Reduced protein kinase C immunoreactivity and altered protein phosphorylation in Alzheimer's disease fibroblasts.

Abnormal protein kinase C levels and protein kinase C-dependent phosphorylation are biochemical alterations in brain tissue obtained from patients with Alzheimer's disease. Because many biochemical and biophysical abnormalities are found in peripheral tissues of patients with Alzheimer's disease, we studied protein kinase C levels and the in vitro phosphorylation of proteins under protein kinase C-activating conditions in fibroblasts derived from patients with Alzheimer's disease. The concentration of protein kinase C-like immunoreactivity was reduced in Alzheimer's disease samples, although the protein kinase C activity determined by the phosphorylation of exogenous histone was not. The degree of in vitro phosphorylation of an Mr 79,000 protein in the presence of protein kinase C activators was less in Alzheimer's disease than in control fibroblast cytosol, and a reduction was more prominent in cases of familial Alzheimer's disease than in sporadic Alzheimer's disease. Therefore, the aberrant phosphorylation mediated by protein kinase C is found not only in the brain but also in fibroblasts.