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beclin-1

Properties1
aliasesBECN1, ATG6, VPS30, beclin 1, coiled-coil myosin-like BCL2-interacting protein

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Beclin-1 (BECN1)

The master scaffold of autophagy initiation β€” a 450 aa protein that nucleates the Class III PI3-kinase (PI3KC3) complex at the phagophore assembly site, generating the phosphatidylinositol 3-phosphate (PI3P) lipid signal required to recruit downstream autophagy machinery. Its BH3 domain is sequestered by bcl-2 and bcl-xl during nutrient sufficiency; cellular stress releases Beclin-1 via BCL-2 phosphorylation or competitive displacement, coupling apoptotic signalling to the autophagy on/off switch.

Identity

  • UniProt: Q14457 (BECN1_HUMAN)
  • NCBI Gene: 8678
  • HGNC symbol: BECN1 (HGNC:1034)
  • Ensembl: ENSG00000126581
  • Mouse ortholog: Becn1 (one-to-one ortholog; highly conserved)
  • Yeast ortholog: Atg6 / Vps30 (functional ortholog; same PI3KC3 scaffold role)
  • Length: 450 amino acids; ~51.9 kDa
  • Chromosomal locus: 17q21 (monoallelic deletion frequent in breast and ovarian cancer)

Domain structure

DomainResidues (approx.)Function
BH3 domain108–127BCL-2 / BCL-xL binding; mouse mutation F121A (= human F123A) decreases interaction
Coiled-coil domain (CCD)142–270Homodimerization; ATG14L or UVRAG docking
BARA / ECD245–450Ξ²-Ξ±-repeated autophagy-specific domain; membrane curvature sensing; Rubicon interaction
Membrane-association region425–450Required for membrane localization

The BH3 domain (UniProt residues 108–127; exact boundaries not independently re-verified against UniProt in this pass) binds the hydrophobic groove of bcl-2 and bcl-xl, positioning Beclin-1 as a molecular bridge between the apoptotic and autophagic machineries 1. Note: Pattingre 2005 characterises the Bcl-2-binding domain as amino acids 88–150 and uses F123A (human numbering) as the binding-deficient mutant; FernΓ‘ndez 2018 uses the mouse equivalent F121A.

PI3KC3 complex composition

Beclin-1 is the non-catalytic scaffold subunit of two functionally distinct PI3KC3 complexes:

SubunitGeneRolePresent in
Beclin-1BECN1Scaffold; regulatoryComplex I + II
VPS34PIK3C3Class III PI3-kinase (catalytic)Complex I + II
VPS15PIK3R4Regulatory/adaptor kinaseComplex I + II
ATG14LATG14ER targeting; phagophore initiationComplex I (autophagy)
UVRAGUVRAGLate-endosome/lysosome maturationComplex II (endosomal)
RubiconRUBCNInhibitory; restricts endosomal complexComplex II (inhibitory branch)

Complex I (Beclin-1/VPS34/VPS15/ATG14L) localises to the omegasome/ER-associated phagophore assembly site and generates PI3P to recruit WIPI2, DFCP1, and downstream ATG machinery. Complex II (Beclin-1/VPS34/VPS15/UVRAG) acts at late endosomes and lysosomes to facilitate membrane trafficking and autophagosome-lysosome fusion.

BCL-2 / BCL-xL inhibition mechanism

During nutrient sufficiency, bcl-2 (ER-localised pool) and bcl-xl hold Beclin-1 in an inactive heterodimer via the BH3-groove interaction, suppressing VPS34 kinase activity and blocking autophagy initiation 1.

