filip1l Antibody

What is FILIP1L and why is it significant in cancer research?

FILIP1L (Filamin A interacting protein 1-like), previously known as "down-regulated in ovarian cancer 1," was identified as a gene upregulated in endothelial cells in response to angiogenesis inhibitors. Research has established that FILIP1L may function as a tumor suppressor by inhibiting cell proliferation and migration, suppressing angiogenesis, and promoting apoptosis. Its expression is decreased in various cancers, including ovarian, prostate, breast, lung, pancreatic, and colorectal cancers, making it a promising target for cancer research and potential therapeutic development .

What types of FILIP1L antibodies are available for research applications?

Based on published research, several types of FILIP1L antibodies have been developed, including mouse monoclonal antibodies generated against full-length FILIP1L protein (893 amino acids) expressed in baculovirus systems. These have been validated for applications including Western blotting, immunofluorescence staining, and immunohistochemistry on formalin-fixed, paraffin-embedded tissue sections. When selecting an antibody, researchers should consider the specific application, target species, and whether the antibody recognizes specific domains or the full-length protein .

How can I validate the specificity of a FILIP1L antibody for my research?

To validate FILIP1L antibody specificity, implement a multi-step approach:

• Perform Western blot analysis comparing cells with known FILIP1L expression levels (e.g., endothelial cells such as HUVECs) to detect the expected 110 kDa band

• Include positive controls (purified recombinant FILIP1L protein) where available

• Utilize siRNA-mediated FILIP1L knockdown and/or overexpression systems to confirm specificity

• Conduct subcellular fractionation to verify localization patterns match expected distribution

• Compare results across multiple detection methods (e.g., Western blot and immunofluorescence)

The literature indicates that endogenous FILIP1L protein expression can be detected in human cells, with a specific 110-kDa band observed in Western blots that matches the size of purified FILIP1L protein .

What is the optimal protocol for immunofluorescence staining with FILIP1L antibodies?

For optimal immunofluorescence staining with FILIP1L antibodies, consider the following methodological approach:

• Fix cells appropriately (paraformaldehyde fixation has been used successfully)

• Include proper permeabilization steps to access intracellular FILIP1L

• Use appropriate blocking solutions to minimize background signal

• Optimize primary antibody dilution (typically starting with manufacturer recommendations)

• Include co-staining with organelle markers such as TOM20 for mitochondria to confirm subcellular localization

• Employ confocal or super-resolution microscopy for detailed subcellular localization studies, as standard widefield microscopy at lower magnifications may not adequately resolve FILIP1L's distinct mitochondrial localization pattern

• When analyzing results, adjust brightness levels carefully to enhance visualization of specific signals while reducing diffuse cytoplasmic background

Research has demonstrated that FILIP1L exhibits a distinctive mitochondrial localization pattern that strongly resembles mitochondrial distribution when imaged by confocal and super-resolution microscopy, which may be less apparent with standard widefield microscopy .

How should I optimize Western blot protocols for detecting FILIP1L protein?

For optimal Western blot detection of FILIP1L protein:

• Prepare samples with RIPA buffer, which has been successfully used for FILIP1L extraction

• Include appropriate protease inhibitors in lysis buffers

• Load 25-50 μg of protein per lane for cellular fractions or whole cell lysates

• Use SDS-PAGE followed by transfer to nitrocellulose membranes

• Block membranes according to antibody manufacturer specifications

• Incubate with primary anti-FILIP1L antibody, followed by horseradish peroxidase-conjugated secondary antibody

• Detect signal using chemiluminescence systems

• Include loading controls such as GAPDH

• For endogenous FILIP1L, expect to detect a specific 110-kDa band

Published protocols have successfully used this approach to detect both endogenous FILIP1L in human cells and overexpressed FILIP1L in experimental systems .

What control samples should be included when working with FILIP1L antibodies?

