HNRNPA3 Antibody

What is HNRNPA3 and what are its primary functions in cellular biology?

HNRNPA3 (heterogeneous nuclear ribonucleoprotein A3) is a 378 amino acid protein containing two RNA recognition motif (RRM) domains that primarily localizes in the nucleus. It belongs to the hnRNP A/B family of RNA-binding proteins that shuttle between nucleus and cytoplasm . HNRNPA3 plays critical roles in:

• Pre-mRNA splicing

• Nuclear import and cytoplasmic trafficking of RNA

• mRNA stability and turnover

• Translation regulation

• Binding to the cis-acting response element, A2RE

The protein contains a glycine-rich C-terminal region following its two N-terminal RNA recognition sites, which is characteristic of the hnRNP A/B family . While primarily nuclear, it can be detected at lower levels in the cytoplasm in some cell types and under certain conditions .

What applications are validated for HNRNPA3 antibodies, and what dilutions are recommended?

HNRNPA3 antibodies have been validated for multiple experimental applications with specific recommended dilutions:

For optimal results, titration is necessary as the optimal dilution may be sample-dependent .

What is the molecular weight of HNRNPA3 and why might observed band sizes differ from the calculated molecular weight?

HNRNPA3 has a calculated molecular weight of approximately 40 kDa (378 amino acids), but observed band sizes typically range between 37-40 kDa on Western blots . This discrepancy can occur due to:

• Post-translational modifications affecting protein mobility

• Different protein isoforms resulting from alternative splicing

• Sample preparation conditions and buffer composition

• Gel percentage and running conditions affecting migration patterns

As noted in the product documentation: "The mobility is affected by many factors, which may cause the observed band size to be inconsistent with the expected size. If a protein in a sample has different modified forms at the same time, multiple bands may be detected on the membrane" .

How should researchers optimize tissue preparation for HNRNPA3 immunohistochemistry?

For optimal HNRNPA3 detection in tissues by IHC, follow these methodological recommendations:

• Fixation and embedding: Standard formalin fixation and paraffin embedding protocols are suitable for HNRNPA3 detection.

• Antigen retrieval: Two validated methods with significant differences in outcomes:

  • Primary recommendation: TE buffer pH 9.0 has shown superior results for exposing HNRNPA3 epitopes

  • Alternative method: Citrate buffer pH 6.0 can be used but may yield different staining patterns

• Blocking: Use 5-10% normal serum (from the species of secondary antibody) in PBS with 0.1% Triton X-100 for 1 hour at room temperature.

• Antibody incubation: Apply primary antibody (dilution 1:50-1:500) in blocking solution overnight at 4°C, followed by appropriate secondary antibody.

• Controls: Include both positive tissue controls (human stomach or colon tissue) and negative controls (primary antibody omission) to validate staining specificity .

The choice between pH 9.0 and pH 6.0 buffers may affect the detection of specific HNRNPA3 forms, particularly in pathological conditions where the protein might undergo modifications.

What are the key considerations for detecting nuclear versus cytoplasmic HNRNPA3?

HNRNPA3 is predominantly nuclear, but detecting its cytoplasmic localization requires specific methodological considerations:

• Fixation timing: Over-fixation can mask cytoplasmic epitopes; limit fixation to 10-15 minutes with 4% paraformaldehyde for cultured cells.

• Permeabilization optimization: For nuclear HNRNPA3, standard 0.1-0.5% Triton X-100 permeabilization works well, but cytoplasmic detection may benefit from milder permeabilization (0.05% Triton X-100 or 0.5% saponin).

• Antibody selection: Different antibodies may preferentially detect nuclear or cytoplasmic forms. The Sigma antibody has shown better detection of both nuclear and rare cytoplasmic forms compared to the Santa Cruz antibody in FTLD studies .

• Imaging parameters: Use confocal microscopy with Z-stack imaging to distinguish true cytoplasmic signal from out-of-focus nuclear signal.

• Quantification approach: When quantifying subcellular distribution, use nuclear/cytoplasmic ratio measurements rather than binary classification, as HNRNPA3 shuttles between compartments .

Researchers have noted significant variability in nuclear HNRNPA3 staining intensity across samples, which may represent either technical variables or physiological/pathological changes in protein levels .

How is HNRNPA3 implicated in C9orf72 repeat expansion disorders, and what methodologies best detect its interactions with dipeptide repeat proteins?

