Three patients diagnosed with acute myeloid leukemia (AML) with reciprocal 21q22/RUNX1(AML1) translocations involving chromosomes 1 and 4 were studied. Three novel RUNX1 translocation partner genes on 1q21.2 (ZNF687), 1p35 (YTHDF2), and 4q31.3 (SH3D19) were identified using a panhandle polymerase chain reaction and the 3' rapid amplification of cDNA ends method. The translocation events occurred between exons 3 and 7 of the RUNX1 gene. The partner gene breakpoints localized to the region in the partner gene with the highest Alu density, suggesting that Alus may contribute to the recombination events. Two out of three of the cases retained RUNX1's entire RUNT domain in the translocation, and RUNX1 mutations were absent in the fusion transcripts, confirmed by reverse transcription-polymerase chain reaction and sequencing analysis. SH3D19 encodes a cytoplasmic protein EBP known to suppress RAS-induced cellular transformation, which can be inhibited by nuclear recruitment. The t(4;21) created a hybrid RUNX1-EBP protein retaining RUNX1's DNA binding domain, which may result in nuclear localization of the chimeric protein and inhibition of EBP's RAS-suppressive functions. Future studies would be useful to further characterize these novel fusion protein products.
(c) 2006 Wiley-Liss, Inc.