Molecular Regulation and Biological Functions of PIKE-A

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DESCRIPTION (provided by applicant): PIKE (PI 3-Kinase Enhancer) plays an essential role in mediating cell survival through PI 3-kinase/Akt signaling. Currently, three isoforms have been characterized: PIKE-L, -S and -A. PIKE-S a brain-specific nuclear GTPase, which binds to PI 3-kinase and stimulates its lipid kinase activity. PIKE-A is coamplified with CDK4 in a variety of human cancers, and it was recently identified in human glioblastoma multiformes. Interestingly, PIKE-A does not bind to PI 3-kinase, instead, it activates Akt in a GTP-dependent manner. Frequently, Akt is abnormally activated in many human cancers and plays a central role in tumorigenesis. However, the molecular mechanism how Akt is regulated in cancers remains incompletely understood. Characterization of Akt signaling cascade machinery in human malignancy not only leads to a better understanding of cancer progression but also promises to provide multiple points of therapeutic intervention for human cancers. Recently, we have showed that PIKE-A promotes cancer cell invasion and inhibits apoptosis through activating Akt. PIKE-A is phosphorylated by Fyn tyrosine kinase, and the phosphorylation is critical for preventing PIKE-A from apoptotic cleavage. Further, we show that PIKE-A is a proto-oncogene and transforms NIH3T3 cells and stimulates its invasion. Our preliminary study reveals that Akt feeds back and phosphorylates PIKE-A, triggering its association with 14-3-3. However, the physiological functions of this action remain unknown. Moreover, how the upstream Fyn and Akt kinases crosstalk mediates PIKE-A oncogenic role is unclear. We hypothesize that Akt and Fyn kinases regulate PIKE-A's pro-survival function, promoting cancer progress. As a part of our long-term goal to understand PIKE GTPase signaling cascades in cell proliferation and survival, in this application we propose: 1) To characterize PIKE-A phosphorylation by Akt and its association with 14-3-3; 2) To determine Akt and Fyn kinases crosstalk on PIKE-A phosphorylation; 3) To determine the physiological functions of PIKE-A in tumorigenesis. Successful accomplishment of the proposed study will further our knowledge about PIKE-A in cancer biology and pave the way for identification of novel drug targets for patients with cancers. PUBLIC HEALTH RELEVANCE: PIKE (PI 3-Kinase Enhancer) is critical for mediating cell survival through PI 3-kinase/Akt signaling pathway. PIKE gene is amplified on chromosome 12 in a variety of human cancers, promoting cancer cell invasion and inhibiting cell death compared to cells with normal PIKE copy number. PIKE is amplified in 15% human glioblastoma and many other cancers. PIKE-A specifically binds to active oncogenic Akt and stimulates its kinase activity. However, the molecular mechanism how Akt is regulated in cancers remains incompletely understood. Characterization of Akt signaling cascade machinery in human malignancy not only leads to a better understanding of cancer progression but also promises to provide multiple points of therapeutic intervention for human cancers. Recently, we have found that numerous kinases phosphorylate PIKE-A and mediate its association with pro-survival effectors. Thus, we hypothesize that the phosphorylation regulates PIKE-A's pro-survival function, promoting cancer progress. As a part of our long-term goal to understand PIKE signaling cascades in cell proliferation and survival, in this application we propose: 1) To characterize PIKE-A phosphorylation by Akt and its association with 14-3-3; 2) To determine Akt and Fyn kinases crosstalk on PIKE-A phosphorylation; 3) To determine the physiological functions of PIKE-A in tumorigenesis. The proposed study is expected to provide insight into the function of PIKE-A in cancer biology. Accomplishing these aims will lead to development of drugs for curing of cancers.