SHARPIN Antibody

What is SHARPIN and what are its primary cellular functions relevant to antibody-based detection?

SHARPIN (SHANK-associated RH domain interactor) is a highly conserved protein that functions as a critical component of the Linear Ubiquitin Assembly Complex (LUBAC), along with HOIP and HOIL-1. This complex plays essential roles in regulating immune responses through NF-κB signaling pathways . SHARPIN contains multiple functional domains including an N-terminal coiled-coil (CC) domain that mediates interaction with scaffold protein SHANK, a ubiquitin-like domain (UBL), and an NPL4 zinc finger domain (NZF) that facilitate ubiquitin-mediated protein recognition and degradation .

Beyond its role in LUBAC and immune regulation, SHARPIN has been identified as:

• A modulator of β1-integrin activation in cell adhesion processes

• A participant in lamellipodium formation through interaction with the Arp2/3 complex

• A protein enriched in postsynaptic density of neurons

Understanding these diverse functions is crucial when selecting appropriate antibodies and designing experiments to study specific SHARPIN-mediated processes.

Which cell lines and tissues are reliable positive controls for SHARPIN antibody validation?

Based on extensive validation data, SHARPIN is reliably detected in the following:

Cell Lines:

Tissues:

• Human lymphoma tissue (IHC)

• Human small intestine tissue (IHC)

• Human ovary (IHC)

• Mouse brain tissue (WB)

• Mouse skeletal muscle tissue (WB)

These validated samples provide crucial positive controls for experimental design and antibody validation.

What are the expected molecular weights for SHARPIN detection in Western blot applications?

SHARPIN is consistently detected at 40-43 kDa in Western blot applications across multiple validated antibodies . While the calculated molecular weight is 40 kDa, researchers should be aware that the observed molecular weight may vary slightly due to post-translational modifications or experimental conditions. SHARPIN has two isoforms produced by alternative splicing, which could potentially be detected as distinct bands in some experimental systems .

What are the optimal conditions for Western blot detection of SHARPIN?

Based on validated protocols, the following conditions are recommended for optimal SHARPIN detection by Western blot:

It is strongly recommended that researchers titrate antibody concentrations in their specific testing systems to obtain optimal results, as the appropriate dilution can be sample-dependent .

How should SHARPIN antibodies be optimized for immunohistochemistry applications?

For successful immunohistochemical detection of SHARPIN in tissue sections:

Note that specific antigen retrieval methods significantly impact staining quality. The choice between TE buffer pH 9.0 and citrate buffer pH 6.0 should be empirically determined for each specific tissue type .

What methodological approaches are needed to study SHARPIN's interactions with LUBAC components?

To effectively investigate SHARPIN's role within the LUBAC complex:

• Co-immunoprecipitation protocols:

  • Use 0.5-4.0 μg of SHARPIN antibody for 1.0-3.0 mg of total protein lysate

  • Include controls for HOIP and HOIL-1 detection

  • Consider gentle lysis conditions to preserve protein-protein interactions

• Functional analysis:

  • Examine NF-κB pathway activation following TNF stimulation

  • Monitor IκBα phosphorylation as a readout of canonical NF-κB activation

  • Compare with CD3-induced non-canonical NF-κB activation (which remains unchanged in SHARPIN deficiency)

• Rescue experiments:

  • Re-expression of wild-type SHARPIN can restore HOIP expression in SHARPIN-deficient cells

  • Test UBL domain mutants that fail to interact with HOIP

Research demonstrates that SHARPIN deficiency leads to reduced HOIP expression and impaired recruitment to HOIL-1, highlighting the interdependence within the LUBAC complex .

How can researchers distinguish between SHARPIN's LUBAC-dependent and LUBAC-independent functions?

SHARPIN has both LUBAC-dependent and independent cellular roles, which presents challenges for data interpretation. Several approaches can help differentiate these functions:

• Parallel analysis of LUBAC components:

  • Compare phenotypes between SHARPIN deficiency and HOIP/HOIL-1 deficiency

  • Examine whether a particular cellular response is affected by all LUBAC components or only SHARPIN

• Domain-specific mutations:

  • Use cells expressing SHARPIN variants lacking the UBL domain (prevents HOIP interaction)

  • Test whether a particular SHARPIN function persists in the absence of LUBAC integration

• Pathway-specific readouts:

  • For LUBAC function: Monitor linear ubiquitination and canonical NF-κB activation

  • For integrin regulation: Assess cell adhesion and focal adhesion kinase (FAK) phosphorylation

  • For lamellipodium formation: Analyze Arp2/3 complex activity

Research shows that while NF-κB activation requires SHARPIN's LUBAC function, other roles may be LUBAC-independent .

