Affinage

PIK3R4

Phosphoinositide 3-kinase regulatory subunit 4 · UniProt Q99570

Length
1358 aa
Mass
153.1 kDa
Annotated
2026-06-10
20 papers in source corpus 15 papers cited in narrative 15 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PIK3R4 (VPS15) is the regulatory pseudokinase subunit at the core of the class III PI3-kinase complex, where it recruits and activates the VPS34 lipid kinase to drive PI3P-dependent vacuolar/lysosomal protein sorting, autophagy, endosomal trafficking, and cytokinesis (PMID:8387919, PMID:7721937). It forms a hetero-oligomeric membrane-associated complex with VPS34, and its protein-kinase-domain integrity—originally characterized in yeast through active-site mutagenesis and conditional alleles—is required for both physical association with VPS34 and for activation of VPS34 lipid kinase activity, with loss of function causing depletion of PI3P and missorting of soluble vacuolar hydrolases (PMID:8387919, PMID:7721937, PMID:1756716). Structurally, the VPS15 WD-repeat domain folds into a seven-bladed beta-propeller that resembles a G-protein beta subunit (PMID:19445518), while cryo-EM of the PI3KC3-C1 complex shows that the VPS15 pseudokinase domain binds GTP and sequesters its covalently linked N-terminal myristate to stabilize an autoinhibited VPS34 conformation; membrane engagement liberates the myristate and activates VPS34 for PI3P production (PMID:39913640). VPS15 assembles into functionally distinct complexes: a Beclin1/UVRAG/BIF-1–containing PI3K-III sub-complex governing endocytic receptor degradation and cytokinesis (PMID:20643123), and a VPS34-independent complex with the golgin GM130 at the cis-Golgi that releases IFT20 for ciliary transport (PMID:27882921). During autophagy initiation VPS15 is phosphorylated by ULK1/2 at multiple sites (including the major site serine 861), tuning VPS34 activity and autophagosome formation (PMID:34121209). Across model organisms VPS15 is essential for autophagic clearance, lysosomal degradation, and tissue homeostasis: it is required downstream of autophagosome initiation for lysosomal fusion/degradation in muscle, where loss causes autophagic vacuolar myopathy (PMID:23630012), and a hypomorphic allele disrupts endosomal-lysosomal trafficking and neuronal migration via a Nischarin–Pak1 signaling axis, with a patient missense mutation (R998Q) selectively impairing the Golgi/ciliary function (PMID:27882921, PMID:29311744).

Mechanistic history

Synthesis pass · year-by-year structured walk · 13 steps
  1. 1991 High

    Established that the protein-kinase activity of Vps15 is functionally essential, answering whether its kinase domain matters for vacuolar protein sorting.

    Evidence Site-directed mutagenesis of conserved kinase residues with in vivo phosphorylation and pulse-chase sorting assays in yeast

    PMID:1756716

    Open questions at the time
    • Did not identify the binding partner or substrate of Vps15
    • Distinction between autophosphorylation and trans-phosphorylation unresolved
  2. 1993 High

    Identified VPS34 as the binding partner and defined VPS15's role as recruiter/activator, explaining how the kinase requirement translates into PI3-kinase function.

    Evidence Chemical cross-linking, native co-IP, subcellular fractionation and kinase-domain mutagenesis in yeast

    PMID:8387919

    Open questions at the time
    • Structural basis of the Vps15-Vps34 interaction unknown
    • Mechanism of membrane recruitment not defined
  3. 1995 High

    Showed the functional Vps15-Vps34 complex is absolutely required for PI3P production and vacuolar delivery, linking complex integrity to lipid output.

    Evidence Temperature-conditional alleles, in vivo PtdIns(3)P measurement and dominant-negative genetics in yeast

    PMID:7721937

    Open questions at the time
    • Did not resolve how PI3P drives downstream sorting machinery
  4. 1999 Medium

    Extended VPS15 function to selective pexophagy, indicating involvement at an early step of organelle-selective autophagy.

    Evidence Gene deletion in Pichia pastoris with peroxisomal marker assays and EM

    PMID:10591966

    Open questions at the time
    • Single divergent yeast species
    • Molecular step within pexophagy not defined
  5. 2008 High

    Demonstrated VPS15 is essential for autophagy in a multicellular animal, establishing conservation of its autophagic role.

