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

Abstract

The role of prion protein (PrP) is insufficiently understood partially because PrP-deficient (Ϫ/Ϫ) neurons from C57BL/6J mice seem to differentiate normally and are functionally mildly impaired. Here, we reassessed this notion and, unexpectedly, discovered that PrP Ϫ/Ϫ 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 Ϫ/Ϫ 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.

Function of Flotillins in Receptor Tyrosine Kinase Signaling and Endocytosis: Role of Tyrosine Phosphorylation and Oligomerization

“…Interestingly, the amount of coprecipitated of N-Cadherin, which is a core protein of adherens junctions in adult neuronal cells, increased in flotillin-2 immunoprecipitates from mouse hippocampal HPL3-4 cells after application of PrP-Fc. Overexpression of a dominant negative TC10 blocked this effect, which indicates that the PrP together with flotillin-2 is important for the recruitment of N-Cadherin, which in turn takes place in a TC10-dependent manner (85). Very recently, the Stuermer group could show that flotillins together with the PrP play a role in E-Cadherin recruitment to adherens junctions (79).…”

“…The core of adherens junctions is composed of proteins of the cadherin and catenin family (84). Insights into a functional association of flotillins with this cell-cell contact type were obtained in the study of Bodrikov et al (85), who showed that a transient knockdown of flotillin-2 in primary hippocampal neurons perturbed axon growth and differentiation. This phenotype was rescued in 62% of the neurons by overexpression of the constitutive active mutant of the GTPase TC10 which participates in the exocyst dependent polarized delivery of cargo to the growth cone (86).…”

Reggie-1/Flotillin-2 regulates integrin trafficking and focal adhesion turnover via Rab11a

“…This implies an interaction of reggies with the cytoskeleton and motor proteins, as exemplified before (Cornfine et al, 2011;Langhorst et al, 2007) and awaits further research. Reggies also interact with the RhoGTPase TC10 (Bodrikov et al, 2011;Fecchi et al, 2006) and RalA which are involved in the exocyst-dependent membrane-directed cargo transport which is further support of the role of reggies in targeted recycling.…”

“…Reggies were also needed for growth cone formation and elongation (Koch et al, 2013;Munderloh et al, 2009) and the targeted delivery of N-cadherin as one of many growth and guidance receptors (Bodrikov et al, 2011) in elongating neurites. The Rab11/ARF-6 dependent recycling of integrins was demonstrated by Eva and colleagues as an essential molecular mechanism for the regeneration of axons in mammals (Eva et al, 2010(Eva et al, , 2012.…”

Molecular and structural bases for postsynaptic signal processing: interaction between postsynaptic density and postsynaptic membrane rafts

“…75 Flotillin induces growth cone formation and neurite outgrowth via an interaction with prion protein. 76 Striatin resides in membrane rafts 77 and associates with caveolin, and plays a role in endocytosis and cellular signaling. Striatin-deficient neurons display atrophic dendrites in vitro, and the transient and specific downregulation of striatin in rat striata is accompanied by a decrease in locomotor activity.…”