LMO2 Expression Research Articles

FOXP3 can modulate TAL1 transcriptional activity through interaction with LMO2

T-cell acute lymphoblastic leukemia (T-ALL) frequently involves aberrant expression of TAL1 (T-cell acute lymphocytic leukemia 1) and LMO2, oncogenic members of the TAL1 transcriptional complex. Transcriptional activity of the TAL1-complex is thought to have a pivotal role in the transformation of thymocytes and is associated with a differentiation block and self-renewal. The transcription factor Forkhead Box P3 (FOXP3) was recently described to be expressed in a variety of malignancies including T-ALL. Here we show that increased FOXP3 levels negatively correlate with expression of genes regulated by the oncogenic TAL1-complex in human T-ALL patient samples as well as a T-ALL cell line ectopically expressing FOXP3. In these cells, FOXP3 expression results in altered regulation of cell cycle progression and reduced cell viability. Finally, we demonstrate that FOXP3 binds LMO2 in vitro, resulting in decreased interaction between LMO2 and TAL1, providing a molecular mechanism for FOXP3-mediated transcriptional modulation in T-ALL. Collectively, our findings provide initial evidence for a novel role of FOXP3 as a tumor suppressor in T-ALL through modulation of TAL1 transcriptional activity.

Constitutive Expression of MEF2C, LYL1, or LMO2 in CD34+ HSCs Blocks the in Vitro Differentiation before the T-Cell Commitment Point and Could be Oncogenic in Early T-Cell Progenitor ALL

Background:T-cell development in the thymus is a complex process that depends on sequential transcriptional and epigenetic events that induce T-cell lineage commitment and simultaneously suppress alternative cell fates. In T-cell acute lymphoblastic leukemia (T-ALL), aberrantly expressed oncogenes result in the arrest of developing thymocytes, which can lead to the acquisition of secondary mutations, uncontrolled proliferation and disease progression. MEF2C is often expressed as a result of chromosomal rearrangements in immature, early T-cell progenitor ALL (ETP-ALL), but is also expressed in normal thymocyte progenitors before T-cell commitment (in the ETP stage). As the only hematopoietic lineage, thymocytes that have passed the T-cell commitment checkpoint (as well as mature T-cells) do no longer express MEF2C.Aims:We aimed to investigate the effect of constitutive MEF2C expression on early T-cell development. OP9-DL1 co-cultures have been most useful for mimicking in vitro T-cell development starting with hematopoietic stem cells (HSCs) derived from human cord blood or bone marrow. We also aimed to investigate the impact of MEF2C in comparison to LYL1 and LMO2; two T-ALL oncogenes also highly expressed at the ETP stage.Methods:We have utilized the OP9-DL1 in vitro co-culture system to gradually differentiate CD34+ HSCs from umbilical cord blood into the T-cell lineage. HSCs in this co-culture will recapitulate in vivo T-cell development as measured by incremental acquisition of surface markers CD7, CD5, CD1a, and reach the CD4, CD8 double-positive (DP) stage. We generated gene expression profiles of 11 subsequent in vitro stages of differentiation to help us match them to in vivo development stages. We investigated in vitro T-cell differentiation of HSCs after lentiviral transduction with MEF2C or control vectors, as well as with other transcriptional regulators LYL1 and LMO2 that are expressed at the ETP stage.Results:The major change in gene expression of subsequent early T-cell differentiation stages defines two distinct T-cell differentiation clusters that correlate with in vivo pre- and post-T-cell commitment profiles. We found that T-cell commitment occurs in CD7+ CD5+ cells before the acquisition of CD1a surface expression. Expression of control vectors in HSCs does not affect the in vitro T-cell differentiation, but MEF2C expression blocks differentiation into the direction of T-cells as measured by the failure of most cells to acquire CD7 as the first marker. Instead, with increased passage number cells gradually lose CD34 expression and eventually disappear from the co-culture. Similar effects were observed for the expression of LYL1 and LMO2; LYL1 expression arrests the cells at the most immature CD7+ ETP stage and prevents the transition towards CD7+ CD5+ cells, whereas LMO2 expressing cells reach the CD7+ CD5+ stage but fail to acquire CD1a as a marker of T-cell commitment.Summary/Conclusion:The gene expression profiles of 11 human in vitro T-cell differentiation subsets has enabled us to pinpoint T-cell commitment to a stage in which cells have acquired CD7 and CD5, just prior to the acquisition of CD1a. MEF2C, LYL1, and LMO2, expressed in ETP-ALL as well as in normal thymocyte progenitors, do not allow the transition to T-cell commitment when constitutively expressed. These proteins each result in the arrest of in vitro differentiating T-cells at different ETP stages, all before the T-cell commitment as marked by CD1a expression. Constitutive expression of MEF2C, LYL1, or LMO2 in very early thymocyte progenitors is incompatible with development into and beyond the T-cell commitment checkpoint and these proteins could therefore play important roles in the pathogenesis of ETP-ALL. DisclosuresNo relevant conflicts of interest to declare.

