IPO7

IPO7 (RanBP7/Imp7) is an importin-β family nuclear transport receptor that recognizes basic import signals on cargo proteins and delivers them across the nuclear pore (PMID:9687515). It was first defined as one of several importin-β-like receptors that directly bind and import ribosomal proteins (rpL23a, rpS7, rpL5), recognizing an archetypal basic import signal (PMID:9687515). Structurally, IPO7 functions with importin-β as a preassembled heterodimer: a short C-terminal nucleoporin-like binding region of IPO7 contacts importin-β through FXFG-type motifs, importin-β allosterically activates IPO7, and only the assembled heterodimer can dock the histone H1 globular domain within IPO7's central cavity for translocation [PMID:bio_10.1101_2025.08.04.668392]. Beyond constitutive cargo, IPO7 serves as the nuclear import step for multiple signaling effectors: it mediates nuclear translocation of the Smad2/3/4 complex in TGF-β-stimulated myofibroblasts (PMID:25968067) and of phospho-p38 under inflammatory (LPS) stimulation, thereby driving NF-κB/p38 MAPK signaling and cytokine production, with IPO7–p-p38 binding inversely related to IPO7–Sirt2 binding (PMID:37769576). In dental papilla cells IPO7 binds odontoblastic transcription factors to import them and promotes HDAC6 nuclear localization, coupling its transport activity to control of odontoblastic versus osteoblastic differentiation through effects on RUNX2 (PMID:35922041). IPO7 is also required for HMGB1 release during inflammatory lung injury, linking it to downstream NET formation and PANoptosis (PMID:38369216), and is exploited by HPV, whose L2 capsid C-terminus directly binds Golgi-associated IPO7 for nuclear entry following COPI-dependent trafficking [PMID:bio_10.1101_2025.01.08.631933]. IPO7 is essential for viability in multiple cell lines (PMID:33664726).

1. 1998 High

   Established IPO7's foundational activity as a nuclear import receptor by showing it directly binds and imports ribosomal proteins, defining its substrate-recognition mode through a basic import signal.

   Evidence In vitro reconstituted nuclear import assay with direct binding and competition experiments using multiple ribosomal protein substrates

   PMID:9687515

   Open questions at the time

   • Did not resolve the structural basis of cargo recognition
   • Did not address signaling-effector cargoes or heterodimer requirement
2. 2015 Medium

   Placed IPO7 in TGF-β signaling by identifying it as the import carrier required for Smad2/3/4 nuclear translocation, connecting receptor-level kinase activity to transcriptional output.

   Evidence Subcellular fractionation, MAPK pharmacological inhibition, and protein/mRNA expression analysis in TGF-β1-stimulated myofibroblasts

   PMID:25968067

   Open questions at the time

   • Imp7 and Imp8 contributions not individually distinguished
   • No direct binding between IPO7 and Smad complex demonstrated
3. 2021 Medium

   Defined IPO7 as an essential gene and a target of viral regulation, showing its dosage is tightly constrained and tuned by EBV miRNAs during infection.

   Evidence CRISPR-Cas9 knockout (lethal) and overexpression growth assays across three cell lines

   PMID:33664726

   Open questions at the time

   • Molecular basis of essentiality (which cargoes) not identified
   • Mechanism by which overexpression inhibits growth unresolved
4. 2022 Medium

   Linked IPO7's transport function to cell-fate control by showing it imports odontoblastic transcription factors and HDAC6 to bias differentiation toward odontoblastic over osteoblastic programs via RUNX2.

   Evidence Reciprocal Co-IP, knockdown/overexpression with differentiation assays, and nuclear-versus-total fractionation

   PMID:35922041

   Open questions at the time

   • Specific transcription-factor cargoes only partially identified
   • Single lab; differentiation phenotype not independently replicated
5. 2023 Medium

   Extended IPO7's role to inflammatory signaling by identifying phospho-p38 as a direct interactor whose nuclear import drives NF-κB/p38 cytokine responses, with Sirt2 as a competing partner.

   Evidence Co-IP of IPO7 with p-p38 and Sirt2, siRNA knockdown, and pathway-activator rescue in dental pulp cells

   PMID:37769576

   Open questions at the time

   • Functional consequence of the IPO7–Sirt2 interaction not directly tested
   • Whether IPO7 imports other MAPK components unaddressed
6. 2024 Medium

   Implicated IPO7 in inflammatory injury physiology by showing it is required for HMGB1 secretion, connecting its activity to downstream NET formation and PANoptosis in vivo.

   Evidence In vivo siRNA-nanoparticle knockdown in ventilator-induced lung injury, ELISA, and histological injury assessment

   PMID:38369216

   Open questions at the time

   • Direct mechanism by which IPO7 controls HMGB1 release not defined
   • Whether effect is via nuclear import of an upstream factor unclear
7. 2025 Medium

   Revealed a viral hijacking mechanism in which Golgi-associated IPO7 is the receptor for HPV nuclear entry through direct binding of the L2 capsid C-terminus after COPI-dependent trafficking.

   Evidence IPO7 knockdown HPV infection assay, Golgi localization, L2 C-terminus pulldown, and COPI inhibition epistasis (preprint)

   PMID:bio_10.1101_2025.01.08.631933

   Open questions at the time

   • Preprint not yet peer-reviewed
   • How Golgi-localized IPO7 transits the virus to the pore unresolved
8. 2025 Medium

   Provided the structural logic for IPO7 cargo handling, showing it functions as an importin-β heterodimer whose central cavity docks histone H1 only after importin-β allosterically activates it via a C-terminal nucleoporin-like region.

   Evidence AlphaFold3 model validated by cross-linking mass spectrometry, ITC, pulldown, and cryo-EM map refinement (preprint)

   PMID:bio_10.1101_2025.08.04.668392

   Open questions at the time

   • Preprint not yet peer-reviewed
   • Whether the heterodimer requirement generalizes to other cargoes untested

• It remains unresolved how IPO7 selects among its diverse cargoes (ribosomal proteins, H1, Smad complexes, p-p38, transcription factors, viral L2) and whether shared structural determinants govern monomeric versus heterodimeric import.
• No unified cargo-selectivity model across constitutive and signaling substrates
• Regulation of monomer-versus-heterodimer assembly in cells unknown