Phospho-STK11 (T189) Antibody

What is STK11/LKB1 and why is phosphorylation at T189 significant?

STK11/LKB1 is a master serine/threonine kinase that functions as a tumor suppressor and metabolic regulator. It controls the activity of AMP-activated protein kinase (AMPK) family members by phosphorylating their T-loop, thus promoting their activity . Phosphorylation at Threonine 189 (T189) is particularly significant as it represents one of the key autophosphorylation sites that regulates STK11's activation and function. When STK11 forms a complex with STRAD (STE-20-related kinase adaptor protein), it enhances STK11 autophosphorylation at several sites including T185, T336, T363, and T402, with T189 being closely related to this activation mechanism . Detection of phosphorylation at this site serves as an important indicator of STK11's active state.

STK11/LKB1 is ubiquitously expressed, with strongest expression in testis and fetal liver . Its inactivation through mutations has been associated with Peutz-Jeghers syndrome and various cancers including skin, pancreatic, and testicular cancers .

What applications is the Phospho-STK11 (T189) Antibody validated for?

The Phospho-STK11 (T189) Antibody has been validated for multiple applications across different experimental systems:

For optimal results, researchers should titrate the antibody in each specific testing system . Different suppliers recommend slightly different dilutions, so optimization for your specific experimental system is essential. Several publications have successfully used this antibody in Western blot applications .

What is the optimal sample preparation protocol for detecting phosphorylated STK11 at T189?

Proper sample preparation is critical for preserving and detecting the phosphorylated form of STK11 at T189:

• Cell/tissue lysis: Use buffer containing phosphatase inhibitors (such as sodium fluoride, sodium orthovanadate) to prevent dephosphorylation during extraction.

• For enhanced phosphorylation detection: Pre-treat cells with Calyculin A, a potent phosphatase inhibitor, which significantly improves the detection of phosphorylated STK11 .

• Storage conditions: Store protein samples at -20°C in a buffer containing PBS with 0.02% sodium azide and 50% glycerol (pH 7.3) .

• For immunoprecipitation-based approaches: Consider using anti-Flag beads if working with tagged constructs, as described in several research protocols .

• Phosphatase controls: Include samples treated with phosphatase to confirm specificity - a genuine phospho-signal should disappear after phosphatase treatment .

The calculated molecular weight of STK11 is approximately 49 kDa, but the observed molecular weight on gels typically ranges from 50-55 kDa , which is important to note when identifying bands.

What positive and negative controls should be used when working with Phospho-STK11 (T189) Antibody?

Proper controls are essential for validating Phospho-STK11 (T189) Antibody specificity:

Positive Controls:

• Calyculin A-treated PC-3, HEK-293, or NIH/3T3 cells

• HeLa cells (for some antibody formulations)

• Cells transfected with wild-type STK11 expression vectors

Negative Controls:

• STK11 knockout or null cell lines (e.g., some A549 cell lines lack functional STK11)

• Samples treated with lambda phosphatase

• Cells expressing T189A mutant (alanine substitution prevents phosphorylation)

• Kinase-dead STK11 mutants (e.g., K78I)

Validation Approaches:

• Peptide competition assays using the synthetic phosphorylated peptide from around T189

• Comparing signals between phospho-specific and total STK11 antibodies

• Gel shift assays that show the presence or absence of the higher molecular weight band corresponding to phosphorylated STK11

These controls help ensure that the observed signal is specific to STK11 phosphorylated at T189 rather than non-specific binding or detection of other phosphorylated proteins.

What experimental factors can affect the detection of phosphorylated STK11 at T189?

Several experimental factors can significantly impact the detection of phosphorylated STK11:

• Phosphatase activity: Endogenous phosphatases rapidly dephosphorylate proteins during sample preparation. Always use fresh phosphatase inhibitors and keep samples cold throughout processing .

• Cell culture conditions: Confluence, serum starvation, and metabolic state can affect STK11 phosphorylation. Standardize these conditions across experiments .

• Stimulation time: For treatments that induce STK11 phosphorylation, optimize the duration - overexposure may lead to secondary effects or feedback inhibition.

