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).
The primary goal of this proposal is to understand the underlying mechanisms of Hsp60 regulation of caspase-3 activation. The proposed research in this application characterizes how Hsp60 localization and its molecular forms play important role in prostate cancer cell survival and apoptosis. Since Hsp60 is highly expressed in prostate cancer cells, this study has relevance in prostate cancer therapy.
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