Affinage

XPOT

Exportin-T · UniProt O43592

Round 2 corrected
Length
962 aa
Mass
110.0 kDa
Annotated
2026-04-28
61 papers in source corpus 12 papers cited in narrative 12 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

XPOT (Exportin-t) is the principal importin-β-family nuclear export receptor for mature tRNA, coupling tRNA biogenesis quality control to cytoplasmic translation. It forms a ternary complex with RanGTP and tRNA in the nucleus, recognizing the processed 5′ and 3′ ends and the TψC/acceptor arm of mature tRNA through a large conformational wrapping motion, and releases cargo in the cytoplasm upon RanGTP hydrolysis (PMID:9660920, PMID:9857198, PMID:19680239). Distinct N- and C-terminal domains mediate interactions with nucleoporins Nup153, RanBP2/Nup358, and CAN/Nup214, concentrating export complexes at the nuclear pore (PMID:12138183). Beyond bulk tRNA export, XPOT selectively transports specific tRNA isodecoders to regulate translation of cytokinesis-essential proteins, exports the transcription factor NFAT5 under hypotonic conditions via a RUVBL2-dependent mechanism, and its depletion suppresses mTORC1 signaling to induce autophagy and triggers NLRP3/caspase-1-dependent pyroptosis in cancer cells (PMID:37928256, PMID:35635291, PMID:20714220, PMID:41438360).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 1998 High

    The identity of the nuclear tRNA export receptor was unknown; identification of Exportin-t as a RanGTP-dependent, importin-β-family factor that directly binds and rate-limits tRNA export established the core transport mechanism.

    Evidence Affinity chromatography, tRNA-binding assays, microinjection into Xenopus oocytes, and chemical/enzymatic footprinting of tRNA–Xpo-t–RanGTP contacts

    PMID:9660920 PMID:9857198

    Open questions at the time
    • Structural basis for simultaneous recognition of all mature tRNAs was not yet resolved
    • Whether Xpo-t exports non-tRNA cargoes was unknown
    • Mechanism of tRNA release in the cytoplasm was not defined
  2. 2002 High

    How Exportin-t navigates the nuclear pore was unclear; mapping of two distinct NPC-binding domains — an N-terminal RanGTP-dependent interaction with Nup153/RanBP2 and a C-terminal Ran-independent interaction with CAN/Nup214 — showed how the transporter concentrates at the pore to enhance export cycle efficiency.

    Evidence In vitro binding assays with isolated nucleoporins, fluorescence microscopy, RanGTP mutant analysis

    PMID:12138183

    Open questions at the time
    • The order and kinetics of nucleoporin engagement during a single translocation cycle were not determined
    • Contribution of each nucleoporin interaction to in vivo export rates was untested
  3. 2009 High

    The atomic mechanism by which Exportin-t recognizes all mature tRNAs while rejecting unprocessed precursors was resolved by crystal structures showing that Xpot wraps around tRNA, directly contacting the 5′ and 3′ ends, coupling export to end-processing quality control.

    Evidence X-ray crystallography of S. pombe Xpot–tRNA–RanGTP (3.2 Å) and free Xpot (3.1 Å)

    PMID:19680239

    Open questions at the time
    • Dynamic steps of cargo release upon RanGTP hydrolysis lacked experimental characterization
    • Whether the same binding mode applies to all isoacceptor tRNAs was not tested
  4. 2010 Medium

    The physiological consequences of impaired tRNA export were unknown; XPOT knockdown revealed that nuclear tRNA accumulation suppresses mTORC1 activity and induces autophagy, linking tRNA subcellular distribution to nutrient-sensing signaling.

    Evidence siRNA knockdown of Xpo-t in human fibroblasts, tRNA localization assays, mTORC1 activity and autophagy measurements

    PMID:20714220

    Open questions at the time
    • The molecular sensor connecting nuclear tRNA levels to mTORC1 was not identified
    • Single-lab finding; independent replication in other cell types was lacking
  5. 2018 Medium

    Whether XPOT is functionally important in cancer cell proliferation was untested; knockdown in hepatocellular carcinoma cells caused G0/G1 arrest with downregulation of multiple CDKs and cyclins both in vitro and in xenograft models, establishing XPOT as a proliferation dependency.

