Virus‐induced alterations of membrane lipids affect the incorporation of PrP^Sc into cells

Abstract

Prion diseases are fatal neurodegenerative disorders characterized by long incubation periods. To investigate whether concurrent diseases can modify the clinical outcome of prion-affected subjects, we tested the effect of viral infection on the binding and internalization of PrP(Sc), essential steps of prion propagation. To this effect, we added scrapie brain homogenate or purified PrP(Sc) to fibroblasts previously infected with minute virus of mice (MVM), a mouse parvovirus. We show here that the rate of incorporation of PrP(Sc) into MVM-infected cells was significantly higher than that observed for naïve cells. Immunostaining of cells and immunoblotting of subcellular fractions using antibodies recognizing PrP and LysoTracker, a lysosomal marker, revealed that in both control and MVM-infected cells the incorporated PrP(Sc) was associated mostly with lysosomes. Interestingly, flotation gradient analysis revealed that the majority of the PrP(Sc) internalized into MVM-infected cells shifted toward raft-containing low-density fractions. Concomitantly, the MVM-infected cells demonstrated increased levels of the glycosphingolipid GM1 (an essential raft lipid component) throughout the gradient and a shift in caveolin 1 (a raft protein marker) toward lighter membrane fractions compared with noninfected cells. Our results suggest that the effect of viral infection on membrane lipid composition may promote the incorporation of exogenous PrP(Sc) into rafts. Importantly, membrane rafts are believed to be the conversion site of PrP(C) to PrP(Sc); therefore, the association of exogenous PrP(Sc) with such membrane microdomains may facilitate prion infection.

Function of Membrane Rafts in Viral Lifecycles and Host Cellular Response

“…Involvement of membrane rafts in infectious particle prion (PrP) infection has been reported [236][237][238][239][240][241][242]. PrP is an infectious protein that does not have a genome, unlike viruses.…”

“…The property of the GPI anchor attached to PrP Sc has been reported to affect the binding of PrP Sc to neurons, distribution to membrane rafts, and conversion of endogenous PrP c in GT1 neuronal cells [245]. Moreover, the increased level of glycosphingolipid GM1 (an essential raft marker) on fibroblast cells by a mouse parvovirus (Parvoviridae) infection may promote prion infection through the incorporation of exogenous PrP Sc into membrane rafts [239].…”

Role of Membrane Rafts in Viral Infection

“…The involvement of membrane rafts in infectious particle prion (PrP) infection has also been investigated [98][99][100][101].…”

“…Membrane rafts are believed to be the conversion site of PrP C to PrP Sc . Moreover, increased level of the glycosphingolipid GM1 (an essential raft marker) on fibroblast cells by a mouse parvovirus (Parvoviridae) infection may promote prion infection through the incorporation of exogenous PrP Sc into rafts [101].…”