ep300

EP300 (E1A Binding Protein p300)

EP300 is a large (~265 kDa, 2,414 aa) transcriptional co-activator and histone acetyltransferase (HAT) that serves as a master regulator of gene expression across many cellular programs. In aging biology, EP300’s most functionally critical role is as an endogenous suppressor of autophagic flux: EP300 acetylates ATG5, ATG7, ATG8 (LC3), and ATG12, and elevated p300 expression inhibits starvation-induced autophagy while p300 knockdown induces it ¹. Spermidine extends lifespan partly by competitively inhibiting EP300, reversing this suppression ². EP300 is a paralog of CBP (CREBBP) (~63% sequence identity); together they form the KAT3 family. Loss-of-function mutations cause Rubinstein-Taybi syndrome type 2 (RSTS2) ³.

Identity

• UniProt: Q09472 (EP300_HUMAN) — Swiss-Prot reviewed
• NCBI Gene: 2033
• HGNC symbol: EP300; HGNC ID 3373
• Aliases: p300, KAT3B, E1A-associated protein p300
• Length: 2,414 amino acids (canonical isoform)
• Mass: ~265 kDa (observed by SDS-PAGE; ~325 kDa apparent due to anomalous migration)
• Mouse ortholog: Ep300 (one-to-one ortholog; high sequence conservation throughout)
• Paralog: CREBBP (CBP); ~63% overall sequence identity; KAT3 family. Canonical page: cbp-p300

Domain architecture

EP300 is a large multidomain scaffold protein; domains listed N→C ⁴:

Domain	Approx. residues	Function
TAZ1 (zinc-finger)	~340–439	Interaction with HIF1A, CITED2, and other transactivators
KIX domain	~566–645	Interaction with phospho-CREB, MYB, and other activation domains
Bromodomain	~1049–1156	Reads acetyl-lysine marks on histones; required for chromatin recruitment
HAT domain (KAT3B)	~1287–1663	Catalytic acetyltransferase; acetylates histones and non-histone proteins; also does crotonylation, butyrylation, propionylation, lactylation
ZZ zinc-finger	1665–1713	Unknown function; conserved with CBP (corrected against UniProt Q09472 — earlier ~1723–1770 was incorrect)
TAZ2 zinc-finger	1728–1809	Interaction with p53, nuclear hormone receptors (corrected against UniProt Q09472 — earlier ~1834–1890 was incorrect)
IBiD (IRF-3 binding domain)	~2059–2117	Interaction with IRF-3; role in innate immune gene activation

The central HAT domain is the principal target of therapeutic development (C646, A-485, CCS1477).

Function

Histone acetyltransferase activity

EP300’s primary enzymatic function is acetylation of lysines on all four core histones in nucleosomes. Key marks established by EP300 [UniProt Q09472]:

• H3K18ac — promoter and enhancer activation
• H3K27ac — distinguishes active enhancers from poised enhancers (along with CBP)
• H3K56ac — involved in DNA damage response and chromatin assembly
• H4K8ac, H4K12ac — histone deposition and transcriptional activation

H3K27ac is the primary ChIP-seq mark used to identify EP300/CBP-occupied active enhancers in the epigenomics literature. unsourced — specific quantitative contribution of EP300 vs CBP to H3K27ac at any given locus depends on cell type; bulk statements conflate the two paralogs.

Non-histone acetylation targets

EP300 acetylates hundreds of non-histone proteins. Aging-relevant substrates:

• p53 K382 — acetylation stabilizes p53 and shifts transcriptional target preference toward cell-cycle arrest programs; mediated by EP300’s TAZ2 domain interaction ⁵
• ATG5, ATG7, ATG8 (LC3), ATG12 — cytoplasmic acetylation events that suppress autophagic flux; p300 knockdown reduces acetylation of these Atg proteins and induces autophagy under both fed and starved conditions; p300 overexpression inhibits starvation-induced autophagy ¹
• HIF-1α — acetylation modulates hypoxic transcriptional response
• STAT family members — acetylation modulates cytokine signaling

Transcriptional co-activator function

Beyond its enzymatic activity, EP300 functions as a physical bridge between sequence-specific transcription factors (bound at enhancers/promoters) and the RNA Pol II general transcription machinery. Its bromodomain anchors it to acetylated chromatin, and its multiple protein-protein interaction domains (KIX, TAZ1, TAZ2) recruit a wide range of activation-domain-containing transcription factors. EP300 is recruited to thousands of active enhancers across diverse cell types; it is one of the most broadly expressed and widely used transcriptional co-regulators in metazoans.

