S100A7A Human

What is S100A7A and how does it differ from S100A7?

S100A7A (koebnerisin) is a protein encoded by the S100A7A (alias: S100A15) gene in humans. It belongs to the S100 calcium-binding protein family that regulates fundamental cellular and extracellular processes including cell proliferation, differentiation, migration, and antimicrobial host defense. While often confused with S100A7 (psoriasin), they are distinct proteins with different expression patterns and functions despite structural similarities.

S100A7A was first identified as upregulated in inflammation-prone psoriatic skin, suggesting involvement in the lesional phenotype of the disease known as Koebner phenomenon . S100A7, by comparison, is a 101 amino acid protein containing two EF-hand motifs, zinc-binding histidine residues, a high-affinity calcium-binding site, and an antibacterial sequence . Both proteins have antimicrobial properties, but their regulatory mechanisms and expression patterns differ significantly.

What are the primary functional roles of S100A7A in human tissue?

S100A7A serves multiple functional roles in human tissues, primarily contributing to epithelial homeostasis and antimicrobial host defense. In normal epidermis, S100A7A is expressed by epidermal basal and differentiated keratinocytes, melanocytes, and Langerhans cells. Within the pilosebaceous unit, it is found in the inner and external root sheath and the basal layer of sebaceous glands .

In the dermis, S100A7A is produced by dendritic cells, smooth muscle cells, endothelial cells, and fibroblasts to control tissue regeneration. In breast tissue, it is expressed by alveolar and small duct luminal cells, epithelial-derived myoepithelial cells around acini, and by surrounding blood vessels . S100A7A functions as an antimicrobial peptide, reducing survival of pathogens such as E. coli and is regulated by bacterial components from Pseudomonas aeruginosa and Staphylococcus aureus .

What are the structural characteristics of S100A7A and S100 proteins?

S100 proteins, including S100A7A, typically possess two calcium-binding domains: an N-terminal non-canonical EF-hand domain and a C-terminal canonical EF-hand domain. These domains are connected by a hinge region consisting of 10-12 amino acid residues that is crucial for target interactions .

How are S100A7A and S100A7 expressed in normal versus pathological conditions?

When normal human keratinocytes (NHKs) are exposed to disruptive stimuli such as Staphylococcus aureus, ultraviolet irradiation, and retinoic acid, the secretion of S100A7 into the culture medium increases while the expression of epidermal differentiation markers decreases . Similarly, S100A7A demonstrates altered expression patterns in inflammatory skin conditions, particularly being upregulated in psoriatic lesions where it contributes to the disease phenotype .

What methodologies are most effective for studying S100A7A protein-protein interactions?

For studying S100A7A protein-protein interactions, researchers should consider multiple complementary approaches:

• Fluorescence-based binding assays: These can measure direct binding between S100A7A and potential interaction partners. Similar to studies with S100A7, researchers can use fluorescence spectroscopy to determine binding constants and stoichiometry with zinc and calcium ions .

• NMR spectroscopy: This technique provides detailed structural information about protein-protein interactions. For S100A7A studies, 2D HSQC NMR can identify specific residues involved in binding events.

• Co-immunoprecipitation (Co-IP): This method can identify physiologically relevant binding partners in cell lysates. When studying S100A7A interactions, it's critical to use antibodies specific to S100A7A rather than S100A7 due to their structural similarities.

• Yeast two-hybrid screening: This can identify novel binding partners from genomic or cDNA libraries, providing insights into previously unknown S100A7A interactions.

• Surface plasmon resonance (SPR): This allows real-time analysis of binding kinetics without labeling requirements, making it valuable for determining association and dissociation constants for S100A7A with its interaction partners.

When studying zinc binding properties specifically, researchers should be aware that data for murine S100A7 may be noisier than for human S100A7, potentially due to the greater tendency of murine S100A7 to aggregate .

How can researchers effectively distinguish between S100A7A and S100A7 in experimental settings?

Distinguishing between S100A7A and S100A7 in experimental settings requires careful consideration of several methodological approaches:

• Specific antibodies: Use monoclonal antibodies that specifically recognize unique epitopes of either S100A7A or S100A7. For example, Mouse Anti-Human S100A7 Monoclonal Antibody (such as Clone # 577513) can be used with appropriate controls to ensure specificity .

• Sequence verification: Confirm protein identity through mass spectrometry or sequencing, focusing on the C-terminal region which shows substantial differences between these proteins .

• Expression analysis: Utilize RT-qPCR with primers specific to unique regions of each transcript. This approach can distinguish expression patterns at the mRNA level.

• Structural analysis: Employ circular dichroism (CD) spectroscopy to detect differences in secondary structure elements, as comparison of murine S100A7 structure to human S100A7 revealed an RMSD of 1.68 Å over all Cα atoms, which is larger than expected for typical homologs .

• Functional assays: Design experiments that exploit known functional differences, such as testing the ability to mediate zinc piracy in Neisseria gonorrhoeae infection models, which is a capability of human S100A7 but not murine S100A7 .

What signaling pathways are activated by S100A7A, and how can they be experimentally monitored?

