Intracellular Generation of Amyloid β-Protein from Amyloid β-Protein Precursor Fragment by Direct Cleavage with β- and γ-Secretase

Abstract

Two amyloid β protein precursor (βAPP) fragments involving Met and 103 amino acids of C-terminus of βAPP (ΔNOR-β) and its KM-NL substitution (ΔNL-β) were expressed in COS-7 cells to clarify the proteolytic cleavages to generate amyloid β protein (Aβ). The 4.5-kD protein, Aβ with additional N-terminal amino acids, and 4-kD Aβ were directly produced and released from 12.5-kD expression proteins without any production of 11.4-kD C-terminal fragment starting at N-terminus of Aβ and 3-kD “p3” Aβ derivative. Intracellular 4-kD Aβ was also detected. The substitution of KM-NL of βAPP found in Swedish familial Alzheimer's disease (AD) promoted the production of intracellular Aβ and its release with no increase in level of 11.4-kD C-terminal fragment. These results suggested the presence of a distinct pathway in which Aβ is directly cleaved at both N- and C-termini from βAPP fragment intracellularly to release Aβ. Since KM-NL substitution enhanced intracellular Aβ generation, this pathway may be associated with amyloidogenesis in AD.