STC 1 Human

What is human Stanniocalcin-1 (STC1) and what are its primary functions?

Human Stanniocalcin-1 (STC1) is a 56 kDa homodimeric glycoprotein hormone that was originally identified in bony fishes as a hypocalcemic hormone secreted by the corpuscles of Stannius . The human STC1 protein consists of a 16 amino acid propeptide region and a 214 amino acid STC1 chain . In humans, STC1 functions extend beyond calcium homeostasis to include diverse physiological and pathological processes.

STC1 plays crucial roles in calcium and phosphate homeostasis, cell proliferation, apoptosis, inflammation, oxidative stress responses, and cancer development . It has been characterized as a "molecular guard" providing cytoprotection against hypoxic, hypercalcaemic, and ischemic damage, primarily by modulating inflammatory responses and oxidative stress . Additionally, STC1 is involved in organogenesis, angiogenesis, cellular metabolism, differentiation, implantation, and lactation .

Research methodologies to study STC1 functions typically employ recombinant protein administration, gene knockout/knockdown approaches, and overexpression systems in cell culture and animal models, followed by biochemical assays to measure specific cellular responses.

How does the tissue distribution of STC1 differ between fish and humans?

The tissue distribution of STC1 shows remarkable evolutionary differences. In fish, STC1 is primarily expressed in and secreted by the corpuscles of Stannius, specialized endocrine glands located on the kidneys . In response to elevated plasma calcium levels, fish STC1 is released in an endocrine manner to inhibit gill and intestinal calcium uptake and renal phosphate excretion .

In contrast, mammalian STC1 demonstrates a fundamentally different expression pattern. Human STC1 is widely expressed across multiple tissues including thyroid, ovary, prostate, adrenal gland, muscle, intestine, kidney, heart, and lung . Despite this broad tissue expression, human STC1 is barely detectable in circulation under normal physiological conditions, suggesting it primarily functions through local paracrine or autocrine mechanisms rather than as a classic endocrine hormone .

To study tissue distribution, researchers typically employ immunohistochemistry, in situ hybridization, qRT-PCR, and tissue-specific knockout models to characterize expression patterns across different organs and cell types.

What are the validated receptors for human STC1?

Identifying the receptor(s) for STC1 has been challenging in the field. Recent research using TriCEPS-based ligand-receptor methodology has identified IGF2R/MPRI (Insulin-like Growth Factor 2 Receptor/Mannose-6-Phosphate Receptor) as a high-affinity binding protein for human STC1 in ThP-1 cells . This represents a significant advance in understanding STC1 signaling mechanisms.

Surface plasmon resonance assays demonstrated that human STC1 binds to immobilized IGF2R/MPRI with high affinity (10-20 nM) and capacity (Rmax 70-100%) . These binding characteristics are comparable to those of CREG (cellular repressor of E1A-stimulated gene), a known ligand of IGF2R/MPRI . Competitive binding assays further showed that CREG competed with hSTC1 for binding to IGF2R/MPRI, suggesting they may share binding sites .

Methodologically, receptor identification studies typically employ techniques such as:

• TriCEPS-based ligand-receptor capture followed by LC-MS/MS analysis

• Surface plasmon resonance for binding kinetics

• Competitive binding assays

• Co-immunoprecipitation

• Functional validation through receptor knockdown/knockout approaches

How does STC1 expression correlate with cancer progression?

Interestingly, in endometrial cancer (EC), the relationship appears inverse. Decreased STC1 expression is associated with factors relating to worse prognosis, including grade 3 endometrioid tumors, deep myometrial invasion, lymphovascular space invasion, and large tumor size . Additionally, STC1 expression was decreased in tumors from obese women and women with diabetes mellitus type 2 .

Research methodologies to study STC1 in cancer typically include:

• Tissue microarray (TMA) analysis with immunohistochemistry scoring

• Correlation of expression with clinicopathological parameters

• Survival analysis using Kaplan-Meier curves

• In vitro functional studies using cancer cell lines

• Analysis of cancer databases such as TCGA

What molecular mechanisms underlie STC1's role in cancer?

