KPNA4

KPNA4 (Qip1/importin alpha3) is a classical nuclear localization signal (NLS) receptor of the importin-alpha family that recognizes NLS-bearing cargo and bridges it to the nuclear import machinery (PMID:9168958). It displays isoform selectivity among importin-alpha members, binding the NLS of DNA helicase Q1/RecQL and of SV40 T antigen in a manner distinct from related receptors such as hSrp1 (PMID:9168958). Through this transport activity KPNA4 controls the nuclear access of regulatory cargoes: it mediates cytoplasm-to-nucleus translocation of the NF-κB subunit p65 (PMID:27941876, PMID:33188837) and is required for p53 nuclear import, with loss of Kpna4 in zebrafish causing p53 accumulation in the lens and cataract-like lens defects (PMID:33798680). By driving NF-κB nuclear translocation, KPNA4 promotes cancer cell migration, invasion, EMT, and metastasis across prostate, glioblastoma, thyroid, and pancreatic models, where it is held in check by tumor-suppressive microRNAs including miR-708, miR-181b, and miR-548b-3p (PMID:27941876, PMID:26283154, PMID:33188837). KPNA4 is also exploited by viruses, contributing to influenza A NP-dependent viral replication beyond simple NP nuclear localization (PMID:23383277). In vivo, Kpna4-deficient mice show an ADHD-like hypermotoric phenotype, indicating a role in neuronal regulation of locomotor behavior (PMID:40565582).

1. 1997 Medium

   Established KPNA4 as a bona fide importin-alpha family NLS receptor and showed it is not redundant with other family members, answering whether a newly identified importin-alpha homologue had cargo-binding specificity.

   Evidence GST-pulldown from human cell lysates and yeast two-hybrid against DNA helicase Q1/RecQL and SV40 T antigen NLS

   PMID:9168958

   Open questions at the time

   • No structural basis for isoform selectivity defined
   • Import competence not demonstrated in a reconstituted transport assay
   • Full cargo repertoire unresolved
2. 2013 Medium

   Showed KPNA4 contributes to influenza A virus replication through preferential binding to the unconventional NP NLS, indicating a transport-linked role in viral RNA synthesis beyond bulk NP nuclear localization.

   Evidence siRNA knockdown of Qip1 in cells infected with NP mutant virus, viral growth and vRNA transcription assays, NP binding assays

   PMID:23383277

   Open questions at the time

   • Mechanism linking KPNA4 to vRNA transcription not defined
   • Does not separate import-dependent from import-independent contributions
   • Single virus mutant system
3. 2015 Medium

   Identified KPNA4 as a direct miR-181b target whose restoration reverses miR-181b suppression of EMT, connecting KPNA4 levels to invasive phenotype control.

   Evidence miRNA overexpression with KPNA4 rescue, in vitro invasion and in vivo tumor models in glioblastoma

   PMID:26283154

   Open questions at the time

   • Molecular cargo driving EMT not pinned down in this study
   • Single tumor type
   • Does not establish transport mechanism
4. 2016 Medium

   Demonstrated that KPNA4-mediated NF-κB nuclear translocation drives cancer cell migration, invasion, and metastasis, and that KPNA4 is repressed by miR-708, linking the transport function to a defined in vivo malignant phenotype.

   Evidence Stable shRNA knockdown, mouse xenograft/metastasis models, cytokine measurement, miR-708 luciferase reporter in prostate cancer

   PMID:27941876

   Open questions at the time

   • Direct p65-KPNA4 binding not structurally resolved
   • Contribution of macrophage/osteoclast effects vs tumor-intrinsic effects not separated
   • Single lab
5. 2020 Medium

   Confirmed KPNA4 controls nuclear p65 abundance and NF-κB transcriptional activity in a second cancer type, reinforcing the NF-κB transport axis and adding miR-548b-3p as a regulator.

   Evidence KPNA4 overexpression/knockdown, NF-κB luciferase reporter, nuclear p65 immunodetection, xenograft in papillary thyroid cancer

   PMID:33188837

   Open questions at the time

   • Direct NLS recognition of p65 not shown biochemically here
   • Apoptosis link to NF-κB loss correlative
   • Single lab
6. 2021 Medium

   Established KPNA4 as the import receptor required for p53 nuclear localization in lens epithelium, giving a developmental/homeostatic cargo and phenotype distinct from cancer NF-κB roles.

   Evidence CRISPR/Cas9 kpna4 knockout zebrafish, electron microscopy, p53 immunostaining, H2O2 stress assay in human lens epithelial cells

   PMID:33798680

   Open questions at the time

   • Direct KPNA4-p53 NLS binding not demonstrated biochemically
   • Whether cataract phenotype is fully p53-dependent unresolved
   • Single model organism
7. 2022 Low

   Linked KPNA4 to FAK and PD-L1 expression in pancreatic adenocarcinoma, extending its pro-tumor role but without a defined transport mechanism.

   Evidence siRNA knockdown with CCK-8, colony formation, wound-healing assays, western blot for FAK and PD-L1

   PMID:35425701

   Open questions at the time

   • No direct KPNA4-FAK interaction shown; correlative only
   • Cargo mediating FAK/PD-L1 changes unidentified
   • Single lab western-blot readouts
8. 2025 Medium

   Revealed a physiological neuronal requirement for KPNA4 by showing loss causes ADHD-like hyperactivity, indicating a behavioral role independent of motor neuron integrity.

   Evidence Kpna4 knockout mouse with behavioral locomotion assays at multiple timepoints

   PMID:40565582

   Open questions at the time

   • Molecular cargo/pathway underlying behavior unknown
   • No cellular or circuit mechanism defined
   • Single lab
9. 2026 Low

   Positioned KPNA4 as an NPC-associated receptor for SV40 nuclear entry downstream of Nesprin-2/SUN1 targeting, expanding its role to viral genome delivery.

   Evidence Knockdown/overexpression, co-immunoprecipitation, nuclear entry assays in cell culture (preprint)

   PMID:41959248

   Open questions at the time

   • Preprint, single lab, mechanistic detail limited
   • Direct virus-KPNA4 binding interface undefined
   • No reciprocal validation reported

• How KPNA4 selects among its many cargoes (NF-κB, p53, viral proteins) in a cell-type- and signal-specific manner, and what molecular cargo underlies its neuronal phenotype, remains unresolved.
• No structural model of KPNA4-cargo NLS recognition
• Cargo specificity determinants vs other importin-alpha members unmapped
• Neuronal cargo/pathway unidentified