EID1

EID1 is a short-lived, ubiquitously expressed nuclear protein that functions as a transcriptional corepressor by inhibiting CBP/p300 histone acetyltransferase activity and thereby restraining differentiation- and developmental-gene programs (PMID:10828624, PMID:24167073). It represses transactivation by multiple sequence-specific factors, including MyoD-responsive myogenic promoters (PMID:18557765), the orphan nuclear receptor SF-1—where it competes with the coactivator SRC-1 (PMID:18182853)—and E2F1 at the Egr-1 promoter in concert with SHP/NR0B2 (PMID:24619556); EID1 also binds the retinoblastoma protein (pRB) (PMID:20541531) and occupies target promoters directly, as shown for the GPDH promoter in adipocytes (PMID:32056205). Through these activities EID1 acts as a brake on lineage commitment: it suppresses adipogenic and brown-fat gene programs (PMID:20541531, PMID:32056205), yet is itself required for adipocyte differentiation of mesenchymal stem cells and for neural stem cell proliferation, where its loss attenuates PI3K/AKT/GSK3β signaling and impairs learning and memory (PMID:20486779, PMID:30926163). EID1 abundance is the dominant control point: it carries a modular peptidic degron overlapping its pRB-binding domain that is recognized by the SCF(FBXO21) ubiquitin ligase for polyubiquitylation and proteasomal degradation (PMID:26631746, PMID:26085330), with MDM2 additionally mediating K48-linked ubiquitination (PMID:24167073); binding partners counteract this turnover, as necdin stabilizes EID1 and relocalizes it to the cytoplasm (PMID:18557765) and Pcid2 blocks MDM2 association to sustain CBP/p300 inhibition in embryonic stem cells (PMID:24167073). Excess nuclear EID1 is pathologically relevant: it accumulates in cortical neurons of Alzheimer's disease brains, and its overexpression in mice disrupts neurofilament organization, reduces long-term potentiation, and impairs spatial memory, consistent with loss of CBP/p300-mediated histone and p53 acetylation (PMID:22186421).

1. 2000 Medium

   Establishing the gene's existence and basic features defined EID1 as a conserved, ubiquitously expressed human protein available for functional study.

   Evidence cDNA cloning, Northern blot, and radiation hybrid mapping of the 187-aa protein

   PMID:10828624

   Open questions at the time

   • No molecular function assigned at cloning
   • No subcellular localization or interaction partners defined
2. 2007 Medium

   Identifying EID1 as a corepressor of the nuclear receptor SF-1 that competes with SRC-1 established a coactivator-displacement mechanism for its transcriptional repression.

   Evidence Yeast two-hybrid, GST pull-down, and transactivation/colocalization assays in mammalian cells

   PMID:18182853

   Open questions at the time

   • Selectivity for SF-1 over related receptors not mechanistically explained
   • Did not link repression to CBP/p300 inhibition directly
3. 2008 Medium

   Showing EID-1 inhibits MyoD-responsive myogenic promoters and is regulated by necdin connected EID1 repression to a differentiation program and to partner-controlled stability and localization.

   Evidence Yeast two-hybrid, transactivation assays, pulse-chase half-life, and subcellular localization in transfected cells

   PMID:18557765

   Open questions at the time

   • Mechanism of necdin-driven nuclear-to-cytoplasmic relocalization unresolved
   • How relocalization relieves repression not biochemically defined
4. 2010 Medium

   Defining EID1 as both a repressor of PPARγ/brown-fat programs and a pRB-binding, miR-138-regulated, differentiation-required factor placed EID1 at a node controlling adipogenic commitment.

   Evidence 3T3-L1 overexpression with transactivation and Co-IP assays; luciferase 3'UTR validation and siRNA knockdown in adipose-derived MSCs

   PMID:20486779 PMID:20541531

   Open questions at the time

   • Apparent opposing roles (represses PPARγ yet required for differentiation) not reconciled
   • pRB interaction rests on a single Co-IP
   • Direct promoter occupancy not yet shown at this stage
5. 2011 Medium

   Linking nuclear EID1 accumulation to Alzheimer's pathology and to in vivo synaptic and cognitive deficits established a disease-relevant consequence of CBP/p300 inhibition.

