Affinage

APPL2

Amyloid beta precursor like protein 2 · UniProt Q06481

Length
763 aa
Mass
87.0 kDa
Annotated
2026-06-09
19 papers in source corpus 13 papers cited in narrative 13 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

APPL2 is a multidomain endosomal adaptor protein that functions as a context-dependent scaffold modulating metabolic, immune, and developmental signaling (PMID:18034774, PMID:25328665). It oligomerizes through its BAR domain, forming both homooligomers and heterooligomers with its paralog APPL1, binds phosphoinositides via its PH and PTB domains, and localizes to dynamic cytosolic membrane structures where it recruits RAB5 (PMID:18034774); direct BAR-domain interactions between APPL1 and APPL2 occur on curved membranes in living cells (PMID:20814572). Functional divergence from APPL1 is established by APPL2's failure to associate with Akt2 (PMID:17030088). In innate immunity, APPL2 forms a complex with APPL1 and the PI3K regulatory subunit p85α and acts as a negative regulator of PI3K/Akt/NF-κB signaling, restraining TNF-α and IL-1β production in LPS-challenged macrophages (PMID:25328665), while controlling NF-κB p65 nuclear translocation and cytokine secretion downstream of TLR4 (PMID:27219021); RAB31-GTP recruits APPL2 to early phagosomes where it drives the PI(4,5)P2-to-PI(3,4,5)P3 transition required for FcγR-mediated phagocytosis (PMID:25568335). In glucose metabolism, APPL2 inhibits insulin-stimulated GLUT4 translocation in skeletal muscle by binding insulin-induced Ser235-phosphorylated TBC1D1 through its BAR domain (PMID:24879834), yet in pancreatic β-cells it promotes glucose-stimulated insulin secretion by binding RacGAP1 via its BAR-PH domain to relieve inhibition of Rac1 and enable F-actin remodeling (PMID:33122440). In transcriptional and developmental contexts, APPL2 activates β-catenin/TCF transcription by disrupting a Reptin-HDAC1/2 repressive complex (PMID:19433865), interacts with Notch1 to bias adult neural stem cells toward gliogenesis (PMID:32468397), and acts upstream of glucocorticoid receptor activity to regulate hippocampal neurogenesis (PMID:28965332).

Mechanistic history

Synthesis pass · year-by-year structured walk · 13 steps
  1. 2006 Medium

    Established that APPL2 is functionally distinct from its paralog APPL1, defining the central question of paralog-specific roles.

    Evidence Reciprocal Co-immunoprecipitation testing multiple binding partners, including a negative result for Akt2

    PMID:17030088

    Open questions at the time
    • Functional consequence of FSHR binding not resolved
    • Did not address endosomal or signaling roles
  2. 2007 High

    Resolved the domain-level basis of APPL2 membrane targeting and oligomerization, showing the BAR domain mediates APPL-APPL interactions and PH/PTB domains bind phosphoinositides.

    Evidence Co-IP, yeast two-hybrid, in vitro phosphoinositide-binding assay, and live-cell imaging of RAB5 recruitment

    PMID:18034774

    Open questions at the time
    • Specific phosphoinositide species preference not fully defined
    • Physiological cargo of these membrane structures not identified
  3. 2009 High

    Showed APPL2 has a nuclear/transcriptional function, relieving Reptin-HDAC-mediated repression of β-catenin/TCF targets, extending its role beyond endosomes.

    Evidence Co-IP, reporter assay, siRNA knockdown, and chromatin immunoprecipitation

    PMID:19433865

    Open questions at the time
    • How endosomal APPL2 reaches transcriptional complexes unclear
    • Direct vs. indirect disruption of Reptin complex not distinguished
  4. 2010 High

    Confirmed that APPL1-APPL2 BAR-domain interactions occur directly on curved membranes in living cells, validating the structural model in situ.

