PI 3-kinase (PI3K) occurs in the nuclei of a broad range of cell types, and various stimuli elicit PI3K nuclear translocation. However, little is known about the biological function of nuclear PI3K. Here we show that nuclear PI3K and its upstream regulator PIKE mediate the antiapoptotic activity of nerve growth factor (NGF) in the isolated nuclei. The nuclei from NGF-treated PC12 cells, EGF-treated HEK293 cells and HeLa cells are resistant to DNA fragmentation initiated by activated cell-free apoptosome. Nuclei from constitutively active PI3K adenovirus-infected cells display the same resistance as those treated by NGF, whereas PI3K inhibitors, dominant-negative PI3K or PIKE abolishes it. Knockdown of either PI3K or PIKE diminishes the antiapoptotic activity of NGF. PI (3,4,5)P3 alone mimics the antiapoptotic activity of NGF, for which nuclear Akt is required. These results demonstrate that PIKE/nuclear PI3K signaling through nuclear PI (3,4,5)P3 and Akt plays an essential role in promoting cell survival.