• Antibody specificity: Some antibodies may cross-react with similar phosphorylation motifs on other proteins. Validate with appropriate controls .

• Detection methods: For Western blotting, ECL sensitivity or fluorescent detection systems can significantly impact sensitivity. The KAM-900P antibody microarray method offers an alternative approach using direct labeling, chemical cleavage at cysteine residues, or biotinylation before detection .

• Sample loading: Uneven protein loading can create misleading results. Always normalize to total protein or a stable housekeeping protein, and ideally compare with total STK11 levels.

How can researchers distinguish between STK11 autophosphorylation at T189 versus phosphorylation by upstream kinases?

Distinguishing between autophosphorylation and trans-phosphorylation requires specialized experimental approaches:

• In vitro kinase assays: Using purified recombinant STK11 with ATP in the presence or absence of potential upstream kinases. A gel shift assay described in the literature demonstrates:

  • STK11 complexes are immunoprecipitated with anti-Flag beads

  • Kinase reactions are performed on the immunoprecipitated complexes

  • SDS-PAGE reveals either a single band (no phosphorylation) or two bands (successful phosphorylation)

  • Phosphatase treatment confirms the second band is due to phosphorylation

• Kinase-dead mutants: Express catalytically inactive STK11 (K78I) in cells and assess T189 phosphorylation. If phosphorylation occurs despite lack of kinase activity, this suggests an upstream kinase is responsible .

• STRAD co-expression studies: STRAD enhances LKB1 autophosphorylation at sites including T185. Comparing phosphorylation in cells with and without STRAD can help determine if T189 is primarily autophosphorylated .

• Inhibitor panels: Systematic treatment with kinase inhibitors targeting candidate upstream kinases can identify potential kinases responsible for T189 phosphorylation.

• Structural analysis: Research shows that SL26 (a 9 bp in-frame deletion at the C-terminus of LKB1) retains intrinsic kinase activity but cannot form complexes with STRAD and accumulates in the nucleus. This structural insight can be used to design experiments separating intrinsic from extrinsic phosphorylation events .

What methodologies can be used to study the relationship between STK11 T189 phosphorylation and AMPK activation in cancer models?

To investigate the STK11-AMPK signaling axis in cancer:

• Coordinated phosphorylation analysis:

  • Use Phospho-STK11 (T189) alongside Phospho-AMPK (T172) antibodies

  • Analyze both under various conditions (energy stress, hypoxia, drug treatments)

  • Quantify correlation between STK11 and AMPK phosphorylation across treatments

• Mutational approaches:

  • Create T189A (cannot be phosphorylated) and T189D/E (phosphomimetic) STK11 mutants

  • Express these in STK11-null cancer cells (like A549)

  • Measure AMPK activation and downstream effects on mTOR, S6K, autophagy markers

• Functional metabolic assays:

  • Measure oxygen consumption, extracellular acidification rate, ATP levels

  • Compare these between cells with wild-type vs. T189 mutant STK11

  • Correlate with glucose uptake or fatty acid oxidation measurements

• Imaging technologies:

  • Use proximity ligation assays to visualize STK11-AMPK interactions

  • Perform fluorescence resonance energy transfer (FRET) with tagged proteins

  • Correlate physical interaction with phosphorylation status

• Cancer tissue analysis:

  • In NSCLC patient samples, STK11 mutations are associated with poor outcomes

  • Compare phospho-T189 STK11 levels with AMPK activation markers in these samples

  • Correlate with clinical parameters like hypoxia or response to therapy

Research indicates that LKB1-AMPK pathway antagonizes protein synthesis by downregulating mechanistic target of rapamycin (mTOR), as demonstrated in various experimental models from cell lines to mouse tissues . Understanding how T189 phosphorylation impacts this regulation is crucial for developing targeted therapies.

How can phosphorylated STK11 (T189) be analyzed in conjunction with other phosphorylation sites to create a comprehensive profile?

