CGRRF1

CGRRF1 is a p53-induced, ER-resident RING-domain E3 ubiquitin ligase that acts as a growth suppressor by directing K48-linked ubiquitination and proteasomal degradation of multiple membrane and signaling substrates (PMID:8968090, PMID:31801577). It was first identified as a p53 primary response gene whose expression inhibits the growth of several cell lines (PMID:8968090). In the endoplasmic reticulum, CGRRF1 partners with the E2-conjugating enzyme UBE2J2 to ubiquitinate the Wnt cargo receptor Evi/Wls, routing it through VCP-dependent ERAD to limit Wnt protein secretion in the absence of Wnt ligands (PMID:29378775). CGRRF1 also directly binds EGFR and promotes its K48-linked polyubiquitination and degradation, dampening EGF-driven AKT phosphorylation and suppressing breast cancer cell growth in vitro and in xenografts in a manner dependent on an intact RING domain (PMID:31801577). It further targets KRAS for K48-linked ubiquitination and degradation, attenuating KRAS/ERK signaling; loss of CGRRF1 through an MSI2-AGO2/miR-30a-3p axis upregulates this pathway and drives chemoresistance (PMID:39522321). Across these substrates CGRRF1 emerges as a broadly acting negative regulator of growth-factor and developmental signaling whose loss contributes to cancer progression.

1. 1996 Medium

   Established CGRRF1 as a p53-responsive, RING-domain gene with intrinsic growth-suppressive activity, framing it as a candidate tumor suppressor before any enzymatic role was known.

   Evidence Differential RT-PCR in rat embryo fibroblasts with temperature-sensitive p53 plus growth-inhibition assays across cell lines

   PMID:8968090

   Open questions at the time

   • No molecular substrate or catalytic activity demonstrated
   • RING-domain function inferred only from sequence annotation
2. 2014 Low

   Linked CGRRF1 expression to metformin-responsive signaling and antiproliferative effects in endometrial cancer, extending its growth-suppressor phenotype to a new tissue context.

   Evidence CGRRF1 overexpression with MTT proliferation assay and RT-qPCR of metformin-treated rat endometrium

   PMID:24680596

   Open questions at the time

   • Single lab overexpression assay without molecular mechanism
   • No defined substrate or signaling pathway
   • Connection to metformin is correlative
3. 2018 High

   Defined CGRRF1's molecular activity for the first time, showing it is an ER-resident E3 ligase that, with UBE2J2 and VCP, degrades the Wnt cargo receptor Evi/Wls to set the scale of Wnt secretion.

   Evidence RNAi, reciprocal Co-IP, in vivo ubiquitination assays, VCP inhibition, and genetic epistasis with Porcn and Wnt-secretion readouts

   PMID:29378775

   Open questions at the time

   • Did not address whether CGRRF1 acts on other ERAD substrates
   • Regulation of CGRRF1 activity by Wnt ligand status not mechanistically resolved
4. 2019 High

   Identified EGFR as a direct CGRRF1 substrate and connected its degradation to suppression of AKT signaling, mechanistically explaining the growth-suppressor phenotype in breast cancer.

   Evidence Reciprocal Co-IP, K48-linkage-specific ubiquitination assay, RING-mutant loss of function, subcellular fractionation, MTT, xenografts, and RPPA substrate identification

   PMID:31801577

   Open questions at the time

   • Whether EGFR degradation occurs via ERAD or another route not specified
   • E2 partner for EGFR ubiquitination not defined
5. 2024 Medium

   Extended CGRRF1's substrate range to KRAS and embedded it in an MSI2-AGO2/miR-30a-3p regulatory axis, explaining how CGRRF1 loss activates KRAS/ERK signaling to drive chemoresistance.

   Evidence MSI2 RNA-binding and AGO2 Co-IP assays, miRNA reporter assays, KRAS ubiquitination and stability experiments, ERK phosphorylation readouts, and pharmacological inhibition

   PMID:39522321

   Open questions at the time

   • Single lab; reciprocal validation of the CGRRF1-KRAS interaction limited
   • E2 enzyme and subcellular site of KRAS ubiquitination not defined

• It remains unresolved how CGRRF1 selects among its diverse substrates and whether a unifying recruitment or regulatory mechanism governs its activity across the ER and cytosolic signaling pools.
• No structural model of substrate engagement
• Substrate-selection determinants unknown
• Interplay between p53 induction and substrate degradation not mapped