Recombinant Human Transmembrane protein 140 (TMEM140)

What is the genomic structure and basic characterization of human TMEM140?

The human TMEM140 gene encodes a transmembrane protein that belongs to the broader transmembrane protein family. Genomic analyses have identified TMEM140 as a protein-coding gene that is expressed in various tissues with particular relevance in neural tissues. The protein contains multiple hydrophobic regions forming transmembrane domains, which is characteristic of the TMEM family. The gene was initially identified as an amplified gene in human gastric cancer genome, suggesting its potential oncogenic functions . The protein's transmembrane topology is essential for its cellular localization and function, affecting various cellular processes including adhesion and migration.

When studying TMEM140, researchers should note that the protein contains several transmembrane domains that anchor it to cellular membranes, which presents challenges for protein isolation and functional studies. Conservation analysis across species reveals structural similarities between human TMEM140 and its orthologues in other vertebrates, suggesting evolutionarily conserved functions.

What expression systems are recommended for producing recombinant human TMEM140?

For successful expression of recombinant human TMEM140, mammalian expression systems are generally preferred over bacterial systems due to the complex nature of transmembrane proteins requiring proper folding and post-translational modifications. HEK293 and CHO cell lines have demonstrated reliable expression of functional TMEM140 protein. When constructing expression vectors, researchers should include a strong promoter (like CMV) and appropriate epitope tags (such as FLAG or His-tag) for detection and purification purposes.

The expression construct design should consider the hydrophobic nature of TMEM140's transmembrane domains. Including a signal peptide can enhance membrane integration and proper folding. For optimal results, researchers should:

• Clone the full TMEM140 coding sequence (CDS) into a mammalian expression vector

• Include a C-terminal or N-terminal tag for detection and purification

• Transfect mammalian cells and select stable transfectants

• Validate expression through Western blotting and immunofluorescence

Studies have shown that TMEM140's hydrophobic and lipophilic transmembrane regions make extraction challenging, with difficulty increasing with the number of transmembrane domains, leading to lower expression levels . Researchers may need to optimize detergent conditions during protein extraction to maintain protein integrity and functionality.

How can researchers validate TMEM140 antibodies for experimental use?

Antibody validation is critical for TMEM140 research due to potential cross-reactivity with other transmembrane proteins. A comprehensive validation approach should include:

• Western blot analysis using positive controls (cells with known TMEM140 expression) and negative controls (TMEM140 knockdown cells)

• Immunohistochemistry (IHC) with similar controls

• Immunoprecipitation followed by mass spectrometry to confirm antibody specificity

• Peptide competition assays to verify epitope-specific binding

In glioma studies, researchers have successfully used immunohistochemical analysis alongside RT-PCR to validate TMEM140 expression patterns in brain tissue samples . When selecting commercial antibodies, prioritize those validated for the specific application intended (WB, IHC, IP) and those that recognize native conformations if studying the protein in its membrane-bound state.

For knockout validation, CRISPR/Cas9-mediated TMEM140 knockout cells serve as excellent negative controls. The guide RNA sequences targeting TMEM140 should be designed with minimal off-target effects, following established design criteria such as those developed by the Zhang laboratory at the Broad Institute .

What is the established role of TMEM140 in glioma progression?

TMEM140 has been identified as a significant factor in glioma progression with multiple lines of evidence supporting its oncogenic role. Studies have demonstrated that TMEM140 expression levels correlate with clinical outcomes in glioma patients . Higher expression of TMEM140 is associated with more aggressive tumor behavior and poorer prognosis in glioma patients. The protein appears to promote malignant phenotypes through several mechanisms.

Functional studies utilizing knockdown approaches in glioma cell lines (U87 and U373) have revealed that inhibition of TMEM140 expression results in reduced cell proliferation, as demonstrated by Cell Counting Kit-8 assays . Additionally, Transwell assays indicate that TMEM140 silencing impairs the invasive capabilities of glioma cells. These findings collectively suggest that TMEM140 functions as an oncogene in glioma, promoting cellular proliferation and invasion.

At the molecular level, silencing of TMEM140 leads to the downregulation of cell adhesion molecules including ICAM1, VCAM1, and Syndecan . This molecular signature explains, at least partly, how TMEM140 suppression inhibits glioma cell adhesion and subsequent metastatic potential. The relationship between TMEM140 expression and malignant phenotypes establishes this protein as a potential therapeutic target and prognostic marker in glioma management.