What controls are essential when using SHARPIN antibodies in knockdown/knockout studies?

When using SHARPIN antibodies in gene silencing experiments, the following controls are critical:

• Validation of knockdown efficiency:

  • Western blot with SHARPIN antibody targeting different epitopes than those potentially affected by the modification

  • qRT-PCR to confirm mRNA reduction (important since some SHARPIN variants may show reduced mRNA but no protein)

• Specificity controls:

  • Include non-targeting siRNA controls

  • Use multiple independent siRNAs targeting different regions of SHARPIN

• Rescue experiments:

  • Re-express siRNA-resistant SHARPIN to confirm phenotype specificity

  • Include domain mutants to map functional regions

• Pathway controls:

  • Monitor effects on known SHARPIN-dependent pathways (e.g., NF-κB activation)

  • Assess consequences on LUBAC complex formation

Published studies have utilized validated siRNA approaches such as those targeting hamster SHARPIN (sequences: 5′-GCACUGGUACGAGAUGCUATT-3′/5′-UAGCAUCUCGUACCAGUGCTT-3′) and mouse SHARPIN (sequences: 5′-GCGGAAGCUGCAAUUGAUATT-3′/5′-UAUCAAUUGCAGCUUCCGCTT-3′) .

How can SHARPIN antibodies be used to investigate its role in inflammatory conditions?

SHARPIN deficiency in humans causes autoinflammatory disease with distinct features from the dermatitis observed in SHARPIN-deficient mice. Antibody-based approaches to study SHARPIN in inflammation include:

• Analysis of inflammatory tissues:

  • Use immunohistochemistry to examine SHARPIN expression in inflamed joints and tissues

  • Co-stain with neutrophil markers to correlate with inflammatory cell infiltration

• Cytokine profiling:

  • Correlate SHARPIN detection with inflammatory cytokines (IL-6, IL-8, CXCL1, CCL3)

  • Study TNF-dependent inflammation through SHARPIN-TNF relationships

• Therapeutic response monitoring:

  • Track SHARPIN expression and localization following anti-TNF therapy

  • Correlate with clinical and transcriptomic resolution of inflammation

• Cell death pathways:

  • Use SHARPIN antibodies alongside markers of cell death to examine relationships between SHARPIN deficiency and cell death-mediated inflammation

Research demonstrates that SHARPIN-deficient patients show elevated IL-6 and neutrophil chemotactic proteins in synovial fluid, with anti-TNF therapy leading to complete resolution of inflammation .

What methodological approaches allow investigation of SHARPIN's role in integrin regulation?

To study SHARPIN's functions in integrin regulation:

• Direct binding studies:

  • NMR spectroscopy and SPR (Surface Plasmon Resonance) with purified proteins

  • Analyze binding between SHARPIN and integrin β cytoplasmic tails

• Structural analysis:

  • Map the interaction domains using purified protein fragments

  • Combine with antibody epitope information to select non-interfering antibodies

• Functional assays:

  • Flow cytometry with activation-specific antibodies (e.g., PAC1, 9EG7, 7E2)

  • Combine SHARPIN knockdown with integrin activity measurements

• Downstream signaling:

  • Monitor FAK and phospho-FAK levels in SHARPIN-manipulated cells

  • Correlate with integrin-dependent cell adhesion

Research has shown that SHARPIN interacts with integrin β cytoplasmic tails, though the functional significance of this interaction may be context-dependent .

How can researchers utilize SHARPIN antibodies to examine its emerging roles in neuro-immunological processes?

Given SHARPIN's dual roles in neuronal function and immune regulation, specialized approaches are needed:

• Co-localization studies in neural tissues:

  • Examine SHARPIN localization with postsynaptic markers (SHANK)

  • Correlate with immune markers in neuroinflammatory conditions

• Neuronal-immune interface:

  • Use SHARPIN antibodies in co-culture systems of neurons and immune cells

  • Track SHARPIN expression changes during neuroinflammation

• Specialized neural techniques:

  • Combine with electrophysiology to correlate SHARPIN levels with synaptic function

  • Utilize microdissection followed by immunoblotting to study SHARPIN in specific neural circuits

• In vivo models:

  • Generate conditional knockout models to eliminate SHARPIN in specific neural populations

  • Use SHARPIN antibodies to validate knockout efficiency in target tissues

SHARPIN's enrichment in postsynaptic density and its complex formation with SHANK in heterologous cells and brain tissue suggest important neuronal functions alongside its established immune roles .