A significant number of genes is involved in a series of cytogenetically distinct translocation events involving more than one fusion partner gene, resulting in “Multi-Partner Translocation (MPT) families”. MPT families share the biochemical properties of one common partner moiety, but at the same time feature very different functions of the unique fusion partner gene parts. An important MPT family in AML comprises fusions involving the NUP98 (Nucleoporin 98) gene, featuring >20 different fusion proteins. The overall frequency of leukemias with NUP98-rearrangements ranges from 2 to 30%, depending on patient age and leukemia subtype. Several members of the NUP98 translocation family have recently been proposed to constitute disease-defining entities by the most recent WHO classification of genetic abnormalities in AML.
We have recently started to assess the leukemogenic potential of FLAG-tagged NUP98 fusion proteins in a murine bone marrow transplantation model. Transplantation of fetal liver cells expressing a FLAG-tagged NUP98-fusion protein induced the development of an aggressive malignant disease, with vriable latency of 40 days or more (Figure 1A). Immuno-phenotypic characterization of bone marrow from leukemic mice revealed excessive accumulation of Mac-1/GR-1-positive donor-derived cells in the bone marrow and spleen of affected animals. As our expression model allows the inducible down-regulation of NUP98-FPs by administration of Doxycycline (Dox), we analysed the consequences of oncogene withdrawal using transplantation of fully transformed NUP98-FP AML cells. While all secondary recipient mice succumbed to an aggressive leukemia in the absence of Dox, Dox-induced down-regulation of NUP98-FP expression efficiently prevented the outbreak of lethal leukemia (Figure 1B).
To assess changes in gene expression caused by down-regulation of NUP98-FPs, we purified leukemic cells after different timepoints of Dox administration. Preliminary analysis of RNA-seq data revealed that acute withdrawal of NUP98-FPs leads to a down-regulation of several genes that have been implicated in leukemic self-renewal, including Hoxa7, Hoxa9 and Hoxa10 (Figure 1C). These data show that the retroviral transplantation model established by us recapitulates critical aspects of human NUP98-FP-induced leukemia, including characteristic changes in immuno-phenotype and gene expression profile.
