Mutations of the AML1 gene in acute myeloid leukemia of FAB types M0 and M7

Interface-guided phenotyping of coding variants in the transcription factor RUNX1

Single-gene missense mutations remain challenging to interpret. Here, we deploy scalable functional screening by sequencing (SEUSS), a Perturb-seq method, to generate mutations at protein interfaces of RUNX1 and quantify their effect on activities of downstream cellular programs. We evaluate single-cell RNA profiles of 115 mutations in myelogenous leukemia cells and categorize them into three functionally distinct groups, wild-type (WT)-like, loss-of-function (LoF)-like, and hypomorphic, that we validate in orthogonal assays. LoF-like variants dominate the DNA-binding site and are recurrent in cancer; however, recurrence alone does not predict functional impact. Hypomorphic variants share characteristics with LoF-like but favor protein interactions, promoting gene expression indicative of nerve growth factor (NGF) response and cytokine recruitment of neutrophils. Accessible DNA near differentially expressed genes frequently contains RUNX1-binding motifs. Finally, we reclassify 16 variants of uncertain significance and train a classifier to predict 103 more. Our work demonstrates the potential of targeting protein interactions to better define the landscape of phenotypes reachable by missense mutations.

Targeting RUNX1 in acute myeloid leukemia: preclinical innovations and therapeutic implications

Introduction: RUNX1 is an essential transcription factor for normal and malignant hematopoiesis. RUNX1 forms a heterodimeric complex with CBFB. Germline mutations and somatic alterations (i.e. translocations, mutations and abnormal expression) are frequently associated with acute myeloid leukemia (AML) with RUNX1 mutations conferring unfavorable prognosis. Therefore, RUNX1 constitutes a potential innovative and interesting therapeutic target. In this review, we discuss recent therapeutic advances of RUNX1 targeting in AML.Areas covered: Firstly, we cover the clinical basis for RUNX1 targeting. We have subdivided recent therapeutic approaches either by common biochemical pathways or by similar pharmacological targets. Genome editing of RUNX1 induces anti-leukemic effects; however, off-target events prohibit clinical use. Several molecules inhibit the interaction between RUNX1/CBFB and control AML development and progression. BET protein antagonists target RUNX1 (i.e. specific BET inhibitors, BRD4 shRNRA, proteolysis targeting chimeras (PROTAC) or expression-mimickers). All these molecules improve survival in mutant RUNX1 AML preclinical models.Expert opinion: Some of these novel molecules have shown encouraging anti-leukemic potency at the preclinical stage. A better understanding of RUNX1 function in AML development and progression and its key downstream pathways, may result in more precise and more efficient RUNX1 targeting therapies.

Clinicopathological Significance of RUNX1 in Non-Small Cell Lung Cancer

This study aimed to understand the clinicopathological significance of runt-related transcription factor 1 (RUNX1) in non-small cell lung cancer (NSCLC). The methylation and mRNA levels of RUNX1 in NSCLC were determined using the Infinium HumanMethylation450 BeadChip and the HumanHT-12 expression BeadChip. RUNX1 protein levels were analyzed using immunohistochemistry of formalin-fixed paraffin-embedded tissues from 409 NSCLC patients. Three CpGs (cg04228935, cg11498607, and cg05000748) in the CpG island of RUNX1 showed significantly different methylation levels (Bonferroni corrected p < 0.05) between tumor and matched normal tissues obtained from 42 NSCLC patients. Methylation levels of the CpGs in the tumor tissues were inversely related to mRNA levels of RUNX1. A logistic regression model based on cg04228935 showed the best performance in predicting NSCLCs in a test dataset (N = 28) with the area under the receiver operating characteristic (ROC) curve (AUC) of 0.96 (95% confidence interval (CI) = 0.81–0.99). The expression of RUNX1 was reduced in 125 (31%) of 409 patients. Adenocarcinoma patients with reduced RUNX1 expression showed 1.97-fold (95% confidence interval = 1.16–3.44, p = 0.01) higher hazard ratio for death than those without. In conclusion, the present study suggests that abnormal methylation of RUNX1 may be a valuable biomarker for detection of NSCLC regardless of race. And, reduced RUNX1 expression may be a prognostic indicator of poor overall survival in lung adenocarcinoma.

Gain-of-Function Effects of N-Terminal CEBPA Mutations in Acute Myeloid Leukemia

Mutations in the CEBPA gene are present in 10–15% of acute myeloid leukemia (AML) patients. The most frequent type of mutations leads to the expression of an N-terminally truncated variant of the transcription factor CCAAT/enhancer-binding protein alpha (C/EBPα), termed p30. While initial reports proposed that p30 represents a dominant-negative version of the wild-type C/EBPα protein, other studies show that p30 retains the capacity to actively regulate gene expression. Recent global transcriptomic and epigenomic analyses have advanced the understanding of the distinct roles of the p30 isoform in leukemogenesis. This review outlines direct and indirect effects of the C/EBPα p30 variant on oncogenic transformation of hematopoietic progenitor cells and discusses how studies of N-terminal CEBPA mutations in AML can be extrapolated to identify novel gain-of-function features in oncoproteins that arise from recurrent truncating mutations in transcription factors.

Identification of chlorprothixene as a potential drug that induces apoptosis and autophagic cell death in acute myeloid leukemia cells

Although acute myeloid leukemia (AML) is a highly heterogeneous malignance, the common molecular mechanisms shared by different AML subtypes play critical roles in AML development. It is possible to identify new drugs that are effective for various AML subtypes based on the common molecular mechanisms. Therefore, we developed a hypothesis-driven bioinformatic drug screening framework by integrating multiple omics data. In this study, we identified that chlorprothixene, a dopamine receptor antagonist, could effectively inhibit growth of AML cells from different subtypes. RNA-seq analysis suggested that chlorprothixene perturbed a series of crucial biological processes such as cell cycle, apoptosis, and autophagy in AML cells. Further investigations indicated that chlorprothixene could induce both apoptosis and autophagy in AML cells, and apoptosis and autophagy could act as partners to induce cell death cooperatively. Remarkably, chlorprothixene was found to inhibit tumor growth and induce in situ leukemic cell apoptosis in the murine xenograft model. Furthermore, chlorprothixene treatment could reduce the level of oncofusion proteins PML-RARα and AML1-ETO, thus elevate the expression of apoptosis-related genes, and lead to AML cell death. Our results provided new insights for drug repositioning of AML therapy and confirmed that chlorprothixene might be a potential candidate for treatment of different subtypes of AML by reducing expression of oncofusion proteins. DATABASE: RNA-seq data are available in GEO database under the accession number GSE124316.

