A seven-residue deletion in PrP leads to generation of a spontaneous prion formed from C-terminal C1 fragment of PrP

Abstract

Prions result from a drastic conformational change of the host-encoded cellular prion protein (PrP), leading to the formation of beta-sheet-rich, insoluble and protease-resistant self-replicating assemblies (PrPSc). The cellular and molecular mechanisms involved in spontaneous prion formation in sporadic and inherited human prion diseases or equivalent animal diseases are poorly understood, in part because cell models of spontaneously-forming prions are currently lacking. Here, extending studies on the role of H2 alpha-helix C-terminus of PrP, we found that deletion of the highly conserved 190HTVTTTT196 segment of ovine PrP led to spontaneous prion formation in the RK13 rabbit kidney cell model. On long-term passage, the mutant cells stably produced proteinase-K resistant, insoluble and aggregated assemblies that were infectious for naïve cells expressing either the mutant protein or other PrPs with slightly different deletions in the same area. The electrophoretic pattern of PK-resistant core of the spontaneous prion (∆Spont) contained mainly C-terminal polypeptides akin to C1, the cell-surface anchored C-terminal moiety of PrP generated by natural cellular processing. RK13 cells expressing solely ∆190-196 C1 PrP construct, in absence of the full-length protein, were susceptible to ∆Spont prions. ∆Spont infection induced the conversion of the mutated C1 into a PK-resistant and infectious form perpetuating the biochemical characteristics of ∆Spont prion. In conclusion this work provides a unique cell-derived system generating spontaneous prions and provides evidence that the 113 C-terminal residues of PrP are sufficient for a self-propagating prion entity.

Pathogenicity, strain properties and interspecies transmission capacity of pure recombinant prion protein assemblies

“…Recently, we showed that the alpha-cleaved C1-fragments from PrP C (truncation at amino acids 113/115, [67]) were convertible into prions in RK13 cells, when part of the a-helix H2 was deleted [68]. This result and the infectivity of LMW PrP Sc fragments stand in apparent contradiction with several reports suggesting that PrP amino acids ~90-100 to 155, notably the central polybasic domain with 4 lysines at aa ~100-110, are an obligate domain of PrP res infectious core [18,[69][70][71].…”

PrPC as a Transducer of Physiological and Pathological Signals

“…Although the regulatory role for C1 fragment production is unresolved, it seems that it negatively modulates key steps of PrP conversion process, namely, misfolding, replication, and fibrillization ( Westergard et al, 2011 ; Campbell et al, 2013 ). Nevertheless, under experimental conditions, C1 lacking the C-terminal portion of H 2 can be converted into a C1 prion by full-length spontaneous prion harboring the same deletion ( Munoz-Montesino et al, 2020 ). Regarding C2 fragment, data strongly suggest that its accumulation would be a key product of the PrP C processing in prion replication ( Dron et al, 2010 ).…”

Caprine PRNP polymorphisms N146S and Q222K are associated with proteolytic cleavage of PrPC

“…This raises the possibility that PrP C cleavage may modulate prion diseases by reducing the amount of full-length PrP C available for conversion or C1 fragment-mediated inhibition of full-length PrP C conversion. Interestingly, a laboratory-generated PrP C deletion mutant was found to undergo spontaneous conversion to a prion of similar size as the C1 fragment [ 13 ]. This new type of prion was also able to infect and propagate in a cell line that expressed the deletion-mutant PrP C C1 fragment only.…”