Novel regulators of PrPC biosynthesis revealed by genome-wide RNA interference

An arrayed genome-wide perturbation screen identifies the ribonucleoprotein Hnrnpk as rate-limiting for prion propagation

A defining characteristic of mammalian prions is their capacity for self-sustained propagation. Theoretical considerations and experimental evidence suggest that prion propagation is modulated by cell-autonomous and non-autonomous modifiers. Using a novel quantitative phospholipase protection assay (QUIPPER) for high-throughput prion measurements, we performed an arrayed genome-wide RNA interference (RNAi) screen aimed at detecting cellular host-factors that can modify prion propagation. We exposed prion-infected cells in high-density microplates to 35,364 ternary pools of 52,746 siRNAs targeting 17,582 genes representing the majority of the mouse protein-coding transcriptome. We identified 1,191 modulators of prion propagation. While 1,151 modified the expression of both the pathological prion protein, PrP^Sc , and its cellular counterpart, PrP^C , 40 genes selectively affected PrP^Sc . Of the latter 40 genes, 20 augmented prion production when suppressed. A prominent limiter of prion propagation was the heterogeneous nuclear ribonucleoprotein Hnrnpk. Psammaplysene A (PSA), which binds Hnrnpk, reduced prion levels in cultured cells and protected them from cytotoxicity. PSA also reduced prion levels in infected cerebellar organotypic slices and alleviated locomotor deficits in prion-infected Drosophila melanogaster expressing ovine PrP^C . Hence, genome-wide QUIPPER-based perturbations can discover actionable cellular pathways involved in prion propagation. Further, the unexpected identification of a prion-controlling ribonucleoprotein suggests a role for RNA in the generation of infectious prions.