RUNX1 is required for oncogenic Myb and Myc enhancer activity in T-cell acute lymphoblastic leukemia

The gene encoding the RUNX1 transcription factor is mutated in a subset of T-cell acute lymphoblastic leukemia (T-ALL) patients, and RUNX1 mutations are associated with a poor prognosis. These mutations cluster in the DNA-binding Runt domain and are thought to represent loss-of-function mutations, indicating that RUNX1 suppresses T-cell transformation. RUNX1 has been proposed to have tumor suppressor roles in T-cell leukemia homeobox 1/3-transformed human T-ALL cell lines and NOTCH1 T-ALL mouse models. Yet, retroviral insertional mutagenesis screens identify RUNX genes as collaborating oncogenes in MYC-driven leukemia mouse models. To elucidate RUNX1 function(s) in leukemogenesis, we generated Tal1/Lmo2/Rosa26-CreER^T2Runx1^f/f mice and examined leukemia progression in the presence of vehicle or tamoxifen. We found that Runx1 deletion inhibits mouse leukemic growth in vivo and that RUNX silencing in human T-ALL cells triggers apoptosis. We demonstrate that a small molecule inhibitor, designed to interfere with CBFβ binding to RUNX proteins, impairs the growth of human T-ALL cell lines and primary patient samples. We demonstrate that a RUNX1 deficiency alters the expression of a crucial subset of TAL1- and NOTCH1-regulated genes, including the MYB and MYC oncogenes, respectively. These studies provide genetic and pharmacologic evidence that RUNX1 has oncogenic roles and reveal RUNX1 as a novel therapeutic target in T-ALL.

Evolved Cellular Mechanisms to Respond to Genotoxic Insults: Implications for Radiation-Induced Hematologic Malignancies

Human exposure to ionizing radiation is highly associated with adverse health effects, including reduced hematopoietic cell function and increased risk of carcinogenesis. The hematopoietic deficits manifest across blood cell types and persist for years after radiation exposure, suggesting a long-lived and multi-potent cellular reservoir for radiation-induced effects. As such, research has focused on identifying both the immediate and latent hematopoietic stem cell responses to radiation exposure. Radiation-associated effects on hematopoietic function and malignancy development have generally been attributed to the direct induction of mutations resulting from radiation-induced DNA damage. Other studies have illuminated the role of cellular programs that both limit and enhance radiation-induced tissue phenotypes and carcinogenesis. In this review, distinct but collaborative cellular responses to genotoxic insults are highlighted, with an emphasis on how these programmed responses impact hematopoietic cellular fitness and competition. These radiation-induced cellular programs include apoptosis, senescence and impaired self-renewal within the hematopoietic stem cell (HSC) pool. In the context of sporadic DNA damage to a cell, these cellular responses act in concert to restore tissue function and prevent selection for adaptive oncogenic mutations. But in the contexts of whole-tissue exposure or whole-body exposure to genotoxins, such as radiotherapy or chemotherapy, we propose that these programs can contribute to long-lasting tissue impairment and increased carcinogenesis.

Frequent coexistence of RAS mutations in RUNX1-mutated acute myeloid leukemia in Arab Asian children

BACKGROUND

RUNX1 mutation plays an important role in adult leukemic transformation. However, its contribution to the development of childhood leukemia remains unclear. In the present study, we analyzed point mutations of RUNX1 gene in children and adolescents with acute myeloid leukemia (AML) from Iraq and Jordan.

PROCEDURE

Bone marrow and/or peripheral blood samples were collected from 178 patients of Arab Asian ethnicity (aged ≤17 years) newly diagnosed with AML: 145 samples from Iraq and 33 samples from Jordan. Direct DNA sequencing was performed on six genes including RUNX1 gene (exons 3-8).

RESULTS

RUNX1 point mutations were identified in 10 (5.6%) of 178 patients. One patient possessed biallelic mutations of RUNX1 gene. C-terminal area was the predominant site of RUNX1 mutations (eight in C-terminal and two in N-terminal). Patients with RUNX1 mutations were significantly older than those with wild-type of the gene. Additionally, AML M0 subtype was more frequently found in patients with RUNX1 mutations. Both RUNX1 mutations and RAS mutations were identified in 4 of 10 children. Three patients with RUNX1 mutation had FLT3-ITD. On the other hand, 36 (21.4%) and 25 (14.9%) of 168 patients with wild-type of the gene had a RAS mutation and FLT3-ITD, respectively. Eight of 10 patients with RUNX1 mutations died of hematological relapse.

CONCLUSION

The incidence of RUNX1 mutations in Arab Asian children and adolescents with AML was 5.6%. Further studies are required to clarify whether RAS mutations contribute to the development of pediatric AML associated with RUNX1 mutations.

RUNX Family Participates in the Regulation of p53-Dependent DNA Damage Response

A proper DNA damage response (DDR), which monitors and maintains the genomic integrity, has been considered to be a critical barrier against genetic alterations to prevent tumor initiation and progression. The representative tumor suppressor p53 plays an important role in the regulation of DNA damage response. When cells receive DNA damage, p53 is quickly activated and induces cell cycle arrest and/or apoptotic cell death through transactivating its target genes implicated in the promotion of cell cycle arrest and/or apoptotic cell death such as p21^WAF1, BAX, and PUMA. Accumulating evidence strongly suggests that DNA damage-mediated activation as well as induction of p53 is regulated by posttranslational modifications and also by protein-protein interaction. Loss of p53 activity confers growth advantage and ensures survival in cancer cells by inhibiting apoptotic response required for tumor suppression. RUNX family, which is composed of RUNX1, RUNX2, and RUNX3, is a sequence-specific transcription factor and is closely involved in a variety of cellular processes including development, differentiation, and/or tumorigenesis. In this review, we describe a background of p53 and a functional collaboration between p53 and RUNX family in response to DNA damage.

RUNX1 mutations are associated with poor outcome in younger and older patients with cytogenetically normal acute myeloid leukemia and with distinct gene and MicroRNA expression signatures

PURPOSE

To determine the association of RUNX1 mutations with therapeutic outcome in younger and older patients with primary cytogenetically normal acute myeloid leukemia (CN-AML) and with gene/microRNA expression signatures.

PATIENTS AND METHODS

Younger (< 60 years; n = 175) and older (≥ 60 years; n = 225) patients with CN-AML treated with intensive cytarabine/anthracycline-based first-line therapy on Cancer and Leukemia Group B protocols were centrally analyzed for RUNX1 mutations by polymerase chain reaction and direct sequencing and for established prognostic gene mutations. Gene/microRNA expression profiles were derived using microarrays.