    Evidence Three independent FRET methods in live cells

    PMID:20814572

    Open questions at the time
    • Stoichiometry of oligomers not determined
    • Regulation of homo- vs. heterotypic interaction not addressed
  5. 2012 Medium

    Identified an endosome- and Akt-independent prosurvival role for APPL2 in glioma cells, indicating functions beyond its canonical scaffolding.

    Evidence siRNA/shRNA knockdown with caspase, colony formation, xenograft, and gene expression readouts

    PMID:22989406

    Open questions at the time
    • Mechanism linking APPL2 to UNC5B/HRK regulation unknown
    • Single lab; cell-type generality untested
  6. 2014 High

    Defined APPL2 as a negative regulator of insulin-stimulated GLUT4 trafficking via phospho-dependent TBC1D1 sequestration, providing a resolved metabolic mechanism.

    Evidence Co-IP with domain mapping, site-directed mutagenesis, conditional knockout mice, and glucose uptake/GLUT4 translocation assays

    PMID:24879834

    Open questions at the time
    • Kinase responsible for Ser235 phosphorylation not identified in this axis
    • Tissue-specific contribution to whole-body glucose homeostasis not fully quantified
  7. 2014 High

    Established APPL2 as a negative regulator of innate immune PI3K/Akt/NF-κB signaling through a complex with APPL1 and p85α, with opposing roles to APPL1.

    Evidence Co-IP, Appl2 knockout mice, LPS challenge, cytokine ELISA, and Akt/NF-κB immunoblotting

    PMID:25328665

    Open questions at the time
    • How APPL2 inhibits p85α/PI3K mechanistically not resolved
    • Relationship to membrane localization not directly tested here
  8. 2015 High

    Showed RAB31-GTP recruits APPL2 to phagosomes to drive phosphoinositide conversion and FcγR-mediated phagocytosis, linking its endosomal localization to immune effector function.

    Evidence siRNA knockdown, fluorescence imaging of phagosome stages, and PI3K/Akt and p38 signaling assays

    PMID:25568335

    Open questions at the time
    • Direct enzymatic role in PIP conversion vs. scaffolding unclear
    • How RAB31 and RAB5 recruitment are coordinated unknown
  9. 2015 Medium

    Demonstrated functional redundancy between APPL1 and APPL2 in HGF-induced Akt signaling and cell motility, clarifying when paralog loss produces phenotypes.

    Evidence Single and double knockout mice and MEF Akt signaling, migration, and invasion assays

    PMID:26445298

    Open questions at the time
    • Molecular basis of redundancy not dissected
    • Whether redundancy extends to other pathways untested
  10. 2016 Medium

    Refined the TLR4-signaling role of APPL2, showing it is required for NF-κB p65 nuclear translocation and cytokine secretion with effects on Akt/MAPK opposite to APPL1.

    Evidence siRNA depletion, immunofluorescence localization, NF-κB translocation, cytokine secretion, and Akt/MAPK immunoblotting

    PMID:27219021

    Open questions at the time
    • Reconciliation with APPL2 as NF-κB suppressor in other contexts unresolved
    • Direct molecular target controlling p65 translocation not identified
  11. 2017 Medium

    Placed APPL2 upstream of glucocorticoid receptor activity in regulating hippocampal neurogenesis, establishing a developmental/neuroendocrine role.

    Evidence APPL2 transgenic mice, GR phosphorylation immunoblotting, neurogenesis quantification, and pharmacological rescue with RU486

    PMID:28965332

    Open questions at the time
    • Direct vs. indirect control of GR phosphorylation unknown
    • Molecular link between APPL2 and GR not mapped
  12. 2020 High

    Resolved a tissue-opposite metabolic role: in β-cells APPL2 promotes insulin secretion by binding RacGAP1 to relieve Rac1 inhibition and enable F-actin remodeling.

    Evidence β-cell-specific knockout mice, Co-IP with domain mapping, genetic epistasis via RacGAP1 double knockdown, F-actin imaging, and Rac1 activation assays

    PMID:33122440

    Open questions at the time
    • Glucose-dependence of the APPL2-RacGAP1 interaction mechanism unclear
    • How this reconciles with APPL2's inhibitory role in muscle not integrated
  13. 2020 Medium

    Identified APPL2-Notch1 interaction as a determinant of adult neural stem cell fate, biasing toward gliogenesis over neurogenesis.

