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Enhanced Release of Amyloid -Protein from Codon 670/671 Swedish Mutant -Amyloid Precursor Protein Occurs in Both Secretory and Endocytic Pathways

1996; Elsevier BV; Volume: 271; Issue: 15 Linguagem: Inglês

10.1074/jbc.271.15.9100

1083-351X

Ruth G. Perez, Sharon L. Squazzo, Edward H. Koo,

Proteins in Food Systems

The mutation at codons 670/671 of β-amyloid precursor protein (βPP) dramatically elevates amyloid β-protein (Aβ) production. Since increased Aβ may be responsible for the disease phenotype identified from a Swedish kindred with familial Alzheimer's disease, evaluation of the cellular mechanism(s) responsible for the enhanced Aβ release may suggest potential therapies for Alzheimer's disease. In this study, we analyzed Chinese hamster ovary cells stably transfected with either wild type βPP (βPP-wt) or "Swedish" mutant βPP (βPP-sw) for potential differences in βPP processing. We confirmed that increased amounts of Aβ and a β-secretase-cleaved COOH-terminally truncated soluble βPP (βPP) were secreted from βPP-sw cells. As shown previously for βPP-wt cells, Aβ was released more slowly than the secretion of βPP from surface-labeled βPP-sw cells, indicating that endocytosis of cell surface βPP is one source of Aβ production. In contrast, by [S]methionine metabolic labeling, the rates of Aβ and βPP release were virtually identical for both cell lines. In addition, the identification of intracellular βPP and Aβ shortly after pulse labeling suggests that Aβ is produced in the secretory pathway. Interestingly, more Aβ was present in medium from βPP-sw cells than βPP-wt cells after either cell surface iodination or [S]methionine labeling, indicating that βPP-sw cells have enhanced Aβ release in both the endocytic and secretory pathways. Furthermore, a variety of drug treatments known to affect protein processing similarly reduced Aβ release from both βPP-wt and βPP-sw cells. Taken together, the data suggest that the processing pathway for βPP is similar for both βPP-wt and βPP-sw cells and that increased Aβ production by βPP-sw cells arises from enhanced cleavage of mutant βPP by β-secretase, the as-yet unidentified enzyme(s) that cleaves at the NH terminus of Aβ. The mutation at codons 670/671 of β-amyloid precursor protein (βPP) dramatically elevates amyloid β-protein (Aβ) production. Since increased Aβ may be responsible for the disease phenotype identified from a Swedish kindred with familial Alzheimer's disease, evaluation of the cellular mechanism(s) responsible for the enhanced Aβ release may suggest potential therapies for Alzheimer's disease. In this study, we analyzed Chinese hamster ovary cells stably transfected with either wild type βPP (βPP-wt) or "Swedish" mutant βPP (βPP-sw) for potential differences in βPP processing. We confirmed that increased amounts of Aβ and a β-secretase-cleaved COOH-terminally truncated soluble βPP (βPP) were secreted from βPP-sw cells. As shown previously for βPP-wt cells, Aβ was released more slowly than the secretion of βPP from surface-labeled βPP-sw cells, indicating that endocytosis of cell surface βPP is one source of Aβ production. In contrast, by [S]methionine metabolic labeling, the rates of Aβ and βPP release were virtually identical for both cell lines. In addition, the identification of intracellular βPP and Aβ shortly after pulse labeling suggests that Aβ is produced in the secretory pathway. Interestingly, more Aβ was present in medium from βPP-sw cells than βPP-wt cells after either cell surface iodination or [S]methionine labeling, indicating that βPP-sw cells have enhanced Aβ release in both the endocytic and secretory pathways. Furthermore, a variety of drug treatments known to affect protein processing similarly reduced Aβ release from both βPP-wt and βPP-sw cells. Taken together, the data suggest that the processing pathway for βPP is similar for both βPP-wt and βPP-sw cells and that increased Aβ production by βPP-sw cells arises from enhanced cleavage of mutant βPP by β-secretase, the as-yet unidentified enzyme(s) that cleaves at the NH terminus of Aβ.