Cloning and discovery

EP300 was isolated in 1994 by Eckner et al. as a 300-kDa nuclear phosphoprotein that bound adenovirus E1A protein ⁴. The study demonstrated by in vitro transcription assays that p300 had properties of a transcriptional adaptor, and noted sequence similarity to the previously cloned CBP. The “p300” designation reflects the ~300-kDa apparent migration on SDS-PAGE.

Knockout and haploinsufficiency phenotypes

Yao et al. 1998 generated germline Ep300 knockouts in mice and showed:

• Ep300−/− homozygous null mice: embryonic lethal between E9.5–E11.5, with heart and neural tube defects, and generalized proliferative defects — demonstrating EP300 is essential for embryonic development ⁶
• Ep300+/− heterozygotes: viability is background-dependent — in the 129×BL6 mixed background heterozygotes were recovered at normal Mendelian ratios with no overt phenotype; in the inbred 129/Sv background ~55% fewer heterozygotes than expected were recovered at weaning (significant in-utero lethality); surviving heterozygotes in both backgrounds lacked overt developmental defects ⁶. Compound haploinsufficiency with Crebbp+/− produces embryonic lethality (no viable double-heterozygotes recovered)
• Gene-dosage sensitivity underlies the human disease presentation: a single functional allele is insufficient for normal development ⁶

Dimension	Status	Notes
Pathway conserved in humans?	yes	Ep300 mouse knockout recapitulates human RSTS2 features; HAT function conserved
Phenotype conserved in humans?	yes	Haploinsufficiency → intellectual disability + morphological features in RSTS2
Replicated in humans?	yes (genetic)	Multiple independent RSTS2 pedigrees with EP300 loss-of-function mutations

Disease associations

Rubinstein-Taybi syndrome type 2 (RSTS2)

Autosomal dominant haploinsufficiency of EP300 causes RSTS2 (OMIM #613684). Features: intellectual disability, behavioral issues, characteristic facial features (broad thumbs and broad big toe, prominent nose with long hanging columella, arched eyebrows), and growth retardation ³. In the Roelfsema 2005 cohort of 92 RSTS patients screened, 36 carried CBP (CREBBP) mutations and 3 carried EP300 mutations (a ratio of ~1:12 EP300:CBP), leaving the majority of RSTS cases genetically unexplained. The widely-cited clinical figure that ~8% of RSTS carry EP300 mutations derives from later, larger case series — this paper does not report that proportion. needs-replication — mutation frequency in EP300-RSTS depends on ascertainment strategy and cohort composition.

Menke-Hennekam syndrome 2 (MKHK2)

A distinct intellectual-disability syndrome caused by EP300 missense mutations in the KIX domain; clinically overlapping with but distinct from RSTS2.

Cancer

EP300 is somatically mutated in many cancers, acting as either a tumor suppressor (loss-of-function — especially in bladder, colon, and lung cancers) or, in other contexts, as an oncogenic co-activator. Chromosomal translocations fusing EP300 to MLL (KMT2A) or MOZ (KAT6A) occur in acute myeloid leukemia and activate aberrant gene-expression programs. EP300/CBP are also amplified in some hormone-driven cancers (prostate, breast).

Aging relevance

EP300 as a repressor of autophagy — the spermidine mechanism

The most directly aging-relevant function of EP300 is its role as a negative regulator of autophagy. Lee and Finkel 2009 demonstrated that p300/EP300 acetyltransferase activity regulates autophagic flux by acetylating Atg proteins (Atg5, Atg7, Atg8/LC3, Atg12) in HeLa cells: p300 knockdown reduced Atg protein acetylation and increased autophagic flux (elevated LC3-II/I ratio; reduced p62) under both fed and starved conditions, while p300 overexpression inhibited starvation-induced autophagy. p300 and Atg7 also physically interact, and this interaction was reduced ~40% after 2 h starvation (n=3; p<0.05), suggesting a nutrient-sensitive regulatory mechanism ¹.

