Breakage and fusion of the TEL (ETV6) gene in immature B lymphocytes induced by apoptogenic signals

TEL-AML1 fusion resulting from the t(12; 21)(p13;q22) is one of the most co mmon genetic abnormalities in childhood acute lymphoblastic leukemia. Recen t findings that site-specific cleavage of the MLL gene can be induced by ch emotherapeutic agents such as topoisomerase-ll inhibitors suggest that apop togenic agents can cause chromosomal translocations in hematopoietic cells, This study demonstrates a possible relationship between exposure to apopto genic stimuli, TEL breaks, and the formation of TEL-AML1 fusion in immature B lymphocytes, Short-term culture of immature B cell lines in the presence of apoptogenic stimuli such as serum starvation, etoposide, or salicylic a cid induced double-strand breaks (DSBs) in intron 5 of the TEL gene and int ron 1 of the AML1 gene. TEL-AML1 fusion transcripts were also identified by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis in cell lines treated by serum starvation or aminophylline. DSBs within the TEL gen e were also associated with fusion to other unknown genes, presumably as a result of chromosomal translocation. We also examined 67 cord blood and 147 normal peripheral blood samples for the existence of inframe TEL-AML1 fusi on transcripts. One cord blood sample (1.5%) and 13 normal peripheral blood samples (8.8%) were positive as detected by nested RT-PCR, These data sugg est that breakage and fusion of TEL and AML I may be relatively common even ts and that sublethal apoptotic signals could play a role in initiating leu kemogenesis via the promotion of DNA damage. (C) 2001 by The American Socie ty of Hematology