Diagnostic Utility of the Germinal Center-associated Markers GCET1, HGAL, and LMO2 in Hematolymphoid Neoplasms.

Implementation of new phenotypic markers in routine diagnostics of hematolymphoid neoplasms is a challenging task with a plethora of potentially relevant proteins. We investigated 3 recently discovered proteins expressed in the germinal centers of lymph nodes (LMO2, GCET1, and HGAL) in a compilation of leukemia, lymphoma, and thymic tumor entities. Altogether, 1590 cases (1519 on tissue microarrays, 71 on conventional slides) were included. Expressions of LMO2, GCET1, and HGAL were investigated by immunohistochemistry, evaluated for their differential diagnostic relevance, and correlated with the clinical outcome of patients. In Hodgkin lymphoma (HL), the expression of LMO2, GCET1, and HGAL could be largely seen in tumor cells of nodular lymphocyte predominant HL (NLPHL) but only occasionally in classic HL. The majority of B-cell lymphoma cases was positive for LMO2 [except for Burkitt lymphoma (BL)] and HGAL with weaker to moderate staining intensity, compared with the intensely staining follicular lymphomas (FL). Except for FL (60% of cases) and diffuse large B-cell lymphomas (DLBCL, 36% of cases), all other B-cell lymphomas expressed little or no GCET1. In thymomas, the non-neoplastic immature T-cells were LMO2-negative, whereas the neoplastic lymphoblasts were LMO2-positive in more than half of the lymphoblastic lymphomas (LBL). Our findings provide new potential assistance in the differential diagnosis of FL to marginal zone lymphoma, classic HL to NLPHL and primary mediastinal B-cell lymphoma, DLBCL to BL, and thymoma to LBL. Finally, HGAL proved to be a prognostic marker for classic HL regarding the background population and in DLBCL regarding the tumor cells.

Contribution of JAK2 mutations to T-cell lymphoblastic lymphoma development.

The JAK-STAT pathway has a substantial role in lymphoid precursor cell proliferation, survival and differentiation. Nonetheless, the contribution of JAK2 to T-cell lymphoblastic lymphoma (T-LBL) development remains poorly understood. We have identified one activating TEL-JAK2 translocation and four missense mutations accumulated in 2 out of 16 T-LBL samples. Two of them are novel JAK2 mutations and the other two are reported for the first time in T-LBL. Notably, R683G and I682T might have arisen owing to RNA editing. Mutated samples showed different mutated transcripts suggesting sub-clonal heterogeneity. Functional approaches revealed that two JAK2 mutations (H574R and R683G) constitutively activate JAK-STAT signaling in γ2A cells and can drive the proliferation of BaF3-EpoR cytokine-dependent cell line. In addition, aberrant hypermethylation of SOCS3 might contribute to enhance the activation of JAK-STAT signaling. Of utmost interest is that primary T-LBL samples harboring JAK2 mutations exhibited increased expression of LMO2, suggesting a mechanistic link between JAK2 mutations and the expression of LMO2, which was confirmed for the four missense mutations in transfected γ2A cells. We therefore propose that active JAK2 contribute to T-LBL development by two different mechanisms, and that the use of pan-JAK inhibitors in combination with epigenetic drugs should be considered in future treatments.

MYB controls erythroid versus megakaryocyte lineage fate decision through the miR-486-3p-mediated downregulation of MAF.

The transcription factor MYB has a key role in hematopoietic progenitor cells (HPCs) lineage choice, by enhancing erythropoiesis at the expense of megakaryopoiesis. We previously demonstrated that MYB controls erythroid versus megakaryocyte lineage decision by transactivating KLF1 and LMO2 expression. To further unravel the molecular mechanisms through which MYB affects lineage fate decision, we performed the integrative analysis of miRNA and mRNA changes in MYB-silenced human primary CD34+ HPCs. Among the miRNAs with the highest number of predicted targets, we focused our studies on hsa-miR-486-3p by demonstrating that MYB controls miR-486-3p expression through the transactivation of its host gene, ankyrin-1 (ANK1) and that miR-486-3p affects HPCs commitment. Indeed, overexpression and knockdown experiments demonstrated that miR-486-3p supports the erythropoiesis while restraining the megakaryopoiesis. Of note, miR-486-3p also favors granulocyte differentiation while repressing the macrophage differentiation. To shed some light on the molecular mechanisms through which miR-486-3p affects HPCs lineage commitment, we profiled the gene expression changes upon miR-486-3p overexpression in CD34+ cells. Among the genes downregulated in miR-486-3p-overexpressing HPCs and computationally predicted to be miR-486-3p targets, we identified MAF as a miR-486-3p target by 3′UTR luciferase reporter assay. Noteworthy, MAF overexpression was able to partially reverse the effects of miR-486-3p overexpression on erythroid versus megakaryocyte lineage choice. Moreover, the MYB/MAF co-silencing constrained the skewing of erythroid versus megakaryocyte lineage commitment in MYB-silenced CD34+ cells, by restraining the expansion of megakaryocyte lineage while partially rescuing the impairment of erythropoiesis. Therefore, our data collectively demonstrate that MYB favors erythropoiesis and restrains megakaryopoiesis through the transactivation of miR-486-3p expression and the subsequent downregulation of MAF. As a whole, our study uncovers the MYB/miR-486-3p/MAF axis as a new mechanism underlying the MYB-driven control of erythroid versus megakaryocyte lineage fate decision.

