Phospho-STK11 (Ser428) Antibody

What is Phospho-STK11 (Ser428) Antibody and what does it specifically detect?

Phospho-STK11 (Ser428) Antibody is a rabbit polyclonal antibody that specifically recognizes the Serine/Threonine Kinase 11 (STK11, also known as LKB1) protein only when phosphorylated at Serine 428. This antibody binds to the endogenous phosphorylated form of STK11 at the amino acid region containing Ser428 . The specificity of this antibody is crucial for studying the phosphorylation state of STK11, which affects its function as a tumor suppressor protein .

Most commercial preparations use a synthetic phosphopeptide derived from human LKB1 around the phosphorylation site of Ser428 (commonly with the sequence R-L-S(p)-A-C) as the immunogen . The antibody is typically affinity-purified using epitope-specific phosphopeptide chromatography, with non-phospho specific antibodies removed by chromatography using non-phosphopeptide .

What applications is this antibody validated for?

The Phospho-STK11 (Ser428) Antibody has been validated for multiple research applications:

Scientific validation data typically demonstrates the antibody's ability to detect phosphorylated STK11 in various cell lines, such as HEK293 cells transfected with human LKB1/STK11 and treated with metformin , or in HeLa cells treated with PMA .

What is the functional significance of STK11/LKB1 in cellular processes?

STK11 (LKB1) is a tumor suppressor serine/threonine-protein kinase that controls the activity of AMP-activated protein kinase (AMPK) family members. Its phosphorylation status influences various cellular processes:

• Cell metabolism regulation through AMPK pathway activation

• Cell polarity establishment and maintenance

• Apoptosis induction

• DNA damage response participation

• Cellular growth inhibition under energy stress conditions

STK11 functions by phosphorylating the T-loop of AMPK family proteins (including PRKAA1, PRKAA2, BRSK1, BRSK2, MARK1-4, NUAK1, NUAK2, SIK1-3, and SNRK), which promotes their activity . It serves as a key upstream regulator of AMPK, mediating phosphorylation and activation of AMPK catalytic subunits that regulate various cellular pathways including inhibition of cell growth when energy levels are low, glucose homeostasis in liver, and activation of autophagy during nutrient deprivation .

How should I optimize Western Blot protocols for detecting phosphorylated STK11?

For optimal Western Blot results with Phospho-STK11 (Ser428) Antibody, follow these methodological considerations:

• Sample Preparation:

  • Preserve phosphorylation status by adding phosphatase inhibitors (e.g., sodium fluoride, sodium orthovanadate) to lysis buffers

  • Use RIPA buffer supplemented with protease inhibitors for efficient extraction

  • Process samples quickly and maintain cold temperatures throughout

• Gel Electrophoresis and Transfer:

  • Use 10% SDS-PAGE for optimal separation (STK11 has a molecular weight of approximately 48-55 kDa)

  • Consider using PVDF membranes for better protein retention and signal strength

• Blocking and Antibody Incubation:

  • Block membranes with 5% non-fat dry milk or BSA in TBST

  • Dilute primary antibody 1:500-1:2000 in blocking buffer

  • Incubate overnight at 4°C for optimal binding

  • Use appropriate HRP-conjugated secondary antibody (typically anti-rabbit IgG)

• Signal Detection:

  • Use enhanced chemiluminescence (ECL) for sensitive detection

  • Expected band size is approximately 48-55 kDa

• Controls:

  • Include both phosphorylated and non-phosphorylated controls

  • Consider using lysates from cells treated with phosphatase inhibitors versus phosphatase treatment

What are the critical storage and handling requirements for maintaining antibody activity?

Proper storage and handling are essential for maintaining antibody sensitivity and specificity:

• Storage Conditions:

  • Store at -20°C or -80°C for long-term stability

  • Avoid repeated freeze-thaw cycles, as this can lead to protein denaturation and loss of activity

  • For frequent use, small aliquots can be stored at 4°C for up to one month

• Formulation Considerations:

  • The antibody is typically provided in liquid form containing:

    • PBS (pH 7.4)

    • 150mM NaCl

    • 50% glycerol (acts as cryoprotectant)

    • 0.02% sodium azide (preservative)

    • Often 0.5% BSA (stabilizer)

• Handling Precautions:

  • Centrifuge briefly before opening the vial

  • Maintain sterile conditions when handling

  • Wear gloves to prevent contamination and for safety (sodium azide is toxic)

  • Allow the antibody to equilibrate to room temperature before opening to prevent condensation

How can this antibody be used to investigate the relationship between STK11 phosphorylation and AMPK activation?

