STRBP Antibody

What is STRBP and why is it studied in research?

STRBP (spermatid perinuclear RNA binding protein) is a 74 kDa protein involved in spermatogenesis, sperm function, and cell growth regulation. It contains a domain associated with zinc fingers (DZF domain) and two double-stranded RNA-binding domains (dsRBD), enabling it to bind to double-stranded DNA and RNA . STRBP has gained increased research attention after being identified as a novel JAK2 fusion partner gene in Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL), suggesting its potential role in oncogenesis . Research on STRBP spans reproductive biology, RNA processing, and cancer biology, making antibodies against this protein valuable tools across multiple disciplines.

STRBP antibodies have demonstrated reactivity across multiple species and sample types:

Some antibodies show broader cross-reactivity across species including rabbit, guinea pig, bat, dog, hamster, and monkey . Researchers should verify compatibility with their specific experimental system before proceeding with extensive studies.

How can I detect the STRBP-JAK2 fusion protein in Ph-like ALL samples?

Detection of the STRBP-JAK2 fusion protein in Ph-like ALL samples requires a multi-modal approach:

• FISH Analysis: Use commercial FISH probes covering Ph-like ALL markers, including JAK2. A positive rearrangement is typically reported when at least 3% of nuclei show break-apart split signals .

• RNA Sequencing: Prepare RNA-sequencing libraries from diagnostic bone marrow samples using appropriate kits (e.g., TruSight RNA Fusion Panel). Analyze reads using alignment tools like STAR against the human reference genome .

• RT-PCR Validation: Design nested RT-PCR with primers specific to STRBP exon 18 and JAK2 exon 19. The STRBP-JAK2 fusion yields a 262bp band that can be confirmed via Sanger sequencing .

• Western Blot Analysis: Use antibodies against the JAK2 kinase domain to detect both wild-type and fusion proteins, with the fusion protein showing a different molecular weight pattern .

The STRBP-JAK2 fusion contains the 5′ STRBP region (including DZF and dsRBD domains) and the 3′ JAK2 region with an intact protein kinase domain (JH1), resulting in constitutive activation of JAK-STAT signaling .

What are the technical considerations for optimizing immunohistochemistry with STRBP antibodies?

Optimizing IHC with STRBP antibodies requires attention to several critical parameters:

• Antigen Retrieval Method: Most validated protocols recommend heat-mediated antigen retrieval with Tris-EDTA buffer (pH 9.0), though citrate buffer (pH 6.0) can be used as an alternative .

• Antibody Dilution Range: Start with a 1:200 dilution for most commercial antibodies and adjust based on signal intensity and background. The optimal range is typically 1:50-1:500 .

• Tissue-Specific Considerations: STRBP shows variable expression across tissues. Positive IHC has been documented in human stomach tissue and ovarian cancer tissue . For reproductive tissues, background staining may be more prominent due to high endogenous expression.

• Blocking Strategy: Use 5-10% normal serum from the species in which the secondary antibody was raised, supplemented with 1% BSA to minimize non-specific binding.

• Controls: Include positive controls (tissues known to express STRBP, such as testis or ovary) and negative controls (primary antibody omission) in each experimental run .

How does the structure of STRBP contribute to its function in the STRBP-JAK2 fusion?

The structural elements of STRBP play crucial roles in the oncogenic function of the STRBP-JAK2 fusion:

• Domain Architecture: STRBP contains a domain associated with zinc fingers (DZF domain) and two double-stranded RNA-binding domains (dsRBD). In the STRBP-JAK2 fusion, these domains from STRBP are joined to the JAK2 kinase domain .

• Oligomerization Function: The DZF and dsRBD domains of STRBP promote protein oligomerization, which is critical in the fusion context. When joined to JAK2, these domains drive STRBP-JAK2 homodimerization .

• Activation Mechanism: The homodimerization leads to auto- and trans-phosphorylation within the activation loop of the JAK2-JH1 domain, resulting in constitutive activation of JAK-STAT signaling pathways that promote cell proliferation and survival .

