TIRAP Human
Description
Introduction to TIRAP Human
TIRAP (TIR domain-containing adaptor protein), also known as MyD88-adaptor like (MAL), is a 221-amino-acid protein critical in innate immune signaling. It serves as an adaptor molecule for Toll-like receptors (TLRs), particularly TLR2 and TLR4, facilitating downstream proinflammatory responses . TIRAP links activated receptors to the MyD88 signaling complex, enabling nuclear factor κB (NF-κB) and mitogen-activated protein kinase (MAPK) pathway activation, which drive cytokine production and immune cell survival . Dysregulation of TIRAP-mediated signaling is implicated in autoimmune diseases, lymphoma, and sepsis, underscoring its therapeutic relevance .
Functional Polymorphisms
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p.R81C (rs137781224):
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Ser180Leu (rs8177374):
Global Allele Frequencies
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The TIRAP 180L allele is prevalent in West Eurasia (e.g., Middle Eastern Bedouins) but rare in African and East Asian populations, suggesting selection during early human migrations .
Functional Role in Immune Signaling
TIRAP orchestrates immune responses through interactions with multiple partners:
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TLR8-specific role: TIRAP enhances IRF5 nuclear translocation and Akt activation during bacterial infection, amplifying IL-12A and IFNβ production .
Mechanistic Insights
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TIRAP-deficient mice show impaired TLR2/4 responses but normal TLR9 signaling, confirming its receptor specificity .
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siRNA knockdown in human primary macrophages reduces TLR8-driven cytokine secretion by 40–60% .
Clinical Implications
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Autoimmunity: Hyperactive TIRAP variants (e.g., p.R81C) correlate with unchecked NF-κB activation, increasing lymphoma risk .
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Sepsis: The Ser180Leu allele associates with heightened cytokine storms and septic shock susceptibility .
Therapeutic Potential
Targeting TIRAP-protein interactions (e.g., with BTK or TRAF6) may mitigate inflammatory diseases. Small-molecule inhibitors of TIRAP’s TIR domain are under preclinical investigation .
Product Specs
Q&A
What is the genomic location and structure of human TIRAP?
The tirap gene is located on chromosome 11q24.2 in humans and encodes the TIRAP/MAL protein. TIRAP contains a C-terminal TIR (Toll/IL-1 receptor) domain that functions as a sorting and bridging adaptor between Toll-like receptors (TLRs) and the MyD88 adaptor protein. Specifically, TIRAP acts as a bridging adaptor between TLR2, TLR4, and TLR9 to bring MyD88 into the immune signaling pathway . The crystal structure of human TIRAP's TIR-domain has been determined and is available in the Protein Data Bank (PDB ID: 4FZ5), providing valuable structural insights for researchers investigating protein-protein interactions involving TIRAP .
How does TIRAP integrate into immune signaling cascades?
TIRAP functions as a critical adaptor protein in the TLR signaling cascade. Upon TLR stimulation, TIRAP facilitates the recruitment of MyD88 to activated TLRs, initiating a signaling cascade that ultimately leads to the activation of transcription factors. This activation results in the production of pro-inflammatory cytokines such as IL-6, IL-12, and TNF-α. The signaling pathway is essential for mounting effective immune responses against pathogens . When investigating TIRAP's role in immune signaling, researchers should consider examining both direct protein interactions through co-immunoprecipitation studies and downstream cytokine production through ELISA or cytometric bead arrays.
How is TIRAP associated with tuberculosis susceptibility?
Interestingly, in humans, resistance to tuberculosis is associated with a loss-of-function in TIRAP. This association suggests that TIRAP may play a role in the pathogenesis of tuberculosis, potentially by influencing the immune response to Mycobacterium tuberculosis . Loss-of-function variants in TIRAP may alter the balance of immune activation, potentially leading to more effective bacterial containment. Researchers investigating this phenomenon should consider utilizing CRISPR-Cas9 gene editing to generate TIRAP-deficient cell lines or knockout mouse models to study the mechanistic basis of this resistance.
What is the role of TIRAP in myelodysplastic syndromes (MDS)?
TIRAP is overexpressed in various types of myelodysplastic syndromes (MDS), a group of hematopoietic stem cell malignancies characterized by dysplastic morphology, cellular dysfunction, and peripheral blood cytopenias. Gene expression analysis of CD34+ cells from MDS patients has shown increased TIRAP expression in del(5q) MDS compared to healthy controls and MDS patients diploid at chromosome 5q . This overexpression contributes to bone marrow failure by suppressing all three major hematopoietic lineages: myeloid, erythroid, and megakaryocytic . When researching TIRAP in MDS, investigators should employ patient-derived samples alongside mouse models to validate findings across species.