Pietrocola et al. 2015 (published 2014 in Cell Death and Differentiation) extended this mechanism by identifying EP300 as a specific, primary target through which spermidine induces autophagy ²:

• A cell-free acetyltransferase assay showed spermidine competitively inhibits EP300 HAT activity against histone H3 substrates (inhibition reversed by raising acetyl-CoA 10-fold)
• A systematic siRNA screen of 43 acetyltransferase candidates identified EP300 (and NAA20) as the only ones whose knockdown fully phenocopied autophagy induction (GFP-LC3 puncta, p62 depletion, s6RP dephosphorylation)
• The selective EP300 inhibitor C646 alone induced autophagy without causing global protein deacetylation, confirming EP300-selectivity rather than pan-HAT inhibition
• EP300 knockdown and C646 treatment each reduced acetylation of ATG5, ATG7, ATG12, and LC3 in cells, establishing these as cytoplasmic EP300 substrates linking to autophagy suppression

Key mechanistic conclusion from Pietrocola 2015: “EP300 acts as an endogenous repressor of autophagy and that potent autophagy inducers including spermidine de facto act as EP300 inhibitors.” This corrects an earlier broader framing (HAT-broad inhibition) that circulated in the autophagy literature ².

This mechanism has direct aging implications: autophagy declines with age in most tissues, and its restoration extends lifespan in multiple organisms. EP300 is a druggable node that, when inhibited, could mimic caloric restriction (caloric-restriction-mimetic) by de-repressing autophagy without dietary restriction.

Dimension	Status	Notes
Pathway conserved in humans?	yes	EP300 and ATG proteins are highly conserved; EP300 HAT domain near-identical in human/mouse
Phenotype conserved in humans?	unknown	Autophagy induction by EP300 inhibition shown in human cell lines; longevity endpoint not tested
Replicated in humans?	no	No human longevity or healthspan trial using EP300 inhibitors; needs-human-replication

EP300 inhibition as a caloric restriction mimetic

Pharmacological EP300 inhibition — like spermidine’s competitive inhibition — produces a CR-mimetic transcriptional signature in multiple cell types: reduced anabolic gene expression, upregulated autophagy, downregulated mTOR-dependent programs. This places EP300 alongside mtor and ampk as a nutrient-sensing effector whose inhibition mimics the beneficial effects of caloric restriction. needs-replication — the CR-mimetic claim for EP300 inhibitors per se (beyond the autophagy endpoint) has limited supporting primary-source evidence outside of the spermidine mechanism.

Epigenetic alterations with age

EP300/CBP occupy thousands of active enhancers; their activity shapes the tissue-specific enhancer landscape. There is emerging evidence that EP300 binding and H3K27ac patterns shift with age at key tissue-homeostasis loci, potentially contributing to the epigenetic-alterations hallmark. unsourced — specific aging EP300 ChIP-seq datasets in aged human tissue are needed; claims in this area remain at the hypothesis level.

Pharmacology and therapeutic angles

C646 — EP300-selective HAT inhibitor (tool compound)

C646 is a cell-permeable competitive inhibitor of EP300’s HAT domain (IC₅₀ ~1.6 µM vs EP300; selectivity over GCN5/PCAF). Used as a research tool to study EP300-dependent autophagy induction and cancer biology. Not in clinical development.

A-485 — potent, selective EP300/CBP HAT inhibitor

A-485 (IC₅₀ ~60 nM vs p300; ~5 nM in cell assays) is a markedly more potent EP300/CBP inhibitor than C646, with good selectivity over the wider HAT family. First described 2017 as a candidate anti-cancer agent in androgen-receptor-driven prostate cancer and hematological malignancies. Preclinical only; no published aging-specific studies.

CCS1477 — clinical-stage EP300/CBP HAT inhibitor

CCS1477 (Inobrodib; currently in phase 1/2 trials for advanced prostate cancer and hematological malignancies, e.g., NCT04068597) is the furthest-advanced EP300/CBP HAT inhibitor in the clinic. Its development is in oncology, but mechanistic proof-of-concept that EP300 is pharmacologically tractable in humans is relevant to aging-intervention planning. long-term-unknown — safety profile in healthy older adults is not characterized.

