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14-3-3

Properties1
aliases14-3-3 proteins, YWHA family, 14-3-3 scaffold, phospho-binding scaffold

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14-3-3 proteins (YWHA family)

Universal phosphoserine/phosphothreonine-binding scaffold proteins that function as cytosolic “hold-and-read” adaptors: they detect AKT/SGK/PKA-generated phospho-marks on key regulatory proteins and translate those marks into altered localization, activity, or protein-complex status. In the aging context, 14-3-3 proteins are the principal output integrators of the IGF-1 signaling axis — they sequester the pro-longevity transcription factors FOXO3, FOXO1, and the lysosomal biogenesis master regulator TFEB in the cytoplasm when nutrient/growth signaling is active, suppressing autophagy, stress resistance, and longevity programs.

Identity

This is a family page covering all seven mammalian paralogs. They are named for their co-migration behavior on DEAE-cellulose chromatography (fraction 14) and gel electrophoresis (3.3 Rf position in the original 1967 nomenclature). The conventional seven-letter designations use Greek characters; the gene-name system uses YWHA (tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein):

Greek nameGene (human)UniProtSizeNotes
14-3-3βYWHABP31946246 aaUbiquitous; forms hetero-dimers preferentially
14-3-3γYWHAGP61981247 aaUbiquitous
14-3-3εYWHAEP62258255 aaUbiquitous; major aging-relevant interactions
14-3-3ηYWHAHQ04917246 aaUbiquitous
14-3-3θ (τ)YWHAQP27348245 aaBrain-enriched
14-3-3σSFNP31947248 aaEpithelial/tumor-specific; p53 target
14-3-3ζYWHAZP63104245 aaUbiquitous; primary aging-relevant isoform

Primary canonical ID for this page (YWHAZ): UniProt P63104, ~27.7 kDa. ncbi-gene and hgnc fields are null here because this is a family page; individual gene IDs should be resolved per paralog on dedicated sub-pages if seeded.

The paralogs share ~50–80% pairwise sequence identity 1. They exist as obligate homo- or hetero-dimers in the cell; the dimer presents two independent ligand-binding grooves 2.

Domain architecture and dimer geometry

Each 14-3-3 monomer folds into 9 antiparallel α-helices (αA–αI), forming a W-shaped cup. Helices αC, αE, αG, and αI line the amphipathic binding groove that contacts the phosphopeptide ligand 2. Key features:

  • The groove is lined with positively charged and hydrophobic residues that create a complementary surface for phosphoserine/phosphothreonine motifs.
  • Dimerization is mediated through the N-terminal helices (αA–αD) of each monomer. The dimer presents two equivalent binding pockets simultaneously, enabling bivalent engagement of clients with two phosphosites (a critical feature for FOXO regulation — see below).
  • A conserved Lys49 (YWHAZ numbering) forms a direct H-bond with the phosphate group; Arg56, Arg127, and Tyr-128 provide additional coordinating contacts — all four residues are listed in the crystal structure as coordinating the phosphoserine 2. (Arg60 adjoins the basic pocket but does not interact directly with the phosphate.)
  • The C-terminal tail of the client can extend through or around the groove, enabling Mode III “C-terminal motif” contacts.

Recognition motifs

14-3-3 proteins recognize three main phosphopeptide consensus motifs, characterized biochemically by Yaffe et al. 1997 using degenerate phosphopeptide libraries 2:

ModeConsensusExample clientKey phosphosite
Mode IR·S·X·pS·X·PRAF-1 (Ser259), mT antigenpSer
Mode IIR·X·[Ar/S]·[+]·pS·[L/E/A/M]·PCDC25C, Raf-1 (Ser621)pSer
Mode IIIpS/pT-X1-2-COOH (C-terminal)—pSer/pThr (near C-terminus)

Mode III attribution note: Yaffe 1997 defines exactly two modes (Mode I and Mode II) from the phosphopeptide library screen. The “Mode III” C-terminal motif classification is from later literature and is not present in Yaffe 1997. The bivalent/tandem observation in Yaffe 1997 refers to proteins with two Mode I or Mode II sites (such as BAD and c-Raf) forming a high-affinity bidentate complex with the 14-3-3 dimer. needs-replication — the Mode III classification requires a post-1997 primary citation.