RESULTS

RUNX1 mutations were found in 8% and 16% of younger and older patients, respectively (P = .02). They were associated with ASXL1 mutations (P < .001) and inversely associated with NPM1 (P < .001) and CEBPA (P = .06) mutations. RUNX1-mutated patients had lower complete remission rates (P = .005 in younger; P = .006 in older) and shorter disease-free survival (P = .058 in younger; P < .001 in older), overall survival (P = .003 in younger; P < .001 in older), and event-free survival (P < .001 for younger and older) than RUNX1 wild-type patients. Because RUNX1 mutations were more common in older patients and almost never coexisted with NPM1 mutations, RUNX1 mutation-associated expression signatures were derived in older, NPM1 wild-type patients and featured upregulation of genes normally expressed in primitive hematopoietic cells and B-cell progenitors, including DNTT, BAALC, BLNK, CD109, RBPMS, and FLT3, and downregulation of promoters of myelopoiesis, including CEBPA and miR-223.

CONCLUSION

RUNX1 mutations are twice as common in older than younger patients with CN-AML and negatively impact outcome in both age groups. RUNX1-mutated blasts have molecular features of primitive hematopoietic and lymphoid progenitors, potentially leading to novel therapeutic approaches.

Functional characterization of the promoter region of the human EVI1 gene in acute myeloid leukemia: RUNX1 and ELK1 directly regulate its transcription

The EVI1 gene (3q26) codes for a transcription factor with important roles in normal hematopoiesis and leukemogenesis. High expression of EVI1 is a negative prognostic indicator of survival in acute myeloid leukemia (AML) irrespective of the presence of 3q26 rearrangements. However, the only known mechanisms that lead to EVI1 overexpression are 3q aberrations, and the MLL-ENL oncoprotein, which activates the transcription of EVI1 in hematopoietic stem cells. Our aim was to characterize the functional promoter region of EVI1, and to identify transcription factors involved in the regulation of this gene. Generation of seven truncated constructs and luciferase reporter assays allowed us to determine a 318-bp region as the minimal promoter region of EVI1. Site-directed mutagenesis and chromatin immunoprecipitation (ChIP) assays identified RUNX1 and ELK1 as putative transcription factors of EVI1. Furthermore, knockdown of RUNX1 and ELK1 led to EVI1 downregulation, and their overexpression to upregulation of EVI1. Interestingly, in a series of patient samples with AML at diagnosis, we found a significant positive correlation between EVI1 and RUNX1 at protein level. Moreover, we identified one of the roles of RUNX1 in the activation of EVI1 during megakaryocytic differentiation. EVI1 knockdown significantly inhibited the expression of megakaryocytic markers after treating K562 cells with TPA, as happens when knocking down RUNX1. In conclusion, we define the minimal promoter region of EVI1 and demonstrate that RUNX1 and ELK1, two proteins with essential functions in hematopoiesis, regulate EVI1 in AML. Furthermore, our results show that one of the mechanisms by which RUNX1 regulates the transcription of EVI1 is by acetylation of the histone H3 on its promoter region. This study opens new directions to further understand the mechanisms of EVI1 overexpressing leukemias.

Reverse engineering of TLX oncogenic transcriptional networks identifies RUNX1 as tumor suppressor in T-ALL

The TLX1 and TLX3 transcription factor oncogenes play an important role in the pathogenesis of T-cell acute lymphoblastic leukemia (T-ALL)^1,2. Here we used reverse engineering of global transcriptional networks to decipher the oncogenic regulatory circuit controlled by TLX1 and TLX3. This Systems Biology analysis defined TLX1 and TLX3 as master regulators of an oncogenic transcriptional circuit governing T-ALL. Notably, network structure analysis of this hierarchical network identified RUNX1 as an important mediator of TLX1 and TLX3 induced T-ALL, and predicted a tumor suppressor role for RUNX1 in T-cell transformation. Consistent with these results, we identified recurrent somatic loss of function mutations in RUNX1 in human T-ALL. Overall, these results place TLX1 and TLX3 atop of an oncogenic transcriptional network controlling leukemia development, demonstrate power of network analysis to identify key elements in the regulatory circuits governing human cancer and identify RUNX1 as a tumor suppressor gene in T-ALL.

Hereditary leukemia due to rare RUNX1c splice variant (L472X) presents with eczematous phenotype

Deleterious mutations in the RUNX1 gene cause hereditary leukemia due to a rare syndrome called Familial platelet Disorder with Associated Myeloid Malignancy (FPDMM). We describe the characteristics of a family with FPDMM due to a novel RUNX1 mutation (L472X), located in the most 3-prime end of the gene reported to date. Our 36-year old proband presented with incidentally detected thrombocytopenia and a family history suggestive of FPDMM. Contrary to previously described families, affected members of our kindred express an eczematous phenotype, reportedly most severe in members who develop leukemia. Pedigree analysis shows that the L472X mutation tracks with thrombocytopenia, acute leukemia, and eczema. The L472X mutation produces a stably expressed RUNX1 protein product with a corresponding decrease in wild type RUNX1 expression. Our data supports the inclusion of eczema in the FPDMM phenotype and suggests the possibility that the RUNX1 L472X mutant causes the type of dominant negative affect that is associated with an elevated risk of leukemia in FPDMM families.

AML1/RUNX1 gene point mutations in childhood myeloid malignancies

BACKGROUND

Currently, it is widely accepted that one of the crucial players in adult leukemic transformation is the RUNX1 gene. However, there is little data available regarding whether mutations in this gene also contribute to pediatric leukemia, especially in childhood myeloid malignancies. Therefore we made a decision to screen patients with pediatric myeloid neoplasias for the presence of RUNX1 mutations in their samples.

PROCEDURES

Patients (n = 238) with diagnoses of de novo acute myeloid leukemia (AML) (n = 198), de novo myelodisplastic syndrome (MDS) (n = 16), therapy-related AML (n = 9), juvenile myelomonocytic leukemia (JMML) (n = 15) were included in this study. All patients were Belarusians between the ages of 0 and 18 years.

RESULTS

The frequency of RUNX1 point mutations in the total group of patients with de novo AML was 3% and de novo MDS was 15%. Cooperation of point mutations in the RUNX1 and NRAS genes, and the cytogenetic abnormality, -7/7q-, was demonstrated in children with therapy-related AML. RUNX1 point mutations predominate in those de novo AML and MDS patients with a normal karyotype in leukemic cells. Frequency of RUNX1 point mutations was about 4% in a group of children with de novo AML aged 0-14 years diagnosed during the period of 1998-2009.