How does TMEM140 affect cellular adhesion mechanisms in cancer progression?

TMEM140 plays a crucial role in regulating cellular adhesion properties, which are fundamental to cancer cell invasion and metastasis. Research has established that TMEM140 influences the expression of key cell adhesion molecules that mediate cell-cell and cell-matrix interactions. When TMEM140 is silenced in glioma cells, there is a significant downregulation of intercellular adhesion molecule 1 (ICAM1), vascular cell adhesion molecule 1 (VCAM1), and Syndecan . These molecular changes translate to functional alterations in cellular behavior.

The adhesion molecules affected by TMEM140 have distinct roles in cancer progression:

• ICAM1: Mediates interactions between tumor cells and immune cells, potentially affecting immune surveillance

• VCAM1: Involved in vascular adhesion and extravasation of tumor cells during metastasis

• Syndecan: A transmembrane proteoglycan that facilitates cell binding to the extracellular matrix and growth factor interactions

The experimental approach to studying TMEM140's impact on adhesion typically involves:

• Silencing TMEM140 using siRNA in cancer cell lines

• Measuring adhesion capabilities through matrix adhesion assays

• Quantifying the expression of adhesion molecules via qRT-PCR and Western blotting

• Conducting invasion assays to correlate adhesion changes with invasive potential

These methodological approaches have revealed that TMEM140 suppression inhibits adhesion and metastasis, thereby affecting the progression of glioma . Understanding these molecular mechanisms provides insight into potential therapeutic strategies targeting TMEM140-mediated adhesion in cancer treatment.

What experimental methods are most effective for analyzing TMEM140 function in cancer cells?

For comprehensive analysis of TMEM140 function in cancer cells, researchers should employ a multi-faceted experimental approach combining genetic manipulation, functional assays, and molecular analyses. Based on successful studies in the field, the following methodological framework is recommended:

Genetic Manipulation Techniques:

• RNA interference (siRNA or shRNA) for transient or stable TMEM140 knockdown

• CRISPR/Cas9-mediated knockout using validated guide RNAs targeting TMEM140

• Overexpression systems using mammalian expression vectors with appropriate tags

Functional Assays:

• Proliferation assessment using Cell Counting Kit-8 (CCK-8) or MTT assays

• Migration analysis through wound healing assays

• Invasion studies using Transwell chambers with Matrigel coating

• Adhesion assays to various substrates (collagen, fibronectin, etc.)

• Colony formation assays for anchorage-independent growth assessment

Molecular Analyses:

• qRT-PCR for mRNA expression quantification

• Western blotting for protein level determination

• Immunohistochemistry for tissue expression patterns

• Immunofluorescence for subcellular localization

• Co-immunoprecipitation to identify protein-protein interactions

In glioma research, combined approaches have been particularly effective. For instance, studies have utilized immunohistochemical analysis and real-time reverse transcription PCR to detect TMEM140 expression in glioma tissue samples, followed by statistical analysis to correlate expression levels with clinical characteristics and outcomes . Functional studies in glioma cell lines then employed knockdown techniques with subsequent proliferation and invasion assays to establish TMEM140's role in cancer cell behavior.

For translational relevance, these experimental findings should be correlated with patient data, including survival analysis, tumor grade, and treatment response to establish the clinical significance of TMEM140 expression and function.

How can CRISPR/Cas9 technology be optimized for TMEM140 functional studies?

CRISPR/Cas9 technology offers a powerful approach for TMEM140 functional studies, providing more complete and stable gene disruption compared to RNA interference methods. For optimal results in TMEM140 editing, researchers should follow these evidence-based guidelines:

Guide RNA Design Considerations:

• Select guide RNAs designed to minimize off-target effects, such as those developed by the Zhang laboratory at the Broad Institute

• Target conserved exons that are present in all functional splice variants of TMEM140

• Design multiple gRNAs (at least two) per gene to increase knockout efficiency

• Verify gRNA sequences against your specific cell line's genome sequence

The TMEM140 CRISPR guide RNA sequences should be carefully designed to efficiently target the TMEM140 gene with minimal risk of off-target Cas9 binding elsewhere in the genome . For complete details on criteria and process for guide RNA design, researchers can reference the methodology in Sanjana et al. (2014).

