Frequent mutations in the GATA-1 gene in the transient myeloproliferative disorder of Down syndrome

Establishment of erythroleukemic GAK14 cells and characterization of GATA1 N-terminal domain

GATA1 is a transcription factor essential for erythropoiesis and megakaryopoiesis. It has been found that Gata1 gene knockdown heterozygous female (Gata1(G1.05/+)) mice spontaneously develop erythroblastic leukemias. In this study, we have generated a novel Gata1 knockdown erythroblastic cell line, designated GAK14, from the leukemia cells in the Gata1(G1.05/+) mice. Although GAK14 cells maintain immature phenotype on OP9 stromal cells in the presence of erythropoietin and stem cell factor, the cells produce Gr-1-, Mac1-, B220-, CD3e- or CD49b-positive hematopoietic cells when co-cultured with DAS104-8 feeder cells. However, GAK14 cells did not produce erythroid and megakaryocytic lineages, perhaps due to the absence of GATA1. Indeed, GAK14 cells became capable of differentiating into mature erythroid cells when complemented with full-length GATA1 and co-cultured with fetal liver-derived FLS5 stromal cells. This differentiation potential was impaired when GATA1 lacking the N-terminal domain was complemented. The N-terminal domain is known to contribute to the pathogenesis of transient abnormal myelopoiesis and acute megakaryoblastic leukemia related to Down syndrome. These results thus showed that GAK14 cells will serve as a powerful tool for dissecting domain function of GATA1 and that the GATA1 N-terminal domain is essential for the erythroid differentiation of GAK14 cells.

Clonal selection in xenografted TAM recapitulates the evolutionary process of myeloid leukemia in Down syndrome

Transient abnormal myelopoiesis (TAM) is a clonal preleukemic disorder that progresses to myeloid leukemia of Down syndrome (ML-DS) through the accumulation of genetic alterations. To investigate the mechanism of leukemogenesis in this disorder, a xenograft model of TAM was established using NOD/Shi-scid, interleukin (IL)-2Rγ(null) mice. Serial engraftment after transplantation of cells from a TAM patient who developed ML-DS a year later demonstrated their self-renewal capacity. A GATA1 mutation and no copy number alterations (CNAs) were detected in the primary patient sample by conventional genomic sequencing and CNA profiling. However, in serial transplantations, engrafted TAM-derived cells showed the emergence of divergent subclones with another GATA1 mutation and various CNAs, including a 16q deletion and 1q gain, which are clinically associated with ML-DS. Detailed genomic analysis identified minor subclones with a 16q deletion or this distinct GATA1 mutation in the primary patient sample. These results suggest that genetically heterogeneous subclones with varying leukemia-initiating potential already exist in the neonatal TAM phase, and ML-DS may develop from a pool of such minor clones through clonal selection. Our xenograft model of TAM may provide unique insight into the evolutionary process of leukemia.

Naturally occurring oncogenic GATA1 mutants with internal deletions in transient abnormal myelopoiesis in Down syndrome

Children with Down syndrome have an increased incidence of transient abnormal myelopoiesis (TAM) and acute megakaryoblastic leukemia. The majority of these cases harbor somatic mutations in the GATA1 gene, which results in the loss of full-length GATA1. Only a truncated isoform of GATA1 that lacks the N-terminal 83 amino acids (GATA1-S) remains. We found through genetic studies of 106 patients with TAM that internally deleted GATA1 proteins (GATA1-IDs) lacking amino acid residues 77-119 or 74-88 (created by splicing mutations) contributed to the genesis of TAM in 6 patients. Analyses of GATA1-deficient embryonic megakaryocytic progenitors revealed that the GATA1 function in growth restriction was disrupted in GATA1-IDs. In contrast, GATA1-S promoted megakaryocyte proliferation more profoundly than that induced by GATA1 deficiency. These results indicate that the internally deleted regions play important roles in megakaryocyte proliferation and that perturbation of this mechanism is involved in the pathogenesis of TAM.

Biology and management of transient abnormal myelopoiesis (TAM) in children with Down syndrome

Children with Down syndrome (DS) have an increased risk of Acute Myeloid Leukaemia (ML-DS), particularly megakaryoblastic leukaemia, which is clonally -related to the neonatal myeloproliferative syndrome, Transient Abnormal Myelopoiesis (TAM) unique to infants with DS. Molecular, biological, and clinical data indicate that TAM is initiated before birth when fetal liver haematopoietic cells trisomic for chromosome 21 acquire mutations in GATA1. TAM usually resolves spontaneously by 6 months; however 20-30% subsequently develop ML-DS harbouring the same GATA1 mutation(s). This review focuses on recent studies describing haematological, clinical and biological features of TAM and discusses approaches to diagnose, treat and monitor minimal residual disease in TAM. An important unanswered question is whether ML-DS is always preceded by TAM as it may be clinically and possibly haematologically 'silent'. We have briefly discussed the role of population-based screening for TAM and development of treatment strategies to eliminate the preleukaemic TAM clone, thereby preventing ML-DS.

The use of mouse models for understanding the biology of down syndrome and aging

Down syndrome is a complex condition caused by trisomy of human chromosome 21. The biology of aging may be different in individuals with Down syndrome; this is not well understood in any organism. Because of its complexity, many aspects of Down syndrome must be studied either in humans or in animal models. Studies in humans are essential but are limited for ethical and practical reasons. Fortunately, genetically altered mice can serve as extremely useful models of Down syndrome, and progress in their production and analysis has been remarkable. Here, we describe various mouse models that have been used to study Down syndrome. We focus on segmental trisomies of mouse chromosome regions syntenic to human chromosome 21, mice in which individual genes have been introduced, or mice in which genes have been silenced by targeted mutagenesis. We selected a limited number of genes for which considerable evidence links them to aspects of Down syndrome, and about which much is known regarding their function. We focused on genes important for brain and cognitive function, and for the altered cancer spectrum seen in individuals with Down syndrome. We conclude with observations on the usefulness of mouse models and speculation on future directions.