Cross-references

• spermidine — dietary polyamine that competitively inhibits EP300 HAT activity; core mechanism verified per Pietrocola 2015 (spermidine.md verified-partial)
• autophagy — process repressed by EP300; inhibition of EP300 de-represses autophagy initiation
• p53 — non-histone substrate; EP300 acetylates K382 to stabilize and tune p53 activity (p53.md verified, cross-link to cbp-p300 interactor)
• cbp-p300 — paralog complex page covering EP300 + CBP as co-equal KAT3 family members
• histone-acetylation — broader process page (planned)
• caloric-restriction — EP300 inhibition produces overlapping transcriptional and metabolic effects
• mtor — parallel nutrient-sensing node; mTOR and EP300 both repress autophagy through distinct mechanisms
• epigenetic-alterations — hallmark; EP300-driven enhancer remodeling contributes

Limitations and gaps

• EP300 vs CBP contribution: Most cell biology uses EP300+CBP together (“p300/CBP”), and selective separation of their individual contributions at any given locus or in any given organism is technically challenging. Claims attributing effects specifically to EP300 (vs CBP) should be treated cautiously unless genetic knockouts or isoform-selective inhibitors were used. contradictory-evidence
• Autophagy in human aging: The EP300–autophagy axis is well-documented in cell lines and mouse models; whether pharmacological EP300 inhibition meaningfully augments autophagic flux in aged human tissue is undemonstrated. needs-human-replication
• Long-term EP300 inhibition safety: EP300/CBP are among the most broadly expressed transcriptional regulators; chronic systemic inhibition would be expected to have pleiotropic effects on tissue homeostasis, immune function, and development (in germline). Long-term safety in adults is unknown. long-term-unknown
• Aging-specific EP300 epigenomics: Whether EP300 occupancy or H3K27ac patterns shift in an aging-causal (rather than correlative) manner at key rejuvenation loci is an open hypothesis. no-mechanism
• GenAge entry: EP300 does not currently appear in GenAge-human or GenAge-models (as of 2026-05-04); inclusion would require evidence of a direct EP300 genetic manipulation affecting lifespan in a model organism. needs-replication

Footnotes

Footnotes

1. doi:10.1074/jbc.M807135200 · Lee IH & Finkel T (2009) “Regulation of autophagy by the p300 acetyltransferase” · J Biol Chem 284(10):6322–6328 · in-vitro / cell culture · model: HeLa cells (human) · n=3 independent experiments per assay · 261 citations · local PDF: ↩ ↩² ↩³

2. doi:10.1038/cdd.2014.215 · Pietrocola F et al. (2015) “Spermidine induces autophagy by inhibiting the acetyltransferase EP300” · Cell Death Differ 22(3):509–516 · in-vitro (cell-free HAT assay, cell culture) + in-vivo (mouse, yeast) · 300 citations; FWCI 9.5 (100th percentile) · local PDF at — VERIFIED on spermidine page (verified-partial); EP300-specific mechanism confirmed from full PDF ↩ ↩² ↩³

3. doi:10.1086/429130 · Roelfsema JH et al. (2005) “Genetic heterogeneity in Rubinstein-Taybi syndrome: mutations in both the CBP and EP300 genes cause disease” · Am J Hum Genet 76(4):572–580 · observational (genetic) · n=92 RSTS patients genotyped; 36 CBP mutations, 3 EP300 mutations found · 467 citations · local PDF: ↩ ↩²

4. doi:10.1101/gad.8.8.869 · Eckner R et al. (1994) “Molecular cloning and functional analysis of the adenovirus E1A-associated 300-kD protein (p300)” · Genes & Development · in-vitro / biochemical + cell biology · 1,047 citations · model: human cell lines; original p300 cloning paper ↩ ↩²

5. EP300 listed as known interactor on p53 (p53.md verified); EP300 acetylation of K382 noted in p53.md interactors section citing cbp-p300. No additional primary source cited here to avoid duplication — see p53 for the canonical claim. ↩

6. doi:10.1016/s0092-8674(00)81165-4 · Yao TP et al. (1998) “Gene dosage-dependent embryonic development and proliferation defects in mice lacking the transcriptional integrator p300” · Cell 93(3):361–372 · in-vivo (mouse, germline KO) · n not specified per group (Table 1 gives survivor counts by genotype; no per-group n reported) · model: Ep300+/− and Ep300−/− on 129/Sv inbred and 129×BL6 mixed backgrounds · 1,001 citations · local PDF: ↩ ↩² ↩³