Direct control of the Forkhead transcription factor AFX by protein kinase B

The phosphatidylinositol-3-OH-kinase (PI(3)K) effector protein kinase B (re fs 1, 2) regulates certain insulin-responsive genes(3,4) but the transcript ion factors regulated by protein kinase B have yet to be identified. Geneti c analysis in Caenorhabditis elegans has shown that the Forkhead transcript ion factor daf-16 is regulated by a pathway consisting of insulin-receptor- like daf-2 and PI(3)K-like age-1 (refs 5-8). Here we show that protein kina se B phosphorylates AFX, a human orthologue of daf-16 (refs 5, 6, 9), both in vitro and in vivo. Inhibition of endogenous PI(3)K and protein kinase B activity prevents protein kinase B-dependent phosphorylation of AFX and rev eals residual protein kinase B-independent phosphorylation that requires Ra s signalling towards the Ra1 GTPase. In addition, phosphorylation of AFX by protein kinase B inhibits its transcriptional activity. Together, these re sults delineate a pathway for PT(3)K-dependent signalling to the nucleus.