Figure 4.

Checkpoint kinases directly phosphorylate human tau at Ser262 in vitro. Recombinant active human Chk2 (A and B) or recombinant active human Chk1 (C and D) were incubated with recombinant human tau in the presence or absence of inhibitors (Chk2 inhibitor II for Chk2 and UCN-01 for Chk1). Proteins were resolved by SDS-PAGE and visualized by western blotting using an anti-pSer262 antibody (A and C). The signals were quantified and the phosphorylation levels are shown as a ratio relative to that of recombinant tau incubated with recombinant kinase in the absence of inhibitor (B and D). Asterisks indicate significant differences (n = 4, P < 0.05, Student's t-test).