How does TIRAP overexpression contribute to bone marrow failure?
TIRAP overexpression in hematopoietic stem/progenitor cells (HSPCs) promotes the upregulation of Ifnγ, which leads to myelosuppression through a specific mechanism. This process involves Ifnγ-Ifnγr–mediated release of the alarmin protein Hmgb1, which subsequently disrupts the bone marrow endothelial niche. The disruption of the endothelial compartment leads to suppression of myelopoiesis. Importantly, deletion of Ifnγ blocks Hmgb1 release and is sufficient to reverse the endothelial defect and restore normal myelopoiesis . Studies examining this pathway should incorporate both in vitro co-culture systems and in vivo transplantation models to fully characterize the cell-cell interactions involved.
How does the TIRAP-Ifnγ-Hmgb1 axis regulate hematopoiesis?
The TIRAP-Ifnγ-Hmgb1 axis represents a novel regulatory pathway for hematopoiesis with distinct mechanisms affecting different hematopoietic lineages. Research has shown that TIRAP-induced activation of Ifnγ has both direct and indirect effects:
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Direct effects: Ifnγ directly suppresses megakaryocyte and erythroid production
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Indirect effects: Ifnγ indirectly suppresses myelopoiesis through the release of Hmgb1, which disrupts the bone marrow endothelial niche
This dual mechanism helps explain the pancytopenia observed in bone marrow failure syndromes . Contrary to previous beliefs, this TIRAP-activated Ifnγ-driven bone marrow suppression operates independently of T cell function or pyroptosis, challenging the current dogma in the field .
What is the relationship between TIRAP and leukemic transformation?
An important finding regarding TIRAP's role in disease progression is that in the absence of Ifnγ, TIRAP drives myeloproliferation rather than myelosuppression. This observation implicates Ifnγ in suppressing the transformation of MDS to acute leukemia . This dual role of TIRAP—promoting either bone marrow failure or myeloproliferation depending on the cytokine context—provides critical insights into the pathophysiology of preleukemic syndromes. Researchers should consider using conditional knockout models to temporally control TIRAP and Ifnγ expression to better understand this relationship.
What are the non-canonical roles of TIRAP in immune regulation?
Beyond its canonical role as an adaptor protein in TLR signaling, TIRAP has been found to have several non-canonical functions. Recent research has revealed novel, non-canonical roles of TIRAP, Hmgb1, and Ifnγ in the bone marrow microenvironment . In particular, TIRAP can influence immune cell development and function through mechanisms distinct from its adaptor function in TLR signaling cascades. These findings expand our understanding of how innate immune components regulate hematopoiesis and tissue homeostasis.
What are the optimal methods for studying TIRAP's role in hematopoiesis?
To study TIRAP's role in hematopoiesis, researchers have employed several complementary approaches:
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Mouse models: Constitutive expression of TIRAP in mouse hematopoietic stem/progenitor cells (HSPCs) followed by transplantation into lethally irradiated recipients
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In vitro culture systems: Comparing TIRAP-expressing HSPCs cultured in vitro versus their behavior in vivo
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Bone marrow homing experiments: To rule out homing defects as a cause of bone marrow failure
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Gene expression profiling: To identify downstream effectors of TIRAP signaling
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Cytokine measurements: ELISA of conditioned medium and serum to quantify cytokine production
These approaches have revealed that TIRAP's effects on hematopoiesis are context-dependent, with different outcomes observed in vitro versus in vivo, highlighting the importance of the bone marrow microenvironment .
How can researchers effectively manipulate TIRAP expression for experimental studies?
| Approach | Application | Advantages | Limitations | Considerations |
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| Lentiviral transduction | Overexpression in HSPCs | High efficiency, stable integration | Potential insertional mutagenesis | Use appropriate controls with empty vectors |
| CRISPR-Cas9 | Gene knockout or mutation | Precise editing, complete knockout | Off-target effects | Validate multiple guide RNAs |
| Conditional systems | Temporal control of expression | Allows study of acute vs. chronic effects | Leakiness of the system | Include appropriate inducer controls |
| Patient-derived samples | Clinical relevance | Direct translation to human disease | Heterogeneity, limited availability | Match for age, sex, and disease status |
Researchers should select the approach based on their specific experimental questions and model systems, considering both the advantages and limitations of each method .
What analytical approaches are recommended for dissecting TIRAP signaling pathways?
