The following antibodies were used in this study: anti-PS1(NT), Ab14, aPS1loop, SP716, polyclonal antibody 3925, PNT2, polyclonal antibody O2C2 (gift of Drs. Paul Fraser and Peter St George-Hyslop), antibody H2D2 (gift of Dr. Gang Yu), polyclonal antibody STC261, polyclonal PrP antibody D13 (gift of Dr. James A. Mastrianni) Anti-PS1loop (Chemicon), monoclonal anti-nicastrin (BD Transduction Laboratories), and polyclonal PrP antibodies were used in primary neuronal culture studies. Antibodies against organelle markers and lipid raft-associated proteins were purchased from commercial sources: anti-KDEL and calnexin (Stressgen); caveolin-1, (Santa Cruz Biotechnology); GM130, p115, g-adaptin, syntaxin 6, EEA1, flotillin-1, and flotillin-2 (BD Transduction Laboratories); cholera toxin (Calbiochem); syntaxin 13, SNAP-23, and VAMP4 (Synaptic Systems); Na+/K+-ATPase (Upstate Biotechnology, Inc.); LAMP-1 (Developmental Studies Hybridoma Bank); OKT8 (ATCC). Cy2-, or Cy3-conjugated secondary antibodies were purchased from Jackson Immunoresearch Laboratories.