Phosphorylation of tau protein by casein kinase-1 converts it to an abnormal Alzheimer-like state.

The microtubule-associated protein tau is abnormally hyperphosphorylated in Alzheimer's disease. Both proline-dependent protein kinases (PDPKs) and non-PDPKs are involved in this hyperphosphorylation of tau. Several PDPKs can phosphorylate tau in vitro and induce Alzheimer-like epitopes to many phosphorylation-dependent antibodies. A similar induction has not been reported with non-PDPKs. In this study we have evaluated six non-PDPKs [cyclic AMP-dependent (A-kinase), calcium/phospholipid-dependent (C-kinase), casein kinase-1 (CK-1), casein kinase-2 (CK-2), calcium/calmodulin-dependent protein kinase II, and calcium/calmodulin-dependent protein kinase from rat cerebellum] for their abilities to induce Alzheimer-like epitopes on tau. Such epitopes were induced by A-kinase, C-kinase, CK-1, and CK-2, but the degree of induction achieved by CK-1 was much greater than with the other kinases. These results suggest that CK-1 may play an important role in the conversion of tau from the normal to the abnormal phosphorylation state in Alzheimer's disease.