NUP50

NUP50 is a nucleoplasmically oriented component of the nuclear pore complex that operates at the heart of the importin-α/β transport cycle and, separately, in chromatin-linked processes (PMID:10891499, PMID:12176322). Its N-terminal domain engages importin-α at two sites—one overlapping the secondary NLS-binding site and one extending along the importin-α C-terminus—and both are required to actively displace NLS cargo, defining NUP50 as a catalyst of import-complex disassembly and importin recycling rather than a passive accompanying factor (PMID:16222336). NUP50 is itself a Ran-binding protein that acts as a tri-stable switch: its C-terminus binds importin-β through RanGTP, its N-terminus binds importin-α, and a central domain binds importin-β, allowing it to function as a cofactor that stimulates classical NLS import (PMID:12176322), while alternative isoforms tune this activity in opposing directions toward cargo stabilization versus release (PMID:20016008). NUP50 directly binds CRM1 on the nuclear face of the NPC and is required for leucine-rich NES-dependent protein export (PMID:10891499). It is scaffolded at the pore by a dual interface with Nup153, disruption of which lowers import efficiency (PMID:23007389). Beyond transport, NUP50 has a transport-independent role in NPC reassembly at mitotic exit: its N-terminal fragment stimulates the RanGEF RCC1, and a conserved central region mediates Nup153 and MEL28/ELYS binding required for assembly (PMID:34725842). NUP50 also shuttles between the NPC and nucleoplasm in a transcription-dependent manner and contributes to chromatin biology, being required for myoblast differentiation (PMID:24943837) and for recruitment of 53BP1 to DNA double-strand break foci in a pathway that counteracts BRCA1/BARD1 to favor NHEJ (PMID:28751496). Targeted deletion in mice causes late embryonic lethality with neural tube defects, accompanied by altered p27(Kip1) expression in the neuroepithelium (PMID:10891500).

1. 2000 High

   Established NUP50's spatial position and a directional transport role by showing it sits on nucleoplasmic NPC fibrils and is a direct docking site for CRM1-dependent export, answering whether it serves import or export functions.

   Evidence Immunogold EM, intranuclear antibody microinjection, and in vitro CRM1 binding in mammalian cells

   PMID:10891499

   Open questions at the time

   • Did not resolve how CRM1 binding is coordinated with cargo release
   • Structural basis of the CRM1 interaction not defined
2. 2000 High

   Connected NUP50 to cell-cycle regulators and development by identifying p27(Kip1) and Nup153 as partners and revealing an essential in vivo role, framing NUP50 as more than a transport factor.

   Evidence Yeast two-hybrid, co-immunoprecipitation, and gene-targeted knockout mice with phenotyping

   PMID:10891500

   Open questions at the time

   • p27 and proliferation defects absent in null MEFs, leaving the mechanism tissue-context dependent and undefined
   • Molecular basis linking NUP50 loss to neural tube defects unknown
3. 2002 High

   Defined NUP50 as a Ran-binding tri-stable switch and import cofactor, explaining mechanistically how it engages both importin-α and importin-β to drive the transport cycle.

   Evidence Domain-mapping binding assays, import reconstitution, and immunolocalization

   PMID:12176322

   Open questions at the time

   • How the three binding states interconvert kinetically in vivo not resolved
   • Stoichiometry within assembled import complexes undefined
4. 2005 High

   Resolved the structural and functional logic of NUP50's importin-α engagement, showing two binding sites are jointly required to actively displace NLS cargo and establishing its disassembly/recycling role.

   Evidence Crystal structure of the importin-α:Nup50 complex, site-directed mutagenesis, in vitro NLS displacement assays

   PMID:16222336

   Open questions at the time

   • Did not address CRM1 or importin-β interaction geometry
   • In vivo contribution of displacement vs recycling not quantified
5. 2009 Medium

   Showed isoform identity dictates the direction of NUP50 activity, with Npap60S stabilizing and Npap60L promoting release of importin-α:NLS-cargo, adding a layer of regulatory tuning to import.

