TAL1 Expression Research Articles

The proto-oncogenic protein TAL1 controls TGF-β1 signaling through interaction with SMAD3

TGF-β1 is involved in many aspects of tissue development and homeostasis including hematopoiesis. The TAL1 transcription factor is also an important player of this latter process and is expressed very early in the myeloid and erythroid lineages. We previously established a link between TGF-β1 signaling and TAL1 by showing that the cytokine was able to induce its proteolytic degradation by the ubiquitin proteasome pathway. In this manuscript we show that TAL1 interacts with SMAD3 that acts in the pathway downstream of TGF-β1 association with its receptor. TAL1 expression strengthens the positive or negative effect of SMAD3 on various genes. Both transcription factors activate the inhibitory SMAD7 factor through the E box motif present in its transcriptional promoter. DNA precipitation assays showed that TAL1 present in Jurkat or K562 cells binds to this SMAD binding element in a SMAD3 dependent manner. SMAD3 and TAL1 also inhibit several genes including ID1, hTERT and TGF-β1 itself. In this latter case TAL1 and SMAD3 can impair the positive effect exerted by E47. Our results indicate that TAL1 expression can modulate TGF-β1 signaling by interacting with SMAD3 and by increasing its transcriptional properties. They also suggest the existence of a negative feedback loop between TAL1 expression and TGF-β1 signaling.

Erythroid activator NF-E2, TAL1 and KLF1 play roles in forming the LCR HSs in the human adult β-globin locus

The β-like globin genes are developmental stage specifically transcribed in erythroid cells. The transcription of the β-like globin genes requires erythroid specific activators such as GATA-1, NF-E2, TAL1 and KLF1. However, the roles of these activators have not fully elucidated in transcription of the human adult β-globin gene. Here we employed hybrid MEL cells (MEL/ch11) where a human chromosome containing the β-globin locus is present and the adult β-globin gene is highly transcribed by induction. The roles of erythroid specific activators were analyzed by inhibiting the expression of NF-E2, TAL1 or KLF1 in MEL/ch11 cells. The loss of each activator decreased the transcription of human β-globin gene, locus wide histone hyperacetylation and the binding of other erythroid specific activators including GATA-1, even though not affecting the expression of other activators. Notably, sensitivity to DNase I was reduced in the locus control region (LCR) hypersensitive sites (HSs) with the depletion of activators. These results indicate that NF-E2, TAL1 and KLF1, all activators play a primary role in HSs formation in the LCR. It might contribute to the transcription of human adult β-globin gene by allowing the access of activators and cofactors. The roles of activators in the adult β-globin locus appear to be different from the roles in the early fetal locus.

UTX inhibition as selective epigenetic therapy against TAL1-driven T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is a heterogeneous group of hematological tumors composed of distinct subtypes that vary in their genetic abnormalities, gene expression signatures, and prognoses. However, it remains unclear whether T-ALL subtypes differ at the functional level, and, as such, T-ALL treatments are uniformly applied across subtypes, leading to variable responses between patients. Here we reveal the existence of a subtype-specific epigenetic vulnerability in T-ALL by which a particular subgroup of T-ALL characterized by expression of the oncogenic transcription factor TAL1 is uniquely sensitive to variations in the dosage and activity of the histone 3 Lys27 (H3K27) demethylase UTX/KDM6A. Specifically, we identify UTX as a coactivator of TAL1 and show that it acts as a major regulator of the TAL1 leukemic gene expression program. Furthermore, we demonstrate that UTX, previously described as a tumor suppressor in T-ALL, is in fact a pro-oncogenic cofactor essential for leukemia maintenance in TAL1-positive (but not TAL1-negative) T-ALL. Exploiting this subtype-specific epigenetic vulnerability, we propose a novel therapeutic approach based on UTX inhibition through in vivo administration of an H3K27 demethylase inhibitor that efficiently kills TAL1-positive primary human leukemia. These findings provide the first opportunity to develop personalized epigenetic therapy for T-ALL patients.

MicroRNAs regulate TAL1 expression in T-cell acute lymphoblastic leukemia.

