Functional genomics screen identifies proteostasis targets that modulate prion protein (PrP) stability

Prion protein (PrP) adopts either a helical conformation (PrP^C) or an alternative, beta sheet-rich, misfolded conformation (PrP^Sc). The PrP^Sc form has the ability to "infect" PrP^C and force it into the misfolded state. Accumulation of PrP^Sc is associated with a number of lethal neurodegenerative disorders, including Creutzfeldt-Jacob disease (CJD). Knockout of PrP^C protects cells and animals from PrP^Sc infection; thus, there is interest in identifying factors that regulate PrP^C stability, with the therapeutic goal of reducing PrP^C levels and limiting infection by PrP^Sc. Here, we assembled a short-hairpin RNA (shRNA) library composed of 25+ shRNA sequences for each of 133 protein homeostasis (aka proteostasis) factors, such as molecular chaperones and co-chaperones. This Proteostasis shRNA Library was used to identify regulators of PrP^C stability in HEK293 Hu129M cells. Strikingly, the screen identified a number of Hsp70 family members and their co-chaperones as putative targets. Indeed, a chemical pan-inhibitor of Hsp70s reduced PrP^C levels and limited conversion to PrP^Sc in N2a cells. These results implicate specific proteostasis sub-networks, especially the Hsp70 system, as potential new targets for the treatment of CJD. More broadly, the Proteostasis shRNA Library might be a useful tool for asking which proteostasis factors are important for a given protein.