TRAPPC4 Antibody

What is TRAPPC4 and what cellular functions does it perform?

TRAPPC4, also known as synbindin, is a core component of the TRAPP complexes that function as multimeric guanine nucleotide-exchange factors regulating multiple membrane trafficking pathways . TRAPPC4 is one of the essential subunits of these complexes, playing a critical role in vesicle-mediated transport between lipid organelles in a process termed vesicular tethering . Recent research has revealed that TRAPPC4 maintains the expression of PD-L1 by acting as a scaffold between PD-L1 and RAB11, promoting RAB11-mediated recycling of PD-L1 to protect it from lysosomal degradation . This function ultimately affects immune evasion and tumor progression. Additionally, TRAPPC4 interacts with ERK2, activating ERK1/2 and modulating its nuclear localization in colorectal cancer cells .

What applications are recommended for TRAPPC4 antibodies?

TRAPPC4 antibodies can be used in multiple applications based on validated testing. According to Proteintech's data for their 12074-1-AP antibody, the following applications and dilutions are recommended:

For optimal results, it is advised to titrate the antibody in each testing system as results may be sample-dependent . When performing IHC, antigen retrieval with TE buffer pH 9.0 is suggested, though citrate buffer pH 6.0 may also be used as an alternative .

What is the reactivity profile of TRAPPC4 antibodies?

The reactivity of TRAPPC4 antibodies depends on the specific antibody used. For example, the Proteintech 12074-1-AP antibody has demonstrated reactivity with human, mouse, and rat samples . Positive Western blot detection has been reported in HL-60 cells, mouse testis tissue, and rat testis tissue. For immunoprecipitation, positive detection has been observed in HL-60 cells. In immunohistochemistry applications, positive detection has been noted in human colon cancer tissue, while immunofluorescence has shown positive results in HeLa cells .

How does TRAPPC4 regulate PD-L1 trafficking and influence immune responses?

TRAPPC4 plays a crucial role in regulating PD-L1 expression by acting as a scaffold that coordinates RAB11-mediated recycling of PD-L1. This recycling process replenishes PD-L1 distribution on tumor cell surfaces, thereby promoting immune evasion .

Research has demonstrated that TRAPPC4 maintains PD-L1 expression through the following mechanisms:

• Direct interaction with PD-L1 in recycling endosomes

• Acting as a scaffold between PD-L1 and RAB11

• Promoting RAB11-mediated recycling of PD-L1

• Protecting PD-L1 from lysosomal degradation

When TRAPPC4 is depleted, there is a significant reduction in PD-L1 expression both in vitro and in vivo, which facilitates T cell-mediated cytotoxicity. Flow cytometry studies show that PD-1 binding to tumor cells is dramatically impaired upon silencing of TRAPPC4 . In vivo experiments with mouse tumor models have shown that knocking down Trappc4 leads to increased CD8+CD69+ T cells and CD8+CD107a+ subsets, suggesting enhanced T-cell-mediated immunity . These findings suggest that TRAPPC4 could be a therapeutic target to enhance anti-tumor immunity, as overexpression of Trappc4 sensitizes tumor cells to checkpoint therapy .

What is the relationship between TRAPPC4 and ERK2, and how does this interaction affect cellular processes?

TRAPPC4 interacts directly with ERK2, as demonstrated through co-immunoprecipitation and GST pull-down experiments . This interaction plays a significant role in activating ERK1/2 and modulating its subcellular localization, particularly in colorectal cancer cells.

When studying the TRAPPC4-ERK2 interaction:

• Co-immunoprecipitation experiments with pCDEF-Myc-TRAPPC4 and pCDEF-Flag-ERK2 vectors showed that both TRAPPC4-myc and ERK2-flag bands were detected from co-transfected cells, confirming their interaction .

• GST pull-down assays demonstrated that TRAPPC4 was pulled down with GST-ERK2 fusion proteins but not with GST alone, indicating a specific and direct interaction between TRAPPC4 and ERK2 in vitro .

