TIE1 Human

What is TIE1 and what is its primary function in human physiology?

TIE1 is a receptor tyrosine kinase primarily expressed in endothelial cells that plays crucial roles in vascular development, maintenance of vascular integrity, and angiogenesis. While structurally similar to TIE2, TIE1 has long been regarded as an orphan receptor without identified ligands, functioning principally by forming heterodimers with TIE2 to regulate its activity . TIE1 is part of the Ang-Tie signaling pathway, which is a major endothelial signaling pathway regulating vascular quiescence, permeability, stability, and growth . Recent research has expanded our understanding of TIE1 beyond its traditional endothelial role, with evidence showing its expression and functional significance in non-endothelial cells, including cancer cells . Methodologically, researchers typically characterize TIE1 function through targeted genetic manipulation in cell culture and animal models, combined with functional assays for vascular development and integrity.

How can researchers effectively measure TIE1 expression in human tissues?

TIE1 expression can be quantified through several complementary approaches. For protein-level detection, immunohistochemistry (IHC) staining is commonly employed for tissue samples, as demonstrated in cervical cancer studies where TIE1 expression was evaluated in 135 cervical cancer tissues with different staining intensities . Western blotting serves as another reliable method for quantifying protein expression in cell lines and tissue lysates, as shown in the comparison of TIE1 expression between cervical cancer cell lines and normal cervical cell line H8 . For transcriptional analysis, quantitative real-time PCR and RNA sequencing can determine TIE1 mRNA levels. When interpreting results, researchers should consider tissue heterogeneity and establish appropriate controls. For instance, when studying TIE1 in cancer, comparing expression between tumor and adjacent normal tissue from the same patient minimizes inter-individual variability. Additionally, validation across multiple methodologies strengthens confidence in expression data.

How does TIE1 contribute to cancer progression?

TIE1 promotes cancer progression through multiple mechanisms that enhance tumor growth and metastasis. In cervical cancer, TIE1 overexpression has been demonstrated to significantly increase proliferation, migration, and invasion of cancer cells in vitro, as confirmed through colony formation assays, transwell assays, and wound healing assays . These findings were further corroborated in vivo, where TIE1 overexpression enhanced tumor growth and increased the incidence of pulmonary metastasis in mouse models .

At the molecular level, TIE1 exerts its tumor-promoting effects through a novel mechanism involving interaction with Basigin, a transmembrane glycoprotein. This interaction was identified through co-immunoprecipitation and mass spectrometry (Co-IP/MS) analysis . TIE1 stabilizes Basigin protein by protecting it from proteasomal degradation, as evidenced by cycloheximide chase and MG132 treatment experiments . The stabilized Basigin subsequently stimulates the expression of matrix metalloproteinases (MMPs), particularly MMP2 and MMP9, which degrade the extracellular matrix to facilitate cancer cell invasion and metastasis . Importantly, knockdown of Basigin or treatment with the Basigin inhibitor AC-73 reversed the tumor-promoting effects of TIE1, confirming the functional significance of this interaction .

What is the relationship between cerebrospinal fluid TIE1 levels and cognitive performance?

Cerebrospinal fluid (CSF) levels of soluble TIE1 (sTie-1) have been demonstrated to have a significant negative association with cognitive performance. According to Mendelian randomization (MR) analyses, higher levels of sTie-1 in CSF were associated with worse cognitive performance (effect estimate: -0.43, 95% CI: -0.62 to -0.23, p = 2.08 × 10^-5) . This finding suggests a potential causal relationship between TIE1 and cognitive function.

Methodologically, Mendelian randomization represents a robust approach for investigating causality as it uses genetic variants as instrumental variables, thereby minimizing confounding and reverse causation issues that often complicate observational studies. The relationship between TIE1 and cognition was further supported by colocalization analyses and by concordant effects on distinct cognition-related and brain-volume measures . These findings highlight the importance of considering TIE1's role beyond traditional vascular functions, potentially extending to neurovascular interactions that influence cognitive processes. Future research should explore the specific mechanisms by which TIE1 affects neuronal function and cognitive performance, possibly through effects on blood-brain barrier integrity or neuroinflammatory processes.

