S100A11 Human

What is the molecular structure of S100A11 and how does it function as a calcium-binding protein?

S100A11 is a member of the S100 protein family with a molecular weight between 10-14 kDa. It possesses a characteristic helix-loop-helix EF hand motif that enables calcium binding. The protein typically forms homodimers and undergoes conformational changes upon calcium binding, which exposes hydrophobic surfaces for target protein interactions. Structurally, S100A11 shows higher sequence similarity with S100G and S100A7L2 compared to other family members . For experimental analysis, researchers should employ X-ray crystallography or NMR spectroscopy to determine structural changes upon calcium binding and target protein interaction.

What is the tissue-specific expression pattern of S100A11 in normal human tissues?

S100A11 demonstrates distinct tissue-specific expression. It is highly expressed in skin, spleen, lung, kidney, subcutaneous white adipose tissue (sWAT), and stomach. Moderate expression is observed in small intestine, heart, and pancreas, while lower expression occurs in liver, brain, and muscle . For accurate determination of expression patterns, researchers should employ both RNA-seq and proteomic analyses, as post-transcriptional regulation may cause discrepancies between mRNA and protein levels. Single-cell RNA sequencing can further delineate cell-type specific expression within heterogeneous tissues.

How is S100A11 subcellular localization regulated in different cell types?

S100A11 exhibits dynamic subcellular distribution that is cell type and condition dependent. It can localize to the nucleus, cytoplasmic matrix, and extracellular regions. In human keratinocytes under normal conditions, S100A11 is uniformly distributed in the cytoplasm. Upon stimulation with high calcium concentration (0.3 mmol/L), it interacts with Annexin I and accumulates at the inner cell membrane through a process requiring tubulin but independent of the classical Golgi/ER export pathway . For investigating subcellular localization, researchers should employ subcellular fractionation followed by Western blotting, combined with immunofluorescence microscopy using organelle-specific markers.

How does S100A11 regulate cell cycle progression and proliferation in epithelial cells?

S100A11 exhibits dual regulatory roles in cell proliferation. Intracellularly, when activated by high calcium or TGF-β, S100A11 translocates to the nucleus where it induces p21WAF1 expression, leading to cell cycle arrest. Conversely, downregulation of S100A11 decreases AKT phosphorylation, activating GSK3 which phosphorylates p21 at threonine-57, causing its degradation and promoting cell proliferation through the PI3K/AKT pathway . For experimental investigation, researchers should employ both gain-of-function and loss-of-function approaches combined with cell cycle analysis by flow cytometry and real-time monitoring of proliferation markers.

What mechanisms govern S100A11 secretion and its extracellular functions?

S100A11 is actively secreted from normal human keratinocytes and functions extracellularly to stimulate cell growth by enhancing production of epidermal growth factor (EGF) family proteins . The secretion process involves exosome generation at the plasma membrane rather than the classical Golgi/ER pathway . Extracellular S100A11 forms dimers that bind to receptor for advanced glycation end products (RAGE), triggering signaling cascades involving NF-κB, Akt, and cAMP response element-binding protein (CREB) . To study this process, researchers should examine exosome isolation techniques, utilize fluorescently-labeled S100A11, and perform receptor blocking experiments.

What role does S100A11 play in calcium homeostasis and signaling in human cells?

S100A11 serves as a crucial intermediator in epidermal growth factor (EGF)-stimulated calcium uptake and release from intracellular calcium stores. Knockdown of S100A11 inhibits EGF-promoted calcium uptake and release from calcium stores . S100A11 proteins predominantly localize to the endoplasmic reticulum, a major intracellular calcium storage site . For investigating calcium dynamics, researchers should employ fluorescent calcium indicators, calcium imaging techniques, and ER-specific calcium sensors, together with S100A11 modification approaches.

How does S100A11 expression correlate with cancer progression and patient outcomes?

S100A11 exhibits variable expression patterns across cancer types, though it is predominantly overexpressed in many cancers including renal cell carcinoma, prostate cancer, breast cancer, and hepatocellular carcinoma. High S100A11 expression often correlates with advanced cancer stage, larger tumor size, and poorer prognosis . In breast cancer specifically, multivariate Cox regression analysis indicates that high S100A11 expression independently influences poor outcomes (HR = 1.738, 95% CI: 1.197–2.524) . For prognostic studies, researchers should develop nomograms incorporating S100A11 expression with other clinical parameters and validate with independent cohorts using Kaplan-Meier analysis and receiver operating characteristic curves.

