SMTNL2 Antibody

What is SMTNL2 and what cellular functions has it been associated with?

SMTNL2 (Smoothelin-like 2) is a 50-52 kDa protein belonging to the smoothelin family. It contains a calponin-homology (CH) domain and functions as an actin-binding protein . SMTNL2 is predicted to be involved in actin cytoskeleton organization and positive regulation of vasoconstriction . Research has identified it as a substrate of the c-Jun N-terminal kinase (JNK) family of MAPKs, containing a specific JNK-docking site (D-site) at residues 180-193 that enables high-affinity binding to multiple MAPKs including JNK1-3 and ERK2 . SMTNL2 protein expression has been detected in numerous mammalian tissues, with notably high expression in skeletal muscle . Its expression is strongly induced during myoblast to myotube transition in differentiating C2C12 cells, suggesting a potential role in muscle differentiation .

What applications are SMTNL2 antibodies commonly used for in laboratory research?

SMTNL2 antibodies have been validated for several key applications:

• Western Blot (WB): Used at dilutions ranging from 1:500-1:3000

• Immunoprecipitation (IP): Typically using 0.5-4.0 μg for 1.0-3.0 mg of total protein lysate

• Immunofluorescence (IF)/Immunocytochemistry (ICC): Used at dilutions of 1:50-1:500

• ELISA: Various dilutions depending on the specific antibody

When designing experiments, researchers should consider that SMTNL2 is typically detected at approximately 50 kDa in Western blots, though some antibodies report observed molecular weights of 68-70 kDa , likely due to post-translational modifications.

What are the common positive controls for validating SMTNL2 antibody specificity?

Based on validation data from multiple sources, the following cell lines and tissues have shown reliable SMTNL2 expression and can be used as positive controls:

• Cell lines: MCF-7, COLO 320, Caco-2, HepG2, SGC-7901, and U2OS cells

• Tissues: Mouse small intestine tissue

For Western blot experiments, loading 30 μg of sample under reducing conditions typically provides sufficient signal for detection . Flow cytometry analysis has been successfully performed using MCF-7 cells fixed with 4% paraformaldehyde and permeabilized prior to staining .

What are the optimal conditions for Western blot detection of SMTNL2?

For optimal Western blot detection of SMTNL2:

• Sample preparation: Use 30 μg of protein lysate under reducing conditions

• Gel electrophoresis: Run on 5-20% SDS-PAGE at 70V (stacking gel) followed by 90V (resolving gel) for 2-3 hours

• Transfer: Transfer proteins to nitrocellulose membrane at 150 mA for 50-90 minutes

• Blocking: Block with 5% non-fat milk in TBS for 1.5 hours at room temperature

• Primary antibody: Incubate with anti-SMTNL2 antibody at 0.5 μg/mL overnight at 4°C

• Washing: Wash with TBS-0.1% Tween 3 times, 5 minutes each

• Secondary antibody: Incubate with goat anti-rabbit IgG-HRP at 1:5000 dilution for 1.5 hours at room temperature

• Detection: Develop using Enhanced Chemiluminescent detection (ECL) kit

The expected band size for SMTNL2 is approximately 50 kDa, though some antibodies report observed molecular weights of 68-70 kDa , possibly due to post-translational modifications or tissue-specific isoforms.

How should researchers optimize immunofluorescence protocols for SMTNL2 detection?

For successful immunofluorescence detection of SMTNL2:

• Sample preparation: Fix cells with 4% paraformaldehyde and permeabilize appropriately

• Antigen retrieval: For some cell types, enzyme antigen retrieval may be necessary (e.g., using IHC enzyme antigen retrieval reagent for 15 minutes)

• Blocking: Block with 10% goat serum

• Primary antibody: Incubate with anti-SMTNL2 antibody at 5 μg/mL overnight at 4°C

• Secondary antibody: Use Cy3-conjugated or other fluorophore-conjugated secondary antibodies at 1:500 dilution, incubated for 30 minutes at 37°C

• Counterstaining: Counterstain with DAPI for nuclear visualization

• Visualization: Use a fluorescence microscope with appropriate filter sets

U2OS and MCF-7 cells have been successfully used for SMTNL2 immunofluorescence studies , showing reliable detection and localization patterns.

What considerations should be made when selecting SMTNL2 antibodies for specific research applications?

