ELAPOR1

ELAPOR1 (EIG121/KIAA1324) is an evolutionarily conserved transmembrane protein with a mannose-6-phosphate receptor domain that organizes vesicular trafficking across the trans-Golgi/late endosome/lysosome axis and acts as a tumor suppressor in multiple epithelial cancers (PMID:21072319, PMID:34816763). Structurally, it forms a square-planar cis homodimer that assembles into a trans-tetramer through copper chelation-dependent head-to-head homophilic interactions, allowing it to function as a membrane tethering factor; a copper chelation-deficient mutant retains cis dimerization but fails to bridge vesicles (PMID:40737321). This tethering activity drives proacrosomal vesicle fusion during acrosome biogenesis, and Elapor1-null males are infertile with a globozoospermia-like phenotype; ELAPOR1 coordinates this trafficking through the SNARE STX12 and through VPS54-dependent assembly of the GARP complex (PMID:40737321, PMID:41993632). As a transcriptional target of MIST1, ELAPOR1 is required for normal secretory granule maturation in gastric zymogenic cells, where it traffics alongside cis-Golgi proteins and CI-M6PR (PMID:34816763). In the autophagy pathway, ELAPOR1 promotes lysosomal degradation of long-lived proteins and supports cell survival under starvation and cytotoxic stress (PMID:21072319). Its anti-tumor activity operates through physical interaction with GRP78, blocking GRP78–caspase-7 binding and GRP78-driven AKT activation to induce apoptosis, and these functions depend on N-linked glycosylation and fucosylation that maintain its stability and proper localization (PMID:26045166, PMID:37612293).

1. 2010 High

   Established ELAPOR1's first cellular function by showing it is an endolysosomal transmembrane protein that drives autophagy and protects cells from stress-induced death.

   Evidence Inducible overexpression, fractionation, EM, transmembrane-domain deletion, LC3 degradation assays and siRNA knockdown in cultured cells

   PMID:21072319

   Open questions at the time

   • No molecular partners or trafficking machinery identified
   • Mechanism by which an endolysosomal protein nucleates autophagosome formation undefined
2. 2015 Medium

   Identified a molecular basis for ELAPOR1's tumor-suppressive activity through physical interaction with the oncoprotein GRP78.

   Evidence Co-immunoprecipitation, xenograft tumor model, and AKT/apoptosis readouts in gastric cancer cells

   PMID:26045166

   Open questions at the time

   • Interaction shown by co-IP without structural mapping of the binding interface
   • Connection between GRP78 inhibition and the earlier autophagy role unresolved
3. 2017 Low

   Linked ELAPOR1-regulated autophagy to cancer stemness and chemoresistance in endometrial carcinoma.

   Evidence Overexpression/knockdown in JEC spheres with stemness markers and paclitaxel sensitivity assays

   PMID:28656197

   Open questions at the time

   • Limited mechanistic detail; correlative cell-based assays only
   • No molecular link established between ELAPOR1 and stemness regulators
4. 2021 High

   Placed ELAPOR1 in a defined secretory trafficking pathway as a MIST1 target required for secretory granule maturation, and related it functionally to the M6P receptor CI-M6PR.

   Evidence Co-IP/mass spectrometry, truncation mutants, Golgi/endosome co-localization, and Elapor1 knockout mouse gastric phenotype

   PMID:34816763

   Open questions at the time

   • Whether ELAPOR1 binds M6P-tagged cargo like CI-M6PR not determined
   • Mechanism of granule maturation defect not resolved at molecular level
5. 2023 High

   Showed that N-glycosylation and fucosylation are required post-translational modifications controlling ELAPOR1 stability, localization, and tumor-suppressive function.

   Evidence Glycosylation-site mutagenesis, fucosyltransferase inhibition, proteasomal degradation, localization, and apoptosis assays in gastric cancer cells

   PMID:37612293

   Open questions at the time

   • Identity of the responsible fucosyltransferase not pinpointed
   • How glycosylation enforces correct localization mechanistically unclear
6. 2025 High

   Defined the structural mechanism of ELAPOR1 as a copper-dependent membrane tethering factor and established its essential role in acrosome biogenesis.

   Evidence Cryo-EM, copper-chelation-deficient mutant in vitro and in vivo, Elapor1 and conditional Stx12 knockout mice, in vitro tethering assays, co-IP with STX12

   PMID:40737321

   Open questions at the time

   • Physiological source/role of copper at the tethering interface unresolved
   • Functional significance of dual membrane topology beyond PAV tethering unclear
7. 2026 High

   Connected ELAPOR1 to the GARP complex, showing it regulates VPS54-associated GARP assembly to control Golgi/endosome vesicle transport and proacrosomal vesicle fusion.

   Evidence Germ cell-specific Elapor1 knockout mice, mass spectrometry, co-IP, proximity labeling, immunofluorescence, and TEM

   PMID:41993632

   Open questions at the time

   • How ELAPOR1 tethering activity and GARP-dependent transport are mechanistically coupled not defined
   • Whether GARP regulation generalizes beyond testis unknown
8. 2026 Medium

   Implicated ELAPOR1 in TDP-43 proteinopathy and a mitochondrial protein network, expanding its relevance to neurodegeneration.

   Evidence IHC of ALS brain, iPSC-derived neurons with TDP-43 depletion, and mass spectrometry of KIAA1324-overexpressing SH-SY5Y cells

   PMID:41668214

   Open questions at the time

   • Alternative polyadenylation/translation mechanism hypothesized but not directly tested
   • Functional consequence of the mitochondrial protein association not established

• It remains unknown how ELAPOR1's structural tethering activity, M6P-receptor domain, and post-translational modifications mechanistically converge to coordinate its diverse roles in autophagy, secretory granule maturation, acrosome biogenesis, and tumor suppression.
• No unified model linking cargo recognition to tethering function
• Whether copper-dependent tetramerization operates outside germ cells untested