Recombinant Mouse Suppressor of tumorigenicity 7 protein (St7)

What is the molecular structure of mouse ST7/LRP12 protein?

Mouse ST7/LRP12 is a type I transmembrane protein belonging to the low-density lipoprotein receptor (LDLR) superfamily. The mouse ST7 cDNA encodes 858 amino acids including a 32 amino acid signal sequence, a 460 amino acid extracellular domain (ECD) containing two CUB domains and five LDLR class A domains, a 21 amino acid transmembrane domain, and a 345 amino acid cytoplasmic domain. The cytoplasmic domain contains motifs implicated in endocytosis and signal transduction pathways. The recombinant form of mouse ST7/LRP12 typically includes amino acids Glu33-Thr491, often with a C-terminal 6-His tag to facilitate purification and detection .

How conserved is ST7/LRP12 across species?

ST7/LRP12 shows remarkably high conservation across mammalian species, suggesting important functional roles. Mouse ST7 shares 97% amino acid sequence homology with rat ST7, and 95% homology with human, bovine, equine, and porcine ST7 within the extracellular domain. This high degree of conservation indicates evolutionary pressure to maintain the protein's structure and function. Human ST7 shares 95% amino acid sequence homology with mouse and rat versions, 96% with canine, and 98% with bovine, equine, and porcine ST7 within the ECD .

What expression pattern does ST7/LRP12 exhibit in normal tissues?

ST7/LRP12 is widely expressed in normal tissues, with particularly notable expression in fibroblasts. Highest mRNA levels have been detected in heart and skeletal muscle. The broad tissue distribution suggests that ST7 may play roles in multiple biological processes rather than having a tissue-specific function. Mouse models and tissue analysis have been valuable in identifying these expression patterns, providing insight into potential physiological roles of the protein .

What is the proper reconstitution protocol for recombinant mouse ST7/LRP12 protein?

For optimal reconstitution of lyophilized recombinant mouse ST7/LRP12 protein:

• Reconstitute at a concentration of 200 μg/mL in phosphate-buffered saline (PBS).

• Allow the lyophilized protein to dissolve completely by gentle mixing.

• After reconstitution, the protein should be aliquoted to avoid repeated freeze-thaw cycles.

• For storage, use a manual defrost freezer and store at -20°C to -70°C for long-term storage (up to 6 months).

• For short-term storage (up to 1 month), store at 2-8°C under sterile conditions .

How does ST7/LRP12 function in relation to tumor suppression mechanisms?

ST7/LRP12 was initially proposed as a tumor suppressor protein, but its role appears more complex than originally thought. Current research indicates that ST7 may mediate tumor suppression through the regulation of genes involved in maintaining cellular structure and those involved in oncogenic pathways. Cell cycle synchronization studies have demonstrated that both ST7 and SERPINE1 are overexpressed when cells are arrested, with their expression diminishing when cells re-enter the cell division cycle .

The protein appears to influence the expression of extracellular matrix molecules involved in remodeling, such as SPARC, IGFBP5, and several matrix metalloproteinases. This suggests ST7 may affect tumor progression through modulation of the tumor microenvironment rather than through direct effects on cell proliferation. Interestingly, ST7 is not consistently downregulated in various cancers. In some cases, expression levels may even be upregulated, indicating context-dependent functions .

What are the optimal conditions for studying ST7/LRP12 protein-protein interactions?

When investigating ST7/LRP12 protein-protein interactions, the following methodology has proven effective:

• Immobilization concentration: For binding studies, immobilize recombinant human ST7 at 0.5 μg/mL.

• Interacting protein concentration: When studying interaction with rhLRPAP, the concentration that produces 50% of the optimal binding response is approximately 0.6-3 μg/mL.

• Tagged fusion proteins: GFP, YFP, or V5-tagged ST7 expression vectors created using gateway cloning systems have been successfully used to visualize ST7 localization and interactions.

• Buffer conditions: PBS-based buffers with physiological pH (7.2-7.4) are suitable for most interaction studies.

• Detection methods: Both fluorescence-based detection (for tagged proteins) and immunological methods have been used successfully .

What subcellular localization patterns does ST7/LRP12 exhibit in different cell types and conditions?

Studies using fluorescently tagged ST7 proteins have consistently shown cytosolic expression of ST7/LRP12 in various cancer cell lines including HCT-116 (colorectal cancer), MCF-7 (breast cancer), and PC-3 (prostate cancer). Interestingly, translocation of ST7 from the cytoplasm to the nucleus has not been observed under any of the conditions tested to date.

This consistent cytoplasmic localization suggests that ST7 likely functions in cytoplasmic signaling pathways or at the cell membrane rather than directly regulating gene expression as a transcription factor or co-factor. The type I transmembrane protein structure supports this observation, with the protein potentially functioning at the cell surface or in membrane-associated complexes .

How does ST7/LRP12 expression change throughout the cell cycle?

Cell cycle synchronization studies have revealed important insights into ST7 expression patterns:

This pattern suggests that ST7 may function as part of the cellular machinery that regulates cell cycle progression, particularly in the transition from arrested states to active division. The coordinated expression with SERPINE1 (encoding the plasminogen activator inhibitor-1 protein) further suggests involvement in pathways related to extracellular matrix remodeling and potentially in signaling pathways that control cellular quiescence versus proliferation .

What experimental approaches are most effective for studying the functional impact of ST7/LRP12 in cancer models?

Based on current research methodologies, the following experimental approaches have proven effective for investigating ST7/LRP12 function in cancer contexts:

• Expression vector systems: Gateway cloning systems for creating tagged ST7 expression vectors (GFP, YFP, V5) from full-length ST7 cDNA.

