Recombinant Mouse Sodium/potassium-transporting ATPase subunit beta-1 (Atp1b1)

What is the structure and function of Atp1b1 in mouse models?

Atp1b1 (ATPase, Na+/K+ transporting, beta 1 polypeptide) is the non-catalytic beta subunit of Na+/K+ ATPase. This enzyme catalyzes ATP hydrolysis coupled with the exchange of Na+ and K+ ions across the plasma membrane. Structurally, the Na+/K+ ATPase consists of a large catalytic alpha subunit and a smaller glycoprotein beta subunit .

The beta subunit regulates the number of sodium pumps transported to the plasma membrane through the assembly of alpha/beta heterodimers . Na+/K+ ATPase-mediated electrochemical gradients are essential for:

• Osmoregulation

• Sodium-coupled transport of organic and inorganic molecules

• Electrical excitability of nerve and muscle tissues

• Cell adhesion and establishing epithelial cell polarity

Additionally, Atp1b1 plays roles beyond ion transport, including enhancing virus-triggered induction of interferons and interferon-stimulated genes by promoting ubiquitination of TRAF3 and TRAF6 and phosphorylation of TAK1 and TBK1 .

How is Atp1b1 expressed across different tissues and cell types?

Atp1b1 demonstrates heterogeneous expression across tissues and cell types:

In the central nervous system, Atp1b1 shows neuronal subtype-specific expression patterns. PV-expressing GABAergic neurons in the hippocampus, somatosensory cortex, and retrosplenial cortex express high levels of Atp1b1 and low levels of Atp1b2 and Atp1b3 . This suggests specialized roles for specific Na+/K+ ATPase subunit combinations in different neuronal populations.

What experimental models are commonly used to study Atp1b1 function?

Several experimental models have been developed to investigate Atp1b1 function:

• Conditional knockout mouse models:

  • AT1 cell-specific knockout using Aqp5-cre Atp1b1^F/F^ mice

  • Combined AT1 and AT2 cell knockout using Sftpc-cre Atp1b1^F/F^ mice

• Circadian regulation models:

  • Dec1-deficient mice (showing enhanced Atp1b1 expression)

  • Clock-mutant mice (showing reduced Atp1b1 expression)

• Cell culture systems:

  • A549 alveolar epithelial cells for protein interaction studies

  • Mouse alveolar epithelial cell monolayers (MAECM) for electrophysiological studies

  • Cancer cell lines for studying Atp1b1's role in cell proliferation and migration

• Recombinant expression systems:

  • cDNA expression plasmids available for in vitro and cellular studies

For in vitro studies, commercially available recombinant Atp1b1 proteins and expression vectors provide valuable tools for studying protein-protein interactions and biochemical properties .

What role does Atp1b1 play in cancer and how can it serve as a biomarker?

Atp1b1 has emerged as a significant factor in cancer progression and prognosis:

In diffuse large B-cell lymphoma (DLBCL):

• Atp1b1 is overexpressed compared to normal CD19+B cells

• ROC curve analysis identified Atp1b1 as a potential diagnostic biomarker with AUC values of 0.576, 0.663, and 0.706 for 1-, 3-, and 5-year survivability

• Downregulation of Atp1b1 inhibited DLBCL cell proliferation, migration, invasion, and cell adhesion

• Pathway analysis linked Atp1b1 to focal adhesion pathways

In cytogenetically normal acute myeloid leukemia (CN-AML):

• High Atp1b1 expression predicts adverse prognosis

• Atp1b1-high expressers showed upregulation of known unfavorable prognostic biomarkers including ERG, BAALC, MN1, WT1, DNMT3B, TCF4, ITPR2, DNMT3A, SPARC, CXXC5, MAPKBP1, and MIR155HG

• Pathway analysis revealed downregulation of apoptotic and natural killer signaling pathways and upregulation of RNA polymerase and CML pathways in Atp1b1-high samples

• Association with 50 differentially expressed microRNAs, including miR-146b, miR-125b, miR-100, and miR-155

These findings suggest Atp1b1 could serve as both a diagnostic and prognostic biomarker in hematological malignancies, though its roles may be context-dependent.

How does conditional knockout of Atp1b1 impact physiological processes?

