Altered Processing of Amyloid Precursor Protein in Cells Undergoing Apoptosis
Figure 3
Activation of caspase-3 and -7 is associated with APP proteolysis in apoptotic cells.
(A) H4-APP cells were treated with CPT in the presence and absence of caspase inhibitors for six hours and analyzed by western blot using antibodies directed against cleaved caspase-3 or cleaved caspase-7. Cleavage of caspase-3 (topmost panel) and caspase-7 (second panel) was observed in cells treated with CPT. Cleavage of these caspases was associated with an induction in the formation of the fragments detected by caspase-cleaved APP antibody (third panel). Blots were probed for β-actin as a loading control (bottom panel). Immunocytochemical analysis of H4-APP cells also showed significant induction in cleaved caspase-3 (B) and cleaved caspase-7 (C) after one and six hours of exposure to CPT. Cells were co-immunostained with 6E10 antibody (green) to show colocalization of both active caspase-3 and active caspase-7 (red) with APP (Magnification: 63X). Cells showing increased levels of cleaved caspases also showed a reduction in the level of APP signal intensity, consistent with the decrease in full length APP observed by western blot in Figure 2A and 2B.