Figure 3.

Cleavage and distribution of I₂^PP2A in nuclear and cytosolic fractions in AD and control brains. Subcellular fractions from temporal cortex (TC) and cerebellum (Cb) of control (C) and AD cases were analyzed by Western blots. I₁^PP2A and I₂^PP2A signals were quantitated using TINA 2.0 software and normalized by topoisomerase I (Topo I) for nuclear fraction and β-actin for cytosol fraction. a–c: In temporal cortex, the level of I₁^PP2A in AD was increased significantly in nuclear fraction (a, b; *P < 0.05) and insignificantly in the cytosol (a, c) as compared to control cases. In contrast, the level of I₂^PP2A in the nuclear fraction was decreased in AD as compared to the control cases (a, d; *P < 0.05). The 39-kd I₂^PP2A in the cytosol fraction was decreased in AD (a, e; *P < 0.05), but an ∼20-kd fragment of I₂^PP2A was significantly increased in AD as compared to controls (a, f; *P < 0.05). Total relative intensity of both 39-kd plus 20-kd I₂^PP2A and as well as of the 39-kd plus all its cleavage product polypeptides (total I₂^PP2A) were increased in AD as compared to control (a, g; *P < 0.05). h: In cerebellum, expression levels of both I₁^PP2A and I₂^PP2A were similar in AD and control cases (h–l), and only background level of 20-kd fragment of I₂^PP2A was seen in cerebellum. b–g, i–l: Mean ± SEM of normalized data relative to control. The left of a and h indicates the molecular weight markers, and on the right of a and h, full-length I₁^PP2A (30 kd) and I₂^PP2A (39 kd) is indicated by arrows, and the cleavage products of I₂^PP2A by arrowheads (from top to bottom, the ∼56-, ∼34-, ∼25-, and ∼20-kd polypeptides).