Simultaneous appearance of leukemoid reaction and phlegmasia cerulea dolens

A leukemoid reaction is an extreme form of reactive leukocytosis defined as granulocytic leukocytosis above 50 × 10(9)/L produced by normal bone marrow, mostly in response to systemic infection or cancer. The mechanism as to how the haematopoetic system is altered to elevate production of myeloid cells is not known. A 69-year-old man presented with phlegmasia cerulea dolens caused by massive iliofemoral thrombosis. His workout at admission revealed absolute white blood cell count of 73.4 × 10(9)/L, with neutrophil granulocyte of 68.5 × 10(9)/L. The new increase in white blood cell count happened at day 5 after admission, when the haematoma of the anteromedial thigh was evacuated in general anaesthesia. There was a gradual decrease in counts until they reached the normal range. Deteriorated general condition with signs of systemic inflammatory response syndrome improved with supportive therapy, and the patient was discharged from hospital after 30 days. During hospitalization we did not identify any infectious focus, or any malignancy. We could not exclude other occult chronic conditions (malignancy) but the patient did not develop any other condition during 4.5 years of follow-up.

A subpopulation of endothelial progenitor cells with low aldehyde dehydrogenase activity attenuates acute ischemic brain injury in rats

Previous studies have examined the therapeutic effect of endothelial progenitor cells (EPCs) during the chronic phase of cerebral infarction in rats; however, few studies have investigated the effects of EPCs during the acute phase of infarction. In this study, we evaluated the therapeutic effect of EPCs with low aldehyde dehydrogenase activity (Alde-Low EPCs) in rats with acute cerebral infarction, and our results provide insight that may help to identify a therapeutic mechanism of EPCs for acute cerebral infarction. The administration of Alde-Low EPCs into rats with acute cerebral infarction results in the accumulation and migration of the Alde-Low EPCs into the infarct area and the subsequent decrease of infarct volume. Moreover, we found that the stromal cell-derived factor-1 (SDF-1) and CXC chemokine receptor 4 (CXCR4) signaling pathway may regulate the accumulation of Alde-Low EPCs. The transplantation of Alde-Low EPCs may represent a potential treatment strategy for acute cerebral infarction.

Defective nuclear localization of Hsp70 is associated with dyserythropoiesis and GATA-1 cleavage in myelodysplastic syndromes

Normal human erythroid cell maturation requests the transcription factor GATA-1 and a transient activation of caspase-3, with GATA-1 being protected from caspase-3-mediated cleavage by interaction with the chaperone heat shock protein 70 (Hsp70) in the nucleus. Erythroid cell dysplasia observed in early myelodysplastic syndromes (MDS) involves impairment of differentiation and excess of apoptosis with a burst of caspase activation. Analysis of gene expression in MDS erythroblasts obtained by ex vivo cultures demonstrates the down-regulation of a set of GATA-1 transcriptional target genes, including GYPA that encodes glycophorin A (GPA), and the up-regulation of members of the HSP70 family. GATA-1 protein expression is decreased in MDS erythroblasts, but restores in the presence of a pan-caspase inhibitor. Expression of a mutated GATA-1 that cannot be cleaved by caspase-3 rescues the transcription of GATA-1 targets, and the erythroid differentiation, but does not improve survival. Hsp70 fails to protect GATA-1 from caspases because the protein does not accumulate in the nucleus with active caspase-3. Expression of a nucleus-targeted mutant of Hsp70 protects GATA-1 and rescues MDS erythroid cell differentiation. Alteration of Hsp70 cytosolic-nuclear shuttling is a major feature of MDS that favors GATA-1 cleavage and differentiation impairment, but not apoptosis, in dysplastic erythroblasts.

GATA Transcription Factors and Cancer

It has been almost a quarter century since it was first appreciated that a class of oncogenes contained in rapidly transforming avian retroviruses encoded DNA-binding transcription factors. As with other oncogenes, genetic recombination with the viral genome led to their overexpression or functional alteration. In the years that followed, alterations of numerous transcription factors were shown to be causatively involved in various cancers in human patients and model organisms. Depending on their normal cellular functions, these factors were subsequently categorized as proto-oncogenes or tumor suppressor genes. This review focuses on the role of GATA transcription factors in carcinogenesis. GATA factors are zinc finger DNA binding proteins that control the development of diverse tissues by activating or repressing transcription. GATA factors thus coordinate cellular maturation with proliferation arrest and cell survival. Therefore, a role of this family of genes in human cancers is not surprising. Prominent examples include structural mutations in GATA1 that are found in almost all megakaryoblastic leukemias in patients with Down syndrome; loss of GATA3 expression in aggressive, dedifferentiated breast cancers; and silencing of GATA4 and GATA5 expression in colorectal and lung cancers. Here, we discuss possible mechanisms of carcinogenesis vis-à-vis the normal functions of GATA factors as they pertain to human patients and mouse models of cancer.

Analysis of GATA1 mutations in Down syndrome transient myeloproliferative disorder and myeloid leukemia

Children with Down syndrome (DS) up to the age of 4 years are at a 150-fold excess risk of developing myeloid leukemia (ML-DS). Approximately 4%-5% of newborns with DS develop transient myeloproliferative disorder (TMD). Blast cell structure and immunophenotype are similar in TMD and ML-DS. A mutation in the hematopoietic transcription factor GATA1 is present in almost all cases. Here, we show that simple techniques detect GATA1 mutations in the largest series of TMD (n = 134; 88%) and ML-DS (n = 103; 85%) cases tested. Furthermore, no significant difference in the mutational spectrum between the 2 disorders was seen. Thus, the type of GATA1 sequence mutation is not a reliable tool and is not prognostic of which patients with TMD are probable to develop ML-DS.

