METABOLISM OF THE SWEDISH AMYLOID PRECURSOR PROTEIN VARIANT IN MADIN-DARBY CANINE KIDNEY-CELLS

The 4-kDa beta-amyloid peptide (A beta), a major constituent of parenc hymal amyloid deposits in Alzheimer's disease, is derived from larger amyloid precursor proteins (APP). We have examined the metabolism of A PP in Madin-Darby canine kidney cells stably transfected with cDNA enc oding either wild-type human APP-695 or human APP-695 that harbors the Swedish double mutation associated with familial early-onset Alzheime r's disease. Although similar to 90% of total soluble APP secreted fro m wild-type cells is secreted basolaterally following cleavage at the alpha-secretase site, soluble derivatives cleaved near or at the amino terminus of A beta (presumably the ''beta-secretase'' site) are prefe rentially secreted into the apical compartment of SWE cells. Concomita ntly, levels of a specific A beta-containing carboxyl-terminal fragmen t are elevated in SWE cell lysates. Using domain-specific biotinylatio n and release assays, we failed to detect a beta-secretase-generated s oluble derivative (APP(s beta)) released from the surface of SWE cells . However, APP(s beta) can be detected in SWE cell lysates, consistent with ''beta-secretase'' cleavage occurring in an intracellular compar tment. Finally, we demonstrate that A beta is secreted into the basola teral compartment of SWE cells and that the majority of these A beta-r elated species contains an aminoterminal aspartate residue (+1).