| PURPOSE: Leukemia is characterized by genetic disruption of the balance between proliferation, differentiation and apoptosis in immature blood cells, which do not follow the normal path of differentiation. Cytogenetic abnormalities have proven to be very relevant for diagnosis and prognosis, and the presence of some of these is related to the response to chemotherapy. In Rotterdam, we recently described a novel recurrent translocation between chromosomes 7 and 12: t(7;12)(q36;p13), so far almost exclusively found in myeloid malignancies in children younger than 18 months of age. Survival data of these patients suggest that the presence of the t(7;12) confers a poor prognosis. Furthermore, we were the first to identify the homeobox gene HLXB9 (7q36) to be the partner gene of ETV6 (12p13) in this translocation, using material from two of our cases. The HLXB9 gene is known to be highly expressed in immature, CD34+, hematopoietic cells, and acute leukemias and is found mutated in the dominantly inherited Currarino syndrome. It is the first time, however, that this gene was reported to be involved in leukemogenesis. AIM: In this project we want to (1) characterize the t(7;12)(q36;p13) and the involved genes in more detail. (2) In addition we want to investigate HLXB9 and ETV6 and the corresponding fusion gene with respect to their relation to treatment outcome and (3) we want to investigate their roles in the development and progression of leukemia and normal hematopoiesis. PLAN OF INVESTIGATION: - 1. Detailed genetic characterization of the t(7;12)(q36;p13) in patients. Investigations will be carried out to determine if HLXB9 is involved in all cases with t(7;12), since breakpoint heterogeneity has been suggested and if the HLXB9-ETV6 fusion product is identical in every patient. Infant ALL cases without MLL rearrangements and other childhood and adult leukemia cases will be analyzed to determine the incidence of the t(7;12) and the involvement of HLXB9 in other leukemia-associated rearrangements. HLXB9 expression will be determined in normal and leukemic bone marrow and expression of HLXB9, ETV6 and the fusion transcript will be quantified in the t(7;12)+ and t(7;12)- cases in both infant, childhood and adult cases. Different genetic subgroups will be compared. Considering the very young age of the patients, analysis of the neonatal blood spots will be carried out to confirm that the leukemia already started in utero. - 2. Relation t(7;12) and therapy outcome. In vitro drug sensitivity profiles will be obtained and compared to other childhood and infant leukemia subgroups. Micro-array analysis of t(7;12)+ leukemias and comparison to other genetic subgroups allows us to determine if t(7;12)+ leukemia is a different entity and if genes/pathways are involved that explain association with poor treatment outcome. - 3. Role in HLXB9-ETV6, HLXB9 and ETV6 in leukemogenesis and hematopoiesis (fluorescently) tagged constructs of HLXB9-ETV6, HLXB9 and ETV6 will be generated. These constructs will be transfected to mouse NIH3T3, D32, or BaF3 cell lines, all well characterized with respect to proliferation, differentiation and apoptosis. These model systems allow additional elucidation of the role of HLXB9-ETV6, HLXB9 and ETV6 in leukemogenesis and hematopoiesis. POSSIBLE RESULTS / RELEVANCE FOR CANCER RESEARCH: The combined expertise in this joint, ambitious, project of the Laboratories of Tumor Cytogenetics and Pediatric Oncology/Hematology creates unique possibilities for the investigation of this type of leukemia. This might possibly result in better treatment strategies and it is anticipated that new insights will be gained into the functioning of ETV6 and HLXB9 in hematopoiesis and leukemogenesis. |
