PTGFRN

PTGFRN (EWI-F/CD9P-1/FPRP) is a heavily glycosylated transmembrane immunoglobulin superfamily protein that serves as a central organizer of tetraspanin-enriched microdomains, linking them to the actin cytoskeleton and modulating diverse signaling pathways at the cell surface. It forms near-stoichiometric complexes with tetraspanins CD9 and CD81 through transmembrane helix contacts, as demonstrated by cryo-EM, and these interactions are required for its regulatory functions including inhibition of CD81-dependent Plasmodium hepatocyte infection and modulation of VEGF-dependent angiogenesis (PMID:11087758, PMID:32958604, PMID:19762465, PMID:21863033). PTGFRN connects tetraspanin microdomains to the cortical cytoskeleton by directly binding ERM proteins through a cytoplasmic basic domain, negatively regulating cell migration and ERM phosphorylation, and also directly interacts with Integrin β1, E-Cadherin, and STAT3 to influence adhesion, autophagy, and branched-chain amino acid metabolism (PMID:16690612, PMID:38924562, PMID:41130302). Additionally, PTGFRN negatively regulates prostaglandin F2α receptor availability by reducing receptor number in a dose-dependent manner, and stabilizes PI3K p110β to sustain AKT signaling and DNA damage repair (PMID:8804121, PMID:31377205).

1. 1996 High

   The first functional role assigned to PTGFRN was as a negative regulator of prostaglandin F2α receptor signaling, establishing that this Ig superfamily protein reduces available FP receptor number rather than affinity, with two discrete regions mediating inhibition.

   Evidence Radioligand binding assays with Scatchard analysis and domain deletion in COS cells

   PMID:8804121

   Open questions at the time

   • Mechanism by which PTGFRN reduces FP receptor number (sequestration vs. degradation vs. trafficking) not determined
   • No in vivo validation of FP receptor regulation
   • Endogenous co-expression context not established
2. 2000 High

   PTGFRN was shown to associate with tetraspanins CD9 and CD81 at near-complete stoichiometry, forming discrete low-molecular-weight complexes distinct from integrin-containing tetraspanin webs, establishing PTGFRN as a primary tetraspanin partner rather than a peripheral associate.

   Evidence Reciprocal co-IP, immunodepletion, gel permeation chromatography, and methyl-β-cyclodextrin treatment

   PMID:11087758

   Open questions at the time

   • Structural basis of the tetraspanin interaction unknown at this stage
   • Functional consequence of the CD9/CD81 partnership not yet demonstrated
3. 2006 High

   Discovery that PTGFRN bridges tetraspanin microdomains to the actin cytoskeleton by directly binding ERM proteins through its cytoplasmic basic domain resolved how tetraspanin complexes connect to cortical actin and established a mechanism by which PTGFRN restrains cell migration.

   Evidence GST pulldown, co-IP, confocal colocalization at microvilli/uropod, dominant-negative moesin and siRNA knockdown

   PMID:16690612

   Open questions at the time

   • Which specific ERM family member is the dominant partner in vivo not resolved
   • Structural detail of the cytoplasmic interaction not determined
4. 2007 Medium

   Comprehensive glycosylation mapping revealed that all nine potential N-glycosylation sites on PTGFRN are occupied, generating at least 17 glycoforms, establishing the protein as one of the most extensively glycosylated tetraspanin partners and raising questions about how glycan heterogeneity influences its interactions.

   Evidence PNGase F deglycosylation, FTICR-MS, MALDI-TOF, ESI-MS/MS, 2-D PAGE, lectin blot

   PMID:17960739

   Open questions at the time

   • Functional significance of glycan diversity for CD9/CD81 binding or signaling not tested
   • Glycoform distribution across tissues unknown
5. 2009 High

   Two studies revealed that PTGFRN forms cis-oligomers at the cell surface and that its interaction with CD81 is functionally required for inhibiting Plasmodium sporozoite infection of hepatocytes, moving PTGFRN from a structural scaffold to an active regulator of pathogen entry.

