LAMTOR2 Human
Description
Functional Roles in Signaling Pathways
LAMTOR2 is integral to mTORC1 activation, MAPK signaling, and endosomal biogenesis:
mTORC1 Regulation
The Ragulator complex (LAMTOR1–5) acts as a guanine nucleotide exchange factor (GEF) for Rag GTPases, enabling mTORC1 recruitment to lysosomes. LAMTOR2 stabilizes the complex and ensures proper Rag GTPase activation .
MAPK Modulation
LAMTOR2 scaffolds MAPK components (e.g., Erk1/2) on endosomes, enhancing signaling efficiency. In B cells, it regulates pre-BCR signaling and receptor internalization .
Endosomal Trafficking
LAMTOR2 controls receptor sorting (e.g., Flt3, BCR) to late endosomes, preventing aberrant signaling. Its loss disrupts receptor degradation, leading to hyperactivation of pathways like AKT/mTOR .
Immunological and Developmental Implications
LAMTOR2 is essential for immune cell differentiation and function:
Human Mutations: Homozygous mutations in LAMTOR2’s 3′ UTR cause partial albinism, neutropenia, and B-cell defects (e.g., hypogammaglobulinemia) .
Recombinant Proteins
Antibodies
Animal Models
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B-cell-specific KO: CD19-Cre or mb1-Cre mice show B-cell developmental arrest .
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DC-specific KO: CD11c-Cre mice exhibit DC proliferation and myeloid syndrome .
Clinical and Therapeutic Relevance
Product Specs
Q&A
What is LAMTOR2 and what is its molecular structure?
LAMTOR2 (also known as p14 or ROBLD3) is an endosomal adaptor protein first identified in 2001. It is a constituent component of the pentameric Ragulator complex, which anchors mTORC1 to the lysosomal surface in response to amino acid signals . Structurally, LAMTOR2 forms a heterodimer with LAMTOR3 within the pentameric LAMTOR complex. Both LAMTOR2 and LAMTOR3 exhibit two alpha helices that are crucial for protein-protein interactions . The structural arrangement shows that while LAMTOR2-LAMTOR3 forms one heterodimer, a second heterodimer composed of LAMTOR4-LAMTOR5 is surrounded by the adaptor LAMTOR1 .
Where is LAMTOR2 expressed in human tissues?
LAMTOR2 displays widespread expression across multiple tissues and cell types. In the immune system, it is expressed in monocytes, macrophages, neutrophils, B cells, T cells, dendritic cells (DCs), and natural killer (NK) cells . Beyond the immune system, LAMTOR2 expression has been documented in the nervous system, lung, liver, muscle, intestine, secretory system, and reproductive system . This broad expression pattern indicates the fundamental importance of LAMTOR2 in cellular functions across different tissue types.
What are the primary signaling pathways regulated by LAMTOR2?
LAMTOR2 plays a significant role in the spatiotemporal regulation of two critical signaling pathways:
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mTORC1 (mammalian target of rapamycin complex 1) pathway - LAMTOR2 as part of the Ragulator complex anchors mTORC1 to lysosomes upon amino acid stimulation .
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ERK (mitogen-activated protein kinase 1) pathway - LAMTOR2 together with MP1 provides a scaffold for recruitment of ERK to endosomes, enabling spatial compartmentalization of signaling .
These pathways coordinate protein synthesis, cell growth, proliferation, differentiation, and other fundamental cellular processes . The late endosomal localization of LAMTOR2 is crucial for its function in regulating these signaling pathways in a context-dependent manner.
What is known about human LAMTOR2 deficiency?
Human LAMTOR2 deficiency causes a primary immunodeficiency syndrome characterized by:
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Severe congenital neutropenia
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Growth failure
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Partial albinism
The condition is caused by a homozygous point mutation in the 3′ untranslated region (UTR) of the LAMTOR2 gene, which generates a 5′ splice site recognized by the spliceosome, leading to suppression of LAMTOR2 poly(A)-site 3′ end processing . The mutation results in massively reduced expression of the protein . LAMTOR2 deficiency is grouped with other primary immunodeficiencies affecting lysosome-related organelles, such as Griscelli syndrome and Hermansky-Pudlak syndrome .
How does LAMTOR2 regulate B cell development and function?
LAMTOR2 plays a critical role in B cell development, particularly at the pre-B1 to pre-B2 developmental transition. Research using conditional knockout mice has revealed:
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Deletion of LAMTOR2 at the pre-B1 stage using mb1-Cre mice results in complete developmental arrest .
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LAMTOR2 is essential for B cell receptor (BCR) trafficking and signaling .
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Loss of LAMTOR2 leads to aberrant BCR signaling due to delayed receptor internalization and endosomal trafficking .
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LAMTOR2-deficient B cells show impaired BCR-mediated expansion that cannot be compensated by increased CD40 co-stimulation .
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BCR triggering in LAMTOR2-deficient follicular B and marginal zone B cells results in higher levels of phosphorylated Syk, Erk, and tyrosines, but reduced calcium flux compared to controls .