When selecting SMTNL2 antibodies, researchers should consider:

• Target species reactivity: Confirm reactivity with species of interest (human, mouse, rat) as this varies between antibodies

• Epitope location: Some antibodies target N-terminal regions (e.g., amino acids 21-48) , while others may target different regions that could affect detection of specific isoforms

• Validation data: Review Western blot, IF/ICC images, and other validation data to ensure the antibody performs as expected in your specific application

• Host species: Consider the host species (typically rabbit for polyclonal antibodies) to avoid cross-reactivity in multi-labeling experiments

• Clonality: Polyclonal antibodies offer broader epitope recognition but may have batch-to-batch variation; monoclonal antibodies provide higher specificity for a single epitope

• Purification method: Antibodies purified by antigen affinity provide higher specificity

For subcellular localization studies, immunofluorescence validation images should demonstrate clear and specific staining patterns consistent with predicted SMTNL2 localization.

How can SMTNL2 phosphorylation be effectively studied using antibody-based approaches?

Studying SMTNL2 phosphorylation requires specialized techniques due to the identification of specific phosphorylation sites (S217, S241, T236, T239) that are targeted by JNK kinases :

• Phospho-specific antibodies: While not mentioned in the search results, phospho-specific antibodies targeting the identified residues would be the ideal approach.

• Kinase assays with antibody detection:

  • Purify full-length SMTNL2 protein or fragments

  • Conduct in vitro kinase reactions with JNK1-3 and 200 µM ATP

  • Detect phosphorylation using general phospho-serine/threonine antibodies

  • Confirm specificity using D-site mutant (DSM) SMTNL2 as a negative control

• Mass spectrometry validation:

  • After kinase reactions, separate products by SDS-PAGE

  • Excise bands corresponding to SMTNL2

  • Digest with trypsin or chymotrypsin

  • Analyze by LC-MS/MS to identify specific phosphorylated residues

• Cellular phosphorylation studies:

  • Transfect cells with V5-tagged SMTNL2 wild-type or D-site mutant constructs

  • Activate JNK pathway with stimuli such as anisomycin (500 nM, 30 min)

  • Use JNK inhibitors (e.g., SP600125) as controls

  • Immunoprecipitate SMTNL2 and detect phosphorylation

What strategies can be employed to investigate SMTNL2 interactions with MAPK signaling components?

To study SMTNL2 interactions with MAPK signaling components:

• GST pull-down assays:

  • Generate GST-MAPK fusion proteins (JNK1-3, ERK2)

  • Express radiolabeled ([35S]-methionine) SMTNL2 using in vitro transcription/translation systems

  • Perform pull-down assays using glutathione Sepharose beads

  • Include appropriate controls (GST alone, D-site mutant SMTNL2)

• Competitive binding assays:

  • Use synthetic peptides corresponding to the SMTNL2 D-site (residues 180-193)

  • Test their ability to inhibit JNK-mediated phosphorylation of other substrates like ATF2

  • Peptide sequences used successfully include: FSAPDPPRPRPVSLSLRLP

• Co-immunoprecipitation:

  • Transfect cells with tagged SMTNL2 constructs

  • Immunoprecipitate SMTNL2 and detect associated MAPKs

  • Alternatively, immunoprecipitate MAPKs and detect associated SMTNL2

  • Include D-site mutants as negative controls

• Bioluminescence resonance energy transfer (BRET) or fluorescence resonance energy transfer (FRET):

  • Generate fusion proteins of SMTNL2 and MAPKs with appropriate donor/acceptor tags

  • Measure energy transfer as an indication of protein-protein interaction

  • Compare wild-type interactions to D-site mutant interactions

What is the significance of SMTNL2 in cancer research and how can antibodies be used to investigate its role?

SMTNL2 shows potential significance in cancer research due to several observations:

• Differential expression in cancers:

  • SMTNL2 gene has been found to be significantly downregulated in several epithelial cancer datasets

  • Human Protein Atlas data indicates variable expression across different cancer types

• Research strategies using antibodies:

  • Tissue microarray analysis: Use anti-SMTNL2 antibodies to perform immunohistochemistry on tissue microarrays containing multiple cancer types and matched normal tissues

  • Expression correlation studies: Combine antibody-based detection of SMTNL2 with markers of epithelial differentiation or cancer progression

  • Functional studies: Use SMTNL2 antibodies to monitor protein levels after genetic manipulation (overexpression, knockdown) in cancer cell lines

• Potential mechanistic connections:

  • SMTNL2's association with actin cytoskeleton organization suggests it may influence cancer cell migration and invasion

  • Its identification as a JNK substrate links it to stress-response pathways relevant in cancer

  • Its location on chromosome 17 , which harbors important tumor suppressor genes like p53 and BRCA1, raises interesting questions about potential coordinated regulation

How can researchers address non-specific binding or high background issues when using SMTNL2 antibodies?

