LRRC59

LRRC59 is a tail-anchored endoplasmic reticulum and nuclear envelope membrane protein that acts as a multifunctional scaffold coordinating membrane protein trafficking, ER-associated translation, and innate immune and nuclear envelope homeostasis (PMID:22321063, PMID:30650545, PMID:32788342). Its single C-terminal transmembrane domain is post-translationally inserted into ER-derived membranes independently of the TRC pathway, and it reaches the inner nuclear membrane by passive diffusion governed by the size of its cytoplasmic domain rather than by importin-dependent import (PMID:30650545). At the ER membrane LRRC59 defines a protein interaction domain distinct from the translocon, associating with SRP pathway components and translation factors and supporting efficient mRNA translation on the ER (PMID:32788342). Through its cytosolic domain it engages importins Kpnα1/Kpnβ1 to drive nuclear import of internalized FGF1 (PMID:22321063), and it associates with UNC93B1 to promote ligand-induced ER-to-endosome trafficking of nucleic acid-sensing TLRs (TLR3, TLR8, TLR9) required for their signaling (PMID:26466955). LRRC59 also positively regulates DDX58/RIG-I antiviral type I interferon responses by binding ISG15-modified DDX58 and blocking LRRC25-mediated, SQSTM1/p62-dependent autophagic degradation (PMID:31068071), and it cooperates with KPNB1 and XPO1 to restrain LEMD2-CHMP7 ESCRT-III complex spreading at nuclear envelope rupture sites, protecting against torsional DNA damage (PMID:41387506).

1. 2012 High

   Established LRRC59 as an ER/nuclear envelope membrane protein with a defined cellular function — mediating nuclear import of internalized FGF1 — answering whether this protein had any trafficking role.

   Evidence siRNA knockdown, co-IP with FGF1 and importins Kpnα1/Kpnβ1, subcellular fractionation, NLS-mutant nuclear import assays

   PMID:22321063

   Open questions at the time

   • Whether LRRC59 imports endogenous cargoes beyond FGF1 unresolved
   • Structural basis of FGF1/importin engagement not defined
2. 2015 High

   Extended LRRC59 function to innate immunity by showing it promotes ligand-induced ER-to-endosome trafficking of nucleic acid-sensing TLRs through UNC93B1, addressing how these receptors relocate for signaling.

   Evidence siRNA knockdown, reciprocal co-IP with UNC93B1, confocal imaging of TLR3 endosomal localization, signaling reporter assays with TLR4 specificity control

   PMID:26466955

   Open questions at the time

   • Ligand-induced signal triggering LRRC59-UNC93B1 association not identified
   • Direct vs indirect nature of the LRRC59-TLR relationship not resolved
3. 2019 High

   Defined a mechanism by which LRRC59 sustains antiviral type I IFN signaling — protecting ISG15-modified DDX58/RIG-I from LRRC25/p62-dependent autophagic degradation — clarifying how RIG-I levels are stabilized during infection.

   Evidence Co-IP, LRRC59 knockout and knockdown, IFN reporter assays, Sendai/VSV infection, Bafilomycin A1 autophagy inhibition, LRRC59-LRRC25 competition assay

   PMID:31068071

   Open questions at the time

   • Whether LRRC59 directly recognizes ISG15 or DDX58 not structurally defined
   • Regulation of the LRRC59/LRRC25 balance unknown
4. 2019 High

   Resolved the biogenesis and topology of LRRC59, showing it is a TRC-independent tail-anchored protein reaching the inner nuclear membrane by diffusion limited by cytoplasmic domain size, separating its membrane targeting from importin-mediated import.

   Evidence In vitro microsome insertion assay, rapamycin-dimerization INM localization assay, importin pathway inhibition, cytoplasmic domain size mutants

   PMID:30650545

   Open questions at the time

   • Insertase mediating TRC-independent insertion not identified
   • Functional consequence of INM versus ER pools not separated
5. 2020 High

   Positioned LRRC59 as an organizer of ER-localized translation, defining an ER membrane interaction domain distinct from the translocon and showing it is required for efficient mRNA translation.

   Evidence BioID proximity proteomics, native IP with SRP/translation factors, [35S]-methionine incorporation, siRNA knockdown

   PMID:32788342

   Open questions at the time

   • Which mRNAs depend on LRRC59 for translation not defined
   • Mechanism linking LRRC59 to ribosome/SRP recruitment unresolved
6. 2024 Medium

   Linked LRRC59 to exosome biology via CKAP4, while reproducing its association with SRP and translation/mRNA-stabilization machinery, broadening its scaffold roles in cancer cells.

   Evidence TAP-MS, co-IP with CKAP4, immunofluorescence, exosome isolation, co-culture and siRNA knockdown in OSCC cells

   PMID:38533057

   Open questions at the time

   • Direct CKAP4 binding versus complex co-purification not distinguished
   • Single cell-type context; generality of exosome role untested
7. 2025 High

   Identified LRRC59 as a regulator of nuclear envelope repair, cooperating with KPNB1/XPO1 to restrain LEMD2-CHMP7 ESCRT-III spreading at NE rupture sites and thereby limit torsional DNA damage.

   Evidence Convergent proximity proteomics, live imaging of NE ruptures, co-IP, loss-of-function and DNA damage assays

   PMID:41387506

   Open questions at the time

   • Molecular mechanism by which LRRC59 limits LEMD2 accumulation not defined
   • Relationship to its ER translation and import functions unclear
8. 2025 Medium

   Placed LRRC59 as a suppressor of PERK-mediated ER stress apoptosis in colorectal cancer, where its loss activates PERK signaling and apoptosis.

   Evidence siRNA/shRNA knockdown, western blot of PERK components, flow cytometry apoptosis, PERK inhibitor rescue, xenograft

   PMID:41133451

   Open questions at the time

   • No direct LRRC59-PERK binding demonstrated
   • Whether PERK regulation is direct or downstream of translation defects unknown

• How LRRC59's distinct roles — nuclear import, TLR trafficking, RIG-I stabilization, ER translation, NE repair, and ER stress — are mechanistically integrated through a single scaffold remains unresolved.
• No structural model of LRRC59 domains engaging its multiple partners
• No unifying biochemical activity established across functions