[Show abstract][Hide abstract] ABSTRACT: Small molecule inhibition of the BET family of proteins, which bind acetylated lysines within histones, has been shown to have a marked therapeutic benefit in pre-clinical models of MLL-fusion protein driven leukemias. Here, we report that I-BET151, a highly specific BET family bromodomain inhibitor, leads to growth inhibition in a human erythroleukemic (HEL) cell line as well as in erythroid precursors isolated from polycythemia vera patients. One of the genes most highly down regulated by I-BET151 was LMO2, an important oncogenic regulator of hematopoietic stem cell development and erythropoiesis. We previously reported that LMO2 transcription is dependent upon JAK2 kinase activity in HEL cells. Here, we show that the transcriptional changes induced by a JAK2 inhibitor (TG101209) and I-BET151 in HEL cells are significantly over-lapping, suggesting a common pathway of action. We generated JAK2 inhibitor resistant HEL cells and showed that these retain sensitivity to I-BET151. These data highlight I-BET151 as a potential alternative treatment against myeloproliferative neoplasms driven by constitutively active JAK2 kinase.Leukemia accepted article preview online, 9 August 2013. doi:10.1038/leu.2013.234.
Full-text · Article · Aug 2013 · Leukemia: official journal of the Leukemia Society of America, Leukemia Research Fund, U.K
[Show abstract][Hide abstract] ABSTRACT: The JAK2 tyrosine kinase is a critical mediator of cytokine-induced signaling. It plays a role in the nucleus, where it regulates transcription by phosphorylating histone H3 at tyrosine 41 (H3Y41ph). We used chromatin immunoprecipitation coupled to massively parallel DNA sequencing (ChIP-seq) to define the genome-wide pattern of H3Y41ph in human erythroid leukemia cells. Our results indicate that H3Y41ph is located at three distinct sites: (1) at a subset of active promoters, where it overlaps with H3K4me3, (2) at distal cis-regulatory elements, where it coincides with the binding of STAT5, and (3) throughout the transcribed regions of active, tissue-specific hematopoietic genes. Together, these data extend our understanding of this conserved and essential signaling pathway and provide insight into the mechanisms by which extracellular stimuli may lead to the coordinated regulation of transcription.
[Show abstract][Hide abstract] ABSTRACT: The SCL/Tal-1 gene encodes a basic helix-loop-helix transcription factor with key roles in hematopoietic and neural development. SCL is
expressed in, and required for, both primitive and definitive erythropoiesis. Thus far, we have identified only one erythroid
SCL enhancer. Located 40 kb downstream of exon 1a, the +40 enhancer displays activity in primitive erythroblasts. We demonstrate
here that a 3.7-kb fragment containing this element also targets expression to the midbrain, a known site of endogenous SCL
expression. Although the 3.7-kb construct was active in primitive, but not definitive, erythroblasts, a larger 5.0-kb fragment,
encompassing the 3.7-kb region, was active in both fetal and adult definitive hematopoietic cells. This included Ter119+ erythroid cells along with fetal liver erythroid and myeloid progenitors. Unlike two other SCL hematopoietic enhancers (+18/19 and −4), +40 enhancer transgenes were inactive in the endothelium. A conserved 400-bp core
region, essential for both hematopoietic and midbrain +40 enhancer activity in embryos, relied on two GATA/E-box motifs and
was bound in vivo by GATA-1 and SCL in erythroid cells. These results suggest a model in which the SCL +18/19 and/or −4 enhancers initiate SCL expression in early mesodermal derivatives capable of generating blood and endothelium, with subsequent activation of the
+40 enhancer via an autoregulatory loop.
Full-text · Article · Nov 2007 · Molecular and Cellular Biology
[Show abstract][Hide abstract] ABSTRACT: Traditionally, polycythaemia has been used to identify a group of varied disorders with an increase in circulating red cells that are typified by a persistently raised haematocrit (Hct). Since only the red cell lineage is involved, the term erythrocytosis has more validity and will be used throughout this article. Polycythaemia will be retained in relation to the clonal disorder, polycythaemia vera (PV), in which three cell lineages are involved.
