PI3K activity regulates the constitutive levels of ApoER2 CTF but is not involved in ApoER2 shedding induced by NGF. (A) PC12-ApoER2 cells were serum-starved and pre-treated with 10 μM DAPT and 50 μM LY294002 or 5 μM ZSTK474 for 1 h. Then, the cells were incubated with 100 ng/mL NGF for 2 h. ApoER2 and p75NTR were recognized using antibodies directed against their intracellular regions. The activation of PI3K, induced by NGF, was determined by detection of phospho-AKT. α-tubulin is shown as a loading control. The blot levels of ApoER2 CTF (B and C) and of p75NTR CTF (D and E) were normalized to the loading control α-tubulin and plotted as the average ± SD of three independent experiments. One way ANOVA, Holm-Sidak post-hoc test, *P < 0.01; N.S, not significant.