When working with FILIP1L antibodies, include these essential controls:

• Positive controls: Cell types with known FILIP1L expression (e.g., HUVECs)

• Negative controls: Primary antibody omission controls to assess non-specific binding of secondary antibodies

• Expression controls: Cells with manipulated FILIP1L expression (knockdown via siRNA or overexpression via expression vectors) to validate antibody specificity

• Subcellular localization controls: Co-staining with established markers of cellular compartments (e.g., TOM20 for mitochondria)

• Isotype controls: Especially for monoclonal antibodies to assess non-specific binding

• Multiple detection methods: Cross-validation using different techniques (Western blot, immunofluorescence, etc.)

Research has demonstrated the value of these controls, particularly the use of genetic manipulation approaches (knockdown/overexpression) to validate antibody specificity across applications .

What is the subcellular localization pattern of FILIP1L protein?

Recent research has revealed that FILIP1L exhibits a predominantly mitochondrial localization pattern in several human cell lines. This localization:

• Strongly resembles mitochondrial distribution when visualized by confocal and super-resolution microscopy

• Shows clear colocalization with the mitochondrial marker TOM20 across multiple cell lines

• May appear as a more diffuse cytoplasmic pattern when imaged by widefield microscopy at lower magnifications

• Can vary slightly between cell types, with some (like HFFc6 cells) showing less obvious but still visible mitochondrial localization

• Is more readily apparent when image contrast and minimum pixel values are adjusted to reduce diffuse cytoplasmic signal

Earlier studies had reported cytoplasmic and nuclear localization patterns, but recent high-resolution imaging provides strong evidence for mitochondrial association. This localization pattern may provide insights into FILIP1L's functional roles in cellular processes including apoptosis regulation .

How does FILIP1L expression change in response to angiogenesis inhibitors?

FILIP1L expression responds dynamically to angiogenesis inhibitors in endothelial cells:

• At the mRNA level, FILIP1L expression is rapidly upregulated (within 1 hour) in human umbilical vein endothelial cells (HUVECs) after treatment with angiogenesis inhibitors including endostatin, fumagillin, and EMAP II

• At the protein level, endostatin-treated HUVECs show increased FILIP1L protein expression at 2, 4, and 8 hours post-treatment compared to vehicle-treated controls

• Subcellular distribution of FILIP1L protein also changes upon endostatin treatment, with serum-starved, vehicle-treated control cells showing weak cytoplasmic staining, while endostatin-treated cells exhibit stronger punctate distribution in the cytoplasm

• Quantitative analysis confirms that FILIP1L immunofluorescent staining is significantly more intense in endostatin-treated HUVECs compared to vehicle-treated control cells (p = 0.0012)

This upregulation of FILIP1L in response to angiogenesis inhibitors suggests a potential role for FILIP1L in mediating the antiangiogenic effects of these agents .

How can I effectively manipulate FILIP1L expression levels for functional studies?

For effective manipulation of FILIP1L expression in functional studies:

• For knockdown approaches:

  • siRNA-mediated FILIP1L silencing has been successfully employed in multiple studies

  • Confirm knockdown efficiency via quantitative real-time RT-PCR using validated primers (e.g., 5′-AACGCTGGTATCATGGCTGAA-3′ and 5′-ATCTCTGCACTGCTCCTCCATT-3′ for FILIP1L)

  • Normalize to housekeeping genes such as GAPDH

  • Validate protein reduction via Western blot

• For overexpression approaches:

  • Gateway entry clones have been developed for FILIP1L and its truncation mutants

  • Full-length FILIP1L and truncation variants (such as FILIP1LΔC103 and FILIP1LΔC243) have been cloned into expression vectors

  • pcDNA-myc vector systems have been used successfully for FILIP1L overexpression

  • Include appropriate tags (such as HA or myc) to facilitate detection of the expressed protein

• For targeted expression in animal models:

  • Adeno-associated virus-phage (AAVP) vectors expressing FILIP1L truncation mutants have been used for tumor vascular-targeted gene therapy

  • Lentiviral systems with doxycycline-inducible expression provide temporal control

These approaches have been successfully implemented to study FILIP1L's effects on cellular processes including proliferation, migration, apoptosis, and angiogenesis .

How does FILIP1L expression correlate with clinicopathological features in cancer?

