Kinase-kinase interaction and modulation of tau phosphorylation.

The microtubule (MT)-associated protein tau attaches to neuronal MT networks and regulates their integrity. The phosphorylation state of tau alters its binding activity. MT integrity is maintained by the phosphorylation state of tau, which is under the control of the kinase-phosphatase balance.

Truncation of CDK5 activator p35 induces intensive phosphorylation of Ser202/Thr205 of human tau.

Hyperphosphorylated tau is a major component of neurofibrillary tangles, one of the hallmarks of Alzheimer's disease. CDK5 is a kinase that phosphorylates the tau protein, and its endogenous activator, p35, regulates its activity. Recently, calpain was found to digest p35 to its truncated product, p25.