S100 calcium binding protein B (S100 beta) is a member of the multifunctional S100 family of proteins. S100 proteins are 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. S100 genes include at least 13 members which are located as a cluster on chromosome 1q21; however, this gene is located at 21q22.3. S100 beta acts as a stimulator of proliferation and migration and as an inhibitor of apoptosis and differentiation in many cell types including astrocytes, Schwann cells, chondrocytes, adipocytes, certain neuronal populations, melanocytes, Langerhans cells, histiocytes, epithelial, and myoepithelial cells. This protein may function in Neurite extension, proliferation of melanoma cells, stimulation of Ca2+ fluxes, inhibition of PKC-mediated phosphorylation, astrocytosis and axonal proliferation, and inhibition of microtubule assembly. Chromosomal rearrangements and altered expression of this gene have been implicated in several neurological, neoplastic, and other types of diseases, including Alzheimer's disease, Down's syndrome, epilepsy, amyotrophic lateral sclerosis, melanoma, and type I diabetes. S100 beta is also expressed in neoplasms derived from these cell types, making it a useful marker for the identification of melanoma and various nervous system tumors. Although ubiquitous, S100 beta has proven to be a sensitive marker for malignant melanoma, including desmoplastic and metastatic variants.