Analysis of FILIP1L expression in cancer tissues reveals significant clinicopathological correlations:

• FILIP1L protein levels are lower in colorectal cancer cells compared to normal colorectal epithelial cells

• Higher FILIP1L expression levels correlate with favorable clinicopathological features, including:

  • Reduced tumor size

  • Better cell differentiation

  • Decreased lymphovascular invasion

  • Earlier cancer stage

  • Reduced depth of invasion

  • Reduced lymph node metastasis

These correlations suggest that FILIP1L may serve as a prognostic biomarker in certain cancers, with higher expression potentially indicating better prognosis. Further studies across multiple cancer types would help determine the broader applicability of these findings .

What signaling pathways are affected by FILIP1L expression in cancer cells?

FILIP1L expression modulates several key signaling pathways in cancer cells:

• Wnt/β-catenin pathway:

  • FILIP1L knockdown decreases phosphorylated β-catenin levels

  • FILIP1L overexpression increases phosphorylated β-catenin levels

• PI3K/Akt pathway:

  • FILIP1L knockdown increases phosphorylated Akt and GSK-3β levels

  • FILIP1L overexpression decreases phosphorylated Akt and GSK-3β levels

• Angiogenesis signaling:

  • FILIP1L knockdown increases pro-angiogenic factors (VEGF-A, HIF-1α) and decreases anti-angiogenic factors (angiostatin)

  • FILIP1L overexpression decreases pro-angiogenic factors (VEGF-A, VEGF-D) and increases anti-angiogenic factors (angiostatin, endostatin)

• Apoptosis regulation:

  • FILIP1L expression promotes apoptosis in colorectal cancer cells

  • FILIP1L knockdown decreases apoptosis rates (15.4% vs. 7.1%, p = 0.014)

  • FILIP1L overexpression increases apoptosis rates (7.2% vs. 10.3%, p = 0.047)

These findings suggest FILIP1L functions as a tumor suppressor by modulating multiple oncogenic pathways .

What technical challenges might arise when detecting FILIP1L in different microscopy systems?

Researchers should be aware of several technical challenges when visualizing FILIP1L:

• Resolution-dependent localization patterns:

  • FILIP1L's mitochondrial localization is clearly visible with confocal and super-resolution microscopy

  • This localization pattern is less apparent with widefield microscopy at lower magnifications

  • Higher resolution imaging systems are recommended for accurate subcellular localization studies

• Cell type variations:

  • Mitochondrial colocalization may be more challenging to detect in certain cell lines (e.g., HFFc6 cells)

  • Adjustment of image contrast and minimum pixel values may be necessary to reduce diffuse cytoplasmic signal

• Antibody validation concerns:

  • Single antibody studies may have limitations

  • Multiple antibodies should be tested when possible to confirm localization patterns

  • Control experiments using fluorophore-only controls are essential to address potential bleed-through

• Signal-to-noise optimization:

  • Linear adjustment of brightness levels may be necessary to enhance visualization

  • Balancing specific signal detection with background reduction requires careful optimization

These technical considerations highlight the importance of using appropriate high-resolution imaging techniques and rigorous controls when studying FILIP1L localization .

How can I improve detection of endogenous FILIP1L in cells with low expression levels?

For improved detection of low-level endogenous FILIP1L:

• Sample preparation optimization:

  • Use cellular fractionation to concentrate FILIP1L from specific compartments

  • Optimize lysis buffers for complete protein extraction (RIPA buffer has been successful)

  • Consider synchronizing cells, as FILIP1L levels may vary with cell cycle

• Signal amplification strategies:

  • For Western blots, use high-sensitivity chemiluminescence detection systems

  • For immunofluorescence, consider tyramide signal amplification

  • Increase exposure time while monitoring background levels

• Imaging enhancements:

  • Use confocal or super-resolution microscopy rather than standard widefield microscopy

  • Adjust image contrast and minimum pixel values to reduce diffuse cytoplasmic signal

  • Consider deconvolution techniques to improve signal-to-noise ratio

• Control experiments:

  • Include known positive control samples (e.g., HUVECs treated with endostatin)

  • Compare results with cells where FILIP1L has been experimentally upregulated

Published studies have demonstrated that endogenous FILIP1L can be detected in human cells, with improved visibility following treatment with factors that upregulate its expression .