Promotion and maintenance of leukemia by ERG

The Ets-related gene (ERG) located on human chromosome 21 encodes a transcription factor and is thought to be causally related to Down syndrome-associated acute megakaryocytic leukemia in childhood. In clinical adult leukemia, however, increased expression of ERG is indicative of poor prognosis in T-cell acute lymphoblastic leukemia and cytogenetically normal acute myeloid leukemia, although the involvement of ERG in the development of adult leukemia remains elusive. Here, we show that forced expression of ERG in adult BM cells alters differentiation and induces expansion of T and erythroid cells and increases frequencies of myeloid progenitors in mouse BM transplantation models. The expanded T cells then develop T-cell acute lymphoblastic leukemia after acquisition of mutations in the Notch1 gene. Targeted expression of ERG into B cells also altered differentiation and promoted growth of precursor B cells. Overall, these findings suggest a general role of ERG in promoting growth of adult hematopoietic cells in various lineages. In line with this, shRNA-mediated silencing of ERG expression attenuated growth of human leukemia cell lines of various lineages. Thus, ERG is capable of promoting the development of leukemia and is crucial for its maintenance.

Heritability of hematologic malignancies: from pedigrees to genomics

Many hematologic malignancies have an underlying heritable component. Although not as well characterized as the acquired genetic abnormalities that define important prognostic and therapeutic subgroups of myeloid and lymphoid neoplasms, investigations are beginning to unravel the role of germline genetic variation in the predisposition to hematologic malignancies. Information gained from the study of striking family pedigrees, epidemiologic data, and candidate genes are now being combined with unbiased genome-wide investigations to outline the network of genetic abnormalities that contribute to hematologic malignancy risk. This article reviews the current understanding of the heritability of hematologic malignancies in the genomics era.

Down syndrome and GATA1 mutations in transient abnormal myeloproliferative disorder: mutation classes correlate with progression to myeloid leukemia

Twenty percent to 30% of transient abnormal myelopoiesis (TAM) observed in newborns with Down syndrome (DS) develop myeloid leukemia of DS (ML-DS). Most cases of TAM carry somatic GATA1 mutations resulting in the exclusive expression of a truncated protein (GATA1s). However, there are no reports on the expression levels of GATA1s in TAM blasts, and the risk factors for the progression to ML-DS are unidentified. To test whether the spectrum of transcripts derived from the mutant GATA1 genes affects the expression levels, we classified the mutations according to the types of transcripts, and investigated the modalities of expression by in vitro transfection experiments using GATA1 expression constructs harboring mutations. We show here that the mutations affected the amount of mutant protein. Based on our estimates of GATA1s protein expression, the mutations were classified into GATA1s high and low groups. Phenotypic analyses of 66 TAM patients with GATA1 mutations revealed that GATA1s low mutations were significantly associated with a risk of progression to ML-DS (P < .001) and lower white blood cell counts (P = .004). Our study indicates that quantitative differences in mutant protein levels have significant effects on the phenotype of TAM and warrants further investigation in a prospective study.

Developmental stage-specific interplay of GATA1 and IGF signaling in fetal megakaryopoiesis and leukemogenesis

Oncogene-mediated transformation of hematopoietic cells has been studied extensively, but little is known about the molecular basis for restriction of oncogenes to certain target cells and differential cellular context-specific requirements for oncogenic transformation between infant and adult leukemias. Understanding cell type-specific interplay of signaling pathways and oncogenes is essential for developing targeted cancer therapies. Here, we address the vexing issue of how developmental restriction is achieved in Down syndrome acute megakaryoblastic leukemia (DS-AMKL), characterized by the triad of fetal origin, mutated GATA1 (GATA1s), and trisomy 21. We demonstrate overactivity of insulin-like growth factor (IGF) signaling in authentic human DS-AMKL and in a DS-AMKL mouse model generated through retroviral insertional mutagenesis. Fetal but not adult megakaryocytic progenitors are dependent on this pathway. GATA1 restricts IGF-mediated activation of the E2F transcription network to coordinate proliferation and differentiation. Failure of a direct GATA1-E2F interaction in mutated GATA1s converges with overactive IGF signaling to promote cellular transformation of DS fetal progenitors, revealing a complex, fetal stage-specific regulatory network. Our study underscores context-dependent requirements during oncogenesis, and explains resistance to transformation of ostensibly similar adult progenitors.

Acute leukemias in children with Down syndrome

Children with Down syndrome have an increased risk for developing both acute myeloid as well as lymphoblastic leukemia. These leukemias differ in presenting characteristics and underlying biology when compared with leukemias occurring in non-Down syndrome children. Myeloid leukemia in children with Down syndrome is preceded by a preleukemic clone (transient leukemia or transient myeloproliferative disorder), which may disappear spontaneously, but may also need treatment in case of severe symptoms. Twenty percent of children with transient leukemia subsequently develop myeloid leukemia. This transition offers a unique model to study the stepwise development of leukemia and of gene dosage effects mediated by aneuploidy.

GATA-1 directly regulates p21 gene expression during erythroid differentiation

Lineage-determination transcription factors coordinate cell differentiation and proliferation by controlling the synthesis of lineage-specific gene products as well as cell cycle regulators. GATA-1 is a master regulator of erythropoiesis. Its role in regulating erythroid-specific genes has been extensively studied, whereas its role in controlling genes that regulate cell proliferation is less understood. Ectopic expression of GATA-1 in erythroleukemia cells releases the block to their differentiation and leads to terminal cell division. An early event in reprogramming the erythroleukemia cells is induction of the cyclin-dependent kinase inhibitor p21. Remarkably, ectopic expression of p21 also induces the erythroleukemia cells to differentiate. We now report that GATA-1 directly regulates transcription of the p21 gene in both erythroleukemia cells and normal erythroid progenitors. Using reporter, electrophoretic mobility shift, and chromatin immunoprecipitation assays, we show that GATA-1 stimulates p21 gene transcription by binding to consensus binding sites in the upstream region of the p21 gene promoter. This activity is also dependent on a binding site for Sp1/KLF-like factors near the transcription start site. Our findings indicate that p21 is a crucial downstream gene target and effector of GATA-1 during red blood cell terminal differentiation.

