Regulation of Cell Survival and Tumor Progression by Akt

描述(由申请人提供)：AKT是调节细胞存活和肿瘤进展的许多信号通路的焦点。AKT与参与这些细胞事件的许多底物相互作用，并通过磷酸化修饰。由于其抗细胞凋亡的特性，Akt在促进人类癌症方面发挥着关键作用。因此，识别与Akt相互作用的分子可能有助于更好地理解Akt在各种局部信号网络中的作用，并使开发专门阻断参与癌症发生和发展的信号通路的策略成为可能。 PAR-4是一种亮氨酸拉链结构域蛋白，当异位表达时，可诱导癌细胞凋亡，但不能诱导正常或永生化细胞的凋亡。异位PAR-4通过抑制核因子-kappaB活性诱导细胞凋亡。由于癌细胞含有合理水平的内源性PAR-4，我们试图确定PAR-4是否以非活性形式存在。我们的初步研究表明，Akt1结合并失活内源性PAR-4，使其在诱导细胞凋亡方面无效。此外，Akt1的失活会释放PAR-4诱导细胞凋亡，这意味着在没有Akt1的情况下，内源性PAR-4在功能上是活跃的。鉴于Akt1的促生存功能和PAR-4的促凋亡功能，本研究的目的是研究Akt1和PAR-4相互作用在前列腺癌细胞存活和肿瘤进展中的分子基础和功能相关性。为此，我们提出了以下具体目标：目的1，阐明Akt对PAR-4的异构体特异性作用的分子基础；目的2，确定Akt1抑制PAR-4胞质内滞留和失活的机制；以及目的3，确定Akt1抑制PAR-4在肿瘤生长中的下游效应和功能相关性。由于PTEN缺失是一种明确的遗传损伤，它可以提高Akt活性，中和前列腺中的凋亡途径，并有助于小鼠前列腺癌模型的发生，因此本研究将侧重于前列腺癌细胞背景的研究，以研究Akt1-PAR-4的相互作用。然而，由于Akt1-PAR-4相互作用发生在不同类型的肿瘤细胞中，我们预计这项研究的发现将对癌症产生广泛的影响。这些发现将在未来的研究中进一步发展，以设计能够阻止PAR-4与Akt1结合并诱导细胞凋亡和肿瘤生长退化的治疗策略。

DESCRIPTION (provided by applicant): Akt is the focal point of a number of signaling pathways that regulate cell survival and tumor progression. Akt interacts with, and modifies via phosphorylation, many substrates involved in these cellular events. Owing to its anti-apoptotic properties, Akt plays a key role in promoting human cancer. Thus, the identification of molecules that interact with Akt may lead to a better understanding of the role of Akt in various local signaling networks and enable the development of strategies for specifically blocking signaling pathways involved in cancer development and progression. Par-4 is a leucine zipper domain protein that, when ectopically expressed, induces apoptosis in cancer cells but not in normal or immortalized cells. Apoptosis by ectopic Par-4 occurs by inhibition of NF-kappaB activity. As cancer cells contain reasonable levels of endogenous Par-4, we sought to determine whether Par-4 exists in an inactive form. Our Preliminary Studies reveal that Akt1 binds and inactivates endogenous Par-4, rendering it ineffective in apoptosis-induction. Moreover, inactivation of Akt1 releases Par-4 to induce apoptosis, implying that endogenous Par-4 is functionally active in the absence of Akt1. In view of the pro-survival functions of Akt1 and the pro-apoptotic functions of Par-4, the objective of this proposal is to study the molecular basis and functional relevance of the interaction between Akt1 and Par-4 in prostate cancer cell survival and tumor progression. Toward this end, we propose the following specific aims: Aim 1, elucidate the molecular basis for the isoform-specific effects of Akt on Par-4; Aim 2, determine the mechanism for cytoplasmic retention and inactivation of Par-4 by Akt1; and Aim 3, determine the downstream effects and functional relevance of Par-4 inhibition by Akt1 in tumor growth. Because PTEN loss is a well defined genetic lesion that elevates Akt activity and neutralizes the apoptotic pathway in the prostate, and contributes to prostate tumors in mouse models, this study will focus on the prostate cancer cell background to study the Akt1-Par-4 interaction. However, as the Akt1-Par-4 interaction occurs in diverse tumor cell types, we anticipate that the findings of this study will have broad implications in cancer. The findings will be further developed in future studies to design therapeutic strategies that can prevent Par-4 binding to Akt1 and induce apoptosis and tumor growth regression.