JKAMP

JKAMP (JAMP) is a seven-transmembrane protein that functions principally as an endoplasmic reticulum-associated degradation (ERAD) scaffold, coupling protein quality control at the ER membrane to proteasomal degradation of misfolded substrates (PMID:18784250). At the ER it bridges chaperones, channel proteins, ubiquitin ligases, and 26S proteasome subunits, recruiting proteasomes to the ER membrane to optimize the disposal of specific misfolded ER-resident proteins; loss of the C. elegans ortholog jamp-1 sensitizes animals to ER stress and elevates the unfolded protein response (PMID:18784250). JKAMP's degradative activity is restrained by the ER-anchored ubiquitin ligase RNF5, which directs Ubc13-dependent K63-linked non-canonical ubiquitination of JKAMP; this modification does not affect JKAMP stability but blocks its association with the proteasomal ATPase Rpt5 and with p97, thereby limiting ERAD and causing accumulation of substrates such as CFTRΔ508 and TCRα (PMID:19269966). Through this scaffolding activity JKAMP also controls the abundance of G protein-coupled receptors, promoting proteasomal degradation of the β2-adrenergic receptor and the prostaglandin D2 receptor DP, with RNF5-mediated ubiquitination protecting these receptors from JKAMP-driven turnover (PMID:23798571). Bi-allelic loss-of-function variants in JKAMP cause a neurodevelopmental syndrome in which defective folding and degradation of the brain-enriched orphan GPCR GPR37 leads to its ER accumulation and impaired plasma-membrane trafficking, with a zebrafish knockout recapitulating developmental abnormalities and impaired myelin production (PMID:41643666). Independently of its ER role, JKAMP binds JNK1 through its C-terminal domain, outcompeting MAP kinase phosphatase MKP5 to sustain JNK1 activity and JNK-dependent apoptosis after UV or tunicamycin stress (PMID:16166642).

1. 2005 High

   Established the first molecular function for JKAMP by showing it modulates stress signaling rather than acting as an inert membrane protein, binding JNK1 to prolong its activity.

   Evidence Reciprocal Co-IP, domain mapping, RNAi knockdown, and competitive binding against MKP5 with apoptosis readouts in mammalian cells

   PMID:16166642

   Open questions at the time

   • Localization assigned to plasma membrane here, later revised to ER
   • Structural basis of the JNK1/MKP5 competition not resolved
   • Physiological contexts where this axis dominates over the ERAD role unclear
2. 2008 High

   Reframed JKAMP as an ER-resident ERAD scaffold that recruits proteasomes to the ER membrane, answering where and how it acts in protein quality control.

   Evidence Biochemical fractionation, Co-IP, proteasome localization assays, and C. elegans jamp-1 deletion with UPR readouts

   PMID:18784250

   Open questions at the time

   • Specific misfolded substrates incompletely enumerated
   • Stoichiometry and architecture of the chaperone-ligase-proteasome assembly unknown
   • How the same protein partitions between ER and JNK-signaling functions not addressed
3. 2009 High

   Identified the negative regulatory switch on JKAMP, showing RNF5/Ubc13-mediated K63 ubiquitination blocks proteasome and p97 recruitment without degrading JKAMP.

   Evidence In vitro ubiquitination with E2 (Ubc13) identification, Co-IP, and CFTRΔ508/TCRα degradation assays with RNF5 manipulation

   PMID:19269966

   Open questions at the time

   • Ubiquitination sites on JKAMP not mapped
   • Signals controlling RNF5 activity toward JKAMP unknown
   • Deubiquitinase reversing this mark not identified
4. 2013 High

   Extended JKAMP substrate scope to GPCRs, showing it drives proteasomal turnover of β2-adrenergic and DP receptors under RNF5 control.

   Evidence Reciprocal Co-IP, siRNA, confocal colocalization, proteasome inhibitor assays, and proteomics in mammalian cells

   PMID:23798571

   Open questions at the time

   • Selectivity rules distinguishing degraded vs spared GPCRs unclear
   • Whether JKAMP acts on folded vs misfolded receptor pools not resolved
5. 2021 Medium

   Linked JKAMP to osteogenic differentiation and Wnt signaling, with epigenetic silencing connecting its expression to a disease state.

   Evidence siRNA and overexpression with osteogenic markers, staining assays, and methylation profiling (BSP, MeDIP-seq) in adipose-derived stem cells

   PMID:33579371

   Open questions at the time

   • Mechanistic link between ERAD scaffolding and Wnt output not established
   • No independent replication
   • Direct Wnt-component interaction not demonstrated
6. 2025 Medium

   Placed JKAMP downstream of a TTC7B-AKT axis driving cancer cell migration and invasion.

   Evidence Migration/invasion assays, TTC7B and JKAMP manipulation, AKT inhibition, and IGF-1 rescue with phospho-AKT/JKAMP blots

   PMID:41392613

   Open questions at the time

   • How AKT signaling controls JKAMP transcription not defined
   • Whether the pro-invasive effect requires JKAMP's ERAD function unknown
   • Single-lab study without in vivo confirmation
7. 2026 High

   Demonstrated human disease causation, tying JKAMP loss to a neurodevelopmental syndrome via failed GPR37 quality control.

   Evidence Bi-allelic variants across 10 families, zebrafish jkamp knockout, and GPR37 folding/trafficking assays showing ER accumulation

   PMID:41643666

   Open questions at the time

   • Whether GPR37 mishandling alone accounts for the full phenotype unclear
   • Mechanism connecting JKAMP loss to myelin defects not detailed
   • Genotype-phenotype correlation across variants not established

• How JKAMP partitions between its ER ERAD scaffold role and its cytoplasmic JNK1-signaling role, and what determines substrate selection, remains unresolved.
• No structural model of the 7TM scaffold or its complexes
• Regulatory logic switching between functions unknown
• Comprehensive substrate repertoire undefined