• Western blotting revealed that TRAPPC4 knockdown via siRNA significantly decreased the level of phosphorylated ERK1/2 (pERK1/2) in the nucleus, while TRAPPC4 overexpression upregulated pERK1/2 expression in the nucleus .

Immunohistochemistry studies on human colorectal cancer tissues showed a correlation between nuclear TRAPPC4 expression and pERK1/2 levels (r = 0.996) and between nuclear TRAPPC4 expression and ERK1/2 levels (r = 0.994) . In normal colonic epithelium, TRAPPC4 staining was restricted to the cytoplasm, whereas in adenocarcinoma samples, 55.89% of cells showed nuclear staining, suggesting that TRAPPC4 nuclear localization may be associated with cancer progression .

How is TRAPPC4 implicated in autoimmune conditions like immune-related pancytopenia?

TRAPPC4 has been identified as a key autoantigen in immune-related pancytopenia (IRP), which is characterized by autoantibody-mediated destruction or suppression of bone marrow cells . Research has shown that:

• TRAPPC4 is overexpressed in CD34+ bone marrow hematopoietic progenitor cells of newly diagnosed IRP patients compared to patients in remission, patients with other hematological conditions, and healthy controls .

• Through screening with a phage-display random peptide library, the epitope peptide YTADGKEVLEYLG within TRAPPC4 was identified as activating Th2 cells, as confirmed by ELISPOT assays .

• Newly diagnosed IRP patients exhibit elevated TRAPPC4 mRNA and protein levels in bone marrow mononuclear cells and higher serum antibody titers compared to controls .

• Immune profiling reveals increased CD19+ and CD5+CD19+ B lymphocytes in IRP patients .

The levels of anti-TRAPPC4 antibodies in the serum of untreated IRP patients (1.35±0.31 AU) were significantly higher compared to IRP patients in remission (1.18±0.32 AU) and healthy controls (1.12±0.21 AU) . The identification of TRAPPC4 and its epitope provides valuable insights into IRP pathogenesis and suggests potential diagnostic and therapeutic strategies.

What genetic variants in TRAPPC4 are associated with neurodevelopmental disorders?

A relatively common homozygous splicing variant in TRAPPC4 (c.454+3A>G, hg38:11:119020256 A>G) has been identified in individuals with early-infantile-onset neurodegenerative presentation . This variant has been reported in at least 23 patients from 17 independent families, who present with:

• Profound psychomotor delay

• Developmental regression

• Early-onset epilepsy

• Microcephaly

• Progressive spastic tetraplegia

RNA sequencing analysis of this variant revealed:

• The variant results in partial exon 3 skipping (~46% of transcripts)

• Generation of an aberrant transcript due to use of a downstream cryptic splice donor site at position c.454+41 (13% of transcripts)

• Both aberrant transcripts predict a frameshift and nonsense-mediated decay

• Only 41% of expressed TRAPPC4 transcripts display wild-type splicing

The carrier frequency of this variant ranges from 2.4-5.4 per 10,000 healthy individuals, making it a relatively common cause of this severe recessive neurological disease . The highest frequency is found in individuals with European and Mediterranean ancestries, whereas it appears to be rare in African and East Asian populations.

What are the optimal conditions for using TRAPPC4 antibodies in Western blotting?

For optimal Western blotting using TRAPPC4 antibodies, follow these recommendations:

• Sample preparation: TRAPPC4 has been successfully detected in various samples including HL-60 cells, mouse testis tissue, and rat testis tissue .

• Antibody dilution: The recommended dilution for Western blotting is 1:1000-1:4000 . Always titrate to determine the optimal concentration for your specific experimental system.

• Expected molecular weight: The calculated molecular weight of TRAPPC4 is 24 kDa (219 amino acids), but the observed molecular weight on Western blots typically ranges from 24-27 kDa , which should be considered when identifying bands.

• Controls: Include positive controls such as HL-60 cell lysates where TRAPPC4 expression has been confirmed. For negative controls, consider using lysates from cells where TRAPPC4 has been knocked down using siRNA .