STC1 participates in multiple cancer-related signaling pathways, including NOTCH1-SOX2, NF-κB, and JNK signaling pathways . The NF-κB pathway has been reported to suppress apoptosis and promote bladder cancer cell proliferation by upregulating survivin expression, while JNK plays an important role in bladder cancer cell invasion .

In terms of cell cycle regulation, STC1 may promote cancer cell proliferation by influencing several cyclins and cyclin-dependent kinases (CDKs). Studies in prostate cancer have shown that STC1 promotes cell proliferation by correlating with the expression levels of cell cycle-related proteins, particularly cyclin E1/CDK2 . Similarly, in clear cell renal cell carcinoma, STC1 can promote cell cycle progression and accelerate G1/S transition by elevating the expression of cyclin D1, Cdk4, and Cdk6 while suppressing p21 .

STC1 may also be involved in the epithelial-mesenchymal transition (EMT) process, thus playing a crucial role in the initiation of the tumor microenvironment and potentially in metastasis .

To study these mechanisms, researchers typically employ:

• Gene knockdown/overexpression in cancer cell lines

• Western blotting for pathway components

• Cell cycle analysis using flow cytometry

• Migration and invasion assays

• Co-immunoprecipitation to detect protein-protein interactions

How does STC1 interact with the tumor immune microenvironment?

Emerging evidence suggests STC1 plays a crucial role in mediating tumor immunity . Analysis of The Cancer Genome Atlas (TCGA) database has revealed positive correlations between STC1 and common immune checkpoints in bladder cancer, including PDL1, PD-L2, OX40L, TIM3, OX40, FOXP3, CTLA4, and B7H3 .

The positive correlation between STC1 and PDL1 has been validated through immunohistochemistry staining, with tumors expressing higher STC1 tending to express higher PDL1 . This relationship suggests that targeting STC1 might potentially enhance the efficacy of immunotherapy approaches, particularly those targeting the PD-1/PDL1 axis.

Comprehensive analysis of STC1-associated immune signatures in bladder cancer identified 377 immune-related genes correlated with STC1 expression, with the majority (318 genes) being positively correlated . Gene Ontology and KEGG pathway analyses of these genes further support STC1's significant role in immune functions in bladder cancer .

Methodological approaches to study STC1's immune interactions include:

• Correlation analysis between STC1 and immune markers in databases

• Immunohistochemistry validation

• Co-culture experiments with cancer cells and immune cells

• In vivo studies using immunocompetent mouse models

• RNA-seq and proteomics to identify immune-related gene signatures

What techniques are most effective for measuring STC1 expression in clinical samples?

Researchers employ several complementary techniques to measure STC1 expression in clinical samples, each with specific advantages:

Immunohistochemistry (IHC) is widely used for examining STC1 protein expression in tissue samples. This approach allows for semi-quantitative assessment and determination of cellular localization. For example, in endometrial cancer studies, TMA slides are digitally scanned, and staining intensity is scored on a scale of 0-3 (negative to high) . The percentage of positive cells can also be scored (e.g., 0-4 for 0% to >75%) . This approach provides spatial information about STC1 expression within the tissue microenvironment.

Immunoreactive score (IRS) calculation combines staining intensity and percentage of positive cells. For instance, multiplying the intensity score (0-3) by the percentage score (0-4) yields an IRS ranging from 0-12, allowing for more nuanced classification of expression levels .

Quantitative RT-PCR provides sensitive detection of STC1 mRNA expression and is useful for validating IHC findings. Western blotting can quantify protein levels when sufficient tissue is available.

ELISA may be employed for detecting STC1 in serum or other body fluids, though circulating levels are typically low under normal conditions .

For comprehensive analysis, researchers should consider using multiple techniques and ensuring proper controls, including positive and negative tissue controls for IHC and appropriate housekeeping genes for qRT-PCR.

What are optimal experimental models for studying STC1 functions?

Various experimental models provide complementary insights into STC1 biology:

Cell Culture Models: Human cell lines such as ThP-1 (human leukemia monocytic cell line) have been used to study STC1 binding partners and signaling mechanisms . Endometrial and bladder cancer cell lines are valuable for investigating STC1's role in these malignancies . Primary cells from relevant tissues can provide more physiologically relevant contexts.

