F2RL3 Antibody

What is F2RL3 and what are its primary physiological roles?

F2RL3 (Coagulation factor II receptor-like 3), also known as PAR4 (Proteinase-activated receptor 4), is a member of the protease-activated receptor subfamily. It functions as a receptor for activated thrombin or trypsin coupled to G proteins that stimulate phosphoinositide hydrolysis . Through its action in pathways involving thrombin, F2RL3 ensures effective hemostasis and also contributes to signaling pathways that mediate inflammation and tissue repair .

F2RL3 is a 7-transmembrane-region receptor that couples to guanosine-nucleotide-binding proteins. It is activated through proteolytic cleavage of its extracellular amino terminus, after which the new amino terminus functions as a tethered ligand to activate the receptor . Recent research indicates that F2RL3 plays a particularly important role in platelet activation, with studies in knockout models showing that absence of PAR4 in mice results in impaired hemostasis and protection against pulmonary embolism .

How is F2RL3 expression regulated, and in which tissues is it predominantly found?

Data from the BLUEPRINT Consortium suggests that F2RL3 expression is enriched in megakaryocytes, with the full-length transcript (ENST00000248076.3) dominating over an alternate truncated transcript (ENST00000599210.1) . Epigenetic data indicates that the 4 CpG sites at the start of exon 2 sit in a hypomethylated region, with the remainder of this exon being designated hypermethylated. This region is characterized by histone H3 lysine 4 trimethylation (H3K4me3) marks, suggesting a promoter region, and is designated a DNase hypersensitivity peak site with greater chromatin accessibility in megakaryocytes compared to other lineages .

F2RL3 has been detected in multiple tissues including lung, pancreas, and various cell lines, with experimental validation through Western blot and immunohistochemistry in mouse lung tissue, mouse pancreas tissue, and human samples including HT29 cell lysate .

How should I select the appropriate F2RL3 antibody for my specific research application?

When selecting an F2RL3 antibody, consider the following criteria:

• Target application compatibility: Different antibodies are validated for specific applications. For instance:

  • ab137927 is suitable for Western blot (WB) and reacts with human samples

  • ab150551 is suitable for immunohistochemistry on paraffin-embedded tissues (IHC-P) and reacts with human samples

  • Proteintech 25306-1-AP is validated for WB and IHC applications with human and mouse reactivity

  • Boster A03645-1 is recommended for ELISA, immunofluorescence (IF), and WB with human, mouse, and rat reactivity

• Species reactivity: Verify that the antibody has been validated for your species of interest. Most commercial F2RL3 antibodies react with human samples, but some also react with mouse and rat samples .

• Epitope recognition: Consider which region of F2RL3 the antibody targets. For example, some antibodies target the extracellular domain (like APR-034-APC50UL ), which may be particularly useful for detecting cell surface expression or investigating receptor activation.

What are effective methods to validate the specificity of an F2RL3 antibody?

To validate F2RL3 antibody specificity, implement these methodological approaches:

• Knockout/knockdown controls: Use F2RL3 knockout models (like F2RL3−/− mice) or cells with F2RL3 knockdown via siRNA . The absence or reduction of signal in these samples compared to wild-type confirms antibody specificity.

• Overexpression validation: Compare signal intensity between endogenous expression and cells transfected with F2RL3 overexpression plasmids .

• Peptide competition assay: Pre-incubate the antibody with the immunizing peptide to block specific binding. This should eliminate the specific signal if the antibody is truly targeting F2RL3.

• Cross-reactivity assessment: Test the antibody against related proteins (other PAR family members) to ensure it doesn't cross-react.

• Multiple antibody comparison: Use antibodies raised against different epitopes of F2RL3 and compare the detection patterns.

Researchers have successfully implemented these approaches, for example, in the development of monoclonal antibodies against PAR4, where F2RL3−/− mice were used to verify specificity .

What are the recommended dilutions and protocols for different F2RL3 antibody applications?

Protocol optimization notes:

• For IHC with Proteintech 25306-1-AP, antigen retrieval with TE buffer pH 9.0 is suggested, or alternatively with citrate buffer pH 6.0

• It is recommended to titrate antibodies in each testing system to obtain optimal results

• For APC-conjugated antibodies, reconstitution requires 15 μL or 50 μL double distilled water, depending on the sample size

What are the best practices for storage and handling of F2RL3 antibodies to maintain reactivity?