The transcription factor TAL1 is a proto-oncogene whose aberrant expression in committed T-cell precursors is associated with the development of T-cell acute lymphoblastic leukemia (T-ALL). The mechanisms leading to aberrant activation of TAL1 in T-ALL patients who lack chromosomal rearrangements involving the TAL1 locus remain largely unknown. We hypothesized that TAL1 levels decrease during normal T-cell development at least in part due to miRNA-dependent silencing, in which case TAL1 over-expression in some T-ALL cases could be the consequence of deregulated miRNA expression. By performing computational prediction of miRNAs that bind to the human TAL1 mRNA we compiled a list of miRNAs that are candidates to regulate TAL1. Using a luciferase reporter system and mutagenesis assays we confirmed the miRNA-TAL1 mRNA interactions and selected candidate miRNAs: miR-101, miR-520d-5p, miR-140-5p, miR-448 and miR-485-5p. Over-expression of these microRNAs in different T-ALL cell lines consistently resulted in the down-regulation of TAL1 protein. In accordance, inhibition of miR-101 and miR-520d-5p promoted TAL1 protein expression. Importantly, we found that miR-101, miR-140-5p, miR-448 and miR-485-5p were down-regulated in T-ALL patient specimens and T-ALL cell lines. Our results show for the first time the existence of epigenetic regulation of TAL1 by specific miRNAs which may contribute, at least in part, to the ectopic expression of TAL1 in some T-ALL cases.

PHO13 deletion-induced transcriptional activation prevents sedoheptulose accumulation during xylose metabolism in engineered Saccharomyces cerevisiae

The deletion of PHO13 (pho13Δ) in Saccharomyces cerevisiae, encoding a phosphatase enzyme of unknown specificity, results in the transcriptional activation of genes related to the pentose phosphate pathway (PPP) such as TAL1 encoding transaldolase. It has been also reported that the pho13Δ mutant of S. cerevisiae expressing a heterologous xylose pathway can metabolize xylose efficiently compared to its parental strain. However, the interaction between the pho13Δ–induced transcriptional changes and the phenotypes of xylose fermentation was not understood. Thus we investigated the global metabolic changes in response to pho13Δ when cells were exponentially growing on xylose. Among the 134 intracellular metabolites that we identified, the 98% reduction of sedoheptulose was found to be the most significant change in the pho13Δ mutant as compared to its parental strain. Because sedoheptulose-7-phosphate (S7P), a substrate of transaldolase, reduced significantly in the pho13Δ mutant as well, we hypothesized that limited transaldolase activity in the parental strain might cause dephosphorylation of S7P, leading to carbon loss and inefficient xylose metabolism. Mutants overexpressing TAL1 at different degrees were constructed, and their TAL1 expression levels and xylose consumption rates were positively correlated. Moreover, as TAL1 expression levels increased, intracellular sedoheptulose concentration dropped significantly. Therefore, we concluded that TAL1 upregulation, preventing the accumulation of sedoheptulose, is the most critical mechanism for the improved xylose metabolism by the pho13Δ mutant of engineered S. cerevisiae.