Animal Models: STC1 knockout and transgenic overexpression mouse models have been instrumental in elucidating in vivo functions. Given the high homology between human and mouse STC1 (95% amino acid identity) , mouse models generally provide translatable insights into human STC1 biology.

Tissue Microarrays (TMAs): These are powerful tools for clinical correlation studies, allowing examination of STC1 expression across large patient cohorts. For example, TMAs containing 832 endometrial cancer samples enabled robust correlation of STC1 expression with clinicopathological features and survival outcomes .

Recombinant Protein Studies: Purified recombinant human STC1 protein allows for controlled functional studies, particularly for investigating receptor binding and downstream signaling events .

The choice of model system should align with specific research questions. Combination approaches are often most informative, with in vitro findings validated in animal models and correlated with clinical observations.

How can protein-protein interactions of STC1 be effectively studied?

Understanding STC1's interactions with other proteins is crucial for elucidating its functions. Several complementary approaches are employed:

Surface Plasmon Resonance (SPR) has been successfully used to demonstrate high-affinity binding between human STC1 and IGF2R/MPRI . This technique provides quantitative binding parameters including affinity (Kd), association/dissociation rates (kon/koff), and binding capacity (Rmax) . SPR also facilitates competitive binding assays to determine whether multiple ligands compete for the same binding site.

TriCEPS-based Ligand-Receptor Capture followed by LC-MS/MS analysis has proven effective for identifying novel STC1-binding proteins . This approach involves chemically coupling the ligand (STC1) to the TriCEPS reagent, incubating with intact cells, and analyzing captured proteins by mass spectrometry.

Co-immunoprecipitation can validate protein-protein interactions identified through other methods and is particularly useful for detecting interactions in cell lysates under more physiological conditions.

Yeast Two-Hybrid Screening and Protein Microarrays represent additional approaches for identifying novel interaction partners, though these have limitations in detecting interactions requiring post-translational modifications or membrane contexts.

Proximity Ligation Assay (PLA) enables visualization of protein-protein interactions in situ within tissue sections or cultured cells, providing spatial information about where interactions occur.

Researchers should consider combining multiple techniques to confirm interactions and characterize their functional significance through downstream assays.

How does STC1 expression correlate with specific disease states?

STC1 expression patterns show distinct correlations with various disease states, particularly in cancer:

Endometrial Cancer: Decreased STC1 expression correlates with factors indicating worse prognosis, including grade 3 endometrioid tumors (p = 0.030), deep myometrial invasion (p = 0.003), lymphovascular space invasion (p = 0.050), and large tumor size (p = 0.001) . Additionally, STC1 expression was decreased in tumors from obese women (p = 0.014) and women with diabetes mellitus type 2 (p = 0.001) . An association between DNA mismatch repair deficiency and weak STC1 expression was also observed .

Other Cancers: Previous studies have shown that STC1 is involved in various human cancers including breast, ovarian, and cervical cancers, regulating cellular proliferation, invasion, and metastasis . In hepatocellular carcinoma, higher serum STC1 levels correlate with larger tumor size and poorer 5-year disease-free survival .

These contrasting patterns across different cancer types highlight the context-dependent roles of STC1 and underscore the importance of cancer-specific investigations before considering STC1 as a diagnostic or prognostic biomarker.

What are the challenges in developing STC1-targeted therapeutics?

Developing therapeutics targeting STC1 faces several challenges:

Context-Dependent Functions: As evidenced by contrasting patterns in different cancers, STC1 appears to have context-dependent effects that may be tumor-promoting in some cancers and tumor-suppressive in others . This complexity necessitates careful disease-specific validation before therapeutic targeting.

Receptor Complexity: While IGF2R/MPRI has been identified as a binding partner for STC1 , the complete receptor system and downstream signaling pathways remain incompletely characterized. This knowledge gap complicates rational drug design efforts.

Normal Physiological Functions: STC1's roles in normal physiological processes including calcium homeostasis, cellular metabolism, and cytoprotection against stress raise concerns about potential side effects of STC1 inhibition. The wide tissue distribution of STC1 in humans further complicates this issue .

Delivery Challenges: If recombinant STC1 were to be considered as a therapeutic (e.g., for conditions where STC1 is protective), effective delivery to target tissues would present challenges given its protein nature and potential for immunogenicity.