S100A7A and related S100 proteins activate several key signaling pathways that can be monitored through specific experimental approaches:

• RAGE-mediated signaling: S100A7 functions depend on the receptor for advanced glycation end products (RAGE). Interaction of S100A7 with RAGE activates p38 MAPK and ERK signaling pathways, leading to production of inflammatory mediators involved in psoriasis, including IL-1α, IL-1β, IL-6, IL-8, and TNF-α . These can be monitored using:

  • Phospho-specific antibodies for Western blot detection of activated p38 and ERK

  • ELISA assays for downstream cytokine production

  • Reporter gene assays using constructs with NF-κB responsive elements

• Jab1-dependent pathways: S100A7 interacts with c-Jun activation domain-binding protein 1 (Jab1), increasing the activity of NF-κB and phospho-Akt . Researchers can monitor this using:

  • Co-immunoprecipitation to confirm S100A7-Jab1 interaction

  • Luciferase reporter assays for NF-κB activation

  • Western blotting for phosphorylated Akt

• MyD88-IκB/NF-κB signaling: The MyD88-IκB/NF-κB signal cascade is activated via RAGE after S100A7 treatment, resulting in upregulation of interleukin-6 . This can be monitored through:

  • IκB degradation assays

  • Nuclear translocation of NF-κB by immunofluorescence

  • Quantitative PCR for IL-6 expression

• MAPK pathways: S100A7 treatment increases expression of transglutaminase I and III via activation of MAPK signaling pathway . Researchers can track this using:

  • Protein and mRNA expression levels of transglutaminase using Western blotting and qPCR

  • Specific MAPK inhibitors to confirm pathway specificity

How do human and murine S100A7 proteins differ, and what are the implications for using mouse models in S100A7A research?

Human and murine S100A7 proteins exhibit significant differences with important implications for research using mouse models:

These differences raise important considerations for researchers using mouse models to study human S100A7A-related conditions. The murine protein appears to be a distinct ortholog rather than a true homolog, potentially limiting the translational value of mouse models for studying bacterial infections in humans and other S100A7A-mediated processes .

What experimental approaches can be used to study the antimicrobial properties of S100A7A?

To investigate the antimicrobial properties of S100A7A, researchers can employ several experimental approaches:

• Bacterial survival assays: Directly measure the ability of purified S100A7A to reduce survival of various bacterial species, particularly E. coli, Pseudomonas aeruginosa, and Staphylococcus aureus . This typically involves:

  • Incubating bacteria with varying concentrations of recombinant S100A7A

  • Plating dilutions on appropriate media

  • Quantifying colony-forming units (CFUs)

• Zinc sequestration studies: Since zinc binding is crucial for the antimicrobial function of S100 proteins, researchers can use:

  • Fluorescence spectroscopy to measure zinc binding affinity and stoichiometry

  • Isothermal titration calorimetry (ITC) for thermodynamic binding parameters

  • Competition assays with zinc-dependent bacterial growth

• Host-pathogen interaction models: Develop in vitro models using human keratinocytes to study:

  • Regulation of S100A7A expression in response to bacterial components

  • Changes in bacterial adherence and invasion when S100A7A is overexpressed or knocked down

  • The impact of S100A7A on bacterial gene expression patterns

• Reconstituted human epidermis models: These can be particularly valuable for studying S100A7A in a more physiologically relevant context, as has been done with S100A7 . These models allow researchers to:

  • Examine antimicrobial effectiveness in a structured tissue environment

  • Study the interplay between antimicrobial activity and epidermal differentiation

  • Test the effects of bacterial species on S100A7A expression and function

• Immunohistochemical analysis: Using specific antibodies such as Mouse Anti-Human S100A7 Monoclonal Antibody for detection in human skin tissues under various conditions . This approach requires:

  • Proper tissue preparation (fixed paraffin-embedded sections)

  • Heat-induced epitope retrieval using appropriate reagents

  • Specific staining protocols to visualize protein localization in relation to infectious agents

What methodologies are appropriate for studying S100A7A's role in epidermal differentiation?

To investigate S100A7A's role in epidermal differentiation, researchers should consider these methodological approaches:

• Keratinocyte differentiation models: Similar to S100A7 studies, researchers can use normal human keratinocytes (NHKs) exposed to differentiation-inducing stimuli while manipulating S100A7A levels . Key approaches include:

  • Calcium switch assays to trigger differentiation

  • Analysis of differentiation markers (keratin 1, keratin 10, involucrin, loricrin)

  • Examination of abnormal differentiation markers (keratin 6, keratin 16)

• Reconstituted human epidermis models: These three-dimensional tissue models more accurately recapitulate the in vivo environment and allow:

  • Treatment with recombinant S100A7A protein

  • Genetic manipulation of S100A7A expression

  • Histological and molecular analysis of differentiation patterns

• Signal pathway analysis: To understand molecular mechanisms, researchers should examine:

  • MyD88-IκB/NF-κB signal cascade activation via RAGE after S100A7A treatment

  • Resulting cytokine profiles, particularly interleukin-6

  • The impact of pathway inhibitors on reverting S100A7A-mediated effects

• Transcriptomic and proteomic analysis: These approaches provide comprehensive views of:

  • Gene expression changes during S100A7A-influenced differentiation

  • Protein expression and post-translational modifications

  • Identification of novel regulatory networks

• Immunohistochemistry protocols: For tissue localization studies, researchers can use protocols similar to those established for S100A7, which include:

  • Immersion fixed paraffin-embedded sections

  • Heat-induced epitope retrieval using Antigen Retrieval Reagent-Basic

  • Visualization using appropriate detection systems like HRP-DAB Cell & Tissue Staining Kit