CHPF2 Antibody

What is CHPF2 and what is its biological significance?

CHPF2 (Chondroitin Polymerizing Factor 2) is an enzyme that transfers glucuronic acid (GlcUA) from UDP-GlcUA to N-acetylgalactosamine residues on the non-reducing end of the elongating chondroitin polymer . It is also known as chondroitin sulfate glucuronyltransferase (CSGlcA-T), chondroitin glucuronyltransferase, chondroitin synthase 3 (CHSY3), and N-acetylgalactosaminyl-proteoglycan 3-beta-glucuronosyltransferase . CHPF2 is crucial for tissue development and morphogenesis, and notably, it also participates in tumor formation and development . Research has shown that CHPF2 is up-regulated in colorectal cancer, suggesting its role in cancer progression . Unlike some related enzymes, CHPF2 has no N-acetylgalactosaminyltransferase activity, making it functionally distinct within its enzyme family .

What types of CHPF2 antibodies are available for research and their validated applications?

Several CHPF2 antibodies are available for research purposes, primarily polyclonal antibodies produced in rabbits. These antibodies have been validated for multiple applications:

Some antibodies, like those in the Prestige Antibodies collection, have undergone extensive validation through the Human Protein Atlas project, which includes testing by immunohistochemistry against hundreds of normal and disease tissues . Enhanced validation methods may include siRNA knockdown, tagged GFP cell lines, or independent antibodies directed towards different epitopes on the protein .

Where is CHPF2 expressed and localized in cells?

CHPF2 is widely expressed in human tissues according to data from the Human Protein Atlas . At the subcellular level, CHPF2 primarily localizes to the Golgi apparatus, specifically in the Golgi stack membrane . It exists as a single-pass type II membrane protein, with its active domain oriented toward the Golgi lumen . This localization is consistent with its function in glycosaminoglycan synthesis, which occurs primarily in the Golgi compartment. Immunofluorescence studies using validated antibodies confirm this Golgi localization pattern, which can be visualized as a perinuclear, reticular staining pattern in most cell types .

How should I design immunohistochemistry experiments using CHPF2 antibodies?

When designing immunohistochemistry (IHC) experiments with CHPF2 antibodies, consider the following methodological approach:

• Sample preparation: Fix tissues with 10% neutral buffered formalin for 24-48 hours, followed by paraffin embedding. Cut sections at 4-5 μm thickness and mount on positively charged slides .

• Antigen retrieval: Perform heat-induced epitope retrieval using citrate buffer (pH 6.0) or EDTA buffer (pH 9.0). The optimal method should be determined empirically, but citrate buffer often works well for CHPF2 .

• Blocking and antibody incubation:

  • Block with 5% normal serum in PBS for 1 hour at room temperature

  • Incubate with primary CHPF2 antibody at recommended dilutions (1:20-1:50 for HPA020992 or 1:100-1:300 for STJ92495 )

  • Incubate overnight at 4°C or for 1-2 hours at room temperature

  • Use an appropriate detection system (e.g., HRP-polymer or avidin-biotin complex)

• Controls: Include both positive controls (tissues known to express CHPF2, such as colorectal cancer samples) and negative controls (primary antibody omission or isotype control) .

• Interpretation: CHPF2 staining should appear primarily in the perinuclear region, consistent with Golgi localization. Evaluate intensity (weak, moderate, strong) and percentage of positive cells. In cancer specimens, compare with adjacent normal tissue to assess upregulation .

What are the optimal conditions for Western blot analysis of CHPF2?

