Recombinant Chlorocebus aethiops Suppressor of tumorigenicity 7 protein (ST7)

What is the Suppressor of Tumorigenicity 7 (ST7) protein and what is its significance in research?

ST7 was originally identified as a putative tumor suppressor gene located on chromosome region 7q31.1-q31.2. Subsequent research has demonstrated that ST7 is a novel member of the low-density lipoprotein receptor (LDLR) superfamily, now also referred to as LRP12. This protein has transmembrane receptor characteristics and functions in both endocytosis and signal transduction pathways .

The significance of ST7 in research lies in its potential role in tumor suppression mechanisms. Studies have shown that ST7 mediates tumor suppression through regulation of genes involved in maintaining cellular structure and those involved in oncogenic pathways. This makes it a valuable target for cancer research, particularly in understanding tumor suppression mechanisms .

What protein interaction partners have been identified for ST7, and what experimental methods were used to discover them?

Research utilizing the yeast two-hybrid system has identified three key proteins that interact with the cytoplasmic domain of ST7:

• RACK1 (Receptor for Activated Protein C Kinase 1) - Involved in signal transduction

• MIBP (Muscle Integrin Binding Protein) - Plays a role in cell adhesion

• SARA (SMAD Anchor for Receptor Activation) - Functions in TGF-β signaling pathways

These interactions suggest that ST7, similar to other members of the LDLR superfamily, participates in both endocytosis and signal transduction pathways. The yeast two-hybrid system was specifically employed to identify proteins that associate with ST7's cytoplasmic domain, complemented by proteomic tools to analyze the functional motifs present in the protein .

The methodological approach involved:

• Construction of bait plasmids containing the cytoplasmic domain of ST7

• Screening against a prey library

• Verification of positive interactions through secondary screening

• Confirmation using co-immunoprecipitation assays

How does the subcellular localization of ST7 protein influence its function, and what techniques have been used to determine its localization?

ST7 exhibits predominantly cytosolic expression in various cancer cell lines, including HCT-116, MCF-7, and PC-3. This localization pattern has been determined using fluorescence microscopy of fusion proteins tagged with GFP, YFP, or V5 sequences, created using gateway cloning systems .

Importantly, studies have not observed ST7 translocation from the cytoplasm to the nucleus under various experimental conditions. This consistent cytoplasmic localization suggests that ST7 primarily functions through cytoplasmic signaling pathways rather than direct nuclear actions .

The methodological approach for localization studies included:

• Creation of various types of ST7 expression vectors tagged with fluorescent proteins

• Transfection into different cell lines

• Live-cell imaging and fixed-cell immunofluorescence

• Analysis under different cellular conditions

This subcellular localization is consistent with ST7's role as a member of the LDLR superfamily, as these receptors typically function at the cell membrane and in the cytoplasm during endocytosis and signal transduction processes .

What are the optimal storage and handling conditions for recombinant Chlorocebus aethiops ST7 protein to maintain its stability and activity?

Based on manufacturer recommendations for recombinant Chlorocebus aethiops ST7 protein:

Storage Conditions:

• Store at -20°C to -80°C for long-term storage

• Working aliquots can be stored at 4°C for up to one week

• Avoid repeated freeze-thaw cycles as they can compromise protein integrity

Reconstitution Protocol:

• Briefly centrifuge the vial before opening to bring contents to the bottom

• Reconstitute lyophilized protein in deionized sterile water to a concentration of 0.1-1.0 mg/mL

• Add glycerol to a final concentration of 5-50% (typically 50%) for long-term storage

• Aliquot to minimize freeze-thaw cycles

Buffer Conditions:

• Typically supplied in Tris/PBS-based buffer with 6% Trehalose, pH 8.0 or

• Tris-based buffer with 50% glycerol, optimized for protein stability

These conditions are designed to maintain the structural integrity and functional activity of the recombinant protein for experimental applications .

What cell-based assays have been developed to study ST7 function, and what are the critical experimental design considerations?