    Evidence Co-IP, in vitro NSC differentiation, APPL2 transgenic mice, immunofluorescence, and olfactory behavioral testing

    PMID:32468397

    Open questions at the time
    • Whether APPL2 modulates Notch1 signaling directly not established
    • Domain mediating Notch1 interaction not mapped

Open questions

Synthesis pass · forward-looking unresolved questions
  • How a single endosomal adaptor coordinates its opposing context-dependent outputs across metabolic, immune, transcriptional, and developmental pathways remains unresolved.
  • No unifying mechanism explaining tissue-opposite effects (e.g. muscle vs. β-cell)
  • Structural basis for differential partner selection by the shared BAR-PH-PTB architecture undefined
  • No structural model of APPL2-partner complexes

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 4 GO:0098772 molecular function regulator activity 3 GO:0008289 lipid binding 2 GO:0140110 transcription regulator activity 1
Localization
GO:0005634 nucleus 2 GO:0005768 endosome 2 GO:0005829 cytosol 1 GO:0005886 plasma membrane 1
Pathway
R-HSA-162582 Signal Transduction 3 R-HSA-168256 Immune System 3 R-HSA-1266738 Developmental Biology 2 R-HSA-5653656 Vesicle-mediated transport 2 R-HSA-74160 Gene expression (Transcription) 1
Partners
APPL1FSHRNOTCH1RAB31RAB5RACGAP1REPTINTBC1D1
Complex memberships
APPL1-APPL2 BAR oligomerAPPL1-APPL2-p85alpha (PI3K) complexReptin-beta-catenin-HDAC1/2 complex