To address non-specific binding or high background issues:

• Antibody titration: Optimize antibody concentration by testing serial dilutions. Recommended ranges include 1:500-1:3000 for WB and 1:50-1:500 for IF/ICC

• Blocking optimization:

  • For Western blot: Use 5% non-fat milk in TBS for 1.5 hours at room temperature

  • For immunofluorescence: Use 10% goat serum (or serum from the species in which the secondary antibody was raised)

• Washing stringency:

  • Increase number of washes or washing duration

  • Consider using higher concentrations of detergent (e.g., 0.1-0.3% Tween-20) in wash buffers

• Negative controls:

  • Include secondary antibody-only controls

  • Use tissue or cells known to not express SMTNL2

  • Consider using SMTNL2 knockdown samples as gold-standard negative controls

• Cross-adsorption: If available, use cross-adsorbed secondary antibodies to minimize species cross-reactivity

• Sample preparation: Ensure complete cell/tissue lysis and protein denaturation for Western blot applications

• Fixation optimization: For IF/ICC, test different fixation methods (paraformaldehyde, methanol, or acetone) as they can affect epitope accessibility

What methodological approaches can help differentiate between SMTNL2 isoforms or distinguish SMTNL2 from related smoothelin family proteins?

To differentiate between SMTNL2 isoforms or distinguish from related proteins:

• Gel resolution optimization:

  • Use lower percentage gels (7-8%) or gradient gels (5-20%) for better separation of higher molecular weight proteins

  • Extend running time to enhance separation of closely-sized isoforms

• Isoform-specific antibodies:

  • Select antibodies raised against unique regions that differ between isoforms

  • Verify the immunogen sequence used to generate the antibody

• Expression patterns:

  • Use tissues with known differential expression of SMTNL2 isoforms as positive controls

  • Muscle tissue is particularly relevant as SMTNL2 shows high expression in skeletal muscle

• Specificity validation:

  • Test antibody against recombinant SMTNL2 and related family members

  • Perform peptide competition assays using the immunizing peptide

  • Use genetic models (knockdown/knockout) as gold-standard controls

• 2D gel electrophoresis:

  • Separate proteins first by isoelectric point, then by molecular weight

  • Helps distinguish post-translationally modified forms of the same protein

• Mass spectrometry:

  • Use tryptic digestion followed by mass spectrometry to identify specific peptides unique to each isoform

  • Can be combined with immunoprecipitation using SMTNL2 antibodies

What are the critical considerations when designing cell-based SMTNL2 phosphorylation assays using specific kinase activators or inhibitors?

When designing cell-based SMTNL2 phosphorylation assays:

• Pathway activation:

  • JNK pathway can be activated using anisomycin (500 nM, 30 min)

  • Include appropriate time courses (15-60 minutes) to capture optimal phosphorylation

  • Consider other MAPK activators such as UV, cytokines, or growth factors

• Inhibitor specificity:

  • JNK inhibitor SP600125 has been successfully used in SMTNL2 studies

  • Include concentration curves to determine optimal inhibitor concentration

  • Consider potential off-target effects of inhibitors by using multiple inhibitors targeting the same pathway

• Experimental controls:

  • Include wild-type SMTNL2 and D-site mutant (DSM) constructs in parallel

  • Use phosphorylation-site mutants (S217A, S241A, T236A, T239A) based on identified target sites

  • Include positive controls for pathway activation (e.g., c-Jun phosphorylation for JNK pathway)

• Detection methods:

  • Immunoprecipitation followed by Western blotting with phospho-specific antibodies (if available)

  • Phos-tag SDS-PAGE to separate phosphorylated from non-phosphorylated proteins

  • Mass spectrometry to identify and quantify site-specific phosphorylation

• Transfection considerations:

  • Optimize transfection for each cell line (e.g., HEK293 cells have been successfully used)

  • Control expression levels to avoid artifacts from overexpression

  • Use inducible expression systems for better temporal control

• Endogenous protein analysis:

  • Where possible, analyze phosphorylation of endogenous SMTNL2

  • This requires sufficient antibody sensitivity and cell lines with detectable SMTNL2 expression

How might SMTNL2 antibodies be utilized to investigate potential roles in muscle differentiation and function?

