FGF acidic, also known as FGF-1, ECGF, and HBGF-1, is a mitogenic peptide that is produced by multiple cell types and stimulates the proliferation of cells of mesodermal, ectodermal, and endodermal origin. FGF acidic is secreted following associations with S100A13, copper ions, and synaptotagmin 1. Its association with heparan sulfate is a prerequisite for activation of FGF receptors. Internalized FGF acidic migrates to the nucleus where it is phosphorylated by nuclear PKC delta, exported to the cytosol, dephosphorylated, and degraded. Intracellular FGF acidic inhibits p53 activity and proapoptotic signaling.