Comparison of the phosphorylation of microtubule-associated protein tau by non-proline dependent protein kinases

Abstract

Microtubule-associated protein tau from Alzheimer brain has been shown to be phosphorylated at several ser/thr-pro and ser/thr-X sites (Hasegawa, M. et al., J. Biol. Chem. 267, 17047-17054, 1992). Several proline-dependent protein kinases (PDPKs) (MAP kinase, cdc2 kinase, glycogen synthase kinase-3, tubulin-activated protein kinase, and 40 kDa neurofilament kinase) are implicated in the phosphorylation of the ser-thr-pro sites. The identity of the kinase(s) that phosphorylate the ser/thr-X sites are unknown. To identify the latter kinase(s) we have compared the phosphorylation of bovine tau by several brain protein kinases. Stoichiometric phosphorylation of tau was achieved by casein kinase-1, calmodulin-dependent protein kinase II, Gr kinase, protein kinase C and cyclic AMP-dependent protein kinase, but not with casein kinase-2 or phosphorylase kinase. Casein kinase-1 and calmodulin-dependent protein kinase II were the best tau kinases, with greater than 4 mol and 3 mol 32P incorporated, respectively, into each mol of tau. With the sequential addition of these two kinases, 32P incorporation approached 6 mol. Peptide mapping revealed that the different kinases largely phosphorylate different sites on tau. After phosphorylation by casein kinase-1, calmodulin-dependent protein kinase II, Gr kinase, cyclic AMP-dependent protein kinase and casein kinase-2, the mobility of tau isoforms as detected by SDS-PAGE was decreased. Protein kinase C phosphorylation did not produce such a mobility shift. Our results suggest that one or more of the kinases studied here may participate in the hyperphosphorylation of tau in Alzheimer disease.(ABSTRACT TRUNCATED AT 250 WORDS)