TAL1 and MYB Abnormalities in Childhood T-Cell Acute Lymphoblastic Leukemia

T-cell acute lymphoblastic leukemia (T-ALL) accounts for 10% to 15% of newly diagnosed cases of childhood acute lymphoblastic leukemia (ALL). Although gene fusions generated through chromosomal translocations, deletions, and inversions are the most frequent genetic abnormalities detected in other types of leukemia, recurrent gene fusions except for SIL-TAL1 have been poorly defined in T-ALL. To discover driver mutations or fusion genes, which involved in the pathogenesis of childhood T-ALL and to identify novel prognostic markers of childhood T-ALL, we performed whole-exome sequencing (WES) and transcriptome sequencing (WTS) in 31 and 46 cases, respectively. We also performed SNP array karyotyping in 46 cases. To detect somatic mutations or fusion transcripts, we used our pipeline "Genomon-exome" and "Genomon-fusion" algorithm. Subsequently, somatic mutations were validated using deep amplicon sequencing. Candidate fusion transcripts were validated by reverse - transcription polymerase-chain-reaction and Sanger sequencing.Recurrent mutations observed in more than 3 cases were detected in NOTCH1 (n = 18, 58%), FBXW7 (n = 7, 23%), PHF6 (n = 5, 16%), GATA3 (n = 4, 13%), MYB (n = 3, 10%), and NRAS (n = 3, 10%), respectively. We identified previously known fusion genes, such as MLL-ENL (n = 2), CALM-AF10 (n = 2), NUP214-ABL1 (n = 1) and FGFROP1-FGFR1 (n = 1). MLL-ENL is one of the frequent translocation in infant multilineage leukemia, but also reported in non-infant B cell precursor ALL and T-ALL. FGFR1OP is ubiquitously expressed, and the predicted chimeric FGFR1OP-FGFR1 protein contains the catalytic domain of FGFR1. It is thought to promote hematopoietic stem cell proliferation and leukemogenesis through a constitutive phosphorylation and activation of the downstream pathway of FGFR1. CALM-AF10 leukemia is reported to increase HOXA cluster gene transcription, we could also confirm elevated HOXA genes expression by FPKM value. Four SIL-TAL1 fusions were detected in our cohort. Recently, a novel mutation in TAL1 enhancer region which introduce de novo MYB biding site has been reported. Since this abnormality lead high expression of TAL1, we also analyzed expression data obtained from WTS. Among 46 specimens, 19 samples showed high expression of TAL1 (FPKM value ≥5). In those cases, 4 cases had SIL-TAL1 fusions (8%), and 3 cases (6%) had insertions in enhancer region of TAL1. Subsequent analysis using Gene Set Enrich Analysis (GSEA) between TAL1 high and low expression samples revealed that "LEE_EARLY_T_LYMPHOCYTE_UP" was enriched in TAL1 high expression samples (Enrichment score = 0.73, FDR = 0.073). This gene set includes genes up-regulated at early stages of progenitor T lymphocyte maturation compared to the late stages, and MYB was included in this gene set. Intriguingly, MYB mutation samples were not represented TAL1 high expression. TAL1 related rearrangement or enhancer insertion was not detected in the rest of 12 cases with TAL1 high expression, suggesting that other mechanisms of TAL1 high expression might be exist. In conclusion, although NOTCH1 and FBXW7 mutations were relatively frequently detected in our series, we also found recurrent MYB mutations. SIL-TAL1 was known as most frequent rearrangement, TAL1 enhancer insertions were also frequent in TAL1 overexpressed samples. TAL1 enhancer insertion and MYB mutation was exclusive, suggesting that TAL1 and MYB have a key role in childhood T-ALL. Consistent with other reports, frequent translocations were not observed in T-ALL, suggesting the genetic differences between T-ALL and other hematological malignancies. Further studies will be necessary to unravel oncogenic mechanisms that implicated in new therapeutic strategy for childhood T-ALL. DisclosuresNo relevant conflicts of interest to declare.

The search for cis-regulatory driver mutations in cancer genomes.

With the advent of high-throughput and relatively inexpensive whole-genome sequencing technology, the focus of cancer research has begun to shift toward analyses of somatic mutations in non-coding cis-regulatory elements of the cancer genome. Cis-regulatory elements play an important role in gene regulation, with mutations in these elements potentially resulting in changes to the expression of linked genes. The recent discoveries of recurrent TERT promoter mutations in melanoma, and recurrent mutations that create a super-enhancer regulating TAL1 expression in T-cell acute lymphoblastic leukaemia (T-ALL), have sparked significant interest in the search for other somatic cis-regulatory mutations driving cancer development. In this review, we look more closely at the TERT promoter and TAL1 enhancer alterations and use these examples to ask whether other cis-regulatory mutations may play a role in cancer susceptibility. In doing so, we make observations from the data emerging from recent research in this field, and describe the experimental and analytical approaches which could be adopted in the hope of better uncovering the true functional significance of somatic cis-regulatory mutations in cancer.

Variation in Gamma-Globin Expression before and after Induction with Hydroxyurea Associated with BCL11A, KLF1 and TAL1.