What are the best methods for quantifying FILIP1L expression changes in response to experimental treatments?

For accurate quantification of FILIP1L expression changes:

• Protein level quantification:

  • Western blot with densitometric analysis normalized to loading controls such as GAPDH

  • Include multiple biological replicates and technical replicates

  • Use a standard curve with recombinant protein if absolute quantification is required

• mRNA level quantification:

  • Quantitative real-time RT-PCR with validated primers

  • Normalize to stable reference genes (GAPDH has been used successfully)

  • Follow MIQE guidelines for qPCR experiments

• Immunofluorescence quantification:

  • Use consistent acquisition parameters across all samples

  • Quantify signal intensity using appropriate image analysis software

  • Analyze multiple cells across multiple fields

  • Consider automated high-content imaging for larger datasets

• Statistical analysis:

  • Apply appropriate statistical tests (t-tests for simple comparisons, ANOVA for multiple conditions)

  • Report p-values and confidence intervals

  • Consider consulting with a biostatistician for complex experimental designs

These approaches have been successfully applied to quantify changes in FILIP1L expression following treatment with angiogenesis inhibitors and in different experimental conditions .

How should I design experiments to study FILIP1L truncation mutants?

When studying FILIP1L truncation mutants:

• Mutant design considerations:

  • Previously characterized truncation mutants include:

    • FILIP1LΔC103 (amino acids 1-790)

    • FILIP1LΔC243 (amino acids 1-650)

  • Include appropriate tags (HA, myc) to facilitate detection

  • Consider the functional domains being removed/retained

• Expression systems:

  • Gateway entry clones with sequence verification

  • Lentiviral systems for stable expression

  • Doxycycline-inducible systems for temporal control

  • AAVP vectors for in vivo targeted expression

• Functional assessments:

  • Compare truncation mutants to wild-type FILIP1L

  • Evaluate differential effects on:

    • Cell proliferation

    • Apoptosis

    • Migration

    • Angiogenesis

• Localization studies:

  • Assess whether truncations affect subcellular localization

  • Co-stain with organelle markers (e.g., TOM20 for mitochondria)

  • Use high-resolution imaging to detect potential localization changes

Research has shown that certain FILIP1L truncation mutants (e.g., FILIP1LΔC103) demonstrate enhanced antiproliferative activity compared to wild-type FILIP1L, making them valuable tools for mechanistic studies and potential therapeutic applications .

How can FILIP1L expression analysis be applied in clinical cancer research?

FILIP1L expression analysis offers several applications in clinical cancer research:

• Prognostic biomarker development:

  • Immunohistochemical staining of FILIP1L in formalin-fixed, paraffin-embedded tissue samples

  • Correlation of expression levels with clinical outcomes and survival data

  • Integration with other biomarkers for improved prognostic models

• Predictive biomarker potential:

  • Assessment of FILIP1L expression in relation to treatment response

  • Correlation with sensitivity to anti-angiogenic therapies

  • Stratification of patients for clinical trials

• Methodological approach:

  • Use standardized immunohistochemical protocols with validated antibodies

  • Implement quantitative scoring systems (e.g., H-score or Allred score)

  • Ensure blinded assessment by multiple pathologists

  • Correlate with clinicopathological data including tumor size, differentiation, lymphovascular invasion, cancer stage, and metastasis

• Translational insights:

  • Analyze FILIP1L levels in relation to tumor microenvironment features

  • Investigate correlations with markers of angiogenesis, apoptosis, and proliferation

Research has demonstrated that FILIP1L expression in colorectal cancer tissues correlates with multiple clinicopathological parameters, suggesting its potential utility as a prognostic biomarker .

What are the considerations for studying FILIP1L in in vivo cancer models?