HNRNPA3 plays a critical role in C9orf72 repeat expansion disorders through several mechanisms:

• Direct binding to G4C2 repeats: HNRNPA3 binds specifically to the G4C2 sequence in pull-down assays .

• Regulation of repeat RNA levels: Knockdown of HNRNPA3 significantly increases G4C2 repeat RNA levels by approximately 2-fold, while overexpression decreases repeat RNA .

• Modulation of dipeptide repeat (DPR) protein production: Reduced HNRNPA3 leads to enhanced generation of poly-GA, poly-GP, and poly-GR proteins, with poly-GA being the most abundant .

• Co-localization with DPR inclusions: HNRNPA3 immunoreactivity is found in a subset of p62-positive inclusions containing DPRs, particularly in hippocampal dentate gyrus granule cells and cerebellar neurons .

Methodologies for studying HNRNPA3-DPR interactions:

• For RNA binding studies: RNA immunoprecipitation followed by qPCR using specific primers for the repeat region .

• For DPR quantification: Western blotting with DPR-specific antibodies and filter trap assays to detect insoluble aggregates .

• For co-localization studies: Double immunofluorescence staining with the Sigma HNRNPA3 antibody and poly-GA antibodies, as the Santa Cruz antibody has shown inconsistent results in pathological tissues .

• For patient-derived samples: RNA fluorescence in situ hybridization (FISH) to detect foci formation, which increases ~2-fold upon HNRNPA3 knockdown .

Notably, semi-quantitative analysis has revealed that HNRNPA3 immunoreactive inclusions are significantly fewer than those detected by p62 immunostaining, suggesting that only a subset of DPR inclusions contain detectable HNRNPA3 .

What is the role of HNRNPA3 in cancer biology, and how can researchers investigate its functional mechanisms?

HNRNPA3 has emerged as a significant player in cancer biology through multiple mechanisms:

• Expression patterns: HNRNPA3 shows aberrant expression in various cancers. While specific cancer-related expression data for HNRNPA3 is limited in the provided search results, other hnRNP A/B family members like hnRNPA1 are overexpressed in 76% of non-small cell lung cancers and correlate with poor prognosis .

• Molecular mechanisms: HNRNPA3 affects cancer progression through:

  • RNA splicing regulation of cancer-related genes

  • Post-transcriptional regulation of gene expression

  • Potential involvement in exosome loading and intercellular communication

Methodological approaches for investigating HNRNPA3 in cancer:

• Expression analysis: Western blot, IHC of tissue microarrays, and qRT-PCR to compare HNRNPA3 levels between tumor and normal tissues.

• Functional studies: siRNA/shRNA knockdown or CRISPR/Cas9 knockout followed by proliferation, migration, and invasion assays.

• Binding partner identification: RNA immunoprecipitation sequencing (RIP-seq) to identify cancer-related RNA targets.

• Splicing analysis: RT-PCR with exon-spanning primers to detect alternative splicing events regulated by HNRNPA3.

• In vivo models: Xenograft models with HNRNPA3 modulation to assess tumor growth and metastasis.

The methodological challenge lies in distinguishing HNRNPA3-specific effects from those of other highly homologous hnRNP family members. Using highly specific antibodies and careful validation of knockdown specificity is crucial for accurate interpretation of results .

How does HNRNPA3 function in viral infection models, and what experimental systems best capture its antiviral properties?

Recent research has revealed HNRNPA3's role in viral infections, particularly with PEDV (Porcine Epidemic Diarrhea Virus):

• Antiviral effects: HNRNPA3 demonstrates antiviral properties against PEDV infection, with reduced HNRNPA3 expression enhancing viral replication .

• Regulatory mechanisms: PEDV can inhibit HNRNPA3 expression through miR-218-5p to enhance its own replication .

Experimental systems and methodologies to study HNRNPA3 in viral infections:

• Cell culture models: Vero E6 cells and intestinal epithelial cell lines for PEDV infection studies.

• Expression modulation: Overexpression and knockdown experiments using plasmids and siRNAs targeting HNRNPA3.

• Viral replication assays: qPCR for viral RNA, plaque assays for infectious virus quantification, and immunofluorescence for viral protein detection.

• miRNA regulation studies: Luciferase reporter assays with HNRNPA3 3'UTR constructs to validate miRNA targeting.

