Because apoptosis, a biochemically distinct form of cell death, is one of the major responses triggered in cancer cells by either chemotherapy or immunotherapy, there has been substantial interest in understanding regulation of the apoptotic process. Studies performed over the past two decades have demonstrated that death receptors, a subfamily of the tumor necrosis factora receptor superfamily, play critical roles in the response to certain cancer chemotherapeutic agents, to death ligands such TNF?-related apoptosis-inducing ligand (TRAIL) and Fas ligand, and to cytotoxic lymphocytes that express these ligands. Thus, improved understanding of factors that determine whether death receptor ligation will induce cell death or not has potential implications for certain aspects of both cancer chemotherapy and immunotherapy. Our preliminary studies have provided new insight into multiple different aspects of death receptor regulation. Working backwards from measurement of cell surface death receptors, we have shown that the outcome of death ligand signaling is impacted by factors that affect trafficking of death receptors to the cell surface, stability of deth receptor mRNA, and transcriptional activation of death receptor genes. To build on these observations, we now propose to 1) elucidate the pathway by which protein kinase C inhibits trafficking of death receptors to the cell surface, 2) investigate how death receptor mRNA half-life is regulated by RNA binding proteins to produce cells that exhibit Bcl-2 independent vs. Bcl-2 inhibitable death ligand- induced signaling, and 3) determine the mechanism by which PARP inhibitors, acting through the transcription factor Sp1, enhance death ligand-induced apoptosis in AML cells and clinical AML samples ex vivo. If successful, the proposed experiments will not only provide new insight into the regulation of death receptor-mediated apoptosis, but also generate preclinical data in further support of testing a novel death ligand/chemotherapy combination.
Death receptors (DRs) are cell surface proteins that contain 'death domains,' intracellular regions that initiate caspase activation upon receptor ligation. Signaling by these DRs has been implicated in killing of neoplastic cells by a number of chemotherapeutic agents, by the cytotoxic ligand TRAIL, by agonistic anti-DR antibodies, and by cytotoxic lymphocytes. This project focuses on understanding biochemical processes that regulate DR-mediated apoptosis with an eye toward improving the efficacy of anticancer treatments that rely on DR signaling.