Given SMTNL2's high expression in skeletal muscle and its induction during myoblast to myotube differentiation , researchers can:

• Temporal expression analysis:

  • Use anti-SMTNL2 antibodies to track protein expression during different stages of muscle differentiation

  • Correlate with markers of myogenic differentiation (MyoD, myogenin, MHC)

  • Compare expression patterns in different muscle types (skeletal, cardiac, smooth)

• Subcellular localization studies:

  • Perform co-immunofluorescence with sarcomeric markers to determine precise localization

  • Investigate potential changes in localization during differentiation, contraction, or under pathological conditions

  • Based on predictions, focus on I band, M band, and microtubule organizing center localization

• Protein-protein interactions:

  • Immunoprecipitate SMTNL2 from muscle tissue or differentiating myoblasts

  • Identify binding partners using mass spectrometry

  • Validate interactions with predicted partners like protein phosphatase 1 and tropomyosin

• Functional studies:

  • Monitor SMTNL2 expression/phosphorylation during muscle hypertrophy or atrophy

  • Investigate changes in SMTNL2 in muscle disease models

  • Analyze effects of SMTNL2 knockdown/overexpression on muscle differentiation and function

• In vivo studies:

  • Use antibodies for immunohistochemistry of muscle biopsies from various physiological conditions (exercise, immobilization, aging)

  • Compare SMTNL2 expression in muscle from healthy controls versus muscle disease patients

What approaches could be used to investigate the potential role of SMTNL2 in epithelial cell polarity and lumen formation?

Based on the downregulation of SMTNL2 in epithelial cancers and its identification in a screen for genes involved in lumen formation , researchers could:

• 3D culture models:

  • Monitor SMTNL2 expression and localization during lumen formation in 3D epithelial cell cultures

  • Compare wild-type cells with SMTNL2 knockdown cells

  • Analyze localization relative to apical-basal polarity markers

• Co-localization studies:

  • Perform co-immunofluorescence of SMTNL2 with:

    • Tight junction proteins (Claudins, ZO-1)

    • Adherens junction proteins (E-cadherin, β-catenin)

    • Apical markers (aPKC, Crumbs)

    • Basolateral markers (Scribble, Dlg)

• Functional rescue experiments:

  • Knock down SMTNL2 and assess effects on lumen formation

  • Attempt rescue with wild-type SMTNL2 versus various mutants (D-site mutants, phosphorylation site mutants)

  • Compare to known regulators of lumen formation (as identified in the screen, such as Claudin-2 and Wrch-1)

• Rho GTPase interaction studies:

  • Investigate potential interactions between SMTNL2 and Rho GTPases mentioned in the lumen formation screen

  • Use active and dominant-negative Rho GTPase mutants to assess effects on SMTNL2 localization

  • Determine if SMTNL2 phosphorylation status affects these interactions

• Tissue analysis:

  • Examine SMTNL2 expression and localization in epithelial tissues with different architectural features

  • Compare normal versus cancerous epithelia, with specific attention to polarity loss during cancer progression

How can researchers effectively investigate the potential cross-talk between SMTNL2 and miRNA regulatory networks?

Based on the prediction that SMTNL2 is a target of multiple miRNAs , researchers could:

• Validation of miRNA targeting:

  • Use luciferase reporter assays with the SMTNL2 3'UTR to validate predicted miRNA binding sites

  • Create 3'UTR mutants to confirm specific miRNA binding sites

  • Focus on the 120+ interacting mature miRNAs predicted to target SMTNL2

• Expression correlation analysis:

  • Analyze inverse correlation patterns between SMTNL2 and predicted targeting miRNAs across tissues and cell lines

  • Use existing RNA-seq and miRNA-seq databases for initial analysis

  • Validate findings with quantitative RT-PCR in specific tissues of interest

• Functional miRNA studies:

  • Overexpress or inhibit specific miRNAs predicted to target SMTNL2

  • Measure effects on SMTNL2 mRNA and protein levels using RT-qPCR and Western blotting with anti-SMTNL2 antibodies

  • Assess functional consequences on processes SMTNL2 is involved in (cytoskeleton organization, muscle differentiation)

• Context-dependent regulation:

  • Investigate whether miRNA regulation of SMTNL2 varies across:

    • Different tissues (particularly skeletal muscle versus epithelial tissues)

    • Different physiological conditions (differentiation, stress response)

    • Normal versus disease states (cancer, muscle disorders)

• Integration with signaling pathways:

  • Determine if JNK pathway activation affects miRNA-mediated regulation of SMTNL2

  • Explore whether phosphorylation of SMTNL2 influences its susceptibility to miRNA regulation

  • Investigate potential feedback loops where SMTNL2 function might influence expression of its regulatory miRNAs