How does TIE1 interact with the Ang-Tie signaling pathway?

TIE1 plays a critical modulatory role in the Ang-Tie signaling pathway through complex interactions with TIE2 and its ligands. While TIE2 directly binds angiopoietins (Ang1 and Ang2), TIE1 lacks known ligands but influences TIE2 signaling through heterodimer formation . Computational modeling validated against experimental data has revealed that TIE1 modulates TIE2's response to the context-dependent agonist Ang2 specifically through junctional interactions . This spatial regulation is crucial for signal transduction specificity.

The Ang-Tie pathway's primary functions include regulating vascular quiescence, permeability, stability, and growth . Dysregulation of this pathway contributes to vascular dysfunction and numerous diseases characterized by abnormal vascular permeability and endothelial cell inflammation . Research methodologies to study these interactions typically employ combinations of receptor mutants, domain-specific antibodies, and fluorescence resonance energy transfer (FRET) to detect protein-protein interactions in living cells. Additionally, computational models integrating experimental data have proven valuable in capturing the complex dynamics of this signaling network, including the time-dependent role of TIE1 .

What mechanisms regulate TIE1 protein stability and turnover?

TIE1 protein stability and turnover are regulated through multiple mechanisms, including proteolytic cleavage and post-translational modifications. Research on TIE1's interaction with Basigin has provided insights into protein stability regulation. Experiments using the protein synthesis inhibitor cycloheximide (CHX) demonstrated that TIE1 overexpression significantly slowed the degradation rate of Basigin protein compared to control cells . Conversely, when investigating TIE1's own stability, researchers should consider:

• Proteolytic processing: TIE1 undergoes extracellular domain cleavage, which modulates its signaling capacity. Inhibition of this cleavage has been identified as a potential strategy for enhancing TIE2 signaling in inflammatory conditions .

• Ubiquitin-proteasome pathway: Similar to many receptor tyrosine kinases, TIE1 likely undergoes ubiquitin-mediated proteasomal degradation. The treatment with MG132, a proteasome inhibitor, can be used to investigate this pathway's role in TIE1 turnover .

• Post-translational modifications: Glycosylation may significantly impact TIE1 function and stability. The observation of double bands in Western blotting experiments suggests different glycosylation states of TIE1, which could influence protein-protein interactions and signaling properties .

To study these processes experimentally, researchers should employ pulse-chase experiments, selective inhibitors of different degradation pathways, and site-directed mutagenesis of key residues involved in post-translational modifications.

What are the optimal techniques for investigating TIE1-protein interactions?

Investigating TIE1-protein interactions requires a multi-faceted approach combining several complementary techniques:

• Co-immunoprecipitation and Mass Spectrometry (Co-IP/MS): This powerful combination was successfully used to identify Basigin as a TIE1-interacting protein in cervical cancer cells . The approach involved immunoprecipitation with anti-FLAG antibodies in TIE1-overexpressing cells followed by LC-MS/MS analysis. This identified 1128 proteins, which were further filtered to 169 candidate interacting proteins based on specific criteria . This method is particularly valuable for unbiased discovery of novel protein interactions.

• Verification techniques: After initial identification, specific interactions should be verified using reciprocal co-immunoprecipitation, where both proteins can pull down each other. Additionally, immunofluorescence co-localization studies provide spatial information about the interaction in cellular contexts .

• Functional validation: Beyond physical interaction, researchers should demonstrate functional relevance through manipulation of the interacting partner. For example, the functional significance of the TIE1-Basigin interaction was confirmed by showing that Basigin knockdown or inhibition reversed the tumor-promoting effects of TIE1 overexpression .