• Lipid metabolism connection: Analysis of lipid droplet formation and SREBF1 pathway activity using Oil Red O staining and qPCR for lipid metabolism genes .

Since PEDV induces lipid accumulation through activation of SREBF1, and HNRNPA3 appears to counteract this process, researchers studying HNRNPA3's antiviral effects should incorporate lipid metabolism analyses into their experimental design .

Why might researchers observe variability in HNRNPA3 nuclear staining intensity across samples, and how can this be addressed?

Variable nuclear staining of HNRNPA3 is a commonly reported issue that can be addressed through careful methodological considerations:

• Observed phenomenon: Studies report highly variable HNRNPA3 nuclear staining, with some nuclei densely staining while others remain unstained, even within the same tissue section .

• Potential causes:

  • Technical factors: Fixation time variations, antigen retrieval efficiency, antibody batch variation

  • Biological factors: Cell cycle-dependent expression, stress responses, disease-specific alterations

  • Protein modifications: Post-translational modifications affecting epitope accessibility

• Methodological solutions:

  • Standardize fixation: Maintain consistent fixation times (8-12 hours in 10% neutral buffered formalin)

  • Optimize antigen retrieval: Use a gradient of retrieval times (10-30 minutes) to determine optimal conditions for each batch

  • Antibody validation: Test multiple antibodies – notably, studies have found that while some samples show no staining with Santa Cruz HNRNPA3 antibody, the Sigma antibody shows variable nuclear staining in the same samples

  • Positive controls: Include tissues known to consistently express HNRNPA3 (like Jurkat cells) in each staining batch

  • Quantification approach: Use integrated optical density measurements rather than positive/negative scoring

• Internal control: Nuclear staining for hnRNP A1 and A2/B1 remains consistent even in samples with variable HNRNPA3 staining, suggesting this variability is specific to HNRNPA3 rather than a general fixation issue .

The challenge of variable nuclear staining illustrates the importance of methodology standardization when working with HNRNPA3 antibodies for comparative studies.

What strategies can resolve cross-reactivity issues when working with HNRNPA3 antibodies in tissues expressing multiple hnRNP family members?

The high sequence homology between hnRNP family members presents challenges for antibody specificity. Researchers can address potential cross-reactivity through these methodological approaches:

• Epitope selection verification:

  • Review the immunogen information - antibodies raised against N-terminal regions (such as ABIN202382) target more unique sequences

  • Antibodies using fusion proteins as immunogens (like 25142-1-AP) may have different specificity profiles

• Validation experiments:

  • Knockout/knockdown controls: Use siRNA knockdown of HNRNPA3 alongside siRNAs for HNRNPA1 and HNRNPA2/B1 to confirm antibody specificity

  • Peptide competition assays: Pre-incubate antibody with immunizing peptide to confirm signal specificity

  • Western blot assessment: Verify that the antibody detects a single band at the expected molecular weight (37-40 kDa)

• Application-specific adjustments:

  • For Western blot: Increase washing times and use higher dilutions (1:1000-1:2000)

  • For IHC/IF: Implement additional blocking steps with 5% BSA and normal serum

  • For IP experiments: Perform stringent washes with higher salt concentrations

• Alternative detection methods:

  • RNA-binding protein immunoprecipitation: Focus on bound RNA profiles which differ between hnRNP family members

  • Mass spectrometry validation: Confirm protein identity in immunoprecipitated samples

It's worth noting that studies examining multiple hnRNP proteins found that while hnRNPA1, A2/B1, and A3 all bind to G4C2 sequences in pull-down assays, only hnRNPA3 co-localizes with dipeptide repeat protein inclusions in C9orf72 expansion cases, suggesting functional differences despite structural similarities .

How can researchers optimize detection of HNRNPA3 in aggregates or inclusions in neurodegenerative disease tissues?

