Nucleoporins are the roughly 30 distinct proteins that build and operate the nuclear pore complex, the massive channel embedded in the nuclear envelope that controls what enters and exits the nucleus of every cell with one. Each human nuclear pore is assembled from about 500 to 1,000 individual nucleoporin molecules arranged in an eightfold symmetric ring, making it one of the largest protein structures in the cell. But nucleoporins turn out to do far more than act as gatekeepers. Over the past two decades, researchers have connected them to gene regulation, cell division, aging, cancer, and neurodegeneration, and have even found them working in unexpected places outside the nucleus entirely.
How Nucleoporins Build a Selective Gate
The nuclear pore complex is not a simple hole in the membrane. It is an elaborate structure with distinct zones: a cytoplasmic ring facing the cell’s interior, a central channel, and a nuclear ring facing the genome. Scaffold nucleoporins form the structural backbone of this assembly, locking the pore into the double membrane of the nuclear envelope. Peripheral nucleoporins then attach to this scaffold, extending filaments into the cytoplasm on one side and forming a basket-like structure on the nuclear side. Cryo-electron microscopy has been instrumental in resolving these details, with recent reconstructions reaching resolutions fine enough to trace the paths of individual protein helices within the cytoplasmic ring.1Cell Research. Structure of the cytoplasmic ring of the Xenopus laevis nuclear pore complex by cryo-electron microscopy single particle analysis Achieving this level of structural insight has required combining cryo-EM with artificial-intelligence-based modeling, crystallography, and mass spectrometry, because no single technique can handle a complex this large on its own.2PubMed. Cryo-electron Microscopy Reveals the Structure of the Nuclear Pore Complex
The most functionally distinctive nucleoporins are the FG-nups, named for the repeating phenylalanine-glycine motifs that stud their long, intrinsically disordered tails. These tails dangle into the central channel and form a selective barrier: small molecules and ions pass freely, but anything larger than about 40 kilodaltons needs a molecular escort called a transport receptor to get through. The FG motifs interact with each other to create a gel-like or brush-like meshwork, and simulations show that most of the intermolecular contacts stabilizing this meshwork are FG-to-FG interactions.3PubMed Central. Phase separation of intrinsically disordered FG-Nups is driven by highly dynamic FG motifs Yet the presence of FG motifs alone is not enough to form this barrier. The amino acid sequences between the FG motifs, known as spacers, also matter: their stickiness helps determine whether a given FG-nup can undergo the phase separation needed to form a cohesive gel in the channel. This means the transport barrier is a tunable, dynamic structure rather than a fixed sieve.
Roles in Gene Regulation
If nucleoporins only managed traffic, they would already be essential. But research over the past decade has revealed that many nucleoporins moonlight as regulators of gene expression. Some do this from their posts at the nuclear pore, where they interact with stretches of chromatin that are physically tethered near the nuclear periphery. Others detach from the pore entirely and operate deeper inside the nucleus, associating with gene promoters and regulatory elements far from the envelope.4PubMed Central. Nuclear Pore Proteins in Regulation of Chromatin State
The mechanisms are varied. Some nucleoporins recruit histone-modifying enzymes that chemically tag the proteins around which DNA is wound, loosening or tightening the packaging and thereby turning genes on or off. Others interact with chromatin-remodeling complexes that physically rearrange how tightly DNA is packed. The pore complex as a whole also acts as an architectural platform, helping organize where chromosomes sit in three-dimensional space within the nucleus and coordinating the timing of gene activation.5Trends in Genetics. Nuclear Pore Complexes and Individual Nucleoporin Proteins (Nups) Mediate Cell Type-Specific Chromatin Structure and Transcription through a Range of Mechanisms in Metazoans This dual life of nucleoporins, part gatekeeper, part gene regulator, helps explain why mutations in these proteins can have such wide-ranging consequences for cells.
Different Cells, Different Pores
For a long time, researchers assumed that nuclear pores were essentially identical from one cell type to another. That assumption has been overturned. Quantitative analysis across five different human cell lines found that while the core scaffold of the pore stays consistent, the peripheral nucleoporins vary in abundance from cell type to cell type. Seven nucleoporins showed significant differences, including those facing the cytoplasm, those on the nuclear side, and the transmembrane anchors that lock the pore into the membrane.6PubMed Central. Cell type-specific nuclear pores: a case in point for context-dependent stoichiometry of molecular machines
This finding carries real implications. If the composition of the pore varies between, say, a neuron and an immune cell, then the transport rules and gene-regulatory contacts at the pore differ too. A pore enriched in a particular nucleoporin might preferentially shuttle certain cargoes or anchor specific genes at the nuclear periphery, giving that cell type its own flavor of nuclear regulation. The scaffold stays the same, but the periphery is customized, a modular design that lets one basic machine serve many specialized purposes.
Nucleoporins During Cell Division
In animal cells, the nuclear envelope breaks down every time a cell divides. The pore complexes must be disassembled, their components scattered, and then the entire structure reassembled once division is complete. This is not just a logistical inconvenience for the cell; it turns out that nucleoporins take on active jobs during mitosis that have nothing to do with transport.