Investigating the STK11-AMPK signaling axis requires careful experimental design:

• Co-detection Approach:

  • Design experiments to simultaneously detect phospho-STK11 (Ser428) and phospho-AMPK (Thr172)

  • Perform parallel Western blots or multiplex immunofluorescence

  • Compare phosphorylation patterns under various conditions (e.g., energy stress, metformin treatment)

• Functional Studies Design:

  • Utilize cell models with STK11 variants (wild-type, phospho-mimetic, phospho-deficient)

  • Transfect cells with constructs such as PEGFP-N1-STK11 wild-type or mutant forms (e.g., c.733C>T, c.910C>T)

  • Measure downstream AMPK activity through substrate phosphorylation

• Inhibitor/Activator Studies:

  • Treat cells with AMPK activators (e.g., metformin, AICAR) and monitor changes in STK11 Ser428 phosphorylation

  • Use specific inhibitors to block STK11 activity and examine effects on AMPK phosphorylation

  • Create time-course experiments to determine the sequential order of phosphorylation events

• Validation Through Molecular Techniques:

  • Implement siRNA knockdown or CRISPR/Cas9 knockout of STK11

  • Reconstitute with phospho-mutant forms to establish causality

  • Analyze downstream readouts such as cellular metabolism, mTOR signaling, or autophagy markers

Research has demonstrated that STK11 phosphorylation at Ser428 can be induced by treatments such as metformin, allowing for analysis of the subsequent activation of AMPK through detection of phospho-AMPK using appropriate antibodies .

What controls should be included when working with phospho-specific antibodies?

Rigorous control strategies are essential for phospho-antibody experiments:

• Positive Controls:

  • Cell lysates from treatments known to induce the specific phosphorylation:

    • PMA treatment for HeLa cells has been demonstrated to induce STK11 phosphorylation

    • Metformin treatment in HEK293 cells transfected with human LKB1/STK11

  • Recombinant phosphorylated protein standards if available

• Negative Controls:

  • Phosphatase-treated samples

  • Lysates from STK11 knockout cell lines (e.g., LKB1/STK11 knockout HEK293T cells)

  • Competing peptide controls - the signal should be blocked when the antibody is pre-incubated with the phosphopeptide used as immunogen

• Specificity Controls:

  • Test antibody recognition of phosphorylated versus non-phosphorylated forms

  • Mutant STK11 with Ser428 substituted to alanine (phospho-deficient) or glutamic acid (phospho-mimetic)

• Loading and Technical Controls:

  • Total STK11 antibody in parallel to assess phosphorylation relative to total protein

  • Housekeeping proteins (e.g., GAPDH, β-actin) for loading normalization

  • Secondary antibody-only control to assess non-specific binding

How can I investigate the role of STK11 Ser428 phosphorylation in cancer research models?

STK11 is a tumor suppressor, and its phosphorylation status may be critical in cancer development:

• Cancer Cell Line Profiling:

  • Compare Ser428 phosphorylation levels across cancer cell lines:

    • MCF-7 (breast cancer)

    • K562 (chronic myelogenous leukemia)

    • HeLa cells (cervical cancer)

  • Correlate phosphorylation status with STK11 mutations or deletions in these lines

• Tumor Tissue Analysis:

  • Perform IHC-P on cancer tissues such as:

    • Breast cancer tissue (where LKB1/STK11 shows both cytoplasmic and nuclear localization)

    • Colon carcinoma samples, where the phospho-peptide can block staining for validation

  • Compare phosphorylation levels between tumor and adjacent normal tissues

• Functional Implications Assessment:

  • Design experiments linking Ser428 phosphorylation to cancer-relevant phenotypes:

    • Cell proliferation assays (e.g., CCK-8)

    • Migration and invasion assays

    • Gene expression changes (RT-qPCR)

    • Metabolic alterations (glucose uptake, lactate production)

• Therapeutic Context:

  • Test how cancer therapeutics affect STK11 Ser428 phosphorylation

  • Investigate whether Ser428 phosphorylation status predicts response to AMPK-targeting drugs

  • Explore the potential of STK11 phosphorylation as a biomarker for treatment selection

Why might I see non-specific bands or background when using this antibody?

