Activated Akt1 enhances the transcriptional activity of ngn3 in complex with the transcriptional coactivators p300 and CBP. P19 cells were transfected with expression vectors for the Gal4-DBD p300 fusion protein (Gal-p300) or Gal4-DBP-CBP fusion protein (Gal-CBP), ngn3, the pFR Gal4-responsive luciferase reporter, and constitutively active Akt1 (C/A Akt) or constitutively active Sgk1 (C/A SGK). The PI3K/Akt inhibitor LY294002 (12.5 μM) was added at the time of transfection, as indicated. (A) ngn3 and C/A Akt1 cooperatively enhance the transcriptional activity of Gal-p300. (B) ngn3 and C/A Akt1 cooperatively enhance the transcriptional activity of Gal-CBP. (C) Inhibition of the endogenous PI3K/Akt signaling pathway with LY294002 decreases the transcriptional activity of Gal-p300 in combination with ngn3, but not in the presence of C/A Akt1. (D) C/A Akt1, but not C/A SGK, enhances the transcriptional activity of ngn3 and Gal-p300.