Several nucleoporins relocate to kinetochores, the protein structures on chromosomes where spindle fibers attach to pull the chromosomes apart. Components of the Y-complex scaffold, along with ELYS and NUP358, accumulate at kinetochores during early mitosis, where they help organize microtubules and promote the connections between spindle fibers and chromosomes that are essential for accurate chromosome segregation.7Trends in Cell Biology. Mitotic nuclear pore complex disassembly and reassembly So the pore complex is not a passive bystander that simply falls apart and reforms. Its parts are repurposed as mitotic machinery, and errors in this process can lead to chromosome mis-segregation, a hallmark of cancer cells.
Aging and Leaky Pores
Not all nucleoporins are replaced at the same pace. Some, like Nup153 and Nup50, are continuously exchanged, cycling on and off the pore over hours. But the scaffold nucleoporins, including members of the Nup107/160 complex, are extraordinarily long-lived. In cells that no longer divide, such as neurons and muscle cells, these scaffold components can persist for the entire lifetime of the cell without being replaced.8PubMed Central. Age-dependent deterioration of nuclear pore complexes causes a loss of nuclear integrity in postmitotic cells
This extraordinary longevity comes with a cost. Over time, these never-replaced proteins accumulate oxidative damage. Experiments in aging roundworms and rats found that old nuclei progressively lose the ability to keep cytoplasmic molecules out. Roughly 30 percent of nuclei from old worms allowed a 70-kilodalton tracer molecule to leak into the nucleus, something young nuclei reliably prevented. In rats, nuclei that had become leaky also showed cytoplasmic proteins like tubulin turning up inside the nucleus where they do not belong. Tellingly, specific nucleoporins such as Nup93 were lost from these leaky old pores, while scaffold components like Nup107 remained in place.9Cell. Long-Lived Nuclear Pore Complexes Maintain Nuclear Integrity without Turnover in Postmitotic Cells The implication is that age-related pore deterioration is selective: certain components fail while the overall structure persists, creating a compromised barrier. For long-lived postmitotic cells like neurons, this gradual loss of nuclear integrity may be one of the fundamental events of biological aging.
Nucleoporins and Cancer
The gene encoding NUP98 is a recurring target of chromosomal translocations in blood cancers. In these events, the NUP98 gene gets fused to a partner gene, creating a hybrid protein that retains NUP98’s FG-repeat domain bolted onto a new functional domain. More than 30 different fusion partners have been identified, spanning transcription factors, chromatin regulators, and other proteins, and the resulting fusions appear across acute myeloid leukemia, myelodysplastic syndromes, and other hematopoietic malignancies.10PubMed Central. NUP98 gene fusions and hematopoietic malignancies: common themes and new biologic insights
These fusion proteins drive disease through several overlapping mechanisms. They can block the normal differentiation of blood cell precursors and enhance the self-renewal of stem or progenitor cells, traits that favor malignant transformation. At a molecular level, NUP98 fusions physically interact with histone-modifying complexes, including MLL1 and the NSL complex, and co-localize with these on chromatin at gene promoters. In leukemia cells driven by a NUP98-HOXA9 fusion, inactivating MLL1 reduced the expression of key target genes and reversed a gene expression signature characteristic of NUP98-rearranged human leukemias.11PubMed Central. NUP98 Fusion Proteins Interact with the NSL and MLL1 Complexes to Drive Leukemogenesis More recently, researchers have found that the FG-repeat domain of NUP98 fusions can drive the formation of abnormal biomolecular condensates in the nucleus, effectively creating rogue compartments that concentrate transcriptional machinery at the wrong genes.12PubMed Central. NUP98 oncofusions in myeloid malignancies: An update on molecular mechanisms and therapeutic opportunities
Beyond NUP98 fusions, broader dysregulation of nucleoporin levels and nuclear transport pathways has been implicated in solid tumors as well. Cancer cells frequently show altered expression of transport receptors and nucleoporins, which can shift the balance of which proteins reach the nucleus and which are exported. Tumor suppressors that need to be in the nucleus to function can be shuttled out, while oncogenic signals that should be excluded can accumulate inside.13PubMed Central. Nuclear export of proteins and drug resistance in cancer
Connections to Neurodegeneration
The most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia is a repeat expansion in the C9orf72 gene, which produces toxic repeat RNA and dipeptide repeat proteins. Studies in fruit fly neurons have shown that expressing these GGGGCC repeats triggers proteasome-mediated degradation of select nucleoporins, dismantling parts of the nuclear pore and disrupting the transport of molecules between nucleus and cytoplasm. Crucially, this degradation depends on a specific cellular machinery: the ESCRT-III complex and the Vps4 ATPase. When researchers knocked down components of this pathway, nucleoporin levels recovered, transport function normalized, and neurodegeneration was suppressed.14Cell Reports. Nuclear ESCRT-III/Vps4 mediates nucleoporin degradation and nucleocytoplasmic transport dysfunction in C9-ALS/FTD
This work connects two seemingly separate phenomena, the toxic repeat proteins of C9-ALS and the age-related vulnerability of nuclear pores described earlier. Neurons, as long-lived postmitotic cells, already struggle to maintain their pore complexes over decades. Layering on a genetic insult that actively degrades nucleoporins could accelerate the loss of nuclear integrity far beyond what normal aging would produce. The prospect that protecting nucleoporins could slow or prevent neurodegeneration has made this a topic of intense interest.
