Mutational analyses of the AML1 gene in patients with myelodysplastic syndrome

Thermodynamic investigation of DNA-binding affinity of wild-type and mutant transcription factor RUNX1

Transcription factor RUNX1 and its binding partner CBFβ play a critical role in gene regulation for hematopoiesis. Mutations of RUNX1 cause ~10% of acute myeloid leukemia (AML) with a particularly poor prognosis. The current paradigm for the leukemogenesis is that insufficient activity of wild-type (WT) RUNX1 impairs hematopoietic differentiation. The majority of mutant RUNX1 proteins lose the DNA-binding affinity and inhibit WT RUNX1 by depletion of CBFβ. Here, isothermal titration calorimetry (ITC) was used to quantitatively study the interactions of WT and three clinical mutant RUNX1, CBFβ and DNA. Our data show that the binding of RUNX1 to DNA is enthalpy-driven, and the affinity decreases in the order of WT > S114L > R139Q >> K83E, which support previous observations and conclusion. To find potentially beneficial RUNX1 mutations that could increase the overall RUNX1 activity, K83R and H179K mutations of RUNX1 were designed, using structure-based computational modeling, and found to possess significantly higher DNA-binding affinities than does WT RUNX1. K83R and H179K mutant RUNX1 could therefore be protein-based RUNX1 activators.

Genetic testing in the myelodysplastic syndromes: molecular insights into hematologic diversity

The myelodysplastic syndromes (MDS) are associated with a diverse set of acquired somatic genetic abnormalities. Bone marrow karyotyping provides important diagnostic and prognostic information and should be attempted in all patients who are suspected of having MDS. Fluorescent in situ hybridization (FISH) studies on blood or marrow may also be valuable in selected cases, such as patients who may have 5q- syndrome or those who have undergone hematopoletic stem cell transplantation. The MDS-associated cytogenetic abnormalities that have been defined by karyotyping and FISH studies have already contributed substantially to our current understanding of the biology of malignant myeloid disorders, but the pathobiological meaning of common, recurrent chromosomal lesions such as del(5q), del(20q), and monosomy 7 is still unknown. The great diversity of the cytogenetic findings described in MDS highlights the molecular heterogeneity of this cluster of diseases. We review the common and pathophysiologically interesting genetic abnormalities associated with MDS, focusing on the clinical utility of conventional cytogenetic assays and selected FISH studies. In addition, we discuss a series of well-defined MDS-associated point mutations and outline the potential for further insights from newer techniques such as global gene expression profiling and array-based comparative genomic hybridization.

A Differential Gene Expression Profile Reveals Overexpression of RUNX1/AML1 in Invasive Endometrioid Carcinoma

Endometrial carcinoma is the most common gynecological malignant disease in industrialized countries. Two clinicopathological types of endometrial carcinoma have been described, based on estrogen relation and grade: endometrioid carcinoma (EEC) and non-EEC (NEEC). Some of the molecular events that occur during the development of endometrial carcinoma have been characterized, showing a dualistic genetic model for EEC and NEEC. However, the molecular bases for endometrial tumorigenesis are not clearly elucidated. In the present work, we attempted to identify new genes that could trigger cell transformation in EEC. We analyzed the differential gene expression profile between tumoral and nontumoral endometrial specimens with cDNA array hybridization. Among the 53 genes for which expression was found to be altered in EEC, the acute myeloid leukemia proto-oncogene, RUNX1/AML1, was one of the most highly up-regulated. The gene expression levels of RUNX1/AML1 were quantified by real-time quantitative PCR, and protein levels were characterized by tissue array immunohistochemistry. Real-time quantitative PCR validated RUNX1/AML1 up-regulation in EEC and demonstrated a specific and significantly stronger up-regulation in those tumor stages associated with myometrial invasion. Furthermore, tissue array immunohistochemistry showed that RUNX1/AML1 up-regulation correlates to the process of tumorigenesis, from normal atrophic endometrium to simple and complex hyperplasia and then, on to carcinoma. These results demonstrate for the first time the up-regulation of RUNX1/AML1 in EEC correlating with the initial steps of myometrial infiltration.

Lymphoid Enhancer Factor-1 Links Two Hereditary Leukemia Syndromes through Core-binding Factor α Regulation of ELA2

Two hereditary human leukemia syndromes are severe congenital neutropenia (SCN), caused by mutations in the gene ELA2, encoding the protease neutrophil elastase, and familial platelet disorder with acute myelogenous leukemia (AML), caused by mutations in the gene AML1, encoding the transcription factor core-binding factor alpha (CBFalpha). In mice, CBFalpha regulates the expression of ELA2, suggesting a common link for both diseases. However, gene-targeted mouse models have failed to reproduce either human disease, thus prohibiting further in vivo studies in mice. Here we investigate CBFalpha regulation of the human ELA2 promoter, taking advantage of bone marrow obtained from patients with either illness. In particular, we have identified novel ELA2 promoter substitutions (-199 C to A) within a potential motif for lymphoid enhancer factor-1 (LEF-1), a transcriptional mediator of Wnt/beta-catenin signaling, in SCN patients. The LEF-1 motif lies adjacent to a potential CBFalpha binding site that is in a different position in human compared with mouse ELA2. We find that LEF-1 and CBFalpha co-activate ELA2 expression. In vitro, the high mobility group domain of LEF-1 interacts with the runt DNA binding and proline-, serine-, threonine-rich activation domains of CBFalpha. ELA2 transcript levels are up-regulated in bone marrow of an SCN patient with the -199 C to A substitution. Conversely, a mutation of the CBFalpha activation domain, found in a patient with familial platelet disorder with AML, fails to stimulate the ELA2 promoter in vitro, and bone marrow correspondingly demonstrates reduced ELA2 transcript. Observations in these complementary patients indicate that LEF-1 cooperates with CBFalpha to activate ELA2 in vivo and also suggest the possibility that up-regulating promoter mutations can contribute to SCN. Two hereditary AML predisposition syndromes may therefore intersect via LEF-1, potentially linking them to more generalized cancer mechanisms.