Retrograde Transport by Clathrin-Coated Vesicles is Involved in Intracellular Transport of PrP(Sc) in Persistently Prion-Infected Cells

Intracellular dynamics of an abnormal isoform of prion protein (PrP(Sc)) are tightly associated with prion propagation. However, the machineries involved in the intracellular trafficking of PrP(Sc) are not fully understood. Our previous study suggested that PrP(Sc) in persistently prion-infected cells dynamically circulates between endocytic-recycling compartments (ERCs) and peripheral regions of the cells. To investigate these machineries, we focused on retrograde transport from endosomes to the trans-Golgi network, which is one of the pathways involved in recycling of molecules. PrP(Sc) was co-localized with components of clathrin-coated vesicles (CCVs) as well as those of the retromer complex, which are known as machineries for retrograde transport. Fractionation of intracellular compartments by density gradient centrifugation showed the presence of PrP(Sc) and the components of CCVs in the same fractions. Furthermore, PrP(Sc) was detected in CCVs isolated from intracellular compartments of prion-infected cells. Knockdown of clathrin interactor 1, which is one of the clathrin adaptor proteins involved in retrograde transport, did not change the amount of PrP(Sc), but it altered the distribution of PrP(Sc) from ERCs to peripheral regions, including late endosomes/lysosomes. These data demonstrated that some PrP(Sc) is transported from endosomes to ERCs by CCVs, which might be involved in the recycling of PrP(Sc).