Conditional knockout studies have revealed crucial insights into Atp1b1's physiological functions. In lung epithelial cells:

• Alveolar fluid clearance (AFC):

  • Aqp5-cre Atp1b1^F/F^ mice (AT1 cell-specific knockout) showed 43% reduction in AFC (p=0.006)

  • Sftpc-cre Atp1b1^F/F^ mice (AT1 and AT2 cell knockout) showed 78% reduction in AFC (p=0.002)

  • Analysis indicated AT1 and AT2 cells contribute approximately 55% and 45% to AFC, respectively

• Lung permeability and fluid homeostasis:

  • No changes in lung permeability to fluorescein-BSA in knockout mice

  • Wet-to-dry lung weight ratios were unchanged

  • Suggests residual Na pump activity is sufficient for baseline fluid homeostasis

• Epithelial ion transport:

  • Alveolar epithelial cell monolayers from Sftpc-cre Atp1b1^F/F^ mice showed significantly reduced equivalent short-circuit current (IEQ)

  • Transepithelial resistance (RT) remained unchanged

  • Indicates Atp1b1 is crucial for active ion transport but not barrier integrity

These findings demonstrate that Atp1b1 plays a key role in active ion transport and fluid clearance, with different cell types making distinct contributions to these processes.

What is the protein interactome of Atp1b1 and how is it analyzed?

A comprehensive analysis of the Atp1b1 protein interactome in alveolar epithelial cells revealed an extensive network of interacting proteins:

Methodology:

• Co-immunoprecipitation coupled with mass spectrometry (Co-IP-MS)

• Protein-protein interaction (PPI) network construction using STRING database

• Functional module analysis using MCODE plugin in Cytoscape

• Validation of key interactions by parallel reaction monitoring (PRM)

Key findings:

• 159 significant proteins were identified as Atp1b1 interactors (fold change >1.5, unique peptide ≥2)

• The PPI network consisted of 130 nodes and 1047 edges

• Two major functional modules were identified:

  • Module 1 (score 37): 37 nodes/666 edges, mainly ribosomal proteins (RPS and RPL subunits)

  • Module 2 (score 6): 6 nodes/15 edges, heat shock proteins (HSPA1A, HSPA5, HSPA8, HSPA9, HSP90AB1, DNAJA1)

• Six proteins (HSP90AB1, EIF4A1, TUBB4B, HSPA8, STAT1, PLEC) were validated as key Atp1b1 binding partners

This interactome analysis suggests Atp1b1 participates in protein translation, posttranslational processing, and function regulation beyond its canonical role in ion transport.

How does Atp1b1 contribute to circadian regulation of blood pressure?

Atp1b1 has been identified as a key mediator in the circadian control of blood pressure:

• Transcriptional regulation:

  • Atp1b1 expression is regulated by circadian clock proteins DEC1 and CLOCK:BMAL1

  • These factors bind to the CACGTG E-box element in the Atp1b1 promoter

• Genetic evidence:

  • Dec1-deficient mice showed enhanced Atp1b1 expression in aorta and heart tissues, correlating with reduced blood pressure

  • Clock-mutant mice exhibited reduced Atp1b1 expression and elevated blood pressure

• Molecular mechanism:

  • Na+/K+ ATPase activity affects vascular tone and renal sodium handling

  • In the kidneys, Na+/K+ ATPase regulates blood pressure by controlling sodium reabsorption in renal tubules

  • In rats of the Milan hypertensive strain (MHS), increased activity and expression of Na-K pump units correlate with hypertension development

• Genetic association in humans:

  • The ATP1B1 variant rs2901029 is significantly associated with systolic blood pressure (SBP)

  • The observed SBP effect size for rs2901029 was 1.698 mmHg

This research establishes a clear molecular pathway connecting the circadian clock system to blood pressure regulation through Atp1b1 expression, providing potential targets for chronotherapeutic approaches to hypertension.

What are the optimal methods for detecting Atp1b1 in research applications?

Multiple validated techniques are available for detecting Atp1b1 at both protein and mRNA levels:

Protein detection:

mRNA detection:

• In situ hybridization:

  • Validated primers for Atp1b1 (513–1336): 5′-AGCCAAGGAGGAAGGCAG-3′ and 5′-ACGCCTTACACTCGACGC-3′

  • Can be performed with digoxigenin (DIG) or fluorescein (FLU) labeled riboprobes

  • Effective for mapping cellular distribution in tissue sections

• RT-PCR and qPCR:

  • Multiple validated primer sets available from literature

  • Effective for quantitative analysis across tissues and experimental conditions

For obtaining consistent results, researchers should note that Atp1b1 molecular weight varies across tissues due to post-translational modifications, particularly glycosylation .

How can researchers design conditional knockout models for Atp1b1?

