Investigations on the molecular consequences of chromosome 3q aberrations in myeloid Leukemia

Research project P 14101 Chromosome 3Q Aberrations in Myeloid Leukemia Rotraud WIESER 24.01.2000 Most leukemias as well as some solid tumors are characterized by the presence of recurrent clonal chromosome aberrations. Cytogenetic and molecular investigations on these rearrangements have yielded important insights into the mechanism of tumorigenesis, provided diagnostic tools, and are expected to lead to improved therapies for maligant diseases. Chromosome rearrangements that simultaneously affect bands 3q2l and 3q26 are observed in a subgroup of patients with myeloid leukemias, and are associated with aggressive disease and poor survival, as well as abnormal megakaryopoiesis. A candidate oncogene, EVI-1, has been identified in 3q26, and a number of studies support the assumption that this transcription factor is involved in leukemogenesis. More recent results indicate that the use of alternative first exons leads to the formation of a transcription activating and a repressing form of the EVI- I protein, thus raising a number of questions about the role that either of these two factors and their mutual antagonism play in normal and malignant cells. Since the known properties of EVI-1 do not explain all the features of leukemias with 3q aberrations, genes in 3q21 are likely to contribute to these characteristics. Recent data from our laboratory indicate that the transcription factor GATA-2 might be a target of chromosome breaks in 3q2l. However, a possible leukemogenic role for GATA-2 needs to be confirmed, and other, in part still unknown genes in the 3q21 breakpoint region have to be considered as candidate oncogenes. Based on published results from other groups and our own previous studies, the following goals shall be pursued in the proposed project: 1. Further characterization of the transcription factor EVI-1. In order to better understand the biological function of the antagonism between the two forms of EVI-1, it is important to learn more about what regulates the expression of each of these two factors, as well as about their target genes. In addition, the interaction between EVI-1 and the transcriptional corepressor, histone deacetylase, shall be studied. 2. Search for oncogenes in 3 q2 1. The possible role of the transcription factor GATA-2 as an oncogene shall be further investigated. In order to obtain a more complete picture about potential targets of 3q2l rearrangements, additional genes in the relevant region shall be cloned and characterized.

The goal of this project was the molecular characterization of rearrangements of human chromosome 3, which contribute to the emergence of a particularly aggressive form of leukemia. Patients with malignant diseases of the hematopoietic system, that is, leukemias and related disorders, often exhibit abnormal, rearranged chromosomes. These aberrations are recurrent and somatically acquired, meaning that the same type of aberration is observed in different patients, and that the rearrangements are present only in the malignant cells, but not in other body cells. The presence or absence of certain chromosome rearrangements constitutes an important prognostic factor. Furthermore, in some cases the identification and analysis of the genes affected and altered by such rearrangements has led to the development of new and more specific treatment modalities. Aberrations of chromosome 3 that simultaneously involve the chromosomal regions 3q21 and 3q26 are associated with a particularly dismal prognosis, because the affected patients respond poorly, if at all, to conventional antileukemic treatment. Despite of its clinical importance, comparatively little is known about the molecular consequences of this specific type of rearrangement. A potential oncogene (i.e., a gene whose inappropriate activation promotes tumor formation), EVI1, is located in 3q26, and its expression appears to be activated in cells with rearrangements of this region. However, the function of this gene in normal and leukemic cells is only partially understood, and a possible contribution to leukemogenesis of genes in 3q21 has been explored only insufficiently. In the course of project P14101-B04, progress was achieved in three major areas: 1) Interphase fluorescence in situ hybridization (FISH) assays were established that allow the rapid diagnosis of rearrangements of chromosome regions 3q21 and 3q26, and that can furthermore be used to monitor the disease of affected patients, i.e., to determine, in a quantitative manner, the response to therapy as well as disease progression. 2) The potential contribution to leukemia formation of GATA-2, a candidate oncogene that we had previously found to be located in close vicinity of the 3q21 breakpoint region, was investigated. However, the results of these experiments did not yield further support for a possible role of GATA-2 in the emergence of leukemia. 3) The expression and function of EVI1 and a variant form of this gene, MDS1/EVI1, were analyzed. MDS1/EVI1, even though only slightly different from EVI1, had been claimed by other researchers not to be activated by 3q aberrations, and to oppose the cellular actions of EVI1. In contrast to these results, we found that both EVI1 and MDS1/EVI1 may be aberrantly expressed in leukemia patients, and that both gene products affect the regulation of other genes in a similar way. We could show that they do so at least in part through a factor, histone deacetylase, that also plays a role in the functioning of other leukemia associated onocogenes, and may therefore represent a target for specifically designed antileukemic therapy.