Families bearing mutations in the presenilin 1 (PS1) gene develop Alzheimer's disease. Previous studies have shown that the Alzheimer-associated mutations in PS1 increase production of amyloid ␤ protein (A␤ 1-42 ). We now show that PS1 also regulates phosphorylation of the microtubule-associated protein tau. PS1 directly binds tau and a tau kinase, glycogen synthase kinase 3␤ (GSK-3␤). Deletion studies show that both tau and GSK-3␤ bind to the same region of PS1, residues 250-298, whereas the binding domain on tau is the microtubule-binding repeat region. The ability of PS1 to bring tau and GSK-3␤ into close proximity suggests that PS1 may regulate the interaction of tau with GSK-3␤. Mutations in PS1 that cause Alzheimer's disease increase the ability of PS1 to bind GSK-3␤ and, correspondingly, increase its tau-directed kinase activity. We propose that the increased association of GSK-3␤ with mutant PS1 leads to increased phosphorylation of tau.The neuropathological diagnosis of Alzheimer's disease (AD) requires the presence of both senile plaques and neurofibrillary tangles (NFT) (1). Senile plaques are largely composed of amyloid ␤ protein (A␤), whereas NFT are composed of hyperphosphorylated tau organized into filamentous structures termed paired helical filaments (2-4). Mutations on the presenilin 1 (PS1) gene cause an early onset form of AD with an autosomal dominant inheritance pattern (5-7). The role of PS1 in AD is particularly interesting because it has a strong causal relationship to the disease; genetic studies show that mutations for PS1 exhibit 100% penetrance in causing AD (8). Although, the mechanism through which PS1 causes AD is unclear. Mutations in presenilins affect A␤ processing. Recent studies indicate that cell lines, transgenic mice, or patients expressing mutant forms of PS1 show a selective increase in production of A␤ 1-42 (9-12). Mutations in the presenilins also activate apoptotic pathways and render neurons more vulnerable to stressors, such as A␤ neurotoxicity (13-16). The ability of PS1 to potentiate A␤ toxicity raises the possibility that PS1 interacts with glycogen synthase kinase 3␤ (GSK-3␤), which we previously have shown to be involved in A␤-mediated cell death (17-20). The enzyme GSK-3␤ also has been implicated in AD because this kinase is one of a group of proline-directed kinases that can phosphorylate the microtubule-associated protein tau, to generate a precursor to NFTs, termed paired helical filaments-tau (21,22). PS1 (23-26) and GSK-3␤ (27, 28) can be found in association with NFTs in the Alzheimer brain, which further suggests that there may be a physiological connection between PS1, GSK-3␤, and tau. To pursue these intriguing connections, we investigated whether PS1 might directly associate with GSK-3␤ and tau. MATERIALS AND METHODSPreparation of Brain Samples. Human brain cortex was obtained at autopsy from patients ranging in age from 44 to 88 years old. Twenty-one samples, from donors age 44-79, showed no evidence of neurological disorders, whereas two sa...

Families bearing mutations in the presenilin-1 (PS1) gene develop Alzheimer's disease (AD). However, the mechanism through which PS1 causes AD is unclear. The co-immunoprecipitation with PS1 in transfected COS-7 cells indicates that PS1 directly interacts with endogenous L L-catenin, and the interaction requires residues 322^450 of PS1 and 445^676 of L L-catenin. Both proteins are co-localized in the endoplasmic reticulum. Over-expression of PS1 reduces the level of cytoplasmic L Lcatenin, and inhibits L L-catenin-T cell factor-regulated transcription. These results indicate that PS1 plays a role as inhibitor of the L L-catenin signal, which may be connected with the AD dysfunction.z 1998 Federation of European Biochemical Societies.

No abstract