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[Biochemistry of presenilin 1]
1Mitsubishi Kasei Institutes of Life Science.
Insights
Mutations in the presenilin 1 (PS1) gene cause early-onset familial Alzheimer disease. These mutations impair PS1 processing by the proteasome, leading to disease development.
Area of Science:
- Neuroscience
- Genetics
- Molecular Biology
Context:
- Early-onset familial Alzheimer disease (FAD) is primarily linked to mutations in the presenilin 1 (PS1) gene.
- PS1 is an integral membrane protein with seven transmembrane domains.
Purpose:
- To characterize the PS1 protein, its localization, processing, and the impact of Alzheimer mutations.
- To produce and utilize monoclonal antibodies for PS1 analysis.
Summary:
- Monoclonal antibodies were generated to detect full-length PS1 (47K) and a major 28K product in human brain and cell lines.
- PS1 localizes to cellular membranes, including the plasma membrane at cell-cell contact sites, suggesting a role in cell adhesion.
- Proteasome inhibition affects PS1 processing, identifying the proteasome as a key enzyme.
- Alzheimer-associated PS1 mutations prevent the generation of the 28K product, indicating impaired proteolytic processing.
Impact:
- This study reveals that PS1 mutations in familial Alzheimer disease may exert their pathogenic effects through disrupted proteasomal processing.
- Findings suggest a potential role for PS1 in cell adhesion and provide insights into the molecular mechanisms of early-onset Alzheimer disease.
Abstract:
The majority of cases of early-onset familial Alzheimer disease are caused by mutations in the recently identified presenilin 1 (PS 1) gene, located on chromosome 14. PS1, a 467 amino acid protein, is predicted to be an integral membrane protein containing seven putative transmembrane domains and a large hydrophilic loop between the sixth and seventh membrane-spanning domain. We produced 7 monoclonal antibodies that react with 3 non-overlapping epitopes on the N-terminal hydrophilic tail of PS1. The monoclonal antibodies can detect the full size PS1 at M(r) 47,000 (47K) and a more abundant M(r) 28,000 (28K) product in membrane from human brain and human cell lines. We examined the sub-cellular localization by using these antibodies. Immuno-electronmicroscopic and biochemical analysis indicated that PS1 is localized on cellular membrane (plasma, endoplasmic reticulum, and perinuclear) in COS-7 cells overexpressing PS1. Interestingly, the PS1 immunoreactivity in the plasma membrane was concentrated in the regions with cell-cell contact. This observation suggests a possible role of PS1 on the cell membrane as a cell adhesion molecule. To determine the protease cleaving the full length PS1 to two fragments, we treated cells with various protease inhibitors. Only proteasome inhibitor affected the PS1 processing, indicating that proteasome is a candidate protease for PS1 proteolytic cleavage. PC12 cells transiently transfected with PS1 constructs containing different Alzheimer mutations fail to generate the 28K degradation product in contrast to PC12 cells transfected with wild type PS1. Our results indicate that missense mutations in this form of familial Alzheimer disease may act via a mechanism of impaired proteolytic processing of PS1.