• Chromosomal Origin: Both JAK2 and STRBP are located on chromosome 9, suggesting that the STRBP-JAK2 fusion may result from an inversion of chromosome 9, either inv(9)(p24q33) or t(9;9)(p24;q33) .

Understanding this structure-function relationship has implications for therapeutic targeting, as standard JAK2 inhibitors like ruxolitinib may have limited efficacy against this fusion protein .

What is the optimal protocol for Western blot detection of STRBP?

The optimal Western blot protocol for STRBP detection includes:

• Sample Preparation:

  • Lyse cells in RIPA buffer supplemented with protease inhibitors

  • Use 20-30 μg of total protein for detection of endogenous STRBP

• Gel Electrophoresis:

  • 7.5-10% SDS-PAGE is recommended due to STRBP's 74 kDa size

  • Include positive control lysates (HeLa cells, PC-3 cells, or testis tissue)

• Antibody Selection and Dilution:

  • Primary antibody: Use at 1:1000-1:5000 dilution (optimize for each antibody)

  • Incubation: Overnight at 4°C or 1.5 hours at room temperature

• Detection:

  • Expected band size: 74 kDa for wild-type STRBP

  • Alternative isoforms may produce additional bands

  • For fusion proteins, expect altered molecular weights

• Validation Controls:

  • Knockdown/knockout samples can confirm antibody specificity

  • Blocking peptides can verify target-specific binding

This protocol has been validated with multiple commercial antibodies including 17362-1-AP, ab111567, and ab237682 .

How can I properly design experiments to study STRBP's RNA-binding properties?

Designing experiments to study STRBP's RNA-binding properties requires multiple complementary approaches:

• RNA Immunoprecipitation (RIP):

  • Crosslink protein-RNA complexes using UV or formaldehyde

  • Immunoprecipitate STRBP using validated antibodies (e.g., 17362-1-AP at 4 μg per 4 mg lysate)

  • Extract and analyze bound RNAs through sequencing or qPCR

  • Include IgG controls and input samples for normalization

• Electrophoretic Mobility Shift Assay (EMSA):

  • Generate labeled RNA probes (poly(I:C), poly(G), or target-specific sequences)

  • Incubate with recombinant STRBP or cell extracts

  • Analyze mobility shifts to assess binding

  • Include competition assays with unlabeled RNA to confirm specificity

• Domain Mutation Analysis:

  • Generate constructs with mutations in the dsRBD domains

  • Compare binding affinity to wild-type protein

  • Correlate structural changes with functional consequences

• Binding Preference Analysis:

  • STRBP binds most efficiently to poly(I:C) RNA compared to poly(dI:dC) DNA

  • It also binds to single-stranded poly(G) RNA

  • Design experiments to test specific RNA structures and sequences

Remember that STRBP binds non-specifically to some RNAs, including mRNA PRM1 3'-UTR and adenovirus VA RNA, which should be considered when interpreting results .

What methodological approaches are best for studying the STRBP-JAK2 fusion in patient samples?

Studying the STRBP-JAK2 fusion in patient samples requires a comprehensive methodological approach:

• Sample Collection and Processing:

  • Collect bone marrow aspirates or peripheral blood samples

  • Process within 24 hours to maintain RNA integrity

  • Store viable cells in liquid nitrogen for functional studies

• Diagnostic Identification:

  • Screen Ph-like ALL patients using FISH with JAK2 break-apart probes

  • Perform RNA-sequencing with fusion-detection algorithms

  • Confirm using nested RT-PCR with primers spanning the fusion junction

• Functional Characterization:

  • Establish patient-derived xenografts (PDX) to maintain the fusion in vivo

  • Create cell line models expressing the fusion protein

  • Test drug sensitivity (JAK inhibitors, conventional chemotherapy)

  • Assess signaling pathway activation (phospho-STAT analysis)

• Treatment Response Monitoring:

  • Track minimal residual disease using patient-specific PCR primers

  • Monitor fusion protein levels before and after therapy

  • Correlate genetic findings with clinical outcomes

• Retrospective Cohort Analysis:

  • Screen archived Ph-like ALL samples for this fusion

  • Correlate presence with clinical features and outcomes

  • Compare to other JAK2 fusion patients

This approach successfully identified the STRBP-JAK2 fusion in a patient who proved resistant to standard induction chemotherapy and ruxolitinib but achieved complete remission after CAR T-cell therapy, allogenic stem cell transplantation, and donor lymphocyte infusion .

