S100 protein is a family of low molecular weight protein found in vertebrates characterized by two EF-hand calcium-binding motifs. There are at least 21 different S100 proteins, and the name is derived from the fact that the protein is 100% soluble in ammonium sulfate at neutral pH. Most S100 proteins are disulfide-linked homodimer, and is normally present in cells derived from the neural crest, chondrocytes, macrophages, dendritic cells, etc. S100 proteins have been implicated in a variety of intracellular and extracellular functions. They are involved in regulation of protein phosphorylation, transcription factors, the dynamics of cytoskeleton constituents, enzyme activities, cell growth and differentiation, and the inflammatory response.
Human Protein S100-A8, also known as S100 calcium-binding protein A8, Cystic fibrosis antigen, Migration inhibitory factor-related protein 8, S100A8, and CAGA, is a member of the S-100 family. S100A8 plays a role in various functions of myeloid cells by forming a heterocomplex with S100A9. S100A8 and S100A9 are known to be overexpressed in certain species of carcinomas. S100A8 plays an important role in dedifferentiation of thyroid carcinoma possibly by forming a complex with S100A9. S100A8 and S100A9 may also play a key role in inflammation-associated cancer.