Two principal mechanisms release Beclin-1 under stress:

  1. JNK1-mediated BCL-2 phosphorylation (starvation): JNK1 (not JNK2) phosphorylates BCL-2 at three residues in the nonstructured loop (Thr69, Ser70, Ser87) during amino-acid withdrawal, disrupting the BCL-2–Beclin-1 heterodimer and liberating free Beclin-1 to engage VPS34 2. The relevant target is the ER-localised pool of BCL-2, not the mitochondrial pool. Evidence is from cell lines (HeLa, MCF7.beclin1) and jnk1βˆ’/βˆ’ / jnk2βˆ’/βˆ’ MEFs; no intact-mouse in vivo data in this paper. needs-human-replication

  2. DAPK-mediated Beclin-1 phosphorylation: Death-associated protein kinase (DAPK1) phosphorylates Beclin-1 at Thr119 within the BH3 domain, directly reducing the affinity of Beclin-1 for BCL-2 and BCL-xL and promoting autophagy 3. This is a cell-intrinsic kinase mechanism distinct from BCL-2 modification. no-fulltext-access β€” Zalckvar 2009 (10.4161/auto.5.5.8625) is closed-access; the Thr119 residue assignment and mechanistic details cannot be verified against the PDF.

DimensionStatusNotes
Pathway conserved in humans?yesBH3-groove interaction and JNK/DAPK regulation demonstrated in human cell lines
Phenotype conserved in humans?partialAutophagy induction under starvation is conserved; age-related Beclin-1 decline is mouse data
Replicated in humans?noLifespan/healthspan effects from Beclin-1 manipulation not yet in human trials

Regulation summary

  • BCL-2 / BCL-xL: inhibitory sequestration via BH3-groove binding (see above)
  • DAPK1 β†’ Thr119 phospho: promotes release from BCL-2/BCL-xL 3
  • JNK1 β†’ BCL-2 multi-site phospho: stress-induced release of Beclin-1 2
  • mTORC1: indirectly represses autophagy; mTORC1 phosphorylates ULK1/ATG13 (see ulk1) β€” Beclin-1 complex activity is downstream of ULK1 activation
  • AMPK: promotes autophagy; activates ULK1 and may directly phosphorylate Beclin-1 at Ser90/Ser93 (UniProt evidence; primary source verification needed) unsourced
  • Ubiquitination: Lys402 (K48-linked, proteasomal degradation) and Lys437 (K63-linked, signalling) noted in UniProt; E3 ligases include TRIM5, TRIM16, TRIM17, TRIM21, TRIM50 unsourced
  • Caspase cleavage: Caspase-3 and Caspase-8 cleave Beclin-1 near Asp133/Asp149, generating a C-terminal fragment (Beclin-1-C, ~35/37 kDa) that localises to mitochondria and may promote apoptosis β€” a negative-feedback mechanism from apoptosis into autophagy suppression

Discovery

Beclin-1 was identified by Liang et al. (1999) via yeast two-hybrid screening for BCL-2 interactors 4. The paper demonstrated: (1) Beclin-1 contains a BH3 domain that binds BCL-2; (2) forced Beclin-1 expression induces autophagy in MCF7 breast carcinoma cells; (3) MCF7 cells (which lack endogenous beclin-1 due to 17q21 hemizygous deletion) show reduced autophagy and enhanced tumorigenesis; (4) Beclin-1 suppresses MCF7 xenograft growth in nude mice. This established Beclin-1 simultaneously as an autophagy inducer and candidate tumor suppressor β€” roles mediated by the same gene through distinct mechanisms. no-fulltext-access β€” Liang 1999 (10.1038/45257) is closed-access; claims from this paper cannot be verified against the PDF.

