Genome-wide identification of microRNAs regulating the human prion protein

The cellular prion protein (PrPC) is best known for its misfolded disease-causing conformer, PrPSc. Because the availability of PrPC is often limiting for prion propagation, understanding its regulation may point to possible therapeutic targets. We sought to determine to what extent the human microRNAome is involved in modulating PrPC levels through direct or indirect pathways. We probed PrPC protein levels in cells subjected to a genome-wide library encompassing 2019 miRNA mimics using a robust time-resolved fluorescence-resonance screening assay. Screening was performed in three human neuroectodermal cell lines: U-251 MG, CHP-212 and SH-SY5Y. The three screens yielded 17 overlapping high-confidence miRNA mimic hits, 13 of which were found to regulate PrPC biosynthesis directly via binding to the PRNP 3'UTR, thereby inducing transcript degradation. The four remaining hits (miR-124-3p, 192-3p, 299-5p and 376b-3p) did not bind either the 3'UTR or CDS of PRNP, and were therefore deemed indirect regulators of PrPC. Our results show that multiple miRNAs regulate PrPC levels both directly and indirectly. These findings may have profound implications for prion disease pathogenesis and potentially also for their therapy. Furthermore, the possible role of PrPC as a mediator of A beta toxicity suggests that its regulation by miRNAs may also impinge on Alzheimer's disease.