    Evidence Drosophila deletion mutant with GFP-Atg8a imaging, EM and biochemical fractionation

    PMID:18326940

    Open questions at the time
    • Step in the autophagy pathway not pinpointed
    • Complex composition in flies not characterized
  6. 2009 High

    Solved the WD-domain structure and revealed a G-protein-coupled signaling role, defining a structural and signaling identity for VPS15 beyond VPS34.

    Evidence X-ray crystallography of the Vps15 WD domain plus Gpa1/Atg14 binding and signaling assays in yeast

    PMID:19445518

    Open questions at the time
    • No independent replication of Gpa1 interaction in corpus
    • Relevance to mammalian VPS15 not established
  7. 2010 Medium

    Defined a distinct mammalian PI3K-III sub-complex (with Beclin1/UVRAG/BIF-1, lacking ATG14L) controlling receptor degradation and cytokinesis, showing complex-specific functions.

    Evidence siRNA depletion with high-content microscopy and midbody localization in mammalian cells

    PMID:20643123

    Open questions at the time
    • No biochemical reconstitution of the sub-complex
    • Single lab
  8. 2013 High

    Placed VPS15/VPS34 downstream of autophagosome initiation at the lysosomal fusion/degradation step, refining its position within the autophagy pathway.

    Evidence Muscle-specific conditional Vps15 knockout mice with LC3/p62/LAMP2 readouts and rescue in Danon myoblasts

    PMID:23630012

    Open questions at the time
    • Molecular basis of lysosomal fusion requirement not defined
  9. 2014 Medium

    Broadened VPS15 function to stress-induced and developmental autophagy and to secretory vesicle trafficking, indicating roles beyond canonical autophagy.

    Evidence Drosophila genetic mutants with autophagy markers, EM and salivary gland secretion assays

    PMID:25342466

    Open questions at the time
    • Mechanism of secretory role not resolved
    • Single lab
  10. 2016 High

    Identified a VPS34-independent VPS15-GM130 Golgi complex required for ciliary cargo (IFT20) export, and linked a patient mutation to a separable function.

    Evidence Reciprocal co-IP, yeast complementation, patient fibroblast IFT20 localization and zebrafish cilia assays

    PMID:27882921

    Open questions at the time
    • Stoichiometry and regulation of the GM130 complex unknown
    • How VPS15 partitions between VPS34 and GM130 complexes unclear
  11. 2018 High

    Connected VPS15-dependent trafficking to a Nischarin-Pak1 signaling axis controlling neuronal migration, revealing a developmental signaling consequence of VPS15 loss.

    Evidence ENU mutant and conditional KO mice with migration assays and epistasis, confirmed in human patients

    PMID:29311744

    Open questions at the time
    • How trafficking defects raise Nischarin levels not mechanistically defined
  12. 2021 High

    Showed ULK1/2 directly phosphorylates VPS15 to tune VPS34 activity, establishing a regulatory input coupling autophagy initiation to lipid kinase output.

    Evidence Phosphoproteomics in Ulk1/2 DKO MEFs, in vitro VPS34 kinase assays with phosphosite mutants and VPS15 KO cells

    PMID:34121209

    Open questions at the time
    • Conformational consequence of serine 861 phosphorylation unknown
  13. 2025 High

    Provided the structural mechanism of VPS34 autoinhibition and activation, explaining how the VPS15 pseudokinase domain controls lipid kinase output via GTP and myristate sequestration.