For optimal Western blot detection of CHPF2, follow these methodological recommendations:

• Sample preparation:

  • Extract proteins using RIPA buffer supplemented with protease inhibitors

  • Include phosphatase inhibitors if investigating potential post-translational modifications

  • Sonicate briefly to shear DNA and reduce sample viscosity

• Gel electrophoresis and transfer:

  • Use 8-10% SDS-PAGE gels (CHPF2 has a molecular weight of approximately 80 kDa)

  • Transfer to PVDF membrane at 100V for 90 minutes in cold transfer buffer containing 20% methanol

• Antibody incubation:

  • Block membrane with 5% non-fat dry milk in TBST for 1 hour at room temperature

  • Incubate with primary CHPF2 antibody at 1:500-1:2000 dilution (as recommended for STJ92495 ) in 5% BSA/TBST overnight at 4°C

  • Wash 3-5 times with TBST

  • Incubate with HRP-conjugated secondary antibody (anti-rabbit) at 1:5000 dilution for 1 hour at room temperature

• Detection and analysis:

  • Develop using enhanced chemiluminescence (ECL) substrate

  • Expected band size: approximately 80 kDa for CHPF2

  • Validate specificity using positive controls (cell lines with known CHPF2 expression) and negative controls (CHPF2 knockdown cells)

• Troubleshooting tips:

  • If multiple bands appear, optimize antibody concentration or try a different lysis buffer

  • For weak signals, increase protein loading or extend primary antibody incubation time

  • Consider using fresh tissue samples as CHPF2 may degrade during lengthy storage

How can I co-localize CHPF2 with other Golgi proteins in immunofluorescence studies?

To effectively co-localize CHPF2 with other Golgi proteins in immunofluorescence studies, implement the following methodology:

• Cell preparation:

  • Culture cells on glass coverslips to 70-80% confluency

  • Fix with 4% paraformaldehyde for 15 minutes at room temperature

  • Permeabilize with 0.1% Triton X-100 in PBS for 10 minutes

• Blocking and antibody application:

  • Block with 5% normal serum in PBS for 30-60 minutes

  • Incubate with CHPF2 antibody at recommended dilution (0.25-2 μg/mL for HPA020992 or 1:50-1:200 for STJ92495 )

  • Co-incubate with antibodies against established Golgi markers such as:

    • GM130 (cis-Golgi)

    • TGN46 (trans-Golgi network)

    • Giantin (Golgi stacks)

  • Ensure primary antibodies are from different host species or use directly conjugated antibodies

• Detection and imaging:

  • Use fluorescently-labeled secondary antibodies with distinct emission spectra

  • Include DAPI nuclear counterstain

  • Image using confocal microscopy for optimal resolution of Golgi structures

  • Collect z-stacks to fully capture the three-dimensional Golgi structure

• Quantitative analysis:

  • Calculate Pearson's correlation coefficient or Manders' overlap coefficient to quantify co-localization

  • Analysis should include at least 30-50 cells across multiple fields

  • Compare CHPF2 distribution with different Golgi markers to determine its precise sub-Golgi localization

How can I investigate the role of CHPF2 in chondroitin synthesis using antibody-based approaches?

To investigate CHPF2's role in chondroitin synthesis using antibody-based approaches, implement the following comprehensive methodology:

• Expression analysis in different tissues:

  • Perform immunohistochemistry on tissue microarrays containing samples from cartilage, brain, and other tissues with high chondroitin sulfate content

  • Compare CHPF2 expression levels with known chondroitin sulfate abundance using alcian blue staining on serial sections

  • Correlate CHPF2 expression with other chondroitin synthase family members (CHSY1, CHPF) via multi-label immunofluorescence

• Functional characterization:

  • Implement siRNA-mediated knockdown of CHPF2 followed by immunoblotting to confirm protein reduction

  • Quantify changes in chondroitin sulfate levels using:

    • ELISA with anti-chondroitin sulfate antibodies

    • Metabolic labeling with [³⁵S]sulfate or [³H]glucosamine

    • HPLC analysis of enzymatically digested glycosaminoglycans

  • Rescue experiments by overexpressing CHPF2 in knockdown cells

• Protein-protein interaction studies:

  • Perform co-immunoprecipitation with CHPF2 antibodies to identify interacting partners

  • Use proximity ligation assay (PLA) to visualize and quantify interactions between CHPF2 and other chondroitin synthesis enzymes (CHSY1, CHPF) in situ

  • Confirm interactions using FRET or BiFC in living cells

• Post-translational modification analysis:

  • Immunoprecipitate CHPF2 using validated antibodies

  • Analyze phosphorylation, glycosylation, or other modifications by mass spectrometry

  • Correlate modifications with enzyme activity and chondroitin synthesis rates

This multi-faceted approach will provide comprehensive insights into CHPF2's specific contributions to chondroitin synthesis in various biological contexts.