Several cell-based assays have been employed to study ST7 function:

Cell Cycle Synchronization Studies:

• Methodology: Cells are synchronized at specific phases of the cell cycle using chemical inhibitors or serum starvation/stimulation

• Analysis: Expression of ST7 and related genes is measured at each stage using quantitative PCR and Western blotting

• Key finding: ST7 and SERPINE1 are overexpressed when cells are arrested, with expression diminishing when cells re-enter cell division

Expression Vector Studies:

• Methodology: Various types of ST7 expression vectors tagged with fluorescent proteins are created using gateway cloning systems

• Analysis: Fusion protein localization is monitored via fluorescence microscopy

• Key finding: Cytosolic ST7 expression is observed in multiple cancer cell lines without nuclear translocation

Critical Experimental Design Considerations:

• Cell type selection - different cell lines may exhibit varied ST7 expression and function

• Expression system - overexpression may alter normal cellular distribution

• Tag selection - some tags may interfere with protein function or localization

• Controls - appropriate negative and positive controls are essential

• Validation - results should be confirmed using multiple approaches (e.g., fluorescence microscopy and biochemical fractionation)

These methodological considerations are crucial for accurately interpreting the biological function of ST7 in cellular contexts.

What is the evidence supporting ST7's role as a tumor suppressor, and how does it compare with other established tumor suppressors?

The evidence supporting ST7's role as a tumor suppressor comes from several key observations:

Genetic Evidence:

• ST7 is located on chromosome region 7q31.1-q31.2, which is frequently deleted in various human cancers

• Initial identification by McCormick and colleagues highlighted ST7 as a putative tumor suppressor gene

Functional Evidence:

• Cell cycle synchronization studies have shown that ST7 is overexpressed when cells are arrested in the cell cycle

• This expression diminishes when cells re-enter cell division status, suggesting a role in growth regulation

• ST7 mediates tumor suppression through regulation of genes involved in maintaining cellular structure and those in oncogenic pathways

Molecular Interaction Evidence:

• ST7's cytoplasmic domain interacts with signaling proteins involved in growth regulation, including RACK1, MIBP, and SARA

• These interactions suggest ST7 may influence growth regulatory pathways similar to other tumor suppressors

Compared to established tumor suppressors like p53 or PTEN, ST7 research is still in earlier stages. While p53 and PTEN have well-characterized mechanisms of action and established mutation profiles in human cancers, ST7's precise mechanism and mutation spectrum in cancer remain areas of active investigation. ST7 appears to function through receptor-mediated signaling as an LRP family member, whereas many classic tumor suppressors function as transcription factors or signaling molecules .

How does ST7 expression correlate with cell cycle progression, and what are the methodological challenges in studying this relationship?

Research has revealed a significant correlation between ST7 expression and cell cycle progression:

Expression Pattern:

• Both ST7 and SERPINE1 are overexpressed when cells are arrested in the cell cycle

• This expression diminishes when cells re-enter cell division status

• Related genes (Survivin, MMP-13, and Cyclin D1) also show differential expression during the cell cycle

Methodological Approach:
Cell cycle synchronization studies have been employed to analyze the expression of endogenous ST7 and potentially related genes at each stage of the cell cycle. The general methodology includes:

• Synchronizing cells using chemical inhibitors or serum starvation/release

• Confirming synchronization by flow cytometry

• Analyzing gene expression at different time points using qRT-PCR and Western blotting

• Correlating expression patterns with cell cycle phases

Methodological Challenges:

• Synchronization efficiency - No method achieves perfect synchronization, leading to mixed populations

• Synchronization artifacts - Chemical synchronization methods may alter normal gene expression patterns

• Temporal resolution - Precise timing of expression changes relative to cell cycle events can be difficult to establish

• Cell type differences - Expression patterns may vary between cell types

• Direct vs. indirect effects - Determining whether expression changes are directly related to cell cycle regulation or are secondary effects

• Protein stability considerations - mRNA and protein levels may not correlate due to post-transcriptional regulation

Addressing these challenges requires combining multiple synchronization methods, using reporter systems, and employing single-cell analysis techniques to establish definitive correlations between ST7 expression and cell cycle progression.

How does Chlorocebus aethiops ST7 compare with ST7 homologs in other species, and what insights does this provide about evolutionary conservation?

The ST7 protein shows interesting evolutionary conservation patterns across species:

Comparative Analysis of ST7 Across Species:

While the search results don't provide exact sequence identity percentages, the high conservation of ST7 across primates is consistent with its important biological function. The fact that ST7/LRP12 homologs are found across diverse vertebrate species including zebrafish suggests that this protein has ancient evolutionary origins and likely serves fundamental cellular functions .