The molecular mechanisms governing γ-globin expression in a subset of fetal hemoglobin (α2γ2: HbF) expressing red blood cells (F-cells) and the mechanisms underlying the variability of response to hydroxyurea induced γ-globin expression in the treatment of sickle cell disease are not completely understood. Here we analyzed intra-person clonal populations of basophilic erythroblasts (baso-Es) derived from bone marrow common myeloid progenitors in serum free cultures and report the level of fetal hemoglobin production in F-cells negatively correlates with expression of BCL11A, KLF1 and TAL1. We then examined the effects of hydroxyurea on these three transcription factors and conclude that a successful induction of γ-globin includes a reduction in BCL11A, KLF1 and TAL1 expression. These data suggests that expression changes in this transcription factor network modulate γ-globin expression in F-cells during steady state erythropoiesis and after induction with hydroxyurea.

Enhanced xylose fermentation and ethanol production by engineered Saccharomyces cerevisiae strain.

We have recently demonstrated that heterologous expression of a bacterial xylose isomerase gene (xylA) of Burkholderia cenocepacia enabled a laboratorial Saccharomyces cerevisiae strain to ferment xylose anaerobically, without xylitol accumulation. However, the recombinant yeast fermented xylose slowly. In this study, an evolutionary engineering strategy was applied to improve xylose fermentation by the xylA-expressing yeast strain, which involved sequential batch cultivation on xylose. The resulting yeast strain co-fermented glucose and xylose rapidly and almost simultaneously, exhibiting improved ethanol production and productivity. It was also observed that when cells were grown in a medium containing higher glucose concentrations before being transferred to fermentation medium, higher rates of xylose consumption and ethanol production were obtained, demonstrating that xylose utilization was not regulated by catabolic repression. Results obtained by qPCR demonstrate that the efficiency in xylose fermentation showed by the evolved strain is associated, to the increase in the expression of genes HXT2 and TAL1, which code for a low-affinity hexose transporter and transaldolase, respectively. The ethanol productivity obtained after the introduction of only one genetic modification and the submission to a one-stage process of evolutionary engineering was equivalent to those of strains submitted to extensive metabolic and evolutionary engineering, providing solid basis for future applications of this strategy in industrial strains.Electronic supplementary materialThe online version of this article (doi:10.1186/s13568-015-0102-y) contains supplementary material, which is available to authorized users.

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].

The hematopoietic regulator TAL1 is required for chromatin looping between the β-globin LCR and human γ-globin genes to activate transcription

TAL1 is a key hematopoietic transcription factor that binds to regulatory regions of a large cohort of erythroid genes as part of a complex with GATA-1, LMO2 and Ldb1. The complex mediates long-range interaction between the β-globin locus control region (LCR) and active globin genes, and although TAL1 is one of the two DNA-binding complex members, its role is unclear. To explore the role of TAL1 in transcription activation of the human γ-globin genes, we reduced the expression of TAL1 in erythroid K562 cells using lentiviral short hairpin RNA, compromising its association in the β-globin locus. In the TAL1 knockdown cells, the γ-globin transcription was reduced to 35% and chromatin looping of the Gγ-globin gene with the LCR was disrupted with decreased occupancy of the complex member Ldb1 and LMO2 in the locus. However, GATA-1 binding, DNase I hypersensitive site formation and several histone modifications were largely maintained across the β-globin locus. In addition, overexpression of TAL1 increased the γ-globin transcription and increased interaction frequency between the Gγ-globin gene and LCR. These results indicate that TAL1 plays a critical role in chromatin loop formation between the γ-globin genes and LCR, which is a critical step for the transcription of the γ-globin genes.