Full-text · Article · Aug 2005 · British Journal of Haematology
[Show abstract][Hide abstract] ABSTRACT: The stem cell leukemia (SCL) gene, also known as TAL-1, encodes a basic helix-loop-helix protein that is essential for the formation of all hematopoietic lineages, including primitive
erythropoiesis. Appropriate transcriptional regulation is essential for the biological functions of SCL, and we have previously
identified five distinct enhancers which target different subdomains of the normal SCL expression pattern. However, it is not known whether these SCL enhancers also regulate neighboring genes within the SCL locus, and the erythroid expression of SCL remains unexplained. Here, we have quantitated transcripts from SCL and neighboring genes in multiple hematopoietic cell types. Our results show striking coexpression of SCL and its immediate downstream neighbor, MAP17, suggesting that they share regulatory elements. A systematic survey of histone H3 and H4 acetylation throughout the SCL locus in different hematopoietic cell types identified several peaks of histone acetylation between SIL and MAP17, all of which corresponded to previously characterized SCL enhancers or to the MAP17 promoter. Downstream of MAP17 (and 40 kb downstream of SCL exon 1a), an additional peak of acetylation was identified in hematopoietic cells and was found to correlate with expression
of SCL but not other neighboring genes. This +40 region is conserved in human-dog-mouse-rat sequence comparisons, functions as an
erythroid cell-restricted enhancer in vitro, and directs β-galactosidase expression to primitive, but not definitive, erythroblasts
in transgenic mice. The SCL +40 enhancer provides a powerful tool for studying the molecular and cellular biology of the primitive erythroid lineage.
[Show abstract][Hide abstract] ABSTRACT: Polycythaemia vera (PV) is a myeloproliferative disorder (MPD) thought to result from transformation of a haemopoietic stem cell. Transforming growth factor beta1 (TGF-beta1) is a negative regulator of haemopoietic stem cells, an effect mediated by direct binding to TGF-beta receptor II (TGF-beta RII). Reduced levels of TGF-beta RII mRNA or protein have been reported in several MPDs including PV, suggesting a role for TGF-beta RII in PV. No mutational analysis of the TGF-beta RII gene has yet been performed in PV. To investigate whether genetic or epigenetic alteration of the TGF-beta RII gene contributes to the pathogenesis of PV, we performed mutation and methylation analysis in 15 PV patients. The promoter, all seven exons and all intron/exon junctions were studied using single-strand conformation polymorphism (SSCP) and heteroduplex analysis (HA). In total, three single nucleotide polymorphisms (SNPs) were identified. These were located in the promoter, intron 2 and exon 5. No acquired mutations were detected in any patient sample. We also present a novel method, termed methylation-specific strand extension (MSSE), for the detection of methylated CpG dinucleotides. The combination of bisulphite modification and MSSE permits rapid analysis of the methylation status of CpG dinucleotides in multiple samples. We analysed the methylation status of the promoter and of a CpG island within exon 1 in 15 PV patients. No aberrant methylation was detected in either of these regions. These data demonstrate that neither mutation nor abnormal methylation of the TGF-beta RII gene is associated with the pathogenesis of PV. Furthermore, MSSE is a rapid and robust approach for assessing the methylation status of a given genomic region.
No preview · Article · Jan 2002 · British Journal of Haematology
[Show abstract][Hide abstract] ABSTRACT: The stem cell leukaemia gene (Scl) encodes a basic helix-loop-helix transcription factor with a pivotal role in both haematopoiesis and endothelial development. During mouse development, Scl is first expressed in extra-embryonic mesoderm, and is required for the generation of all haematopoietic lineages and normal yolk sac angiogenesis. Ectopic expression of Scl during zebrafish development specifies haemangioblast formation from early mesoderm. These results suggest that SCL is essential for establishing the transcriptional programme responsible for the formation of haematopoietic stem cells and have focused attention on the transcriptional regulation of Scl itself. Previous studies have identified a panel of Scl enhancers each of which directed expression to a subdomain of the normal Scl expression pattern. Among them, a 3' enhancer directed expression during development to vascular endothelium and haematopoietic progenitors but not to Ter119(+) erythroid cells. The expression in haematopoietic stem cells, however, remained undetermined. We demonstrate that this 3' enhancer directs lacZ expression in transgenic mice to most foetal and adult long-term repopulating haematopoietic stem cells, and therefore functions as a stem cell enhancer. Consistent with these results, expression in Scl(-/-) embryos of exogenous Scl driven by the stem cell enhancer rescued the formation of early haematopoietic progenitors and also resulted in normal yolk sac angiogenesis. By contrast, erythropoiesis remained markedly deficient in rescued embryos. This observation is consistent with the inactivity of the stem cell enhancer in erythroid cells and reveals an essential role for SCL during erythroid differentiation in vivo.