For studying FILIP1L in in vivo cancer models:

• Model selection and design:

  • Xenograft models have been successfully used (e.g., M21 human melanoma cells)

  • Consider orthotopic models for tissue-specific effects

  • Design appropriate group sizes for statistical power (n=11 per group has been used)

  • Include relevant control groups (PBS-treated, vector-only controls)

• FILIP1L modulation strategies:

  • AAVP vectors for targeted delivery of FILIP1L or its truncation mutants

  • Administration routes: intravenous injection has been successful (1 × 10^11 transducing units per dose)

  • Treatment schedule: multiple administrations may be required (e.g., day 0 and day 7)

• Outcome measurements:

  • Tumor volume measurements (calculated as the product of length × width × height × 0.52)

  • Perform measurements in a blinded manner

  • Collect tissue for molecular and histological analyses

• Molecular analyses:

  • Confirm FILIP1L expression in tumor tissue via Western blot

  • Assess markers of angiogenesis, apoptosis, and proliferation

  • Analyze tumor vasculature and necrosis

Research has demonstrated that targeted expression of FILIP1L truncation mutants in tumor vasculature successfully inhibits tumor growth in vivo, suggesting therapeutic potential .

How does FILIP1L's mitochondrial localization relate to its function in apoptosis regulation?

The recently discovered mitochondrial localization of FILIP1L raises important questions about its mechanistic role in apoptosis:

• Current understanding:

  • FILIP1L has been shown to promote apoptosis in cancer cells

  • FILIP1L knockdown decreases apoptosis rates while overexpression increases them

  • Mitochondria are central organelles in intrinsic apoptotic pathways

• Potential mechanisms requiring investigation:

  • FILIP1L may interact with mitochondrial membrane proteins involved in apoptosis regulation

  • It could influence mitochondrial membrane permeability

  • It might affect the release of pro-apoptotic factors from mitochondria

  • It could modulate mitochondrial dynamics (fission/fusion) which influence apoptotic processes

• Methodological approaches to address this question:

  • Co-immunoprecipitation studies to identify FILIP1L-interacting proteins in mitochondria

  • Mitochondrial fractionation to determine precise submitochondrial localization

  • Live-cell imaging to track FILIP1L dynamics during apoptosis induction

  • Mutational analyses to identify domains required for both mitochondrial localization and apoptotic function

This represents an important area for future research, as understanding the relationship between FILIP1L's localization and function could provide new insights into cancer biology and potential therapeutic approaches .

What is the relationship between FILIP1L and other tumor suppressor pathways?

The integration of FILIP1L with established tumor suppressor pathways requires further investigation:

• Current evidence suggests FILIP1L intersects with:

  • Wnt/β-catenin pathway (affects phosphorylated β-catenin levels)

  • PI3K/Akt pathway (modulates phosphorylated Akt and GSK-3β levels)

  • Angiogenesis regulation (influences VEGF, HIF-1α, angiostatin, and endostatin levels)

• Key questions for further research:

  • Is FILIP1L a direct component of these pathways or does it exert indirect effects?

  • Are there feedback mechanisms between FILIP1L and these pathways?

  • How does FILIP1L expression interact with mutations in established tumor suppressor genes?

  • Could FILIP1L serve as a compensatory mechanism when other tumor suppressors are inactivated?

• Experimental approaches:

  • Epistasis studies using combined knockdown/overexpression of FILIP1L and key pathway components

  • Chromatin immunoprecipitation to identify potential transcriptional targets

  • Proteomic analysis of FILIP1L interactome under different cellular conditions

  • Analysis of FILIP1L expression and function in cell lines with defined tumor suppressor mutations

Understanding these relationships would provide deeper insights into FILIP1L's role in tumor suppression and potentially identify synergistic approaches for cancer therapy .

What technical advancements are needed to better characterize FILIP1L protein interactions and modifications?

Further technical advancements would enhance our understanding of FILIP1L:

• Protein interaction studies:

  • Development of proximity labeling approaches (BioID, APEX) with FILIP1L as the bait protein

  • Creation of stable cell lines expressing tagged FILIP1L for interactome studies

  • Application of crosslinking mass spectrometry to capture transient interactions

  • Investigation of potential protein complex formation under different cellular conditions

• Post-translational modification mapping:

  • Comprehensive phosphoproteomic analysis of FILIP1L

  • Investigation of other potential modifications (ubiquitination, acetylation, etc.)