Chromatin looping defines expression of TAL1, its flanking genes, and regulation in T-ALL

AbstractTAL1 is an important regulator of hematopoiesis and its expression is tightly controlled despite complexities in its genomic organization. It is frequently misregulated in T-cell acute lymphoblastic leukemia (T-ALL), often due to deletions between TAL1 and the neighboring STIL gene. To better understand the events that lead to TAL1 expression in hematopoiesis and in T-ALL, we studied looping interactions at the TAL1 locus. In TAL1-expressing erythroid cells, the locus adopts a looping “hub” which brings into close physical proximity all known TAL1 cis-regulatory elements including CTCF-bound insulators. Loss of GATA1 results in disassembly of the hub and loss of CTCF/RAD21 from one of its insulators. Genes flanking TAL1 are partly dependent on hub integrity for their transcriptional regulation. We identified looping patterns unique to TAL1-expressing T-ALL cells, and, intriguingly, loops occurring between the TAL1 and STIL genes at the common TAL1/STIL breakpoints found in T-ALL. These findings redefine how TAL1 and neighboring genes communicate within the nucleus, and indicate that looping facilitates both normal and aberrant TAL1 expression and may predispose to structural rearrangements in T-ALL. We also propose that GATA1-dependent looping mechanisms may facilitate the conservation of TAL1 regulation despite cis-regulatory remodeling during vertebrate evolution.

The role ofTal2andTal1in the differentiation of midbrain GABAergic neuron precursors

SummaryMidbrain- and hindbrain-derived GABAergic interneurons are critical for regulation of sleep, respiratory, sensory-motor and motivational processes, and they are implicated in human neurological disorders. However, the precise mechanisms that underlie generation of GABAergic neuron diversity in the midbrain–hindbrain region are poorly understood. Here, we show unique and overlapping requirements for the related bHLH proteins Tal1 and Tal2 in GABAergic neurogenesis in the midbrain. We show that Tal2 and Tal1 are specifically and sequentially activated during midbrain GABAergic neurogenesis. Similar to Gata2, a post-mitotic selector of the midbrain GABAergic neuron identity, Tal2 expression is activated very early during GABAergic neuron differentiation. Although the expression of Tal2 and Gata2 genes are independent of each other, Tal2 is important for normal midbrain GABAergic neurogenesis, possibly as a partner of Gata2. In the absence of Tal2, the majority of midbrain GABAergic neurons switch to a glutamatergic-like phenotype. In contrast, Tal1 expression is activated in a Gata2 and Tal2 dependent fashion in the more mature midbrain GABAergic neuron precursors, but Tal1 alone is not required for GABAergic neuron differentiation from the midbrain neuroepithelium. However, inactivation of both Tal2 and Tal1 in the developing midbrain suggests that the two factors co-operate to guide GABAergic neuron differentiation in a specific ventro-lateral midbrain domain. The observed similarities and differences between Tal1/Tal2 and Gata2 mutants suggest both co-operative and unique roles for these factors in determination of midbrain GABAergic neuron identities.

FoxO3a and nilotinib-induced erythroid differentiation of CML-BC cells

We explored the potential involvement of FoxO3a activation in erythroid and granulocytic differentiation for Ph(+) cells of chronic myeloid leukemia blast crisis (CML BC). We demonstrate that FoxO3a activation in CML blast crisis (BC) cells by overexpressing FoxO3a leads to the maturation of CML BC cells. Hemoglobin production significantly increased upon FoxO3a activation in CML BC cells. FoxO3a activation upregulated erythroid surface protein (glycophorin A, GPA), but did not significantly modulate granulocytic markers (CD11b). Additionally, FoxO3a activation reduced the mRNA and protein expression of Tal1. Similar results were observed in cells that were given nilotinib. Our results indicate that FoxO3a activation may promote erythroid differentiation of BC cells via down-regulating Tal1 expression.

Ectopic Runx1 Expression Rescues Tal-1-Deficiency in the Generation of Primitive and Definitive Hematopoiesis