    Evidence Cryo-EM of the full PI3KC3-C1 complex with structural and functional analysis of pseudokinase-GTP and myristate release

    PMID:39913640

    Open questions at the time
    • In vivo trigger and kinetics of membrane-induced myristate release not defined
    • How phosphorylation/partners feed into this switch unresolved

Open questions

Synthesis pass · forward-looking unresolved questions
  • How VPS15 is partitioned among its distinct complexes (VPS34/Beclin-UVRAG, GM130-Golgi) and how upstream signals select between trafficking, autophagy and ciliary functions remains open.
  • No quantitative model of complex partitioning
  • Mammalian relevance of WD-domain G-protein signaling untested
  • Direct VPS15-PDK1/PKC interaction not biochemically demonstrated

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0098772 molecular function regulator activity 3 GO:0140096 catalytic activity, acting on a protein 3 GO:0060089 molecular transducer activity 1
Localization
GO:0005768 endosome 2 GO:0005886 plasma membrane 2 GO:0005794 Golgi apparatus 1 GO:0005829 cytosol 1
Pathway
R-HSA-9612973 Autophagy 4 R-HSA-5653656 Vesicle-mediated transport 3 R-HSA-9609507 Protein localization 2 R-HSA-1640170 Cell Cycle 1
Complex memberships
PI3K-III Beclin1/UVRAG/BIF-1 sub-complexPI3KC3 (class III PI3K) complex (VPS15-VPS34)VPS15-GM130 cis-Golgi complex