These findings highlight that LAMTOR2 does not simply strengthen or weaken BCR signaling but rather orchestrates a balanced activation of downstream pathways necessary for proper B cell development and function.
What role does LAMTOR2 play in invariant natural killer T (iNKT) cell development?
LAMTOR2 is essential for early iNKT cell development in the thymus. Studies using T cell-specific knockout mice show:
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Deletion of Lamtor2 causes severe defects in early iNKT cell development, while conventional T cell development remains intact .
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Loss of LAMTOR2 impairs glycolipid presentation on double-positive T cells, which is crucial for positive selection of iNKT cells .
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LAMTOR2 ablation reduces mTORC1 signaling and increases cell death during the transition from developmental stage ST1 to ST2, following positive selection .
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LAMTOR2 deficiency results in unresponsiveness of peripheral iNKT cells .
These findings demonstrate that LAMTOR2-mediated endosomal trafficking and signaling are critical for iNKT cell development, particularly during the positive selection phase and early developmental transitions.
How does LAMTOR2 function within the LAMTOR/Ragulator complex?
LAMTOR2 functions as a structural and functional component within the pentameric LAMTOR/Ragulator complex. The complex organization and function includes:
| Component | Binding Partner(s) | Structural Feature | Primary Function |
|---|---|---|---|
| LAMTOR1 | Surrounds other components | Adaptor protein | Anchors complex to lysosomal membrane |
| LAMTOR2 | LAMTOR3 | Two alpha helices | Forms heterodimer with LAMTOR3; scaffold for ERK recruitment |
| LAMTOR3 | LAMTOR2 | Two alpha helices | Forms heterodimer with LAMTOR2 (also known as MP1) |
| LAMTOR4 | LAMTOR5 | - | Forms second heterodimer |
| LAMTOR5 | LAMTOR4 | - | Forms second heterodimer |
The complete LAMTOR complex is essential for:
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Amino acid-dependent mTORC1 activation
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Spatial organization of late endosomes/lysosomes
Deletion of LAMTOR2 results in complete abrogation of the LAMTOR/Ragulator complex, highlighting its essential role in maintaining complex integrity .
What mechanisms explain the phenotypic overlap between LAMTOR2 deficiency and other lysosomal-related organelle disorders?
LAMTOR2 deficiency shares phenotypic features with disorders like Griscelli syndrome (GS), Hermansky-Pudlak syndrome (HPS), and Chediak-Higashi syndrome (CHS). These overlapping mechanisms include:
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Disrupted endosomal trafficking affecting multiple lysosome-related organelles
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Impaired biogenesis of specialized secretory compartments
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Affected organelles include:
The cell biological studies of LAMTOR2-deficient patient cells demonstrate perturbed subcellular distribution of late endosomes and highlight LAMTOR2's role in regulating endosomal trafficking in immune cells and biosynthesis of lysosomal-related organelles .
What are the optimal approaches for studying LAMTOR2 function in immune cells?
When investigating LAMTOR2 function in immune cells, researchers should consider:
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Conditional knockout models: Using lineage-specific Cre recombinase systems (e.g., mb1-Cre for B cells, CD19-Cre for later B-cell stages) allows study of cell-specific functions while avoiding embryonic lethality associated with constitutive LAMTOR2 deletion .
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Methylcellulose cultures: For studying pre-B cell development, methylcellulose cultures of pre-B1 cells in the presence of IL-7 can help discriminate between IL-7 and pre-BCR signaling pathways .
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Phosphorylation analysis: For BCR signaling studies, analyze phosphorylation of multiple targets (Syk, Erk, general tyrosines) and include H₂O₂ co-treatment to inhibit phospho-tyrosine phosphatase activity .
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Calcium flux measurement: Important for comprehensive assessment of BCR signaling, as calcium responses may show different patterns than phosphorylation events .
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Cell proliferation assays: Use varying concentrations of stimuli (anti-IgM, anti-CD40, CpG) to assess pathway-specific effects on cell expansion .
These methodological approaches enable comprehensive assessment of LAMTOR2's multifaceted roles in immune cell development and function.
How can researchers effectively detect and measure LAMTOR2 protein expression?
For optimal detection and quantification of LAMTOR2 protein expression:
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Western blotting: Use antibodies specific to LAMTOR2 (p14); important to include controls for specificity given the small size of the protein (~14 kDa).
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Immunofluorescence microscopy: Enables visualization of LAMTOR2 subcellular localization, ideally with co-staining for late endosomal/lysosomal markers such as LAMP1.
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Flow cytometry: Can be used for intracellular staining of LAMTOR2 in fixed and permeabilized cells to quantify expression levels across cell populations.
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qRT-PCR: Useful for measuring LAMTOR2 mRNA levels, especially when assessing deletion efficiency in conditional knockout models .
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Proximity ligation assays: Can detect interactions between LAMTOR2 and its binding partners (LAMTOR3/MP1) in situ.