Delivery and Validation Protocol:

• Deliver gRNA and Cas9 using appropriate vectors (lentiviral systems for difficult-to-transfect cells)

• Select and isolate clonal populations following transfection

• Validate knockout through genomic sequencing of the target region

• Confirm protein elimination via Western blot and immunofluorescence

• Assess functional consequences using appropriate assays (proliferation, migration, etc.)

For activation rather than knockout studies, the TMEM140 SAM guide RNA system can be employed to robustly activate transcription of the endogenous TMEM140 gene . This approach maintains natural regulatory elements and expression patterns, providing more physiologically relevant data than traditional overexpression methods.

When interpreting results from CRISPR studies, researchers should be aware of potential compensatory mechanisms that may arise following complete TMEM140 knockout, which might not be observed in partial knockdown studies using siRNA approaches.

What protocols yield optimal results for analyzing TMEM140 expression in patient tissue samples?

Analysis of TMEM140 expression in patient tissue samples requires careful methodological consideration to ensure accurate, reproducible results with clinical relevance. Based on successful approaches in the literature, the following protocol recommendations are provided:

Tissue Processing and Preservation:

• Fresh tissue samples should be snap-frozen in liquid nitrogen immediately after collection

• For FFPE (formalin-fixed paraffin-embedded) samples, limit fixation time to 24 hours

• Use tissue microarrays for comparative analysis across multiple patient samples

Expression Analysis Methods:

• Immunohistochemistry (IHC):

  • Use validated antibodies with appropriate positive and negative controls

  • Implement standardized scoring systems (H-score or Allred score)

  • Include normal adjacent tissue as internal control

  • Consider multiplex IHC to assess TMEM140 in relation to other markers

• Real-time RT-PCR:

  • Extract RNA using specialized kits for FFPE if using archived samples

  • Include reference genes validated for the specific tissue type

  • Perform triplicate reactions for each sample

  • Calculate relative expression using the 2^(-ΔΔCt) method

In glioma studies, researchers have effectively combined immunohistochemical analysis and real-time reverse transcription PCR to detect TMEM140 expression in 70 glioma brain tissue samples . This dual approach allows for both visualization of protein localization and accurate quantification of expression levels.

Data Analysis and Correlation:

• Correlate TMEM140 expression with clinical parameters (tumor grade, stage, patient age)

• Perform survival analysis (Kaplan-Meier with log-rank test)

• Use multivariate analysis to determine if TMEM140 is an independent prognostic factor

• Categorize expression levels based on clinically relevant thresholds

This methodological framework has successfully demonstrated the prognostic significance of TMEM140 in glioma patients , providing a template for similar studies in other cancer types.

What approaches are recommended for studying TMEM140 interaction with other proteins?

Investigating TMEM140's protein interactions is crucial for understanding its functional mechanisms in normal and pathological contexts. Due to the challenges associated with transmembrane protein analysis, researchers should consider these specialized approaches:

Proximity-Based Interaction Studies:

• BioID or TurboID: Fusion of TMEM140 with a biotin ligase to biotinylate proximal proteins, followed by streptavidin pulldown and mass spectrometry

• APEX2 proximity labeling: Similar approach using peroxidase-mediated labeling

• Split-GFP complementation: For validating specific hypothesized interactions

These methods are particularly valuable for transmembrane proteins like TMEM140, as they can capture transient and weak interactions that may be disrupted during traditional co-immunoprecipitation.

Co-immunoprecipitation Optimization:

• Use membrane-compatible detergents (digitonin, CHAPS, or NP-40) at minimal effective concentrations

• Include crosslinking steps to stabilize interactions before solubilization

• Perform reciprocal co-IPs with antibodies against both TMEM140 and suspected interactors

• Validate interactions using overexpression systems with differentially tagged proteins

Functional Validation of Interactions:

• Knockdown or knockout of interaction partners to assess impact on TMEM140 function

• Mutagenesis of interaction domains to disrupt specific protein-protein contacts

• Competitive peptide inhibition to block specific interactions

For analyzing TMEM140's role in adhesion regulation, researchers should investigate its interaction with adhesion molecules like ICAM1, VCAM1, and Syndecan . The functional consequence of these interactions can be validated through adhesion and migration assays following manipulation of either TMEM140 or its binding partners.

When reporting interaction studies, provide detailed methodological parameters including buffer compositions, detergent concentrations, and controls for specificity, as these factors significantly impact the reliability and reproducibility of transmembrane protein interaction data.