Evolutionary Insights:

• The conservation of functional domains across species suggests selective pressure to maintain ST7's role in signal transduction and endocytosis

• Species-specific variations may reflect adaptations to different cellular environments

• The maintenance of ST7 across vertebrate evolution indicates its fundamental importance in cellular processes

These comparative analyses provide valuable insights into the core functions of ST7 that have been preserved through evolution, helping researchers identify the most critical aspects of its biology.

What unique genetic characteristics of Chlorocebus aethiops should researchers consider when studying ST7 in this model organism?

Researchers working with Chlorocebus aethiops ST7 should consider several unique genetic characteristics of this species:

Genome Structural Considerations:

• Chlorocebus aethiops possesses 29 autosomes (CAE1-CAE29) and two sex chromosomes (CAEX and CAEY)

• The species exhibits unique chromosomal fission events that differentiate vervets and their close relatives from most other catarrhine primates

• These karyotype differences may affect gene regulation and expression patterns

Genetic Diversity:

• Analysis of sequenced genomes from different vervet subspecies reveals high levels of genetic diversity

• Caribbean C. a. sabaeus vervets show extremely low diversity in major histocompatibility complex (MHC) polymorphisms compared to vervets from putatively ancestral West African regions

• This reduced genetic diversity may influence immune responses and susceptibility to disease

Transposable Elements:

• The Chlorocebus aethiops genome contains distinct patterns of transposable elements that differ from those in humans and rhesus macaques

• Some chromosomes show significant over-representation or under-representation of specific elements

• These genomic features may influence gene expression and regulation

Structural Variations:

• Researchers have identified structural variations in C. a. sabaeus research populations that are predicted to have potential deleterious effects

• These variations must be considered when interpreting experimental results

Understanding these species-specific genetic characteristics is essential for researchers using Chlorocebus aethiops as a model organism for ST7 studies, as they may impact gene expression, regulation, and function in ways that differ from other model systems .

What are the most effective methods for studying ST7-mediated signaling pathways, and how can researchers overcome technical limitations?

Studying ST7-mediated signaling pathways requires sophisticated experimental approaches:

Effective Methodological Approaches:

• Protein-Protein Interaction Studies:

  • Yeast two-hybrid screening has successfully identified ST7 interaction partners (RACK1, MIBP, SARA)

  • Co-immunoprecipitation followed by mass spectrometry can identify broader interaction networks

  • Proximity-based labeling methods (BioID, APEX) can capture transient interactions

  • Förster resonance energy transfer (FRET) can detect direct interactions in living cells

• Pathway Analysis:

  • Phospho-proteomics to identify changes in signaling pathway activation

  • Reporter gene assays using pathway-specific response elements

  • Transcriptomics to identify genes regulated downstream of ST7

  • Pharmacological inhibition or activation of suspected pathways to establish hierarchy

• Functional Genomics:

  • CRISPR/Cas9-mediated gene editing to create knockout or knock-in models

  • RNA interference for temporary knockdown

  • Rescue experiments using wild-type or mutant ST7 constructs

Technical Limitations and Solutions:

These methodological considerations help researchers design robust experiments to elucidate the complex signaling pathways mediated by ST7 protein .

How do ST7 expression and function vary across different tissue types, and what specialized techniques are required to study tissue-specific effects?

Understanding tissue-specific ST7 expression and function is critical for comprehensive characterization:

Tissue-Specific Expression Patterns:
While the search results don't provide comprehensive data on tissue-specific expression of ST7 in Chlorocebus aethiops, studies in human and other model systems suggest differential expression across tissues. Research has particularly focused on ST7 expression in cancer cell lines (HCT-116, MCF-7, and PC-3), demonstrating cytosolic expression patterns .

Specialized Techniques for Tissue-Specific Studies:

• Tissue-Specific Expression Analysis:

  • Single-cell RNA sequencing to identify cell-type specific expression

  • Laser capture microdissection to isolate specific cell populations

  • Spatial transcriptomics to map expression patterns while preserving tissue architecture

  • Immunohistochemistry with validated antibodies for protein localization

• Tissue-Specific Functional Studies:

  • Conditional knockout models using tissue-specific promoters

  • Organoid cultures to study ST7 function in three-dimensional tissue-like structures

  • Xenograft models to study function in tumor microenvironments

  • Co-culture systems to examine interactions between different cell types

• Data Integration Approaches:

  • Multi-omics integration (transcriptomics, proteomics, metabolomics)

  • Network analysis to identify tissue-specific interaction partners

  • Computational modeling of tissue-specific pathways

  • Cross-species comparisons to identify conserved tissue-specific functions

• Methodological Considerations:

  • Tissue preservation techniques to maintain protein integrity

  • Optimization of extraction protocols for different tissue types

  • Validation across multiple biological replicates

  • Controls for tissue-specific background and non-specific signals

These specialized techniques allow researchers to comprehensively characterize the tissue-specific roles of ST7, which is essential for understanding its biological functions in normal physiology and disease contexts .

