LAMTOR2

LAMTOR2 (p14) is a late endosomal/lysosomal scaffold subunit of the LAMTOR/Ragulator complex that integrates ERK/MAPK and mTOR signaling with intracellular membrane trafficking, and its loss disrupts both pathways with broad consequences for immune cell development and homeostasis (PMID:24092934). As a component of the p14–MP1 (LAMTOR2/3) module, it positions late endosomes for kinesin1- and Arl8b-dependent microtubule transport to focal adhesions, where it drives IQGAP1 release and focal adhesion turnover required for cell migration (PMID:24841562), and it acts upstream of mTOR to support multivesicular body recycling tubule formation and transferrin receptor recycling (PMID:25677580). LAMTOR2 governs the trafficking and signaling output of multiple surface receptors: it restrains Flt3 surface accumulation and downstream AKT/mTOR-driven dendritic cell expansion (PMID:25336251), controls BCR internalization and endosomal trafficking during B-cell development (PMID:30936881), modulates TrkA/MAPK signaling-module release from early endosomes during NGF-induced neurite outgrowth (PMID:24752675), and sustains TGFβ receptor II expression in Langerhans cell homeostasis (PMID:25078666). In macrophages it promotes phagosome-lysosome fusion and ERK phosphorylation for bacterial clearance (PMID:33144310), and together with LAMTOR1 it is recruited to damaged pathogen-containing endosomes where it binds the autophagy receptors NBR1, TAX1BP1, and p62 to drive xenophagic autolysosome formation (PMID:30428163). Its scaffolding role is further tuned by partner proteins, with VSIG2 stabilizing the LAMTOR2–mTOR interaction to enhance mTOR activation (PMID:37626304).

1. 2013 High

   Established that LAMTOR2 is the linchpin holding the LAMTOR complex together, so that its loss simultaneously cripples both ERK and mTOR signaling and a defined immune cell population.

   Evidence CD11c-specific conditional knockout mouse with in vivo Langerhans cell repopulation and signaling analysis

   PMID:24092934

   Open questions at the time

   • Does not resolve which downstream effectors of ERK vs mTOR drive the proliferation/apoptosis phenotype
   • Mechanism of complex disassembly upon p14 loss not structurally defined
2. 2014 High

   Showed LAMTOR2 couples endosome positioning to cytoskeletal motors and adhesion dynamics, linking the complex to cell migration beyond canonical signaling.

   Evidence p14-deficient mouse fibroblasts with Arl8b siRNA depletion, live imaging and colocalization at focal adhesions

   PMID:24841562

   Open questions at the time

   • Direct biochemical link between LAMTOR2 cargo and IQGAP1 release unresolved
   • Whether ERK/mTOR signaling is required for the FA-turnover function not separated
3. 2014 High

   Demonstrated that LAMTOR2 restrains surface receptor abundance, with Flt3 accumulation driving AKT/mTOR-dependent DC expansion that is pharmacologically reversible.

   Evidence DC-specific conditional KO with in vivo Flt3 and mTOR inhibitor rescue and surface receptor quantification

   PMID:25336251

   Open questions at the time

   • Trafficking step at which Flt3 is normally degraded not pinpointed
   • Whether other receptors are similarly retained at the surface unaddressed here
4. 2014 Medium

   Extended LAMTOR2's receptor-trafficking role to TGFβ signaling and to TrkA/MAPK kinetics, framing it as a brake on signaling-module release from endosomes.

   Evidence Langerin-specific conditional KO with TGFβRII surface staining (TGFβ); PC12 siRNA knockdown plus siRNA-resistant rescue with NGF-induced MAPK kinetics and TrkA endosome imaging (TrkA)

   PMID:24752675 PMID:25078666

   Open questions at the time

   • Mechanism by which LAMTOR2 controls TGFβRII expression vs trafficking not distinguished
   • How LAMTOR2 retards TrkA/MAPK endosome-to-nucleus transit biochemically undefined
5. 2015 High

   Placed LAMTOR2 upstream of mTOR in endo/lysosomal membrane remodeling by showing mTOR inhibition phenocopies the KO ultrastructural defect.

   Evidence Quantitative immunoelectron microscopy of LAMTOR2-KO MEFs with mTOR-inhibitor epistasis and transferrin receptor recycling assays

   PMID:25677580

   Open questions at the time

   • Molecular machinery of recycling-tubule scission downstream of mTOR not identified
   • Generality of the MVB phenotype beyond fibroblasts untested
6. 2019 Medium

   Identified LAMTOR2 as a receptor for selective autophagy, recruiting xenophagy adaptors to damaged pathogen-containing endosomes.

   Evidence Co-IP of LAMTOR2 with NBR1/TAX1BP1/p62, LAMTOR2 KO cells and TAX1BP1 KO bacterial degradation assays during GAS/Salmonella infection

   PMID:30428163

   Open questions at the time

   • Direct vs indirect nature of LAMTOR2–TAX1BP1 binding not established
   • Whether autophagy-receptor recruitment depends on the canonical Ragulator/mTOR function unclear
7. 2019 High

   Defined a stage-specific requirement for LAMTOR2 in B-cell development driven by its control of BCR internalization and endosomal trafficking.

   Evidence Two independent conditional KO models (mb1-Cre, Cd19-Cre) with BCR internalization and endosomal trafficking assays

   PMID:30936881

   Open questions at the time

   • Whether the pre-B1 arrest reflects signaling vs trafficking failure not separated
   • Effector linking BCR trafficking defect to aberrant signaling unidentified
8. 2020 Medium

   Connected extracellular SCFA/GPR43 signaling to LAMTOR2-dependent phagosome-lysosome fusion and ERK activation in antimicrobial macrophage function.

   Evidence Macrophage-specific conditional Lamtor2 KO with SCFA/GPR43 stimulation, phagosome-lysosome fusion and ERK phosphorylation assays

   PMID:33144310

   Open questions at the time

   • Transcriptional mechanism by which GPR43 upregulates LAMTOR2 not detailed
   • Whether ERK and fusion functions are mechanistically coupled unaddressed
9. 2023 Medium

   Showed LAMTOR2's mTOR-activating scaffold function can be amplified by a partner, VSIG2, that bridges LAMTOR2 and mTOR.

   Evidence Mass spectrometry and reciprocal co-IP with VSIG2 overexpression/knockdown and mTOR phosphorylation readouts in PDAC cells

   PMID:37626304

   Open questions at the time

   • Structural basis of the trimeric VSIG2–LAMTOR2–mTOR assembly unknown
   • Single cancer-cell context; generality untested
10. 2025 Low

    Proposed a nuclear-signaling arm in which LAMTOR2 controls BCLAF1 nuclear translocation in chondrocytes affecting cartilage degradation.

    Evidence Immunoprecipitation/mass spectrometry and BCLAF1 nuclear translocation assay in chondrocytes

    PMID:39990659

    Open questions at the time

    • Single Co-IP/MS identification without reciprocal validation
    • Mechanism by which an endosomal scaffold controls nuclear translocation undefined
    • Downstream cartilage-degradation pathway not mechanistically traced

• How LAMTOR2 partitions its scaffold time between Ragulator/mTOR signaling, receptor trafficking, autophagy-receptor recruitment, and motor-driven endosome positioning—and what determines context-specific output—remains unresolved.
• No structural model of LAMTOR2 engaging its diverse partners across functions
• Rules governing which cargo/pathway LAMTOR2 serves in a given cell type unknown