How Viruses Exploit the Pore
Because nearly every important cellular signal passes through the nuclear pore at some point, viruses have evolved multiple strategies to hijack or disable nucleoporin-mediated transport. Some viruses, including poliovirus and SARS coronavirus, inhibit protein import into the nucleus, which can cripple the cell’s ability to mount an immune response. Others, like influenza A, target and disrupt host mRNA export, trapping the cell’s own messenger RNAs inside the nucleus while viral RNAs are preferentially processed. In each case, the virus gains an advantage by co-opting the transport machinery that nucleoporins provide, either to silence the host’s defenses or to redirect cellular resources toward making more virus.
Nucleoporins Outside the Nucleus
One of the more surprising discoveries about nucleoporins is that they are not confined to the nuclear pore. Several nucleoporins localize to the base of cilia, the hair-like projections on cell surfaces involved in signaling, fluid movement, and sensory detection. This ciliary pore complex shares functional similarities with its nuclear counterpart: it imposes a size-dependent diffusion barrier that restricts entry of cytoplasmic molecules into the cilium, much as the nuclear pore restricts entry into the nucleus.15PubMed Central. A size-exclusion permeability barrier and nucleoporins characterize a ciliary pore complex that regulates transport into cilia
NUP98 specifically has been shown to set the size-exclusion limit for diffusion through the ciliary base. Knocking down NUP98 in cultured cells allowed larger molecules to leak into cilia, including soluble tubulin, the protein subunit that builds the cilium’s internal skeleton. With too much tubulin flooding in uncontrollably, cilia became shorter and more sensitive to fluctuations in cytoplasmic tubulin levels.16Current Biology. NUP98 Sets the Size-Exclusion Limit for Diffusion through the Ciliary Base and Regulates Microtubule Dynamics The cilium, it turns out, needs to be insulated from the cytoplasm to maintain its own internal environment, and nucleoporins provide that insulation. This finding extends the relevance of nucleoporins well beyond the nucleus into a completely different cellular compartment.
Evolutionary Roots
Where did nucleoporins come from? Structural analysis of Nup133, one of the scaffold nucleoporins, has revealed features shared with membrane-coating complexes like COPI and clathrin-coated vesicles. The presence of specific lipid-sensing motifs in coatomer-like nucleoporins suggests they share a common ancestor with the protein coats that wrap transport vesicles, supporting what is known as the protocoatomer hypothesis. In this view, the nuclear pore and the vesicle trafficking machinery of the cell both descended from a single ancient membrane-bending system.17PubMed Central. Integrative structure-function mapping of the nucleoporin Nup133 suggests a conserved mechanism for membrane anchoring of the nuclear pore complex If true, the nuclear pore is not just one of the largest structures in the cell but one of the most ancient, evolving from the same toolkit that cells used to build internal membranes in the first place.
Therapeutic Targeting and Biomaterial Engineering
The involvement of nucleoporins in cancer and neurodegeneration has made them targets for drug development. In the cancer space, there is growing interest in several approaches: molecular glues that induce selective degradation of specific nucleoporins involved in tumor growth, small-molecule inhibitors of nuclear export receptors like CRM1, and drugs that disrupt the epigenomic signaling that NUP98 fusions hijack.18PubMed Central. Nucleoporins in Cancer: Functional Roles and Therapeutic Opportunities CRM1 inhibitors, sometimes called selective inhibitors of nuclear export, have advanced furthest. Selinexor, one such inhibitor, has already been approved for certain blood cancers, and next-generation compounds aim to improve on its tolerability.19PubMed Central. Nuclear export of proteins and drug resistance in cancer
Meanwhile, the way nucleoporins manage selective transport has inspired a completely different application: the design of synthetic hydrogels that mimic the pore’s selectivity. Researchers have created gels for recognition and selective permeation, or GRASP, built from a polymer network studded with short peptides that bind specific target molecules. Just as the nuclear pore lets transport-receptor-bound cargo pass through while blocking unescorted molecules, these engineered gels speed up the passage of a target biomolecule (in one demonstration, a monoclonal antibody) while blocking similarly sized molecules that lack the right binding interaction.20Biomacromolecules. Nucleopore-Inspired Polymer Hydrogels for Selective Biomolecular Transport The concept flips the usual logic of filtration, where binding to the filter slows you down, into a system where binding is the ticket to faster transit. It is a principle that biology worked out billions of years ago, and that materials scientists are just beginning to borrow.