Many aging-relevant 14-3-3 clients do not match these motifs perfectly — the consensus is permissive, and additional contacts outside the core motif contribute substantially to binding affinity 2.

Functional consequences of 14-3-3 binding

14-3-3 binding exerts one of four principal effects on its client:

  1. Cytoplasmic sequestration — most common in aging biology. 14-3-3 buries nuclear localization sequences (NLS) or competes with nuclear import machinery, trapping the client in the cytoplasm. Key examples: FOXO3, FOXO1, TFEB, BAD (partial).

  2. Conformational change affecting catalytic activity — binding can allosterically activate or inhibit enzymatic substrates without necessarily changing localization.

  3. Masking of docking motifs — 14-3-3 binding can occlude substrate sites for other kinases, phosphatases, or E3 ligases, altering the client’s downstream signaling capacity.

  4. Scaffold for protein-complex assembly — some 14-3-3 interactions promote formation of ternary complexes; 14-3-3 may simultaneously contact two different proteins, stabilizing the complex.

Aging-relevant substrates

BAD — AKT-driven anti-apoptotic survival

BAD (BCL-2 antagonist of cell death) is phosphorylated by AKT at Ser136 (primary in vivo kinase) and by various kinases at Ser112 (e.g., RSK1). Either phosphosite alone is sufficient for 14-3-3 binding; the S112A/S136A double mutant is required to abolish 14-3-3 binding 3. When bound, 14-3-3 sequesters phospho-BAD in the cytoplasm, preventing BAD from binding BCL-2/BCL-xL at the OMM and thereby freeing BCL-xL to suppress apoptosis. This is a canonical survival pathway downstream of AKT.

PhosphositeKinaseOutcome
Ser112RSK1 (primary in vitro); others14-3-3 binding → cytoplasmic retention
Ser136AKT (primary in vivo)14-3-3 binding → cytoplasmic retention
Ser155PKA (proposed)Disrupts BCL-xL interaction directly; 14-3-3 involvement uncertain needs-primary-source

See bad for verified BAD biology and the per-site kinase evidence grades.

FOXO3 — longevity transcription factor retention

FOXO3a (FKHRL1) is phosphorylated by AKT at Thr32 + Ser253 (corresponding to Ser253/Ser315 in some earlier FOXO numbering systems). Both sites together are required for robust 14-3-3 binding; the T32A+S253A double mutant abolishes coimmunoprecipitation with 14-3-3. The S315A single mutant does NOT disrupt 14-3-3 binding — Ser315 drives a distinct nuclear export mechanism (cytoplasmic retention via AKT-dependent phosphorylation), not 14-3-3 docking 4. (Note: Brunet 1999 demonstrates Ser315 promotes nuclear exclusion independently of 14-3-3 but does not name CRM1 as the export receptor; CRM1/XPO1 attribution to this process derives from later literature.)

When AKT is active (e.g., under high insulin/IGF-1), phospho-Thr32/pSer253-FOXO3 is sequestered in the cytoplasm by 14-3-3, preventing FOXO3 from transcriptionally activating longevity effectors: stress-resistance genes, autophagy-inducing genes (e.g., LC3, BNIP3), and pro-apoptotic genes (e.g., PUMA, FasL). Reducing IIS → less AKT activity → less phospho-FOXO3 → 14-3-3 releases FOXO3 → nuclear entry → longevity programs 4.

See foxo3 for verified FOXO3 biology, Brunet 1999 full citation, and the daf-16/DAF-2 C. elegans orthology.

PhosphositeKinaseOutcome
Thr32AKT (+ SGK)14-3-3 docking (required for bivalent retention)
Ser253AKT (+ SGK)14-3-3 docking (required for bivalent retention)
Ser315AKTAKT-dependent nuclear export/cytoplasmic retention (NOT 14-3-3 docking); CRM1 involvement inferred from later literature, not established in Brunet 1999

FOXO1 — analogous IIS-longevity axis

FOXO1 uses the analogous bivalent 14-3-3 engagement: AKT phosphorylates Thr24 + Ser256 (human; Thr32/Ser253 in FOXO3). Ser319 (FOXO1) drives nuclear export independently of 14-3-3, directly parallel to FOXO3 Ser315 4. (CRM1 involvement in FOXO1 export is inferred from later literature.) FOXO1 is the dominant FOXO paralog in liver, adipose, and pancreatic beta-cells; FOXO3 is dominant in neurons and longevity associations.