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

Non-specific binding is a common challenge with STRBP antibodies that can be addressed through several optimization strategies:

• Antibody Selection:

  • Choose affinity-purified antibodies (most commercial STRBP antibodies undergo antigen affinity purification)

  • Verify the immunogen used (antibodies raised against specific domains may reduce cross-reactivity)

  • Consider antibodies validated for your specific application

• Blocking Optimization:

  • Increase blocking agent concentration (5-10% normal serum or BSA)

  • Extend blocking time (1-2 hours at room temperature)

  • Try alternative blocking agents (casein, fish gelatin) if persistent issues occur

• Washing Protocols:

  • Increase washing stringency (0.1-0.3% Tween-20 in PBS)

  • Extend washing duration (5 washes of 5 minutes each)

  • Use TBS instead of PBS for phospho-specific applications

• Antibody Dilution:

  • Titrate antibody across a broader range (1:500-1:5000)

  • Prepare antibodies in blocking solution to reduce non-specific binding

• Sample-Specific Considerations:

  • Pre-adsorb antibodies against tissues from knockout models when available

  • For reproductive tissues with high endogenous expression, include additional controls

  • Consider antigen competition assays to confirm specificity

These approaches have successfully reduced non-specific binding in applications ranging from Western blot to immunohistochemistry with various commercially available STRBP antibodies .

What controls should be included when validating a new STRBP antibody?

Comprehensive validation of a new STRBP antibody requires multiple controls:

• Positive Controls:

  • Tissues/cells known to express STRBP (testis, ovary, HeLa cells, PC-3 cells)

  • Recombinant STRBP protein (full-length or domain-specific)

  • Overexpression systems with tagged STRBP constructs

• Negative Controls:

  • STRBP knockout/knockdown samples when available

  • Tissues known to have minimal STRBP expression

  • Primary antibody omission controls

  • Isotype controls (same species and isotype as primary antibody)

• Specificity Controls:

  • Peptide competition/blocking experiments using the immunizing peptide

  • Multiple antibodies targeting different epitopes of STRBP

  • Western blot confirmation of correct molecular weight (74 kDa)

• Application-Specific Controls:

  • For IHC: Adjacent tissue sections with primary antibody omission

  • For IF: Secondary antibody-only controls

  • For IP: Non-specific IgG precipitation controls

  • For WB: Ladder markers flanking the expected band size

• Cross-Reactivity Assessment:

  • Test across multiple species if cross-reactivity is claimed

  • Evaluate closely related protein family members

Following this validation protocol ensures that observed signals are specific to STRBP rather than experimental artifacts or cross-reactivity with other proteins .

How does the discovery of STRBP-JAK2 fusion impact therapeutic approaches for Ph-like ALL?

The discovery of the STRBP-JAK2 fusion has several important implications for therapeutic approaches in Ph-like ALL:

• Targeted Therapy Limitations:
  The reported STRBP-JAK2 fusion case demonstrated resistance to the JAK2 inhibitor ruxolitinib, suggesting that not all JAK2 fusions respond equally to targeted inhibition . This resistance may be due to the specific structural properties of the fusion, particularly the oligomerization domains from STRBP.

• Cellular Immunotherapy Efficacy:
  CAR T-cell therapy proved effective in achieving initial remission in the STRBP-JAK2 fusion patient, highlighting the potential of immunotherapy approaches when targeted therapies fail . This suggests a treatment algorithm where JAK2 inhibitor-resistant patients may be directed to immunotherapy earlier.

