MAPPING AND CLONING TRANSLOCATION BREAKPOINTS

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DESCRIPTION: (adapted from the applicant's abstract) Malignant cells from human leukemia and lymphoma have a very high frequency of chromosome abnormalities, especially translocations. Careful cytogenetic analysis has defined the breakpoints in recurring chromosome rearrangements, and this has been the major tool leading to identification of genes critically involved in leukemia and lymphoma. Mapping and cloning chromosome translocation breakpoints in leukemia, lymphoma and sarcoma have been one of the most efficient ways to discover new genes that are important in malignant transformation of hematopoietic cells. Although most of the common recurring rearrangements in leukemia have been cloned, the mapping and cloning of rare rearrangements continues to provide a wealth of biologically relevant information. The long-term goal of this project is to identify new genes involved in leukemia and lymphoma. The strategy will be to use translocation breakpoints to identify the chromosome location of the involved genes using defined genomic probes and fluorescence in situ hybridization (FISH). Samples containing malignant cells will be analyzed from two groups. The first group will be patients known to have rearrangements of MLL, TEL, or AML1 (Specific Aim 1). These three genes are very important in human acute leukemia as well as in other hematologic diseases. They have been shown to be involved in translocations with many other genes. Cloning these partner genes has identified a large number of previously unknown genes that play a role in transformation of hematopoietic cells. The second group includes patients with breakpoints in 11q, 12p, and 21q whose breaks do not involve MLL, TEL or AML1 (Specific Aim 2). The breakpoints of rearrangements in these three regions will be mapped using FISH to determine whether any of them cluster in a particular location. For translocations in which neither partner gene is known, probes that are split will be identified to determine the involved gene. DNA probes appropriate for the genes will be used to determine whether these "new" genes are involved in other rearrangements in samples that have the same breakpoint. Various cDNA selection strategies will be used to clone the involved gene as well as the partner gene. This research will identify genes involved in leukemogenesis and based on past results, most of these will be novel genes whose identification will enrich our understanding of the complex genetic changes involved in malignant transformation of hematopoietic cells. Identification of these genes has provided a very valuable resource for clinical medicine because they are used to improve the diagnostic precision with which the genotype of the malignant cells can be determined. Moreover, particular cytogenetic abnormalities have very great prognostic implications so that patients are stratified for treatment based on the karyotype of their malignant cells. The more translocations we can identify, the more complete will be our diagnostic tests. Especially with the advent of DNA chip technology, we could screen for all of the fusion genes and the prognostic implications of even rare rearrangements could be determined. In the future, when we have sufficient understanding of the biology of these genes, we can hope to develop genotypic specific treatment.