    Evidence siRNA knockdown, proliferation/invasion assays, subcutaneous xenograft model, Western blotting

    PMID:30334580

    Open questions at the time
    • Whether cell-cycle arrest results from global tRNA depletion or selective loss of specific tRNAs was not distinguished
    • No direct mechanistic link between tRNA export deficiency and CDK/cyclin protein levels was established
  6. 2022 Medium

    Whether XPOT exports non-tRNA cargoes was an open question; an siRNA screen and proteomics identified XPOT as the export receptor for transcription factor NFAT5 under hypotonic conditions, with RUVBL2 serving as an essential chaperone, broadening XPOT function beyond tRNA.

    Evidence siRNA screen, mass spectrometry, co-immunoprecipitation, live-cell imaging

    PMID:35635291

    Open questions at the time
    • Whether XPOT binds NFAT5 directly or via RUVBL2-bridged interaction was not resolved
    • The NFAT5 export signal recognized by XPOT was not mapped
    • Generality of XPOT as a protein exporter for other transcription factors is unknown
  7. 2023 Medium

    Whether XPOT exhibits selectivity among tRNA species was unknown; demonstration that XPOT preferentially exports the isodecoder tRNA-Ala-AGC-10-1 to drive translation of the cytokinesis factor TTC19 in TNBC cells revealed cargo-selective export coupled to codon-biased translation.

    Evidence siRNA knockdown, high-throughput tRNA-seq, codon preferential analysis, protein mass spectrometry in TNBC cells

    PMID:37928256

    Open questions at the time
    • The structural basis for isodecoder selectivity is unknown
    • Whether selectivity is intrinsic to XPOT or mediated by adaptor proteins was not addressed
    • Applicability beyond TNBC cells not tested
  8. 2025 Medium

    XPOT knockdown in breast cancer cells activates the NLRP3/caspase-1/GSDMD pyroptosis pathway, an effect reversed by a pyroptosis inhibitor, connecting tRNA export deficiency to inflammatory cell death.

    Evidence siRNA knockdown, Western blotting, ELISA for IL-1β/IL-18, pharmacological rescue with azalamellarin N

    PMID:41438360

    Open questions at the time
    • The molecular link between tRNA export loss and NLRP3 inflammasome activation is not defined
    • Single-lab study; independent confirmation needed
    • Relevance to non-cancer cell types is untested

Open questions

Synthesis pass · forward-looking unresolved questions
  • Critical open questions remain: the molecular sensor linking nuclear tRNA accumulation to mTORC1 and inflammasome pathways, the structural basis for isodecoder selectivity, and the full repertoire of non-tRNA protein cargoes of XPOT are unknown.
  • No sensor/adaptor connecting tRNA compartmentalization to mTORC1 or pyroptosis has been identified
  • Structural determinants of isodecoder-selective export are uncharacterized
  • Systematic identification of XPOT protein cargoes beyond NFAT5 has not been performed

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0003723 RNA binding 4 GO:0005215 transporter activity 4 GO:0003924 GTPase activity 2
Localization
GO:0005634 nucleus 2 GO:0005635 nuclear envelope 1 GO:0005829 cytosol 1
Pathway
R-HSA-9609507 Protein localization 5 R-HSA-8953854 Metabolism of RNA 4 R-HSA-9612973 Autophagy 1
Partners
NFAT5NUP153NUP214RANRANBP2RUVBL2