Creating conditional knockout models for Atp1b1 requires several key steps:

• Generation of floxed Atp1b1 mice (Atp1b1^F/F^):

  • Insert loxP sites flanking critical exon(s) of the Atp1b1 gene

  • Validate that the floxed allele maintains normal expression and function

• Selection of appropriate Cre driver lines:

  • For alveolar type I cell specificity: Aqp5-cre transgene

  • For both alveolar type I and II cells: Sftpc-cre transgene

  • For neuronal studies: Neuron-specific promoters (e.g., Camk2a-cre, Pvalb-cre)

• Validation of conditional knockout:

  • Genotyping to confirm floxed allele and Cre transgene presence

  • RT-PCR/qPCR to verify reduced Atp1b1 mRNA in target tissues

  • Western blot to confirm protein reduction

  • Functional assays to demonstrate physiological impact

• Experimental considerations:

  • Include appropriate controls (Cre-negative Atp1b1^F/F^ littermates)

  • Consider potential developmental compensation mechanisms

  • Assess for off-target effects of Cre expression

This approach allows cell type-specific investigation of Atp1b1 function while avoiding the potential embryonic lethality of global knockout. Using different Cre lines enables comparing the contribution of Atp1b1 in different cell types to physiological processes, as demonstrated in the lung study where AT1 and AT2 cells contributed 55% and 45% to alveolar fluid clearance, respectively .

How should researchers interpret contradictory findings across different Atp1b1 studies?

When evaluating seemingly contradictory findings regarding Atp1b1 function, researchers should consider:

• Tissue and cell-type specificity:

  • Atp1b1 functions differently in alveolar type I versus type II cells

  • Expression varies significantly across neuronal subtypes

  • Context matters: specify the exact cell types being studied

• Alpha/beta subunit pairing:

  • Atp1b1 can pair with different alpha subunits (α1, α2, α3)

  • In neurons, PV-expressing cells show a distinct pattern of high Atp1a3/Atp1b1

  • Different subunit combinations may yield different functional properties

• Methodological differences:

  • Complete knockout vs. partial knockdown reveal different aspects of function

  • Acute vs. chronic perturbation may lead to different compensatory mechanisms

  • In vivo vs. in vitro studies may not align due to complex physiological context

• Disease-specific contexts:

  • In DLBCL, Atp1b1 appears to promote cancer progression

  • In CN-AML, high Atp1b1 expression correlates with poor prognosis

  • These findings may reflect disease-specific molecular contexts

• Interaction networks:

  • Atp1b1 interacts with at least 159 proteins in alveolar epithelial cells

  • Perturbations may have ripple effects through multiple pathways

  • Consider secondary effects beyond direct ion transport function

When encountering contradictory results, researchers should carefully evaluate these factors and potentially employ multiple complementary approaches (genetic, biochemical, physiological) in well-defined biological systems to build a more comprehensive understanding of Atp1b1 function.

What is the neuronal subtype-specific expression pattern of Atp1b1 and its implications?

Recent research has revealed intricate patterns of Atp1b1 expression across neuronal subtypes with significant functional implications:

• Expression patterns:

  • Parvalbumin (PV)-expressing GABAergic neurons in the hippocampus, somatosensory cortex, and retrosplenial cortex express high levels of Atp1b1

  • These neurons simultaneously express low levels of Atp1b2 and Atp1b3

  • This distinctive expression pattern correlates with a unique alpha subunit profile: low Atp1a1 and high Atp1a3

• Methodological approach:

  • In situ hybridization targeting mRNA coding sequence regions

  • Multiple histochemical labeling to detect co-expression patterns

  • Age-controlled analysis using 8-12 week mice (post-development, pre-aging)

• Functional implications:

  • Different neuronal subtypes may require specific Na+/K+ ATPase isoform combinations for their unique electrophysiological properties

  • PV neurons, which are fast-spiking interneurons, may particularly depend on the Atp1a3/Atp1b1 combination

  • This may explain selective neuronal vulnerability in disorders associated with Na+/K+ ATPase dysfunction

• Clinical relevance:

  • Mutations in ATP1A3 (α3 subunit) cause neurological disorders including rapid-onset dystonia-parkinsonism, alternating hemiplegia of childhood, and CAPOS syndrome

  • Neurons highly expressing Atp1a3/Atp1b1 may be selectively vulnerable in these conditions

  • Amyloid β oligomers directly inhibit NAKα3-derived pump activity, potentially linking to neurodegenerative mechanisms

This research provides fundamental information for understanding how specific neuronal populations may be differentially affected in neurological disorders associated with Na+/K+ ATPase dysfunction.

What genetic polymorphisms in ATP1B1 are associated with human disease?

Several genetic variants in ATP1B1 have been associated with human diseases and physiological traits:

• Hypertension associations:

  • The ATP1B1 variant rs2901029 shows significant association with systolic blood pressure (SBP)

  • Effect size: 1.698 mmHg increase in SBP

  • Mechanism likely involves altered regulation of renal sodium reabsorption

  • Previously reported ATP1B1 SNPs (rs3766031, rs12079745, rs1138486) showed larger effect sizes (3.5–5.1 mmHg)

• Molecular mechanism in hypertension:

  • Na+/K+ ATPase influences blood pressure by regulating sodium reabsorption in renal tubules

  • In the Milan hypertensive strain (MHS) rat model, increased activity and expression of Na-K pump units correlates with hypertension development

  • The finding of association between ATP1B1 variants and hypertension is consistent with the gene's biological function in sodium handling

• Other associated conditions:

  • According to GeneCards, ATP1B1 is associated with:

    • Essential hypertension

    • Familial hemiplegic migraine

These genetic associations provide potential targets for personalized medicine approaches and further mechanistic studies into the role of ATP1B1 in disease pathophysiology.

