PEA-15 (Phosphoprotein enriched in astrocytes of 15kD) is a 15kD cytoplasmic protein that regulates cell proliferation and apoptosis. It is expressed in multiple cell types such as astrocytes; skeletal muscle and adipocytes. Human PEA-15 is 130aa in length. It contains a death effector domain (aa3-81), plus two regulatory Ser phosphorylation sites. In a quiescent cell, it is either non-phosphorylated or constitutively phosphorylated at Ser116. Non-phosphorylated PEA-15 binds ERK, inhibiting cell proliferation. Phosphorylation at Ser116 promotes PEA-15 binding to FADD, blocking apoptosis. And activation-induced phosphorylation at Ser104 blocks PEA-15 binding to ERK, promoting cell proliferation. There is one potential alternate start site 21aa upstream of the standard start site, and a second isoform that shows an Asn substitution for aa 36-58. Full-length human and mouse PEA-15 show 99% aa identity.