CONCLUSION

During the course of this investigation, valuable data were obtained concerning RUNX1 gene mutation frequencies in different clinical, morphological, and cytogenetic groups of patients with myeloid malignancies, and its cooperation with other molecular aberrations.

RUNX1 mutations are frequent in de novo AML with noncomplex karyotype and confer an unfavorable prognosis

Analyses of 164 RUNX1 mutations (RUNX1mut) in 147 of 449 patients (32.7%) with normal karyotype or noncomplex chromosomal imbalances were performed. RUNX1mut were most frequent in acute myeloid leukemia French-American-British classification M0 (65.2%) followed by M2 (32.4%) and M1 (30.2%). Considering cytogenetics, RUNX1mut were most frequent in cases with +13 (27 of 30, 90%), whereas frequencies were similar in other cytogenetic groups (26%-36%). The molecular genetic markers most frequently associated with RUNX1mut were partial tandem duplication in the MLL gene (19.7%), internal tandem duplication in the FLT3 gene (FLT3-ITD; 16.3%), and NRAS mutations (9.5%). Patients with RUNX1mut had shorter overall and event-free survival compared with RUNX1 wild-type cases (median, 378 days vs not reached, P = .003; and median, 285 vs 450 days, P = .003, respectively). In addition, it was shown that the adverse effect of RUNX1 was independent of the adverse effect of FLT3-ITD as well as of the high frequency of prognostically favorable NPM1mut and CEBPAmut in the RUNX1wt group. No effect of the type or localization of the individual RUNX1 mutations was observed. Multivariate analysis showed independent prognostic relevance for overall survival for RUNX1mut (P = .029), FLT3-ITD (P = .003), age (P < .001), and white blood cell count (P < .002).

RUNX1 mutations in acute myeloid leukemia: results from a comprehensive genetic and clinical analysis from the AML study group

PURPOSE

To evaluate frequency, biologic features, and clinical relevance of RUNX1 mutations in acute myeloid leukemia (AML).

PATIENTS AND METHODS

Diagnostic samples from 945 patients (age 18 to 60 years) were analyzed for RUNX1 mutations. In a subset of cases (n = 269), microarray gene expression analysis was performed.

RESULTS

Fifty-nine RUNX1 mutations were identified in 53 (5.6%) of 945 cases, predominantly in exons 3 (n = 11), 4 (n = 10), and 8 (n = 23). RUNX1 mutations clustered in the intermediate-risk cytogenetic group (46 of 640, 7.2%; cytogenetically normal, 34 of 538, 6.3%), whereas they were less frequent in adverse-risk cytogenetics (five of 109, 4.6%) and absent in core-binding-factor AML (0 of 77) and acute promyelocytic leukemia (0 of 61). RUNX1 mutations were associated with MLL-partial tandem duplications (P = .0007) and IDH1/IDH2 mutations (P = .03), inversely correlated with NPM1 (P < .0001), and in trend with CEBPA (P = .10) mutations. RUNX1 mutations were characterized by a distinct gene expression pattern; this RUNX1 mutation-derived signature was not exclusive for the mutation, but also included mostly adverse-risk AML [eg, 7q-, -7, inv(3), or t(3;3)]. RUNX1 mutations predicted for resistance to chemotherapy (rates of refractory disease 30% and 19%, P = .047, for RUNX1-mutated and wild-type patients, respectively), as well as inferior event-free survival (EFS; P < .0001), relapse-free survival (RFS, P = .022), and overall survival (P = .051). In multivariable analysis, RUNX1 mutations were an independent prognostic marker for shorter EFS (P = .007). Explorative subgroup analysis revealed that allogeneic hematopoietic stem-cell transplantation had a favorable impact on RFS in RUNX1-mutated patients (P < .0001).

CONCLUSION

AML with RUNX1 mutations are characterized by distinct genetic properties and are associated with resistance to therapy and inferior outcome.

Molecular mechanisms involved in the progression of myelodysplastic syndrome

Myelodysplastic syndromes (MDS) are a heterogeneous group of diseases characterized by ineffective hematopoiesis presenting with peripheral cytopenias in combination with a hyperplastic bone marrow. MDS patients have an increased risk of disease evolution to acute leukemia. Strong efforts have been made to gain further insights into the pathobiology of MDS. Development and progression of MDS to acute myeloid leukemia is suggested to be a multistep alteration to hematopoietic stem cells consisting of class I and class II alterations: the former targeting genes that are involved in signal transduction (e.g., FLT3, RAS and KIT), whereas the latter affect transcription factors (e.g., RUNX, RARA, EVI1 and WT1). These alterations consist of not only genomic mutations but also epigenetic aberrations, which can lead to reversible gene silencing. However, whether numerical and structural alterations of chromosomes and/or single genes or epigenetic changes represent the initiating event or, more likely, secondary events remains part of the discussion. Accumulation of such defects may finally cause the leukemic transformation of MDS.

AML1/RUNX1 mutations in 470 adult patients with de novo acute myeloid leukemia: prognostic implication and interaction with other gene alterations

Somatic mutation of the AML1/RUNX1(RUNX1) gene is seen in acute myeloid leukemia (AML) M0 subtype and in AML transformed from myelodysplastic syndrome, but the impact of this gene mutation on survival in AML patients remains unclear. In this study, we sought to determine the clinical implications of RUNX1 mutations in 470 adult patients with de novo non-M3 AML. Sixty-three distinct RUNX1 mutations were identified in 62 persons (13.2%); 32 were in N-terminal and 31, C-terminal. The RUNX1 mutation was closely associated with male sex, older age, lower lactic dehydrogenase value, French-American-British M0/M1 subtypes, and expression of HLA-DR and CD34, but inversely correlated with CD33, CD15, CD19, and CD56 expression. Furthermore, the mutation was positively associated with MLL/PTD but negatively associated with CEBPA and NPM1 mutations. AML patients with RUNX1 mutations had a significantly lower complete remission rate and shorter disease-free and overall survival than those without the mutation. Multivariate analysis demonstrated that RUNX1 mutation was an independent poor prognostic factor for overall survival. Sequential analysis in 133 patients revealed that none acquired novel RUNX1 mutations during clinical courses. Our findings provide evidence that RUNX1 mutations are associated with distinct biologic and clinical characteristics and poor prognosis in patients with de novo AML.

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.