   Evidence Immunostaining of human AD brains, transgenic mouse overexpression, LTP electrophysiology, and spatial memory testing

   PMID:22186421

   Open questions at the time

   • Causal contribution of CBP/p300 inhibition inferred rather than directly demonstrated
   • Trigger of increased nuclear translocation in AD unknown
6. 2014 Medium

   Identifying MDM2 as an E3 ligase for EID1 and Pcid2 as a stabilizing partner within the CBP/p300-EID1 complex revealed how EID1 turnover gates developmental gene expression in ESCs.

   Evidence Co-IP, K48-linkage ubiquitylation assay, and Pcid2 KO in mouse and human ESCs

   PMID:24167073

   Open questions at the time

   • Relative contributions of MDM2 versus other ligases not quantified
   • Structural basis of Pcid2 blocking MDM2 not defined
7. 2014 Medium

   Demonstrating direct EID1 binding to SHP and E2F1 and co-occupancy of the Egr-1 promoter extended EID1 repression to E2F1-driven transcription on specific chromatin targets.

   Evidence GST pull-down, ChIP, and reporter assays in hepatoma and stellate cells

   PMID:24619556

   Open questions at the time

   • Generality of EID1-SHP corepression beyond Egr-1 untested
   • Recruitment hierarchy among EID1, SHP, and E2F1 unresolved
8. 2015 High

   Reconstituting SCF(FBXO21)-mediated polyubiquitylation of a modular EID1 degron overlapping its pRB-binding domain defined the principal pathway controlling EID1 stability in cycling and quiescent cells.

   Evidence In vitro ubiquitylation, in vivo Co-IP and interaction mapping, degron mutagenesis, CRISPR/Cas9 disruption of FBXO21, and proteasome inhibition; two independent labs

   PMID:26085330 PMID:26631746

   Open questions at the time

   • Signals controlling FBXO21 substrate recognition not defined
   • Interplay between FBXO21 and MDM2 pathways not resolved
9. 2015 Low

   Implicating palmitoylation in EID1 turnover and CBP/p300 activity proposed a lipid modification as an additional regulatory layer at the NSC self-renewal/differentiation switch.

   Evidence 2-bromopalmitate inhibitor treatment with NSC differentiation, cell-cycle, and HAT activity assays

   PMID:26497028

   Open questions at the time

   • Palmitoylation inferred from inhibitor treatment without direct acylation assay or site mutagenesis
   • Modified residues unidentified
   • Mechanistic link to degradation not established
10. 2019 Medium

    Knockout of EID1 reducing NSC proliferation and attenuating PI3K/AKT/GSK3β signaling with cognitive deficits revealed a positive, partner-independent requirement for EID1 in neural development.

    Evidence Knockout mice, neurosphere and CCK-8 assays, Western blotting of pathway components, and behavioral testing

    PMID:30926163

    Open questions at the time

    • Direct molecular link between EID1 and PI3K/AKT/GSK3β not established
    • Reconciliation with EID1's transcriptional-repressor role unclear
11. 2020 Medium

    Showing nuclear-speckle localization and direct GPDH promoter binding with repression of lipid accumulation provided direct chromatin-level evidence for EID1 action at an adipogenic target gene.

    Evidence Confocal microscopy, ChIP for GPDH promoter, DNA microarray, and 3T3-L1 overexpression

    PMID:32056205

    Open questions at the time

    • Whether EID1 binds DNA directly or via partners not resolved
    • Functional integration of GPDH repression with PPARγ/pRB axes unclear

• How EID1's opposing context-dependent roles—repressing differentiation genes versus being required for stem-cell proliferation and differentiation—are reconciled at the molecular level remains unresolved.
• No unified model linking EID1 abundance, partner identity, and lineage outcome
• No structural data on the CBP/p300-EID1 complex
• Direct DNA-binding capacity versus recruitment by partners undefined