TNPO2

TNPO2 (Transportin-2) is a non-classical nuclear transport receptor whose dosage and cargo interactions govern nucleocytoplasmic distribution of developmental and neuronal proteins (PMID:34314705). It controls subcellular localization of estrogen receptor-α (ERα) by competitively binding the basic NLS of ERα against importin-α, thereby inhibiting importin-α/β-dependent ERα nuclear import rather than exporting it; this retention engages PY motifs of ERα and modulates downstream PI3K/AKT phosphorylation, with TNPO2 knockdown enhancing ERα nuclear localization (PMID:33122699). In neurons, TNPO2 is required for maintenance and survival, and both loss and gain of activity produce dosage-dependent developmental defects; pathogenic human variants confer graded severity that maps to functional domains, with RAN-binding-domain variants most deleterious, acidic-loop variants least, and cargo-binding-domain variants showing tissue-dependent effects (PMID:34314705). In gastric cancer cells, TNPO2 acts downstream of a DYNC1I1→SP1→P300 transcriptional axis to drive proliferation and suppress apoptosis via P21 (PMID:31605449). Additional binding partners and cargoes beyond these contexts have not been characterized in the available corpus.

1. 2019 Medium

   Established a transcriptional and pro-tumorigenic role for TNPO2 by placing it downstream of a defined regulatory cascade in cancer cells.

   Evidence Expression profiling, siRNA knockdown, ChIP for SP1 and P300-acetylated histones at the TNPO2 promoter, and proliferation/apoptosis assays in gastric cancer cells

   PMID:31605449

   Open questions at the time

   • The P21-dependent mechanism downstream of TNPO2 is not fully dissected
   • Whether TNPO2's transport function contributes to the proliferative phenotype is untested
2. 2020 Medium

   Defined a specific molecular mechanism by which TNPO2 retains a cargo in the cytoplasm, showing it competes with importin-α at the cargo NLS rather than mediating export.

   Evidence Co-IP, siRNA knockdown with nuclear/cytoplasmic fractionation, phosphorylation assays, and PY-motif mutant ERα constructs

   PMID:33122699

   Open questions at the time

   • Demonstrated for ERα in one cell system; generality to other cargoes unknown
   • Direct competition kinetics with importin-α not quantified
3. 2021 High

   Connected TNPO2 dosage and domain architecture to neuronal maintenance and human neurodevelopmental disease, mapping variant severity to specific functional domains.

   Evidence Drosophila RNAi, mutant alleles, and ectopic expression of wild-type and patient-variant TNPO2 with lethality, eye/wing morphology, and neuronal activity/survival readouts

   PMID:34314705

   Open questions at the time

   • Molecular cargoes underlying the neuronal requirement are not identified
   • Mechanistic link between domain-specific transport defects and fly phenotypes is inferred, not biochemically resolved
4. 2023 Low

   Nominated a candidate developmental cargo/partner (MAB21L2) for TNPO2.

   Evidence Yeast two-hybrid screens using human adult retina and zebrafish embryo libraries

   PMID:36576422

   Open questions at the time

   • Single Y2H screen with no Co-IP or pulldown validation for the TNPO2-MAB21L2 pair
   • Functional consequence of any interaction untested
5. 2026 Medium

   Tested whether TNPO2 mRNA shares the nuclear-envelope localization of its C. elegans ortholog, establishing a species-specific difference.

   Evidence smiFISH and fluorescence microscopy in U2OS, HeLa, and pluripotent stem cells (preprint)

   PMID:42239225

   Open questions at the time

   • Preprint, single lab
   • Negative mRNA-localization result does not address TNPO2 protein localization

• The full cargo repertoire of TNPO2 and how cargo selectivity, RAN-binding, and the acidic loop coordinate to drive its transport cycle remain undefined.
• No structural model of TNPO2-cargo or TNPO2-RAN complexes in the corpus
• Direct biochemical validation of most candidate cargoes absent