Lineage-specific transcription factor aberrations in AML

Transcription factors play a key role in the commitment of hematopoietic stem cells to differentiate into specific lineages [78]. This is particularly important in that a block in terminal differentiation is the key contributing factor in acute leukemias. This general theme of the role of transcription factors in differentiation may also extend to other tissues, both in terms of normal development and cancer. Consistent with the role of transcription factors in hematopoietic lineage commitment is the frequent finding of aberrations in transcription factors in AML patients. Here, we intend to review recent findings on aberrations in lineage-restricted transcription factors as observed in patients with acute myeloid leukemia (AML).

Five new pedigrees with inherited RUNX1 mutations causing familial platelet disorder with propensity to myeloid malignancy

Familial platelet disorder with propensity to myeloid malignancy (FPD/AML) is an autosomal dominant syndrome characterized by platelet abnormalities and a predisposition to myelodysplasia (MDS) and/or acute myeloid leukemia (AML). The disorder, caused by inherited mutations in RUNX1, is uncommon with only 14 pedigrees reported. We screened 10 families with a history of more than one first degree relative with MDS/AML for inherited mutations in RUNX1. Germ- line RUNX1 mutations were identified in 5 pedigrees with a 3:2 predominance of N-terminal mutations. Several affected members had normal platelet counts or platelet function, features not previously reported in FPD/AML. The median incidence of MDS/AML among carriers of RUNX1 mutation was 35%. Individual treatments varied but included hematopoietic stem cell transplantation from siblings before recognition of the inherited leukemogenic mutation. Transplantation was associated with a high incidence of complications including early relapse, failure of engraftment, and posttransplantation lymphoproliferative disorder. Given the small size of modern families and the clinical heterogeneity of this syndrome, the diagnosis of FPD/AML could be easily overlooked and may be more prevalent than previously recognized. Therefore, it would appear prudent to screen young patients with MDS/AML for RUNX1 mutation, before consideration of sibling hematopoietic stem cell transplantation.

Cooperating gene mutations in acute myeloid leukemia: a review of the literature

Acute myeloid leukemia (AML) is a heterogeneous group of neoplastic disorders with great variability in clinical course and response to therapy, as well as in the genetic and molecular basis of the pathology. Major advances in the understanding of leukemogenesis have been made by the characterization and the study of acquired cytogenetic abnormalities, particularly reciprocal translocations observed in AML. Besides these major cytogenetic abnormalities, gene mutations also constitute key events in AML pathogenesis. In this review, we describe the contribution of known gene mutations to the understanding of AML pathogenesis and their clinical significance. To gain more insight in this understanding, we clustered these alterations in three groups: (1) mutations affecting genes that contribute to cell proliferation (FLT3, c-KIT, RAS, protein tyrosine standard phosphatase nonreceptor 11); (2) mutations affecting genes involved in myeloid differentiation (AML1 and CEBPA) and (3) mutations affecting genes implicated in cell cycle regulation or apoptosis (P53, NPM1). This nonexhaustive review aims to show how gene mutations interact with each other, how they contribute to refine prognosis and how they can be useful for risk-adapted therapeutic management of AML patients.

AML1 mutations induced MDS and MDS/AML in a mouse BMT model

Myelodysplastic syndrome (MDS) is a hematopoietic stem-cell disorder characterized by trilineage dysplasia and susceptibility to acute myelogenous leukemia (AML). Analysis of molecular basis of MDS has been hampered by the heterogeneity of the disease. Recently, mutations of the transcription factor AML1/RUNX1 have been identified in 15% to 40% of MDS-refractory anemia with excess of blasts (RAEB) and MDS/AML. We performed mouse bone marrow transplantation (BMT) using bone marrow cells transduced with the AML1 mutants. Most mice developed MDS and MDS/AML-like symptoms within 4 to 13 months after BMT. Interestingly, among integration sites identified, Evi1 seemed to collaborate with an AML1 mutant harboring a point mutation in the Runt homology domain (D171N) to induce MDS/AML with an identical phenotype characterized by marked hepatosplenomegaly, myeloid dysplasia, leukocytosis, and biphenotypic surface markers. Collaboration between AML1-D171N and Evi1 was confirmed by a BMT model where coexpression of AML1-D171N and Evi1 induced acute leukemia of the same phenotype with much shorter latencies. On the other hand, a C-terminal truncated AML1 mutant (S291fsX300) induced pancytopenia with erythroid dysplasia in transplanted mice, followed by progression to MDS-RAEB or MDS/AML. Thus, we have developed a useful mouse model of MDS/AML that should help in the understanding of the molecular basis of MDS and the progression of MDS to overt leukemia.

Transcriptional dysregulation during myeloid transformation in AML

The current paradigm on leukemogenesis indicates that leukemias are propagated by leukemic stem cells. The genomic events and pathways involved in the transformation of hematopoietic precursors into leukemic stem cells are increasingly understood. This concept is based on genomic mutations or functional dysregulation of transcription factors in malignant cells of patients with acute myeloid leukemia (AML). Loss of the CCAAT/enhancer binding protein-alpha (CEBPA) function in myeloid cells in vitro and in vivo leads to a differentiation block, similar to that observed in blasts from AML patients. CEBPA alterations in specific subgroups of AML comprise genomic mutations leading to dominant-negative mutant proteins, transcriptional suppression by leukemic fusion proteins, translational inhibition by activated RNA-binding proteins, and functional inhibition by phosphorylation or increased proteasomal-dependent degradation. The PU.1 gene can be mutated or its expression or function can be blocked by leukemogenic fusion proteins in AML. Point mutations in the RUNX1/AML1 gene are also observed in specific subtypes of AML, in addition to RUNX1 being the most frequent target for chromosomal translocation in AML. These data are persuasive evidence that impaired function of particular transcription factors contributes directly to the development of human AML, and restoring their function represents a promising target for novel therapeutic strategies in AML.

Insight into the molecular pathogenesis of myeloid malignancies

PURPOSE OF REVIEW

Molecular mutations play an increasing role for classification, prognostication, and therapeutic strategies in acute myeloid leukemia and myelodysplastic syndrome. Due to the rapid expansion of known molecular markers, this paper aims to outline some of the recent progress to improve understanding of the pathogenesis in these myeloid malignancies.

RECENT FINDINGS

Novel concepts conceive myelodysplastic syndrome and acute myeloid leukemia as endpoints of a continuous process of leukemogenesis, which is characterized by the interaction of mutations interfering with transcription and differentiation with activating mutations enhancing proliferation. The detection of novel molecular mutations such as NPM1 widened the spectrum of molecular markers in acute myeloid leukemia. Finally, attention focusses on detailed subtyping of already known molecular markers.

