OVEREXPRESSION OF THE NUCLEOPORIN CAN NUP214 INDUCES GROWTH ARREST, NUCLEOCYTOPLASMIC TRANSPORT DEFECTS, AND APOPTOSIS/

The human CAN gene was first identified as a target of t(6;9)(p23;q34) , associated with acute myeloid leukemia and myelodysplastic syndrome, which results in the expression of a DEK-CAN fusion gene. CAN, also c alled NUP214, is a nuclear pore complex (NPC) protein that contains mu ltiple FG-peptide sequence motifs. It interacts at the NPC with at lea st two other proteins, the nucleoporin NUP88 and hCRM1 (esportin 1), w hich was recently shown to function as a nuclear export receptor, Depl etion of CAN in knockout mouse embryonic cells results in cell cycle a rrest in G(2), followed by inhibition of nuclear protein import and a block of mRNA export. We overexpressed CAN and DEK-CAN in U937 myeloid precursor cells, DEK-CAN expression did not interfere with terminal m yeloid differentiation of U937 cells, whereas CAN-overexpressing cells arrested in G(0), accumulated mRNA in their nuclei, and died in an ap optotic manner. Interestingly, we found that hCRM1 and import factor p 97/importin beta colocalized with the ectopically expressed CAN protei n, resulting in depletion of both factors from the NPC, Overexpression of the C-terminal FG-repeat region of CAN, which contains the binding site for hCRM1, caused sequestering of hCRM1 in the nucleoplasm and w as sufficient to inhibit cell growth and to induce apoptosis, These re sults confirm that CAN plays a crucial role in nucleocytoplasmic trans port and imply an essential role for hCRM1 in tell growth and survival .