Based on manufacturer recommendations across multiple F2RL3 antibodies:

• Storage temperature:

  • Long-term storage: -20°C (stable for one year after shipment)

  • Short-term/frequent use: 4°C for up to one month or one week for reconstituted solutions

• Buffer conditions:

  • Most antibodies are provided in PBS with additives like glycerol (50%), BSA (0.5%), and sodium azide (0.02%)

  • Some antibodies ship as lyophilized powder and require reconstitution

• Handling precautions:

  • Avoid repeated freeze-thaw cycles to maintain antibody integrity

  • For lyophilized antibodies that require reconstitution, centrifuge all preparations before use (10000 × g for 5 min)

  • For 20 μl sizes of some products, 0.1% BSA may be included in the formulation

  • Aliquoting is usually unnecessary for -20°C storage of glycerol-containing formulations

How can I effectively use F2RL3 antibodies to study epithelial-mesenchymal transition (EMT) in cancer models?

Recent research has identified F2RL3 as a regulator of epithelial-mesenchymal transition (EMT) in gastric cancer cells . When designing experiments to study this relationship, consider:

• Knockdown/overexpression approaches:

  • Use siRNA targeting F2RL3 (like that employed in AGS and HGC-27 cells) to observe effects on EMT markers

  • Transfect cells with F2RL3 overexpression plasmids using appropriate transfection reagents (e.g., jetPRIME®)

  • Validate knockdown/overexpression efficiency by qPCR (24h post-transfection) and Western blot (72h post-transfection)

• EMT marker assessment:

  • Monitor changes in epithelial markers (E-cadherin) and mesenchymal markers (Snail, vimentin) via Western blot

  • The research shows that knocking down F2RL3 in gastric cancer cells leads to upregulation of E-cadherin and downregulation of Snail and vimentin

• Functional assays:

  • Cell viability/activity assays to assess proliferation changes

  • Transwell assays to evaluate migration and invasion capabilities

  • Scratch assays to measure wound healing capacity

  • Research demonstrates that F2RL3 knockdown significantly reduces these metastatic behaviors in gastric cancer cells

• Signaling pathway analysis:

  • Investigate the Rap1/MAPK signaling pathway, which has been identified as regulated by F2RL3

  • Consider using pathway activators (SA) in combination with F2RL3 knockdown to determine if the effects are reversed

What role does F2RL3 play in angiogenesis, and how can this be investigated experimentally?

F2RL3 has been shown to regulate angiogenesis through the Rap1/MAPK pathway . To investigate this mechanism:

• Cell culture supernatant experiments:

  • Knockdown F2RL3 in cancer cells (e.g., AGS and HGC-27)

  • Collect the cell culture supernatants

  • Culture HUVECs (Human Umbilical Vein Endothelial Cells) with these supernatants

  • Assess HUVEC activity, metastasis, invasion, and angiogenic capacity

• Pathway manipulation:

  • Compare results from normal cancer cells, control siRNA-treated cells, F2RL3 knockdown cells, and F2RL3 knockdown cells treated with Rap1/MAPK signaling pathway activator (SA)

  • Results have shown that HUVEC activity decreases with F2RL3 knockdown in cancer cells, and this effect can be attenuated by pathway activation

• Angiogenesis assays:

  • Tube formation assays with HUVECs to directly visualize the impact on angiogenesis

  • Quantify branching points and tube length to measure angiogenic potential

How is F2RL3 epigenetically regulated, and what are the implications for myocardial infarction risk?

Research on the epigenetic regulation of F2RL3 has revealed important connections to myocardial infarction risk :

• Methylation patterns:

  • F2RL3 gene contains specific CpG sites that exhibit differential methylation patterns

  • The 4 CpG sites at the start of exon 2 sit in a hypomethylated region, while the remainder of this exon is designated hypermethylated

  • This region is characterized by histone H3 lysine 4 trimethylation (H3K4me3) marks, suggestive of a promoter region

• Functional regulation mechanisms:

  • Reporter assay experiments combining the F2RL3 promoter and exon 2 fragment have shown increased luciferase activity compared to promoter-only constructs, indicating that exon 2 has enhancer activity

  • A CEBP (CCAAT/enhancer binding protein) recognition sequence in exon 2 appears to be important, as mutation of this sequence attenuated luciferase reporter gene activity

  • Chromatin immunoprecipitation experiments in human coronary artery endothelial cells showed increased occupancy of the F2RL3 exon 2 CEBP recognition site with CEBP-β following global demethylation with 5-Azacytidine

• Tissue-specific expression patterns:

  • Data from BLUEPRINT suggests F2RL3 expression is enriched in megakaryocytes

  • The full-length transcript (ENST00000248076.3) dominates over an alternate truncated transcript (ENST00000599210.1)

  • Megakaryocytes show greater chromatin accessibility in this region compared to other lineages

What techniques are most effective for developing and characterizing new monoclonal antibodies against F2RL3?

