The serine-threonine protein kinase encoded by theAKT1 gene is catalytically inactive in serum-starvedprimary and immortalized fibroblasts. AKT1 and therelated AKT2 are activated by platelet-derived growth factor. The activation is rapid and specific, and it is abrogated by mutations in the pleckstrin homology domain of AKT1. It was shown that the activation occurs through phosphatidylinositol 3-kinase. In the developing nervous systemAKT is acritical mediator of growth factor-induced neuronal survival. Survival factors can suppress apoptosis inatranscription-independent manner by activating theserine/threonine kinase AKT1, which then phosphorylates and inactivates components of theapoptotic machinery. Mutations in this gene have been associated with the Proteus syndrome. Multiple alternatively spliced transcript variants have been found for this gene.