MKRN1

MKRN1 is a RING-finger E3 ubiquitin ligase and RNA-binding protein that governs diverse cellular processes—including telomere maintenance, cell-cycle control, apoptosis, energy metabolism, and ribosome-associated quality control—by ubiquitinating and targeting a broad array of substrates for proteasomal degradation. Under basal conditions MKRN1 ubiquitinates p53 (at K291/K292), p21, and p14ARF to restrain tumor-suppressor activity, whereas DNA damage triggers a SIRT1-dependent substrate switch from p53 to MDM2, thereby stabilizing p53 and promoting apoptosis (PMID:19536131, PMID:41617974). MKRN1 also ubiquitinates AMPKα and LKB1 to suppress AMPK signaling, and genetic deletion in mice protects against diet-induced metabolic syndrome and cardiac bioenergetic impairment (PMID:30143610, PMID:40546121). Through direct, RNA-independent binding to PABPC1, MKRN1 positions itself at poly(A) sequences on mRNAs and ubiquitinates PABPC1 and RPS10 to promote ribosome stalling during ribosome-associated quality control (PMID:31640799).

1. 2005 High

   Establishing MKRN1 as a bona fide E3 ubiquitin ligase: the first substrate identified was hTERT, whose MKRN1-dependent ubiquitination and proteasomal degradation directly linked MKRN1 to telomerase regulation and telomere maintenance.

   Evidence Yeast two-hybrid identification, in vivo ubiquitination, proteasome degradation, and telomerase activity assays in human cells

   PMID:15805468

   Open questions at the time

   • Physiological relevance of MKRN1–hTERT axis in primary cells or in vivo not tested
   • Ubiquitination sites on hTERT not mapped
2. 2006 Medium

   Beyond its E3 ligase function, MKRN1 was found to act as a transcriptional co-repressor of c-Jun, androgen receptor, and retinoic acid receptors independently of its RING-finger catalytic activity, revealing a dual-function protein.

   Evidence Reporter gene assays with truncation mutants and RING-finger catalytic-dead mutant in mammalian cells

   PMID:16785614

   Open questions at the time

   • No endogenous target gene expression data provided
   • Mechanism of ligase-independent transcriptional repression remains undefined
   • No in vivo confirmation
3. 2009 High

   MKRN1 was shown to ubiquitinate both p53 and p21 under normal conditions, but under DNA damage stress it preferentially degrades p21, stabilizing p53 to promote apoptosis—establishing the concept of stress-regulated substrate switching.

   Evidence Ubiquitination assays, K291/K292 mutagenesis, siRNA knockdown, and apoptosis assays across multiple cell lines

   PMID:19536131

   Open questions at the time

   • The signal that redirects MKRN1 from p53 to p21 during stress was not identified in this study
   • In vivo relevance of the substrate switch not demonstrated
4. 2010 High

   MKRN1's substrate repertoire was extended to viral proteins: it ubiquitinates West Nile virus capsid protein at K101/K103/K104, promoting its degradation and limiting viral cytotoxicity, positioning MKRN1 as a host antiviral factor.

   Evidence Co-IP, ubiquitination assay, site-directed mutagenesis of WNV capsid lysines, domain mapping, and viral replication assays

   PMID:19846531

   Open questions at the time

   • Relevance to other flaviviruses not tested
   • Whether viruses counter MKRN1 activity was not addressed
5. 2011 Medium

   A short MKRN1 isoform in neurons was found to bind PABP in an RNA-independent manner and stimulate translation when tethered to mRNA, and to accumulate in dendritic granules following synaptic stimulation, revealing a role in local translational regulation.

   Evidence RNA-independent Co-IP, tethering reporter assay, in vivo perforant-path stimulation in rat hippocampus, immunofluorescence co-localization

   PMID:22128154

   Open questions at the time

   • Endogenous mRNA targets in neurons not identified
   • Mechanism by which MKRN1-short stimulates translation is unclear
   • Single lab study
6. 2012 High

   MKRN1 was identified as an E3 ligase for p14ARF, promoting senescence bypass: MKRN1 knockout MEFs showed elevated ARF and premature senescence, and high MKRN1 expression in gastric cancer correlated with low ARF levels.

   Evidence Ubiquitination assay, MKRN1 KO MEFs, xenograft model, immunohistochemistry of gastric tumors

   PMID:23104211

   Open questions at the time

   • ARF ubiquitination sites not mapped
   • Whether ARF degradation is linked to p53 substrate switching was not tested
7. 2013 High

   MKRN1 was shown to ubiquitinate PPARγ at K184/K185, suppressing adipocyte differentiation, which broadened its role beyond cell-cycle/apoptosis regulation to adipogenesis and metabolic control.

   Evidence K184/K185 mutagenesis, ubiquitination assay, MKRN1 KO MEF adipocyte differentiation assay

   PMID:24336050

   Open questions at the time

   • Signals regulating MKRN1 activity toward PPARγ not defined
   • In vivo adipose tissue phenotype in MKRN1 KO mice not fully characterized at this stage
8. 2018 High

   Three contemporaneous studies expanded MKRN1's role in signaling: ubiquitination-driven degradation of AMPKα controls metabolic syndrome in mice, ubiquitination of the tumor suppressor APC activates Wnt/β-catenin signaling, and adenovirus pVII triggers MKRN1 self-ubiquitination to evade host defense.