What strategies can be employed to study CHPF2's role in cancer using antibody-based methods?

To investigate CHPF2's role in cancer using antibody-based methods, consider this comprehensive research strategy:

• Expression profiling in cancer tissues:

  • Perform immunohistochemistry on tissue microarrays containing multiple cancer types and matched normal tissues

  • Score CHPF2 expression using standardized methods (H-score or Allred score)

  • Correlate expression with clinicopathological parameters and patient survival data

  • Focus particularly on colorectal cancer, where CHPF2 upregulation has been reported

• Functional studies in cancer cell lines:

  • Establish CHPF2 knockdown and overexpression models in cancer cell lines

  • Verify alterations using Western blot with validated CHPF2 antibodies

  • Assess effects on:

    • Proliferation (MTT/XTT assays)

    • Migration and invasion (transwell assays)

    • Anchorage-independent growth (soft agar colony formation)

  • Analyze changes in chondroitin sulfate composition using specific antibodies or mass spectrometry

• Signaling pathway analysis:

  • Immunoprecipitate CHPF2 to identify cancer-specific interaction partners

  • Use Western blotting to analyze how CHPF2 modulation affects key cancer-related signaling pathways (MAPK, PI3K/Akt, Wnt/β-catenin)

  • Employ reverse phase protein arrays (RPPA) to broadly assess signaling changes

  • Use phospho-specific antibodies to track activation states of relevant pathways

• In vivo studies:

  • Develop xenograft models using CHPF2-modulated cancer cells

  • Perform immunohistochemical analysis of tumor sections for:

    • CHPF2 expression

    • Proliferation markers (Ki-67)

    • Angiogenesis markers (CD31)

    • Chondroitin sulfate distribution

  • Correlate CHPF2 expression with tumor growth and metastatic potential

This comprehensive approach can reveal both the prognostic value of CHPF2 expression and its functional contributions to cancer development and progression.

How can I address non-specific binding when using CHPF2 antibodies?

Non-specific binding is a common challenge when working with CHPF2 antibodies. To address this issue, implement the following methodological solutions:

• Antibody validation and selection:

  • Prioritize antibodies with enhanced validation data, such as those from the Human Protein Atlas project

  • Consider using antibodies targeting different epitopes (e.g., amino acids 31-80 as in STJ92495 ) to confirm specificity

  • Review literature for previously validated antibodies in your specific application

• Optimization strategies for Western blotting:

  • Increase blocking stringency using 5% BSA instead of milk, or add 0.1% Tween-20 to blocking buffer

  • Optimize primary antibody concentration through titration experiments (try 1:500, 1:1000, 1:2000 dilutions)

  • Increase washing duration and frequency (5 x 10 minutes with TBST)

  • Use gradient SDS-PAGE to better resolve proteins of similar molecular weight

  • Include competitive peptide blocking controls (pre-incubate antibody with immunogen peptide)

• Optimization for immunohistochemistry/immunofluorescence:

  • Test multiple antigen retrieval methods (citrate buffer pH 6.0, EDTA buffer pH 9.0, enzymatic retrieval)

  • Increase blocking time and concentration (use 10% serum from the same species as the secondary antibody)

  • Add protein blockers (0.5% BSA, 0.1% gelatin, 0.1% casein) to antibody diluent

  • Consider using polymer detection systems instead of biotin-based methods to reduce background

  • Include tissue-specific negative controls lacking CHPF2 expression

• Confirmatory approaches:

  • Perform siRNA knockdown of CHPF2 followed by Western blot or immunofluorescence to confirm antibody specificity

  • Use recombinant CHPF2-expressing cells as positive controls

  • Compare staining patterns with transcript data from public databases

Implementing these systematic approaches will help distinguish between genuine CHPF2 signal and non-specific binding, enhancing the reliability of your experimental data.