• Storage conditions: Store antibodies at -20°C. They are typically stable for one year after shipment, and aliquoting is unnecessary for -20°C storage .

How can researchers validate TRAPPC4 antibody specificity?

Validating the specificity of TRAPPC4 antibodies is crucial for reliable experimental results. Consider these validation approaches:

• Knockdown/knockout validation: Treat cells with TRAPPC4-specific siRNAs and confirm reduced signal in Western blot compared to control siRNA-treated cells. Several studies have used this approach to validate TRAPPC4 antibody specificity .

• Recombinant protein controls: Express recombinant TRAPPC4 protein (e.g., with a histidine tag) and use it as a positive control .

• Immunoprecipitation: Perform immunoprecipitation with the TRAPPC4 antibody followed by mass spectrometry analysis to confirm that TRAPPC4 is indeed pulled down .

• Multiple antibodies: Use different antibodies targeting distinct epitopes of TRAPPC4 and compare the results.

• Peptide competition: Pre-incubate the antibody with the immunizing peptide before applying to the sample. A specific antibody signal should be significantly reduced.

In research studies, TRAPPC4 antibody specificity has been validated through gene silencing experiments where knockdown of TRAPPC4 using specific siRNAs resulted in diminished detection of the protein .

What techniques are recommended for studying TRAPPC4-protein interactions?

Several techniques have been successfully employed to study TRAPPC4 interactions with other proteins:

• Co-immunoprecipitation (Co-IP): This method has been effectively used to demonstrate the interaction between TRAPPC4 and ERK2, as well as between TRAPPC4 and PD-L1 . The protocol typically involves:

  • Transfection of cells with tagged proteins (e.g., pCDEF-Myc-TRAPPC4 and pCDEF-Flag-ERK2)

  • Lysis of cells using appropriate buffer

  • Immunoprecipitation with anti-tag antibodies

  • Western blot analysis to detect co-precipitated proteins

• GST pull-down assays: This technique has confirmed direct interaction between TRAPPC4 and ERK2 :

  • Expression of GST-ERK2 fusion proteins and His-tagged TRAPPC4

  • Binding of GST-ERK2 to beads

  • Incubation with purified TRAPPC4 protein

  • Detection of pulled-down proteins using Coomassie staining or Western blotting

• Mass spectrometry analysis: This approach has been used to identify interactions between PD-L1 and various TRAPP subunits including TRAPPC4 .

• Proximity ligation assay (PLA): This technique can be used to visualize protein-protein interactions in situ, providing spatial information about where in the cell the interaction occurs.

• Yeast two-hybrid system: While not specifically mentioned in the provided search results, this is another valuable method for studying protein interactions.

When designing experiments to study TRAPPC4 interactions, consider cellular context, as TRAPPC4 localization may differ between normal and cancer cells, potentially affecting its interaction partners .

How should researchers approach TRAPPC4 knockdown or knockout experiments?

For effective TRAPPC4 knockdown or knockout experiments, consider the following approaches:

• siRNA-mediated knockdown:

  • Several studies have successfully used siRNAs targeting TRAPPC4 mRNA

  • Validate knockdown efficiency using qRT-PCR and Western blotting

  • Include appropriate negative controls (non-targeting siRNAs)

  • Consider potential off-target effects by using multiple siRNA sequences

• shRNA-mediated stable knockdown:

  • This approach has been used in murine tumor models to study the effects of Trappc4 knockdown on tumor growth and immune response

  • Allows for longer-term studies compared to transient siRNA knockdown

  • Can be delivered via lentiviral vectors for efficient transduction

• CRISPR-Cas9 knockout:

  • For complete elimination of TRAPPC4 expression

  • Design guide RNAs targeting early exons of TRAPPC4

  • Validate knockout by sequencing and Western blotting

  • Be aware that complete TRAPPC4 knockout might be lethal or severely affect cell viability based on its essential role in vesicular trafficking

• Rescue experiments:

  • Include re-expression of TRAPPC4 in knockdown or knockout cells to confirm specificity

  • Lentiviral expression of wild-type TRAPPC4 has been shown to restore trafficking defects in patient-derived fibroblasts with reduced TRAPPC4 levels

When interpreting results, consider that TRAPPC4 is involved in multiple cellular processes, so phenotypes may be complex and multifaceted. It's also important to examine both immediate effects (changes in protein interactions or localization) and longer-term consequences (alterations in cellular function or viability).