See foxo1 for verified FOXO1-specific biology.

TFEB — mTORC1-driven lysosomal biogenesis suppression

TFEB (transcription factor EB), the master regulator of lysosomal biogenesis and the CLEAR (coordinated lysosomal expression and regulation) gene network, is sequestered in the cytoplasm by 14-3-3 via phospho-Ser211. Roczniak-Ferguson 2012 established Ser211 as the 14-3-3 docking site 5. Settembre et al. 2012 independently showed that mTORC1 phosphorylates TFEB at Ser142 (primary kinase-assay site) and identified Ser211 as an additional mTORC1 phosphorylation site that controls TFEB nuclear localization; they also demonstrated that the lysosomal surface is the co-localization platform for the mTORC1–TFEB kinase-substrate encounter 6.

When mTORC1 is inhibited (nutrient deprivation, rapamycin, AMPK activation), Ser211 is dephosphorylated, 14-3-3 releases TFEB, and TFEB translocates to the nucleus to transcriptionally activate autophagy and lysosomal biogenesis. This positions 14-3-3 as a key brake on the lysosome axis that is released by reduced nutrient sensing.

Note: TFEB primary mTOR phosphosite is Ser142 per kinase-assay evidence (Settembre 2012); Ser211 is the 14-3-3 docking site per Roczniak-Ferguson 2012. These papers are concordant but emphasize different sites 6 5.

PhosphositeKinaseOutcome
Ser211mTORC1 (also candidate; 14-3-3 binding established by Roczniak-Ferguson 2012)14-3-3 docking site → cytoplasmic retention of TFEB
Ser142mTORC1 (primary kinase-assay confirmed, Settembre 2012 Fig 3B)Rapamycin-resistant phosphorylation; S142A causes nuclear accumulation; works cooperatively with Ser211

See tfeb for verified TFEB biology and the Roczniak-Ferguson 2012 / Settembre 2012 full citations.

TSC2 — AKT-driven mTORC1 activation

TSC2 (tuberous sclerosis complex 2) is phosphorylated by AKT at Thr1462 (human) in the C-terminal region. Phospho-Thr1462 creates a 14-3-3 docking site that sequesters TSC2 from the lysosomal surface, inhibiting its GAP activity toward Rheb (Ras homolog enriched in brain). With TSC2 GAP activity suppressed, Rheb-GTP accumulates → mTORC1 activation 1. This positions 14-3-3 as a relay node in the AKT→mTORC1 branch: AKT both directly activates mTORC1 (via Raptor interactions) and indirectly does so by using 14-3-3 to neutralize the TSC1/TSC2 brake on Rheb.

See tsc1-tsc2 for verified TSC2 biology and AMPK phosphosite numbering.

Other notable substrates

14-3-3 proteins interact with hundreds of phosphoproteins beyond the four canonical aging substrates above 1:

  • CDC25A/B/C phosphatases — 14-3-3 binding sequesters CDC25 in the cytoplasm after checkpoint activation, preventing CDK activation and cell-cycle progression.
  • Raf-1 (CRAF) — 14-3-3 binding at phospho-Ser259 maintains Raf-1 in an inactive cytoplasmic state; PKA-mediated phosphorylation here negatively regulates the RAS-MAPK pathway.
  • YAP1 (Yes-associated protein) — Hippo pathway output; LATS1/2-phosphorylated YAP1 at Ser127 is sequestered by 14-3-3, preventing transcriptional co-activation of proliferative genes.
  • p53/TP53 — 14-3-3σ (SFN) is a direct p53 transcriptional target and creates a 14-3-3-mediated negative feedback on cell-cycle re-entry after DNA damage.

unsourced — the “hundreds of clients” figure for 14-3-3 interactomes requires a phosphoproteomics or proteomics citation; functional significance of most interactions is not established.