To comprehensively analyze TIRAP signaling pathways, researchers should consider:
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RNA-sequencing: For genome-wide transcriptional profiling to identify differentially expressed genes following TIRAP manipulation
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Pathway analysis: Using tools like Ingenuity Pathway Analysis (IPA) to predict upstream regulators and identify enriched signaling pathways
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Cytokine profiling: Multiplex assays to quantify multiple cytokines simultaneously in conditioned medium or serum
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Validation experiments: RT-qPCR and ELISA to confirm expression changes of key genes and proteins
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Co-immunoprecipitation: To identify protein-protein interactions involving TIRAP
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Phospho-proteomics: To map signaling cascades activated downstream of TIRAP
Such analytical approaches have successfully identified the Ifnγ-Hmgb1 axis as a critical mediator of TIRAP's effects on hematopoiesis .
How might targeting TIRAP be developed as a therapeutic strategy?
Given TIRAP's role in various disease processes, it represents a potential therapeutic target. For MDS and bone marrow failure syndromes, strategies to inhibit TIRAP or its downstream effectors might be beneficial. Conversely, in tuberculosis, where loss-of-function is associated with resistance, enhancing TIRAP function might be detrimental. Therapeutic approaches could include:
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Small molecule inhibitors targeting the TIR domain
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Peptide inhibitors disrupting TIRAP-MyD88 interactions
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RNA interference to reduce TIRAP expression
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Blocking antibodies against downstream cytokines like Ifnγ
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Inhibitors of Hmgb1 release to prevent disruption of the bone marrow niche
Researchers developing such approaches should carefully consider the context-dependent effects of TIRAP manipulation and potential off-target effects on immune function.
What are the implications of TIRAP polymorphisms in human populations?
Genetic variability in the TIRAP gene contributes to differential immune responses and disease susceptibility. Loss-of-function variants in TIRAP are associated with resistance to tuberculosis in humans . Further investigation of TIRAP polymorphisms across different human populations could provide insights into evolutionary selection pressures and differential disease susceptibility. Researchers studying these polymorphisms should employ population genetics approaches, including genome-wide association studies (GWAS) and targeted sequencing of the TIRAP locus in diverse populations.
How does TIRAP interact with other inflammatory pathways in complex diseases?
TIRAP's interaction with other inflammatory pathways in complex diseases represents an important area for future research. Given its role in activating Ifnγ and other cytokines, TIRAP likely participates in cross-talk with multiple inflammatory networks. Understanding these interactions could provide insights into the pathogenesis of various inflammatory and hematological disorders. Researchers investigating these interactions should consider systems biology approaches, including network analysis and multi-omics integration, to comprehensively map TIRAP's position within the broader inflammatory landscape.
Product Science Overview
TIRAP is characterized by the presence of a Toll/Interleukin-1 receptor (TIR) domain. This domain is a conserved region found in a variety of proteins involved in immune signaling, including Toll-like receptors (TLRs) and interleukin-1 receptors (IL-1Rs). The TIR domain is responsible for mediating protein-protein interactions that are essential for downstream signaling events .
In the context of TLR signaling, TIRAP acts as an adaptor protein that bridges the interaction between TLRs and other signaling molecules. Specifically, TIRAP is involved in the signaling pathways of TLR2 and TLR4. Upon recognition of pathogen-associated molecular patterns (PAMPs) by TLRs, TIRAP facilitates the recruitment of another adaptor protein, MyD88, to the TLRs. This recruitment is crucial for the activation of downstream signaling cascades that lead to the production of pro-inflammatory cytokines and other immune responses .
The primary function of TIRAP is to mediate the activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), mitogen-activated protein kinases (MAPKs), and other transcription factors that regulate the expression of genes involved in inflammation and immune responses. By doing so, TIRAP plays a pivotal role in the body’s ability to respond to infections and other immune challenges .
From an evolutionary standpoint, TIR domain-containing proteins, including TIRAP, are conserved across a wide range of species. This conservation underscores their fundamental role in immune signaling. Studies have shown that TIRAP and other TIR domain-containing adaptor proteins have undergone evolutionary divergence, leading to the specialization of their functions in different species .
Given its central role in immune signaling, TIRAP has been the subject of extensive research in the context of various diseases. Dysregulation of TIRAP-mediated signaling pathways has been implicated in inflammatory and autoimmune diseases. Additionally, genetic variations in the TIRAP gene have been associated with susceptibility to infections and other immune-related conditions .
Recombinant TIRAP, produced through genetic engineering techniques, is used in research to study its function and role in immune signaling. By using human recombinant TIRAP, scientists can investigate the molecular mechanisms underlying TIRAP-mediated signaling pathways and explore potential therapeutic targets for modulating immune responses.
