An antipsychotic drug exerts anti-prion effects by altering the localization of the cellular prion protein

Prion diseases are neurodegenerative conditions characterized by the conformational conversion of the cellular prion protein (PrP(C)), an endogenous membrane glycoprotein of uncertain function, into PrP(Sc), a pathological isoform that replicates by imposing its abnormal folding onto PrP(C) molecules. A great deal of evidence supports the notion that PrP(C) plays at least two roles in prion diseases, by acting as a substrate for PrP(Sc) replication, and as a mediator of its toxicity. This conclusion was recently supported by data suggesting that PrP(C) may transduce neurotoxic signals elicited by other disease-associated protein aggregates. Thus, PrP(C) may represent a convenient pharmacological target for prion diseases, and possibly other neurodegenerative conditions. Here, we sought to characterize the activity of chlorpromazine (CPZ), an antipsychotic previously shown to inhibit prion replication by directly binding to PrP(C). By employing biochemical and biophysical techniques, we provide direct experimental evidence indicating that CPZ does not bind PrP(C) at biologically relevant concentrations. Instead, the compound exerts anti-prion effects by inducing the relocalization of PrP(C) from the plasma membrane. Consistent with these findings, CPZ also inhibits the cytotoxic effects delivered by a PrP mutant. Interestingly, we found that the different pharmacological effects of CPZ could be mimicked by two inhibitors of the GTPase activity of dynamins, a class of proteins involved in the scission of newly formed membrane vesicles, and recently reported as potential pharmacological targets of CPZ. Collectively, our results redefine the mechanism by which CPZ exerts anti-prion effects, and support a primary role for dynamins in the membrane recycling of PrP(C), as well as in the propagation of infectious prions.