• Combination Therapy Approach:
  The successful treatment regimen involved a sequential approach of CAR T-cell therapy, allogeneic stem cell transplantation, and donor lymphocyte infusion . This multi-modal strategy may be necessary for patients with similar gene fusions.

• Diagnostic Implications:
  The discovery necessitates expanding diagnostic screening for JAK2 fusions beyond commonly known partners. FISH analysis with JAK2 break-apart probes appears to be an effective screening tool, followed by RNA sequencing for precise fusion characterization .

• Mechanistic Insights for Drug Development:
  Understanding the structural basis of ruxolitinib resistance in STRBP-JAK2 fusion could guide development of next-generation JAK inhibitors specifically designed to overcome resistance mechanisms related to dimerization domains .

This case highlights the importance of comprehensive molecular profiling in Ph-like ALL to guide personalized treatment approaches and the need for alternative strategies when standard targeted therapies fail .

What are the emerging methodologies for studying STRBP interactions with RNA and microtubules?

Emerging methodologies for studying STRBP's dual functionality in RNA binding and microtubule association include:

• Advanced RNA-Protein Interaction Techniques:

  • CLIP-seq (Cross-linking immunoprecipitation followed by sequencing) using STRBP-specific antibodies

  • RNA Bind-n-Seq for quantitative analysis of RNA sequence preferences

  • RNA-protein structural studies using cryo-electron microscopy

  • Proximity labeling approaches (BioID or APEX) to identify RNA-binding partners in living cells

• Microtubule Association Analysis:

  • Super-resolution microscopy (STORM, PALM) to visualize STRBP-microtubule interactions

  • Live-cell imaging with fluorescently tagged STRBP to track dynamic associations

  • In vitro reconstitution assays with purified components to define direct interactions

  • Domain mapping to identify specific regions mediating microtubule binding

• Integrative Approaches:

  • Simultaneous visualization of RNA and microtubule interactions using multi-color imaging

  • Quantitative proteomics to identify interaction partners in different cellular compartments

  • Structure-function studies correlating STRBP domains with specific cellular functions

  • Computational modeling of domain interactions based on structural data

• Functional Assessment Tools:

  • CRISPR-Cas9 genome editing to create domain-specific mutations

  • Optogenetic approaches to spatiotemporally control STRBP activity

  • Small molecule screening to identify inhibitors of specific STRBP functions

  • Patient-derived models to study pathological alterations in STRBP function

These methodologies can help elucidate how STRBP coordinates its RNA binding and cytoskeletal functions, particularly in contexts like spermatogenesis where both roles may be critical .

How can researchers distinguish between the two reported STRBP isoforms in experimental systems?

Distinguishing between the two reported STRBP isoforms requires a combination of specific techniques:

• Molecular Weight Discrimination:

  • High-resolution SDS-PAGE (7.5-10%) can separate the isoforms based on size differences

  • Use gradient gels for better resolution of closely migrating bands

  • Western blot with antibodies targeting shared epitopes will detect both isoforms

• Isoform-Specific Detection:

  • Design PCR primers spanning alternative splice junctions for transcript identification

  • Develop custom antibodies against unique epitopes present in only one isoform

  • Use domain-specific antibodies that may preferentially detect one isoform based on epitope accessibility

• Expression Pattern Analysis:

  • Examine tissue-specific expression patterns, as isoforms may show differential tissue distribution

  • Analyze subcellular localization, which may differ between isoforms

  • Study temporal expression during developmental processes like spermatogenesis

• Functional Differentiation:

  • Perform isoform-specific knockdown experiments using targeted siRNAs

  • Create isoform-specific expression constructs for complementation studies

  • Assess binding partners unique to each isoform through co-immunoprecipitation

• Mass Spectrometry Approaches:

  • Use targeted proteomics to identify unique peptides from each isoform

  • Perform post-translational modification analysis, which may differ between isoforms

  • Implement top-down proteomics for intact protein analysis

By combining these approaches, researchers can effectively distinguish and characterize the specific roles of each STRBP isoform in various cellular contexts .