Structural basis for DNA recognition by FoxO1 and its regulation by posttranslational modification.

FoxO transcription factors regulate the transcription of genes that control metabolism, cellular proliferation, stress tolerance, and possibly life span. A number of posttranslational modifications within the forkhead DNA-binding domain regulate FoxO-mediated transcription. We describe the crystal structures of FoxO1 bound to three different DNA elements and measure the change in FoxO1-DNA affinity with acetylation and phosphorylation. The structures reveal additional contacts and increased DNA distortion for the highest affinity DNA site. The flexible wing 2 region of the forkhead domain was not observed in the structures but is necessary for DNA binding, and we show that p300 acetylation in wing 2 reduces DNA affinity. We also show that MST1 phosphorylation of FoxO1 prevents high-affinity DNA binding. The observation that FoxO-DNA affinity varies between response elements and with posttranslational modifications suggests that modulation of FoxO-DNA affinity is an important component of FoxO regulation in health and misregulation in disease.