Molecular Regulation and Biological Functions of PIKE-A

描述(由申请人提供)：Pike(PI3-Kinase Enhator)在通过PI3-Kinase/Akt信号调节细胞生存中发挥重要作用。目前已鉴定出三种亚型：Pike-L、-S和-A。Pike-S是一种脑特异性核型GTP酶，能与PI-3-激酶结合，刺激其脂蛋白激酶活性。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不与PI3-Kinase结合，而是以GTP依赖的方式激活Akt。通常，Akt在许多人类癌症中被异常激活，并在肿瘤发生中发挥核心作用。然而，Akt如何在癌症中受到调控的分子机制仍不完全清楚。人类恶性肿瘤中Akt信号级联机制的特征不仅有助于更好地了解癌症的进展，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促进癌细胞侵袭和抑制细胞凋亡。Pike-A被Fyn酪氨酸激酶磷酸化，该磷酸化是防止Pike-A被细胞凋亡切割的关键。此外，我们发现Pike-A是一个原癌基因，可以转化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，这一作用的生理功能仍不清楚。此外，上游的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。作为我们长期目标的一部分，了解Pike GTPase信号在细胞增殖和存活中的级联作用，在本应用中，我们建议：1)表征Akt对Pike-A的磷酸化及其与14-3-3的关联；2)确定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。这项拟议研究的成功完成将进一步加深我们对Pike-A在癌症生物学方面的了解，并为确定癌症患者的新药物靶点铺平道路。 公共卫生相关性：PIKE(PI3-Kinase Enhancer)是通过PI3-Kinase/Akt信号通路调节细胞存活的关键。Pike基因在人类多种癌症的12号染色体上扩增，与Pike拷贝数正常的细胞相比，可促进癌细胞侵袭，抑制细胞死亡。Pike在15%的人胶质母细胞瘤和许多其他癌症中被扩增。Pike-A特异性地与活性致癌Akt结合并刺激其激酶活性。然而，Akt如何在癌症中受到调控的分子机制仍不完全清楚。人类恶性肿瘤中Akt信号级联机制的特征不仅有助于更好地了解癌症的进展，而且有望为人类癌症提供多点治疗干预。最近，我们发现许多激酶使Pike-A磷酸化，并介导其与支持生存的效应器的联系。因此，我们假设，磷酸化调节Pike-A的促生存功能，促进癌症进展。作为我们长期目标的一部分，了解Pike信号在细胞增殖和存活中的级联作用，在本应用中，我们建议：1)表征Akt对Pike-A的磷酸化及其与14-3-3的关联；2)确定Akt和Fyn Kinase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。这项拟议的研究有望为深入了解Pike-A在癌症生物学中的功能提供依据。实现这些目标将导致治疗癌症的药物的开发。

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.