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2006 APPL2 interacts with FSHR (follicle stimulating hormone receptor) and with APPL1 via the N-terminus/BAR domain of APPL1; unlike APPL1, APPL2 does not associate with Akt2, establishing a functional distinction between the two paralogs. Co-immunoprecipitation Molecular and cellular endocrinology Medium 17030088
2007 APPL2 forms homooligomers and heterooligomers with APPL1 through its BAR domain (necessary and sufficient for APPL-APPL interactions); full-length APPL2 binds phosphoinositides via its PH and PTB domains; APPL2-YFP localizes to cytosolic membrane structures that undergo movement, fusion and fission events and recruits endogenous RAB5 to enlarged membrane structures. Co-immunoprecipitation, yeast two-hybrid, in vitro phosphoinositide-binding assay, live-cell fluorescence imaging Traffic (Copenhagen, Denmark) High 18034774
2009 APPL2 activates beta-catenin/TCF-mediated transcription by directly interacting with the transcriptional repressor Reptin (via the PH domain of APPL1, mapped for APPL1; APPL2 similarly interacts); APPL2 is present in an endogenous complex containing Reptin, beta-catenin, HDAC1, and HDAC2; overexpression of APPL2 relieves Reptin-dependent repression and reduces amounts of HDACs and beta-catenin associated with Reptin. Co-immunoprecipitation, reporter assay, siRNA knockdown, chromatin immunoprecipitation The Journal of biological chemistry High 19433865
2010 APPL1 and APPL2 BAR domains interact directly on curved cell membranes in a homotypic (APPL1-APPL1, APPL2-APPL2) and heterotypic (APPL1-APPL2) manner, as demonstrated by FRET. FRET microscopy (sensitized emission, acceptor photobleaching, sequential acceptor photobleaching) in live cells PloS one High 20814572
2012 APPL2 knockdown in glioma cells reduces cell survival and enhances apoptosis by upregulating apoptosis-related genes UNC5B and HRK; this prosurvival activity is independent of Akt/GSK3β modulation and of APPL2's endosomal localization. siRNA/shRNA knockdown, caspase activity assay, colony formation assay, xenograft tumor growth, gene expression analysis Molecular oncology Medium 22989406
2014 APPL2 inhibits insulin-stimulated GLUT4 translocation and glucose uptake in skeletal muscle by interacting with TBC1D1; insulin stimulates TBC1D1 phosphorylation on Ser235, which enhances binding to the BAR domain of APPL2, suppressing subsequent TBC1D1 phosphorylation on Thr596 needed for GLUT4 trafficking. Ser235Ala substitution in TBC1D1 abolishes this inhibitory axis. Co-immunoprecipitation, site-directed mutagenesis, conditional knockout mice, glucose uptake assay, GLUT4 translocation assay Diabetes High 24879834
2014 APPL2 forms a complex with APPL1 and the PI3K regulatory subunit p85α; in LPS-challenged macrophages, loss of APPL2 enhances PI3K/Akt/NF-κB signaling and increases TNF-α and IL-1β production, whereas loss of APPL1 reduces Akt activation and cytokine production, indicating APPL2 is a negative regulator of innate immune signaling through this complex. Co-immunoprecipitation, Appl2 knockout mice, LPS challenge, cytokine ELISA, Akt/NF-κB phosphorylation immunoblotting Cell & bioscience High 25328665
2015 Rab31-GTP recruits APPL2 to early-stage phagosomes; siRNA depletion of APPL2 delays the PI(4,5)P2-to-PI(3,4,5)P3 transition, impairs phagocytic cup closure, reduces PI3K/Akt signaling, and enhances p38 signaling from FcγR, thereby reducing FcγR-mediated phagocytosis in macrophages. siRNA knockdown, fluorescence imaging of phagosome stages, PI3K/Akt and p38 signaling assays Molecular biology of the cell High 25568335
2015 APPL1 and APPL2 double-knockout mouse embryonic fibroblasts exhibit defects in HGF-induced Akt activation, migration, and invasion, while individual knockouts of either protein do not impair development, indicating redundant roles in HGF signaling. Conditional/constitutive knockout mice, MEF Akt signaling assay, migration/invasion assay Journal of cellular physiology Medium 26445298
2016 APPL2 localizes to distinct surface and endocytic membrane domains in LPS-activated macrophages; depletion of APPL2 specifically impairs nuclear translocation of NF-κB p65 and constrains secretion of pro- and anti-inflammatory cytokines downstream of TLR4, with APPL2 having opposing regulatory effects to APPL1 on Akt and MAPK signaling. siRNA depletion, immunofluorescence localization, NF-κB nuclear translocation assay, cytokine secretion assay, Akt/MAPK phosphorylation immunoblotting Traffic (Copenhagen, Denmark) Medium 27219021
2017 APPL2 overexpression in transgenic mice enhances glucocorticoid receptor (GR) phosphorylation under basal conditions and impairs hippocampal neurogenesis; this neurogenesis defect is reversed by the GR antagonist RU486, placing APPL2 upstream of GR activity. APPL2 transgenic mice, GR phosphorylation immunoblotting, hippocampal neurogenesis quantification, pharmacological rescue with RU486 Molecular neurobiology Medium 28965332
2020 APPL2 enhances glucose-stimulated insulin secretion (GSIS) by promoting F-actin depolymerization via Rac1 in pancreatic β-cells; APPL2 interacts with RacGAP1 in a glucose-dependent manner through its BAR-PH domain, suppressing RacGAP1's inhibitory action on Rac1, thereby enabling F-actin remodeling. Concurrent knockdown of RacGAP1 rescues APPL2-deficiency-induced defects in GSIS, F-actin remodeling, and Rac1 activation. β-cell-specific APPL2 knockout mice, Co-immunoprecipitation with domain mapping, siRNA knockdown, live-cell F-actin imaging, phalloidin staining, Rac1 activation assay, pharmacological rescue Proceedings of the National Academy of Sciences of the United States of America High 33122440
2020 APPL2 interacts with Notch1 and promotes gliogenesis over neurogenesis in adult olfactory bulb neural stem cells; APPL2 overexpression switches NSC fate from neuronal differentiation to gliogenesis, while knockdown promotes neurogenesis, and APPL2 transgenic mice show higher glial cell populations and impaired olfactory discrimination. Co-immunoprecipitation (APPL2-Notch1), in vitro NSC differentiation assay, APPL2 transgenic mice, immunofluorescence quantification, olfactory behavioral testing Neuroscience bulletin Medium 32468397

