Molecular Regulation and Biological Functions of PIKE-A

描述（由申请人提供）：PIKE （PI 3-Kinase Enhancer）通过PI 3-激酶/Akt信号传导在介导细胞存活中起重要作用。目前已鉴定出三种同工异构体：PIKE-L、-S和-A。PIKE-S是一种脑特异性核GTPase，与pi3 -激酶结合并刺激其脂质激酶活性。PIKE-A在多种人类癌症中与CDK4共扩增，最近在人类多形性胶质母细胞瘤中被发现。有趣的是，PIKE-A不结合pi3 -激酶，相反，它以gtp依赖的方式激活Akt。通常，Akt在许多人类癌症中异常激活，并在肿瘤发生中发挥核心作用。然而，Akt在癌症中调控的分子机制仍不完全清楚。Akt信号级联机制在人类恶性肿瘤中的表征不仅有助于更好地了解癌症进展，而且有望为人类癌症提供多点治疗干预。最近，我们发现PIKE-A通过激活Akt促进癌细胞侵袭并抑制细胞凋亡。PIKE-A被Fyn酪氨酸激酶磷酸化，磷酸化对于阻止PIKE-A的凋亡裂解至关重要。此外，我们发现PIKE-A是一种原癌基因，可转化NIH3T3细胞并刺激其侵袭。我们的初步研究表明Akt反馈并磷酸化PIKE-A，触发其与14-3-3的关联。然而，这种作用的生理功能尚不清楚。此外，上游Fyn和Akt激酶串扰如何介导PIKE-A的致癌作用尚不清楚。我们假设Akt和Fyn激酶调节PIKE-A的促生存功能，促进癌症进展。作为我们了解PIKE GTPase信号级联在细胞增殖和存活中的长期目标的一部分，在本应用中，我们提出：1)表征Akt对PIKE- a的磷酸化及其与14-3-3的关系；2)检测Akt和Fyn激酶对PIKE-A磷酸化的串扰；3)确定PIKE-A在肿瘤发生中的生理功能。该研究的成功完成将进一步加深我们对PIKE-A在癌症生物学中的认识，并为癌症患者寻找新的药物靶点铺平道路。

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.