The development of monoclonal antibodies against F2RL3 requires specialized methodology, as demonstrated in previous research :

• Immunization strategy:

  • Use F2RL3−/− mice (lacking the target protein) for immunization to enhance immune response to the human protein

  • Administer subcutaneous injections of antigen (e.g., MBP-hPAR4(18–78)) in complete Freud's adjuvant

  • Follow with intraperitoneal injections every 2 weeks for 6 weeks

  • Provide additional boosts daily for three days prior to harvesting splenocytes

• Hybridoma generation:

  • Isolate mouse primary splenocytes and fuse with myeloma cell line (e.g., NS-1) using polyethylene glycol

  • Plate fusion into 96-well plates and treat with aminopterin to remove unfused myeloma cells

  • Screen hybridoma supernatants by immunoblotting against maltose binding protein (MBP) and MBP-PAR4 antigen

  • Select positive hybridomas by limiting dilution and maintain in appropriate media

• Validation approaches:

  • Test for specificity against the target protein versus control proteins

  • Confirm reactivity with endogenous expression in relevant cell types

  • Validate functionality in multiple applications (WB, IHC, flow cytometry, etc.)

  • Verify lack of reactivity in knockout tissue/cells

What are common challenges when detecting endogenous F2RL3, and how can they be overcome?

When working with F2RL3 antibodies to detect endogenous protein expression, researchers may encounter several challenges:

• Low expression levels:

  • F2RL3 may be expressed at low levels in certain tissues or cell types

  • Solution: Consider using more sensitive detection methods such as chemiluminescence with extended exposure times for Western blot or signal amplification systems for IHC/IF

  • Load higher amounts of protein for Western blot (30 μg has been successfully used with HT29 cell lysate)

• Background signal:

  • Non-specific binding can mask true signal

  • Solution: Optimize blocking conditions (try different blocking agents such as BSA, milk, or commercial blockers)

  • Increase antibody dilution (test a range as recommended by manufacturers, e.g., 1:500-1:2000 for WB)

  • Include appropriate negative controls (F2RL3 knockout or knockdown samples)

• Epitope accessibility issues:

  • In fixed tissues or certain sample preparations, the epitope may be masked

  • Solution: For IHC, optimize antigen retrieval methods (try both TE buffer pH 9.0 and citrate buffer pH 6.0 as suggested for some antibodies)

  • For proteins embedded in membranes, ensure adequate membrane permeabilization

• Post-translational modifications:

  • F2RL3 undergoes proteolytic activation that may affect antibody recognition

  • Solution: Choose antibodies that target regions not affected by proteolytic cleavage, or use antibodies specifically designed to detect either the inactive or active form

How can I study F2RL3 activation and signaling pathways using available antibodies?

To effectively study F2RL3 activation and downstream signaling:

• Detecting activated receptor:

  • Use antibodies that specifically recognize the cleaved/activated form of F2RL3

  • Compare results with total F2RL3 expression to determine the proportion of activated receptor

• Signaling pathway analysis:

  • Investigate the Rap1/MAPK pathway, which has been identified as regulated by F2RL3

  • Measure phosphorylation of downstream effectors following F2RL3 activation

  • Use pathway inhibitors or activators (like the Rap1/MAPK signaling pathway activator) to verify pathway involvement

• Cell-based assays:

  • Monitor calcium flux following F2RL3 activation with thrombin or trypsin

  • Measure phosphoinositide hydrolysis, which is stimulated by F2RL3 coupled to G proteins

  • Track changes in EMT markers (E-cadherin, Snail, vimentin) to assess pathway activation in cancer models

• Receptor activation methods:

  • Activate F2RL3 using thrombin or trypsin, its natural activators

  • Consider using synthetic peptides that mimic the tethered ligand formed after proteolytic cleavage

  • In overexpression systems, mutate the receptor to create constitutively active forms for pathway studies