-) counterparts. The clonal populations do not display increased RBP-Jkappa expression compared with nontransformed thymocytes, suggesting there is no selection for clones that have not fully deleted RBP-Jkappa. However, RBPJ-deficient clonal populations do not expand as aggressively as their RBPJ-sufficient counterparts, suggesting a qualitative role for deregulated Notch target gene activation in the leukemogenic process. Finally, these studies show that RBP-Jkappa plays no role in Notch target gene repression in double-positive thymocytes but rather that it is Ikaros that is required for the repression of these genes at this critical stage of T cell development.

Alu-derived cis-element regulates tumorigenesis-dependent gastric expression of GASDERMIN B (GSDMB)

GASDERMIN B (GSDMB) belongs to the novel gene family GASDERMIN (GSDM). All GSDM family members are located in amplicons, genomic regions often amplified during cancer development. Given that GSDMB is highly expressed in cancerous cells and the locus resides in an amplicon, GSDMB may be involved in cancer development and/or progression. However, only limited information is available on GSDMB expression in tissues, normal and cancerous, from cancer patients. Furthermore, the molecular mechanisms that regulate GSDMB expression in gastric tissues are poorly understood. We investigated the spatiotemporal expression patterns of GSDMB in gastric cancer patients and the 5' regulatory sequences upstream of GSDMB. GSDMB was not expressed in the majority of normal gastric-tissue samples, and the expression level was very low in the few normal samples with GSDMB expression. Most pre-cancer samples showed moderate GSDMB expression, and most cancerous samples showed augmented GSDMB expression. Analysis of genome sequences revealed that an Alu element resides in the 5' region upstream of GSDMB. Reporter assays using intact, deleted, and mutated Alu elements clearly showed that this Alu element positively regulates GSDMB expression and that a putative IKZF binding motif in this element is crucial to upregulate GSDMB expression.

Expression of Helios, an Ikaros transcription factor family member, differentiates thymic-derived from peripherally induced Foxp3+ T regulatory cells

Helios, a member of the Ikaros transcription factor family, is preferentially expressed at the mRNA level by regulatory T cells (Treg cells). We evaluated Helios protein expression using a newly generated mAb and demonstrated that it is expressed in all thymocytes at the double negative 2 stage of thymic development. Although Helios was expressed by 100% of CD4(+)CD8(-)Foxp3(+) thymocytes, its expression in peripheral lymphoid tissues was restricted to a subpopulation ( approximately 70%) of Foxp3(+) T cells in mice and humans. Neither mouse nor human naive T cells induced to express Foxp3 in vitro by TCR stimulation in the presence of TGF-beta expressed Helios. Ag-specific Foxp3(+) T cells induced in vivo by Ag feeding also failed to express Helios. Collectively, these results demonstrate that Helios is potentially a specific marker of thymic-derived Treg cells and raises the possibility that a significant percentage of Foxp3(+) Treg cells are generated extrathymically.

Early T cell differentiation lessons from T-cell acute lymphoblastic leukemia

T cells develop from bone marrow-derived self-renewing hematopoietic stem cells (HSC). Upon entering the thymus, these cells undergo progressive commitment and differentiation driven by the thymic stroma and the pre-T cell receptor (pre-TCR). These processes are disrupted in T-cell acute lymphoblastic leukemia (T-ALL). More than 70% of recurring chromosomal rearrangements in T-ALL activate the expression of oncogenic transcription factors, belonging mostly to three families, basic helix-loop-helix (bHLH), homeobox (HOX), and c-MYB. This prevalence is indicative of their importance in the T lineage, and their dominant mechanisms of transformation. For example, bHLH oncoproteins inhibit E2A and HEB, revealing their tumor suppressor function in the thymus. The induction of T-ALL, nonetheless, requires collaboration with constitutive NOTCH1 signaling and the pre-TCR, as well as loss-of-function mutations for CDKN2A and PTEN. Significantly, NOTCH1, the pre-TCR pathway, and E2A/HEB proteins control critical checkpoints and branchpoints in early thymocyte development whereas several oncogenic transcription factors, HOXA9, c-MYB, SCL, and LYL-1 control HSC self-renewal. Together, these genetic lesions alter key regulatory processes in the cell, favoring self-renewal and subvert the normal control of thymocyte homeostasis.