Insulin inhibits FoxO transcription factors, which downregulate the expression of genes involved in metabolism, cell cycle arrest and apoptosis. After being phosphorylated by PKB on S253 in its DNA-binding domain, Foxo1 is phosphorylated on T24 and additional sites, which overall triggers its nuclear exclusion. During this process, Foxo1 is thought to retain some transcriptional activity and signaling potential. To evaluate this Foxo1 action, we used a Foxo1-ADA mutant which is constitutively nuclear due to mutation of T24 and S316 to A, and harbours a mutation of S253 to D. Adenoviral-mediated expression of Foxo1-ADA in hepatocytes activates PKB and MAPK pathways more than expression of wild-type (WT) or of a transactivation domain-deleted mutant (256). PKB activation can not be accounted for by a Foxo1-mediated increase in upstream signaling components such as IRS-1 or -2, or by Foxo1-mediated downregulation of TRB3. In contrast, p38 activity is required for Foxo1 effects on PKB, at least in part. We propose that Foxo1 turns on a feed-forward loop, relayed by p38 and acting to amplify both PKB activation and Foxo1 inhibition. To conclude, key signaling pathways are activated in hepatocytes through nuclear Foxo1.