High Throughput Screening for Small-molecules Facilitating Prion Study

Transmissible spongiform encephalopathies (TSEs), also known as prion diseases, are a group of unusual infectious mammalian neurodegenerative disorders. The pathogen of TSEs is believed to be a misfolded form (PrPSc) of a normal functional host cellular protein (PrPC). Partly due to the complication of protein-based pathology, TSEs remain incurable and currently there is no treatment that can halt their rapid progressions. Intriguingly, the budding yeast, Saccharomyces cerevisiae, contains several non-Mendelian genetic elements that are transmitted as altered protein conformations and are termed as yeast prions. Its simplicity and genetic trackability has made yeast a powerful model organism for prion research. In this proposal, we plan to use the yeast prion [SWI+] system as a platform to identify small molecules that can inhibit prion propagation through a high-throughput screen approach. [SWI+] was discovered in our laboratory, whose protein determinant is Swi1, a subunit of an evolutionarily conserved chromatin-remodeling complex – SWI/SNF. We found that the expression of FLO1, a SWI/SNF target gene encoding a cell wall protein required for yeast filamentous growth is severely suppressed by [SWI+]. By replacing the FLO1-ORF with the URA3-coding region, we created a faithful FLO1promoter-URA3-based chromosomal reporter. While [SWI+] cannot grow in media lacking uracil, the isogenic non-prion cells can. Thus, chemical compounds that can eliminate [SWI+] can be positively selected in a simple, one-step growth assay in media lacking uracil. We demonstrate that this cost-effective assay is suitable for high-throughput screens in a 384-well format. Our pilot screens have already yielded a number of hits (chemical compounds that can effectively eliminate [SWI+]). We anticipate that some anti-prion compounds obtained from this study will likely become valuable molecular probes for prion research and further investigation of their prion-curing mechanism will lead to identification of novel components important for prion formation and propagation and development of promising anti-prion therapeutic drugs. Due to the amyloid nature of the [SWI+] prion, we also expect that some identified anti-prion compounds are also effective in suppressing non-prion amyloidogenic diseases resulted from protein misfolding, such as Alzheimer’s disease (AD), Parkinson disease (PD), and amyotrophic lateral sclerosis (ALS).