Forkhead box O3, also known as FOXO3 or FOXO3a, is a human protein encoded by the FOXO3 gene. FOXO3 belongs to the O subclass of the forkhead family of transcription factors which are characterized by a distinct fork head DNA-binding domain.
There are three other FoxO family members in humans, FOXO1, FOXO4 and FOXO6. This protein likely functions as a trigger for apoptosis through upregulation of genes necessary for cell death, such as Bim and PUMA,[3] or downregulation of anti-apoptotic proteins such as FLIP.