Evidence

Reading pass · 12 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1998 Exportin-t (XPOT) was identified as a specific nuclear export receptor for tRNA. It is an importin-beta-related, RanGTP-binding protein with predominantly nuclear localization that shuttles between nucleus and cytoplasm, interacts with nuclear pore complexes, binds tRNA directly and with high affinity, and its cellular concentration in Xenopus oocytes was rate-limiting for export of all tRNAs tested. RanGTP regulates the substrate–exportin-t interaction such that tRNA is preferentially bound in the nucleus and released in the cytoplasm. Affinity chromatography, microinjection into Xenopus oocytes, RanGTP-binding assays, tRNA-binding assays Molecular cell High 9660920
1998 Exportin-t–RanGTP selectively exports mature tRNAs by making extensive contacts with the backbone of the TψC and acceptor arms of tRNA; accurate 5' and 3' end-processing is required for efficient Xpo-t–RanGTP interaction and nuclear export, whereas aminoacylation is not essential. Intron-containing but end-processed pre-tRNAs can be exported when Xpo-t is present in excess, indicating at least two mechanisms discriminate pre-tRNAs from mature tRNAs. Chemical and enzymatic footprinting, phosphate modification interference, mutant/precursor tRNA microinjection into Xenopus oocyte nuclei, antibody-blocking experiments The EMBO journal High 9857198
2002 The steady-state nuclear localization of Xpo-t depends on its interaction with RanGTP. Two distinct NPC-interaction domains were identified: the N-terminus binds Nup153 and RanBP2/Nup358 in a RanGTP-dependent manner, while the C-terminus binds CAN/Nup214 independently of Ran. These interactions increase the concentration of tRNA export complexes and empty Xpo-t near NPCs, enhancing transport cycle efficiency. In vitro binding assays with isolated nucleoporins, fluorescence microscopy for steady-state localization, RanGTP mutant analysis Molecular and cellular biology High 12138183
2009 Crystal structures of S. pombe Xpot in complex with tRNA and RanGTP (3.2 Å) and of unbound Xpot (3.1 Å) revealed that Xpot undergoes a large conformational change upon cargo binding, wrapping around the tRNA and specifically contacting the tRNA 5' and 3' ends. This binding mode explains how Xpot recognizes all mature tRNAs while discriminating against improperly processed ones, coupling tRNA export to quality control. X-ray crystallography (3.2 Å and 3.1 Å resolution crystal structures) Nature High 19680239
2001 Xpo-t/RanGTP can bind tRNA-attached ribozymes (tRNA-Rz) with an extended 3' end both in vitro and in somatic cells, enabling their export to the cytoplasm. This recognition is similar to that of mature tRNAs. An inhibitor present in Xenopus oocyte nuclear extract selectively blocks Xpo-t-dependent export of tRNA-Rz but not mature tRNAs, suggesting a proofreading mechanism in oocytes that is relaxed in somatic cells. In vitro binding assays, microinjection into somatic cells and Xenopus oocytes, nuclear extract inhibition experiments Biomacromolecules Medium 11777397
2010 Downregulation of XPOT (Xpo-t) in human fibroblasts causes nuclear accumulation of tRNA, leading to reduced mTORC1 activity and upregulated autophagy, demonstrating that subcellular tRNA localization mediated by Xpo-t can regulate intracellular nutritional stress signaling independently of cellular nutritional status. siRNA knockdown of Xpo-t, tRNA localization assays, mTORC1 activity assay, autophagy measurement in human fibroblasts Cell cycle (Georgetown, Tex.) Medium 20714220
2016 Molecular dynamics simulations of Xpot complexes revealed dynamic structural hinges that mediate the nuclear-to-cytosolic conformational transition; post-RanGTP hydrolysis, local conformational changes in Ran and loss of critical contacts at the Xpot/tRNA interface drive tRNA release. HEAT repeat flexibility varies depending on cargo-binding state. Classical all-atom and accelerated molecular dynamics simulations of free and cargo-bound Xpot Biophysical journal Low 27028637
2022 XPOT mediates nuclear export of NFAT5 under hypotonic conditions in an unconventional, tonicity-dependent manner. siRNA screening and proteomics identified that XPOT drives NFAT5 nuclear export under hypotonicity, and that RUVBL2 (a RuvB-like AAA-type ATPase) is an indispensable chaperone for this process. siRNA screening, proteomics/mass spectrometry, co-immunoprecipitation, live-cell imaging Journal of cell science Medium 35635291
2023 XPOT knockdown in triple-negative breast cancer (TNBC) cells inhibited proliferation and caused cytokinesis failure. XPOT was shown to preferentially export a specific tRNA isodecoder (tRNA-Ala-AGC-10-1) from the nucleus, thereby promoting translation of TTC19, a protein required for cytokinesis completion in TNBC cells. siRNA knockdown, high-throughput tRNA sequencing, codon preferential analysis, protein mass spectrometry, RNA-seq, in vitro cell proliferation assays International journal of biological sciences Medium 37928256
2018 XPOT knockdown in hepatocellular carcinoma (HCC) cell lines inhibited tumor proliferation and invasion in vitro and in vivo. Mechanistically, XPOT knockdown caused G0/G1 cell cycle arrest accompanied by downregulation of CDK1, CDK2, CDK4, CyclinA1, CyclinB1, CyclinB2, and CyclinE2. siRNA knockdown, CCK-8 proliferation assay, wound-healing and Transwell invasion assays, subcutaneous xenograft mouse model, GSEA, western blotting Molecular carcinogenesis Medium 30334580
2025 XPOT knockdown in breast cancer cells promoted pyroptosis, as evidenced by increased IL-1β and IL-18 secretion, elevated N-terminal GSDMD cleavage, and upregulation of NLRP3, ASC, and cleaved-caspase-1. The pyroptosis inhibitor azalamellarin N reversed these effects, linking XPOT to suppression of the NLRP3 inflammasome/caspase-1/GSDMD pyroptotic pathway. siRNA knockdown, Western blotting, ELISA, CCK-8, Transwell, TUNEL assays, pharmacological inhibition Central-European journal of immunology Medium 41438360
2025 XPOT knockdown in breast cancer cells inhibited proliferation and invasion; mechanistically, XPOT knockdown reduced activation of the PI3K/AKT/mTOR signaling pathway and downregulated cyclin D and CDK4/6. siRNA knockdown, CCK-8 assay, Transwell assay, Western blotting for PI3K/AKT/mTOR pathway components Journal of inflammation research Low 40416714