Evidence

Reading pass · 15 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1993 Vps15 protein kinase forms a hetero-oligomeric membrane-associated complex with the Vps34 PI 3-kinase; Vps15 is responsible for recruiting Vps34 to intracellular membranes, and an intact Vps15 kinase domain is required for activation of Vps34 PI 3-kinase activity. Chemical cross-linking, native immunoprecipitation, subcellular fractionation, sucrose density gradients, kinase domain mutagenesis, genetic suppression assay The EMBO journal High 8387919
1995 Active Vps15p kinase domain is necessary for physical association with Vps34p and for recruitment of Vps34p to the membrane; catalytically inactive Vps15p mutants cannot associate with Vps34p. Functional Vps15p-Vps34p complex is absolutely required for efficient vacuolar protein delivery, as shown by temperature-conditional alleles causing loss of PI(3)P and missorting of soluble vacuolar proteins. Temperature-conditional allele analysis, in vivo PtdIns(3)P measurements, genetic dominant-negative analysis, mutagenesis of kinase/lipid kinase domains The Journal of cell biology High 7721937
1991 Alterations of conserved protein kinase residues in Vps15p biologically inactivate the protein, blocking vacuolar sorting of soluble hydrolases (CPY, PrA) but not the membrane protein alkaline phosphatase. C-terminal truncations of Vps15p abolish in vivo phosphorylation of Vps15p and cause a temperature-conditional vacuolar protein sorting defect, suggesting autophosphorylation is required for full activity. Site-directed mutagenesis of conserved kinase residues, in vivo 32P-phosphorylation assay, temperature-shift experiments, pulse-chase sorting assay The EMBO journal High 1756716
2009 The Vps15 WD-repeat domain forms a seven-bladed beta-propeller resembling a G-protein beta subunit and is sufficient to bind the G protein alpha subunit Gpa1 (preferentially GDP-bound) and Atg14. The kinase and intermediate domains of Vps15 additionally contribute to Gpa1 binding and are necessary for G protein signaling at endosomes. X-ray crystal structure of the Vps15 WD domain, binding assays (Gpa1-Vps15 interaction), domain deletion analysis, G protein signaling assays Biochemistry High 19445518
2010 A specific PI3K-III sub-complex containing VPS15, VPS34, Beclin 1, UVRAG and BIF-1 (but not ATG14L) regulates endocytic receptor degradation and cytokinesis in mammalian cells. siRNA depletion of individual subunits, high-content microscopy-based assays for receptor degradation and cytokinesis, midbody localization of UVRAG and BIF-1 Experimental cell research Medium 20643123
2008 Drosophila Vps15 is required for starvation-induced autophagy in fat body and gut; loss of vps15 leads to accumulation of ubiquitin- and Ref(2)P/p62-positive, partially detergent-insoluble protein aggregates, establishing Vps15 as essential for autophagic clearance of protein aggregates in a multicellular organism. Drosophila deletion mutant, GFP-Atg8a fluorescence microscopy, electron microscopy, biochemical fractionation, Western blot, immuno-electron microscopy Autophagy High 18326940
2013 Vps15 is required for lysosomal function in skeletal muscle; muscle-specific Vps15 knockout mice show accumulation of autophagosomes, p62, LC3, and Lamp2-positive vesicles, and develop autophagic vacuolar myopathy. Importantly, autophagosome formation (LC3-positive) and mTOR activation are maintained in Vps15-deficient cells, indicating Vps15/Vps34 is specifically required downstream (lysosomal fusion/degradation) rather than for autophagosome initiation per se. Conditional (muscle-specific) Vps15 knockout mouse, immunofluorescence, electron microscopy, LC3/p62/LAMP2 Western blot, creatine kinase assay, Vps15 rescue by overexpression in Danon disease myoblasts EMBO molecular medicine High 23630012
2016 VPS15 interacts with the golgin GM130 at the cis-Golgi, forming a complex devoid of VPS34, and is required for IFT20 release from the Golgi for transport to the primary cilium. A patient missense mutation VPS15-R998Q impairs this Golgi trafficking function without fully disrupting VPS34-dependent activities. VPS15 regulates primary cilium length in human fibroblasts. Missense mutation identification in ciliopathy patients, co-immunoprecipitation of VPS15 with GM130, subcellular localization (Golgi), humanized yeast complementation assay, IFT20 localization in patient fibroblasts, zebrafish cilia assay Nature communications High 27882921
2018 A hypomorphic Vps15 mutation in mice causes defects in endosomal-lysosomal trafficking and autophagy, resulting in upregulation of Nischarin, which inhibits Pak1 signaling, thereby disrupting neuronal migration and causing hippocampal pyramidal cell layer defects. Complete Vps15 ablation causes accumulation of autophagic substrates, apoptosis, and severe cortical atrophy. ENU-induced mouse mutant, conditional knockout, neuronal migration assays, Western blot for Nischarin and Pak1 phosphorylation, epistasis between Vps15, Nischarin, and Pak1 pathways Nature neuroscience High 29311744
2021 ULK1/2 kinases phosphorylate VPS15 at six sites (including serine 861 as the major site); mutation of these sites reduces VPS34 activity in vitro and impairs autophagosome formation in cells. VPS15 knockout also reveals ULK-dependent starvation-independent accumulation of ULK substrates and kinase activity-regulated recruitment of autophagy proteins to ubiquitin-positive structures. Unbiased phosphoproteomics in Ulk1/2 double-knockout MEFs, in vitro VPS34 kinase assay with VPS15 phosphosite mutants, autophagosome formation assays, VPS15 knockout cell lines The EMBO journal High 34121209
2025 Cryo-EM structure of the PI3KC3-C1 complex reveals that the VPS15 pseudokinase domain binds GTP and sequesters its covalently-linked N-terminal myristate in the N-lobe, stabilizing the inactive conformation of VPS34. Upon membrane binding (activation), myristate is liberated, disrupting the inhibitory interaction and enabling VPS34 to catalyze PI3P production on membranes. Cryo-electron microscopy of full PI3KC3-C1 complex, structural analysis of pseudokinase-GTP interaction, myristate sequestration/release mechanism, functional validation of VPS34 activation Science (New York, N.Y.) High 39913640
1999 Pichia pastoris Vps15 (PpVPS15) is required at an early stage of selective peroxisome autophagy (pexophagy); deletion of PpVPS15 prevents vacuolar uptake of peroxisomes upon glucose or ethanol exposure. Gene deletion in Pichia pastoris, measurement of peroxisomal marker enzyme levels, electron microscopy of peroxisome uptake Current genetics Medium 10591966
2014 Drosophila Vps15 is required for autophagy induced by multiple stresses (nutrient deprivation, hypoxia, oxidative stress) and for developmentally programmed autophagy in fat body, intestine, and salivary gland. Additionally, Vps15 is necessary for efficient protein secretion from salivary glands, demonstrating a role in secretory vesicle trafficking beyond autophagy. Drosophila vps15 genetic mutants, autophagy markers (Atg8, lysotracker), electron microscopy, salivary gland secretion assay Cell death and differentiation Medium 25342466
2019 VPS15 knockdown in HUVECs inhibits AngII-induced autophagy and reduces phosphorylation of PDK1 and PKC substrates, while re-expression of Vps15 rescues autophagy; PDK1 and PKC inhibitors phenocopy Vps15 knockdown, placing Vps15 upstream of a PDK1/PKC signaling axis in autophagy regulation. shRNA knockdown of Vps15, MDC staining, LC3-II/I Western blot, pharmacological inhibition of PDK1/PKC, rescue by Vps15 re-expression, flow cytometry for apoptosis Life sciences Low 31356904
2025 Loss of Vps15 (core PI3K-III subunit) in Drosophila wing imaginal discs selectively impairs an endocytosis-dependent pool of Wingless (Wg) secretion, causing apical accumulation of Wg in secreting cells, while a glypican-mediated Wg pool is unaffected. Evi/Wls cargo receptor undergoes proteasome-dependent degradation rather than accumulation in PI3K-III mutant cells. In vivo CRISPR-Cas9 kinome/phosphatome screen, endogenously fluorescently tagged Wg, super-resolution microscopy, ex vivo pharmacological treatments (proteasome inhibitor) bioRxivpreprint Medium bio_10.1101_2025.05.20.655092