• Cell cycle synchronization studies: To analyze endogenous ST7 expression at different cell cycle stages.

• Fluorescence microscopy: To detect ST7 subcellular localization using fusion proteins.

• Gene expression analysis: To identify correlations between ST7 expression and other genes involved in extracellular matrix remodeling and oncogenic pathways.

• Loss and gain of function studies: Using siRNA knockdown or overexpression systems to evaluate the impact on cellular phenotypes and gene expression profiles.

These approaches allow researchers to comprehensively investigate the molecular mechanisms by which ST7 influences cancer cell behavior, potentially leading to insights for therapeutic targeting .

How does ST7/LRP12 expression correlate with cancer progression and prognosis?

The relationship between ST7/LRP12 expression and cancer outcomes presents a complex picture. Initially proposed as a tumor suppressor gene located in chromosome region 7q31.1-q31.2, subsequent research has shown that ST7 is not consistently downregulated across different cancer types. Some studies have demonstrated that in certain cancers, ST7 expression may actually be upregulated rather than lost.

The inconsistent pattern of expression changes suggests that ST7's role may be context-dependent, possibly influenced by tissue type, genetic background, or other alterations in signaling pathways. While loss of heterozygosity in the ST7 region has been observed in some cancers, definitive mutational inactivation patterns characteristic of classic tumor suppressors have not been consistently identified .

What methodologies are recommended for validating potential ST7/LRP12-targeted therapies?

For researchers developing and validating potential therapeutic approaches targeting ST7/LRP12, the following methodological framework is recommended:

• Target validation: Confirm ST7 expression and function in the specific cancer type using immunohistochemistry, western blotting, and functional assays.

• In vitro models: Establish cell line models with controlled ST7 expression levels to test therapeutic candidates.

• Binding studies: For compounds designed to interact with ST7, validate binding using surface plasmon resonance or similar techniques with immobilized recombinant ST7.

• Functional readouts: Assess impact on downstream pathways, particularly those related to extracellular matrix remodeling and cell cycle regulation.

• In vivo models: Test in mouse xenograft models, particularly observing effects on tumor growth, invasion, and metastasis.

• Combinatorial approaches: Evaluate potential synergies with existing therapeutic approaches targeting complementary pathways .

What are the critical quality control parameters for recombinant mouse ST7/LRP12 protein production?

When producing and validating recombinant mouse ST7/LRP12 protein for research applications, the following quality control parameters should be carefully monitored:

• Purity assessment: SDS-PAGE analysis to confirm >95% purity, with minimal contaminating proteins.

• Identity confirmation: Western blot analysis using specific antibodies against ST7 and/or the His-tag.

• Endotoxin testing: Ensure levels are below 1.0 EU/μg of protein for cell culture applications.

• Functional validation: Binding assays with known interaction partners (e.g., LRPAP) to confirm biological activity.

• Stability testing: Evaluate protein stability after reconstitution under various storage conditions.

• Batch consistency: Compare between production lots to ensure reproducible experimental results .

How can researchers optimize immunodetection of native and recombinant ST7/LRP12 in different experimental systems?

For optimal detection of ST7/LRP12 in various experimental contexts:

• Western blotting:

  • Use reducing conditions for optimal epitope exposure

  • For mouse ST7, antibodies targeting the extracellular domain (ECD) between Glu33-Thr491 typically provide good specificity

  • Expected molecular weight of approximately 55-60 kDa for the recombinant ECD

• Immunohistochemistry/Immunofluorescence:

  • Fixation with 4% paraformaldehyde preserves epitope recognition

  • Antigen retrieval may be necessary for formalin-fixed tissues

  • Blocking with 5% normal serum reduces background

• Flow cytometry:

  • For cell surface expression, avoid permeabilization

  • For total cellular expression, use gentle permeabilization with 0.1% saponin

• ELISA:

  • Direct coating at 1-2 μg/mL on high-binding plates

  • Use carrier-free recombinant protein as standard

• Cross-reactivity considerations:

  • Antibodies raised against human ST7 may cross-react with mouse ST7 due to high sequence homology (95%) .

What are the current knowledge gaps in ST7/LRP12 research that require further investigation?

Despite significant progress in understanding ST7/LRP12, several critical knowledge gaps remain:

• Signaling pathways: The precise signaling mechanisms through which ST7 influences cell behavior remain incompletely characterized.

• Interaction partners: A comprehensive interactome for ST7 has not been established.

• Splicing variants: Genomic sequencing suggests the possibility of up to 18 splicing isoforms, but their expression and functions remain poorly understood.

• Tissue-specific roles: The function of ST7 may vary by tissue type, but these differences have not been systematically investigated.

• Post-translational modifications: Little is known about how phosphorylation or other modifications affect ST7 function.

• Therapeutic potential: Whether modulation of ST7 expression or function represents a viable therapeutic approach requires further exploration .

What emerging technologies and approaches might advance ST7/LRP12 research in the coming years?

Several emerging technologies and approaches hold promise for advancing our understanding of ST7/LRP12:

• CRISPR/Cas9 genome editing: For creating precise genetic models to study ST7 function in vivo.

• Single-cell transcriptomics: To understand cell-specific expression patterns and responses to ST7 modulation.

• Cryo-EM structural analysis: To determine the three-dimensional structure of ST7 and its complexes.

• Proteomics approaches: To identify interaction partners and post-translational modifications.

• Patient-derived organoids: To study ST7 function in more physiologically relevant models.

• Systems biology approaches: To integrate ST7 into broader signaling networks and identify potential therapeutic vulnerabilities.