How reliable is TMEM140 as a prognostic biomarker in glioma and other cancers?

TMEM140 has demonstrated promising potential as a prognostic biomarker in glioma, with evidence supporting its correlation with clinical outcomes. Studies have shown that TMEM140 expression levels in glioma tissue samples can be reliably detected using immunohistochemical analysis and real-time RT-PCR techniques . The expression patterns of TMEM140 have been statistically correlated with clinical characteristics and outcomes in glioma patients, providing substantial evidence for its prognostic value.

Key findings regarding TMEM140 as a prognostic marker include:

• Higher TMEM140 expression correlates with more aggressive glioma phenotypes

• Expression levels show association with tumor grade and stage

• Patient survival outcomes appear to be inversely related to TMEM140 expression

• The prognostic value remains significant in multivariate analyses, suggesting independence from other established prognostic factors

For clinical application as a biomarker, standardization of detection methods is essential. Immunohistochemical protocols should include standardized scoring systems, while qRT-PCR analysis requires validated reference genes and defined threshold values for high versus low expression. Tissue microarrays can facilitate comparative analysis across patient cohorts, enhancing the reliability of TMEM140 as a biomarker.

What is the current evidence for TMEM140 as a therapeutic target in cancer?

TMEM140 represents an emerging therapeutic target in cancer research, particularly in gliomas, based on functional studies demonstrating its role in promoting malignant phenotypes. The rationale for targeting TMEM140 is supported by multiple lines of evidence:

• Knockdown of TMEM140 in glioma cell lines (U87 and U373) results in reduced cell proliferation as demonstrated by Cell Counting Kit-8 assays

• TMEM140 silencing inhibits cellular invasion in Transwell assays

• TMEM140 depletion leads to downregulation of adhesion molecules (ICAM1, VCAM1, and Syndecan), suppressing adhesion and metastasis in glioma

These functional effects suggest that therapeutic strategies targeting TMEM140 could potentially inhibit tumor growth and invasion. Several approaches could be considered for therapeutic development:

Potential Therapeutic Strategies:

• RNA interference: siRNA or antisense oligonucleotides targeting TMEM140 mRNA

• Small molecule inhibitors: Compounds designed to interfere with TMEM140 function or interactions

• Monoclonal antibodies: For extracellular domains if accessible

• PROTAC approach: Proteolysis-targeting chimeras to induce TMEM140 degradation

The challenges in developing TMEM140-targeted therapies include the hydrophobic and lipophilic features of the transmembrane regions, which make extraction and targeting challenging . Additionally, the increased number of transmembrane regions leads to lower expression levels in host cells and greater preparation difficulties.

While direct targeting of TMEM140 is being explored, combination approaches with existing therapies may also be valuable. For instance, studies on treatment resistance patterns in relation to TMEM140 expression could inform combinatorial approaches that enhance the efficacy of standard treatments by simultaneously targeting TMEM140-mediated pathways.

What are common challenges in TMEM140 protein expression systems and how can they be addressed?

Recombinant expression of transmembrane proteins like TMEM140 presents several technical challenges that researchers must navigate to obtain functional protein for study. These challenges and their solutions include:

Challenge 1: Low Expression Yields

• The hydrophobic and lipophilic features of TMEM140's transmembrane regions often result in poor expression, with difficulty increasing with the number of transmembrane domains

• Solution: Optimize codon usage for the expression host; use specialized expression vectors with strong, inducible promoters; consider fusion tags that enhance solubility (SUMO, MBP); test multiple host cell lines to identify optimal expression systems

Challenge 2: Protein Misfolding and Aggregation

• Transmembrane proteins frequently misfold when overexpressed, leading to aggregation and degradation

• Solution: Lower induction temperature (16-20°C); reduce inducer concentration; co-express molecular chaperones; include chemical chaperones in culture media (glycerol, sorbitol); use mild detergents during extraction

Challenge 3: Difficult Extraction and Purification

• Membrane integration makes extraction challenging without disrupting protein structure

• Solution: Screen multiple detergents (DDM, CHAPS, digitonin) for optimal solubilization; employ gentle extraction methods; use affinity tags for efficient purification; consider nanodiscs or amphipols for stabilization in solution

Challenge 4: Functional Validation

• Confirming that the recombinant protein retains native function is essential but challenging

• Solution: Develop activity assays specific to known TMEM140 functions; compare recombinant protein behavior to native protein; utilize binding studies with known interaction partners; perform complementation studies in knockout cell lines

Optimization Table for TMEM140 Expression:

By systematically addressing these challenges, researchers can improve the yield and quality of recombinant TMEM140 for structural and functional studies.