[Show abstract][Hide abstract] ABSTRACT: Chronic myeloid leukemia (CML) is characterized by formation of the BCR-ABL fusion gene, usually as a consequence of the Philadelphia (Ph) translocation between chromosomes 9 and 22. Large deletions on the derivative chromosome 9 have recently been reported, but it was unclear whether deletions arose during disease progression or at the time of the Ph translocation. Fluorescence in situ hybridization (FISH) analysis was used to assess the deletion status of 253 patients with CML. The strength of deletion status as a prognostic indicator was then compared to the Sokal and Hasford scoring systems. The frequency of deletions was similar at diagnosis and after disease progression but was significantly increased in patients with variant Ph translocations. In patients with a deletion, all Ph(+) metaphases carried the deletion. The median survival of patients with and without deletions was 38 months and 88 months, respectively (P =.0001). By contrast the survival difference between Sokal or Hasford high-risk and non-high-risk patients was of only borderline significance (P =.057 and P =.034). The results indicate that deletions occur at the time of the Ph translocation. An apparently simple reciprocal translocation may therefore result in considerable genetic heterogeneity ab initio, a concept that is likely to apply to other malignancies associated with translocations. Deletion status is also a powerful and independent prognostic factor for patients with CML. The prognostic significance of deletion status should now be studied prospectively and, if confirmed, should be incorporated into management decisions and the analysis of clinical trials.
[Show abstract][Hide abstract] ABSTRACT: The stem cell leukemia (SCL) gene encodes a tissue-specific basic helix-loop-helix (bHLH) protein with a pivotal role in hemopoiesis and vasculogenesis. Several enhancers have been identified within the murine SCL locus that direct reporter gene expression to subdomains of the normal SCL expression pattern, and long-range sequence comparisons of the human and murine SCL loci have identified additional candidate enhancers. To facilitate the characterization of regulatory elements, we have sequenced and analyzed 33 kb of the SCL genomic locus from the pufferfish Fugu rubripes, a species with a highly compact genome. Although the pattern of SCL expression is highly conserved from mammals to teleost fish, the genes flanking pufferfish SCL were unrelated to those known to flank both avian and mammalian SCL genes. These data suggest that SCL regulatory elements are confined to the region between the upstream and downstream flanking genes, a region of 65 kb in human and 8.5 kb in pufferfish. Consistent with this hypothesis, the entire 33-kb pufferfish SCL locus directed appropriate expression to hemopoietic and neural tissue in transgenic zebrafish embryos, as did a 10.4-kb fragment containing the SCL gene and extending to the 5' and 3' flanking genes. These results demonstrate the power of combining the compact genome of the pufferfish with the advantages that zebrafish provide for studies of gene regulation during development. Furthermore, the pufferfish SCL locus provides a powerful tool for the manipulation of hemopoiesis and vasculogenesis in vivo.
Full-text · Article · Jul 2001 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: A range of fluorescent in situ hybridization techniques have been used to reveal hidden variant Philadelphia translocations in two cases of Ph-positive chronic-phase chronic myeloid leukaemia. In one patient, a highly complex variant Ph translocation affecting four chromosomes had resulted in the formation of structures with the appearance of i(17q) and +8. Misinterpretation of these karyotypes has direct clinical relevance. Our findings illustrate that even established cytogenetic abnormalities may contain cryptic abnormalities beyond the resolution of conventional cytogenetic methods.
No preview · Article · Jun 2001 · British Journal of Haematology
[Show abstract][Hide abstract] ABSTRACT: Leukemia is one of the leading journals in hematology and oncology. It is published monthly and covers all aspects of the research and treatment of leukemia and allied diseases. Studies of normal hemopoiesis are covered because of their comparative relevance.
[Show abstract][Hide abstract] ABSTRACT: Long-range comparative sequence analysis provides a powerful strategy for identifying conserved regulatory elements. The stem cell leukemia (SCL) gene encodes a bHLH transcription factor with a pivotal role in hemopoiesis and vasculogenesis, and it displays a highly conserved expression pattern. We present here a detailed sequence comparison of 193 kb of the human SCL locus to 234 kb of the mouse SCL locus. Four new genes have been identified together with an ancient mitochondrial insertion in the human locus. The SCL gene is flanked upstream by the SIL gene and downstream by the MAP17 gene in both species, but the gene order is not collinear downstream from MAP17. To facilitate rapid identification of candidate regulatory elements, we have developed a new sequence analysis tool (SynPlot) that automates the graphical display of large-scale sequence alignments. Unlike existing programs, SynPlot can display the locus features of more than one sequence, thereby indicating the position of homology peaks relative to the structure of all sequences in the alignment. In addition, high-resolution analysis of the chromatin structure of the mouse SCL gene permitted the accurate positioning of localized zones accessible to restriction endonucleases. Zones known to be associated with functional regulatory regions were found to correspond precisely with peaks of human/mouse homology, thus demonstrating that long-range human/mouse sequence comparisons allow accurate prediction of the extent of accessible DNA associated with active regulatory regions.