The transcription factors SCL/Tal-1 and AML1/Runx1 control the generation of pluripotent hematopoietic stem cells (pHSC) and, thereby, primitive and definitive hematopoiesis, during embryonic development of the mouse from mesoderm. Thus, Runx1-deficient mice generate primitive, but not definitive hematopoiesis, while Tal-1-deficient mice are completely defective. Primitive as well as definitive hematopoiesis can be developed “in vitro” from embryonic stem cells (ESC). We show that wild type, as well as Tal-1−/− and Runx1−/− ESCs, induced to differentiation, all expand within 5 days to comparable numbers of Flk1+ mesodermal cells. While wild type ESCs further differentiate to primitive and definitive erythrocytes, to c-fms+Gr1+Mac1+ myeloid cells, and to B220+CD19+ B- and CD4+/CD8+ T-lymphoid cells, Runx1−/− ESCs, as expected, only develop primitive erythrocytes, and Tal-1−/− ESCs do not generate any hematopoietic cells. Retroviral transduction with Runx1 of Runx1−/− ESCs, differentiated for 4 days to mesoderm, rescues definitive erythropoiesis, myelopoiesis and lymphopoiesis, though only with 1–10% of the efficiencies of wild type ESC hematopoiesis. Surprisingly, Tal-1−/− ESCs can also be rescued at comparably low efficiencies to primitive and definitive erythropoiesis, and to myelopoiesis and lymphopoiesis by retroviral transduction with Runx1. These results suggest that Tal-1 expression is needed to express Runx1 in mesoderm, and that ectopic expression of Runx1 in mesoderm is sufficient to induce primitive as well as definitive hematopoiesis in the absence of Tal-1. Retroviral transduction of “in vitro” differentiating Tal-1−/− and Runx1−/− ESCs should be a useful experimental tool to probe selected genes for activities in the generation of hematopoietic progenitors “in vitro”, and to assess the potential transforming activities in hematopoiesis of mutant forms of Tal-1 and Runx1 from acute myeloid leukemia and related tumors.

Transcriptomic and phospho‐proteomic analyzes of erythroblasts expanded in vitro from normal donors and from patients with polycythemia vera

Erythropoiesis is a tightly regulated process which becomes decoupled from its normal differentiation program in patients with polycythemia vera (PV). Somatic mutations in JAK2 are commonly associated with this myeloid proliferative disorder. To gain insight into the molecular events that are required for abnormally developing erythroid cells to escape dependence on normal growth signals, we performed in vitro expansion of mature erythroblasts (ERY) from seven normal healthy donors and from seven polycythemic patients in the presence of IL3, EPO, SCF for 10, 11, or 13 days. Normal ERYs required exposure to the glucocorticoid dexamethasone (Dex) for expansion, while PV-derived ERYs expanded in the absence of dexamethasone. RNA expression profiling revealed enrichment of two known oncogenes, GPR56 and RAB4a, in PV-derived ERYs along with reduced expression levels of transcription factor TAL1 (ANOVA FDR < 0.05). While both normal and polycythemic-derived ERYs integrated signaling cascades for growth, they did so via different signaling pathways which are represented by their differential phospho-profiles. Our results show that normal ERYs displayed greater levels of phosphorylation of EGFR, PDGFRβ, TGFβ, and cKit, while PV-derived ERYs were characterized by increased phosphorylation of cytoplasmic kinases in the JAK/STAT, PI3K, and GATA1 pathways. Together these data suggest that PV erythroblast expansion and maturation may be maintained and enriched in the absence of dexamethasone through reduced TAL1 expression and by accessing additional signaling cascades. Members of this acquired repertoire may provide important insight into the pathogenesis of aberrant erythropoiesis in myeloproliferative neoplasms such as polycythemia vera.

Aberrant TAL1 activation is mediated by an interchromosomal interaction in human T-cell acute lymphoblastic leukemia.

Long-range chromatin interactions control metazoan gene transcription. However, the involvement of intra- and interchromosomal interactions in development and oncogenesis remains unclear. TAL1/SCL is a critical transcription factor required for the development of all hematopoietic lineages; yet, aberrant TAL1 transcription often occurs in T-cell acute lymphoblastic leukemia (T-ALL). Here, we report that oncogenic TAL1 expression is regulated by different intra- and interchromosomal loops in normal hematopoietic and leukemic cells, respectively. These intra- and interchromosomal loops alter the cell-type-specific enhancers that interact with the TAL1 promoter. We show that human SET1 (hSET1)-mediated H3K4 methylations promote a long-range chromatin loop, which brings the +51 enhancer in close proximity to TAL1 promoter 1 in erythroid cells. The CCCTC-binding factor (CTCF) facilitates this long-range enhancer/promoter interaction of the TAL1 locus in erythroid cells while blocking the same enhancer/promoter interaction of the TAL1 locus in human T-cell leukemia. In human T-ALL, a T-cell-specific transcription factor c-Maf-mediated interchromosomal interaction brings the TAL1 promoter into close proximity with a T-cell-specific regulatory element located on chromosome 16, activating aberrant TAL1 oncogene expression. Thus, our study reveals a novel molecular mechanism involving changes in three-dimensional chromatin interactions that activate the TAL1 oncogene in human T-cell leukemia.