   Evidence Chemical cross-linking/LC-MS/MS for oligomerization; siRNA, overexpression, and CD81-binding-deficient chimera for infection regulation

   PMID:19703604 PMID:19762465

   Open questions at the time

   • Whether oligomerization state modulates anti-parasitic function not tested
   • Mechanism of CD81-dependent Plasmodium entry inhibition (receptor masking vs. membrane organization) not resolved
6. 2011 Medium

   PTGFRN was shown to be required for VEGF-dependent angiogenesis, and disruption of PTGFRN-CD81 association by IFITM5 remodeled tetraspanin complexes to activate interferon-induced gene expression, broadening PTGFRN's role to vascular biology and innate immune regulation.

   Evidence siRNA knockdown in endothelial tube formation assays; truncated protein treatment; co-IP of FKBP11-CD81-PTGFRN complex with IFITM5

   PMID:21600883 PMID:21863033

   Open questions at the time

   • Direct mechanism linking PTGFRN to VEGFR signaling not identified
   • IFITM5-mediated complex remodeling studied only in osteoblasts
7. 2019 Medium

   PTGFRN was found to stabilize PI3K p110β protein and sustain AKT phosphorylation, with knockdown impairing nuclear p110β localization, DNA damage sensing/repair, and radiosensitizing glioblastoma cells, connecting PTGFRN to survival signaling and genomic integrity.

   Evidence shRNA knockdown, western blot for p110β/pAKT, nuclear fractionation, DNA damage repair assays in GBM cells

   PMID:31377205

   Open questions at the time

   • Whether PTGFRN directly binds p110β or acts indirectly through tetraspanin complexes not resolved
   • Mechanism of p110β stabilization (proteasomal, lysosomal) not defined
   • Single cancer type studied
8. 2020 High

   Cryo-EM structure of the CD9–EWI-F complex revealed the precise architecture: an EWI-F ectodomain dimer flanked by two CD9 molecules contacting EWI-F transmembrane helices via CD9 helices h3/h4, providing the first atomic-level model for how tetraspanin-enriched microdomains are assembled through concatenation.

   Evidence Cryo-EM structure determination complemented by crystal structures of CD9 large extracellular loop with nanobodies

   PMID:32958604

   Open questions at the time

   • Structure of the analogous CD81–EWI-F complex not determined
   • How ERM binding at the cytoplasmic face is coordinated with ectodomain dimerization unknown
9. 2024 Medium

   PTGFRN's interactome was expanded to include direct binding to Integrin β1 and E-Cadherin, and proteomic profiling linked it to protein processing/metabolism and VEGF signaling networks, while its loss upregulated innate immune pathways.

   Evidence Co-IP, co-IP/LC-MS/MS proteomics, shRNA knockdown with proteomic and functional readouts in cancer cell lines

   PMID:38559916 PMID:38924562

   Open questions at the time

   • Whether Integrin β1 and E-Cadherin bind PTGFRN independently of CD9/CD81 not determined
   • Autophagy regulation mechanism downstream of PTGFRN not elucidated
10. 2025 Medium

    PTGFRN was placed upstream of a STAT3–BCAT1 metabolic axis: it stabilizes STAT3 protein, enhancing STAT3 occupancy on the BCAT1 promoter and driving branched-chain amino acid metabolism in NSCLC, extending PTGFRN's role to metabolic reprogramming in cancer.

    Evidence Co-IP, ChIP for STAT3 at BCAT1 promoter, shRNA knockdown, metabolic assays in NSCLC cells

    PMID:41130302

    Open questions at the time

    • Direct vs. indirect nature of PTGFRN–STAT3 interaction not distinguished by structural or in vitro reconstitution methods
    • Whether STAT3 stabilization is a general PTGFRN function or cancer-specific is unknown

• Key unresolved questions include how PTGFRN's extensive glycosylation modulates its partner selectivity, the structural basis of the CD81–EWI-F complex, whether PTGFRN's roles in PI3K/AKT and STAT3 stabilization proceed through tetraspanin-dependent or -independent mechanisms, and how ERM-mediated cytoskeletal coupling is coordinated with ectodomain dimerization.
• No structure of CD81–PTGFRN complex
• No reconstituted system distinguishing tetraspanin-dependent from -independent signaling
• Functional relevance of 17 glycoforms untested