Anti-prion Protein Antibody 6D11 Restores Cellular Proteostasis of Prion Protein Through Disrupting Recycling Propagation of PrP and Targeting PrP for Lysosomal Degradation.

PrP is an infectious and disease-specific conformer of the prion protein, which accumulation in the CNS underlies the pathology of prion diseases. PrP replicates by binding to the cellular conformer of the prion protein (PrP) expressed by host cells and rendering its secondary structure a likeness of itself. PrP is a plasma membrane anchored protein, which constitutively recirculates between the cell surface and the endocytic compartment. Since PrP engages PrP along this trafficking pathway, its replication process is often referred to as "recycling propagation." Certain monoclonal antibodies (mAbs) directed against prion protein can abrogate the presence of PrP from prion-infected cells. However, the precise mechanism(s) underlying their therapeutic propensities remains obscure. Using N2A murine neuroblastoma cell line stably infected with 22L mouse-adapted scrapie strain (N2A/22L), we investigated here the modus operandi of the 6D11 clone, which was raised against the PrP conformer and has been shown to permanently clear prion-infected cells from PrP presence. We determined that 6D11 mAb engages and sequesters PrP and PrP at the cell surface. PrP/6D11 and PrP/6D11 complexes are then endocytosed from the plasma membrane and are directed to lysosomes, therefore precluding recirculation of nascent PrP back to the cell surface. Targeting PrP by 6D11 mAb to the lysosomal compartment facilitates its proteolysis and eventually shifts the balance between PrP formation and degradation. Ongoing translation of PrP allows maintaining the steady-state level of prion protein within the cells, which was not depleted under 6D11 mAb treatment. Our findings demonstrate that through disrupting recycling propagation of PrP and promoting its degradation, 6D11 mAb restores cellular proteostasis of prion protein.