Figure 4.

Loss of presenilins decreases proteolysis of long-lived proteins. A, B, PSDKO cells have decreased proteolysis for long-lived proteins shown by radiolabeled [S³⁵]l-methionine. Quantification of radiographs in E was performed by densiometric analysis and is presented as percentage of control. Error bars represent ± SEM; n = 3; unpaired Student's t test, *p < 0.05. Con, Control; DKO, double knock-out. C, PSDKO fibroblasts again show a decrease in proteolysis for long-lived proteins shown by radiolabeled [H³]l-valine measured by scintillation counter. Results are presented as percentage proteolysis. Error bars represent ± SEM; n = 4; unpaired Student's t test, *p < 0.05. D, PSDKO fibroblasts do not have an increase in proteolysis with rapamycin treatment (0.2 μm, 12 h time point). Error bars represent ± SEM; n = 4; one-way ANOVA, post hoc comparison Tukey's HSD, *p < 0.05.