Accurate inheritance of genomic content during cell division is dependent on synchronized changes in cellular organization and chromosome dynamics. Elucidating how these events are coordinated is necessary for a complete understanding of cell proliferation. Previous in vitro studies have suggested that the nuclear pore protein Nup153 is a good candidate for participating in mitotic coordination. To decipher whether this is the case in mammalian somatic cells, we reduced the levels of Nup153 in HeLa cells and monitored consequences on cell growth. Reduction of Nup153 resulted in a delay during the late stages of mitosis accompanied by an increase in unresolved midbodies. Depletion of Nup153 to an even lower threshold led to a pronounced defect early in mitosis and an accumulation of cells with multilobed nuclei. Although global nucleocytoplasmic transport was not significantly altered under these depletion conditions, the FG-rich region of Nup153 was required to rescue defects in late mitosis. Thus, this motif may play a specialized role as cells exit mitosis. Rescue of the multilobed nuclei phenotype, in contrast, was independent of the FG-domain, revealing two separable roles for Nup153 in the execution of mitosis.

Background: An interaction network involving soluble factors and nuclear pore proteins underlies nucleocytoplasmic transport. Results: Nup50 interacts with two regions of Nup153, one of which is bridged by importin ␣. Conclusion: Efficient import is dependent on the interaction between Nup153 and Nup50. Significance: Nup153 provides a scaffold to facilitate interactions that contribute to trafficking through the nuclear pore.

When higher eukaryotic cells transition into mitosis, the nuclear envelope, nuclear pore complexes, and nuclear lamina are coordinately disassembled. The COPI coatomer complex, which plays a major role in membrane remodeling at the Golgi, has been implicated in the process of nuclear envelope breakdown and requires interactions at the nuclear pore complex for recruitment to this new site of action at mitosis. Nup153, a resident of the nuclear pore basket, was found to be involved in COPI recruitment, but the molecular nature of the interface between COPI and the nuclear pore has not been fully elucidated. To better understand what occurs at the nuclear pore at this juncture, we have probed the role of the nucleoporin Nup358/RanBP2. Nup358 contains a repetitive zinc finger domain with overall organization similar to a region within Nup153 that is critical to COPI association, yet inspection of these two zinc finger domains reveals features that also clearly distinguish them. Here, we found that the Nup358 zinc finger domain, but not a zinc finger domain from an unrelated protein, binds to COPI and dominantly inhibits progression of nuclear envelope breakdown in an assay that robustly recapitulates this process in vitro. Moreover, the Nup358 zinc finger domain interferes with COPI recruitment to the nuclear rim. Consistent with a role for this pore protein in coordinating nuclear envelope breakdown, Nup358-specific antibodies impair nuclear disassembly. Significantly, targeting either Nup153 or Nup358 for inhibition perturbs nuclear envelope breakdown, supporting a model in which these nucleoporins play nonredundant roles, perhaps contributing to COPI recruitment platforms on both the nuclear and cytoplasmic faces of the pore. We found that an individual zinc finger is the minimal interface for COPI association, although tandem zinc fingers are optimal. These results provide new information about the critical components of nuclear membrane remodeling and lay the foundation for a better understanding of how this process is regulated. INTRODUCTIONThe nuclear envelope creates a barrier that is critical to maintenance of the environment in the nucleus, specialized to support transcription and DNA replication. This double lipid membrane bilayer consists of an outer nuclear membrane, which is continuous with the endoplasmic reticulum (ER), and an inner nuclear membrane, which contains at least 78 different proteins, anchored via protein-protein interactions to the underlying nuclear lamina and chromatin . The nuclear envelope is perforated by nuclear pores, through which communication between the cytoplasm and nucleus occurs (Suntharalingam and Wente, 2003;Weis, 2003;Fahrenkrog et al., 2004;Pante, 2004). Despite the large size of the macromolecular nuclear pore complex (125 MDa in vertebrates), it is comprised of only ϳ30 different proteins, or nucleoporins (Nups), each present in multiple copies (Rout et al., 2000;Cronshaw et al., 2002). In metazoan cells, all these components-the lamina, nuclear pores, as well as the ...