SUMMARY

The fast progress in the molecular characterization of acute myeloid leukemia and myelodysplastic syndrome in recent years provides the basis for an optimization of therapeutic concepts. The introduction of new methods such as gene expression profiling catalyzes this process.

Expression of human liver HSPGs on acute myeloid leukemia

Heparan sulfate proteoglycans (HSPGs) play important biological roles in cell-matrix adhesion processes and are essential regulators of growth actions. The expression of the different HSPGs in itself is tightly regulated providing strict controls on the activities of the bound ligands. Human liver is a target for a number of pathogens, and HSPGs have been demonstrated in several cases to play a pivotal role in infectivity. Despite HSPGs important biological functions, little is known about its cell-specific distribution patterns. Human liver HSPG was isolated, and a specific monoclonal antibody (mAb) 1E4-1C2 was produced. Distribution of HSPG reactive to this mAb was studied in normal blood cells, hematopoietic cell lines and blood cells isolated from patients with various hematologic disorders using indirect immunofluorescence. There was no expression of molecules recognized by this mAb on lymphoid (Daudi, Jurkat, SupT-1) and monocytoid (U937) cell lines. Peripheral blood cells, normal bone marrow, together with leukocytes isolated from patients with acute lymphoblastic leukemia, chronic myelocytic leukemia, Hodgkin's disease or Non-Hodgkin's lymphoma, were also negative. In contrast, 1E4-1C2 showed significant positive results on human myeloid cell lines HL-60 and K562. Moreover, it is interesting that this mAb also recognized epitopes on leukocytes isolated from acute myeloblastic leukemia. These results suggest that malignancies of cells in myeloid lineage may cause expression of HSPGs that are detected by this specific mAb, making it a potential co-marker for the diagnosis of acute myeloid leukemia.

Normal and transforming functions of RUNX1: a perspective

Converging studies from many investigators indicate that RUNX1 has a critical role in the correct maintenance of essential cellular functions during embryonic development and after birth. The discovery that this gene is also frequently mutated in human leukemia has increased the interest in the role that RUNX1 plays in both normal and transforming pathways. Here, we provide an overview of the many roles of RUNX1 in hematopoietic self-renewal and differentiation and summarize the information that is currently available on the many mechanisms of RUNX1 deregulation in human leukemia.

Loss of Runx1 perturbs adult hematopoiesis and is associated with a myeloproliferative phenotype

Homozygous loss of function of Runx1 (Runt-related transcription factor 1 gene) during murine development results in an embryonic lethal phenotype characterized by a complete lack of definitive hematopoiesis. In light of recent reports of disparate requirements for hematopoietic transcription factors during development as opposed to adult hematopoiesis, we used a conditional gene-targeting strategy to effect the loss of Runx1 function in adult mice. In contrast with the critical role of Runx1 during development, Runx1 was not essential for hematopoiesis in the adult hematopoietic compartment, though a number of significant hematopoietic abnormalities were observed. Runx1 excision had lineage-specific effects on B- and T-cell maturation and pronounced inhibition of common lymphocyte progenitor production. Runx1 excision also resulted in inefficient platelet production. Of note, Runx1-deficient mice developed a mild myeloproliferative phenotype characterized by an increase in peripheral blood neutrophils, an increase in myeloid progenitor populations, and extramedullary hematopoiesis composed of maturing myeloid and erythroid elements. These findings indicate that Runx1 deficiency has markedly different consequences during development compared with adult hematopoiesis, and they provide insight into the phenotypic manifestations of Runx1 deficiency in hematopoietic malignancies.

Point mutations in the RUNX1/AML1 gene: another actor in RUNX leukemia

The RUNX1/AML1 gene is the most frequent target for chromosomal translocation in leukemia. In addition, recent studies have demonstrated point mutations in the RUNX1 gene as another mode of genetic alteration in development of leukemia. Monoallelic germline mutations in RUNX1 result in familial platelet disorder predisposed to acute myelogenous leukemia (FPD/AML). Sporadic point mutations are frequently found in three leukemia entities: AML M0 subtype, MDS-AML, and secondary (therapy-related) MDS/AML. Therapy-related leukemias resulting from anticancer treatments are not uncommon, and the incidence of RUNX1 point mutations appears comparable to the incidence of the t(8;21) AML M2 subtype and the inv(16) AML M4Eo subtype. Half of the point mutations in M0 cases are biallelic, although the frequency varies with ethnicity. Most of the RUNX1 mutations are clustered in the Runt domain and result in defective DNA binding but active beta-subunit binding, which is consistent with three-dimensional structural findings and may explain the dominant inhibitory effects. Unlike the classical tumor suppressor genes requiring biallelic inactivation, haploinsufficient RUNX1 is apparently leukemogenic. However, RUNX1 abnormalities per se are insufficient to cause full-blown leukemia. Intensive investigation of cooperating genetic alterations should elucidate leukemic mechanisms.

Adult acute myeloid leukaemia

The curability of acute myeloid leukaemia (AML) in a fraction of adult patients was demonstrated a long time ago. Currently, the probability of cure is consistently above fifty per cent in patients with de novo disease expressing favourable-risk associated cytogenetic features. Even better, the cure rate exceeds 75% in the acute promyelocytic subtype since the introduction of retinoic acid-containing regimens. In the meantime, continuing progress in supportive care systems and stem cell transplant procedures is making myeloablative therapies, when needed, somewhat less toxic-and thereby more effective-than in the recent past. Therefore, evidence is accumulating to indicate an improved therapeutic trend over the years, with the notable exception of older (>55 years) patients with adverse-risk chromosomal aberrations and/or leukemia secondary to myelodysplasia or prior cancer-related chemotherapy and/or radiotherapy. This review conveys the many facets of this progress, focusing on diagnostic subsets, risk classes, newer biological issues and conventional as well as innovative therapeutic interventions with or without autologous/allogeneic stem cell transplantation.

Deletion of one copy of the p16INK4A tumor suppressor gene is implicated as a predisposing factor in pediatric leukemia

The p16INK4A tumor suppressor gene is frequently disrupted by mutation or deletion in a wide range of cancer types, ranging from leukemia to cancers of the bladder, skin, lung, liver, and spleen. We have previously shown that deletion of at least one copy of the p16INK4A gene is associated with an increased risk of relapse in pediatric leukemia. Our data suggest that hemizygous p16INK4A deletion may be constitutional, conferring susceptibility to leukemia. Confirmation of this association is worthy of a larger study. Data from primary leukemia specimens are also presented here which examined the possibility that the remaining allele of the gene was inactivated by another mechanism such as mutation or was silenced by methylation. These possibilities were formally excluded in a case of hemizygous loss of the p16INK4A gene in leukemia, establishing that in this case the p16INK4A deletion was either semidominant or fully haploinsufficient for relapse susceptibility in this disease. Implementation of high throughput methods such as those used here for detecting hemizygous loss of tumor suppressor genes will become increasingly important for molecular diagnosis of cancer. This is particularly true for the emerging class of tumor suppressor genes where deletion of one allele is sufficient to confer cancer susceptibility or poor prognosis with standard treatment.