What are the most promising research directions for ST7 that could lead to translational applications, and what methodological advances are needed?

Several promising research directions for ST7 could lead to translational applications:

Promising Research Directions:

• Cancer Diagnostics and Prognostics:

  • Evaluation of ST7 expression or mutation status as biomarkers for cancer prognosis

  • Development of diagnostic tools based on ST7 pathway dysregulation

  • Correlation of ST7 status with treatment response

• Therapeutic Target Development:

  • Identification of compounds that modulate ST7 signaling

  • Development of approaches to restore ST7 function in cancers with ST7 inactivation

  • Targeting of ST7 interaction partners in cancers with intact ST7

• Pathway-Based Therapeutic Approaches:

  • Exploiting synthetic lethality with ST7 loss in cancer cells

  • Targeting downstream effectors in ST7-deficient tumors

  • Combination therapies based on ST7 pathway status

Methodological Advances Needed:

• Improved Research Tools:

  • Development of highly specific antibodies for different ST7 domains and modifications

  • Creation of reporter systems for ST7 activity in live cells

  • Generation of better animal models with tissue-specific ST7 modulation

• Advanced Screening Platforms:

  • High-throughput screening methods to identify ST7 modulators

  • Patient-derived organoid models for personalized medicine approaches

  • CRISPR screens to identify synthetic lethal interactions

• Clinical Translation Tools:

  • Standardized assays for measuring ST7 status in patient samples

  • Biomarker panels incorporating ST7 pathway components

  • Imaging approaches to visualize ST7 activity in vivo

The translational potential of ST7 research will depend on advancing our understanding of its fundamental biology while simultaneously developing the methodological tools needed to apply this knowledge in clinical settings .

What are the key contradictions or knowledge gaps in current ST7 research, and how might these be resolved through innovative experimental approaches?

Current ST7 research contains several important knowledge gaps and apparent contradictions:

Key Knowledge Gaps and Contradictions:

• Functional Classification Contradiction:

  • ST7 was initially identified as a tumor suppressor gene, but later classified as a low-density lipoprotein receptor-related protein (LRP12)

  • Resolution approach: Integrated studies examining both its tumor suppressor functions and its role in receptor-mediated endocytosis to determine how these roles interconnect

• Mechanism of Tumor Suppression:

  • The precise mechanisms by which ST7 suppresses tumorigenesis remain unclear

  • Resolution approach: Comprehensive pathway mapping using phospho-proteomics, transcriptomics, and functional genomics to identify key nodes in ST7-mediated tumor suppression

• Subcellular Localization and Function:

  • As an LDLR family member, ST7 would be expected at the cell membrane, yet studies show primarily cytosolic localization

  • Resolution approach: Advanced imaging techniques like super-resolution microscopy and live-cell imaging to track dynamic localization and trafficking

• Species Differences in Function:

  • The extent to which ST7 function differs between Chlorocebus aethiops and humans remains unexplored

  • Resolution approach: Comparative functional studies using orthologous proteins in different model systems

Innovative Experimental Approaches:

• Integrative Multi-Omics:

  • Combine proteomics, transcriptomics, and metabolomics to build comprehensive models of ST7 function

  • Apply systems biology approaches to predict and test network effects

• Advanced Genome Editing:

  • CRISPR-based approaches for precise domain modifications

  • Base editing to introduce specific mutations found in human cancers

  • Prime editing for complex sequence alterations

• Structural Biology:

  • Cryo-EM studies of ST7 protein complexes

  • Hydrogen-deuterium exchange mass spectrometry to map protein interactions

  • Computational modeling of structural dynamics

• Single-Cell Approaches:

  • Single-cell transcriptomics to capture heterogeneity in response

  • Single-cell proteomics to identify rare cellular states

  • Spatial transcriptomics to maintain tissue context