抄録
Hyperphosphorylated tau is a chemical deposit in brain of Alzheimer's disease(AD) patient and characterized by double phosphorylation of closely located residues such as Ser202 and Thr205, Thr212 and Ser214. Such double phosphorylation seems to require complex regulations. For example involvement of more than two tau kinases or activators is considered.
We have focused on sequential phosphorylation of tau by CDK5, glycogen synthase kinase 3β(GSK3β) and cyclic-AMP dependent kinase (PKA), which regulates AT100 reactivity on Ser202, Thr205, Thr212, and Ser214.
First we had conduced in vitro tau phosphorylation by single kinase. Western blot analysis clearly showed phosphorylation on Ser202, Thr205, and Thr212 was fully dependent on CDK5. Truncation of CDK5 activator p35 enhanced most of phosphorylation sites except Ser202. Phosphorylation on Ser214 is highly functioned by PKA. GSK3β mostly shared phosphorylation sites with CDK5 and had less activity than CDK5.
Second we had examined sequential phosphorylation by CDK5, GSK3β, then PKA. The change in phosphorylation preference of CDK5, resulted from cleavage of p35 to p25, had little effect on sequential phosphorylation. Phosphorylation of Ser202 or Thr205 by sequential regulation was dependent on CDK5 and Ser214 was phosphorylated by PKA. Surprisingly GSK3β evoked striking enhancement of phosphorylation on Thr212 after CDK5 preincubation even faint phosphorylation on Thr212 was detected by 48hr incubation of GSK3βalone.
These results indicated that sequential phosphorylation was highly responsible for hyperphosphorylation of tau in consequence of stimulation of AD specific phosphorylation. [Jpn J Physiol 54 Suppl:S217 (2004)]