What is the significance of S100A11 mutations in human cancers?

S100A11 mutation rate in breast cancer is reported at 14%, with survival analysis suggesting that patients with S100A11 mutations have worse prognosis . For comprehensive mutation analysis, researchers should perform whole-exome sequencing followed by functional characterization of identified mutations using site-directed mutagenesis and cellular assays to determine effects on protein stability, calcium binding, dimerization, and downstream signaling.

How does S100A11 contribute to reproductive function and fertility?

S100A11 is expressed in human endometrium and plays a crucial role in endometrial receptivity and embryo implantation. Significantly lower S100A11 protein levels are observed in endometrium of women with failed pregnancy compared to women with successful pregnancy outcomes . Knockdown of endometrial S100A11 reduces embryo implantation rates in mouse models and adversely affects factors related to endometrial receptivity and immune responses in human endometrial cells . For reproductive research, investigators should employ both in vitro models (JAr spheroid attachment assays) and in vivo mouse models, while analyzing markers of endometrial receptivity and immune tolerance.

What is the relationship between S100A11 and immune cell infiltration in cancer?

S100A11 expression correlates with immune cell infiltration in breast cancer and shows positive associations with 17 immune checkpoint-related genes . S100A11 may influence cancer progression through the IL-17 signaling pathway as revealed by KEGG pathway enrichment analysis . To investigate immune relationships, researchers should perform comprehensive immune profiling using cytometry by time of flight (CyTOF), spatial transcriptomics, and multiplex immunohistochemistry to characterize the tumor immune microenvironment in relation to S100A11 expression.

What are the optimal techniques for recombinant S100A11 protein production and purification?

For recombinant S100A11 production, researchers should clone S100A11 cDNA into appropriate expression vectors (e.g., pET3a). Purification can be achieved through differential precipitation using polyethylenimine and ammonium sulfate, followed by ion exchange column chromatography . To prepare S100A11 dimers, the purified protein should be incubated in HEPES buffer (pH 7.5) at 4°C for 2 weeks, followed by gel filtration to isolate the dimeric form . For functional studies, biotinylation can be performed using Biotin-(AC5)2sulfo-OSu with a 3:1 molar ratio to S100A11, with unincorporated biotin removed via size exclusion chromatography .

What are effective strategies for studying S100A11 protein-protein interactions?

To investigate S100A11 interactions, researchers can employ:

• Co-immunoprecipitation with specific anti-S100A11 antibodies

• Pull-down assays using GST-fusion proteins

• Yeast two-hybrid screening

• Biolayer interferometry or surface plasmon resonance for kinetic measurements

• Proximity ligation assays for in situ interaction detection

For the S100A11-Annexin A1 interaction specifically, researchers should examine the C-terminal region of S100A11, as deletion of 14 amino acid residues in this region abolishes this interaction .

How can researchers effectively modulate S100A11 expression in cellular models?

For knockdown experiments, S100A11-specific siRNA has proven effective in reducing expression . For overexpression, transfection with expression vectors containing S100A11 cDNA under strong promoters should be employed. CRISPR-Cas9 genome editing can generate stable S100A11 knockout cell lines for long-term studies. For temporal control, inducible expression systems like Tet-On/Off can be utilized. Verification of expression changes should be performed at both mRNA (qRT-PCR) and protein (Western blot) levels.

What detection methods provide the most sensitive and specific measurement of S100A11 in clinical samples?

For clinical samples, researchers should consider:

• Immunohistochemistry with specific anti-S100A11 antibodies for tissue samples

• ELISA for quantitative measurement in plasma or serum

• Multiplex protein arrays for simultaneous detection with other S100 family members

• Digital PCR for absolute quantification of mRNA levels

• Mass spectrometry for proteomic profiling

Validation across multiple platforms is recommended to ensure reliability of results. Custom antibodies raised against S100A11 dimer as immunogen have been successfully used for detection and neutralization experiments .