How might TRAPPC4 testing be relevant in autoimmune disease diagnosis?

TRAPPC4 testing could potentially be valuable in the diagnosis of immune-related pancytopenia (IRP) and other autoimmune conditions. Research indicates several diagnostic applications:

• Anti-TRAPPC4 antibody detection: The levels of anti-TRAPPC4 antibodies in serum are significantly higher in untreated IRP patients (1.35±0.31 AU) compared to patients in remission (1.18±0.32 AU) and healthy controls (1.12±0.21 AU) . This suggests that measuring these antibodies could serve as a biomarker for IRP diagnosis or monitoring disease activity.

• TRAPPC4 expression in CD34+ cells: TRAPPC4 is overexpressed in CD34+ bone marrow hematopoietic progenitor cells of newly diagnosed IRP patients, making this a potential diagnostic parameter .

• Epitope-specific assays: The identified TRAPPC4 epitope peptide YTADGKEVLEYLG activates Th2 cells in IRP patients. Developing assays that detect immune responses to this specific epitope could improve diagnostic specificity .

• Immune cell profiling: IRP patients show increased CD19+ and CD5+CD19+ B lymphocytes, which could be included in a comprehensive diagnostic panel alongside TRAPPC4 testing .

For clinical implementation, standardized ELISA or other immunoassays would need to be developed and validated for detecting anti-TRAPPC4 antibodies. Additionally, combining TRAPPC4 testing with other biomarkers would likely improve diagnostic accuracy.

What is the potential of TRAPPC4 as a therapeutic target in cancer immunotherapy?

TRAPPC4 shows promise as a therapeutic target in cancer immunotherapy based on its role in regulating PD-L1 trafficking and immune evasion:

• Enhancement of immune checkpoint blockade therapy: Research shows that overexpression of Trappc4 sensitizes tumor cells to checkpoint therapy in murine tumor models, suggesting that targeting TRAPPC4 could enhance the efficacy of existing immunotherapies .

• Restoration of T cell-mediated cytotoxicity: TRAPPC4 depletion leads to significant reduction of PD-L1 expression both in vitro and in vivo, which facilitates T cell-mediated cytotoxicity. This suggests that inhibiting TRAPPC4 could help overcome immune evasion by tumor cells .

• Potential approaches to target TRAPPC4:

  • Small molecule inhibitors that disrupt the interaction between TRAPPC4 and PD-L1 or TRAPPC4 and RAB11

  • Antisense oligonucleotides or siRNAs to reduce TRAPPC4 expression

  • Antibodies that bind to TRAPPC4 and prevent its function in vesicular trafficking

• Combination therapy potential: Targeting TRAPPC4 along with other immune checkpoint inhibitors (anti-PD-1/PD-L1 antibodies) could potentially produce synergistic effects .

• Biomarker for treatment response: TRAPPC4 expression levels could potentially serve as a biomarker to predict response to immunotherapy, particularly in tumors where PD-L1 trafficking plays a significant role in immune evasion.

Further research is needed to develop specific TRAPPC4 inhibitors and to determine the optimal therapeutic window where TRAPPC4 inhibition affects tumor cells without disrupting essential vesicular trafficking in normal cells.

How might genetic testing for TRAPPC4 variants be implemented in clinical settings?

Given the association of TRAPPC4 variants with neurodevelopmental disorders, implementing genetic testing in clinical settings could be valuable:

• Target population for testing: Children presenting with early-onset seizures, profound intellectual disability, microcephaly, sensorineural hearing loss, and progressive cortical and cerebellar atrophy should be considered for TRAPPC4 genetic testing, particularly the c.454+3A>G variant .