Rat Stem-Cell Leukemia Gene Expression Increased during Testis Maturation

We found that stem-cell leukemia (SCL), also known as T cell acute-lymphocytic leukemia (Tal-1) gene expression, was upregulated in the maturing rat testis. Strong expression of Tal-1 was detected in the normal maturing rat testis by Northern blotting. Western blotting revealed the protein size to be about 34 kDa. Protein expression was wide-spread in spermatocytes, spermtids and spermatogonia in accordance with the seminiferous epithelium cycle, as determined by an analysis of immunohistochemistry. Gene expression of Tal-1 regulatory gene, NKX3.1, was negatively correlated with Tal-1 expression. Human Tal-1 expression in the maturing testis as well as in bone marrow was observed, which suggests that the gene product is a novel cancer-testis antigen candidate. Taken together, TAL-1 may be involved in cell division, morphological changes, and the development of spermatogenic cells in the normal rat testis.

Genetics of Teenage and Young Adult Acute Lymphoblastic T-Cell Leukaemia.

AbstractAbstract 2521 Purpose:The outcome for Teenagers and Young Adults (TYA) with T-cell Acute Lymphoblastic Leukaemia (T-ALL) has improved significantly using paediatric based chemotherapy protocols. Event free survival figures from the recently closed UKALL2003 highlight this observation. It remains poorly understood however why their outlook remains inferior to children aged 1 – 15 years whilst receiving identical treatment. Possible explanations for this phenomenon are distinct tumour biology, host factors and treatment adherence. The primary aim of this study is to characterise the tumour associated genetic events leading to TYA T-ALL and establish whether T-ALL in Teenagers and Young Adults is a distinct disease entity. The secondary aims are to identify new prognostic markers and potential targets to optimise therapy. Methods:DNA and RNA were extracted from 60 TYA T-ALL (15 – 25 years) historic samples. The DNA was derived from blasts at diagnosis or relapse, and matched with germ line DNA where available. The DNA was examined at high resolution for Copy Number Alterations (CNAs) and Loss of Heterozygosity (LOH) using the Affymetrix SNP6.0 platform and analysed by CNAG, dCHIP and Partek. The most frequent CNAs were confirmed by MLPA (P-383-T-ALL). In addition the DNA was screened for mutations in NOTCH1/FBXW7/PTEN using conventional Sanger sequencing and for mutations in NRAS, KRAS, CBL, FLT3 and SHP2 using denaturing high performance liquid chromatography. In cases without CDKN2A gene deletion we initially performed CDKN2A gene promoter methylation by SABiosciences EpiTect Methyl qPCR Arrays, followed up by Methylation Specific PCR (MSP). Where available, RNA was extracted from viable cells and the quality confirmed by Bioanalyser. Next the RNA was reverse transcribed to cDNA and subjected to real-time PCR gene expression analysis for CDKN2A and T-ALL related oncogenes. Results:The most frequent CNA was deletion of CDKN2A in 72.7% of patient samples (91.6% homozygous deletions). Other frequent CNAs were loss of MLLT3 (31%), STIL (27%), PTEN (19%), LEF1 (15%) and gain of MYB (12%). These CNAs were confirmed by MLPA. The STIL-TAL fusion occurred in 27% of patients. The only recurrent region of Copy Number Neutral LOH encompassed 9p24.3-p13.3, including the gene CDKN2A (27%). NOTCH1, FBXW7 and PTEN mutations occurred at expected frequencies. Rare mutations were identified in NRAS and CBL, and these mutations represented known variants. Bisulphite modified DNA was subjected to CDKN2A gene promoter methylation analysis. All samples examined were negative by Epitect Methyl Array, including the positive control cell line Raji. Promoter methylation was positive by MSP for the Raji cell line and some TYA T-ALL cases without CDKN2A gene deletion. Conclusions:This data identifies the frequency of recurrent mutations in T-ALL of Teenagers and Young Adults but reveals no striking differences with those observed in T-ALL in younger children. We are in the process of analysing additional cases to complete a total of 75 patients, including whole exome sequencing of a subset of cases. This sample size will allow us to detect genomic aberrations with a 5% incidence within this cohort (>90% probability) and to determine any prognostic significance. The most frequently observed aberration is CDKN2A gene deletion. In some cases without CDKN2A deletion we identified CDKN2A gene promoter methylation, offering an alternative mechanism of CDKN2A inactivation. To be able to appreciate potential cooperation between genetic abnormalities, we are correlating aberrant expression of the oncogenes TAL1, LYL1, LMO1, LMO2, TLX1, TLX3, NKX2, ERG and MEF2C with the genomic abnormalities identified. Disclosures:Gribben:Celgene: Honoraria; Roche: Honoraria; Merck: Honoraria; Mundipharma: Honoraria; Pharmacyclics: Honoraria.