How should I interpret discrepancies in CHPF2 detection between different antibodies?

When encountering discrepancies in CHPF2 detection between different antibodies, apply the following analytical approach:

• Evaluate antibody characteristics:

  • Compare epitope regions targeted by each antibody (e.g., amino acids 31-80 versus other regions)

  • Review antibody types (polyclonal versus monoclonal) and production methods

  • Assess validation data available for each antibody, prioritizing those with enhanced validation through knockdown or orthogonal techniques

  • Consider species cross-reactivity and whether antibodies were raised against full-length protein or peptide fragments

• Consider protein biochemistry factors:

  • Post-translational modifications may mask epitopes in certain contexts

  • Protein conformation differences between applications (native vs. denatured)

  • Potential splice variants or isoforms that might be differentially detected

  • Protein complex formation that could sequester specific epitopes

• Perform comparative validation experiments:

  • Side-by-side testing of multiple antibodies on the same samples

  • Correlation analysis between protein levels detected by different antibodies

  • Comparison with mRNA expression data (RT-qPCR or RNA-seq)

  • Confirmation with genetic approaches (CRISPR knockout/knockdown followed by antibody testing)

• Decision framework for resolving discrepancies:

• Reporting guidelines:

  • Clearly document all antibodies used (catalog number, lot, dilution)

  • Specify exact experimental conditions for each antibody

  • Present data from multiple antibodies when discrepancies exist

  • Discuss potential biological explanations for observed differences

This systematic approach transforms antibody discrepancies from experimental frustrations into potential biological insights about CHPF2 regulation and function.

What controls should I include when studying CHPF2 in different experimental systems?

A robust experimental design for studying CHPF2 requires comprehensive controls tailored to different experimental approaches. Implement the following control strategy:

• Essential controls for immunoblotting:

  • Positive control: Lysate from cells with confirmed CHPF2 expression (e.g., HeLa cells)

  • Negative control: CHPF2 knockdown/knockout cell lysate

  • Loading control: Probing for housekeeping proteins (β-actin, GAPDH) on the same membrane

  • Molecular weight marker: To confirm the expected ~80 kDa size of CHPF2

  • Antibody specificity control: Primary antibody omission or isotype control

• Controls for immunohistochemistry/immunofluorescence:

  • Positive tissue control: Tissues with documented CHPF2 expression

  • Negative tissue control: Tissues with minimal CHPF2 expression

  • Technical negative control: Primary antibody omission

  • Absorption control: Pre-incubation of antibody with immunizing peptide

  • Subcellular localization control: Co-staining with Golgi markers (GM130, TGN46)

• Functional study controls:

  • Expression verification: Confirm CHPF2 expression changes by both protein (Western blot) and mRNA (qRT-PCR) analysis

  • Rescue controls: Re-expression of CHPF2 in knockdown models to confirm phenotype specificity

  • Off-target effect controls: Use multiple siRNA sequences or shRNA constructs targeting different regions of CHPF2

  • Enzymatic activity control: Measure chondroitin synthesis as a functional readout

• Specialized controls for specific applications:

• Experimental system-specific controls:

  • Cell line studies: Include multiple cell lines with varying CHPF2 expression levels

  • Primary cell studies: Age and sex-matched controls

  • Tissue studies: Adjacent normal tissue, tissue-specific controls

  • Animal models: Wild-type littermates, sham-operated controls

Implementing this comprehensive control strategy ensures robust, reproducible data that can withstand rigorous peer review and provide genuine insights into CHPF2 biology.

How can I characterize the enzymatic activity of CHPF2 after immunoprecipitation?