Source papers

Stage 0 corpus · 61 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2002 Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences. Proceedings of the National Academy of Sciences of the United States of America 1479 12477932
2010 Network organization of the human autophagy system. Nature 1286 20562859
2017 Architecture of the human interactome defines protein communities and disease networks. Nature 1085 28514442
2015 A human interactome in three quantitative dimensions organized by stoichiometries and abundances. Cell 1015 26496610
2020 A reference map of the human binary protein interactome. Nature 849 32296183
2018 VIRMA mediates preferential m6A mRNA methylation in 3'UTR and near stop codon and associates with alternative polyadenylation. Cell discovery 829 29507755
2003 Complete sequencing and characterization of 21,243 full-length human cDNAs. Nature genetics 754 14702039
2021 Dual proteome-scale networks reveal cell-specific remodeling of the human interactome. Cell 705 33961781
2012 A census of human soluble protein complexes. Cell 689 22939629
2011 Phylogenetic-based propagation of functional annotations within the Gene Ontology consortium. Briefings in bioinformatics 656 21873635
2015 SLC38A9 is a component of the lysosomal amino acid sensing machinery that controls mTORC1. Nature 548 25561175
2021 Multilevel proteomics reveals host perturbations by SARS-CoV-2 and SARS-CoV. Nature 532 33845483
2011 Mapping the NPHP-JBTS-MKS protein network reveals ciliopathy disease genes and pathways. Cell 507 21565611
2004 The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC). Genome research 438 15489334
2022 OpenCell: Endogenous tagging for the cartography of human cellular organization. Science (New York, N.Y.) 432 35271311
2015 Panorama of ancient metazoan macromolecular complexes. Nature 407 26344197
2021 A proximity-dependent biotinylation map of a human cell. Nature 339 34079125
2010 Dynamics of cullin-RING ubiquitin ligase network revealed by systematic quantitative proteomics. Cell 318 21145461
1998 Identification of a tRNA-specific nuclear export receptor. Molecular cell 316 9660920
2020 Virus-Host Interactome and Proteomic Survey Reveal Potential Virulence Factors Influencing SARS-CoV-2 Pathogenesis. Med (New York, N.Y.) 291 32838362
2012 A high-throughput approach for measuring temporal changes in the interactome. Nature methods 273 22863883
2010 Aire's partners in the molecular control of immunological tolerance. Cell 250 20085707
1998 Identification of a nuclear export receptor for tRNA. Current biology : CB 245 9512417
2015 ∆F508 CFTR interactome remodelling promotes rescue of cystic fibrosis. Nature 209 26618866
2018 An AP-MS- and BioID-compatible MAC-tag enables comprehensive mapping of protein interactions and subcellular localizations. Nature communications 201 29568061
1998 The role of exportin-t in selective nuclear export of mature tRNAs. The EMBO journal 179 9857198
2017 Energy stress-induced lncRNA FILNC1 represses c-Myc-mediated energy metabolism and inhibits renal tumor development. Nature communications 178 28978906
2017 The E3 ubiquitin ligase and RNA-binding protein ZNF598 orchestrates ribosome quality control of premature polyadenylated mRNAs. Nature communications 176 28685749
2011 Copy number variations on chromosome 12q14 in patients with normal tension glaucoma. Human molecular genetics 173 21447600
2000 Exportin 4: a mediator of a novel nuclear export pathway in higher eukaryotes. The EMBO journal 171 10944119
2020 UFMylation maintains tumour suppressor p53 stability by antagonizing its ubiquitination. Nature cell biology 168 32807901
2019 A protein-interaction network of interferon-stimulated genes extends the innate immune system landscape. Nature immunology 159 30833792
2009 Structures of the tRNA export factor in the nuclear and cytosolic states. Nature 109 19680239
2015 RNA Export through the NPC in Eukaryotes. Genes 88 25802992
