INTRACELLULAR GENERATION OF AMYLOID BETA-PROTEIN FROM AMYLOID BETA-PROTEIN PRECURSOR FRAGMENT BY DIRECT CLEAVAGE WITH BETA-SECRETASE AND GAMMA-SECRETASE

Two amyloid beta protein precursor (beta APP) fragments involving Met and 103 amino acids of C-terminus of beta APP (Delta OR-beta) and its KM-NL substitution (Delta NL-beta) were expressed in COS-7 cells to cl arify the proteolytic cleavages to generate amyloid beta protein (A be ta). The 4.5-kD protein, A beta with additional N-terminal amino acids , and 4-kD A beta were directly produced and released from 12.5-kD exp ression proteins without any production of 11.4-kD C-terminal fragment starting at N-terminus of A beta and 3-kD ''p3'' A beta derivative. I ntracellular 4-kD A beta was also detected. The substitution of KM-NL of beta APP found in Swedish familial Alzheimer's disease (AD) promote d the production of intracellular A beta and its release with no incre ase in level. of 11.4-kD C-terminal fragment. These results suggested the presence of a distinct pathway in which A beta is directly cleaved at both N- and C-termini from beta APP fragment intracellularly to re lease A beta. Since KM-NL substitution enhanced intracellular A beta g eneration, this pathway may be associated with amyloidogenesis in AD. (C) 1996 Academic Press, Inc.