Detecting HNRNPA3 in pathological inclusions presents unique challenges requiring specific methodological approaches:

• Antibody selection is critical:

  • The Santa Cruz HNRNPA3 antibody has shown poor results in detecting inclusions across multiple studies

  • The Sigma HNRNPA3 antibody has successfully detected HNRNPA3 in a subset of p62-positive inclusions in C9orf72 expansion cases

• Tissue processing optimization:

  • Fixation: Limit fixation time to preserve epitope accessibility in aggregates

  • Antigen retrieval: Extended retrieval (30 minutes) in TE buffer pH 9.0 has shown superior results compared to citrate buffer pH 6.0

  • Section thickness: Use thinner sections (5-6 μm) for better penetration

• Detection enhancement strategies:

  • Signal amplification: Implement tyramide signal amplification for weak signals

  • Co-staining approach: Always perform double immunofluorescence with p62 or poly-GA antibodies as reference markers

  • Sequential staining: When antibodies are from the same species, use sequential staining with complete blocking between steps

• Quantification considerations:

  • Expected distribution: HNRNPA3-positive inclusions are most common in dentate gyrus granule cells, less frequent in CA4 neurons, and rare in cerebellum

  • Comparative quantification: Always compare with p62 staining, as only a subset of p62-positive inclusions contain detectable HNRNPA3

  • Semi-quantitative scale: Use a 0-3 scale (0=none, 1=rare, 2=occasional, 3=common) for each region separately

• Controls and validation:

  • Include known positive cases (C9orf72 expansion carriers with confirmed inclusions)

  • Perform Western blot of sarkosyl-insoluble fractions to confirm aggregate presence

What new methodologies might improve understanding of HNRNPA3's role in RNA metabolism and disease pathogenesis?

Several emerging methodologies hold promise for advancing HNRNPA3 research:

• Advanced RNA-protein interaction studies:

  • CLIP-seq (Cross-linking immunoprecipitation followed by sequencing) to identify direct RNA targets of HNRNPA3 in disease-relevant tissues

  • RNA pull-down assays coupled with mass spectrometry to identify HNRNPA3-associated protein complexes on specific RNA targets

  • Single-molecule imaging of HNRNPA3-RNA interactions in living cells

• Structural biology approaches:

  • Cryo-EM structures of HNRNPA3 bound to disease-relevant RNA repeats

  • NMR studies of the dynamics between RRM domains and their interactions with RNA targets

  • In silico modeling of HNRNPA3 phase separation properties

• Disease modeling improvements:

  • Patient-derived iPSC neurons expressing fluorescently tagged HNRNPA3 to track its dynamics in disease states

  • CRISPR-edited mice with humanized HNRNPA3 and disease-relevant mutations

  • Organoid models combining multiple cell types to study HNRNPA3's role in tissue-specific pathology

• Therapeutic targeting strategies:

  • Small molecule screens to identify compounds that stabilize HNRNPA3's RNA binding in disease states

  • Antisense oligonucleotides targeting specific HNRNPA3 interactions

  • RNA aptamer development to modulate HNRNPA3 activity in specific cellular compartments

Current research methods have revealed HNRNPA3's role in regulating C9orf72 repeat RNA levels and dipeptide repeat protein production , but more sophisticated approaches are needed to understand how HNRNPA3 dysfunction contributes to disease progression and whether it represents a viable therapeutic target.

How do post-translational modifications affect HNRNPA3 function, and what techniques best characterize these modifications?

Post-translational modifications (PTMs) of HNRNPA3 likely play crucial roles in regulating its function, though specific data on HNRNPA3 PTMs is limited in the provided search results. Based on studies of related hnRNP family members:

• Types of relevant PTMs:

  • Phosphorylation: Studies of hnRNPA1 have shown that phosphorylation by S6K2 affects RNA binding

  • Methylation: PRMT3-mediated methylation influences the RNA binding activity of hnRNPA1

  • Acetylation: ESCO2-mediated acetylation affects hnRNPA1 localization and its impact on alternative splicing

  • Ubiquitylation: SPSB1-induced ubiquitylation influences hnRNPA1 function

• Methodological approaches for PTM analysis:

  • Phosphorylation mapping: Phos-tag gels followed by Western blotting to detect mobility shifts

  • Mass spectrometry: Tandem MS/MS with phospho-enrichment strategies (TiO2, IMAC)

  • Site-specific antibodies: Generate phospho-specific or methyl-specific antibodies against predicted HNRNPA3 modification sites

  • In vitro enzyme assays: Reconstitution of PTM reactions with purified kinases, methyltransferases, etc.

  • Mutational analysis: Site-directed mutagenesis of predicted PTM sites followed by functional assays

• PTM dynamics in disease states:

  • Compare PTM profiles between normal and disease tissues using quantitative proteomics

  • Investigate stress-induced changes in PTM patterns using cellular stress models

  • Examine PTM interplay with protein localization in neurodegenerative disease models