Cholesterol Removal by Methyl- -Cyclodextrin Inhibits Poliovirus Entry

Upon binding to the poliovirus receptor (PVR), the poliovirus 160S particles undergo a conformational transition to generate 135S particles, which are believed to be intermediates in the virus entry process. The 135S particles interact with host cell membranes through exposure of the N termini of VP1 and the myristylated VP4 protein, and successful cytoplasmic delivery of the genomic RNA requires the interaction of these domains with cellular membranes whose identity is unknown. Because detergent-insoluble microdomains (DIMs) in the plasma membrane have been shown to be important in the entry of other picornaviruses, it was of interest to determine if poliovirus similarly required DIMs during virus entry. We show here that methyl-cyclodextrin (M CD), which disrupts DIMs by depleting cells of cholesterol, inhibits virus infection and that this inhibition was partially reversed by partially restoring cholesterol levels in cells, suggesting that M CD inhibition of virus infection was mediated by removal of cellular cholesterol. However, fractionation of cellular membranes into DIMs and detergent-soluble membrane fractions showed that both PVR and poliovirus capsid proteins localize not to DIMs but to detergent-soluble membrane fractions during entry into the cells, and their localization was unaffected by treatment with M CD. We further demonstrate that treatment with M CD inhibits RNA delivery after formation of the 135S particles. These data indicate that the cholesterol status of the cell is important during the process of genome delivery and that these entry pathways are distinct from those requiring DIM integrity.