• Protein stability assays: Cycloheximide chase experiments and proteasome inhibition (e.g., with MG132) can reveal whether an interaction affects protein stability, as demonstrated for TIE1's effect on Basigin degradation .

• Domain mapping: To identify specific interaction domains, truncation mutants and site-directed mutagenesis should be employed, allowing precise determination of the molecular basis for protein-protein interactions.

How can researchers effectively model TIE1 function in different disease contexts?

Modeling TIE1 function across disease contexts requires tailored approaches for each pathological condition:

• Cancer models: For studying TIE1 in cancer, researchers can employ both in vitro and in vivo approaches. Cell line models with stable overexpression or knockdown of TIE1 allow investigation of cellular behaviors including proliferation, migration, and invasion through colony formation, wound healing, and transwell assays . In vivo models include subcutaneous xenografts for tumor growth assessment and tail vein injection for evaluating metastatic potential . When establishing such models, researchers should consider cell type-specific effects and validate findings across multiple cell lines.

• Vascular dysfunction models: Computational modeling has proven valuable for understanding TIE1's role in vascular biology. Models incorporating junctional localization and downstream signaling can capture complex behaviors of the Ang-Tie pathway . These computational approaches should be validated against experimental data from endothelial cell cultures under various conditions, including inflammation and hypoxia.

• Neurological disease models: To study TIE1's impact on cognitive function, researchers might employ transgenic mouse models with conditional TIE1 knockout or overexpression in specific cell types, combined with comprehensive cognitive assessment batteries. Additionally, blood-brain barrier models can help elucidate TIE1's role in neurovascular function .

• Translational approaches: Clinical samples should be incorporated whenever possible to validate experimental findings. For instance, the correlation between TIE1 expression and clinical outcomes in cervical cancer was established through analysis of 135 patient samples, providing crucial translational relevance .

How might TIE1 serve as a biomarker or therapeutic target in cancer?

TIE1 shows significant potential as both a biomarker and therapeutic target in cancer based on several lines of evidence:

As a biomarker, high TIE1 expression has been associated with poor survival in cervical cancer patients . Clinical analysis of 135 cervical cancer patients demonstrated that TIE1 expression positively correlated with lymphovascular space invasion and other adverse clinicopathological features . Similar prognostic associations have been observed in gastric cancer, ovarian cancer, and metastatic breast cancer . These findings suggest that TIE1 expression analysis could help stratify patients for more aggressive treatment approaches.

As a therapeutic target, several strategies could be explored:

• Disrupting TIE1-Basigin interaction: Since this interaction promotes tumor progression through MMP activation, small molecule inhibitors or peptides targeting the interaction interface could potentially reduce cancer cell invasion and metastasis .

• Reducing TIE1 expression: RNA interference approaches targeting TIE1 significantly weakened cervical cancer cell migratory and invasive capacities in experimental models .

• Combination therapies: TIE1 has been shown to promote cisplatin resistance in ovarian cancer by upregulating xeroderma pigmentosum complementation group C (XPC)-mediated nucleotide excision repair . This suggests potential benefit from combining TIE1 inhibition with conventional chemotherapy.

• Targeting downstream effectors: Inhibiting the Basigin-matrix metalloproteinase axis with agents like AC-73 (a Basigin inhibitor) could counteract TIE1's tumor-promoting effects .

Research methodologies for evaluating these therapeutic approaches should include comprehensive in vitro efficacy and toxicity testing, followed by in vivo validation in appropriate animal models before clinical translation.

What are the potential approaches for modulating TIE1 in vascular diseases?

Based on current understanding of TIE1's role in vascular biology, several therapeutic strategies could be developed for vascular diseases:

• Modulation of TIE1's junctional localization: Computational modeling has identified that TIE1's junctional localization is crucial for its function in the Ang-Tie signaling pathway . Developing compounds that affect this localization could potentially enhance beneficial vascular signaling in disease states.