Creating a comprehensive STK11 phosphorylation profile requires integrated methodologies:

• Multiplex Western blotting approaches:

  • Use antibodies against different phosphorylation sites (T189, S428, T363, S307)

  • Compare phosphorylation patterns across treatments or conditions

  • Calculate ratios between different phosphorylation sites

• Mass spectrometry-based phosphoproteomics:

  • Immunoprecipitate STK11 from cells under various conditions

  • Perform tryptic digestion followed by phosphopeptide enrichment

  • Use liquid chromatography-tandem mass spectrometry to identify and quantify all phosphorylation sites

• Correlation analysis:

  • Different phosphorylation sites have distinct functions:

    • T189: Associated with activation and autophosphorylation

    • S428: Required for growth inhibition and neuronal polarization

    • S307: A novel phosphorylation site

    • T363: Phosphorylated by ATM following ionizing radiation

  • Analyze which sites change coordinately vs. independently

• Antibody microarray technology:

  • The KAM-900P antibody microarray provides semi-quantitative analysis of protein phosphorylation states

  • Multiple methodologies (direct labeling, chemical cleavage, biotinylation) can be used

  • This approach allows parallel analysis of multiple phosphorylation sites

• Sequential phosphatase treatments:

  • Use phosphatases with different specificities to selectively remove phosphate groups

  • Re-probe with site-specific antibodies to determine hierarchy of phosphorylation

By profiling these sites together, researchers can develop a more comprehensive understanding of STK11 regulation in different cellular contexts.

What considerations should be made when using Phospho-STK11 (T189) Antibody in cells with STK11 mutations or STK11-knockout models?

When working with STK11 mutant or knockout models:

• For STK11-null models:

  • Confirm complete absence of STK11 protein expression

  • Any signal from Phospho-STK11 (T189) Antibody likely represents non-specific binding

  • Include wild-type controls to determine background signal levels

• For STK11 mutant models:

  • Different mutations may affect antibody epitope recognition

  • Mutations near T189 may directly interfere with antibody binding

  • Mutations in the kinase domain may prevent autophosphorylation

• Analysis of patient-derived samples:

  • STK11 mutations are common in non-small cell lung cancer (15-35%)

  • Mutations often lead to loss of function rather than altered phosphorylation

  • In a luciferase assay study, STK11 variants showed variable effects on p53 transcriptional activity, which could be correlated with phosphorylation status

• Validation approaches:

  • Use both phospho-specific and total STK11 antibodies

  • Include rescue experiments with wild-type STK11

  • Compare with downstream markers of STK11 activity

How can Phospho-STK11 (T189) Antibody be used to investigate the relationship between STK11 phosphorylation and tumor microenvironment factors like hypoxia?

The relationship between STK11 phosphorylation and tumor microenvironment factors:

• Experimental designs for hypoxia studies:

  • Culture cells under controlled oxygen conditions (1-5% O₂)

  • Use chemical mimetics of hypoxia (CoCl₂, DFO)

  • Measure STK11 T189 phosphorylation at different time points

  • Compare with hypoxia markers (HIF-1α, GLUT1, CA9)

• In vivo approaches:

  • Use pimonidazole staining to identify hypoxic tumor regions

  • Perform dual immunohistochemistry for hypoxia markers and phospho-STK11

  • Analyze spatial correlation between hypoxic regions and STK11 phosphorylation

• Clinical correlations:

  • Recent research has demonstrated that STK11 inactivation shows a novel association with clinical hypoxia

  • This may explain its correlation with medical inoperability in early-stage non-small cell lung cancer

  • Research shows that receiving supplemental oxygen (odds ratio = 5.5), heavy smoking history (odds ratio = 6.1), and Black race (odds ratio = 4.3) were associated with increased frequency of STK11 mutations

• Potential mechanisms:

  • Under hypoxic conditions, AMPK activation is crucial for cellular adaptation

  • STK11's role as an upstream regulator of AMPK suggests its phosphorylation status may change

  • Investigate whether hypoxia alters STK11 subcellular localization, which could affect its access to substrates

Understanding the relationship between STK11 phosphorylation and hypoxia could provide insights into tumor progression mechanisms and potential therapeutic targets, particularly in cancers with high rates of STK11 mutation like lung adenocarcinoma.