Novel loss-of-function mutations of the haematopoiesis-related transcription factor, acute myeloid leukaemia 1/runt-related transcription factor 1, detected in acute myeloblastic leukaemia and myelodysplastic syndrome

AML1/RUNX1, which encodes a transcription factor essential for definitive haematopoiesis, is a frequent target of leukaemia-associated chromosome translocations. Point mutations of this gene have also recently been associated with leukaemia and myelodysplastic syndrome (MDS). To further define the frequency and biological characteristics of AML1 mutations, we have examined 170 cases of such diseases. Mutations within the runt-domain were identified in five cases: one of de novo acute myeloid leukaemia (AML) and four of MDS. Where multiple time point samples were available, mutations were detected in the earliest samples, which persisted throughout the disease course. Of the five mutations, one was a silent mutation, two were apparent loss-of-function mutations caused by N-terminal truncation, and two were insertions, I150ins and K168ins, which preserved most of the AML1 DNA-binding domain. Both AML1 molecules with insertion mutations were non-functional in that they were unable to rescue haematological defects in AML1-deficient mouse embryonic stem cells. In addition, activating mutations of N-ras, deletion of chromosome 12p, or inactivation of TP53 accompanied some of the AML1 mutations. Together, these observations strongly suggest that one-allele inactivation of AML1 serves as an initial or early event that plays an important role in the eventual development of overt diseases with additional genetic alterations.

Dual mutations in the AML1 and FLT3 genes are associated with leukemogenesis in acute myeloblastic leukemia of the M0 subtype

Point mutations of the transcription factor AML1 are associated with leukemogenesis in acute myeloblastic leukemia (AML). Internal tandem duplications (ITDs) in the juxtamembrane domain and mutations in the second tyrosine kinase domain of the Fms-like tyrosine kinase 3 (FLT3) gene represent the most frequent genetic alterations in AML. However, such mutations per se appear to be insufficient for leukemic transformation. To evaluate whether both AML1 and FLT3 mutations contribute to leukemogenesis, we analyzed mutations of these genes in AML M0 subtype in whom AML1 mutations were predominantly observed. Of 51 patients, eight showed a mutation in the Runt domain of the AML1 gene: one heterozygous missense mutation with normal function, five heterozygous frameshift mutations and two biallelic nonsense or frameshift mutations, resulting in haploinsufficiency or complete loss of the AML1 activities. On the other hand, a total of 10 of 49 patients examined had the FLT3 mutation. We detected the FLT3 mutation in five of eight (63%) patients with AML1 mutation, whereas five of 41 (12%) without AML1 mutation showed the FLT3 mutation (P=0.0055). These observations suggest that reduced AML1 activities predispose cells to the acquisition of the activating FLT3 mutation as a secondary event leading to full transformation in AML M0.

Familial platelet disorder with propensity to acute myelogenous leukemia: Genetic heterogeneity and progression to leukemia via acquisition of clonal chromosome anomalies

Familial platelet disorder with propensity to acute myelogenous leukemia, or FPD/AML (OMIM #601399), is a rare autosomal dominant condition, with only 12 families reported. It is characterized by qualitative and quantitative platelet defects and predisposition to the development of myeloid malignancies. Causal mutations have been identified in the RUNX1 gene (also known as AML1, CBFA2) in the 11 families so far analyzed. RUNX1 is a gene frequently involved in the pathogenesis of sporadic leukemia and myelodysplastic syndromes, through acquired chromosome rearrangements and point mutations. We report an Italian family with three members affected with FPD/AML, two sibs and their father, who developed myelodysplastic syndromes (which in one subsequently evolved into AML). Direct sequencing and polymorphisms haplotype analysis of the region of chromosome 21 where RUNX1 is mapped demonstrated that FPD/AML in this family was not caused by any mutation of the RUNX1 gene, thus providing evidence for the genetic heterogeneity of this disorder. Cytogenetic studies showed monosomy 7 in the marrow of all the three affected subjects, as well as an independent clone with trisomy 8 in the father. The importance of mutator effects in the pathogenesis of familial myeloid malignancies characterized by relevant chromosome changes, in the presence or absence of an underlying Mendelian disorder, has already been suggested. Our results and a review of the cytogenetic literature led us to postulate that mutations also causing FPD/AML may have a mutator effect that could give origin to myelodysplastic syndromes and acute myeloid leukemias through acquired chromosome changes.

High incidence of somatic mutations in the AML1/RUNX1 gene in myelodysplastic syndrome and low blast percentage myeloid leukemia with myelodysplasia

A high incidence of somatically acquired point mutations in the AML1/RUNX1 gene has been reported in poorly differentiated acute myeloid leukemia (AML, M0) and in radiation-associated and therapy-related myelodysplastic syndrome (MDS) or AML. The vast majority of AML1 mutations identified in these diseases were localized in the amino (N)-terminal region, especially in the DNA-binding Runt homology domain. In this report, we show that AML1 point mutations were found in 26 (23.6%) of 110 patients with refractory anemia with excess blasts (RAEB), RAEB in transformation (RAEBt), and AML following MDS (defined these 3 disease categories as MDS/AML). Among them, 9 (8.2%) mutations occurred in the carboxy (C)-terminal region, which were exclusively found in MDS/AML and were strongly correlated with sporadic MDS/AML. All patients with MDS/AML with an AML1 mutation expressed wild-type AML1 protein and had a significantly worse prognosis than those without AML1 mutations. Most AML1 mutants lost trans-activation potential, regardless of their DNA binding potential. These data suggested that AML1 point mutation is one of the major driving forces of MDS/AML, and these mutations may represent a distinct clinicopathologic-genetic entity.

A pilot study of high-throughput, sequence-based mutational profiling of primary human acute myeloid leukemia cell genomes

In this pilot study, we used primary human acute myeloid leukemia (AML) cell genomes as templates for exonic PCR amplification, followed by high-throughput resequencing, analyzing approximately 7 million base pairs of DNA from 140 AML samples and 48 controls. We identified six previously described, and seven previously undescribed sequence changes that may be relevant for AML pathogenesis. Because the sequencing templates were generated from primary AML cells, the technique favors the detection of mutations from the most dominant clones within the tumor cell mixture. This strategy represents a viable approach for the detection of potentially relevant, nonrandom mutations in primary human cancer cell genomes.

