| Prions are the causative agents of a group of lethal, neurodegenerative conditions that include sheep scrapie, bovine spongiform encephalopathy (BSE), and human Creutzfeldt-Jakob disease (CJD). Prions are derived from the conversion of a normal, primarily alpha-helical, cellular prion protein (PrPC ), to an infectious, beta sheet-rich conformer (PrPSc). Many unresolved issues surround the process of PrP conversion, and we know very little about cellular responses to these unique pathogens. Our lack of knowledge relates, in part, to the difficulty of infecting cells in vitro with prions. While expression of PrPC is an absolute requirement for prion propagation, I show here that not all cells that express PrP C are capable of propagating PrPSc. The goal of this thesis is to understand the role that host factors play in sustaining prion infection and to develop systems in which the cellular response to prion infection can be assessed. We hypothesize that cellular permissiveness to prion infectivity is co-dependent on unidentified additional cellular factors. To study the role of PrPC expression in susceptibility to prion infectivity, and identify these cofactors in cell culture, we utilized cells which fail to express endogenous PrPC, but become susceptible to prions following stable expression of PrPC. Following transfection of a species specific PrP expression construct and isolation of single cell clones, we assessed PrP expression and susceptibility to prion infectivity by measuring accumulation of protease resistant PrPSc . Differential gene expression studies suggest significant transcriptional differences between susceptible and resistant clones. Using three independent gene expression databases our analyses suggest that the resistant transcriptional profile favors cell division/cycle and chromosomal regulation pathways, while the sensitive transcriptional profile is involved in protein homeostasis and quality control. The results of these studies will not only lead to a greater understanding of PrP cell biology and the mechanisms of prion pathogenesis, but should ultimately lead to sensitive and expedient methods for detecting and characterizing prion infectivity from a wide range of sources.;KEYWORDS: Prions; Cellular Permissiveness; Cellular PrPC; Protease Resistant PrPSc; Transcriptional Differences. |
