CHARACTERIZATION OF TAU-PHOSPHORYLATION IN GLYCOGEN-SYNTHASE-KINASE-3-BETA AND CYCLIN-DEPENDENT-KINASE-5 ACTIVATOR (P23) TRANSFECTED CELLS

One of the histopathological markers in Alzheimer's disease is the acc umulation of hyperphosphorylated tau in neurons called neurofibrillary tangles (NFT) composing paired helical filaments (PHF). Combined tau protein kinase II (TPK II), which consists of CDK5 and its activator ( p23), and glycogen synthase kinase-3 beta (GSK-3 beta) phosphorylate t au to the PHF-form in vitro. To investigate tau phosphorylation by the se kinases in intact cells, the phosphorylation sites were examined in detail using well-characterized phosphorylation-dependent anti-tau an tibodies after overexpressing the kinases in COS-7 cells with a human tau isoform. The overexpression of tau in COS-7 cells showed extensive phosphorylation at Ser-202 and Ser-404. The p23 overexpression induce d a mobility shift of tau, but most of the phosphorylation sites overl apped the endogenous phosphorylation sites. GSK-3 beta transfection sh owed the phosphorylation at Ser-199, Thr-231, Ser-396, and Ser-413. Tr iplicated transfection resulted in phosphorylation of tau at 8 observe d sites (Ser-199, Ser-202, Thr-205, Thr-231, Ser-235, Ser-396, Ser-404 , and Ser-413). (C) 1998 Elsevier Science B.V.