title: Cyclin-dependent protein kinase 5 primes microtubule-associated protein tau site-specifically for glycogen synthase kinase 3beta.
abstract: In the preceding paper, we showed that GSK3beta phosphorylates tau at S(202), T(231), S(396), and S(400) in vivo. Phosphorylation of S(202) occurs without priming. Phosphorylation of T(231), on the other hand, requires priming phosphorylation of S(235). Similarly, priming phosphorylation of S(404) is essential for the sequential phosphorylation of S(400) and S(396) by GSK3beta. The priming kinase that phosphorylates tau at S(235) and S(404) in the brain is not known. In this study, we find that in HEK-293 cells cotransfected with tau, GSK3beta, and Cdk5, Cdk5 phosphorylates tau at S(202), S(235), and S(404). S(235) phosphorylation enhances GSK3beta-catalyzed T(231) phosphorylation. Similarly, Cdk5 by phosphorylating S(404) stimulates phosphorylation of S(400) and S(396) by GSK3beta. These data indicate that Cdk5 primes tau for GSK3beta in intact cells. To evaluate if Cdk5 primes tau for GSK3beta in mammalian brain, we examined localizations of Cdk5, tau, and GSK3beta in rat brain. We also analyzed the interaction of Cdk5 with tau and GSK3beta in brain microtubules. We found that Cdk5, GSK3beta, and tau are virtually colocalized in rat brain cortex. When bovine brain microtubules are analyzed by FPLC gel filtration, Cdk5, GSK3beta, and tau coelute within an approximately 450 kDa complex. From the fractions containing the approximately 450 kDa complex, tau, Cdk5, and GSK3beta co-immunoprecipitate with each other. In HEK-293 cells transfected with tau, Cdk5, and GSK3beta in different combinations, tau binds to Cdk5 in a manner independent of GSK3beta and to GSK3beta in a manner independent of Cdk5. However, Cdk5 and GSK3beta bind to each other only in the presence of tau, suggesting that tau connects Cdk5 and GSK3beta. Our results suggest that in the brain, tau, Cdk5, and GSK3beta are components of an approximately 450 kDa complex. Within the complex, Cdk5 phosphorylates tau at S(235) and primes it for phosphorylation of T(231) by GSK3beta. Similarly, Cdk5 by phosphorylating tau at S(404) primes tau for a sequential phosphorylation of S(400) and S(396) by GSK3beta.
authors.affiliation: Bloomfield Center for Research in Aging, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital, Montreal, Quebec H3T 1E2, Canada.
authors.forename: Tong
authors.initials: T
authors.lastname: Li
authors.forename: Cheryl
authors.initials: C
authors.lastname: Hawkes
authors.forename: Hamid Y
authors.initials: HY
authors.lastname: Qureshi
authors.forename: Satyabrata
authors.initials: S
authors.lastname: Kar
authors.forename: Hemant K
authors.initials: HK
authors.lastname: Paudel
mesh_terms: D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D051360:Cyclin-Dependent Kinase 5 / Q000378:metabolism / Q000494:pharmacology*; D005455:Fluorescent Antibody Technique; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D008297:Male; D010766:Phosphorylation; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D012694:Serine / Q000378:metabolism; D014162:Transfection; D016875:tau Proteins / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D016875:tau Proteins; D012694:Serine; D051360:Cyclin-Dependent Kinase 5; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605508:Gsk3b protein, rat; D038362:Glycogen Synthase Kinase 3