Source papers

Stage 0 corpus · 19 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2006 APPL1, APPL2, Akt2 and FOXO1a interact with FSHR in a potential signaling complex. Molecular and cellular endocrinology 78 17030088
2009 Endosomal adaptor proteins APPL1 and APPL2 are novel activators of beta-catenin/TCF-mediated transcription. The Journal of biological chemistry 54 19433865
2007 Membrane targeting by APPL1 and APPL2: dynamic scaffolds that oligomerize and bind phosphoinositides. Traffic (Copenhagen, Denmark) 45 18034774
2018 Baicalin Modulates APPL2/Glucocorticoid Receptor Signaling Cascade, Promotes Neurogenesis, and Attenuates Emotional and Olfactory Dysfunctions in Chronic Corticosterone-Induced Depression. Molecular neurobiology 40 29675572
2015 Rab31 and APPL2 enhance FcγR-mediated phagocytosis through PI3K/Akt signaling in macrophages. Molecular biology of the cell 37 25568335
2020 The adaptor protein APPL2 controls glucose-stimulated insulin secretion via F-actin remodeling in pancreatic β-cells. Proceedings of the National Academy of Sciences of the United States of America 30 33122440
2014 The adaptor protein APPL2 inhibits insulin-stimulated glucose uptake by interacting with TBC1D1 in skeletal muscle. Diabetes 28 24879834
2013 Association of genetic variation in adaptor protein APPL1/APPL2 loci with non-alcoholic fatty liver disease. PloS one 17 23977033
2012 Multifunctional protein APPL2 contributes to survival of human glioma cells. Molecular oncology 17 22989406
2010 APPL proteins FRET at the BAR: direct observation of APPL1 and APPL2 BAR domain-mediated interactions on cell membranes using FRET microscopy. PloS one 17 20814572
2017 Adaptor Protein APPL2 Affects Adult Antidepressant Behaviors and Hippocampal Neurogenesis via Regulating the Sensitivity of Glucocorticoid Receptor. Molecular neurobiology 15 28965332
2015 Appl1 and Appl2 are Expendable for Mouse Development But Are Essential for HGF-Induced Akt Activation and Migration in Mouse Embryonic Fibroblasts. Journal of cellular physiology 14 26445298
2016 Distinct Roles for APPL1 and APPL2 in Regulating Toll-like Receptor 4 Signaling in Macrophages. Traffic (Copenhagen, Denmark) 13 27219021
2014 Absence of Appl2 sensitizes endotoxin shock through activation of PI3K/Akt pathway. Cell & bioscience 12 25328665
2018 The reversal effect of physical exercise on aging-related increases in APPL2 content in skeletal muscle. Life sciences 8 30189216
2018 Overexpressed in colorectal carcinoma gene (OCC-1) upregulation and APPL2 gene downregulation in breast cancer specimens. Molecular biology reports 4 30218350
2020 APPL2 Negatively Regulates Olfactory Functions by Switching Fate Commitments of Neural Stem Cells in Adult Olfactory Bulb via Interaction with Notch1 Signaling. Neuroscience bulletin 1 32468397
2024 Aspongopus chinensis ach-miR-276a-3p induces breast cancer cell cycle arrest by targeting APPL2 to regulate the CDK2-Rb-E2F1 signaling pathway. Toxicology and applied pharmacology 0 38431228
2024 Lack of T04C9.1, the Homologue of Mammalian APPL2, Leads to Premature Ageing and Shortens Lifespan in Caenorhabditis elegans. Genes 0 38927595

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