Source papers

Stage 0 corpus · 20 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1993 A membrane-associated complex containing the Vps15 protein kinase and the Vps34 PI 3-kinase is essential for protein sorting to the yeast lysosome-like vacuole. The EMBO journal 301 8387919
1995 Vesicle-mediated protein transport: regulatory interactions between the Vps15 protein kinase and the Vps34 PtdIns 3-kinase essential for protein sorting to the vacuole in yeast. The Journal of cell biology 204 7721937
2010 A phosphatidylinositol 3-kinase class III sub-complex containing VPS15, VPS34, Beclin 1, UVRAG and BIF-1 regulates cytokinesis and degradative endocytic traffic. Experimental cell research 154 20643123
1991 A genetic and structural analysis of the yeast Vps15 protein kinase: evidence for a direct role of Vps15p in vacuolar protein delivery. The EMBO journal 96 1756716
2013 Defects of Vps15 in skeletal muscles lead to autophagic vacuolar myopathy and lysosomal disease. EMBO molecular medicine 94 23630012
2008 The PI 3-kinase regulator Vps15 is required for autophagic clearance of protein aggregates. Autophagy 60 18326940
2016 A mutation in VPS15 (PIK3R4) causes a ciliopathy and affects IFT20 release from the cis-Golgi. Nature communications 53 27882921
2021 Phosphoproteomic identification of ULK substrates reveals VPS15-dependent ULK/VPS34 interplay in the regulation of autophagy. The EMBO journal 52 34121209
2018 Mutations in Vps15 perturb neuronal migration in mice and are associated with neurodevelopmental disease in humans. Nature neuroscience 39 29311744
1999 A Pichia pastoris VPS15 homologue is required in selective peroxisome autophagy. Current genetics 37 10591966
2006 ird1 is a Vps15 homologue important for antibacterial immune responses in Drosophila. Cellular microbiology 34 17166233
2009 Structure and function of Vps15 in the endosomal G protein signaling pathway. Biochemistry 29 19445518
2025 Structural pathway for PI3-kinase regulation by VPS15 in autophagy. Science (New York, N.Y.) 26 39913640
2014 Vps15 is required for stress induced and developmentally triggered autophagy and salivary gland protein secretion in Drosophila. Cell death and differentiation 25 25342466
2019 Vps15 is critical to mediate autophagy in AngII treated HUVECs probably by PDK1/PKC signaling pathway. Life sciences 8 31356904
2022 A VPS15-like kinase regulates apicoplast biogenesis and autophagy by promoting PI3P generation in Toxoplasma gondii. PLoS pathogens 5 36318587
2020 Aspirin restores endothelial function by mitigating 17β-estradiol-induced α-SMA accumulation and autophagy inhibition via Vps15 scaffold regulation of Beclin-1 phosphorylation. Life sciences 4 32896555
2026 Genome-wide association study links COL6A6 and PIK3R4 to delayed cerebral ischaemia. Brain : a journal of neurology 0 42189192
2025 Identification of NMT1/MA/VPS15 signal pathway as potential therapeutic target in rat cerebral ischemia injury. Experimental neurology 0 40221008
2025 CryoEM provides detailed insights into how VPS15 regulates VPS34 activity. Trends in biochemical sciences 0 40537377

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