sSORLA triggers EGFR and ERK activation. A, Characterizing sSORLA interaction with cell surface proteins. FLAG beads coupled to sSORLA-FLAGhis₆ (or control FLAG beads) were incubated with WT mouse brain lysate, and associated proteins were detected by immunoblotting as indicated (20 ng lysate input shown). B, Effects of sSORLA on EGFR/ERK activation. Cortical neurons at DIV8 were treated with sSORLA for 0.5 h, and neuronal lysates were immunoblotted for pY1173 EGFR, EGFR, pERK, ERK, or actin as indicated. Densitometric measurements from additional experiments were plotted in the adjacent graph (p = 0.0008, t test). C, D, sSORLA and SORLA overexpression triggers ERK activation. C, DIV9 cortical neurons were treated with sSORLA for 0.5 h, and neuronal lysates were immunoblotted for pERK, ERK, or actin. pERK levels were quantified by densitometry, and normalized to ERK levels are shown in the adjacent graph (control set to 1.0; 6 replicates from three experiments) (p = 0.0016, t test). D, Hippocampal lysates from 3.5-month-old WT (n = 6) and SORLA TG (TG) (n = 6) animals were immunoblotted for SORLA, pERK, or ERK as indicated. pERK and ERK levels were quantified and normalized as in C (p = 0.0061, t test). Data are mean ± SE. **p < 0.01; ***p < 0.001; Student's t test.