• Inhibition of TIE2 extracellular domain cleavage: This approach has been identified as a potential molecular strategy for potentiating Ang2's agonistic activity and rescuing Tie2 signaling in inflammatory endothelial cells .

• Inhibition of VE-PTP: This strategy has shown promise in enhancing Tie2 signaling in the presence of dysregulated TIE1 function .

• Context-specific modulation: Since TIE1's effects can vary by disease context, therapies should be tailored appropriately. For example, in diseases characterized by excessive vascular permeability, strategies to enhance TIE1-TIE2 stabilizing functions might be beneficial, while in pathological angiogenesis, inhibition might be more appropriate.

Methodologically, researchers should evaluate these approaches using disease-specific models, such as retinal permeability assays for diabetic retinopathy, ischemia-reperfusion models for vascular dysfunction, and appropriate inflammatory models for systemic inflammation . Additionally, biomarkers of vascular function, such as vascular leakage, endothelial activation, and tissue perfusion, should be incorporated to assess therapeutic efficacy.

What are the key unresolved questions about TIE1 function in human biology?

Despite significant advances, several critical questions about TIE1 remain unanswered:

• Ligand identification: While TIE1 has long been considered an orphan receptor, the possibility of unidentified ligands remains. Systematic screening approaches using receptor-binding assays and functional readouts could potentially identify TIE1-specific ligands or co-ligands.

• TIE2-independent functions: Recent evidence suggests TIE1 may have functions independent of TIE2, as demonstrated by its role in cervical cancer progression through Basigin interaction . Further investigation of TIE1's autonomous signaling capabilities is warranted.

• Post-translational regulation: The observation of potential glycosylation differences in TIE1 suggests complex post-translational regulation . Comprehensive characterization of these modifications and their functional consequences would enhance our understanding of TIE1 regulation.

• Tissue-specific roles: Beyond endothelial cells and cancer, TIE1's function in other cell types and physiological processes requires investigation, particularly given its unexpected association with cognitive function .

• Mechanistic basis for cognitive effects: The causal relationship between CSF TIE1 levels and cognitive performance identified through Mendelian randomization requires mechanistic explanation . Investigation of TIE1's role in neurovascular coupling, blood-brain barrier function, and neuronal health would be valuable.

Methodologically, addressing these questions will require integrated approaches combining genetic manipulation, high-resolution imaging, proteomics, and computational modeling across multiple experimental systems from cell culture to animal models and human samples.

How might emerging technologies advance TIE1 research?

Emerging technologies offer exciting opportunities to deepen our understanding of TIE1 biology:

• CRISPR-Cas9 genome editing: Precise manipulation of TIE1 and interacting proteins in relevant cell types will allow detailed functional analysis. Creating knockin models with fluorescent tags or specific mutations can provide insights into TIE1 dynamics and signaling.

• Single-cell technologies: Single-cell RNA sequencing and proteomics can reveal cell-specific expression patterns and responses to TIE1 modulation, capturing heterogeneity that bulk analysis might miss.

• Advanced imaging techniques: Super-resolution microscopy and live-cell imaging can track TIE1 trafficking, junctional localization, and interactions with other proteins in real-time, providing dynamic information about its function .

• Proteomics advances: Proximity labeling methods like BioID or APEX could map the complete TIE1 interactome in different cellular contexts, extending beyond the initial discoveries made through conventional Co-IP/MS .

• Computational biology: Building on existing computational models of the Ang-Tie pathway , more comprehensive models incorporating newly discovered interactions (such as with Basigin) could predict system-level responses to perturbations.

• Organoid and microfluidic systems: Three-dimensional culture systems and organ-on-chip technologies can provide more physiologically relevant contexts for studying TIE1 function in vasculature, tumors, and neurovascular units.

These technologies should be applied in an integrated fashion to comprehensively characterize TIE1's multifaceted roles in health and disease, with particular attention to translational implications for vascular disorders, cancer, and cognitive function.