KO and transgenic phenotypes

  • Becn1βˆ’/βˆ’ (homozygous KO): Embryonic lethal at E7.5; developmental arrest at gastrulation 5. Demonstrates that autophagy is essential for early embryogenesis.
  • Becn1+/βˆ’ (heterozygous): Viable; haploinsufficient β€” increased tumour incidence (lymphomas, lung carcinomas, hepatocellular carcinoma), confirming tumor-suppressor function 5.
  • Beclin-1 F121A knock-in mice (BCL-2-binding-deficient): The F121A point mutation in the BH3 domain (mouse residue; human equivalent is F123A) decreases β€” but does not abolish β€” BCL-2/BCL-xL binding. Homozygous F121A (Becn1^F121A/F121A) mice are viable and fertile, with constitutively increased basal autophagy across multiple tissues. Both male and female F121A knock-in mice show a statistically significant median lifespan extension vs wild-type littermates on a pure C57BL/6J background (backcrossed >12 generations): combined WT median = 26 months (n=68), KI median = 29 months (n=102), p<0.0001 log-rank (Mantel-Cox); females WT = 27 mo vs KI = 30 mo, p=0.0004; males WT = 25 mo vs KI = 28 mo, p=0.0004 6. Maximal lifespan also increased (WT max = 36 mo; KI max = 39 mo). Delayed age-related renal and cardiac pathological changes (fibrosis, nuclear DNA damage) and reduced spontaneous tumorigenesis (non-lymphoid malignancies, chi-square p=0.024) were also observed in 20-month-old KI mice.
DimensionStatusNotes
Pathway conserved in humans?yesBCL-2/Beclin-1 BH3 interaction conserved; F121A equivalent not tested in humans
Phenotype conserved in humans?unknownNo Beclin-1 F121A human equivalent; no clinical cohort data yet
Replicated in humans?noMouse-only lifespan data; needs-human-replication

Role in aging

Beclin-1 protein levels decline with age in the mouse brain and other tissues β€” a pattern consistent with the broader age-related decline in autophagic flux that contributes to the disabled-macroautophagy hallmark. unsourced β€” the specific Beclin-1 age-decline data is not from FernΓ‘ndez 2018 (which did not report age-related Beclin-1 protein level changes); primary source for this claim needs to be identified. The causal role of reduced autophagic tone in aging is supported by the F121A mouse data: constitutively increased basal autophagy via Beclin-1/BCL-2 decoupling extends lifespan without apparent toxicity 6. needs-human-replication

The convergence of Beclin-1 on the autophagy/apoptosis decision point is aging-relevant because:

  • Reduced Beclin-1 β†’ less autophagy β†’ impaired proteostasis β†’ loss-of-proteostasis hallmark
  • Chronic BCL-2 sequestration of Beclin-1 in aged tissues β†’ autophagic insufficiency despite normal BECN1 mRNA
  • Caspase-mediated Beclin-1 cleavage in apoptotic/stressed cells may inactivate autophagy precisely when proteostatic rescue is most needed

Beclin-1 is listed in GenAge models (gene manipulations in model organisms affecting lifespan). needs-canonical-id β€” GenAge entry ID for BECN1 could not be confirmed via API during this seeding pass; manual verification needed.

Pathway membership

  • autophagy β€” core scaffold of the PI3KC3 initiation complex
  • mitophagy β€” PI3P generation also required for mitophagy phagophore formation
  • apoptosis-pathway β€” BH3 domain engages BCL-2/BCL-xL; caspase cleavage generates pro-apoptotic C-terminal fragment
  • bcl-2-family-signaling β€” competing BH3-groove occupancy with BH3-only proteins

Key interactors

  • bcl-2 β€” inhibitory; ER-localised pool sequesters Beclin-1 BH3 domain
  • bcl-xl β€” inhibitory; analogous to BCL-2, cytoplasmic and mitochondrial pools
  • vps34 (PIK3C3) β€” catalytic partner; Beclin-1 activates VPS34 lipid kinase activity
  • atg14l β€” Complex I-specific; directs complex to phagophore assembly site
  • uvrag β€” Complex II-specific; directs complex to late endosomes
  • dapk1 β€” phosphorylates Thr119 β†’ releases from BCL-2/BCL-xL
  • ulk1 β€” upstream activator of the autophagy cascade; ULK1 phosphorylates Beclin-1 and ATG14L

