Translocation t(6;9) in acute non-lymphocytic leukaemia results in the formation of a DEK-CAN fusion gene

Abstract

The t(6;9) that characterizes a specific subtype of ANLL fuses the 3' part of a gene located on chromosome 9q34, CAN, to the 5' part of a gene located on chromosome 6p23, DEK. On the 6p- chromosome, the resulting DEK-CAN fusion gene is transcribed into a leukaemia-specific 5.5 kb chimaeric mRNA that encodes a putative DEK-CAN fusion protein. No transcription could be detected from the reciprocal CAN-DEK fusion on chromosome 9q+. Analysis of 17 t(6;9) ANLL cases showed that the translocation breakpoints occur in a single intron of 7.5 kb in the CAN gene (ICB9) and in a single intron of 9 kb in the DEK gene (ICB6). As a result, the presence of a t(6;9) in blood or bone marrow cells can be faithfully diagnosed by Southern blotting. Moreover, the result of the translocation is an invariable DEK-CAN transcript, which can be sensitively monitored by RNA-PCR. Surprisingly, a SET-CAN fusion gene was found in leukaemic cells from a patient with AUL. Like CAN, SET is located on chromosome 9q34, which explains the apparently normal karyotype of the leukaemic cells. The occurrence of a SET-CAN fusion gene indicates that CAN may be the relevant oncogene involved in leukaemogenesis, and that activation of CAN can be effectuated through fusion of its 3' part to either DEK or SET. As yet, the function of CAN, DEK or SET is unknown. None of the proteins shows consistent homology to any known protein sequences. However, preliminary localization data and analysis of sequence motifs suggested that DEK-CAN may have a role in transcription regulation. CAN contains several dimerization domains and a repeated motif that can function as an ancillary DNA-binding domain. DEK and SET are non-related proteins, but they share a stretch of acidic amino acids, which is also present in the fusion proteins.