CTCF Mediated Enhancer and Promoter Interaction Regulates Differential Expression of TAL1 Oncogene in Normal and Malignant Hematopoiesis

AbstractAbstract 281The key hematopoietic transcription factor TAL1/SCL is essential for the specification of hematopoietic stem cells (HSCs) and differentiation along myeloid and erythroid lineages. However, ectopic activation of TAL1 gene is the most frequent gain-of-function mutation associated with childhood T-cell acute lymphoblastic leukemia (T-ALL) in approximately 60% of patients. To understand underlying epigenetic mechanisms of TAL1 activation in normal and in malignant hematopoiesis, we performed ChIP, ChIP-seq, and chromatin conformation capture assays to investigate chromatin structure profile which correlates with transcriptional activation, at the TAL1 locus comparing erythroid progenitors, K562 and CD36+ cells, with T-ALL cells, Jurkat and Rex cells. We found distinct epigenetic landscape and chromatin organization across the TAL1 locus in these two different types of hematopoietic cells. Although H3K4me3 is enriched at the TAL1 promoter in both erythroid progenitors and in T-ALL cells, the erythroid specific +51 enhancer is marked by active histone modifications only in erythroid progenitors, but not in T-ALL cells. Furthermore, we demonstrated that +51 enhancer interacts with the TAL1 promoter 1a via a long range chromatin loop in vivo in erythroid CD36+ and K562 cells. The recruitment of hSET1 HMT complex facilitates this enhancer/promoter chromatin interaction and depletion of hSET1 leads to loss of H3K4 methylation, enhancer/promoter interaction, RNA PolII loading, and TAL1 transcription at both the TAL1 promoter 1a and the +51 enhancer. In addition, loss of SET1 in CD34+ HSCs exhibited a significant reduction in the formation of CFU-E and BFU-E colonies. In contrast, neither H3K4 methylation nor enhancer/promoter interaction was detected at the +51 enhancer in T-ALL cells. Finally, we investigated the role of insulator protein CTCF in the regulation of TAL1 expression in normal and in malignant cells. We found that regardless of similar CTCF binding patterns at the TAL1 locus in erythroid progenitors and T-ALL cells, CTCF elements flanking the TAL1 locus mediate a long-range loop that encloses TAL1 promoter and enhancer in the same chromatin domain in erythroid progenitors, whereas in T-ALL Jurkat cells the CTCF site located between the promoter 1a and the +51 enhancer forms a repressive loop that expels the +51 enhancer from the same domain with the promoter 1a. Overall, our study demonstrates that a novel long range intrachromosomal interaction between the TAL1 promoter 1a and the +51 enhancer regulated and organized by hSET1 histone methyltransferase and insulator protein CTCF controls TAL1 promoter activity in normal versus malignant hematopoiesis. Disclosures:No relevant conflicts of interest to declare.