Perturbed hematopoiesis in the Tc1 mouse model of Down syndrome

Trisomy of human chromosome 21 (Hsa21) results in Down syndrome (DS), a disorder that affects many aspects of physiology, including hematopoiesis. DS children have greatly increased rates of acute lymphoblastic leukemia and acute megakaryoblastic leukemia (AMKL); DS newborns present with transient myeloproliferative disorder (TMD), a preleukemic form of AMKL. TMD and DS-AMKL almost always carry an acquired mutation in GATA1 resulting in exclusive synthesis of a truncated protein (GATA1s), suggesting that both trisomy 21 and GATA1 mutations are required for leukemogenesis. To gain further understanding of how Hsa21 contributes to hematopoietic abnormalities, we examined the Tc1 mouse model of DS, which carries an almost complete freely segregating copy of Hsa21, and is the most complete model of DS available. We show that although Tc1 mice do not develop leukemia, they have macrocytic anemia and increased extramedullary hematopoiesis. Introduction of GATA1s into Tc1 mice resulted in a synergistic increase in megakaryopoiesis, but did not result in leukemia or a TMD-like phenotype, demonstrating that GATA1s and trisomy of approximately 80% of Hsa21 perturb megakaryopoiesis but are insufficient to induce leukemia.

Mutations in the ribosomal protein genes in Japanese patients with Diamond-Blackfan anemia

BACKGROUND

Diamond-Blackfan anemia is a rare, clinically heterogeneous, congenital red cell aplasia: 40% of patients have congenital abnormalities. Recent studies have shown that in western countries, the disease is associated with heterozygous mutations in the ribosomal protein (RP) genes in about 50% of patients. There have been no studies to determine the incidence of these mutations in Asian patients with Diamond-Blackfan anemia.

DESIGN AND METHODS

We screened 49 Japanese patients with Diamond-Blackfan anemia (45 probands) for mutations in the six known genes associated with Diamond-Blackfan anemia: RPS19, RPS24, RPS17, RPL5, RPL11, and RPL35A. RPS14 was also examined due to its implied involvement in 5q- syndrome.

RESULTS

Mutations in RPS19, RPL5, RPL11 and RPS17 were identified in five, four, two and one of the probands, respectively. In total, 12 (27%) of the Japanese Diamond-Blackfan anemia patients had mutations in ribosomal protein genes. No mutations were detected in RPS14, RPS24 or RPL35A. All patients with RPS19 and RPL5 mutations had physical abnormalities. Remarkably, cleft palate was seen in two patients with RPL5 mutations, and thumb anomalies were seen in six patients with an RPS19 or RPL5 mutation. In contrast, a small-for-date phenotype was seen in five patients without an RPL5 mutation.

CONCLUSIONS

We observed a slightly lower frequency of mutations in the ribosomal protein genes in patients with Diamond-Blackfan anemia compared to the frequency reported in western countries. Genotype-phenotype data suggest an association between anomalies and RPS19 mutations, and a negative association between small-for-date phenotype and RPL5 mutations.

Functional differences between myeloid leukemia-initiating and transient leukemia cells in Down's syndrome

Children with constitutional trisomy 21 or Down's syndrome (DS) are predisposed to develop myeloid leukemia (ML) at a young age. DS-ML is frequently preceded by transient leukemia (TL), a spontaneously resolving accumulation of blasts during the newborn period. Somatic mutations of GATA1 in the blasts of TL and DS-ML likely function as an initiating event. We hypothesized that the phenotypic difference between TL and DS-ML is due to a divergent functional repertoire of the leukemia-initiating cells. Using an NOD/SCID model, we found that cells initiating DS-ML engrafted, disseminated to distant bone marrow sites, and propagated the leukemic clone in secondary recipients. In contrast, TL cells lacked the ability to expand and to migrate, but were able to persist in the recipient bone marrow. We found some evidence of genomic progression with 1 of 9 DS-ML samples and none of 11 TL samples harboring a mutation of N-RAS. The findings of this pilot study provide evidence for the functional impact of second events underlying the transformation of TL into DS-ML and a needed experimental tool for the functional testing of these promoting events.

Loss of the Gata1 gene IE exon leads to variant transcript expression and the production of a GATA1 protein lacking the N-terminal domain

GATA1 is essential for the differentiation of erythroid cells and megakaryocytes. The Gata1 gene is composed of multiple untranslated first exons and five common coding exons. The erythroid first exon (IE exon) is important for Gata1 gene expression in hematopoietic lineages. Because previous IE exon knockdown analyses resulted in embryonic lethality, less is understood about the contribution of the IE exon to adult hematopoiesis. Here, we achieved specific deletion of the floxed IE exon in adulthood using an inducible Cre expression system. In this conditional knock-out mouse line, the Gata1 mRNA level was significantly down-regulated in the megakaryocyte lineage, resulting in thrombocytopenia with a marked proliferation of megakaryocytes. By contrast, in the erythroid lineage, Gata1 mRNA was expressed abundantly utilizing alternative first exons. Especially, the IEb/c and newly identified IEd exons were transcribed at a level comparable with that of the IE exon in control mice. Surprisingly, in the IE-null mouse, these transcripts failed to produce full-length GATA1 protein, but instead yielded GATA1 lacking the N-terminal domain inefficiently. With low level expression of the short form of GATA1, IE-null mice showed severe anemia with skewed erythroid maturation. Notably, the hematological phenotypes of adult IE-null mice substantially differ from those observed in mice harboring conditional ablation of the entire Gata1 gene. The present study demonstrates that the IE exon is instrumental to adult erythropoiesis by regulating the proper level of transcription and selecting the correct transcription start site of the Gata1 gene.