2003 PAUSED encodes the Arabidopsis exportin-t ortholog. Plant physiology 67 12913168
2000 Review: transport of tRNA out of the nucleus-direct channeling to the ribosome? Journal of structural biology 58 10806079
2002 Steady-state nuclear localization of exportin-t involves RanGTP binding and two distinct nuclear pore complex interaction domains. Molecular and cellular biology 38 12138183
2011 Copy number variations and primary open-angle glaucoma. Investigative ophthalmology & visual science 33 21310917
2010 Linking tRNA localization with activation of nutritional stress responses. Cell cycle (Georgetown, Tex.) 32 20714220
2014 Expression status of candidate genes in mesothelioma tissues and cell lines. Mutation research 29 25771974
2018 Exportin-T promotes tumor proliferation and invasion in hepatocellular carcinoma. Molecular carcinogenesis 24 30334580
2001 Recognition of engineered tRNAs with an extended 3' end by Exportin-t (Xpo-t) and transport of tRNA-attached ribozymes to the cytoplasm in somatic cells. Biomacromolecules 22 11777397
2011 Altered nuclear tRNA metabolism in La-deleted Schizosaccharomyces pombe is accompanied by a nutritional stress response involving Atf1p and Pcr1p that is suppressible by Xpo-t/Los1p. Molecular biology of the cell 21 22160596
2019 The general mRNA exporters Mex67 and Mtr2 play distinct roles in nuclear export of tRNAs in Trypanosoma brucei. Nucleic acids research 19 31392978
2013 TBK1 and flanking genes in human retina. Ophthalmic genetics 15 23421332
2012 Integration analysis of quantitative proteomics and transcriptomics data identifies potential targets of frizzled-8 protein-related antiproliferative factor in vivo. BJU international 13 22738385
2021 Molecular profiling of nucleocytoplasmic transport factor genes in breast cancer. Heliyon 12 33553736
2023 Virus-induced lncRNA-BTX allows viral replication by regulating intracellular translocation of DHX9 and ILF3 to induce innate escape. Cell reports 10 37864796
2017 Clinical and molecular characterization of a second family with the 12q14 microdeletion syndrome and review of the literature. American journal of medical genetics. Part A 7 28407409
2023 XPOT Disruption Suppresses TNBC Growth through Inhibition of Specific tRNA Nuclear Exportation and TTC19 Expression to Induce Cytokinesis Failure. International journal of biological sciences 6 37928256
2022 Unconventional tonicity-regulated nuclear trafficking of NFAT5 mediated by KPNB1, XPOT and RUVBL2. Journal of cell science 6 35635291
2022 Attenuated Viral Replication of Avian Infectious Bronchitis Virus with a Novel 82-Nucleotide Deletion in the 5a Gene Indicates a Critical Role for 5a in Virus-Host Interactions. Microbiology spectrum 6 35766501
2016 Insights into the Structural Dynamics of Nucleocytoplasmic Transport of tRNA by Exportin-t. Biophysical journal 5 27028637
2013 Characterization of export receptor exportins (XPOs) in the parasite Schistosoma mansoni. Parasitology research 2 24013345
2010 Flexibility of the exportins Cse1p and Xpot depicted by elastic network model. Journal of molecular modeling 2 21058036
2025 Exportin-T Promotes Breast Cancer Progression via PI3K/AKT/mTOR Signaling Pathway. Journal of inflammation research 1 40416714
2025 Integrating single-cell and bulk RNA sequencing data establishes a cuproptosis-related gene predictive signature in breast cancer. Discover oncology 1 41021161
2013 The intrinsic dynamics of Cse1p and Xpot elucidated by coarse-grained models. Computational biology and chemistry 1 24334215
2025 Uncovering genomic traces of local adaptation and milk production traits in the Comisana Sheep, a Mediterranean dairy breed. Animal : an international journal of animal bioscience 0 41380350
2025 Inhibition of XPOT promotes breast cancer cell pyroptosis to suppress cancer progression. Central-European journal of immunology 0 41438360
2025 Surviving the Heat: Genetic Diversity and Adaptation in Sudanese Butana Cattle. Genes 0 41465102