The Nucleoporin Nup358/RanBP2 Promotes Nuclear Import in a Cargo- and Transport Receptor-Specific Manner

Department of Biochemistry I, Faculty of Medicine, Georg-August-University of Göttingen, Humboldtallee 23, 37073, Göttingen, Germany.
Traffic (Impact Factor: 4.35). 02/2012; 13(2):218-33. DOI: 10.1111/j.1600-0854.2011.01302.x
Source: PubMed


In vertebrates, the nuclear pore complex (NPC), the gate for transport of macromolecules between the nucleus and the cytoplasm, consists of approximately 30 different nucleoporins (Nups). The Nup and SUMO E3-ligase Nup358/RanBP2 are the major components of the cytoplasmic filaments of the NPC. In this study, we perform a structure-function analysis of Nup358 and describe its role in nuclear import of specific proteins. In a screen for nuclear proteins that accumulate in the cytoplasm upon Nup358 depletion, we identified proteins that were able to interact with Nup358 in a receptor-independent manner. These included the importin α/β-cargo DBC-1 (deleted in breast cancer 1) and DMAP-1 (DNA methyltransferase 1 associated protein 1). Strikingly, a short N-terminal fragment of Nup358 was sufficient to promote import of DBC-1, whereas DMAP-1 required a larger portion of Nup358 for stimulated import. Neither the interaction of RanGAP with Nup358 nor its SUMO-E3 ligase activity was required for nuclear import of all tested cargos. Together, Nup358 functions as a cargo- and receptor-specific assembly platform, increasing the efficiency of nuclear import of proteins through various mechanisms.

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    • "NUP358 plays an important role in nucleocytoplasmic transport, being the site of interaction with Ran (the small GTPase that regulates nucleocytoplasmic transport by proteins of the karyopherin β family [47]), SUMO-modified RanGAP (the mammalian RanGTPase-activating protein that is highly concentrated at the cytoplasmic side of the nuclear pore complex [48,49]), and the export receptor CRM1 [50]. Nup358 has also been suggested to act as a platform to recruit import receptors to pre-bound cargos, as cellular substrates DBC-1 and DMAP-1 have been shown to directly bind to NUP358 and be transported by importin α/β [51]. Therefore, recruiting to the nuclear pore via CA interaction with NUP358 may allow HIV-1 access to importin or transportin routes into the nucleus and drive integration into actively transcribing regions of the genome. "
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    ABSTRACT: Lentiviruses such as HIV-1 can be distinguished from other retroviruses by the cyclophilin A-binding loop in their capsid and their ability to infect non-dividing cells. Infection of non-dividing cells requires transport through the nuclear pore but how this is mediated is unknown. Here we present the crystal structure of the N-terminal capsid domain of HIV-1 in complex with the cyclophilin domain of nuclear pore protein NUP358. The structure reveals that HIV-1 is positioned to allow single-bond resonance stabilisation of exposed capsid residue P90. NMR exchange experiments demonstrate that NUP358 is an active isomerase, which efficiently catalyzes cis-trans isomerization of the HIV-1 capsid. In contrast, the distantly related feline lentivirus FIV can bind NUP358 but is neither isomerized by it nor requires it for infection. Isomerization by NUP358 may be preserved by HIV-1 to target the nuclear pore and synchronize nuclear entry with capsid uncoating.
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    • "Nonetheless, one recent report has implicated a role for the nuclear pore-associated SUMO E3 ligase, Nup358/RanBP-2 in facilitating nuclear import of Ad2/5 (Strunze et al., 2011). Nup358/RanBP-2 is required for the import of numerous cellular proteins into the nucleus independent of its sumoylating activity (Walde et al., 2011). Nup358/RanBP-2 was also identified as a cell factor that promotes nuclear import of the HIV pre-integration complex (Brass et al., 2008). "
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