BCL6--regulated by AhR/ARNT and wild-type MEF2B--drives expression of germinal center markers MYBL1 and LMO2.

Genetic heterogeneity is widespread in tumors, but poorly documented in cell lines. According to immunoglobulin hypermutation analysis, the diffuse large B-cell lymphoma cell line U-2932 comprises two subpopulations faithfully representing original tumor subclones. We set out to identify molecular causes underlying subclone-specific expression affecting 221 genes including surface markers and the germinal center oncogenes BCL6 and MYC. Genomic copy number variations explained 58/221 genes differentially expressed in the two U-2932 clones. Subclone-specific expression of the aryl-hydrocarbon receptor (AhR) and the resulting activity of the AhR/ARNT complex underlaid differential regulation of 11 genes including MEF2B. Knock-down and inhibitor experiments confirmed that AhR/ARNT regulates MEF2B, a key transcription factor for BCL6. AhR, MEF2B and BCL6 levels correlated not only in the U-2932 subclones but in the majority of 23 cell lines tested, indicting overexpression of AhR as a novel mechanism behind BCL6 diffuse large B-cell lymphoma. Enforced modulation of BCL6 affected 48/221 signature genes. Although BCL6 is known as a transcriptional repressor, 28 genes were up-regulated, including LMO2 and MYBL1 which, like BCL6, signify germinal center diffuse large B-cell lymphoma. Supporting the notion that BCL6 can induce gene expression, BCL6 and the majority of potential targets were co-regulated in a series of B-cell lines. In conclusion, genomic copy number aberrations, activation of AhR/ARNT, and overexpression of BCL6 are collectively responsible for differential expression of more than 100 genes in subclones of the U-2932 cell line. It is particularly interesting that BCL6 - regulated by AhR/ARNT and wild-type MEF2B - may drive expression of germinal center markers in diffuse large B-cell lymphoma.

High frequency of cryptic chromosomal rearrangements involving the LMO2 gene in T-cell acute lymphoblastic leukemia

High frequency of cryptic chromosomal rearrangements involving the LMO2 gene in T-cell acute lymphoblastic leukemia

Controlling pre-leukemic thymocyte self-renewal.

T cell acute lymphoblastic leukemia (T-ALL) develops in a multistep process whereby thymic progenitor cells gradually accumulate genetic and epigenetic changes, eventually leading to fully transformed immature lymphoblasts. Aberrant activation of transcription factor oncogenes is considered a core component of the oncogenic program that drives malignant T cell transformation. For example, the TAL1 (SCL) and LYL1 basic Helix-Loop-Helix (bHLH) transcription factors, as well as the LIM domain–only proteins LMO1 or LMO2, are activated by chromosomal translocations or interstitial deletions in a large fraction of primary T-ALLs. Notably, these leukemias often present with activating NOTCH1 mutations, suggesting that enhanced NOTCH signaling and aberrant TAL1, LYL1, LMO1, and/or LMO2 expression are collaborative events in the multistep pathogenesis of T-ALL [1], [2]. Recent experimental evidence uncovered the existence of long-lived pre-leukemic stem cells (pre-LSCs) with self-renewal properties, allowing clonal expansion and subsequent acquisition of oncogenic mutations leading to cancer [3], [4]. For example, DNMT3A mutant pre-LSCs were shown to survive chemotherapy and represent a reservoir for leukemic progression and hematological relapse in acute myeloid leukemia (AML) [5], [6]. Although the concept of pre-leukemic stem cells has been previously proposed in the context of T-ALL [7], the actual molecular mechanisms by which T cell-specific oncogenes regulate pre-LSC activity of thymic precursors remains largely unexplored. Notably, these mechanistic insights could provide valuable input for the development of novel therapeutic strategies that can effectively eradicate quiescent and therapy-resistant clones [4], [6], [7].

BCL6 Overexpression – Regulated By AhR/ARNT and Wild-Type MEF2B – Drives Expression of Germinal Center Markers MYBL1 and LMO2