How does Atp1b1 contribute to innate immunity?

Emerging research has revealed unexpected roles for Atp1b1 in innate immune responses:

• Enhancement of antiviral signaling:

  • Atp1b1 enhances virus-triggered induction of interferons (IFNs) and interferon-stimulated genes (ISGs)

  • Mechanistically, it promotes the ubiquitination of TRAF3 and TRAF6

  • Additionally enhances the phosphorylation of TAK1 and TBK1

  • These pathways are critical for antiviral innate immune responses

• Integration with ion transport function:

  • The relationship between Atp1b1's canonical ion transport role and its immune functions remains an area of active investigation

  • Ion balance may influence signaling pathway activity and immune cell function

  • Cell membrane potential can affect immune receptor clustering and signaling

• Research approaches:

  • Protein interaction studies to identify binding partners in immune signaling pathways

  • Conditional knockout in immune cell populations

  • Functional assays measuring interferon production and viral resistance

This novel aspect of Atp1b1 function represents an exciting frontier for understanding the integration of basic cellular processes with immune defense mechanisms.

What technical challenges arise when studying Atp1b1 in the Na+/K+ ATPase complex?

Studying Atp1b1 within the Na+/K+ ATPase complex presents several technical challenges:

• Subunit heterogeneity:

  • Multiple alpha (α1, α2, α3) and beta (β1, β2, β3) subunit isoforms exist

  • Different alpha-beta combinations may have distinct functional properties

  • Isolating the specific role of Atp1b1 requires careful experimental design

• Post-translational modifications:

  • Atp1b1 undergoes tissue-specific glycosylation

  • Detected at ~42kDa in liver and ~55kDa in kidney samples

  • These modifications affect antibody recognition and may influence protein function

• Membrane protein biochemistry:

  • As an integral membrane protein, Atp1b1 requires special solubilization conditions

  • Standard protein analysis techniques may need optimization

  • Maintaining native conformation during purification is challenging

• Functional redundancy:

  • Other beta subunits may compensate for Atp1b1 loss

  • Even in Atp1b1 knockout models, residual Na pump activity exists

  • This complicates interpretation of knockout/knockdown studies

• Specialized physiological assays:

  • Functional studies require sophisticated measurements

  • Examples include alveolar fluid clearance, electrophysiological recordings, and ion flux assays

  • These techniques demand specialized expertise and equipment

Addressing these challenges requires integrated approaches combining genetic models, biochemical assays, and advanced imaging techniques, often necessitating collaboration between laboratories with complementary expertise.

How can researchers quantify Atp1b1 activity in different experimental systems?

Quantifying Atp1b1 activity presents unique challenges due to its role as a regulatory subunit rather than the catalytic component. Several approaches can be employed:

• Na+/K+ ATPase enzyme activity assays:

  • Ouabain-sensitive ATP hydrolysis measurement

  • Colorimetric detection of inorganic phosphate release

  • Requires comparing wild-type vs. Atp1b1-deficient samples to determine contribution

• Ion flux measurements:

  • Radioactive tracer studies (^86^Rb+ uptake as K+ surrogate)

  • Fluorescent ion indicators (SBFI for Na+, PBFI for K+)

  • Ion-selective electrodes for direct measurement

• Electrophysiological approaches:

  • Equivalent short-circuit current (IEQ) measurements in epithelial monolayers

  • Whole-cell patch clamp recording of pump currents

  • As demonstrated in mouse alveolar epithelial cell monolayers, Sftpc-cre Atp1b1^F/F^ knockout monolayers showed significantly reduced IEQ compared to control monolayers

• Physiological function assays:

  • Alveolar fluid clearance (AFC) measurements

  • Blood pressure monitoring in animal models

  • In Aqp5-cre Atp1b1^F/F^ mice, AFC was reduced by 43% compared to controls

  • In Sftpc-cre Atp1b1^F/F^ mice, AFC was reduced by 78%

• Surface expression quantification:

  • Cell surface biotinylation followed by Western blot

  • Flow cytometry with non-permeabilized cells

  • Immunofluorescence with membrane markers

  • These approaches assess Atp1b1's role in regulating pump trafficking to the plasma membrane

The choice of method depends on the specific research question, experimental system, and available equipment. Combining multiple approaches provides the most comprehensive assessment of Atp1b1's functional contribution.