Isoform-specific notes

While many clients bind multiple 14-3-3 isoforms, some paralog preferences are recognized:

  • 14-3-3ζ (YWHAZ) and 14-3-3ε (YWHAE) are the most broadly expressed and are the primary isoforms implicated in FOXO and BAD regulation in most cell types.
  • 14-3-3σ (SFN) is uniquely induced by p53 in response to DNA damage, making it a tumor-suppressive isoform; its expression pattern is epithelial-restricted and context-dependent.
  • 14-3-3θ (YWHAQ) is brain-enriched; associated with neurodegeneration contexts (14-3-3 proteins are major components of Lewy bodies in Parkinson’s disease).
  • For most aging-biology purposes (IIS/AKT/FOXO/TFEB axis), isoform specificity has not been rigorously delineated. Pan-isoform statements are the norm in the literature. needs-replication — paralog-selective functions in aging tissues remain understudied.

Aging context — synthesis

14-3-3 proteins occupy a pivotal position in the aging-decision logic:

1. AKT/SGK output integrator for the IIS-longevity axis. The downstream effect of high IIS on FOXO transcription factors is almost entirely mediated through 14-3-3 sequestration. Reducing IIS (genetically in C. elegans, pharmacologically, or via caloric-restriction) reduces AKT activity → reduces 14-3-3–phosphosubstrate formation → FOXO/TFEB nuclear → autophagy, stress resistance, and longevity gene programs engaged. In this sense, 14-3-3 is the molecular gate between nutrient-sensing kinase activity and longevity effector access to the nucleus.

2. mTORC1 output integrator for lysosomal biogenesis. The TFEB-Ser211/14-3-3 arm is an independent (non-FOXO) mechanism by which mTORC1 hyperactivity suppresses autophagy. Chronic mTORC1 hyperactivation (as posited by the hyperfunction-theory) would maintain constitutive TFEB cytoplasmic retention via 14-3-3, gradually impairing lysosomal biogenesis and autophagy flux.

3. Hyperfunction theory implications. Chronic IIS/mTORC1 hyperactivation → constitutive phosphorylation of 14-3-3 clients → stable cytoplasmic sequestration of FOXO/TFEB → failure of stress-response and autophagy programs → aging. Under this framing, the 14-3-3 interaction network is not a cause of aging per se but the molecular mechanism through which chronically elevated growth signaling suppresses aging-resistance programs.

DimensionStatus
Phospho-binding mechanism conserved in humans?yes — crystal structure (Yaffe 1997) is from human 14-3-3ζ; FOXO/BAD sites verified in human cells
FOXO/TFEB/BAD pathway logic conserved across species?yes — conserved from yeast to mammals; DAF-16/14-3-3 axis in C. elegans
Replicated in humans (longevity axis)?partial — FOXO3A polymorphisms associate with human longevity (Willcox 2008; Flachsbart 2009); 14-3-3 interaction mechanism not directly tested in human aging; indirect

Therapeutic angles and limitations

Pan-isoform inhibition is not a viable therapeutic strategy. 14-3-3 proteins have >200–300 characterized clients and are essential for cell survival; germline-null of most isoforms causes embryonic lethality 1. Pan-inhibitors (e.g., BV02) show severe cytotoxicity in preclinical models.

Paralog-selective or client-selective approaches are being explored (preclinical):

  • 14-3-3σ (SFN) agonists to reinforce G2/M checkpoint in cancer.
  • Peptidomimetics that disrupt specific 14-3-3/client interactions (e.g., disrupting 14-3-3:FOXO to reactivate FOXO in muscle atrophy/aging; disrupting 14-3-3:TSC2 to suppress mTORC1 hyperactivation) — all preclinical; no clinical-stage agents targeting 14-3-3 specifically in aging.

long-term-unknown — paralog-selective modulators for aging-biology applications exist only at early tool-compound stage; no human aging trial data.