The evolution of tumor clones and the clonal architecture of tumors can be followed by the analysis of clone-specific mutations. The diffuse large B-cell lymphoma (DLBCL)-derived cell line U-2932 comprises two subclones (R1 and R2). Immunoglobulin gene hypermutation analysis showed that R1 and R2 represent subclones of the original tumor. Thus, the two U-2932 subclones seemed to be ideal to study the cellular consequences of clonal evolution. Both clones were derived from a presumptive mother clone with genomic BCL2 amplification, which acquired distinct sets of secondary rearrangements leading alternatively to the overexpression of BCL6 (R1) and MYC (R2) in the respective daughter clones. R2 carries t(8;14) a classical activating rearrangement of MYC in B-cells. R1 did not show any of the typical BCL6 translocations responsible for aberrant BCL6 expression. We applied a whole genome array to find out whether numerical aberrations might explain BCL6 expression in R1 and to investigate if subclone-specific gene expression might be attributable to numerical aberrations in general. More than 200 genes showed >10 fold expression differences between R1 and R2. Statistical analysis of results from copy number aberration and expression data analysis revealed that for 58/221 of the differentially expressed genes, numerical differences between the two subclones effectively predict differences in gene expression (sensitivity 0.64; specificity 0.94; accuracy 0.78). Thus, for a sizeable minority of genes numerical aberrations provided an explanation for the differences in gene expression between the U-2932 subclones. However, BCL6 was none of these genes. Thus, we searched for an alternative explanation for the R1-restricted overexpression of this germinal center oncogene. MEF2B point mutations occur in 11% of DLBCL contributing to the genesis of BCL6 positive lymphomas. The U-2932 subclones did not carry MEF2B mutations. Interestingly however, expression levels of MEF2B paralleled those of BCL6 in the U-2932 subclones. Knockdown experiments showed that wild-type MEF2B controlled BCL6 transcription. To test whether MEF2B and BCL6 showed coordinated expression in general, we analyzed the expression and the mutational status of these genes in 23 DLBCL cell lines. Confirming a positive correlation, independence of MEF2B and BCL6 expression levels could be rejected with a p-value according to Fisher´s exact test of 0.0001 against a level of significance of 0.05 (sensitivity 0.92, specificity 0.9, accuracy 0.91).The MEF2B promoter carries binding sites of the AhR/ARNT transcriptional complex. AhR inhibition and ARNT knockdown experiments with the U-2932 subclones revealed that MEF2B is a downstream target of AhR/ARNT signalling. A positive correlation between AhR and MEF2B expression levels could be shown for the majority of 23 DLBCL cell lines tested (sensitivity 0.61, specificity 1.0, accuracy 0.78). These results indicate that the AhR/ARNT-induced expression of wild-type MEF2B might be an independent regulator for BCL6 expression in DLBCL, besides canonical BCL6 translocations, BCL6 promoter hypermutation and MEF2B mutations. To find out the extent to which BCL6 contributed to the subclone-specific gene expression in the U-2932 subclones, we ectopically expressed BCL6 in subclone R2: 48/221 differentially expressed genes were affected. Interestingly, 28/48 genes were upregulated by BCL6 inducing the germinal center markers MYBL1 and LMO2, although BCL6 is believed to act as a transcriptional repressor.In summary, the two subclones of the DLBCL cell line U-2932 faithfully model tumor heterogeneity. Significant expression differences were shown for 221 genes, more than half of which were attributable to genomic copy number differences or to clone-specific expression of the signal transducer AhR and the oncogene BCL6. Moreover, we could show that BCL6 overexpression – regulated by AhR/ARNT and wild-type MEF2B – drives expression of subclone-specific germinal center markers MYBL1 and LMO2 in the DLBCL cell line U-2932. DisclosuresNo relevant conflicts of interest to declare.

C-Myb Restrains Megakaryopoiesis through the Hsa-MiR-486-3p-Driven Down-Regulation of C-Maf

INTRODUCTIONThe transcription factor c-Myb plays a key role in human primary CD34+ hematopoietic progenitor cells (HPCs) lineage choice, by enhancing erythropoiesis at the expense of megakaryopoiesis. We previously demonstrated that c-Myb affects erythroid versus megakaryocyte lineage decision in part by transactivating KLF1 and LMO2 expression. To further unravel the molecular mechanisms through which c-myb affects lineage fate decision, we profiled the miRNA and mRNA changes in myb-silenced CD34+ HPCs.METHODSRNA from CD34+ HPCs transfected with c-myb-targeting/non targeting control synthetic siRNAs was collected 24 hours post-Nucleofection for a set of 5 independent experiments.mRNA and miRNA expression for each sample were profiled by Affymetrix U219 GeneAtlas and Exiqon Human miRNome PCR Panel, respectively. miRNA/mRNA data were integrated by Ingenuity Pathway Analysis.The effects of hsa-miR-486-3p overexpression and c-Maf silencing on CD34+ cells differentiation ability were studied by morphological and immunophenotypic analyses after liquid culture and by collagen-based clonogenic assay. Furthermore, gene expression changes in CD34+ cells upon hsa-miR-486-3p overexpression were profiled by Affymetrix U219.RESULTSThe integrative analysis of miRNA/mRNA expression changes upon c-myb silencing in human CD34+ HPCs highlighted a set of 19 miRNA with 150 anticorrelated putative target mRNAs. Among the miRNAs down-regulated in myb-silenced progenitors with the highest number of predicted target mRNAs, we selected hsa-miR-486-3p based on the in vitro effects of its overexpression on HPCs commitment. Indeed, morphological and flow cytometric analyses after liquid culture showed that hsa-miR-486-3p overexpression in HPCs enhanced erythroid and granulocyte differentiation while restraining megakaryocyte and macrophage differentiation. Moreover, collagen-based clonogenic assay demonstrated a strong impairement megakaryocyte commitment upon hsa-miR-486-3p-overexpression in CD34+ cells.Gene expression profiling of hsa-miR-486-3p overexpressing CD34+ cells enabled us to identify a set of 8 genes down-regulated and computationally predicted, putative hsa-miR-486-3p targets. Among them, we selected c-maf transcript as up-regulated upon myb silencing. Worth of note, c-maf silencing in CD34+ progenitor cells was able to reverse the affects of myb silencing on erythroid versus megakaryocyte lineage choice.CONCLUSIONSIntegrative miRNA/mRNA analysis highlighted a set of miRNAs and anticorrelated putative target mRNAs modulated upon myb silencing, therefore potential players in myb-driven HPCs lineage choice. Among them, we demonstrated the hsa-miR-486-3p/c-maf pair as partially contributing to the effects of myb on HPCs commitment. Therefore, our data collectively identified myb-driven hsa-miR-486-3p up-regulation and subsequent c-maf down-regulation as a new molecular mechanism through which c-Myb favours erythropoiesis while restraining megakaryopoiesis. DisclosuresNo relevant conflicts of interest to declare.