Mutational spectrum at GATA1 provides insights into mutagenesis and leukemogenesis in Down syndrome

Down syndrome (DS) children have a unique genetic susceptibility to develop leukemia, in particular, acute megakaryocytic leukemia (AMkL) associated with somatic GATA1 mutations. The study of this genetic susceptibility with the use of DS as a model of leukemogenesis has broad applicability to the understanding of leukemia in children overall. On the basis of the role of GATA1 mutations in DS AMkL, we analyzed the mutational spectrum of GATA1 mutations to begin elucidating possible mechanisms by which these sequence alterations arise. Mutational analysis revealed a predominance of small insertion/deletion, duplication, and base substitution mutations, including G:C>T:A, G:C>A:T, and A:T>G:C. This mutational spectrum points to potential oxidative stress and aberrant folate metabolism secondary to genes on chromosome 21 (eg, cystathionine-beta-synthase, superoxide dismutase) as potential causes of GATA1 mutations. Furthermore, DNA repair capacity evaluated in DS and non-DS patient samples provided evidence that the base excision repair pathway is compromised in DS tissues, suggesting that inability to repair DNA damage also may play a critical role in the unique susceptibility of DS children to develop leukemia. A model of leukemogenesis in DS is proposed in which mutagenesis is driven by cystathionine-beta-synthase overexpression and altered folate homeostasis that becomes fixed as the ability to repair DNA damage is compromised.

ERG is a megakaryocytic oncogene

Ets-related gene (ERG) is a member of the ETS transcription factor gene family located on Hsa21. ERG is known to have a crucial role in establishing definitive hematopoiesis and is required for normal megakaryopoiesis. Truncated forms of ERG are associated with multiple cancers such as Ewing's sarcoma, prostate cancer, and leukemia as part of oncogenic fusion translocations. Increased expression of ERG is highly indicative of poor prognosis in acute myeloid leukemia and ERG is expressed in acute megakaryoblastic leukemia (AMKL); however, it is unclear if expression of ERG per se has a leukemogenic activity. We show that ectopic expression of ERG in fetal hematopoietic progenitors promotes megakaryopoiesis and that ERG alone acts as a potent oncogene in vivo leading to rapid onset of leukemia in mice. We observe that the endogenous ERG is required for the proliferation and maintenance of AMKL cell lines. ERG also strongly cooperates with the GATA1s mutated protein, found in Down syndrome AMKL, to immortalize megakaryocyte progenitors, suggesting that the additional copy of ERG in trisomy 21 may have a role in Down syndrome AMKL. These data suggest that ERG is a hematopoietic oncogene that may play a direct role in myeloid leukemia pathogenesis.

Detection of mutations in GATA1 gene using automated denaturing high-performance liquid chromatography and direct sequencing in children with Down syndrome

Denaturing high-performance liquid chromatography (dHPLC) was developed to screen DNA variations by separating heteroduplex and homoduplex DNA fragments by ion-pair reverse-phase liquid chromatography. In this study, we have evaluated the dHPLC screening method and direct sequencing for the detection of GATA1 mutations in peripheral blood and bone marrow aspirates samples from children with Down syndrome (DS). Cases were ascertained consecutively as part of an epidemiological study of DS and hematological disorders in Brazil. A total of 130 samples corresponding to 115 children with DS were analysed using dHPLC and direct sequencing methods to detect mutations in GATA1 exons 2, 3 and 4 gene sequences. The overall detection rate of sequencing and dHPLC screening methods was similar. Twenty mutations were detected in exon 2 and one mutation in exon 3 (c.231_232 dupGT) sequences of acute megakaryoblastic leukemia and transient leukemia samples. Four GATA1 mutations were newly described [c.155C > G; c.156_178 del23 bp; c.29_30 del GG; c.182C > A and c.151A > T,c.153_162 del 10 bp). Out of four, three had single nucleotide change. In conclusion, our results indicate that dHPLC is an efficient and valuable tool for GATA1 mutational analysis.

Stem cells of GATA1-related leukemia undergo pernicious changes after 5-fluorouracil treatment

OBJECTIVE

Transcription factor GATA1 plays a critical role in erythropoiesis through the integrated regulation of cell proliferation, differentiation, and apoptosis. In Gata1.05 gene knockdown mice, Gata1 expression deteriorates to 5% of wild-type allelic expression, a level insufficient for supporting normal erythropoiesis and one that leads to accumulation of erythroid progenitors that are readily transformed into erythroblastic leukemia. Serial engraftment of leukemic cells into primary or subsequent nude mice reconstituted complete leukemic phenotype in recipient. To delineate characteristics of leukemic stem cells (LSCs), we analyzed LSCs of Gata1.05 leukemia, which have a potential to reestablish leukemia in mice.

MATERIALS AND METHODS

Leukemic cells isolated from the first recipient mice of Gata1.05 leukemia cells were divided into two fractions using Hoechst dye. Fractionated cells were transplanted into second recipient, or analyzed gene expression profiles and cell-cycle status. Consequences of 5-fluorouracil (5-FU) treatment on leukemic cells in vivo were studied.

RESULTS

LSCs were enriched in the Hoechst dye-excluded side population (SP), and leukemic cells in the SP population (LSP cells) were morphologically and immunophenotypically indistinguishable from other leukemic cells. However, expression of hematopoietic stem cell (HSC)-related genes was upregulated in the LSP cells. In cell-cycle analyses, LSP cells were quiescent like HSCs, but reentry into the cell cycle was stimulated by 5-FU treatment. Nonetheless, 5-FU treatment established a point of newly adjusted equilibrium in the LSP cells and the cells never recovered to their previous quiescent state.

