CGRRF1

CGRRF1 is a p53-inducible, ER-localized RING-domain E3 ubiquitin ligase that suppresses cell growth by targeting multiple oncogenic substrates for K48-linked ubiquitination and proteasomal degradation. It ubiquitinates the Wnt cargo receptor Evi/Wls in partnership with the E2 enzyme UBE2J2, directing Evi to VCP-dependent ERAD and thereby limiting Wnt secretion (PMID:29378775). CGRRF1 also ubiquitinates EGFR via its RING-finger domain, promoting EGFR degradation and attenuating AKT signaling (PMID:31801577), and mediates K48-linked ubiquitination of KRAS to suppress KRAS/ERK signaling (PMID:39522321). Originally identified as a p53-responsive growth suppressor (PMID:8968090), its broad substrate repertoire positions it as a tumor-suppressive E3 ligase operating at the intersection of Wnt, EGFR, and RAS signaling pathways.

1. 1996 Medium

   The discovery that CGR19 (CGRRF1) is transcriptionally induced by p53 and contains a RING-finger domain established it as a candidate growth suppressor, but its molecular mechanism was unknown.

   Evidence Differential RT-PCR in rat embryo fibroblasts with temperature-sensitive p53; overexpression growth inhibition assays in multiple cell lines

   PMID:8968090

   Open questions at the time

   • No enzymatic activity demonstrated
   • No substrates identified
   • Subcellular localization not defined
2. 2014 Low

   Confirmation that CGRRF1 overexpression inhibits cancer cell proliferation and is induced by metformin linked it to metabolic signaling, but the molecular targets remained unidentified.

   Evidence MTT assay, RT-qPCR, and Western blot in endometrial cancer cells and obese rat endometrium

   PMID:24680596

   Open questions at the time

   • No defined molecular mechanism beyond growth inhibition
   • Single lab; not independently confirmed
   • Causal relationship between metformin and CGRRF1 induction not mechanistically resolved
3. 2018 High

   Demonstration that CGRRF1 is an ER-resident E3 ligase that ubiquitinates Evi/Wls with UBE2J2 for VCP-dependent ERAD provided the first defined substrate and placed CGRRF1 within the ERAD quality-control pathway controlling Wnt secretion.

   Evidence RNAi knockdown, reciprocal co-immunoprecipitation, in vivo ubiquitination assays, VCP inhibition, genetic epistasis with Porcn

   PMID:29378775

   Open questions at the time

   • Whether CGRRF1-mediated Evi degradation operates in all Wnt-secreting tissues in vivo
   • Structural basis of CGRRF1–Evi recognition unknown
   • Extent of CGRRF1 substrate repertoire beyond Evi not yet explored
4. 2019 High

   Identification of EGFR as a second CGRRF1 substrate, degraded via RING-domain-dependent K48-linked ubiquitination, broadened CGRRF1's role from Wnt regulation to EGFR/AKT signaling suppression and validated its tumor-suppressive function in vivo.

   Evidence Co-immunoprecipitation, in vivo ubiquitination assays with RING-domain mutants, subcellular fractionation, MTT assay, xenograft experiments, RPPA

   PMID:31801577

   Open questions at the time

   • Whether EGFR ubiquitination by CGRRF1 occurs on newly synthesized ER-resident EGFR versus mature receptor
   • No structural model of CGRRF1 RING domain–E2 interaction
   • E2 partner for EGFR ubiquitination not confirmed
5. 2024 Medium

   Discovery that CGRRF1 mediates K48-linked ubiquitination and degradation of KRAS, suppressing KRAS/ERK signaling, revealed a third major oncogenic substrate and connected CGRRF1 loss to chemoresistance via the MSI2/miR-30a-3p axis.

   Evidence Ubiquitination assays, KRAS protein stability measurements, AGO2 interaction assays, luciferase reporter for miR-30a-3p/CGRRF1 3′UTR

   PMID:39522321

   Open questions at the time

   • Independent replication of CGRRF1-KRAS direct ubiquitination needed
   • Whether KRAS ubiquitination is RING-domain dependent not tested with domain mutants
   • In vivo relevance of the MSI2/miR-30a-3p/CGRRF1/KRAS axis not demonstrated in animal models

• Key unresolved questions include the full substrate repertoire of CGRRF1 in ERAD, its structural basis for substrate recognition, and whether its tumor-suppressive functions are tissue-specific.
• No structural model of CGRRF1
• No systematic substrate identification (e.g., ubiquitin remnant proteomics)
• In vivo phenotype of CGRRF1 knockout in mammalian models not reported