KCMF1

KCMF1 is a RING zinc-finger E3 ubiquitin ligase that operates within the Arg/N-degron protein quality-control machinery, coupling substrate recognition to either autophagic or proteasomal degradation (PMID:40992840). Through its ZZ-type zinc finger it acts as an N-recognin, binding N-terminal arginine and oxidized/arginylated Nt-Cys degrons to assemble K63-linked ubiquitin chains that recruit p62-type autophagic receptors; under oxidative or hypoxic stress this directs substrates to autophagy, and KCMF1 itself undergoes N-degron-stimulated self-polymerization (PMID:40992840). KCMF1 also nucleates a tripartite RAD6 (E2)–KCMF1–UBR4 complex: its C-terminus binds RAD6 while its N-terminal region binds UBR4, and the assembly localizes to late endosomes and lysosomes where it controls vesicle dynamics (PMID:25582440). Within the resulting megadalton UBR4–KCMF1 machine, UBR4 functions as an E4 ligase extending K48-linked chains on pre-ubiquitinated orphan protein subunits, with KCMF1 serving as the substrate filter that gates entry; efficient targeting requires both prior mono-ubiquitination by a priming E3 and a specific N-degron. Beyond orphan quality control, KCMF1 directly ubiquitinates discrete substrates with defined chain specificity and physiological consequence: K48-linked degradation of AMPKα suppresses hepatic AMPK signaling and drives MASLD (PMID:42162901), degradation of the HRI kinase restrains the integrated stress response (PMID:41391693), and K63-linked degradation of nucleoredoxin (NXN) activates β-catenin signaling (PMID:41721648). KCMF1 additionally engages 14-3-3σ and FUS, and promotes proliferation, migration, and invasion across several cancer models (PMID:41184988, PMID:23840115, PMID:20473331).

1. 2010 Medium

   Established KCMF1 as a pro-tumorigenic factor with an in vivo phenotype before any enzymatic activity was known, linking it to proliferation control.

   Evidence Cell proliferation/migration/invasion assays, CAM model, gene-trap knockdown crossed to TGF-α transgenic mice, IHC for cyclin D/CDK4

   PMID:20473331

   Open questions at the time

   • No molecular activity or substrate identified
   • Mechanism linking KCMF1 to cyclin D/CDK4 unresolved
   • Nuclear localization not mechanistically explained
2. 2013 Medium

   Identified 14-3-3σ as a physical partner supporting a proliferative role in cancer stem cells, expanding the KCMF1 interaction landscape.

   Evidence Yeast two-hybrid and co-immunoprecipitation with siRNA knockdown proliferation/colony assays in colon cancer stem cells

   PMID:23840115

   Open questions at the time

   • Functional consequence of the interaction at the molecular level undefined
   • No ubiquitination link established
   • Single lab
3. 2015 High

   Defined KCMF1 as the scaffolding hub of a RAD6–KCMF1–UBR4 E2–E3 complex localized to the endolysosomal system, establishing its architecture and a disease-relevant binding interface.

   Evidence Affinity purification–MS, NMR direct binding, in vitro/in vivo interaction mapping, colocalization imaging; RAD6A XLID mutants lose KCMF1/UBR4 binding

   PMID:25582440

   Open questions at the time

   • Catalytic output and substrates of the complex not yet defined
   • Chain-type specificity unknown at this stage
   • Role in vesicle dynamics mechanistically incomplete
4. 2024 High

   Resolved the structure and pathway logic of the UBR4–KCMF1 machine, showing it is an E4 chain-elongating ligase acting downstream of a priming E3 to clear orphan subunits, with KCMF1 as substrate filter.

   Evidence Cryo-EM of the 1.3 MDa UBR4–KCMF1–CALM1 ring (preprint), cellular epistasis, and in vitro reconstitution with multiple orphan substrates (preprint)

   Open questions at the time

   • Preprint, not peer-reviewed
   • Precise KCMF1 contribution to substrate selection vs. UBR4 not fully separated
   • Identity of priming E3 not defined
5. 2025 High

   Demonstrated KCMF1 is an autophagic N-recognin that reads Nt-Arg and oxidized/arginylated Nt-Cys degrons to build K63 chains, connecting it to stress-induced autophagy.

   Evidence In vitro ubiquitination and binding assays with synthetic N-degrons and ZZ-domain mutants

   PMID:40992840

   Open questions at the time

   • Endogenous physiological substrates of the autophagic branch not enumerated
   • Mechanism of self-polymerization unresolved
   • Interplay between K63-autophagic and K48-proteasomal branches unclear
6. 2025 Medium

   Identified a non-degradative KCMF1–FUS axis in renal cell carcinoma, broadening KCMF1 function beyond canonical ubiquitin-ligase activity.

   Evidence Co-IP, immunofluorescence, flow cytometry, loss-/gain-of-function cell assays and xenograft

   PMID:41184988

   Open questions at the time

   • Whether FUS is ubiquitinated by KCMF1 not established
   • Mechanism of FUS nuclear translocation unclear
   • Single lab
7. 2026 Medium

   Established specific physiological substrates with defined chain linkages — AMPKα (K48), HRI (degradation), and NXN (K63) — linking KCMF1 to metabolic disease, stress signaling, and Wnt/β-catenin signaling.

   Evidence Co-IP/GST pull-down/Ni-NTA ubiquitination with linkage specificity, IP-LC/MS substrate ID, hepatocyte-specific KO mice, and pharmacological rescue (AMPK activator; ISR inhibitor)

   PMID:41391693 PMID:41721648 PMID:42162901

   Open questions at the time

   • Whether these substrates share the N-degron recognition mode is untested
   • Tissue/context determinants of substrate choice unknown
   • AMPKα and NXN findings each from single labs

• How KCMF1 switches between K63-linked autophagic targeting and K48-linked proteasomal targeting, and how degron recognition selects among its diverse substrates, remains unresolved.
• No unified model linking N-degron recognition to chain-type choice
• Regulatory inputs controlling branch selection unknown
• Endogenous substrate repertoire incompletely mapped