What controls are essential in experimental design for TMEM140 functional studies?

Rigorous experimental design with appropriate controls is crucial for generating reliable data on TMEM140 function. Based on research best practices, the following control framework is recommended:

For Expression Analysis Studies:

• Positive controls: Cell lines or tissues with verified high TMEM140 expression

• Negative controls: TMEM140 knockout cells generated via CRISPR/Cas9

• Reference controls: Housekeeping genes (GAPDH, β-actin) for qRT-PCR normalization

• Antibody controls: Peptide competition assays to confirm antibody specificity

For Knockdown/Knockout Experiments:

• Non-targeting controls: Scrambled siRNA or non-targeting gRNA for RNAi and CRISPR studies

• Rescue controls: Re-expression of TMEM140 in knockdown/knockout cells to confirm phenotype specificity

• Off-target validation: Multiple siRNA sequences or gRNAs targeting different regions of TMEM140

• Phenotype validation: Multiple assays to confirm functional effects (e.g., complementary proliferation assays)

In glioma cell line studies, researchers have effectively used knockdown methods with siRNA in multiple cell lines (U87 and U373) with appropriate controls to investigate TMEM140 function . This approach allows for cross-validation of results across different cellular contexts.

For Clinical Correlation Studies:

• Normal tissue controls: Adjacent non-tumor tissue from the same patient

• Demographic controls: Age and sex-matched samples

• Technical controls: Inclusion of positive and negative control samples in each experimental batch

For Protein Interaction Studies:

• Bait-only controls: Immunoprecipitation with non-specific IgG

• Prey-only controls: Cells not expressing the bait protein

• Specificity controls: Competition with excess untagged protein

Implementing this comprehensive control framework will enhance the reliability and reproducibility of TMEM140 functional studies, ensuring that observed phenotypes are genuinely attributable to TMEM140 and not experimental artifacts.

What are the most promising avenues for future TMEM140 research?

The study of TMEM140 is still in relatively early stages, with several promising research directions that could significantly advance our understanding of this protein's function and therapeutic potential. Based on current knowledge gaps and technological advances, the following research avenues appear most promising:

Structural Biology Approaches:
The three-dimensional structure, full length, and epitopes of TMEM140 have not yet been well characterized . Advanced structural biology techniques such as cryo-electron microscopy, which has revolutionized membrane protein structural studies, could provide crucial insights into TMEM140's functional domains and interaction interfaces. This structural information would facilitate rational drug design targeting TMEM140.

Comprehensive Protein Interaction Network:
Systematic identification of TMEM140's protein interactome using proximity labeling approaches (BioID, APEX) could reveal unknown functions and regulatory mechanisms. Particular focus should be placed on interactions with adhesion molecules like ICAM1, VCAM1, and Syndecan, which have been implicated in TMEM140-mediated effects on cell adhesion and metastasis .

Immune Regulation Studies:
Emerging evidence suggests that transmembrane proteins play important roles in immune regulation. For instance, TMEM176B influences anti-tumor immunity by affecting CD8+ T cell-dependent responses . Similar studies on TMEM140's potential immunomodulatory functions could open new therapeutic avenues, particularly in conjunction with immunotherapy approaches.

Development of Specific Inhibitors:
Based on the oncogenic functions of TMEM140 in glioma , the development of molecular targeted activators or inhibitors specifically targeting TMEM140 represents an important future direction . This approach would benefit from the structural and interaction studies mentioned above and could employ various innovative delivery platforms to overcome the challenges associated with targeting transmembrane proteins.

Single-Cell Analysis of TMEM140 in Tumor Heterogeneity:
Understanding how TMEM140 expression varies within tumors at the single-cell level could provide insights into its role in tumor heterogeneity, treatment resistance, and cancer stem cell properties. This approach could identify specific cellular subpopulations where TMEM140 targeting would be most effective.

These research directions collectively address the current knowledge gaps regarding TMEM140 and hold promise for translating basic research findings into clinical applications for cancer patients.