Figure 9

Internalization of APP mutants into the endosomal/lysosomal system in SN56 cells. SN56 cells were cotransfected with the indicated βAPP and fluorescent-tagged compartment marker protein constructs as indicated. Cells were then surface labeled with AlexaFluor 647-labeled anti-HA antibody on ice for 30 min and were then allowed to internalize this antibody at 37°C for the time indicated, fixed and imaged. For each time point, the colocalization of the brightest 2% of the anti-HA signal and the compartment marker was quantified (as in Figure 3). A. Internalization of surface-labeled APP into the Rab5 compartment (early endosome). * indicates statistically significant difference between the βAPP-SW and βAPP-Lon mutants and all other markers (P < 0.05). ** indicates statistically significant difference between βAPP-Lon, βAPP-wt, and dextran (P < 0.05). *** indicates statistically significant difference between βAPP-Lon, βAPP-SW, and βAPP-wt (P < 0.05). B. Internalization of surface-labeled βAPP (wt and mutant) into the Rab9 compartment (late endosome). * indicates statistically significant difference between APP-SW and all other markers. C. Internalization of surface-labeled βAPP (wt and mutant) into the LAMP1 compartments. These means were compared statistically by ANOVA at each time point. * indicates statistically significant difference between APP-wt and all other markers (P < 0.05). ** indicates statistically significant difference between βAPP-SW and βAPP-wt from βAPP-Lon and dextran (P < 0.05).