The U.S. PI has a long-standing interest in the various aspects of protein kinase C (PKC) isozyme signaling within cells. The PI has previously investigated in detail one particular pKC isozyme, PKC B2, and has generated a considerable amount of knowledge regarding the mechanisms surrounding activation of this isozyme. The present parent project for this FIRCA application by the PI has now shifted to explore the functional characterization of an atypical PKC isozyme, PKCi, in human leukemia cell survival. In examining factors responsible for the nuclear activation of PKC B2 prior to mitosis, the PI's laboratory isolated a nuclear PI-PLC from G2 phase nuclei. Preliminary experiments using antibodies to known PI-PLC isozymes indicated that this nuclear PI-PLC did not correspond to any of the previously identified PI-PLC isozymes. The foreign collaborator, while working with regenerating rat hepatocytes, also observed the presence of a novel nuclear PI-PLC activity involved in cell cycle regulation. Given these common findings and interests, and given the foreign collaborator's expertise in the biochemical analysis of phosphatidylinositol-metabolizing enzymes, a new collaborative effort has arisen between these investigators. Therefore, the main thrust of this proposal is to identify this novel nuclear PI-PLC activity. In addition, recent data suggests that a phosphatidylinositol 3-kinase (PI3K) signaling system exists within the nucleus and that this nuclear PI3K signaling system is distinct from the well described cytoplasmic-cell membrane PI3K system. The novel nuclear PI3K pathway is responsible for PKB activation. These preliminary results suggest that PI3K and PKB activation may play a direct physiologic role in nuclear events associated with cellular proliferation and cell cycle progression. The second and third specific aims therefore propose to expand and confirm these preliminary results of the roles of nuclear PI3K and PKB in these cellular events.