MODULATION OF GSK-3-CATALYZED PHOSPHORYLATION OF MICROTUBULE-ASSOCIATED PROTEIN-TAU BY NON-PROLINE-DEPENDENT PROTEIN-KINASES

The phosphorylation of bovine tau, either by GSK-3 alone or by a combi nation of GSK-3 and several non-proline-dependent protein kinases (non -PDPKs), was studied, GSK-3 alone catalyzed the incorporation of simil ar to 3 mol P-32/mol tau at a relatively slow rate. Prephosphorylation of tau by A-kinase, C-kinase, or CK-2 (but not by CK-1, CaM kinase II or Gr kinase) increased both the rate and extent of a subsequent phos phorylation catalyzed by GSK-3 by several-fold. These results suggest that the phosphorylation of tau by PDPKs such as GSK-3 (and possibly M AP kinase, cdk5) may be positively modulated at the substrate level by non-PDPK-catalyzed phosphorylations.