CONCLUSION

Based on this observation, distinct self-renewal regulatory mechanisms in LSCs may be considered as one of the causes of worsening of the features of leukemia after injury and relapse.

Insights into the manifestations, outcomes, and mechanisms of leukemogenesis in Down syndrome

Children with Down syndrome (DS) show a spectrum of clinical anomalies, including cognitive impairment, cardiac malformations, and craniofacial dysmorphy. Moreover, hematologists have also noted that these children commonly show macrocytosis, abnormal platelet counts, and an increased incidence of transient myeloproliferative disease (TMD), acute megakaryocytic leukemia (AMKL), and acute lymphoid leukemia (ALL). In this review, we summarize the clinical manifestations and characteristics of these leukemias, provide an update on therapeutic strategies and patient outcomes, and discuss the most recent advances in DS-leukemia research. With the increased knowledge of the way in which trisomy 21 affects hematopoiesis and the specific genetic mutations that are found in DS-associated leukemias, we are well on our way toward designing improved strategies for treating both myeloid and lymphoid malignancies in this high-risk population.

Hematopoietic defects in the Ts1Cje mouse model of Down syndrome

Down syndrome (DS) persons are born with various hematopoietic abnormalities, ranging from relatively benign, such as neutrophilia and macrocytosis, to a more severe transient myeloproliferative disorder (TMD). In most cases, these abnormalities resolve in the first few months to years of life. However, sometimes the TMD represents a premalignant disease that develops into acute megakaryocytic leukemia (AMKL), usually in association with acquired GATA1 mutations. To gain insight into the mechanisms responsible for these abnormalities, we analyzed the hematopoietic development of the Ts1Cje mouse model of DS. Our analyses identified defects in mature blood cells, including macrocytosis and anemia, as well as abnormalities in fetal liver and bone marrow stem and progenitor cell function. Despite these defects, the Ts1Cje mice do not develop disease resembling either TMD or AMKL, and this was not altered by a loss of function allele of Gata1. Thus, loss of Gata1 and partial trisomy of chromosome 21 orthologs, when combined, do not appear to be sufficient to induce TMD or AMKL-like phenotypes in mice.

Malignancy in children with trisomy 21

Patients with Down syndrome (DS) display a unique spectrum of malignancies, with a 10- to 20-fold higher risk of acute leukemias, and a markedly lower incidence of solid tumors. This review discusses the current understanding of the basis for this distinctive pattern of cancer incidence and the clinical and biologic features of the malignant disorders most frequent in DS individuals: transient myeloproliferative disease, acute megakaryoblastic leukemia, and acute lymphoblastic leukemia. We also review distinctive pharmacogenetic issues, highlighting the differential chemosensitivity and toxicity profiles of DS patients compared with the general population, and epidemiologic studies of protective and adverse environmental risk factors for the development of leukemia.

Clinical significance of Gata-1, Gata-2, EKLF, and c-MPL expression in acute myeloid leukemia

The aim of this study was to evaluate the biological correlation and prognostic impact of Gata-1, Gata-2, EKLF, and c-MPL transcript level in a group of 41 acute myeloid leukemia (AML) patients. Gata-1 overexpression was related to advanced age and a low percentage of bone marrow blasts and was associated with the expression of CD34 antigen and lymphoid T markers. The negative impact of Gata-1 expression on the probability of achieving complete remission has been confirmed. Gata-2 overexpression was associated with a low percentage of blasts in BM and males. Expression of c-MPL was associated with CD34+ AML and M2 FAB AML subtype. A higher expression of EKLF was found in secondary AML versus primary AML. Nevertheless, patients expressing EKLF had a longer overall survival and event free survival than those patients that did not express EKLF. Our study has identified expression of EKLF as a factor with a favorable impact on prognosis in AML.

Transient abnormal myelopoiesis in a Down syndrome newborn followed by acute myeloid leukemia: identification of the same chromosomal abnormality in both stages

A transient abnormal myelopoiesis was observed in a newborn with Down syndrome. Cytogenetic study revealed multiple oligoclonal abnormalities: 47,XY,inv(6)(p23q21),+21c[3]/47,XY,der(7)t(1;7)(q25;p15),+21c[1]/47,XY,del(13)(q?),+21c[1]/47,XY,+21c[15]. Ten months after the patient achieved remission, the transient abnormal myelopoiesis evolved to an acute megakaryoblastic leukemia. Cytogenetic study revealed only a single clonal abnormality, 47,XY,der(7)t(1;7)(q25;p15),+21c, identical to one of the structural changes seen at birth. Sequence analysis of the GATA1 gene revealed a deletion-insertion mutation within the exon 2 introducing a stop codon after Arg 64. It may be that the der(7)t(1;7)(q25;p15) abnormality played some selective role in the development of acute megakaryoblastic leukemia in this patient. To our knowledge, the present case is unique in demonstrating a subclone with der(7)t(1;7)(q25;p15) evolving to acute leukemia.

Differential contribution of the Gata1 gene hematopoietic enhancer to erythroid differentiation

GATA1 is a key regulator of erythroid cell differentiation. To examine how Gata1 gene expression is regulated in a stage-specific manner, transgenic mouse lines expressing green fluorescent protein (GFP) reporter from the Gata1 locus in a bacterial artificial chromosome (G1BAC-GFP) were prepared. We found that the GFP reporter expression faithfully recapitulated Gata1 gene expression. Using GFP fluorescence in combination with hematopoietic surface markers, we established a purification protocol for two erythroid progenitor fractions, referred to as burst-forming units-erythroid cell-related erythroid progenitor (BREP) and CFU-erythroid cell-related erythroid progenitor (CREP) fractions. We examined the functions of the Gata1 gene hematopoietic enhancer (G1HE) and the highly conserved GATA box in the enhancer core. Both deletion of the G1HE and substitution mutation of the GATA box caused almost complete loss of GFP expression in the BREP fraction, but the CREP stage expression was suppressed only partially, indicating the critical contribution of the GATA box to the BREP stage expression of Gata1. Consistently, targeted deletion of G1HE from the chromosomal Gata1 locus provoked suppressed expression of the Gata1 gene in the BREP fraction, which led to aberrant accumulation of BREP stage hematopoietic progenitor cells. These results demonstrate the physiological significance of the dynamic regulation of Gata1 gene expression in a differentiation stage-specific manner.