When working with human samples from patients with partial LAMTOR2 deficiency, researchers should be aware that residual expression may confound results, necessitating careful quantification and comparison with appropriate controls.
What experimental designs best reveal the impact of LAMTOR2 on endosomal trafficking and signaling?
To investigate LAMTOR2's effects on endosomal trafficking and signaling:
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Receptor internalization assays: Track BCR internalization using fluorescently labeled antibodies and flow cytometry or microscopy with time-course analysis .
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Endosomal fractionation: Separate cellular compartments by density centrifugation to analyze the distribution of signaling components across endosomal populations.
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Live cell imaging: Monitor dynamics of receptor trafficking and colocalization with endosomal markers in real-time.
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Spatiotemporal signaling analysis: Compare early (plasma membrane) versus late (endosomal) signaling events following receptor stimulation.
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Complementation studies: Rescue experiments using wild-type versus mutant LAMTOR2 constructs can identify critical domains for specific functions.
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Inhibitor studies: Use selective inhibitors of endocytosis, endosomal maturation, or specific signaling pathways to dissect LAMTOR2-dependent processes.
These approaches can resolve the mechanisms by which LAMTOR2 coordinates endosomal trafficking with signaling pathway activation, revealing how compartmentalization contributes to signal specificity.
What therapeutic approaches might target the LAMTOR2 pathway in immunological disorders?
Potential therapeutic strategies targeting the LAMTOR2 pathway include:
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Gene therapy approaches: For primary immunodeficiencies caused by LAMTOR2 mutations, targeted gene correction or supplementation might restore normal immune function.
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Small molecule modulators: Compounds that stabilize the LAMTOR/Ragulator complex or enhance its assembly could potentially improve function in partial deficiency states.
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Pathway-specific interventions: Selective targeting of downstream pathways (mTORC1 or ERK) might compensate for LAMTOR2 dysfunction in specific cellular contexts.
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Cell-based therapies: Autologous stem cell transplantation with genetically corrected cells could provide long-term reconstitution of the immune system in LAMTOR2-deficient patients.
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Targeted protein delivery: Methods to deliver functional LAMTOR2 protein to specific cellular compartments could bypass genetic defects.
The development of these approaches requires deeper understanding of LAMTOR2's tissue-specific functions and the consequences of its dysregulation in different disease contexts.
How might LAMTOR2 function differ across tissue types and developmental stages?
Research suggests that LAMTOR2 may have context-dependent functions across different tissues and developmental stages:
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Immune system: Critical roles in B cells, T cells, and especially iNKT cells during development and activation .
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Nervous system: Expression in neural tissues suggests potential roles in neuronal signaling and endosomal trafficking.
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Developmental regulation: Embryonic lethality of constitutive knockout indicates essential functions during early embryogenesis .
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Tissue homeostasis: Studies in epidermis-specific deletion models highlight importance in tissue maintenance .
Future research should employ tissue-specific and inducible conditional knockout models to systematically investigate LAMTOR2 functions across diverse physiological contexts and developmental windows. Comparative studies between tissues could reveal both conserved and specialized roles of the LAMTOR/Ragulator complex.
Product Science Overview
LAMTOR2 is a member of the GAMAD family and is highly conserved across species. The human recombinant LAMTOR2 protein is typically produced in Escherichia coli (E. coli) and is a single, non-glycosylated polypeptide chain containing 148 amino acids, with a molecular mass of approximately 15.9 kDa . The protein is often fused to a polyhistidine tag (His-tag) at the N-terminus to facilitate purification .
LAMTOR2 is an essential component of the Ragulator complex, which is involved in the activation of the mTORC1 (mechanistic target of rapamycin complex 1) signaling pathway. This pathway is critical for regulating cell growth, proliferation, and survival in response to nutrients, energy levels, and growth factors . LAMTOR2, along with other components of the Ragulator complex, recruits the Rag GTPases and the mTORC1 complex to lysosomes, a key step in the activation of the mTOR signaling cascade by amino acids .
Additionally, LAMTOR2 acts as an adaptor protein that enhances the efficiency of the MAP kinase (MAPK) cascade, facilitating the activation of MAPK2 . This interaction is crucial for various cellular processes, including endosomal biogenesis and signal transduction.
Mutations in the LAMTOR2 gene have been associated with primary immunodeficiency syndrome in humans . This suggests that LAMTOR2 plays a significant role in the immune system, particularly in the development and function of immune cells. The protein’s involvement in endosomal biogenesis further underscores its importance in cellular homeostasis and immune responses .
Human recombinant LAMTOR2 is produced using recombinant DNA technology. The gene encoding LAMTOR2 is cloned into an expression vector and introduced into E. coli cells, which then produce the protein. The recombinant protein is purified using chromatographic techniques, often involving the His-tag for affinity purification .
The purified LAMTOR2 protein is typically formulated in a buffer solution containing Tris-HCl, NaCl, glycerol, and DTT (dithiothreitol) to maintain stability and activity . The protein is stored at low temperatures to prevent degradation and maintain its functional integrity .
