Integrin-linked kinase (ILK) is a focal adhesion
serine/threonine protein kinase with an important role in
integrin and
growth factor signaling pathways. Recently, we demonstrated that ILK is expressed in N1E-115
neuroblastoma cells and controls
integrin-dependent neurite outgrowth in serum-starved cells grown on
laminin (Ishii, T., Satoh, E., and Nishimura, M. (2001) J. Biol. Chem. 276, 42994-43003). Here we report that ILK controls tau phosphorylation via regulation of
glycogen synthase kinase-3beta (GSK-3beta) activity in N1E-115 cells. Stable transfection of a
kinase-deficient ILK mutant (DN-ILK) resulted in aberrant tau phosphorylation in N1E-115 cells at sites recognized by the
Tau-1 antibody that are identical to some of the phosphorylation sites in paired helical filaments, PHF-tau, in brains of patients with
Alzheimer's disease. The tau phosphorylation levels in the DN-ILK-expressing cells are constant under normal and differentiating conditions. On the other hand, aberrant tau phosphorylation was not observed in the parental control cells. ILK inactivation resulted in an increase in the active form but a decrease in the inactive form of
GSK-3beta, which is a candidate
kinase involved in PHF-tau formation. Moreover, inhibition of
GSK-3beta with
lithium prevented aberrant tau phosphorylation in the DN-ILK-expressing cells. These results suggest that ILK inactivation results in aberrant tau phosphorylation via sustained activation of
GSK-3beta in N1E-115 Cells. ILK directly phosphorylates
GSK-3beta and inhibits its activity. Therefore, endogenous ILK protects against GSK-3beta-induced aberrant tau phosphorylation via inhibition of
GSK-3beta activity in N1E-115 cells.