Cyclin-dependent protein kinase 5 primes microtubule-associated protein tau site-specifically for glycogen synthase kinase 3β

Li, Tong and Hawkes, Cheryl and Qureshi, Hamid Y. and Kar, Satyabrata and Paudel, Hemant K. (2006) Cyclin-dependent protein kinase 5 primes microtubule-associated protein tau site-specifically for glycogen synthase kinase 3β. Biochemistry, 45 (10). pp. 3134-3145. ISSN 0006-2960

Abstract

In the preceding paper, we showed that GSK3β phosphorylates tau at S202, T231, S396, and S400 in vivo. Phosphorylation of S202 occurs without priming. Phosphorylation of T231, on the other hand, requires priming phosphorylation of S 235. Similarly, priming phosphorylation of S404 is essential for the sequential phosphorylation of S400 and S 396 by GSK3β. The priming kinase that phosphorylates tau at S235 and S404 in the brain is not known. In this study, we find that in HEK-293 cells cotransfected with tau, GSK3β, and Cdk5, Cdk5 phosphorylates tau at S202, S235, and S404. S235 phosphorylation enhances GSK3β-catalyzed T231 phosphorylation. Similarly, Cdk5 by phosphorylating S404 stimulates phosphorylation of S400 and S396 by GSK3β. These data indicate that Cdk5 primes tau for GSK3β in intact cells. To evaluate if Cdk5 primes tau for GSK3β in mammalian brain, we examined localizations of Cdk5, tau, and GSK3β in rat brain. We also analyzed the interaction of Cdk5 with tau and GSK3β in brain microtubules. We found that Cdk5, GSK3β, and tau are virtually colocalized in rat brain cortex. When bovine brain microtubules are analyzed by FPLC gel filtration, Cdk5, GSK3β, and tau coelute within an ∼450 kDa complex. From the fractions containing the ∼450 kDa complex, tau, Cdk5, and GSK3β coimmunoprecipitate with each other. In HEK-293 cells transfected with tau, Cdk5, and GSK3β in different combinations, tau binds to Cdk5 in a manner independent of GSK3β and to GSK3β in a manner independent of Cdk5. However, Cdk5 and GSK3β bind to each other only in the presence of tau, suggesting that tau connects Cdk5 and GSK3β. Our results suggest that in the brain, tau, Cdk5, and GSK3β are components of an ∼450 kDa complex. Within the complex, Cdk5 phosphorylates tau at S235 and primes it for phosphorylation of T231 by GSK3β. Similarly, Cdk5 by phosphorylating tau at S404 primes tau for a sequential phosphorylation of S400 and S396 by GSK3β.