Interleukin-7 receptor mutants initiate early T cell precursor leukemia in murine thymocyte progenitors with multipotent potential

Early T cell precursor acute lymphoblastic leukemia (ETP-ALL) exhibits lymphoid, myeloid, and stem cell features and is associated with a poor prognosis. Whole genome sequencing of human ETP-ALL cases has identified recurrent mutations in signaling, histone modification, and hematopoietic development genes but it remains to be determined which of these abnormalities are sufficient to initiate leukemia. We show that activating mutations in the interleukin-7 receptor identified in human pediatric ETP-ALL cases are sufficient to generate ETP-ALL in mice transplanted with primitive transduced thymocytes from p19(Arf-/-) mice. The cellular mechanism by which these mutant receptors induce ETP-ALL is the block of thymocyte differentiation at the double negative 2 stage at which myeloid lineage and T lymphocyte developmental potential coexist. Analyses of samples from pediatric ETP-ALL cases and our murine ETP-ALL model show uniformly high levels of LMO2 expression, very low to undetectable levels of BCL11B expression, and a relative lack of activating NOTCH1 mutations. We report that pharmacological blockade of Jak-Stat signaling with ruxolitinib has significant antileukemic activity in this ETP-ALL model. This new murine model recapitulates several important cellular and molecular features of ETP-ALL and should be useful to further define novel therapeutic approaches for this aggressive leukemia.

Five Transcription Factors and FGF Pathway Inhibition Efficiently Induce Erythroid Differentiation in the Epiblast

SummaryPrimitive erythropoiesis follows a stereotypic developmental program of mesoderm ventralization and internalization, hemangioblast formation and migration, and erythroid lineage specification. Induction of erythropoiesis is inefficient in either ES/iPS cells in vitro or nonhemangioblast cell populations in vivo. Using the chick model, we report that epiblast cells can be directly and efficiently differentiated into the erythroid lineage by expressing five hematopoietic transcription regulators (SCL+LMO2+GATA2+LDB1+E2A) and inhibiting the FGF pathway. We show that these five genes are expressed with temporal specificity during normal erythropoiesis. Initiation of SCL and LMO2 expression requires FGF activity, whereas erythroid differentiation is enhanced by FGF inhibition. The lag between hematopoiesis and erythropoiesis is attributed to sequential coregulator expression and hemangioblast migration. Globin gene transcription can be ectopically and prematurely induced by manipulating the availability of these factors and the FGF pathway activity. We propose that similar approaches can be taken for efficient erythroid differentiation in vitro.

LMO2 andBCL6 are associated with improved survival in primary central nervous system lymphoma

Primary central nervous system lymphoma (PCNSL) is an aggressive sub-variant of non-Hodgkin lymphoma (NHL) with morphological similarities to diffuse large B-cell lymphoma (DLBCL). While methotrexate (MTX)-based therapies have improved patient survival, the disease remains incurable in most cases and its pathogenesis is poorly understood. We evaluated 69 cases of PCNSL for the expression of HGAL (also known as GCSAM), LMO2 and BCL6 - genes associated with DLBCL prognosis and pathobiology, and analysed their correlation to survival in 49 PCNSL patients receiving MTX-based therapy. We demonstrate that PCNSL expresses LMO2, HGAL(also known as GCSAM) and BCL6 proteins in 52%, 65% and 56% of tumours, respectively. BCL6 protein expression was associated with longer progression-free survival (P=0·006) and overall survival (OS, P=0·05), while expression of LMO2 protein was associated with longer OS (P=0·027). Further research is needed to elucidate the function of BCL6 and LMO2 in PCNSL.

LIM domain only-2 (LMO2) induces T-cell leukemia by two distinct pathways.