   Evidence In vitro binding assays and in vivo time-lapse nuclear import assays

   PMID:20016008

   Open questions at the time

   • Single lab; isoform ratios and their regulation in tissues unknown
   • Structural basis for opposing isoform functions not defined
6. 2010 Medium

   Placed the NUP50 ortholog upstream of CDK-1 inactivation in an anoxia-induced prophase checkpoint, linking the nucleoporin to cell-cycle arrest under stress.

   Evidence C. elegans loss-of-function mutants, CDK-1 phospho-state immunofluorescence, epistasis

   PMID:20053678

   Open questions at the time

   • Molecular mechanism connecting NPP-16 to CDK-1 inactivation unknown
   • Mammalian conservation not tested
7. 2012 Medium

   Defined how NUP50 is anchored at the pore, identifying a dual Nup153 interface required for NUP50 localization and import efficiency.

   Evidence Domain mapping, binding assays, import efficiency assays

   PMID:23007389

   Open questions at the time

   • Single lab; relative contribution of the two interfaces in vivo unresolved
   • Whether anchoring regulates the import switch not addressed
8. 2014 Medium

   Revealed NUP50 as a mobile nucleoporin whose NPC-nucleoplasm shuttling depends on active transcription, uncovering a transport-independent role in chromatin biology required for myoblast differentiation.

   Evidence FRAP/live-cell imaging, RNAi, transcription inhibition, C2C12 differentiation assay

   PMID:24943837

   Open questions at the time

   • Chromatin targets engaged during differentiation not identified
   • Mechanistic basis of transcription-dependent mobility undefined
9. 2017 Medium

   Implicated NUP50 in DNA double-strand break repair choice, showing it promotes 53BP1 focus recruitment in a BRCA1/BARD1-dependent manner to favor NHEJ over homologous recombination.

   Evidence RNAi depletion, 53BP1 immunofluorescence, epistasis with BRCA1/BARD1/BRCA2 knockouts

   PMID:28751496

   Open questions at the time

   • Direct molecular link between NUP50 and 53BP1 recruitment unknown
   • Whether this requires NPC localization or the mobile pool not resolved
10. 2021 High

    Separated NUP50's assembly function from transport, demonstrating it stimulates RCC1 to drive NPC reassembly at mitotic exit and mapping a conserved central region for Nup153/ELYS binding.

    Evidence Xenopus egg extract immunodepletion, in vitro NPC assembly, mutagenesis, RCC1 stimulation and rescue assays

    PMID:34725842

    Open questions at the time

    • How RCC1 stimulation is spatially restricted during assembly not defined
    • Relationship between assembly role and transcription-dependent mobility unexplored
11. 2021 Low

    Linked NUP50 to viral biology and microRNA control, showing its knockdown impairs HIV-1 replication and that miR-191-5p represses it.

    Evidence siRNA knockdown, viral replication assay, miRNA target validation

    PMID:33420627

    Open questions at the time

    • Mechanism of NUP50's role in HIV-1 replication not defined
    • Single method without orthogonal validation
12. 2026 Medium

    Connected NUP50 to metabolic and oncogenic signaling, showing GALNT7-mediated O-glycosylation stabilizes NUP50, activates fatty acid β-oxidation, and promotes lung adenocarcinoma metastasis.

    Evidence Glycosylation assays, knockdown/overexpression, NUP50-MUT rescue, xenograft and lung metastasis mouse models

    PMID:42173248

    Open questions at the time

    • How NUP50 glycosylation mechanistically activates β-oxidation unknown
    • Single lab; precise glycosylated residues' structural impact undefined
13. 2025 Low

    Proposed a transport-independent metabolic-longevity function in which AMPK controls NUP50 abundance and its IDR transactivates lipid catabolic genes.

    Evidence C. elegans genetic epistasis, in vitro IDR-transcriptional machinery interaction, lifespan and transcriptomic analysis (preprint)

    PMID:bio_10.1101_2025.02.17.638704

    Open questions at the time

    • Preprint; IDR-transcription machinery interaction details sparse
    • Human conservation asserted but not directly demonstrated

• How NUP50's distinct activities—import-complex disassembly, CRM1-dependent export, RCC1-stimulated NPC assembly, and transcription-coupled chromatin/repair functions—are integrated and regulated within a single protein remains unresolved.
• No unified model connecting the transport-dependent and transport-independent roles
• Regulatory switching between functions undefined
• Direct chromatin/repair binding partners not identified