Prion Protein Promotes Growth Cone Development through Reggie/Flotillin-Dependent N-Cadherin Trafficking

The role of prion protein (PrP) is insufficiently understood partially because PrP-deficient (-/-) neurons from C57BL/6J mice seem to differentiate normally and are functionally mildly impaired. Here, we reassessed this notion and, unexpectedly, discovered that PrP-/- hippocampal growth cones were abnormally small and poor in filopodia and cargo-containing vesicles. Based on our findings that PrP-PrP trans-interaction recruits E-cadherin to cell contact sites and reggie microdomains, and that reggies are essential for growth by regulating membrane trafficking, we reasoned that PrP and reggie might promote cargo (N-cadherin) delivery via PrP-reggie-connected signaling upon PrP activation (by PrP-Fc-induced trans-interaction). In wild-type but not PrP-/- neurons, PrP activation led to (1) enhanced PrP-reggie cocluster formation, (2) reggie-associated fyn and MAP kinase activation, (3) Exo70 and N-cadherin (cargo) recruitment to reggie, (4) the preference of the growth cone for PrP-Fc as substrate, and (5) longer neurites. Conversely, PrP-reggie-induced N-cadherin recruitment was blocked by mutant TC10, the GTPase downstream of reggie, triggering exocyst-assisted cargo delivery. This implies that PrP functions in reggie-mediated signaling and cargo trafficking, thus promoting growth cone complexity and vitality and thereby growth cone elongation.