  • Development of modification-specific antibodies

  • Determination of how modifications affect FILIP1L localization and function

• Structural biology approaches:

  • X-ray crystallography or cryo-EM studies of FILIP1L domains

  • NMR analysis of FILIP1L interaction interfaces

  • In silico modeling of FILIP1L structure-function relationships

• Advanced imaging techniques:

  • Development of live-cell imaging tools for FILIP1L

  • Application of super-resolution microscopy for detailed localization studies

  • FRET/FLIM approaches to study protein-protein interactions in situ

These technical advancements would address current limitations in FILIP1L research and provide more detailed mechanistic insights into its cellular functions .

What are the key unresolved questions about FILIP1L function in normal physiology?

Despite progress in understanding FILIP1L's role in cancer, several fundamental questions about its normal physiological functions remain unanswered:

• Developmental biology:

  • What is the expression pattern of FILIP1L during embryonic and tissue development?

  • Does FILIP1L play essential roles in normal development?

  • Are there tissue-specific functions of FILIP1L?

• Cellular homeostasis:

  • What is FILIP1L's role in normal endothelial cell function beyond response to angiogenesis inhibitors?

  • How does FILIP1L contribute to mitochondrial function in normal cells?

  • Is FILIP1L expression regulated during cell cycle progression?

• Stress responses:

  • How does FILIP1L respond to various cellular stressors beyond angiogenesis inhibition?

  • Is FILIP1L involved in normal damage response pathways?

  • Does FILIP1L play a role in cellular adaptation to environmental challenges?

• Methodological approaches:

  • Development of conditional knockout models to study tissue-specific functions

  • Single-cell analysis to examine cell-type specific expression patterns

  • Transcriptional profiling under various physiological conditions

Understanding FILIP1L's normal physiological roles would provide context for its dysregulation in cancer and potentially identify new therapeutic approaches .

How might FILIP1L-targeted therapies be developed for cancer treatment?

The tumor suppressive properties of FILIP1L suggest potential therapeutic applications:

• Gene therapy approaches:

  • AAVP-mediated delivery of FILIP1L or its more potent truncation mutants (FILIP1LΔC103) to tumor vasculature has shown promise in preclinical models

  • Development of tumor-targeted nanoparticles for FILIP1L delivery

  • Investigation of small molecules that could induce endogenous FILIP1L expression

• Combination therapy strategies:

  • Exploration of synergistic effects between FILIP1L-targeted approaches and established anti-angiogenic therapies

  • Investigation of combinations with conventional chemotherapeutics

  • Testing with immunotherapeutic approaches

• Biomarker-guided treatment:

  • Stratification of patients based on FILIP1L expression levels

  • Development of companion diagnostics for FILIP1L-targeted therapies

  • Monitoring FILIP1L expression as a marker of treatment response

• Methodological considerations:

  • Optimization of delivery systems for clinical translation

  • Development of appropriate dosing schedules

  • Design of clinical trials with relevant endpoints and biomarkers

Preliminary research has demonstrated that targeted expression of FILIP1L truncation mutants in tumor vasculature inhibits tumor growth in vivo, providing proof of concept for therapeutic development .

What contradictions in the literature about FILIP1L require resolution?

Several apparent contradictions in the FILIP1L literature warrant further investigation:

• Subcellular localization discrepancies:

  • Earlier studies reported cytoplasmic and nuclear localization

  • Recent high-resolution microscopy reveals predominantly mitochondrial localization

  • Resolution approaches: Standardized protocols, multiple validated antibodies, and consistent imaging technologies across studies

• Cell type-specific effects:

  • FILIP1L localization and function may vary between cell types

  • Some cell lines show clearer mitochondrial localization than others

  • Resolution approaches: Systematic comparison across multiple cell types under standardized conditions

• Functional mechanisms:

  • The precise molecular mechanisms by which FILIP1L inhibits proliferation, migration, and angiogenesis remain incompletely understood

  • Resolution approaches: Comprehensive interactome studies, detailed structure-function analyses, and pathway mapping

• Technical considerations:

  • Antibody specificity concerns - most studies rely on limited antibodies

  • Resolution approaches: Development and validation of multiple antibodies against different FILIP1L epitopes