Non-specific signals may appear due to several factors:

• Cross-reactivity Issues:

  • Some phospho-antibodies may detect similar phosphorylation motifs in other proteins

  • Solution: Include competing peptide controls and STK11 knockout samples

• Inadequate Blocking:

  • Insufficient blocking can lead to non-specific antibody binding

  • Solution: Optimize blocking conditions (5% milk or BSA, longer blocking time)

• Sample Processing Problems:

  • Protein degradation can create fragments that appear as additional bands

  • Solution: Add fresh protease inhibitors to lysis buffers and maintain cold temperatures

• Protocol-specific Issues:

  • For Western blot: Excessive antibody concentration or prolonged exposure times

  • For IHC/IF: Endogenous peroxidase activity or autofluorescence

  • Solutions: Titrate antibody dilutions, include appropriate quenching steps

• Validation Approaches:

  • Compare band patterns with literature reports (expected MW ~48-55 kDa)

  • Perform pre-absorption tests with phosphorylated and non-phosphorylated peptides

  • Use siRNA knockdown to confirm specificity of the primary band

What quantitative methods can be used to analyze phosphorylation levels of STK11?

Several techniques can be used for quantitative analysis:

• Western Blot Densitometry:

  • Measure band intensity of phospho-STK11 normalized to total STK11

  • Use software like ImageJ for quantification

  • Calculate phospho/total ratio across experimental conditions

• ELISA-based Methods:

  • Commercial phospho-STK11 ELISA kits

  • In-house sandwich ELISA using capture antibody against total STK11 and detection with phospho-specific antibody

  • Recommended dilution for ELISA using this antibody is approximately 1:40000

• Immunofluorescence Quantification:

  • Measure mean fluorescence intensity in subcellular compartments

  • Use high-content imaging systems for automated quantification

  • Perform co-localization analysis with markers of relevant compartments

• Phosphoproteomics Approach:

  • Mass spectrometry-based quantification of STK11 phosphopeptides

  • SILAC or TMT labeling for comparative analysis

  • Correlation of MS data with antibody-based detection methods

• Bead-based Assays:

  • Luminex or similar multiplexed bead-based immunoassays

  • Allow simultaneous measurement of multiple phospho-proteins in the STK11 pathway

How has Phospho-STK11 (Ser428) Antibody been used to study STK11 variants in disease models?

Case study examples demonstrate the utility of this antibody in characterizing STK11 variants:

• Missense Variant Analysis:

  • Researchers used Phospho-STK11 (Ser428) antibody to evaluate the impact of STK11 variants c.889A>G (p.Arg297Gly) and c.733C>T (p.Leu245Phe) on phosphorylation status

  • Transfected HeLa cells with wild-type and mutant constructs

  • Western blot analysis revealed decreased phosphorylation at Ser428 in variant forms

  • Correlation with reduced AMPK phosphorylation (p-AMPK) suggested functional impairment

• Cancer Mutation Screening:

  • Detection of phospho-STK11 levels in cell lines harboring different STK11 mutations

  • Western blot combined with RT-qPCR to assess both protein phosphorylation and gene expression

  • Cell proliferation assays (CCK-8) demonstrated enhanced growth in cells with mutant STK11 showing reduced Ser428 phosphorylation

• Metabolic Disease Connections:

  • Analysis of STK11 Ser428 phosphorylation in response to metabolic stress

  • Links to diabetes models and metabolic syndrome

  • Changes in the STK11-AMPK signaling axis with implications for cellular energy homeostasis

What are the key differences between phosphorylated and total STK11 antibody detection systems?

Understanding the complementary nature of phospho-specific and total antibodies:

When used together, these antibodies provide more comprehensive information:

• Phospho-STK11 indicates the proportion of activated protein

• Total STK11 shows whether changes in phospho-signal are due to altered phosphorylation or protein levels

• The phospho/total ratio normalizes for expression differences across samples

This combined approach is essential for studies examining both STK11 expression and its activation state in response to various stimuli or in disease models.