Hsp60 regulation of apoptosis in prostate cancer

描述(申请人提供)：热休克蛋白60(HSP60)在前列腺癌(PCa)中高表达，与不良预后有关。患者预后不良的原因是细胞凋亡信号的缺陷。Pca细胞中Hsp60的高表达是导致细胞凋亡缺陷的原因之一，但其潜在的分子机制尚不完全清楚。我们的目标是确定Hsp60是如何调控PCa细胞的凋亡的。我们和其他人观察到，在正常前列腺上皮细胞中，HSP60定位于线粒体，而在前列腺癌细胞中，HSP60既存在于线粒体中，也存在于胞浆中。我们提供了线粒体Hsp60(MHsp60)促进caspase-3激活从而诱导细胞凋亡的证据，而胞浆Hsp60(CHsp60)不支持caspase-3激活而抑制细胞凋亡。MHsp60以低聚物形式存在，而cHsp60以单体形式存在。此外，Hsp60-寡聚体能诱导caspase-3的激活，而Hsp60-单体则缺乏这一功能。因此，Hsp60对抗癌药物的作用是促进还是抑制细胞凋亡，取决于它的定位和分子形式。由于caspase-3主要分布在细胞质中，而Hsp60-寡聚体存在于线粒体中，我们推测Hsp60-寡聚体在细胞质中的积聚可以诱导有效的细胞凋亡。此外，我们建议，定义mHsp60如何激活线粒体中的caspase-3有可能改进现有的PCA治疗。为了解决这一假说并测试可能的治疗潜力，我们将：目的1.确定mHsp60激活caspase-3的机制，并鉴定未知的mHsp60-/cHsp60相互作用蛋白。这些发现将描绘出寡聚mHsp60如何与线粒体中的caspase-3相互作用并激活，以及线粒体中活跃的caspase-3如何放大caspase级联。目的2.研究热休克蛋白60的寡聚状态及其对细胞凋亡的影响。这一目标的目的是关联caspase-3激活功能的Hsp60寡聚体在癌细胞和正常细胞中的影响。目的3.探讨Hsp60-寡聚体是否是PCa肿瘤细胞凋亡的关键决定因素。这一目标的拟议研究的完成可能会使Hsp60-寡聚体成为PCA治疗的关键靶点。重要影响：caspase-3的大部分存在于胞浆中，因此，新的抗PCA药物可以触发/增强cHsp60的寡聚和/或mHsp60从线粒体释放到胞浆，将诱导有效的caspase-3激活和凋亡。由于单体cHsp60在癌细胞和肿瘤细胞胞浆中高表达，而在正常细胞中不表达，因此诱导/增强胞浆中Hsp60寡聚的抗癌药将选择性地诱导癌细胞凋亡。重要的是 Hsp60-寡聚体是一种新的caspase-3激活复合体，Hsp60-寡聚体直接激活caspase-3将是诱导PCa细胞凋亡的高效手段，因为它不依赖于启动子caspase-9和caspase-8的激活。

DESCRIPTION (provided by applicant): Heat shock protein 60 (Hsp60) is highly expressed in prostate cancer (PCa) and is associated with poor prognosis. Poor prognosis in patients results from defective apoptosis signaling. Defective apoptosis is due to high expression of Hsp60 in PCa cells, however, the underlying molecular mechanisms are not yet fully defined. Our goal is to determine how Hsp60 regulates PCa cell apoptosis. We and others observed that Hsp60 is localized to mitochondria in normal prostate epithelial cells, whereas in PCa cells Hsp60 is in both mitochondria and cytosol. We provided evidence that mitochondrial Hsp60 (mHsp60) promotes caspase-3 activation and thus induces apoptosis, whereas cytosolic Hsp60 (cHsp60) fails to support caspase-3 activation and suppresses apoptosis. The majority of mHsp60 exists as oligomers, whereas cHsp60 is in monomeric form. In addition, Hsp60-oligomer induces caspase-3 activation but Hsp60-monomer lacks this function. Therefore, whether Hsp60 promotes or suppresses apoptosis in response to anticancer agents is dependent upon both its localization and its molecular forms. Because majority of caspase-3 localizes in the cytosol and Hsp60-oligomer resides in mitochondria, we hypothesized that accumulation of Hsp60-oligomer in the cytosol induces efficient apoptosis. Further we propose that defining how mHsp60 activates caspase-3 in mitochondria has the potential to improve existing PCa therapy. To address the hypothesis and test possible therapeutic potentials, we will: Aim 1. Define the mechanisms of caspase-3 activation by mHsp60, and identify unknown mHsp60-/cHsp60-interacting proteins. The findings will delineate how oligomeric mHsp60 interacts with and activates caspase-3 in mitochondria, and how active caspase-3 in mitochondria amplifies the caspase cascade. Aim 2. Investigate the oligomerization status of Hsp60 and its impact on apoptosis. The goal of this Aim is to correlate the impact of caspase-3 activating function of Hsp60-oligomer in cancer and normal cells. Aim 3. Evaluate whether Hsp60-oligomer is a key determinant of apoptosis in PCa tumor. The completion of proposed research in this Aim may establish Hsp60-oligomer as a key target for PCa therapy. Important impact: The majority of caspase-3 resides in the cytosol, thus new anti-PCa agents that trigger/enhance oligomerization of cHsp60 and/or release of mHsp60 from mitochondria to the cytosol will induce efficient caspase-3 activation and apoptosis. Since monomeric cHsp60 is highly expressed in the cytosol of cancer and tumor cells but not in normal cells, anticancer agents that induce/enhance oligomerization of Hsp60 in the cytosol will selectively induce cancer cell apoptosis. Importantly, this proposal will identify Hsp60-oligomer as a new caspase-3-activating complex in apoptosis, and direct activation of caspase-3 by Hsp60 oligomer will be highly efficient means to induce PCa cell apoptosis because it does not rely on activation of initiator caspases (e.g., caspase-9, and -8).