S100A8, also known MRP8, is a member of the S100 family, EF-hand superfamily of calcium binding proteins. This protein is localized in the cytoplasm and/or nucleus of a wide range of cells, and involved in the regulation of a number of cellular processes such as cell cycle progression and differentiation. It functions both intracellularly and extracellularly, where it binds to RAGE and CD36. Altered expression of this protein is associated with the disease cystic fibrosis.