How should researchers address the apparent dual role of S100A11 in growth regulation?

The dual nature of S100A11 in both growth inhibition and promotion presents an analytical challenge. Researchers should:

• Distinguish between intracellular and extracellular effects by using cell-impermeable neutralizing antibodies

• Perform compartment-specific expression modifications (nuclear-targeted vs. secreted forms)

• Design time-course experiments to capture sequential effects

• Utilize single-cell analysis to identify potential cellular heterogeneity in responses

• Develop mathematical models accounting for concentration-dependent effects and feedback loops

Careful experimental design with appropriate controls for localization is essential for dissecting these opposing functions .

What analytical approaches best reveal the relationship between S100A11 and clinical outcomes?

For robust clinical correlation analyses, researchers should:

• Perform multivariate Cox regression analysis to determine if S100A11 is an independent prognostic factor

• Develop predictive nomograms incorporating S100A11 with established clinical parameters

• Use machine learning approaches to identify non-linear relationships

• Stratify patients by molecular subtypes to identify context-dependent effects

• Validate findings across independent cohorts with sufficient statistical power

A nomogram incorporating five factors (S100A11, age, clinical stage, N, and M) has demonstrated good consistency and accuracy for breast cancer prognosis prediction .

How can researchers distinguish the effects of S100A11 from other S100 family proteins in functional studies?

Given the structural and functional similarities among S100 proteins, researchers should:

• Use highly specific antibodies validated for lack of cross-reactivity

• Design siRNAs targeting unique regions of S100A11 mRNA

• Perform rescue experiments with siRNA-resistant S100A11 expression

• Compare effects with other S100 family members (e.g., S100A2, S100A6, S100A10) in parallel experiments

• Consider potential compensatory mechanisms by analyzing expression changes in other S100 proteins after S100A11 modulation

Recombinant proteins of multiple S100 family members should be prepared similarly to enable valid comparisons .

What are promising therapeutic strategies targeting S100A11 in cancer and inflammatory diseases?

Potential therapeutic approaches include:

• Neutralizing antibodies against extracellular S100A11

• Small molecule inhibitors of S100A11-RAGE interaction

• Peptide antagonists derived from the S100A11 N-terminus (19 amino acid region)

• Targeted delivery of siRNA to reduce S100A11 expression in specific tissues

• Inhibitors of downstream pathways (NF-κB, Akt, CREB)

Research indicates that a 19 amino acid peptide from the N-terminus of S100A11 can promote AIF translocation from cytoplasm to nucleus, inducing apoptosis in tumor cells , which might form the basis for peptide-based therapeutics.

How might S100A11 serve as a biomarker in precision medicine approaches?

S100A11 shows potential as a biomarker for:

• Cancer prognosis, particularly in breast, renal, and hepatocellular carcinomas

• Predicting response to specific therapies through correlation with immune checkpoint molecules

• Monitoring reproductive health and predicting pregnancy outcomes

• Assessing inflammatory status in conditions like osteoarthritis

Researchers should focus on developing standardized detection methods with established clinical thresholds and validate in large, diverse patient cohorts. Integration with other biomarkers in multi-parameter panels may enhance predictive power .

What aspects of S100A11 calcium-binding properties remain unexplored?

Future research directions should investigate:

• The structural basis for calcium-dependent conformational changes using advanced biophysical techniques

• Differential calcium binding affinities across various cellular compartments

• Competitive interactions with other calcium-binding proteins

• Calcium-dependent protein-protein interaction networks

• Effects of post-translational modifications on calcium binding properties

Fluorescence methods examining cytosolic Ca²⁺ changes and Ca²⁺ release from intracellular stores in response to S100A11 modulation will be valuable for these investigations .

How does S100A11 contribute to cellular stress responses and adaptation?

Emerging research should explore:

• S100A11's role in cellular response to various stressors (oxidative, ER stress, DNA damage)

• Its contribution to cellular adaptation to chronic stress conditions

• Potential involvement in cellular senescence and tissue aging

• Cross-talk with major stress response pathways (heat shock, unfolded protein response)

• Role in stress granule formation and regulation of stress-responsive gene expression

These studies will provide insights into S100A11's fundamental role in cellular homeostasis beyond its currently known functions.