S100 protein family of calcium binding proteins with 2 distinct helix-loop-helix motifs (EF-hands) shows cell typespecific expression and consists of 20 members. The protein family functions by being secreted extracellularly as well as involved in intracellular signaling.

S100 proteins are normally present in cells derived from the neural crest (Schwann cells, and melanocytes), chondrocytes, adipocytes, myoepithelial cells, macrophages, Langerhans cells, dendritic cells, and keratinocytes. It may be present in some breast epithelial cells.

S100 proteins have been implicated in a variety of intracellular and extracellular functions. S100 proteins are involved in regulation of protein phosphorylation, transcription factors, Ca2+ homeostasis, the dynamics of cytoskeleton constituents, enzyme activities, cell growth and differentiation, and the inflammatory response.

S100A7 (psoriasin) and S100A15 have been found to act as cytokines in inflammation, particularly in autoimmune skin conditions such as psoriasis Several members of the S100 protein family are useful as markers for certain tumors and epidermal differentiation. It can be found in melanomas, 100% of schwannomas, 100% of neurofibromas (weaker than schwannomas), 50% of malignant peripheral nerve sheath tumors (may be weak and/or focal), paraganglioma stromal cells, histiocytoma and clear cell sarcomas. Further, S100 proteins are markers for inflammatory diseases and can mediate inflammation and act as antimicrobials.

S100 proteins have been used in the lab as cell markers for anatomic pathology.

S100A: Metastatic Promotion factor in breast cancer

A100A6: Expression Upregulated in Alzheimers disease amyotrophic lateral Sclerosis and melanoma.

S100 A7: Expression upregulated in many chronic inflammatory diseases.

S100A8: expression upregulated in many chronic inflammatory diseases.

 

S100 A9: expression Upregulated in many chronic inflammatory diseases,

 

S100A10: contributes to malignancy expression is upregulated in an aplastic thyroid cancer

S100A11: Participates in two processes: intracelulary suppresses proliferation . extracellulary promotes proliferation

S100A12: expression upregulated in chronic inflammatory diseases. Such as chrohns participation in other sclerosis

S100A13: Drug targetfor allergy

S100A14: expression upregulated in ovarian breast and uterine cancer

S100P: Noted as a pancreatic cancer marker, promoting cell proliferation