The LMO2 oncogene is deregulated in the majority of human T-cell leukemia cases and in most gene therapy-induced T-cell leukemias. We made transgenic mice with enforced expression of Lmo2 in T-cells by the CD2 promoter/enhancer. These transgenic mice developed highly penetrant T-ALL by two distinct patterns of gene expression: one in which there was concordant activation of Lyl1, Hhex, and Mycn or alternatively, with Notch1 target gene activation. Most strikingly, this gene expression clustering was conserved in human Early T-cell Precursor ALL (ETP-ALL), where LMO2, HHEX, LYL1, and MYCN were most highly expressed. We discovered that HHEX is a direct transcriptional target of LMO2 consistent with its concordant gene expression. Furthermore, conditional inactivation of Hhex in CD2-Lmo2 transgenic mice markedly attenuated T-ALL development, demonstrating that Hhex is a crucial mediator of Lmo2's oncogenic function. The CD2-Lmo2 transgenic mice offer mechanistic insight into concordant oncogene expression and provide a model for the highly treatment-resistant ETP-ALL subtype.

Molecular Functions of the LIM-Homeobox Transcription Factor Lhx2 in Hematopoietic Progenitor Cells Derived from Mouse Embryonic Stem Cells

We previously demonstrated that hematopoietic stem cell (HSC)-like cells are robustly expanded from mouse embryonic stem cells (ESCs) by enforced expression of Lhx2, a LIM-homeobox domain (LIM-HD) transcription factor. In this study, we analyzed the functions of Lhx2 in that process using an ESC line harboring an inducible Lhx2 gene cassette. When ESCs are cultured on OP9 stromal cells, hematopoietic progenitor cells (HPCs) are differentiated and these HPCs are prone to undergo rapid differentiation into mature hematopoietic cells. Lhx2 inhibited differentiation of HPCs into mature hematopoietic cells and this effect would lead to accumulation of HSC-like cells. LIM-HD factors interact with LIM domain binding (Ldb) protein and this interaction abrogates binding of LIM-only (Lmo) protein to Ldb. We found that one of Lmo protein, Lmo2, was unstable due to dissociation of Lmo2 from Ldb1 in the presence of Lhx2. This effect of Lhx2 on the amount of Lmo2 contributed into accumulation of HSC-like cells, since enforced expression of Lmo2 into HSC-like cells inhibited their self-renewal. Expression of Gata3 and Tal1/Scl was increased in HSC-like cells and enforced expression of Lmo2 reduced expression of Gata3 but not Tal1/Scl. Enforced expression of Gata3 into HPCs inhibited mature hematopoietic cell differentiation, whereas Gata3-knockdown abrogated the Lhx2-mediated expansion of HPCs. We propose that multiple transcription factors/cofactors are involved in the Lhx2-mediated expansion of HSC-like cells from ESCs. Lhx2 appears to fine-tune the balance between self-renewal and differentiation of HSC-like cells.

The Role Of tet2 DNA Methylcytosine Dioxygenase In Zebrafish Early Hematopoiesis

Loss-of-function mutations in Ten-Eleven-Translocation 2 (TET2) gene have been identified in various human myeloid and lymphoid malignancies. Recently, the TET gene family (TET1, TET2, and TET3) was found to function as DNA methylcytosine dioxygenase that is able to oxidize 5-methylcytosine (5-mC) into 5-hydroxymethylcytosine (5-hmC). In Tet2-deficient mouse models, Tet2 has been shown to play an important role in regulating self-renewal and differentiation of hematopoietic stem cells. These Tet2-deficient mice would gradually develop a chronic myeloid neoplasm resembling human chronic myelomonocytic leukemia suggesting that TET2 may function as a tumor suppressor. In the present study, we investigated the role of tet2 in zebrafish early hematopoiesis. During zebrafish early development, the expression of tet1, tet2, and tet3 by qRT-PCR can be detected mainly after the segmentation stage (26-somite), with fluctuated expression levels thereafter. Whole-mount in situ hybridization revealed that tet2 expression was strong over aorta-gonad-mesonephros region at 48 hours post-fertilization (hpf). Morpholino oligonucleotide (MO) knock-down of tet2 increased the expression of tet1, tet3, dnmt3aa, gata-1, alpha-Hb and fli1a (48 hpf) as well as rag2 and lck (4 days post-fertilization), and the expression of spi1b and mpo decreased (48 hpf). The expression of primitive hematopoietic stem cell markers scl and lmo2, as well as dnmt3ab, beta-Hb, l-plastin, and rag1 were unaffected. The levels of 5-mC and 5-hmC measured by ELISA were also decreased after MO knock-down of tet2. The number of gata-1 expressing red blood cells increased after tet2 MO knock-down as evaluated by flow-cytometry indicating that tet2 deficiency increased erythropoiesis. These preliminary results suggest that tet2 might play a role in the epigenetic regulation of zebrafish early hematopoiesis including erythropoiesis. Recently, transcription activator-like effector nuclease (TALEN) has been shown to generate targeted genomic editing in zebrafish. To validate our observation, we therefore utilized customized TALENs pair to generate tet2 knock-out zebrafish animal model. We designed a pair of TALENs targeting first exon of tet2 and our tet2 TALENs were able to generate insertion and/or deletion in targeted region of tet2 exon 1 in 25% to 44% zebrafish embryos. We obtained a total of fifteen different tet2 mutation genotypes F1 fish, and seven of them were predicted to cause early termination of transcription. The in-cross of these F1 genotypes matched the Mendelian inheritance. The tet2-/- knock-out F2 zebrafish is not embryonic lethal and can grow to sexually mature adult fish. The detailed analysis of tet2-/- knock-out zebrafish early hematopoiesis will be presented at the meeting. Disclosures:No relevant conflicts of interest to declare.

