Genes encoding the Phe-Gly (FG) repeat-containing nucleoporins NUP98 and CAN/NUP214 are at the breakpoints of several chromosomal translocations associated with human acute myeloid leukemia (AML), but their role in oncogenesis is unclear. Here we demonstrate that the NUP98-HOXA9 fusion gene encodes two nuclear oncoproteins with either 19 or 37 NUP98 FG repeats fused to the DNA binding and PBX heterodimerization domains of the transcription factor HOXA9. Both NUP98-HOXA9 chimeras transformed NIH 3T3 fibroblasts, and this transformation required the HOXA9 domains for DNA binding and PBX interaction. Surprisingly, the FG repeats acted as very potent transactivators of gene transcription. This NUP98-derived activity is essential for transformation and can be replaced by the bona fide transactivation domain of VP16. Interestingly, FG repeat-containing segments derived from the nucleoporins NUP153 and CAN/NUP214 functioned similarly to those from NUP98. We further demonstrate that transactivation by FG repeat-rich segments of NUP98 correlates with their ability to interact functionally and physically with the transcriptional coactivators CREB binding protein (CBP) and p300. This finding shows, for the first time, that a translocation-generated fusion protein appears to recruit CBP/p300 as an important step of its oncogenic mechanism. Together, our results suggest that NUP98-HOXA9 chimeras are aberrant transcription factors that deregulate HOX-responsive genes through the transcriptional activation properties of nucleoporin-specific FG repeats that recruit CBP/p300. Indeed, FG repeat-mediated transactivation may be a shared pathogenic function of nucleoporins implicated human AML.

Gle2p is implicated in nuclear export of poly(A)+ RNA and nuclear pore complex (NPC) structure and distribution in Saccharomyces cerevisiae. Gle2p is anchored at the nuclear envelope (NE) via a short Gle2p-binding motif within Nup116p called GLEBS. The molecular mechanism by which Gle2p and the Gle2p–Nup116p interaction function in mRNA export is unknown. Here we show that RAE1, the mammalian homologue of Gle2p, binds to a GLEBS-like NUP98 motif at the NPC through multiple domains that include WD-repeats and a COOH-terminal non–WD-repeat extension. This interaction is direct, as evidenced by in vitro binding studies and chemical cross-linking. Microinjection experiments performed in Xenopus laevis oocytes demonstrate that RAE1 shuttles between the nucleus and the cytoplasm and is exported from the nucleus in a temperature-dependent and RanGTP-independent manner. Docking of RAE1 to the NE is highly dependent on new mRNA synthesis. Overexpression of the GLEBS-like motif also inhibits NE binding of RAE1 and induces nuclear accumulation of poly(A)+ RNA. Both effects are abrogated either by the introduction of point mutations in the GLEBS-like motif or by overexpression of RAE1, indicating a direct role for RAE1 and the NUP98–RAE1 interaction in mRNA export. Together, our data suggest that RAE1 is a shuttling transport factor that directly contributes to nuclear export of mRNAs through its ability to anchor to a specific NUP98 motif at the NPC.