Cross-talk of GATA-1 and P-TEFb in megakaryocyte differentiation

The transcription factor GATA-1 participates in programming the differentiation of multiple hematopoietic lineages. In megakaryopoiesis, loss of GATA-1 function produces complex developmental abnormalities and underlies the pathogenesis of megakaryocytic leukemia in Down syndrome. Its distinct functions in megakaryocyte and erythroid maturation remain incompletely understood. In this study, we identified functional and physical interaction of GATA-1 with components of the positive transcriptional elongation factor P-TEFb, a complex containing cyclin T1 and the cyclin-dependent kinase 9 (Cdk9). Megakaryocytic induction was associated with dynamic changes in endogenous P-TEFb composition, including recruitment of GATA-1 and dissociation of HEXIM1, a Cdk9 inhibitor. shRNA knockdowns and pharmacologic inhibition both confirmed contribution of Cdk9 activity to megakaryocytic differentiation. In mice with megakaryocytic GATA-1 deficiency, Cdk9 inhibition produced a fulminant but reversible megakaryoblastic disorder reminiscent of the transient myeloproliferative disorder of Down syndrome. P-TEFb has previously been implicated in promoting elongation of paused RNA polymerase II and in programming hypertrophic differentiation of cardiomyocytes. Our results offer evidence for P-TEFb cross-talk with GATA-1 in megakaryocytic differentiation, a program with parallels to cardiomyocyte hypertrophy.

Abnormalities in the myeloid progenitor compartment in Down syndrome fetal liver precede acquisition of GATA1 mutations

Down syndrome (DS) children have a high frequency of acute megakaryoblastic leukemia (AMKL) in early childhood. At least 2 in utero genetic events are required, although not sufficient, for DS-AMKL: trisomy 21 (T21) and N-terminal-truncating GATA1 mutations. To investigate the role of T21 in DS-AMKL, we compared second trimester hemopoiesis in DS without GATA1 mutations to gestation-matched normal controls. In all DS fetal livers (FLs), but not marrows, megakaryocyte-erythroid progenitor frequency was increased (55.9% +/- 4% vs 17.1% +/- 3%, CD34(+)CD38(+) cells; P < .001) with common myeloid progenitors (19.6% +/- 2% vs 44.0% +/- 7%) and granulocyte-monocyte (GM) progenitors (15.8% +/- 4% vs 34.5% +/- 9%) commensurately reduced. Clonogenicity of DS-FL versus normal FL CD34(+) cells was markedly increased (78% +/- 7% vs 15% +/- 3%) affecting megakaryocyte-erythroid ( approximately 7-fold higher) and GM and colony-forming unit-granulocyte, erythrocyte macrophage, megakaryocyte (CFU-GEMM) progenitors. Replating efficiency of CFU-GEMM was also markedly increased. These data indicate that T21 itself profoundly disturbs FL hemopoiesis and they provide a testable hypothesis to explain the increased susceptibility to GATA1 mutations in DS-AMKL and DS-associated transient myeloproliferative disorder.

Transient myeloproliferative disorder in a newborn with Down syndrome

This is the report of a newborn with Down syndrome diagnosed with transient myeloproliferative disorder (TMD) that required chemotherapy on the first day of life. Children with Down syndrome have a 10- to 20-fold increased risk of developing TMD. TMD is characterized by an uncontrolled proliferation of myeloblasts in the infant's peripheral blood and bone marrow. In most instances, this unique disorder has the ability to spontaneously "turn off" the overproliferation and enter a state of remission. Only supportive care is recommended for TMD during the first months of life unless the clinical condition requires intervention. As more cases of this baffling disorder are presented, it is important to share our experience to aid in management and diagnosis.

Thrombocytopenia in the neonate

Thrombocytopenia is one of the commonest haematological problems in neonates, affecting at least 25% of all admissions to neonatal intensive care units (NICUs) [Murray NA, Howarth LJ, McCloy MP et al. Platelet transfusion in the management of severe thrombocytopenia in neonatal intensive care unit patients. Transfus Med 2002;12:35-41; Garcia MG, Duenas E, Sola MC et al. Epidemiologic and outcome studies of patients who received platelet transfusions in the neonatal intensive care unit. J Perinatol 2001;21:415-20; Del Vecchio A, Sola MC, Theriaque DW et al. Platelet transfusions in the neonatal intensive care unit: factors predicting which patients will require multiple transfusions. Transfusion 2001;41:803-8]. Although a long list of disorders associated with neonatal thrombocytopenia can be found in many textbooks, newer classifications based on the timing of onset of thrombocytopenia (early vs. late) are more useful for planning diagnostic investigations and day-to-day management. The mainstay of treatment of neonatal thrombocytopenia remains platelet transfusion although it is important to note that no studies have yet shown clinical benefit of platelet transfusion in this setting. Indeed some reports even suggest that there may be significant adverse effects of platelet transfusion in neonates, including increased mortality, and that the effects of transfusion may differ in different groups of neonates with similar degrees of thrombocytopenia [Bonifacio L, Petrova A, Nanjundaswamy S, Mehta R. Thrombocytopenia related neonatal outcome in preterms. Indian J Pediatr 2007;74:269-74; Kenton AB, Hegemier S, Smith EO et al. Platelet transfusions in infants with necrotizing enterocolitis do not lower mortality but may increase morbidity. J Perinatol 2005;25:173-7]. There is also considerable variation in transfusion practice between different countries and between different neonatal units. Here we review recent progress in understanding the prevalence, causes and pathogenesis of thrombocytopenia in the newborn, the clinical consequences of thrombocytopenia and developments in neonatal platelet transfusion.