[Show abstract][Hide abstract] ABSTRACT: We have used interphase fluorescence in situ hybridization (IFISH) to detect trisomy 8, trisomy 9 and 20q deletion in circulating granulocytes from patients with polycythaemia vera (PV). Out of 64 PV patients, 15 (23%) exhibited an abnormality. Two patients had trisomy 9, three had trisomy 8 and 10 patients had hemizygous deletion of D20S108 (a locus in the 20q common deleted region). Aberrant nuclei ranged from 10% to 80% in these 15 cases. There was no correlation between the presence of a marker and sex, age, interval between presentation and IFISH analysis, neutrophil or platelet count or therapy. Conventional marrow cytogenetic karyotype results were available in 23 cases and there was concurrence between these and blood IFISH in 16 cases (13 normal and three with 20q/D20S108 deletion by both methods). Three patients with D20S108 deletion by IFISH were normal by previous marrow cytogenetic testing and four cases with 20q deletion by previous marrow cytogenetics had normal blood granulocytes according to IFISH. Thus, we confirm that trisomies 8 and 9 and deletion of 20q are diagnostically useful markers of PV. IFISH analysis of blood granulocytes is a practical method for detecting these markers, but as an adjunct to, not as a substitute for, conventional marrow cytogenetics.
Full-text · Article · Oct 2000 · British Journal of Haematology
[Show abstract][Hide abstract] ABSTRACT: Deletion of the long arm of chromosome 20 represents the most common chromosomal abnormality associated with the myeloproliferative disorders (MPDs) and is also found in other myeloid malignancies including myelodysplastic syndromes (MDS) and acute myeloid leukaemia (AML). Previous studies have identified a common deleted region (CDR) spanning approximately 8 Mb. We have now used G-banding, FISH or microsatellite PCR to analyse 113 patients with a 20q deletion associated with a myeloid malignancy. Our results define a new MPD CDR of 2.7 Mb, an MDS/AML CDR of 2.6 Mb and a combined 'myeloid' CDR of 1.7 Mb. We have also constructed the most detailed physical map of this region to date--a bacterial clone map spanning 5 Mb of the chromosome which contains 456 bacterial clones and 202 DNA markers. Fifty-one expressed sequences were localized within this contig of which 37 lie within the MPD CDR and 20 within the MDS/AML CDR. Of the 16 expressed sequences (six genes and 10 unique ESTs) within the 'myeloid' CDR, five were expressed in both normal bone marrow and purified CD34 positive cells. These data identify a set of genes which are both positional and expression candidates for the target gene(s) on 20q.
[Show abstract][Hide abstract] ABSTRACT: The transformation of chronic myeloid leukemia (CML) from a chronic phase to an acute phase is frequently accompanied by additional chromosome changes. Extensive chromosome G-banded studies have revealed the secondary changes are nonrandom and frequently include trisomy 8, isochromosome 17q, trisomy 19, or an extra copy of the Philadelphia chromosome. In addition to these secondary chromosome changes, complex structural rearrangements often occur to form marker structures that remain unidentified by conventional G-banded analysis. The CML-derived cell line, K562, has been widely used in research since it was originally established in 1975. The K562 karyotype however, has remained incomplete, and marker structures have never been fully described. Recent advances in fluorescence in situ hybridization (FISH) technology have introduced the possibility of chromosome classification based on 24-color chromosome painting (M-FISH). In this study, we report a clarified karyotype for K562 obtained by a combination of the following molecular cytogenetic techniques: comparative genomic hybridization (CGH), FISH mapping using locus-specific probes, and M-FISH. Multicolor FISH has identified the marker structures in this cell line. The characteristic marker chromosome in K562 has been confirmed by this study to be a der(18)t(1;18). Multicolor FISH confirmed the identity of marker structures partially identified by G-banding as der(6)t(6;6),der(17)t(9;17),der(21)t(1;21),der(5)t(5;6). In addition M-FISH has revealed a deleted 20q and a complex small metacentric marker comprised of material from chromosomes 1, 6, and 20. A cryptic rearrangement was revealed between chromosomes 12 and 21 that produced a structure that looks like a normal chromosome 12 homologue by G-banding analysis. Finally, M-FISH detected regions from chromosome 13 intercalated into two acrocentric markers.
No preview · Article · May 2000 · Cancer Genetics and Cytogenetics