COMPARISON OF THE PHOSPHORYLATION OF MICROTUBULE-ASSOCIATED PROTEIN-TAU BY NON-PROLINE DEPENDENT PROTEIN-KINASES

Microtubule-associated protein tau from Alzheimer brain has been shown to be phosphorylated at several ser/thr-pro and ser/thr-X sites (Hase gawa, M. et al., J. Biol. Chem. 267, 17047-17054, 1992). Several proli ne-dependent protein kinases (PDPKs) (MAP kinase, cdc2 kinase, glycoge n synthase kinase-3, tubulin-activated protein kinase, and 40 kDa neur ofilament kinase) are implicated in the phosphorylation of the ser-thr -pro sites. The identity of the kinase(s) that phosphorylate the ser/t hr-X sites are unknown. To identify the latter kinase(s) we have compa red the phosphorylation of bovine tan 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 pro tein kinase II were the best tan kinases, with greater than 4 mol and 3 mol P-32 incorporated, respectively, into each mol of tau. With the sequential addition of these two kinases, P-32 incorporation approache d 6 mol. Peptide mapping revealed that the different kinases largely p hosphorylate different sites on tau. After phosphorylation by casein k inase-1, calmodulin-dependent protein kinase II, Gr kinase, cyclic AMP -dependent protein kinase and casein kinase-2, the mobility of tau iso forms as detected by SDS-PAGE was decreased. Protein kinase C phosphor ylation did not produce such a mobility shift. Our results suggest tha t one or more of the kinases studied here may participate in the hyper phosphorylation of tau in Alzheimer disease. Such phosphorylation may serve to modulate the activities of other tau kinases such as the PDPK s.