LMO2 (LIM domain only 2) is expressed in a subset of acute myeloid leukaemia and correlates with normal karyotype

LMO2 is a transcription factor that plays a key role in haematopoiesis. Expression of LMO2 has been demonstrated in germinal centre B cells, various B cell lymphomas and T lymphoblastic lymphoma/leukaemia (T-ALL), but has not been studied extensively in acute myeloid leukaemia (AML). We studied LMO2 expression by immunohistochemistry in biopsies from a cohort of AML patients (n = 196) and correlated it with established prognostic factors such as age, bone marrow morphology and cytogenetic findings. Forty per cent (79 of 196) of the samples from AML patients showed moderate/strong expression of LMO2 protein. LMO2 expression showed a significant positive correlation with normal cytogenetics (65% versus 24%, P < 0.0001) and a moderately negative correlation with complex karyotype [rs (98) = -0.218, P < 0.002]. AML associated with core binding factor [(t(8;21)/inv(16)/t(16;16)] had low LMO2 expression compared to diploid karyotype (29% versus 65%; P = 0.013). Expression of LMO2 protein exhibited an insignificant association with age (P = 0.197). Lower expression of LMO2 protein was noted in AML associated with myelodysplasia-related changes, compared to AML subtypes based on FAB classification (M0-M7) (21% versus 44%, P = 0.0187). LMO2 is expressed in a subset of AML patients and is associated with normal karyotype, which is different from T-ALL, where specific translocation (11p13) mediates protein expression.

Tissue microarray in a subset of South African patients with DLBCL

Tissue samples from 93 de novo diffuse large B-cell lymphoma patients seen between 1995 and 2009 randomly receiving either standard combination chemotherapy (CHOP, n=48) or the identical program with rituximab (n=45) were subtyped using an investigational immunohistochemical (IHC) based tissue microarray (TMA) and contrasted to the approximately corresponding categories as defined either by Hans and associates using a three marker panel into germinal or non-germinal centre subtypes or by Choi and colleagues with two additional antibodies into germinal centre (GCB) or activated B-cells (ABC). Each of these primary subdivisions was further evaluated for expression of BCL2 and LMO2 both of which are recognised to predicate response.The addition of rituximab to the uniform drug regimen did not show any significant improvement in 5years overall (63% versus 59%, p 0.68) or event-free survival (42% versus 39%, p 0.94), for CHOP versus R-CHOP comparisons. Similarly no differences were evident in subtype analysis. Interestingly however, when segregated on the Choi criteria, cytotoxic drugs alone showed a non-significant trend in improved survival (74% versus 55%, p 0.32) as well as event-free survival (44% versus 40%, p 0.42) for the germinal centre as opposed to the activated B-cell subtype. Nevertheless not even a small difference could be demonstrated in the presence of the anti CD 20 monoclonal antibody.According to Choi, both regimens (chemotherapy or immunotherapy antibody) revealed similar results to the Hans algorithm on 5years OS as well as 3year EFS when comparing GCB versus ABC or non-GCB subgroups.BCL2 and LMO2 marker expression of the respective immunohistochemical (IHC) subtype, despite small sample size, revealed the following. Analysis by Choi criteria on survival for BCL2, no matter for which subsets (GCB or ABC) or treatment modality (chemotherapy with or without the addition of rituximab) showed no difference in 5years OS or EFS. In contrast, a significant difference for better EFS (p=0.0015) in the BCL2 positive group of the ABC subgroups subtypes treated with rituximab containing chemotherapy. For LMO2 similar results on survival outcome were seen thus showing no difference in 5years OS or EFS – regardless of subtype or treatment modality. Also here, this was contrasted by better EFS (p=0.039) in the LMO2 positive group of ABC subtypes when treated with the rituximab containing regimen.The use of the IHC based TMA methodology has shown to be a simple, cost effective and a robust alternative to gene expression profiling (GEP) which is currently regarded as the gold standard for the classification in lymphomas. It provides a useful prognostic tool in stratifying DLBCL or other entities in future, even when frozen tissue samples are not available for GEP analysis.With the current budgetary limitations in South African public hospitals chemotherapy protocols for lymphoproliferative disorders exclude agents such as rituximab. Local therapeutic drug committees consider the approximately 15% overall survival benefit seen at 5years for DLBCL when rituximab is added to combination chemotherapy as too marginal for justifying the arising additional expenses.Accordingly, demonstration that a specific molecular subtype accounts for superior outcome, when using these regimens, is needed. Such an option would provide convincing evidence for the use of immunochemotherapy in a resource constrained setting.