To characterize CHPF2 enzymatic activity following immunoprecipitation, implement this comprehensive methodological approach:

• Optimized immunoprecipitation protocol:

  • Lyse cells in mild, non-denaturing buffer (e.g., 25 mM Tris-HCl pH 7.4, 150 mM NaCl, 1% NP-40, 5% glycerol) with protease inhibitors

  • Use validated CHPF2 antibodies coupled to protein A/G magnetic beads

  • Perform binding at 4°C for 2-4 hours with gentle rotation

  • Include extensive washing steps (at least 5 washes) while maintaining mild conditions

  • Elute using gentle methods (competitive peptide elution rather than boiling in SDS)

• In vitro glucuronyltransferase activity assay:

  • Prepare reaction mixture containing:

    • Immunoprecipitated CHPF2 protein

    • UDP-[¹⁴C]glucuronic acid or UDP-[³H]glucuronic acid (radiolabeled substrate)

    • Acceptor substrate (N-acetylgalactosamine-containing oligosaccharides)

    • Buffer components (50 mM MES pH 6.5, 10 mM MnCl₂)

  • Incubate at 37°C for 1-2 hours

  • Terminate reaction by heating at 100°C for 1 minute

  • Separate products by paper chromatography or HPLC

  • Quantify incorporation of radiolabeled glucuronic acid using scintillation counting

• Alternative non-radioactive assay approach:

  • Use UDP-glucuronic acid with fluorescent or chromogenic tags

  • Conduct reaction as above

  • Measure product formation using specialized HPLC or mass spectrometry

  • Quantify enzyme activity by measuring the rate of product formation

• Essential controls and validation:

  • Positive control: Recombinant CHPF2 with confirmed activity

  • Negative controls:

    • Immunoprecipitation with isotype control antibody

    • Heat-inactivated enzyme preparation

    • Reaction without acceptor substrate

  • Specificity controls:

    • Competitive inhibition with excess unlabeled UDP-glucuronic acid

    • Comparison with other glucuronyltransferases (CHPF, B3GAT3)

• Kinetic characterization:

  • Determine Km and Vmax by varying substrate concentrations

  • Assess effects of divalent cations (Mn²⁺, Mg²⁺) on enzyme activity

  • Test pH dependence of the reaction

  • Evaluate potential inhibitors

This comprehensive approach will provide detailed information about CHPF2's enzymatic properties while confirming that immunoprecipitation preserves its catalytic function.

What are the best approaches for studying CHPF2 interactions with other chondroitin synthase family members?

To effectively study CHPF2 interactions with other chondroitin synthase family members, implement the following multi-technique strategy:

• Co-immunoprecipitation studies:

  • Perform reciprocal co-IPs using antibodies against CHPF2 and other family members (CHSY1, CHSY2, CHPF)

  • Use mild lysis conditions to preserve protein complexes (1% digitonin or 0.5% NP-40)

  • Include appropriate controls (IgG control, lysate input)

  • Analyze precipitated complexes by Western blotting or mass spectrometry

  • Consider crosslinking approaches to stabilize transient interactions

• Proximity-based interaction assays:

  • Proximity Ligation Assay (PLA):

    • Co-stain fixed cells with CHPF2 antibody and antibodies against other family members

    • Use species-specific PLA probes to generate fluorescent signals only when proteins are in close proximity (<40 nm)

    • Quantify interaction signals across different cell types and conditions

  • FRET/BRET approaches:

    • Generate fluorescent protein fusions with CHPF2 and other family members

    • Measure energy transfer as indicator of protein proximity

    • Perform acceptor photobleaching FRET to confirm interactions

• Bimolecular Fluorescence Complementation (BiFC):

  • Create split fluorescent protein constructs (e.g., split Venus) fused to CHPF2 and potential partners

  • Transfect into relevant cell lines

  • Monitor reconstitution of fluorescence as indicator of protein interaction

  • Analyze subcellular localization of interaction complexes

• Functional complex analysis:

  • Perform simultaneous knockdown/overexpression experiments of multiple family members

  • Assess combinatorial effects on:

    • Chondroitin synthesis rates

    • Chain length and sulfation patterns

    • Golgi morphology

    • Cellular phenotypes

• Structural biology approaches:

  • Generate recombinant proteins for in vitro binding assays

  • Use hydrogen-deuterium exchange mass spectrometry (HDX-MS) to map interaction interfaces

  • Consider cryo-EM for larger complexes

This comprehensive approach will provide detailed insights into how CHPF2 works in concert with other chondroitin synthase family members to regulate glycosaminoglycan synthesis in various biological contexts.