• Testing methods:

  • Whole exome or genome sequencing to identify the c.454+3A>G variant

  • Targeted sequencing panels focusing on genes associated with neurodevelopmental disorders

  • Family-based rare variant analyses for cases with suspected genetic etiology

• Carrier screening: Given the carrier frequency of 2.4-5.4 per 10,000 individuals , targeted screening may be beneficial in populations with European and Mediterranean ancestry, especially in families with a history of neurodevelopmental disorders.

• Confirmatory testing: RNA sequencing can be used to confirm the impact of the c.454+3A>G variant on splicing, as demonstrated by studies showing partial exon 3 skipping and generation of aberrant transcripts .

• Genetic counseling: For families with affected individuals or identified carriers, genetic counseling should address:

  • Recessive inheritance pattern

  • 25% risk of affected offspring when both parents are carriers

  • Reproductive options including preimplantation genetic diagnosis

Implementation of such testing could aid in early diagnosis, allowing for appropriate management strategies and providing closure for families seeking diagnostic clarification. The relatively common nature of the c.454+3A>G variant in certain populations makes it a particularly important target for clinical genetic testing.

What are the key unanswered questions about TRAPPC4 function?

Despite significant progress in understanding TRAPPC4, several key questions remain unanswered:

• Complete interactome: While interactions with ERK2, PD-L1, and RAB11 have been identified, a comprehensive map of TRAPPC4's protein interaction network across different cellular contexts is still needed.

• Tissue-specific functions: TRAPPC4 is widely expressed, but how its functions vary across different tissues and cell types remains poorly understood. This is particularly relevant given its role in both vesicular trafficking and signaling pathways.

• Relationship to other TRAPP subunits: How TRAPPC4 functionally interacts with other TRAPP complex subunits and whether it has independent functions outside these complexes requires further investigation.

• Post-translational modifications: The regulation of TRAPPC4 through phosphorylation or other modifications and how these affect its function, localization, and interactions needs clarification.

• Nuclear function: The observation that TRAPPC4 accumulates in the nucleus of colorectal cancer cells raises questions about potential nuclear functions distinct from its established role in vesicular trafficking.

• Role in development: Given the severe neurodevelopmental phenotypes associated with TRAPPC4 variants , its specific contributions to normal brain development warrant further study.

• Therapeutic targeting specificity: How to selectively target TRAPPC4 functions in disease contexts while preserving its essential cellular roles remains a significant challenge.

Addressing these questions will require multidisciplinary approaches combining structural biology, proteomics, advanced imaging, and in vivo models.

What novel methodologies might advance TRAPPC4 research?

Advancing TRAPPC4 research will likely benefit from several cutting-edge methodologies:

• Proximity labeling proteomics (BioID, APEX): These techniques could provide a more comprehensive understanding of the TRAPPC4 interactome in living cells and how it changes under different conditions or in different subcellular compartments.

• Single-cell analysis: Examining TRAPPC4 expression and function at the single-cell level could reveal cell-type-specific roles and heterogeneity in responses to TRAPPC4 manipulation.

• CRISPR-Cas9 screening: Genome-wide or targeted CRISPR screens could identify synthetic lethal interactions with TRAPPC4 or genes that modify phenotypes associated with TRAPPC4 dysfunction.

• Live-cell imaging: Advanced techniques such as lattice light-sheet microscopy combined with specific labeling of TRAPPC4 could provide insights into the dynamics of TRAPPC4-containing complexes during vesicular trafficking.

• Cryo-electron microscopy: Structural studies of TRAPPC4 within TRAPP complexes could provide atomic-level insights into how TRAPPC4 contributes to complex assembly and function.

• Patient-derived organoids: Developing brain or other tissue organoids from patients with TRAPPC4 mutations could provide valuable models for studying disease mechanisms and testing potential therapies.

• Spatially resolved transcriptomics and proteomics: These techniques could reveal how TRAPPC4 expression and its downstream effects vary across different regions of tissues or tumors.

• Nanobodies or intrabodies: Developing highly specific tools to modulate TRAPPC4 function in specific cellular compartments could help dissect its context-dependent roles.