Functional analysis of JAK3 mutations in transient myeloproliferative disorder and acute megakaryoblastic leukaemia accompanying Down syndrome

JAK3 mutations have been reported in transient myeloproliferative disorder (TMD) as well as in acute megakaryoblastic leukaemia of Down syndrome (DS-AMKL). However, functional consequences of the JAK3 mutations in TMD patients remain undetermined. To further understand how JAK3 mutations are involved in the development and/or progression of leukaemia in Down syndrome, additional TMD patients and the DS-AMKL cell line MGS were screened for JAK3 mutations, and we examined whether each JAK3 mutation is an activating mutation. JAK3 mutations were not detected in 10 TMD samples that had not previously been studied. Together with our previous report we detected JAK3 mutations in one in 11 TMD patients. Furthermore, this study showed for the first time that a TMD patient-derived JAK3 mutation (JAK3(I87T)), as well as two novel JAK3 mutations (JAK3(Q501H) and JAK3(R657Q)) identified in an MGS cell line, were activating mutations. Treatment of MGS cells and Ba/F3 cells expressing the JAK3 mutants with JAK3 inhibitors significantly decreased their growth and viability. These results suggest that the JAK3 activating mutation is an early event during leukaemogenesis in Down syndrome, and they provide proof-of-principle evidence that JAK3 inhibitors would have therapeutic effects on TMD and DS-AMKL patients carrying activating JAK3 mutations.

GATA1-related leukaemias

GATA1 is a prototypical lineage-restricted transcription factor that is central to the correct differentiation, proliferation and apoptosis of erythroid and megakaryocytic cells. Mutations in GATA1 can generate a truncated protein, which contributes to the genesis of transient myeloproliferative disorder (TMD) and acute megakaryoblastic leukaemia (AMKL) in infants with Down syndrome. Similarly, Gata1 knockdown to 5% of its wild-type level causes high incidence of erythroid leukaemia in mice. The GATA1-related leukaemias in both human and mouse could provide important insights into the mechanism of multi-step leukaemogenesis. Efforts are afoot to produce mouse models that are reflective of TMD and AMKL.

Platelet-derived growth factor may be associated with fibrosis in a Down syndrome patient with transient myeloproliferative disorder

Transient myeloproliferative disorder (TMD) is experienced by approximately 10% of neonates with Down syndrome (DS). Most TMD is asymptomatic and the patients undergo spontaneous remission within a few months. However, some cases are fatal because of systemic organ dysfunctions including hepatic fibrosis. Some cytokines such as platelet-derived growth factor (PDGF) may be involved in the development of hepatic fibrosis in TMD. The report describes a fatal case of TMD accompanying DS. The patient presented with pulmonary hypertension and hepatic failure. An autopsy disclosed severe fibrosis in the lung, liver, kidney and pancreas. Immunohistochemical analysis revealed high expression of PDGF receptor beta in the severe fibrotic areas of the fibrotic tissues. A real-time polymerase chain reaction (PCR) analysis demonstrated the expression of PDGFalpha and PDGFbeta in the peripheral blood samples of the patient. The finding indicates that the PDGF pathway may play an important role in the fibrosis of several organs in patients with TMD.

Acute leukemias in children with Down syndrome

Children with Down syndrome have an increased risk for developing both acute myeloid as well as lymphoblastic leukemia. These leukemias differ in presenting characteristics and underlying biology when compared with leukemias occurring in non-Down syndrome children. Myeloid leukemia in children with Down syndrome is preceded by a preleukemic clone (transient leukemia or transient myeloproliferative disorder), which may disappear spontaneously, but may also need treatment in case of severe symptoms. Twenty percent of children with transient leukemia subsequently develop myeloid leukemia. This transition offers a unique model to study the stepwise development of leukemia, and of gene dosage effects mediated by aneuploidy.

Highly penetrant myeloproliferative disease in the Ts65Dn mouse model of Down syndrome

Children with Down syndrome (DS) display macrocytosis, thrombocytosis, and a 500-fold increased risk of developing megakaryocytic leukemia; however, the specific effects of trisomy 21 on hematopoiesis remain poorly defined. To study this question, we analyzed blood cell development in the Ts65Dn mouse model of DS. Ts65Dn mice are trisomic for 104 orthologs of Hsa21 genes and are the most widely used mouse model for DS. We discovered that Ts65Dn mice display persistent macrocytosis and develop a myeloproliferative disease (MPD) characterized by profound thrombocytosis, megakaryocyte hyperplasia, dysplastic megakaryocyte morphology, and myelofibrosis. In addition, these animals bear distorted hematopoietic stem and myeloid progenitor cell compartments compared with euploid control littermates. Of the 104 trisomic genes in Ts65Dn mice, Aml1/Runx1 attracts considerable attention as a candidate oncogene in DS-acute megakaryoblastic leukemia (DS-AMKL). To determine whether trisomy for Aml1/Runx1 is essential for MPD, we restored disomy at the Aml1/Runx1 locus in the Ts65Dn strain. Surprisingly, trisomy for Aml1/Runx1 is not required for megakaryocyte hyperplasia and myelofibrosis, suggesting that trisomy for one or more of the remaining genes can promote this disease. Our studies demonstrate the potential of DS mouse models to improve our understanding of chromosome 21 gene dosage effects in human hematologic malignancies.