AML1/RUNX1 mutations are infrequent, but related to AML-M0, acquired trisomy 21, and leukemic transformation in pediatric hematologic malignancies

AML1/RUNX1, located on chromosome band 21q22, is one of the most important hematopoietic transcription factors. AML1 is frequently affected in leukemia and myelodysplastic syndrome with 21q22 translocations. Recently, AML1 mutations were found in adult hematologic malignancies, especially acute myeloid leukemia (AML)-M0 or leukemia with acquired trisomy 21, and familial platelet disorder with a predisposition toward AML. Through the use of polymerase chain reaction-single-strand conformation polymorphism analysis, we examined the AML1 gene for mutations in 241 patients with pediatric hematologic malignancies, and we detected AML1 mutations in seven patients (2.9%). Deletion was found in one patient, and point mutations in four patients, including three missense mutations, two silent mutations, and one mutation within an intron resulting in an abnormal splice acceptor site. All of the mutations except for one were heterozygous. Mutations within the runt domain were found in six of seven patients. Six of seven patients with AML1 mutations were diagnosed with AML, and one had acute lymphoblastic leukemia. In three of these seven patients, AML evolved from other hematologic disorders. AML1 mutations were found in two of four AML-M0 and two of three patients with acquired trisomy 21. Patients with AML1 mutations tended to be older children. Three of four patients with AML1 mutations who received stem cell transplantation (SCT) are alive, whereas the remaining three patients with mutations without SCT died. These results suggest that AML1 mutations in pediatric hematologic malignancies are infrequent, but are possibly related to AML-M0, acquired trisomy 21, and leukemic transformation. These patients may have a poor clinical outcome.

Energetic contribution of residues in the Runx1 Runt domain to DNA binding

Core-binding factors (CBFs) are a small family of heterodimeric transcription factors that play critical roles in hematopoiesis and in the development of bone, stomach epithelium, and proprioceptive neurons. Mutations in CBF genes are found in leukemias, bone disorders, and gastric cancer. CBFs consist of a DNA-binding CBF alpha subunit and a non-DNA-binding CBF beta subunit. DNA binding and heterodimerization with CBF beta are mediated by the Runt domain in CBF alpha. Here we report an alanine-scanning mutagenesis study of the Runt domain that targeted amino acids identified by structural studies to reside at the DNA or CBF beta interface, as well as amino acids mutated in human disease. We determined the energy contributed by each of the DNA-contacting residues in the Runt domain to DNA binding both in the absence and presence of CBF beta. We propose mechanisms by which mutations in the Runt domain found in hematopoietic and bone disorders affect its affinity for DNA.

Structural and functional characterization of Runx1, CBF beta, and CBF beta-SMMHC

Core binding factors (CBFs) are heterodimeric transcription factors consisting of a DNA-binding CBF alpha subunit and non-DNA-binding CBF beta subunit. DNA binding and heterodimerization is mediated by a single domain in the CBF alpha subunit called the Runt domain, while sequences flanking the Runt domain confer other biochemical activities such as transactivation. On the other hand, the heterodimerization domain in CBF beta is the only functional domain that has been identified in this subunit. The biophysical properties of the Runt domain and the CBF beta heterodimerization domain, and the structures of the isolated domains as well as of the Runt domain-DNA, Runt domain-CBF beta, and ternary Runt domain-CBF beta-DNA complexes, have been characterized over the past several years, and are summarized in this review.

Identification of RUNX1/AML1 as a classical tumor suppressor gene

Based on our previous results indicating the presence of a tumor suppressor gene (TSG), chromosome 21 was analysed for loss of heterozygosity (LOH) in 18 patients with acute myeloid leukemia (17, AML-M0; one, AML-M1). Allelotyping at polymorphic loci was performed on purified material, allowing unequivocal detection of allelic loss and homozygous deletions. Six AML-M0 patients shared a common region of LOH harboring a single gene: RUNX1 (AML1), the most frequent site of translocations in acute leukemia and a well-known fusion oncogene. Fluorescence in situ hybridization allowed the identification of deletions with breakpoints within RUNX1 in two patients as the cause of LOH. In the four others the LOH pattern and the presence of two karyotypically normal chromosomes 21 were in line with mitotic recombination. Further molecular and cytogenetic analyses showed that this caused homozygosity of primary RUNX1 mutations: two point mutations, a partial deletion and, most significantly, a complete deletion of RUNX1. These findings identify RUNX1 as a classical TSG: both alleles are mutated or absent in cancer cells from four of the 17 AML-M0 patients examined. In contrast to AML-M0, the AML-M1 patient was trisomic for chromosome 21 and has two mutated and one normal RUNX1 allele, suggesting that the order of mutagenic events leading to leukemia may influence the predominant tumor type.

New mechanisms of AML1 gene alteration in hematological malignancies

The human AML1 gene (also named CBFA2 or RUNX1), located in the 21q22 chromosomal band, encodes for one of the two subunits forming a heterodimeric transcription factor, the human core binding factor (CBF). AML1 protein contains a highly evolutionary conserved domain of 128 amino acids called runt domain, responsible for both heterodimerization with the beta subunit of CBF and for DNA binding. AML1 is normally expressed in all hematopoietic lineages and acts to regulate the expression of various genes specific to hematopoiesis playing a pivotal role in myeloid differentiation. AML1 is one of the genes most frequently deregulated in leukemia through different mechanisms including translocation, mutation and amplification. Translocations lead to the formation of fusion genes encoding for chimerical proteins such as AML1-ETO which induces leukemogenesis. Recently, new mechanisms of AML1 deregulation by point mutations or amplification have been reported. To our knowledge, 51 patients (among 805 studied) with AML1 point mutations have been described. Forty of them have acute myeloid leukemia (AML) most often M0 AML. In this subtype of AML, the frequency of AML1 mutation is significantly higher; 21.5% of patients mutated (34/158). Mutations have also been found with lower frequency in other FAB subtype AML (6 cases), in myeloproliferative disorders (6 cases), in myelodysplastic syndrome (3 cases) and rarely in acute lymphoblastic leukemia (1 case). AML1 gene amplification has been found essentially in childhood ALL (12 cases) and more rarely in myeloid malignancies (4 cases). Here, we reviewed all these cases of AML1 point mutations and amplification and focused on the mechanisms of AML1 deregulation induced by these alterations.