Biomarker Development: Before STC1-targeted therapy, robust biomarkers are needed to identify patients most likely to benefit. This requires standardized detection methods and validated cutoff values for STC1 expression levels.

Addressing these challenges requires comprehensive preclinical studies including detailed mechanism investigations, tissue-specific conditional knockout models, and careful toxicology assessments before clinical translation.

How might STC1 be utilized as a biomarker in precision medicine?

STC1's differential expression across disease states positions it as a potential biomarker in precision medicine approaches:

Cancer Prognosis: In endometrial cancer, decreased STC1 expression correlates with aggressive features and potentially worse outcomes . Conversely, in bladder cancer, increased STC1 expression is associated with advanced disease and shorter survival . These patterns suggest STC1 could serve as a prognostic biomarker, helping stratify patients into risk categories that inform treatment decisions.

Immunotherapy Response Prediction: The positive correlation between STC1 and immune checkpoint molecules (including PDL1) in bladder cancer suggests potential utility in predicting immunotherapy response . Patients with high STC1/PDL1 co-expression might represent a distinct subgroup for checkpoint inhibitor therapy.

Therapeutic Target Identification: Beyond its role as a biomarker, STC1 expression patterns could identify patients who might benefit from therapies targeting STC1 or its downstream pathways. In cancers where STC1 promotes progression, inhibition strategies might be beneficial.

Implementation Approaches: For clinical implementation, standardized immunohistochemistry scoring systems have been developed, including semi-quantitative approaches evaluating both staining intensity (0-3) and percentage of positive cells . These could be further refined into clinical grade assays.

Future development requires prospective validation in larger patient cohorts, standardization of detection methods, establishment of clinically relevant cutoff values, and integration with other biomarkers into comprehensive predictive models.

What is the relationship between STC1 and metabolism in cancer?

The relationship between STC1 and metabolism in cancer represents an emerging research area:

Obesity and diabetes, both conditions with significant metabolic dysregulation, appear to influence STC1 expression in cancer. In endometrial cancer, STC1 expression was decreased in tumors obtained from obese women (p = 0.014) and women with diabetes mellitus type 2 (p = 0.001) . This suggests potential interactions between metabolic signaling pathways and STC1 regulation.

STC1 has been reported to influence mitochondrial metabolism, though the detailed mechanisms remain to be fully characterized . Given the critical role of metabolic reprogramming in cancer, including altered mitochondrial function, this represents an important area for further investigation.

The association of STC1 with insulin-like growth factor pathways, particularly its binding to IGF2R/MPRI , suggests potential cross-talk with insulin/IGF signaling networks that are central to cellular metabolism and frequently dysregulated in cancer.

Methodological approaches to study these relationships include:

• Metabolic profiling of cancer cells with altered STC1 expression

• Measuring mitochondrial function parameters in response to STC1

• Investigating STC1 expression in metabolic disease models

• Analyzing correlations between STC1 and metabolic gene signatures in cancer databases

How does the molecular structure of STC1 influence its function?

Understanding structure-function relationships is crucial for comprehending STC1's diverse roles:

Human STC1 is a homodimeric glycoprotein with each monomer consisting of a 16 amino acid propeptide region followed by a 214 amino acid STC1 chain . The mature protein forms a disulfide-linked dimer with a molecular weight of approximately 56 kDa .

The amino acid sequence of human STC1 shares 36% identity with human STC2, suggesting some functional overlap but also distinct roles for these family members . More notably, human STC1 shares 95% amino acid identity with mouse STC1, indicating high evolutionary conservation among mammals despite the divergence from fish STC1 .

Post-translational modifications, particularly glycosylation, likely play important roles in STC1 function. The "glycoprotein" nature of STC1 suggests carbohydrate modifications that could influence protein folding, stability, receptor binding, and biological activity .

The high binding affinity (10-20 nM) observed between human STC1 and IGF2R/MPRI suggests specific structural domains involved in this interaction . Competitive binding with CREG further suggests potential shared binding sites or structural features .

Methodological approaches to study STC1 structure-function relationships include:

• Site-directed mutagenesis to identify critical residues

• Glycosylation analysis by mass spectrometry

• Structural determination by X-ray crystallography or cryo-EM

• Structure-guided design of inhibitors or mimetics