Pathway membership

  • insulin-igf1 — primary upstream activator (INSR → AKT → phospho-FOXO/BAD → 14-3-3 sequestration)
  • pi3k-akt-pathway — AKT is the kinase that generates most aging-relevant 14-3-3 docking marks
  • mtor — mTORC1 generates phospho-Ser211 on TFEB for 14-3-3 sequestration; 14-3-3 also relays AKT→TSC2 inhibition upstream of mTOR

Key interactors

  • akt — primary kinase upstream; generates pSer/pThr docking marks on FOXO3/FOXO1/BAD/TSC2
  • foxo3 — sequestered by 14-3-3 at pThr32 + pSer253; primary longevity axis link
  • foxo1 — sequestered by 14-3-3 at pThr24 + pSer256; liver/adipose/beta-cell dominant
  • foxo-transcription-factors — family overview page
  • bad — sequestered at pSer112 or pSer136 (either alone sufficient); anti-apoptotic arm
  • tfeb — sequestered by 14-3-3 at pSer211 (mTORC1-driven); lysosomal biogenesis suppression
  • tsc1-tsc2 — pThr1462 TSC2 sequestration by 14-3-3 → Rheb-GTP → mTORC1 activation
  • sgk1 — parallel to AKT; also phosphorylates FOXO3 at Thr32/Ser253 → 14-3-3 binding

Limitations and gaps

  • needs-canonical-id — ncbi-gene and hgnc fields are null on this family page; individual paralog gene IDs require dedicated sub-pages for full canonical-database linkage.
  • needs-replication — paralog-selective functions in aging contexts are not well characterized; most published aging-biology data treats 14-3-3 proteins as a functional class.
  • needs-human-replication — direct evidence that modulating 14-3-3/FOXO or 14-3-3/TFEB interactions alters human aging trajectories does not yet exist; all evidence is from model organisms or cultured cells.
  • unsourced — the “hundreds of 14-3-3 clients” claim requires a phosphoproteomics citation (Yaffe 2002 Nat Biotechnol proteomics study or equivalent).
  • dose-response-unclear — AKT activity threshold at which phospho-FOXO/14-3-3 complex formation becomes dominant vs. basal nuclear FOXO activity is not quantified in human cells.
  • No clinical-stage compound specifically targets the 14-3-3/FOXO or 14-3-3/TFEB interface for aging indications.

Footnotes

Footnotes

  1. doi:10.1016/j.semcancer.2006.03.005 · Aitken A. 2006 · Seminars in Cancer Biology · review · citation_count=835; 100th percentile; not_oa no-fulltext-access — quantitative claims derived from this review should be independently verified against primary literature ↩ ↩2 ↩3 ↩4

  2. doi:10.1016/s0092-8674(00)80487-0 · Yaffe MB et al. 1997 · Cell · n=not applicable (biochemical/structural) · phosphopeptide library screen + crystal structure · model: in vitro / recombinant human 14-3-3ζ · citation_count=1,629; 100th percentile; local PDF available ↩ ↩2 ↩3 ↩4 ↩5

  3. zha-1996-bad-14-3-3 · doi:10.1016/s0092-8674(00)81382-3 · Zha J et al. 1996 · Cell · n=not applicable (biochemical) · site-directed mutagenesis + coimmunoprecipitation · model: in vitro + transfected 293T · citation_count=2,617; 100th percentile; local PDF available; verified on bad.md (Zha 1996 verified) ↩

  4. brunet-1999-akt-foxo3-14-3-3 · doi:10.1016/s0092-8674(00)80595-4 · Brunet A et al. 1999 · Cell · n=not applicable (biochemical) · mutagenesis + coIP + nuclear/cytoplasmic fractionation · model: CCL39 fibroblasts, 293T cells, cerebellar granule neurons, Jurkat T cells · citation_count=6,504; 100th percentile; local PDF available; verified on foxo3.md (Brunet 1999 verified) ↩ ↩2 ↩3

  5. doi:10.1126/scisignal.2002790 · Roczniak-Ferguson A et al. 2012 · Science Signaling · n=not applicable (biochemical) · phosphomutant analysis + 14-3-3 coIP · model: HeLa cells + in vitro kinase assay · citation_count=1,313; 100th percentile; not_oa; abstract confirmed; verified on tfeb.md (Roczniak-Ferguson 2012 verified) ↩ ↩2

  6. doi:10.1038/emboj.2012.32 · Settembre C et al. 2012 · EMBO J · n=not applicable (biochemical) · mTOR lysosomal signaling + TFEB phospho-mutant analysis · model: HeLa + HEK293 + MEFs · citation_count=1,865; 100th percentile; local PDF available; verified on tfeb.md (Settembre 2012 verified) ↩ ↩2

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