Limitations and gaps

  • GenAge entry ID unconfirmed β€” GenAge search returned no BECN1 entry during this seeding pass; may not be in GenAge-human (evidence is model-organism). Tag: needs-canonical-id
  • F121A lifespan replication β€” the ~12% median lifespan extension (26 β†’ 29 months combined) from FernΓ‘ndez 2018 is a single study in one mouse strain (#gap/needs-replication) with no independent confirmation yet
  • Human Beclin-1 age-decline data β€” the claim that Beclin-1 protein declines with age in mouse brain/tissues is not sourced to FernΓ‘ndez 2018; primary source needs identification (#gap/unsourced). Quantitative data in human tissues is sparse needs-human-replication
  • Liang 1999 claims unverified β€” paper is closed-access (not_oa); BH3 domain residue boundaries and xenograft data cannot be confirmed from PDF no-fulltext-access
  • Zalckvar 2009 claims unverified β€” paper is closed-access (not_oa); DAPK1 β†’ Thr119 phosphorylation mechanism cannot be confirmed from PDF no-fulltext-access
  • AMPK direct phosphorylation sites β€” Ser90/Ser93 listed in UniProt but primary experimental source not confirmed in this pass unsourced
  • Beclin-1 C-fragment pro-apoptotic function β€” caspase-cleavage generating the mitochondrion-targeted fragment is noted in UniProt; functional significance in vivo is not well established no-mechanism
  • VPS34 kinase activation mechanism β€” exactly how Beclin-1 allosterically stimulates VPS34 remains partially resolved; recent cryo-EM structures exist but are not cited here unsourced

Footnotes

Footnotes

  1. doi:10.1016/j.cell.2005.07.002 Β· in-vitro (MCF7, NIH3T3) + in-vivo (mouse heart, viral infection) Β· n not specified per figure Β· model: multiple cell lines + transgenic mice; BCL-2 overexpression inhibits Beclin-1-dependent autophagy; ER-BCL-2 required for inhibition (mitochondria-targeted BCL-2 does not suppress autophagy) ↩ ↩2

  2. doi:10.1016/j.molcel.2008.06.001 Β· in-vitro (HeLa, MCF7.beclin1, MEFs including jnk1βˆ’/βˆ’ and jnk2βˆ’/βˆ’ MEFs, WT Bcl-2 MEFs and AAA Bcl-2 MEFs) Β· n not specified Β· model: cell lines + jnk1/2-KO MEFs; JNK1 (not JNK2) phosphorylates BCL-2 at Thr69/Ser70/Ser87 in the nonstructured loop β†’ Bcl-2 dissociates from Beclin-1 β†’ starvation-induced autophagy; ER-localised pool of Bcl-2 (not mitochondrial) is the relevant target ↩ ↩2

  3. doi:10.4161/auto.5.5.8625 Β· in-vitro (HeLa, HEK293T) Β· n not specified Β· model: human cell lines; DAPK1 phosphorylates Beclin-1 Thr119 in BH3 domain β†’ reduces BCL-2/BCL-xL affinity β†’ autophagy ↩ ↩2

  4. doi:10.1038/45257 Β· in-vitro + in-vivo (MCF7 xenograft, nude mouse) Β· n not specified for xenograft arms Β· model: MCF7 human breast carcinoma; original BECN1 cloning + autophagy induction + tumour suppression ↩

  5. doi:10.1073/pnas.2436255100 Β· in-vivo (mouse KO, Becn1βˆ’/βˆ’) Β· n not specified Β· model: C57BL/6 Γ— 129 hybrid; Becn1βˆ’/βˆ’ embryonic lethal E7.5; Becn1+/βˆ’ viable with increased tumour incidence; haploinsufficient tumour suppressor ↩ ↩2

  6. doi:10.1038/s41586-018-0162-7 Β· in-vivo (mouse knock-in, Becn1^F121A/F121A) Β· n=68 WT + 102 KI (all); females n=31 WT + 43 KI; males n=37 WT + 59 KI Β· p<0.0001 log-rank (combined); p=0.0004 females; p=0.0004 males Β· model: pure C57BL/6J (>12 backcross generations); median lifespan WT=26 mo, KI=29 mo (combined); delayed renal and cardiac aging; reduced non-lymphoid spontaneous tumors ↩ ↩2

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