   Evidence AMPKα: reciprocal Co-IP, KO mice on high-fat diet, shRNA rescue in obese mice; APC: Co-IP, E3-dead mutant, β-catenin reporter; pVII: Co-IP, self-ubiquitination assay, proteasome inhibitor

   PMID:29142133 PMID:29713058 PMID:30143610

   Open questions at the time

   • Relative contribution of MKRN1 versus other AMPK regulators in vivo unclear
   • Whether APC ubiquitination sites are shared with other E3 ligases not addressed
   • Whether pVII-induced MKRN1 self-destruction occurs in all adenovirus serotypes unknown
9. 2019 High

   MKRN1 was revealed to function in ribosome-associated quality control (RQC): it binds PABPC1 in an RNA-independent manner, is positioned upstream of poly(A) sequences on mRNAs, and ubiquitinates both PABPC1 and RPS10 to promote stalling at aberrant poly(A) tracts.

   Evidence Co-IP, in vitro ubiquitination, ubiquitin-remnant mass spectrometry, polysome profiling, iCLIP/PAR-CLIP

   PMID:31640799

   Open questions at the time

   • How MKRN1-mediated ubiquitination triggers downstream RQC effectors (e.g., ZNF598 coordination) not resolved
   • Structural basis of PABPC1–MKRN1 interaction not determined
10. 2021 High

    MKRN1 was identified as an ER-associated E3 ligase for the Eag1 voltage-gated K+ channel, ubiquitinating immature (core-glycosylated) Eag1 for proteasomal degradation as part of ER quality control, distinct from CUL7-mediated peripheral quality control.

    Evidence Yeast two-hybrid, Co-IP, ubiquitination assay, glycosylation analysis, domain mapping

    PMID:33647316

    Open questions at the time

    • Whether MKRN1 regulates other ion channels is unknown
    • Structural determinants on Eag1 recognized by MKRN1 not fully defined
11. 2022 Medium

    MKRN1 was shown to mediate K63-linked ubiquitination of M. tuberculosis PPE68 at K166, which recruits SHP1 to suppress NF-κB/AP-1 signaling, revealing an unconventional K63-linked ligase activity co-opted by a pathogen for immune evasion.

    Evidence K63-linkage-specific ubiquitination assay, K166 mutagenesis, SHP1 interaction, NF-κB/AP-1 reporter in macrophages

    PMID:35603194

    Open questions at the time

    • Single lab study; independent replication needed
    • Whether MKRN1 catalyzes K63 chains on endogenous human substrates is unclear
    • In vivo infection model not used
12. 2023 High

    Quantitative proteomics identified SNIP1 as a MKRN1 substrate whose degradation relieves inhibition of TGF-β signaling, promoting EMT and metastasis in colorectal cancer, validated by conditional MKRN1 KO in mice.

    Evidence Proteomics-guided substrate discovery, ubiquitination omics, Co-IP, in vitro ubiquitination, conditional KO mice, xenograft

    PMID:37620897

    Open questions at the time

    • Whether SNIP1 degradation is relevant in non-colorectal contexts not tested
    • Relative contribution of MKRN1 vs. other SNIP1-regulatory mechanisms unknown
13. 2025 Medium

    Multiple 2025 studies extended the MKRN1–AMPK axis: MKRN1 ubiquitinates LKB1 at K146 to suppress AMPK in cardiomyocytes (regulated by FOXM1), while the drug ebastine promotes MKRN1 self-ubiquitination at R298/K360 to stabilize AMPK and alleviate metabolic steatohepatitis; additionally, MKRN1 promotes osteoclastogenesis through Akt/AMPK modulation, and ubiquitinates AGC1 via K11/K29 chains to reprogram mitochondrial metabolism and confer chemoresistance.

    Evidence Site-specific ubiquitinome profiling, cardiomyocyte-specific Mkrn1 KO, ebastine binding-site mutagenesis, AAV8 liver knockdown, RANKL-induced osteoclast assays with Mkrn1 KO mouse bone phenotyping, CRISPR screen identifying AGC1 as substrate

    PMID:39888429 PMID:40546121 PMID:40722058 PMID:41457534

    Open questions at the time

    • LKB1 ubiquitination site confirmation limited to a single study
    • Ebastine selectivity for MKRN1 over other RING ligases not demonstrated
    • AGC1 K11/K29 chain specificity mechanism unknown
    • Single-lab validations for most findings
14. 2026 Medium

    The molecular switch governing MKRN1 substrate specificity was elucidated: upon DNA damage, SIRT1-mediated deacetylation of MKRN1 redirects its activity from p53 to MDM2, placing MKRN1 as a master regulator of the p53–MDM2 feedback loop.

    Evidence Ubiquitination assays, Co-IP, SIRT1 epistasis, DNA-damage time-course, mutagenesis

    PMID:41617974

    Open questions at the time

    • Acetylation sites on MKRN1 controlling the switch not mapped
    • In vivo validation of the substrate switch not performed
    • Single study from one lab

• Key unresolved questions include the structural basis for MKRN1's remarkably broad substrate selectivity, the coordination between its E3 ligase and RNA-binding/translational regulatory functions, and whether the stress-induced substrate-switching mechanism (SIRT1-dependent) extends beyond the p53/MDM2/p21 axis to its metabolic substrates.
• No crystal or cryo-EM structure of MKRN1 or its complexes
• No unified model explaining how one E3 ligase selects among >10 structurally diverse substrates
• Relative physiological importance of E3 ligase vs. translational regulatory functions untested in vivo