Identification of PML as novel PAX5 fusion partner in childhood acute lymphoblastic leukaemia

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Abstract
PAX5 encodes the B-cell lineage specific activator protein (BSAP) and is required for B-cell development and maintenance. In B-cell precursor acute lymphoblastic leukaemia (ALL), PAX5 is involved in several chromosome translocations that fuse the N-terminal paired DNA-binding domain of PAX5 with the C-terminal regulatory sequences of ETV6, FOXP1, ZNF521 or ELN. Herein, we describe the identification of a novel recurrent t(9;15)(p13;q24) in two cases of childhood ALL, which results in an in-frame fusion of PAX5 to the promyelocytic leukaemia (PML) gene. The putative PAX5-PML fusion gene encodes a chimaeric protein that retains the paired domain, the octapeptid and the partial homeodomain of PAX5, and virtually the whole PML protein. The steadily increasing number of PAX5 rearrangements suggests that PAX5 is not only crucial for B-cell lymphopoiesis but also for the development of B-cell malignancies.