The overall objective of this project is to elucidate the mechanisms that control the activation of caspase-9. Caspase-9 is a major initiator caspase in mammalian cells. It exists in healthy cells as a latent precursor and becomes activated in response to a wide range of cell-intrinsic apoptosis stimuli such as developmental lineage information, oncogene activation, DNA damage, and nutritional deprivation. The intrinsic apoptosis pathway that activates caspase-9 is the major mechanism by which the formation of tumor cells is prevented in the first place, and by which tumor cells are killed by chemo- and radiation therapy. The activation of caspase- 9 occurs in a large cytosolic complex known as the apoptosome, the formation of which is triggered by the release of mitochondrial cytochrome c to the cytosol and the subsequent binding of cytochrome c to Apaf-1. This binding enables Apaf-1 to assemble into the heptameric apoptosome, which recruits procaspase-9 and permits its auto-activation. Previous studies by us and others demonstrated that the activation of initiator caspases is induced by their oligomerization. We will determine the mechanism for oligomerization-induced procaspase-9 activation (Aim 1). In addition, we found that tRNAs inhibit caspase-9 activation through direct interaction with cytochrome c and preventing the formation of the apoptosome. We will determine this important function of tRNAs which is beyond their well-established role in the transmission of genetic information. We will also examine this function of tRNAs in apoptosis resistance of tumor cells (Aim 2). Finally, the activation of caspase-9 in the apoptosome is inhibited by the inhibitor of apoptosis proteins (IAPs). This inhibitory effect of IAPs is countered during apoptosis by mitochondrial IAP-binding proteins. Compounds mimicking the effect of IAP-binding proteins show promise in tumor therapy. We recently identified a novel IAP- interacting protein residing in mitochondria. We will elucidate the role of this protein in caspase-9 activation (Aim 3). These three aims represent a concerted effort to elucidate the intricate control of caspase-9 activation at multiple levels. We believe that they will help the development of more effective treatments for apoptosis- related diseases, particularly cancer.

Public Health Relevance

Apoptosis is critical for development and for protection against cancer. The intrinsic/mitochondrial pathway is a major apoptosis pathway in mammalian cells, which leads to the activation of caspase-9 and subsequent cell death. In this proposal, we plan to study the regulation of caspase-9 activation. We believe that this study will further the understanding of the intrinsic apoptosis pathway and have practical implications for treating diseases related to this pathway, including cancer, autoimmune disorders, and immunodeficiency.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Cellular Signaling and Regulatory Systems Study Section (CSRS)
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Maas, Stefan
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University of Pennsylvania
Schools of Medicine
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Liu, Cuiping; Stonestrom, Aaron J; Christian, Thomas et al. (2016) Molecular Basis and Consequences of the Cytochrome c-tRNA Interaction. J Biol Chem 291:10426-36
Guo, Lili; Prall, Wil; Yang, Xiaolu (2016) Assays for the Degradation of Misfolded Proteins in Cells. J Vis Exp :
Guo, Lili; Giasson, Benoit I; Glavis-Bloom, Alex et al. (2014) A cellular system that degrades misfolded proteins and protects against neurodegeneration. Mol Cell 55:15-30
Hou, Ya-Ming; Yang, Xiaolu (2013) Regulation of cell death by transfer RNA. Antioxid Redox Signal 19:583-94
Du, Wenjing; Jiang, Peng; Mancuso, Anthony et al. (2013) TAp73 enhances the pentose phosphate pathway and supports cell proliferation. Nat Cell Biol 15:991-1000
Jiang, Peng; Du, Wenjing; Wang, Xingwu et al. (2011) p53 regulates biosynthesis through direct inactivation of glucose-6-phosphate dehydrogenase. Nat Cell Biol 13:310-6
Mei, Yide; Hahn, Allison Alcivar; Hu, Shimin et al. (2011) The USP19 deubiquitinase regulates the stability of c-IAP1 and c-IAP2. J Biol Chem 286:35380-7
Chu, Y; Yang, X (2011) SUMO E3 ligase activity of TRIM proteins. Oncogene 30:1108-16
Mei, Yide; Yong, Jeongsik; Liu, Hongtu et al. (2010) tRNA binds to cytochrome c and inhibits caspase activation. Mol Cell 37:668-78
Mei, Yide; Stonestrom, Aaron; Hou, Ya-Ming et al. (2010) Apoptotic regulation and tRNA. Protein Cell 1:795-801

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