GATA2 and Lmo2 control angiogenesis and lymphangiogenesis via direct transcriptional regulation of neuropilin-2

GATA-binding protein 2 (GATA2) and LIM domain only 2 (Lmo2) form common transcription complexes during hematopoietic differentiation. Here we show that these two transcription factors also play a key role in endothelial cells (EC) and lymphatic EC (LEC) function. Primary EC and tumor-associated blood vessels expressed GATA2 and Lmo2. VEGF-induced sprouting angiogenesis in both differentiating embryonic stem cells (embryoid bodies) and primary EC increased GATA2 and Lmo2 levels. Conversely, silencing of GATA2 and Lmo2 expression in primary EC inhibited VEGF-induced angiogenic activity, including EC migration and sprouting in vitro, two key steps of angiogenesis in vivo. This inhibition of EC function was associated with downregulated expression of neuropilin-2 (NRP2), a co-receptor of VEGFRs for VEGF, at the protein, mRNA and promoter levels. NRP2 overexpression partially rescued the impaired angiogenic sprouting in the GATA2/Lmo2 knockdown EC, confirming that GATA2 and Lmo2 mediated EC function, at least in part, by directly regulating NRP2 gene expression. Furthermore, it was found that primary LEC expressed GATA2 and Lmo2 as well. Silencing of GATA2 and Lmo2 expression in LEC inhibited VEGF-induced LEC sprouting, also in a NRP2-dependent manner. In conclusion, our results demonstrate that GATA2 and Lmo2 cooperatively regulate VEGF-induced angiogenesis and lymphangiogenesis via NRP2.

Expression of microRNA-223 in lymphocytic leukemia cells and its action mechanism

This study was aimed to investigate the expression level and mechanism of microRNA-223 and LMO2 in acute lymphoblastic leukemia (ALL) and chronic lymphocytic leukemia (CLL) cells and the mechanism. MicroRNA-223 mimics was transfected to increase the expression of MicroRNA-223 in the lymphocytes sorted by ficoll separation from the bone marrow mononuclear cells (BMMNC) of ALL and CLL patients. MicroRNA-223 inhibitor was transfected to decrease the expression of the MicroRNA-223 in the lymphocytes of normal controls. Then the expression of the MicroRNA-223 and LMO2 in transfected lymphocytes before and after cultivating for 72 hours were detected by RT-PCR, the apoptosis and cell cycle of these cells were measured by flow cytometery. The results indicated that before the transfection, the expression of MicroRNA-223 in ALL and CLL cells was (433.11 ± 144.88), which was significantly lower than that in the normal lymphocyte (949.59 ± 267.39); the expression of LMO2 was (807.10 ± 238.41), which was significantly higher than that in the normal lymphocytes (455.32 ± 176.83) (P < 0.05); after the transfection, the expression of MicroRNA-223 was (571.86 ± 142.00) in ALL and CLL cells, which was significantly higher than that before transfection (P < 0.05), but the expression of LMO2 was significantly lower than that before transfection (651.97 ± 230.12) (P < 0.05); in the normal control the expression of MicroRNA-223 obviously decreased (646.32 ± 172.93) (P < 0.05), the expression of LMO2 was significantly increased (541.27 ± 158.86.2) (P < 0.05). After transfection, the cell cycle G1/G2 phase and apoptosis changed in ALL and CLL cells. Before transfection the cell ratio in cell cycle G1/G2 phase was (94.75 ± 3.15)%, the cell ratio in S phase was (5.14 ± 3.12)%; after transfection the cell ratio in cell cycle G1/G2 phase was (97.03 ± 2.08)% and obviously increased (P < 0.05), the cell ratio in S phase was (2.97 ± 2.08)% and significantly decreased (P < 0.05). Before transfection the apoptosis rate was (54.47 ± 8.72)%, and obviously was higher than that after transfection (60.48 ± 8.81)%. And in the normal control, the cell ratio in G1/G2 phase was significantly higher than that after transfection [(96.73 ± 2.26)%, (94.55 ± 2.77)%, P < 0.05)], and the cell ratio in S phase was significantly increased [(3.25 ± 2.26)%, (5.45 ± 2.77)% (P < 0.05)]. The apoptotic rate in the ALL and CLL patients was significantly higher than that after the transfection [(54.47 ± 8.72)% vs (60.48 ± 8.81)%, respectively (P < 0.05)]. The apoptotic rate in the normal control was significantly lower than that after the transfection [(59.02 ± 10.20)%, (51.96 ± 10.20)%, respectively (P < 0.05)]. It is concluded that the expression of MicroRNA-223 decreases, and the expression of LMO2 increases in lymphocytic leukemia cells which leads to the lymphocytes over-proliferation and abnormal apoptosis, thus may be one of pathogenesis in lymphocytic leukemia.